diff --git a/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl01.rst b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl01.rst
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index 0000000..8ee0d92
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+=====================================================
+Kaleidoscope: Kaleidoscope Introduction and the Lexer
+=====================================================
+
+.. contents::
+   :local:
+
+The Kaleidoscope Language
+=========================
+
+This tutorial will be illustrated with a toy language that we'll call
+"`Kaleidoscope <http://en.wikipedia.org/wiki/Kaleidoscope>`_" (derived
+from "meaning beautiful, form, and view"). Kaleidoscope is a procedural
+language that allows you to define functions, use conditionals, math,
+etc. Over the course of the tutorial, we'll extend Kaleidoscope to
+support the if/then/else construct, a for loop, user defined operators,
+JIT compilation with a simple command line interface, etc.
+
+Because we want to keep things simple, the only datatype in Kaleidoscope
+is a 64-bit floating point type (aka 'double' in C parlance). As such,
+all values are implicitly double precision and the language doesn't
+require type declarations. This gives the language a very nice and
+simple syntax. For example, the following simple example computes
+`Fibonacci numbers: <http://en.wikipedia.org/wiki/Fibonacci_number>`_
+
+::
+
+    # Compute the x'th fibonacci number.
+    def fib(x)
+      if x < 3 then
+        1
+      else
+        fib(x-1)+fib(x-2)
+
+    # This expression will compute the 40th number.
+    fib(40)
+
+We also allow Kaleidoscope to call into standard library functions (the
+LLVM JIT makes this completely trivial). This means that you can use the
+'extern' keyword to define a function before you use it (this is also
+useful for mutually recursive functions). For example:
+
+::
+
+    extern sin(arg);
+    extern cos(arg);
+    extern atan2(arg1 arg2);
+
+    atan2(sin(.4), cos(42))
+
+A more interesting example is included in Chapter 6 where we write a
+little Kaleidoscope application that `displays a Mandelbrot
+Set <LangImpl06.html#kicking-the-tires>`_ at various levels of magnification.
+
+Lets dive into the implementation of this language!
+
+The Lexer
+=========
+
+When it comes to implementing a language, the first thing needed is the
+ability to process a text file and recognize what it says. The
+traditional way to do this is to use a
+"`lexer <http://en.wikipedia.org/wiki/Lexical_analysis>`_" (aka
+'scanner') to break the input up into "tokens". Each token returned by
+the lexer includes a token code and potentially some metadata (e.g. the
+numeric value of a number). First, we define the possibilities:
+
+.. code-block:: c++
+
+    // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+    // of these for known things.
+    enum Token {
+      tok_eof = -1,
+
+      // commands
+      tok_def = -2,
+      tok_extern = -3,
+
+      // primary
+      tok_identifier = -4,
+      tok_number = -5,
+    };
+
+    static std::string IdentifierStr; // Filled in if tok_identifier
+    static double NumVal;             // Filled in if tok_number
+
+Each token returned by our lexer will either be one of the Token enum
+values or it will be an 'unknown' character like '+', which is returned
+as its ASCII value. If the current token is an identifier, the
+``IdentifierStr`` global variable holds the name of the identifier. If
+the current token is a numeric literal (like 1.0), ``NumVal`` holds its
+value. Note that we use global variables for simplicity, this is not the
+best choice for a real language implementation :).
+
+The actual implementation of the lexer is a single function named
+``gettok``. The ``gettok`` function is called to return the next token
+from standard input. Its definition starts as:
+
+.. code-block:: c++
+
+    /// gettok - Return the next token from standard input.
+    static int gettok() {
+      static int LastChar = ' ';
+
+      // Skip any whitespace.
+      while (isspace(LastChar))
+        LastChar = getchar();
+
+``gettok`` works by calling the C ``getchar()`` function to read
+characters one at a time from standard input. It eats them as it
+recognizes them and stores the last character read, but not processed,
+in LastChar. The first thing that it has to do is ignore whitespace
+between tokens. This is accomplished with the loop above.
+
+The next thing ``gettok`` needs to do is recognize identifiers and
+specific keywords like "def". Kaleidoscope does this with this simple
+loop:
+
+.. code-block:: c++
+
+      if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+        IdentifierStr = LastChar;
+        while (isalnum((LastChar = getchar())))
+          IdentifierStr += LastChar;
+
+        if (IdentifierStr == "def")
+          return tok_def;
+        if (IdentifierStr == "extern")
+          return tok_extern;
+        return tok_identifier;
+      }
+
+Note that this code sets the '``IdentifierStr``' global whenever it
+lexes an identifier. Also, since language keywords are matched by the
+same loop, we handle them here inline. Numeric values are similar:
+
+.. code-block:: c++
+
+      if (isdigit(LastChar) || LastChar == '.') {   // Number: [0-9.]+
+        std::string NumStr;
+        do {
+          NumStr += LastChar;
+          LastChar = getchar();
+        } while (isdigit(LastChar) || LastChar == '.');
+
+        NumVal = strtod(NumStr.c_str(), 0);
+        return tok_number;
+      }
+
+This is all pretty straight-forward code for processing input. When
+reading a numeric value from input, we use the C ``strtod`` function to
+convert it to a numeric value that we store in ``NumVal``. Note that
+this isn't doing sufficient error checking: it will incorrectly read
+"1.23.45.67" and handle it as if you typed in "1.23". Feel free to
+extend it :). Next we handle comments:
+
+.. code-block:: c++
+
+      if (LastChar == '#') {
+        // Comment until end of line.
+        do
+          LastChar = getchar();
+        while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+        if (LastChar != EOF)
+          return gettok();
+      }
+
+We handle comments by skipping to the end of the line and then return
+the next token. Finally, if the input doesn't match one of the above
+cases, it is either an operator character like '+' or the end of the
+file. These are handled with this code:
+
+.. code-block:: c++
+
+      // Check for end of file.  Don't eat the EOF.
+      if (LastChar == EOF)
+        return tok_eof;
+
+      // Otherwise, just return the character as its ascii value.
+      int ThisChar = LastChar;
+      LastChar = getchar();
+      return ThisChar;
+    }
+
+With this, we have the complete lexer for the basic Kaleidoscope
+language (the `full code listing <LangImpl02.html#full-code-listing>`_ for the Lexer
+is available in the `next chapter <LangImpl02.html>`_ of the tutorial).
+Next we'll `build a simple parser that uses this to build an Abstract
+Syntax Tree <LangImpl02.html>`_. When we have that, we'll include a
+driver so that you can use the lexer and parser together.
+
+`Next: Implementing a Parser and AST <LangImpl02.html>`_
+
diff --git a/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl02.rst b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl02.rst
new file mode 100644
index 0000000..6982e96
--- /dev/null
+++ b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl02.rst
@@ -0,0 +1,737 @@
+===========================================
+Kaleidoscope: Implementing a Parser and AST
+===========================================
+
+.. contents::
+   :local:
+
+Chapter 2 Introduction
+======================
+
+Welcome to Chapter 2 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. This chapter shows you how to use the
+lexer, built in `Chapter 1 <LangImpl01.html>`_, to build a full
+`parser <http://en.wikipedia.org/wiki/Parsing>`_ for our Kaleidoscope
+language. Once we have a parser, we'll define and build an `Abstract
+Syntax Tree <http://en.wikipedia.org/wiki/Abstract_syntax_tree>`_ (AST).
+
+The parser we will build uses a combination of `Recursive Descent
+Parsing <http://en.wikipedia.org/wiki/Recursive_descent_parser>`_ and
+`Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_ to
+parse the Kaleidoscope language (the latter for binary expressions and
+the former for everything else). Before we get to parsing though, let's
+talk about the output of the parser: the Abstract Syntax Tree.
+
+The Abstract Syntax Tree (AST)
+==============================
+
+The AST for a program captures its behavior in such a way that it is
+easy for later stages of the compiler (e.g. code generation) to
+interpret. We basically want one object for each construct in the
+language, and the AST should closely model the language. In
+Kaleidoscope, we have expressions, a prototype, and a function object.
+We'll start with expressions first:
+
+.. code-block:: c++
+
+    /// ExprAST - Base class for all expression nodes.
+    class ExprAST {
+    public:
+      virtual ~ExprAST() {}
+    };
+
+    /// NumberExprAST - Expression class for numeric literals like "1.0".
+    class NumberExprAST : public ExprAST {
+      double Val;
+
+    public:
+      NumberExprAST(double Val) : Val(Val) {}
+    };
+
+The code above shows the definition of the base ExprAST class and one
+subclass which we use for numeric literals. The important thing to note
+about this code is that the NumberExprAST class captures the numeric
+value of the literal as an instance variable. This allows later phases
+of the compiler to know what the stored numeric value is.
+
+Right now we only create the AST, so there are no useful accessor
+methods on them. It would be very easy to add a virtual method to pretty
+print the code, for example. Here are the other expression AST node
+definitions that we'll use in the basic form of the Kaleidoscope
+language:
+
+.. code-block:: c++
+
+    /// VariableExprAST - Expression class for referencing a variable, like "a".
+    class VariableExprAST : public ExprAST {
+      std::string Name;
+
+    public:
+      VariableExprAST(const std::string &Name) : Name(Name) {}
+    };
+
+    /// BinaryExprAST - Expression class for a binary operator.
+    class BinaryExprAST : public ExprAST {
+      char Op;
+      std::unique_ptr<ExprAST> LHS, RHS;
+
+    public:
+      BinaryExprAST(char op, std::unique_ptr<ExprAST> LHS,
+                    std::unique_ptr<ExprAST> RHS)
+        : Op(op), LHS(std::move(LHS)), RHS(std::move(RHS)) {}
+    };
+
+    /// CallExprAST - Expression class for function calls.
+    class CallExprAST : public ExprAST {
+      std::string Callee;
+      std::vector<std::unique_ptr<ExprAST>> Args;
+
+    public:
+      CallExprAST(const std::string &Callee,
+                  std::vector<std::unique_ptr<ExprAST>> Args)
+        : Callee(Callee), Args(std::move(Args)) {}
+    };
+
+This is all (intentionally) rather straight-forward: variables capture
+the variable name, binary operators capture their opcode (e.g. '+'), and
+calls capture a function name as well as a list of any argument
+expressions. One thing that is nice about our AST is that it captures
+the language features without talking about the syntax of the language.
+Note that there is no discussion about precedence of binary operators,
+lexical structure, etc.
+
+For our basic language, these are all of the expression nodes we'll
+define. Because it doesn't have conditional control flow, it isn't
+Turing-complete; we'll fix that in a later installment. The two things
+we need next are a way to talk about the interface to a function, and a
+way to talk about functions themselves:
+
+.. code-block:: c++
+
+    /// PrototypeAST - This class represents the "prototype" for a function,
+    /// which captures its name, and its argument names (thus implicitly the number
+    /// of arguments the function takes).
+    class PrototypeAST {
+      std::string Name;
+      std::vector<std::string> Args;
+
+    public:
+      PrototypeAST(const std::string &name, std::vector<std::string> Args)
+        : Name(name), Args(std::move(Args)) {}
+
+      const std::string &getName() const { return Name; }
+    };
+
+    /// FunctionAST - This class represents a function definition itself.
+    class FunctionAST {
+      std::unique_ptr<PrototypeAST> Proto;
+      std::unique_ptr<ExprAST> Body;
+
+    public:
+      FunctionAST(std::unique_ptr<PrototypeAST> Proto,
+                  std::unique_ptr<ExprAST> Body)
+        : Proto(std::move(Proto)), Body(std::move(Body)) {}
+    };
+
+In Kaleidoscope, functions are typed with just a count of their
+arguments. Since all values are double precision floating point, the
+type of each argument doesn't need to be stored anywhere. In a more
+aggressive and realistic language, the "ExprAST" class would probably
+have a type field.
+
+With this scaffolding, we can now talk about parsing expressions and
+function bodies in Kaleidoscope.
+
+Parser Basics
+=============
+
+Now that we have an AST to build, we need to define the parser code to
+build it. The idea here is that we want to parse something like "x+y"
+(which is returned as three tokens by the lexer) into an AST that could
+be generated with calls like this:
+
+.. code-block:: c++
+
+      auto LHS = llvm::make_unique<VariableExprAST>("x");
+      auto RHS = llvm::make_unique<VariableExprAST>("y");
+      auto Result = std::make_unique<BinaryExprAST>('+', std::move(LHS),
+                                                    std::move(RHS));
+
+In order to do this, we'll start by defining some basic helper routines:
+
+.. code-block:: c++
+
+    /// CurTok/getNextToken - Provide a simple token buffer.  CurTok is the current
+    /// token the parser is looking at.  getNextToken reads another token from the
+    /// lexer and updates CurTok with its results.
+    static int CurTok;
+    static int getNextToken() {
+      return CurTok = gettok();
+    }
+
+This implements a simple token buffer around the lexer. This allows us
+to look one token ahead at what the lexer is returning. Every function
+in our parser will assume that CurTok is the current token that needs to
+be parsed.
+
+.. code-block:: c++
+
+
+    /// LogError* - These are little helper functions for error handling.
+    std::unique_ptr<ExprAST> LogError(const char *Str) {
+      fprintf(stderr, "LogError: %s\n", Str);
+      return nullptr;
+    }
+    std::unique_ptr<PrototypeAST> LogErrorP(const char *Str) {
+      LogError(Str);
+      return nullptr;
+    }
+
+The ``LogError`` routines are simple helper routines that our parser will
+use to handle errors. The error recovery in our parser will not be the
+best and is not particular user-friendly, but it will be enough for our
+tutorial. These routines make it easier to handle errors in routines
+that have various return types: they always return null.
+
+With these basic helper functions, we can implement the first piece of
+our grammar: numeric literals.
+
+Basic Expression Parsing
+========================
+
+We start with numeric literals, because they are the simplest to
+process. For each production in our grammar, we'll define a function
+which parses that production. For numeric literals, we have:
+
+.. code-block:: c++
+
+    /// numberexpr ::= number
+    static std::unique_ptr<ExprAST> ParseNumberExpr() {
+      auto Result = llvm::make_unique<NumberExprAST>(NumVal);
+      getNextToken(); // consume the number
+      return std::move(Result);
+    }
+
+This routine is very simple: it expects to be called when the current
+token is a ``tok_number`` token. It takes the current number value,
+creates a ``NumberExprAST`` node, advances the lexer to the next token,
+and finally returns.
+
+There are some interesting aspects to this. The most important one is
+that this routine eats all of the tokens that correspond to the
+production and returns the lexer buffer with the next token (which is
+not part of the grammar production) ready to go. This is a fairly
+standard way to go for recursive descent parsers. For a better example,
+the parenthesis operator is defined like this:
+
+.. code-block:: c++
+
+    /// parenexpr ::= '(' expression ')'
+    static std::unique_ptr<ExprAST> ParseParenExpr() {
+      getNextToken(); // eat (.
+      auto V = ParseExpression();
+      if (!V)
+        return nullptr;
+
+      if (CurTok != ')')
+        return LogError("expected ')'");
+      getNextToken(); // eat ).
+      return V;
+    }
+
+This function illustrates a number of interesting things about the
+parser:
+
+1) It shows how we use the LogError routines. When called, this function
+expects that the current token is a '(' token, but after parsing the
+subexpression, it is possible that there is no ')' waiting. For example,
+if the user types in "(4 x" instead of "(4)", the parser should emit an
+error. Because errors can occur, the parser needs a way to indicate that
+they happened: in our parser, we return null on an error.
+
+2) Another interesting aspect of this function is that it uses recursion
+by calling ``ParseExpression`` (we will soon see that
+``ParseExpression`` can call ``ParseParenExpr``). This is powerful
+because it allows us to handle recursive grammars, and keeps each
+production very simple. Note that parentheses do not cause construction
+of AST nodes themselves. While we could do it this way, the most
+important role of parentheses are to guide the parser and provide
+grouping. Once the parser constructs the AST, parentheses are not
+needed.
+
+The next simple production is for handling variable references and
+function calls:
+
+.. code-block:: c++
+
+    /// identifierexpr
+    ///   ::= identifier
+    ///   ::= identifier '(' expression* ')'
+    static std::unique_ptr<ExprAST> ParseIdentifierExpr() {
+      std::string IdName = IdentifierStr;
+
+      getNextToken();  // eat identifier.
+
+      if (CurTok != '(') // Simple variable ref.
+        return llvm::make_unique<VariableExprAST>(IdName);
+
+      // Call.
+      getNextToken();  // eat (
+      std::vector<std::unique_ptr<ExprAST>> Args;
+      if (CurTok != ')') {
+        while (1) {
+          if (auto Arg = ParseExpression())
+            Args.push_back(std::move(Arg));
+          else
+            return nullptr;
+
+          if (CurTok == ')')
+            break;
+
+          if (CurTok != ',')
+            return LogError("Expected ')' or ',' in argument list");
+          getNextToken();
+        }
+      }
+
+      // Eat the ')'.
+      getNextToken();
+
+      return llvm::make_unique<CallExprAST>(IdName, std::move(Args));
+    }
+
+This routine follows the same style as the other routines. (It expects
+to be called if the current token is a ``tok_identifier`` token). It
+also has recursion and error handling. One interesting aspect of this is
+that it uses *look-ahead* to determine if the current identifier is a
+stand alone variable reference or if it is a function call expression.
+It handles this by checking to see if the token after the identifier is
+a '(' token, constructing either a ``VariableExprAST`` or
+``CallExprAST`` node as appropriate.
+
+Now that we have all of our simple expression-parsing logic in place, we
+can define a helper function to wrap it together into one entry point.
+We call this class of expressions "primary" expressions, for reasons
+that will become more clear `later in the
+tutorial <LangImpl6.html#user-defined-unary-operators>`_. In order to parse an arbitrary
+primary expression, we need to determine what sort of expression it is:
+
+.. code-block:: c++
+
+    /// primary
+    ///   ::= identifierexpr
+    ///   ::= numberexpr
+    ///   ::= parenexpr
+    static std::unique_ptr<ExprAST> ParsePrimary() {
+      switch (CurTok) {
+      default:
+        return LogError("unknown token when expecting an expression");
+      case tok_identifier:
+        return ParseIdentifierExpr();
+      case tok_number:
+        return ParseNumberExpr();
+      case '(':
+        return ParseParenExpr();
+      }
+    }
+
+Now that you see the definition of this function, it is more obvious why
+we can assume the state of CurTok in the various functions. This uses
+look-ahead to determine which sort of expression is being inspected, and
+then parses it with a function call.
+
+Now that basic expressions are handled, we need to handle binary
+expressions. They are a bit more complex.
+
+Binary Expression Parsing
+=========================
+
+Binary expressions are significantly harder to parse because they are
+often ambiguous. For example, when given the string "x+y\*z", the parser
+can choose to parse it as either "(x+y)\*z" or "x+(y\*z)". With common
+definitions from mathematics, we expect the later parse, because "\*"
+(multiplication) has higher *precedence* than "+" (addition).
+
+There are many ways to handle this, but an elegant and efficient way is
+to use `Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_.
+This parsing technique uses the precedence of binary operators to guide
+recursion. To start with, we need a table of precedences:
+
+.. code-block:: c++
+
+    /// BinopPrecedence - This holds the precedence for each binary operator that is
+    /// defined.
+    static std::map<char, int> BinopPrecedence;
+
+    /// GetTokPrecedence - Get the precedence of the pending binary operator token.
+    static int GetTokPrecedence() {
+      if (!isascii(CurTok))
+        return -1;
+
+      // Make sure it's a declared binop.
+      int TokPrec = BinopPrecedence[CurTok];
+      if (TokPrec <= 0) return -1;
+      return TokPrec;
+    }
+
+    int main() {
+      // Install standard binary operators.
+      // 1 is lowest precedence.
+      BinopPrecedence['<'] = 10;
+      BinopPrecedence['+'] = 20;
+      BinopPrecedence['-'] = 20;
+      BinopPrecedence['*'] = 40;  // highest.
+      ...
+    }
+
+For the basic form of Kaleidoscope, we will only support 4 binary
+operators (this can obviously be extended by you, our brave and intrepid
+reader). The ``GetTokPrecedence`` function returns the precedence for
+the current token, or -1 if the token is not a binary operator. Having a
+map makes it easy to add new operators and makes it clear that the
+algorithm doesn't depend on the specific operators involved, but it
+would be easy enough to eliminate the map and do the comparisons in the
+``GetTokPrecedence`` function. (Or just use a fixed-size array).
+
+With the helper above defined, we can now start parsing binary
+expressions. The basic idea of operator precedence parsing is to break
+down an expression with potentially ambiguous binary operators into
+pieces. Consider, for example, the expression "a+b+(c+d)\*e\*f+g".
+Operator precedence parsing considers this as a stream of primary
+expressions separated by binary operators. As such, it will first parse
+the leading primary expression "a", then it will see the pairs [+, b]
+[+, (c+d)] [\*, e] [\*, f] and [+, g]. Note that because parentheses are
+primary expressions, the binary expression parser doesn't need to worry
+about nested subexpressions like (c+d) at all.
+
+To start, an expression is a primary expression potentially followed by
+a sequence of [binop,primaryexpr] pairs:
+
+.. code-block:: c++
+
+    /// expression
+    ///   ::= primary binoprhs
+    ///
+    static std::unique_ptr<ExprAST> ParseExpression() {
+      auto LHS = ParsePrimary();
+      if (!LHS)
+        return nullptr;
+
+      return ParseBinOpRHS(0, std::move(LHS));
+    }
+
+``ParseBinOpRHS`` is the function that parses the sequence of pairs for
+us. It takes a precedence and a pointer to an expression for the part
+that has been parsed so far. Note that "x" is a perfectly valid
+expression: As such, "binoprhs" is allowed to be empty, in which case it
+returns the expression that is passed into it. In our example above, the
+code passes the expression for "a" into ``ParseBinOpRHS`` and the
+current token is "+".
+
+The precedence value passed into ``ParseBinOpRHS`` indicates the
+*minimal operator precedence* that the function is allowed to eat. For
+example, if the current pair stream is [+, x] and ``ParseBinOpRHS`` is
+passed in a precedence of 40, it will not consume any tokens (because
+the precedence of '+' is only 20). With this in mind, ``ParseBinOpRHS``
+starts with:
+
+.. code-block:: c++
+
+    /// binoprhs
+    ///   ::= ('+' primary)*
+    static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
+                                                  std::unique_ptr<ExprAST> LHS) {
+      // If this is a binop, find its precedence.
+      while (1) {
+        int TokPrec = GetTokPrecedence();
+
+        // If this is a binop that binds at least as tightly as the current binop,
+        // consume it, otherwise we are done.
+        if (TokPrec < ExprPrec)
+          return LHS;
+
+This code gets the precedence of the current token and checks to see if
+if is too low. Because we defined invalid tokens to have a precedence of
+-1, this check implicitly knows that the pair-stream ends when the token
+stream runs out of binary operators. If this check succeeds, we know
+that the token is a binary operator and that it will be included in this
+expression:
+
+.. code-block:: c++
+
+        // Okay, we know this is a binop.
+        int BinOp = CurTok;
+        getNextToken();  // eat binop
+
+        // Parse the primary expression after the binary operator.
+        auto RHS = ParsePrimary();
+        if (!RHS)
+          return nullptr;
+
+As such, this code eats (and remembers) the binary operator and then
+parses the primary expression that follows. This builds up the whole
+pair, the first of which is [+, b] for the running example.
+
+Now that we parsed the left-hand side of an expression and one pair of
+the RHS sequence, we have to decide which way the expression associates.
+In particular, we could have "(a+b) binop unparsed" or "a + (b binop
+unparsed)". To determine this, we look ahead at "binop" to determine its
+precedence and compare it to BinOp's precedence (which is '+' in this
+case):
+
+.. code-block:: c++
+
+        // If BinOp binds less tightly with RHS than the operator after RHS, let
+        // the pending operator take RHS as its LHS.
+        int NextPrec = GetTokPrecedence();
+        if (TokPrec < NextPrec) {
+
+If the precedence of the binop to the right of "RHS" is lower or equal
+to the precedence of our current operator, then we know that the
+parentheses associate as "(a+b) binop ...". In our example, the current
+operator is "+" and the next operator is "+", we know that they have the
+same precedence. In this case we'll create the AST node for "a+b", and
+then continue parsing:
+
+.. code-block:: c++
+
+          ... if body omitted ...
+        }
+
+        // Merge LHS/RHS.
+        LHS = llvm::make_unique<BinaryExprAST>(BinOp, std::move(LHS),
+                                               std::move(RHS));
+      }  // loop around to the top of the while loop.
+    }
+
+In our example above, this will turn "a+b+" into "(a+b)" and execute the
+next iteration of the loop, with "+" as the current token. The code
+above will eat, remember, and parse "(c+d)" as the primary expression,
+which makes the current pair equal to [+, (c+d)]. It will then evaluate
+the 'if' conditional above with "\*" as the binop to the right of the
+primary. In this case, the precedence of "\*" is higher than the
+precedence of "+" so the if condition will be entered.
+
+The critical question left here is "how can the if condition parse the
+right hand side in full"? In particular, to build the AST correctly for
+our example, it needs to get all of "(c+d)\*e\*f" as the RHS expression
+variable. The code to do this is surprisingly simple (code from the
+above two blocks duplicated for context):
+
+.. code-block:: c++
+
+        // If BinOp binds less tightly with RHS than the operator after RHS, let
+        // the pending operator take RHS as its LHS.
+        int NextPrec = GetTokPrecedence();
+        if (TokPrec < NextPrec) {
+          RHS = ParseBinOpRHS(TokPrec+1, std::move(RHS));
+          if (!RHS)
+            return nullptr;
+        }
+        // Merge LHS/RHS.
+        LHS = llvm::make_unique<BinaryExprAST>(BinOp, std::move(LHS),
+                                               std::move(RHS));
+      }  // loop around to the top of the while loop.
+    }
+
+At this point, we know that the binary operator to the RHS of our
+primary has higher precedence than the binop we are currently parsing.
+As such, we know that any sequence of pairs whose operators are all
+higher precedence than "+" should be parsed together and returned as
+"RHS". To do this, we recursively invoke the ``ParseBinOpRHS`` function
+specifying "TokPrec+1" as the minimum precedence required for it to
+continue. In our example above, this will cause it to return the AST
+node for "(c+d)\*e\*f" as RHS, which is then set as the RHS of the '+'
+expression.
+
+Finally, on the next iteration of the while loop, the "+g" piece is
+parsed and added to the AST. With this little bit of code (14
+non-trivial lines), we correctly handle fully general binary expression
+parsing in a very elegant way. This was a whirlwind tour of this code,
+and it is somewhat subtle. I recommend running through it with a few
+tough examples to see how it works.
+
+This wraps up handling of expressions. At this point, we can point the
+parser at an arbitrary token stream and build an expression from it,
+stopping at the first token that is not part of the expression. Next up
+we need to handle function definitions, etc.
+
+Parsing the Rest
+================
+
+The next thing missing is handling of function prototypes. In
+Kaleidoscope, these are used both for 'extern' function declarations as
+well as function body definitions. The code to do this is
+straight-forward and not very interesting (once you've survived
+expressions):
+
+.. code-block:: c++
+
+    /// prototype
+    ///   ::= id '(' id* ')'
+    static std::unique_ptr<PrototypeAST> ParsePrototype() {
+      if (CurTok != tok_identifier)
+        return LogErrorP("Expected function name in prototype");
+
+      std::string FnName = IdentifierStr;
+      getNextToken();
+
+      if (CurTok != '(')
+        return LogErrorP("Expected '(' in prototype");
+
+      // Read the list of argument names.
+      std::vector<std::string> ArgNames;
+      while (getNextToken() == tok_identifier)
+        ArgNames.push_back(IdentifierStr);
+      if (CurTok != ')')
+        return LogErrorP("Expected ')' in prototype");
+
+      // success.
+      getNextToken();  // eat ')'.
+
+      return llvm::make_unique<PrototypeAST>(FnName, std::move(ArgNames));
+    }
+
+Given this, a function definition is very simple, just a prototype plus
+an expression to implement the body:
+
+.. code-block:: c++
+
+    /// definition ::= 'def' prototype expression
+    static std::unique_ptr<FunctionAST> ParseDefinition() {
+      getNextToken();  // eat def.
+      auto Proto = ParsePrototype();
+      if (!Proto) return nullptr;
+
+      if (auto E = ParseExpression())
+        return llvm::make_unique<FunctionAST>(std::move(Proto), std::move(E));
+      return nullptr;
+    }
+
+In addition, we support 'extern' to declare functions like 'sin' and
+'cos' as well as to support forward declaration of user functions. These
+'extern's are just prototypes with no body:
+
+.. code-block:: c++
+
+    /// external ::= 'extern' prototype
+    static std::unique_ptr<PrototypeAST> ParseExtern() {
+      getNextToken();  // eat extern.
+      return ParsePrototype();
+    }
+
+Finally, we'll also let the user type in arbitrary top-level expressions
+and evaluate them on the fly. We will handle this by defining anonymous
+nullary (zero argument) functions for them:
+
+.. code-block:: c++
+
+    /// toplevelexpr ::= expression
+    static std::unique_ptr<FunctionAST> ParseTopLevelExpr() {
+      if (auto E = ParseExpression()) {
+        // Make an anonymous proto.
+        auto Proto = llvm::make_unique<PrototypeAST>("", std::vector<std::string>());
+        return llvm::make_unique<FunctionAST>(std::move(Proto), std::move(E));
+      }
+      return nullptr;
+    }
+
+Now that we have all the pieces, let's build a little driver that will
+let us actually *execute* this code we've built!
+
+The Driver
+==========
+
+The driver for this simply invokes all of the parsing pieces with a
+top-level dispatch loop. There isn't much interesting here, so I'll just
+include the top-level loop. See `below <#full-code-listing>`_ for full code in the
+"Top-Level Parsing" section.
+
+.. code-block:: c++
+
+    /// top ::= definition | external | expression | ';'
+    static void MainLoop() {
+      while (1) {
+        fprintf(stderr, "ready> ");
+        switch (CurTok) {
+        case tok_eof:
+          return;
+        case ';': // ignore top-level semicolons.
+          getNextToken();
+          break;
+        case tok_def:
+          HandleDefinition();
+          break;
+        case tok_extern:
+          HandleExtern();
+          break;
+        default:
+          HandleTopLevelExpression();
+          break;
+        }
+      }
+    }
+
+The most interesting part of this is that we ignore top-level
+semicolons. Why is this, you ask? The basic reason is that if you type
+"4 + 5" at the command line, the parser doesn't know whether that is the
+end of what you will type or not. For example, on the next line you
+could type "def foo..." in which case 4+5 is the end of a top-level
+expression. Alternatively you could type "\* 6", which would continue
+the expression. Having top-level semicolons allows you to type "4+5;",
+and the parser will know you are done.
+
+Conclusions
+===========
+
+With just under 400 lines of commented code (240 lines of non-comment,
+non-blank code), we fully defined our minimal language, including a
+lexer, parser, and AST builder. With this done, the executable will
+validate Kaleidoscope code and tell us if it is grammatically invalid.
+For example, here is a sample interaction:
+
+.. code-block:: bash
+
+    $ ./a.out
+    ready> def foo(x y) x+foo(y, 4.0);
+    Parsed a function definition.
+    ready> def foo(x y) x+y y;
+    Parsed a function definition.
+    Parsed a top-level expr
+    ready> def foo(x y) x+y );
+    Parsed a function definition.
+    Error: unknown token when expecting an expression
+    ready> extern sin(a);
+    ready> Parsed an extern
+    ready> ^D
+    $
+
+There is a lot of room for extension here. You can define new AST nodes,
+extend the language in many ways, etc. In the `next
+installment <LangImpl03.html>`_, we will describe how to generate LLVM
+Intermediate Representation (IR) from the AST.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example. Because this
+uses the LLVM libraries, we need to link them in. To do this, we use the
+`llvm-config <http://llvm.org/cmds/llvm-config.html>`_ tool to inform
+our makefile/command line about which options to use:
+
+.. code-block:: bash
+
+    # Compile
+    clang++ -g -O3 toy.cpp `llvm-config --cxxflags`
+    # Run
+    ./a.out
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter2/toy.cpp
+   :language: c++
+
+`Next: Implementing Code Generation to LLVM IR <LangImpl03.html>`_
+
diff --git a/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl03.rst b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl03.rst
new file mode 100644
index 0000000..da465ef
--- /dev/null
+++ b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl03.rst
@@ -0,0 +1,568 @@
+========================================
+Kaleidoscope: Code generation to LLVM IR
+========================================
+
+.. contents::
+   :local:
+
+Chapter 3 Introduction
+======================
+
+Welcome to Chapter 3 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. This chapter shows you how to transform
+the `Abstract Syntax Tree <LangImpl02.html>`_, built in Chapter 2, into
+LLVM IR. This will teach you a little bit about how LLVM does things, as
+well as demonstrate how easy it is to use. It's much more work to build
+a lexer and parser than it is to generate LLVM IR code. :)
+
+**Please note**: the code in this chapter and later require LLVM 3.7 or
+later. LLVM 3.6 and before will not work with it. Also note that you
+need to use a version of this tutorial that matches your LLVM release:
+If you are using an official LLVM release, use the version of the
+documentation included with your release or on the `llvm.org releases
+page <http://llvm.org/releases/>`_.
+
+Code Generation Setup
+=====================
+
+In order to generate LLVM IR, we want some simple setup to get started.
+First we define virtual code generation (codegen) methods in each AST
+class:
+
+.. code-block:: c++
+
+    /// ExprAST - Base class for all expression nodes.
+    class ExprAST {
+    public:
+      virtual ~ExprAST() {}
+      virtual Value *codegen() = 0;
+    };
+
+    /// NumberExprAST - Expression class for numeric literals like "1.0".
+    class NumberExprAST : public ExprAST {
+      double Val;
+
+    public:
+      NumberExprAST(double Val) : Val(Val) {}
+      virtual Value *codegen();
+    };
+    ...
+
+The codegen() method says to emit IR for that AST node along with all
+the things it depends on, and they all return an LLVM Value object.
+"Value" is the class used to represent a "`Static Single Assignment
+(SSA) <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+register" or "SSA value" in LLVM. The most distinct aspect of SSA values
+is that their value is computed as the related instruction executes, and
+it does not get a new value until (and if) the instruction re-executes.
+In other words, there is no way to "change" an SSA value. For more
+information, please read up on `Static Single
+Assignment <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+- the concepts are really quite natural once you grok them.
+
+Note that instead of adding virtual methods to the ExprAST class
+hierarchy, it could also make sense to use a `visitor
+pattern <http://en.wikipedia.org/wiki/Visitor_pattern>`_ or some other
+way to model this. Again, this tutorial won't dwell on good software
+engineering practices: for our purposes, adding a virtual method is
+simplest.
+
+The second thing we want is an "LogError" method like we used for the
+parser, which will be used to report errors found during code generation
+(for example, use of an undeclared parameter):
+
+.. code-block:: c++
+
+    static LLVMContext TheContext;
+    static IRBuilder<> Builder(TheContext);
+    static std::unique_ptr<Module> TheModule;
+    static std::map<std::string, Value *> NamedValues;
+
+    Value *LogErrorV(const char *Str) {
+      LogError(Str);
+      return nullptr;
+    }
+
+The static variables will be used during code generation. ``TheContext``
+is an opaque object that owns a lot of core LLVM data structures, such as
+the type and constant value tables. We don't need to understand it in
+detail, we just need a single instance to pass into APIs that require it.
+
+The ``Builder`` object is a helper object that makes it easy to generate
+LLVM instructions. Instances of the
+`IRBuilder <http://llvm.org/doxygen/IRBuilder_8h-source.html>`_
+class template keep track of the current place to insert instructions
+and has methods to create new instructions.
+
+``TheModule`` is an LLVM construct that contains functions and global
+variables. In many ways, it is the top-level structure that the LLVM IR
+uses to contain code. It will own the memory for all of the IR that we
+generate, which is why the codegen() method returns a raw Value\*,
+rather than a unique_ptr<Value>.
+
+The ``NamedValues`` map keeps track of which values are defined in the
+current scope and what their LLVM representation is. (In other words, it
+is a symbol table for the code). In this form of Kaleidoscope, the only
+things that can be referenced are function parameters. As such, function
+parameters will be in this map when generating code for their function
+body.
+
+With these basics in place, we can start talking about how to generate
+code for each expression. Note that this assumes that the ``Builder``
+has been set up to generate code *into* something. For now, we'll assume
+that this has already been done, and we'll just use it to emit code.
+
+Expression Code Generation
+==========================
+
+Generating LLVM code for expression nodes is very straightforward: less
+than 45 lines of commented code for all four of our expression nodes.
+First we'll do numeric literals:
+
+.. code-block:: c++
+
+    Value *NumberExprAST::codegen() {
+      return ConstantFP::get(TheContext, APFloat(Val));
+    }
+
+In the LLVM IR, numeric constants are represented with the
+``ConstantFP`` class, which holds the numeric value in an ``APFloat``
+internally (``APFloat`` has the capability of holding floating point
+constants of Arbitrary Precision). This code basically just creates
+and returns a ``ConstantFP``. Note that in the LLVM IR that constants
+are all uniqued together and shared. For this reason, the API uses the
+"foo::get(...)" idiom instead of "new foo(..)" or "foo::Create(..)".
+
+.. code-block:: c++
+
+    Value *VariableExprAST::codegen() {
+      // Look this variable up in the function.
+      Value *V = NamedValues[Name];
+      if (!V)
+        LogErrorV("Unknown variable name");
+      return V;
+    }
+
+References to variables are also quite simple using LLVM. In the simple
+version of Kaleidoscope, we assume that the variable has already been
+emitted somewhere and its value is available. In practice, the only
+values that can be in the ``NamedValues`` map are function arguments.
+This code simply checks to see that the specified name is in the map (if
+not, an unknown variable is being referenced) and returns the value for
+it. In future chapters, we'll add support for `loop induction
+variables <LangImpl5.html#for-loop-expression>`_ in the symbol table, and for `local
+variables <LangImpl7.html#user-defined-local-variables>`_.
+
+.. code-block:: c++
+
+    Value *BinaryExprAST::codegen() {
+      Value *L = LHS->codegen();
+      Value *R = RHS->codegen();
+      if (!L || !R)
+        return nullptr;
+
+      switch (Op) {
+      case '+':
+        return Builder.CreateFAdd(L, R, "addtmp");
+      case '-':
+        return Builder.CreateFSub(L, R, "subtmp");
+      case '*':
+        return Builder.CreateFMul(L, R, "multmp");
+      case '<':
+        L = Builder.CreateFCmpULT(L, R, "cmptmp");
+        // Convert bool 0/1 to double 0.0 or 1.0
+        return Builder.CreateUIToFP(L, Type::getDoubleTy(TheContext),
+                                    "booltmp");
+      default:
+        return LogErrorV("invalid binary operator");
+      }
+    }
+
+Binary operators start to get more interesting. The basic idea here is
+that we recursively emit code for the left-hand side of the expression,
+then the right-hand side, then we compute the result of the binary
+expression. In this code, we do a simple switch on the opcode to create
+the right LLVM instruction.
+
+In the example above, the LLVM builder class is starting to show its
+value. IRBuilder knows where to insert the newly created instruction,
+all you have to do is specify what instruction to create (e.g. with
+``CreateFAdd``), which operands to use (``L`` and ``R`` here) and
+optionally provide a name for the generated instruction.
+
+One nice thing about LLVM is that the name is just a hint. For instance,
+if the code above emits multiple "addtmp" variables, LLVM will
+automatically provide each one with an increasing, unique numeric
+suffix. Local value names for instructions are purely optional, but it
+makes it much easier to read the IR dumps.
+
+`LLVM instructions <../LangRef.html#instruction-reference>`_ are constrained by strict
+rules: for example, the Left and Right operators of an `add
+instruction <../LangRef.html#add-instruction>`_ must have the same type, and the
+result type of the add must match the operand types. Because all values
+in Kaleidoscope are doubles, this makes for very simple code for add,
+sub and mul.
+
+On the other hand, LLVM specifies that the `fcmp
+instruction <../LangRef.html#fcmp-instruction>`_ always returns an 'i1' value (a
+one bit integer). The problem with this is that Kaleidoscope wants the
+value to be a 0.0 or 1.0 value. In order to get these semantics, we
+combine the fcmp instruction with a `uitofp
+instruction <../LangRef.html#uitofp-to-instruction>`_. This instruction converts its
+input integer into a floating point value by treating the input as an
+unsigned value. In contrast, if we used the `sitofp
+instruction <../LangRef.html#sitofp-to-instruction>`_, the Kaleidoscope '<' operator
+would return 0.0 and -1.0, depending on the input value.
+
+.. code-block:: c++
+
+    Value *CallExprAST::codegen() {
+      // Look up the name in the global module table.
+      Function *CalleeF = TheModule->getFunction(Callee);
+      if (!CalleeF)
+        return LogErrorV("Unknown function referenced");
+
+      // If argument mismatch error.
+      if (CalleeF->arg_size() != Args.size())
+        return LogErrorV("Incorrect # arguments passed");
+
+      std::vector<Value *> ArgsV;
+      for (unsigned i = 0, e = Args.size(); i != e; ++i) {
+        ArgsV.push_back(Args[i]->codegen());
+        if (!ArgsV.back())
+          return nullptr;
+      }
+
+      return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+    }
+
+Code generation for function calls is quite straightforward with LLVM. The code
+above initially does a function name lookup in the LLVM Module's symbol table.
+Recall that the LLVM Module is the container that holds the functions we are
+JIT'ing. By giving each function the same name as what the user specifies, we
+can use the LLVM symbol table to resolve function names for us.
+
+Once we have the function to call, we recursively codegen each argument
+that is to be passed in, and create an LLVM `call
+instruction <../LangRef.html#call-instruction>`_. Note that LLVM uses the native C
+calling conventions by default, allowing these calls to also call into
+standard library functions like "sin" and "cos", with no additional
+effort.
+
+This wraps up our handling of the four basic expressions that we have so
+far in Kaleidoscope. Feel free to go in and add some more. For example,
+by browsing the `LLVM language reference <../LangRef.html>`_ you'll find
+several other interesting instructions that are really easy to plug into
+our basic framework.
+
+Function Code Generation
+========================
+
+Code generation for prototypes and functions must handle a number of
+details, which make their code less beautiful than expression code
+generation, but allows us to illustrate some important points. First,
+let's talk about code generation for prototypes: they are used both for
+function bodies and external function declarations. The code starts
+with:
+
+.. code-block:: c++
+
+    Function *PrototypeAST::codegen() {
+      // Make the function type:  double(double,double) etc.
+      std::vector<Type*> Doubles(Args.size(),
+                                 Type::getDoubleTy(TheContext));
+      FunctionType *FT =
+        FunctionType::get(Type::getDoubleTy(TheContext), Doubles, false);
+
+      Function *F =
+        Function::Create(FT, Function::ExternalLinkage, Name, TheModule.get());
+
+This code packs a lot of power into a few lines. Note first that this
+function returns a "Function\*" instead of a "Value\*". Because a
+"prototype" really talks about the external interface for a function
+(not the value computed by an expression), it makes sense for it to
+return the LLVM Function it corresponds to when codegen'd.
+
+The call to ``FunctionType::get`` creates the ``FunctionType`` that
+should be used for a given Prototype. Since all function arguments in
+Kaleidoscope are of type double, the first line creates a vector of "N"
+LLVM double types. It then uses the ``Functiontype::get`` method to
+create a function type that takes "N" doubles as arguments, returns one
+double as a result, and that is not vararg (the false parameter
+indicates this). Note that Types in LLVM are uniqued just like Constants
+are, so you don't "new" a type, you "get" it.
+
+The final line above actually creates the IR Function corresponding to
+the Prototype. This indicates the type, linkage and name to use, as
+well as which module to insert into. "`external
+linkage <../LangRef.html#linkage>`_" means that the function may be
+defined outside the current module and/or that it is callable by
+functions outside the module. The Name passed in is the name the user
+specified: since "``TheModule``" is specified, this name is registered
+in "``TheModule``"s symbol table.
+
+.. code-block:: c++
+
+  // Set names for all arguments.
+  unsigned Idx = 0;
+  for (auto &Arg : F->args())
+    Arg.setName(Args[Idx++]);
+
+  return F;
+
+Finally, we set the name of each of the function's arguments according to the
+names given in the Prototype. This step isn't strictly necessary, but keeping
+the names consistent makes the IR more readable, and allows subsequent code to
+refer directly to the arguments for their names, rather than having to look up
+them up in the Prototype AST.
+
+At this point we have a function prototype with no body. This is how LLVM IR
+represents function declarations. For extern statements in Kaleidoscope, this
+is as far as we need to go. For function definitions however, we need to
+codegen and attach a function body.
+
+.. code-block:: c++
+
+  Function *FunctionAST::codegen() {
+      // First, check for an existing function from a previous 'extern' declaration.
+    Function *TheFunction = TheModule->getFunction(Proto->getName());
+
+    if (!TheFunction)
+      TheFunction = Proto->codegen();
+
+    if (!TheFunction)
+      return nullptr;
+
+    if (!TheFunction->empty())
+      return (Function*)LogErrorV("Function cannot be redefined.");
+
+
+For function definitions, we start by searching TheModule's symbol table for an
+existing version of this function, in case one has already been created using an
+'extern' statement. If Module::getFunction returns null then no previous version
+exists, so we'll codegen one from the Prototype. In either case, we want to
+assert that the function is empty (i.e. has no body yet) before we start.
+
+.. code-block:: c++
+
+  // Create a new basic block to start insertion into.
+  BasicBlock *BB = BasicBlock::Create(TheContext, "entry", TheFunction);
+  Builder.SetInsertPoint(BB);
+
+  // Record the function arguments in the NamedValues map.
+  NamedValues.clear();
+  for (auto &Arg : TheFunction->args())
+    NamedValues[Arg.getName()] = &Arg;
+
+Now we get to the point where the ``Builder`` is set up. The first line
+creates a new `basic block <http://en.wikipedia.org/wiki/Basic_block>`_
+(named "entry"), which is inserted into ``TheFunction``. The second line
+then tells the builder that new instructions should be inserted into the
+end of the new basic block. Basic blocks in LLVM are an important part
+of functions that define the `Control Flow
+Graph <http://en.wikipedia.org/wiki/Control_flow_graph>`_. Since we
+don't have any control flow, our functions will only contain one block
+at this point. We'll fix this in `Chapter 5 <LangImpl05.html>`_ :).
+
+Next we add the function arguments to the NamedValues map (after first clearing
+it out) so that they're accessible to ``VariableExprAST`` nodes.
+
+.. code-block:: c++
+
+      if (Value *RetVal = Body->codegen()) {
+        // Finish off the function.
+        Builder.CreateRet(RetVal);
+
+        // Validate the generated code, checking for consistency.
+        verifyFunction(*TheFunction);
+
+        return TheFunction;
+      }
+
+Once the insertion point has been set up and the NamedValues map populated,
+we call the ``codegen()`` method for the root expression of the function. If no
+error happens, this emits code to compute the expression into the entry block
+and returns the value that was computed. Assuming no error, we then create an
+LLVM `ret instruction <../LangRef.html#ret-instruction>`_, which completes the function.
+Once the function is built, we call ``verifyFunction``, which is
+provided by LLVM. This function does a variety of consistency checks on
+the generated code, to determine if our compiler is doing everything
+right. Using this is important: it can catch a lot of bugs. Once the
+function is finished and validated, we return it.
+
+.. code-block:: c++
+
+      // Error reading body, remove function.
+      TheFunction->eraseFromParent();
+      return nullptr;
+    }
+
+The only piece left here is handling of the error case. For simplicity,
+we handle this by merely deleting the function we produced with the
+``eraseFromParent`` method. This allows the user to redefine a function
+that they incorrectly typed in before: if we didn't delete it, it would
+live in the symbol table, with a body, preventing future redefinition.
+
+This code does have a bug, though: If the ``FunctionAST::codegen()`` method
+finds an existing IR Function, it does not validate its signature against the
+definition's own prototype. This means that an earlier 'extern' declaration will
+take precedence over the function definition's signature, which can cause
+codegen to fail, for instance if the function arguments are named differently.
+There are a number of ways to fix this bug, see what you can come up with! Here
+is a testcase:
+
+::
+
+    extern foo(a);     # ok, defines foo.
+    def foo(b) b;      # Error: Unknown variable name. (decl using 'a' takes precedence).
+
+Driver Changes and Closing Thoughts
+===================================
+
+For now, code generation to LLVM doesn't really get us much, except that
+we can look at the pretty IR calls. The sample code inserts calls to
+codegen into the "``HandleDefinition``", "``HandleExtern``" etc
+functions, and then dumps out the LLVM IR. This gives a nice way to look
+at the LLVM IR for simple functions. For example:
+
+::
+
+    ready> 4+5;
+    Read top-level expression:
+    define double @0() {
+    entry:
+      ret double 9.000000e+00
+    }
+
+Note how the parser turns the top-level expression into anonymous
+functions for us. This will be handy when we add `JIT
+support <LangImpl4.html#adding-a-jit-compiler>`_ in the next chapter. Also note that the
+code is very literally transcribed, no optimizations are being performed
+except simple constant folding done by IRBuilder. We will `add
+optimizations <LangImpl4.html#trivial-constant-folding>`_ explicitly in the next
+chapter.
+
+::
+
+    ready> def foo(a b) a*a + 2*a*b + b*b;
+    Read function definition:
+    define double @foo(double %a, double %b) {
+    entry:
+      %multmp = fmul double %a, %a
+      %multmp1 = fmul double 2.000000e+00, %a
+      %multmp2 = fmul double %multmp1, %b
+      %addtmp = fadd double %multmp, %multmp2
+      %multmp3 = fmul double %b, %b
+      %addtmp4 = fadd double %addtmp, %multmp3
+      ret double %addtmp4
+    }
+
+This shows some simple arithmetic. Notice the striking similarity to the
+LLVM builder calls that we use to create the instructions.
+
+::
+
+    ready> def bar(a) foo(a, 4.0) + bar(31337);
+    Read function definition:
+    define double @bar(double %a) {
+    entry:
+      %calltmp = call double @foo(double %a, double 4.000000e+00)
+      %calltmp1 = call double @bar(double 3.133700e+04)
+      %addtmp = fadd double %calltmp, %calltmp1
+      ret double %addtmp
+    }
+
+This shows some function calls. Note that this function will take a long
+time to execute if you call it. In the future we'll add conditional
+control flow to actually make recursion useful :).
+
+::
+
+    ready> extern cos(x);
+    Read extern:
+    declare double @cos(double)
+
+    ready> cos(1.234);
+    Read top-level expression:
+    define double @1() {
+    entry:
+      %calltmp = call double @cos(double 1.234000e+00)
+      ret double %calltmp
+    }
+
+This shows an extern for the libm "cos" function, and a call to it.
+
+.. TODO:: Abandon Pygments' horrible `llvm` lexer. It just totally gives up
+   on highlighting this due to the first line.
+
+::
+
+    ready> ^D
+    ; ModuleID = 'my cool jit'
+
+    define double @0() {
+    entry:
+      %addtmp = fadd double 4.000000e+00, 5.000000e+00
+      ret double %addtmp
+    }
+
+    define double @foo(double %a, double %b) {
+    entry:
+      %multmp = fmul double %a, %a
+      %multmp1 = fmul double 2.000000e+00, %a
+      %multmp2 = fmul double %multmp1, %b
+      %addtmp = fadd double %multmp, %multmp2
+      %multmp3 = fmul double %b, %b
+      %addtmp4 = fadd double %addtmp, %multmp3
+      ret double %addtmp4
+    }
+
+    define double @bar(double %a) {
+    entry:
+      %calltmp = call double @foo(double %a, double 4.000000e+00)
+      %calltmp1 = call double @bar(double 3.133700e+04)
+      %addtmp = fadd double %calltmp, %calltmp1
+      ret double %addtmp
+    }
+
+    declare double @cos(double)
+
+    define double @1() {
+    entry:
+      %calltmp = call double @cos(double 1.234000e+00)
+      ret double %calltmp
+    }
+
+When you quit the current demo (by sending an EOF via CTRL+D on Linux
+or CTRL+Z and ENTER on Windows), it dumps out the IR for the entire
+module generated. Here you can see the big picture with all the
+functions referencing each other.
+
+This wraps up the third chapter of the Kaleidoscope tutorial. Up next,
+we'll describe how to `add JIT codegen and optimizer
+support <LangImpl04.html>`_ to this so we can actually start running
+code!
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM code generator. Because this uses the LLVM libraries, we need
+to link them in. To do this, we use the
+`llvm-config <http://llvm.org/cmds/llvm-config.html>`_ tool to inform
+our makefile/command line about which options to use:
+
+.. code-block:: bash
+
+    # Compile
+    clang++ -g -O3 toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core` -o toy
+    # Run
+    ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter3/toy.cpp
+   :language: c++
+
+`Next: Adding JIT and Optimizer Support <LangImpl04.html>`_
+
diff --git a/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl04.rst b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl04.rst
new file mode 100644
index 0000000..bdd21d6
--- /dev/null
+++ b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl04.rst
@@ -0,0 +1,659 @@
+==============================================
+Kaleidoscope: Adding JIT and Optimizer Support
+==============================================
+
+.. contents::
+   :local:
+
+Chapter 4 Introduction
+======================
+
+Welcome to Chapter 4 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. Chapters 1-3 described the implementation
+of a simple language and added support for generating LLVM IR. This
+chapter describes two new techniques: adding optimizer support to your
+language, and adding JIT compiler support. These additions will
+demonstrate how to get nice, efficient code for the Kaleidoscope
+language.
+
+Trivial Constant Folding
+========================
+
+Our demonstration for Chapter 3 is elegant and easy to extend.
+Unfortunately, it does not produce wonderful code. The IRBuilder,
+however, does give us obvious optimizations when compiling simple code:
+
+::
+
+    ready> def test(x) 1+2+x;
+    Read function definition:
+    define double @test(double %x) {
+    entry:
+            %addtmp = fadd double 3.000000e+00, %x
+            ret double %addtmp
+    }
+
+This code is not a literal transcription of the AST built by parsing the
+input. That would be:
+
+::
+
+    ready> def test(x) 1+2+x;
+    Read function definition:
+    define double @test(double %x) {
+    entry:
+            %addtmp = fadd double 2.000000e+00, 1.000000e+00
+            %addtmp1 = fadd double %addtmp, %x
+            ret double %addtmp1
+    }
+
+Constant folding, as seen above, in particular, is a very common and
+very important optimization: so much so that many language implementors
+implement constant folding support in their AST representation.
+
+With LLVM, you don't need this support in the AST. Since all calls to
+build LLVM IR go through the LLVM IR builder, the builder itself checked
+to see if there was a constant folding opportunity when you call it. If
+so, it just does the constant fold and return the constant instead of
+creating an instruction.
+
+Well, that was easy :). In practice, we recommend always using
+``IRBuilder`` when generating code like this. It has no "syntactic
+overhead" for its use (you don't have to uglify your compiler with
+constant checks everywhere) and it can dramatically reduce the amount of
+LLVM IR that is generated in some cases (particular for languages with a
+macro preprocessor or that use a lot of constants).
+
+On the other hand, the ``IRBuilder`` is limited by the fact that it does
+all of its analysis inline with the code as it is built. If you take a
+slightly more complex example:
+
+::
+
+    ready> def test(x) (1+2+x)*(x+(1+2));
+    ready> Read function definition:
+    define double @test(double %x) {
+    entry:
+            %addtmp = fadd double 3.000000e+00, %x
+            %addtmp1 = fadd double %x, 3.000000e+00
+            %multmp = fmul double %addtmp, %addtmp1
+            ret double %multmp
+    }
+
+In this case, the LHS and RHS of the multiplication are the same value.
+We'd really like to see this generate "``tmp = x+3; result = tmp*tmp;``"
+instead of computing "``x+3``" twice.
+
+Unfortunately, no amount of local analysis will be able to detect and
+correct this. This requires two transformations: reassociation of
+expressions (to make the add's lexically identical) and Common
+Subexpression Elimination (CSE) to delete the redundant add instruction.
+Fortunately, LLVM provides a broad range of optimizations that you can
+use, in the form of "passes".
+
+LLVM Optimization Passes
+========================
+
+.. warning::
+
+   Due to the transition to the new PassManager infrastructure this tutorial
+   is based on ``llvm::legacy::FunctionPassManager`` which can be found in
+   `LegacyPassManager.h <http://llvm.org/doxygen/classllvm_1_1legacy_1_1FunctionPassManager.html>`_.
+   For the purpose of the this tutorial the above should be used until
+   the pass manager transition is complete.
+
+LLVM provides many optimization passes, which do many different sorts of
+things and have different tradeoffs. Unlike other systems, LLVM doesn't
+hold to the mistaken notion that one set of optimizations is right for
+all languages and for all situations. LLVM allows a compiler implementor
+to make complete decisions about what optimizations to use, in which
+order, and in what situation.
+
+As a concrete example, LLVM supports both "whole module" passes, which
+look across as large of body of code as they can (often a whole file,
+but if run at link time, this can be a substantial portion of the whole
+program). It also supports and includes "per-function" passes which just
+operate on a single function at a time, without looking at other
+functions. For more information on passes and how they are run, see the
+`How to Write a Pass <../WritingAnLLVMPass.html>`_ document and the
+`List of LLVM Passes <../Passes.html>`_.
+
+For Kaleidoscope, we are currently generating functions on the fly, one
+at a time, as the user types them in. We aren't shooting for the
+ultimate optimization experience in this setting, but we also want to
+catch the easy and quick stuff where possible. As such, we will choose
+to run a few per-function optimizations as the user types the function
+in. If we wanted to make a "static Kaleidoscope compiler", we would use
+exactly the code we have now, except that we would defer running the
+optimizer until the entire file has been parsed.
+
+In order to get per-function optimizations going, we need to set up a
+`FunctionPassManager <../WritingAnLLVMPass.html#what-passmanager-doesr>`_ to hold
+and organize the LLVM optimizations that we want to run. Once we have
+that, we can add a set of optimizations to run. We'll need a new
+FunctionPassManager for each module that we want to optimize, so we'll
+write a function to create and initialize both the module and pass manager
+for us:
+
+.. code-block:: c++
+
+    void InitializeModuleAndPassManager(void) {
+      // Open a new module.
+      TheModule = llvm::make_unique<Module>("my cool jit", TheContext);
+
+      // Create a new pass manager attached to it.
+      TheFPM = llvm::make_unique<FunctionPassManager>(TheModule.get());
+
+      // Do simple "peephole" optimizations and bit-twiddling optzns.
+      TheFPM->add(createInstructionCombiningPass());
+      // Reassociate expressions.
+      TheFPM->add(createReassociatePass());
+      // Eliminate Common SubExpressions.
+      TheFPM->add(createGVNPass());
+      // Simplify the control flow graph (deleting unreachable blocks, etc).
+      TheFPM->add(createCFGSimplificationPass());
+
+      TheFPM->doInitialization();
+    }
+
+This code initializes the global module ``TheModule``, and the function pass
+manager ``TheFPM``, which is attached to ``TheModule``. Once the pass manager is
+set up, we use a series of "add" calls to add a bunch of LLVM passes.
+
+In this case, we choose to add four optimization passes.
+The passes we choose here are a pretty standard set
+of "cleanup" optimizations that are useful for a wide variety of code. I won't
+delve into what they do but, believe me, they are a good starting place :).
+
+Once the PassManager is set up, we need to make use of it. We do this by
+running it after our newly created function is constructed (in
+``FunctionAST::codegen()``), but before it is returned to the client:
+
+.. code-block:: c++
+
+      if (Value *RetVal = Body->codegen()) {
+        // Finish off the function.
+        Builder.CreateRet(RetVal);
+
+        // Validate the generated code, checking for consistency.
+        verifyFunction(*TheFunction);
+
+        // Optimize the function.
+        TheFPM->run(*TheFunction);
+
+        return TheFunction;
+      }
+
+As you can see, this is pretty straightforward. The
+``FunctionPassManager`` optimizes and updates the LLVM Function\* in
+place, improving (hopefully) its body. With this in place, we can try
+our test above again:
+
+::
+
+    ready> def test(x) (1+2+x)*(x+(1+2));
+    ready> Read function definition:
+    define double @test(double %x) {
+    entry:
+            %addtmp = fadd double %x, 3.000000e+00
+            %multmp = fmul double %addtmp, %addtmp
+            ret double %multmp
+    }
+
+As expected, we now get our nicely optimized code, saving a floating
+point add instruction from every execution of this function.
+
+LLVM provides a wide variety of optimizations that can be used in
+certain circumstances. Some `documentation about the various
+passes <../Passes.html>`_ is available, but it isn't very complete.
+Another good source of ideas can come from looking at the passes that
+``Clang`` runs to get started. The "``opt``" tool allows you to
+experiment with passes from the command line, so you can see if they do
+anything.
+
+Now that we have reasonable code coming out of our front-end, let's talk
+about executing it!
+
+Adding a JIT Compiler
+=====================
+
+Code that is available in LLVM IR can have a wide variety of tools
+applied to it. For example, you can run optimizations on it (as we did
+above), you can dump it out in textual or binary forms, you can compile
+the code to an assembly file (.s) for some target, or you can JIT
+compile it. The nice thing about the LLVM IR representation is that it
+is the "common currency" between many different parts of the compiler.
+
+In this section, we'll add JIT compiler support to our interpreter. The
+basic idea that we want for Kaleidoscope is to have the user enter
+function bodies as they do now, but immediately evaluate the top-level
+expressions they type in. For example, if they type in "1 + 2;", we
+should evaluate and print out 3. If they define a function, they should
+be able to call it from the command line.
+
+In order to do this, we first prepare the environment to create code for
+the current native target and declare and initialize the JIT. This is
+done by calling some ``InitializeNativeTarget\*`` functions and
+adding a global variable ``TheJIT``, and initializing it in
+``main``:
+
+.. code-block:: c++
+
+    static std::unique_ptr<KaleidoscopeJIT> TheJIT;
+    ...
+    int main() {
+      InitializeNativeTarget();
+      InitializeNativeTargetAsmPrinter();
+      InitializeNativeTargetAsmParser();
+
+      // Install standard binary operators.
+      // 1 is lowest precedence.
+      BinopPrecedence['<'] = 10;
+      BinopPrecedence['+'] = 20;
+      BinopPrecedence['-'] = 20;
+      BinopPrecedence['*'] = 40; // highest.
+
+      // Prime the first token.
+      fprintf(stderr, "ready> ");
+      getNextToken();
+
+      TheJIT = llvm::make_unique<KaleidoscopeJIT>();
+
+      // Run the main "interpreter loop" now.
+      MainLoop();
+
+      return 0;
+    }
+
+We also need to setup the data layout for the JIT:
+
+.. code-block:: c++
+
+    void InitializeModuleAndPassManager(void) {
+      // Open a new module.
+      TheModule = llvm::make_unique<Module>("my cool jit", TheContext);
+      TheModule->setDataLayout(TheJIT->getTargetMachine().createDataLayout());
+
+      // Create a new pass manager attached to it.
+      TheFPM = llvm::make_unique<FunctionPassManager>(TheModule.get());
+      ...
+
+The KaleidoscopeJIT class is a simple JIT built specifically for these
+tutorials, available inside the LLVM source code
+at llvm-src/examples/Kaleidoscope/include/KaleidoscopeJIT.h.
+In later chapters we will look at how it works and extend it with
+new features, but for now we will take it as given. Its API is very simple:
+``addModule`` adds an LLVM IR module to the JIT, making its functions
+available for execution; ``removeModule`` removes a module, freeing any
+memory associated with the code in that module; and ``findSymbol`` allows us
+to look up pointers to the compiled code.
+
+We can take this simple API and change our code that parses top-level expressions to
+look like this:
+
+.. code-block:: c++
+
+    static void HandleTopLevelExpression() {
+      // Evaluate a top-level expression into an anonymous function.
+      if (auto FnAST = ParseTopLevelExpr()) {
+        if (FnAST->codegen()) {
+
+          // JIT the module containing the anonymous expression, keeping a handle so
+          // we can free it later.
+          auto H = TheJIT->addModule(std::move(TheModule));
+          InitializeModuleAndPassManager();
+
+          // Search the JIT for the __anon_expr symbol.
+          auto ExprSymbol = TheJIT->findSymbol("__anon_expr");
+          assert(ExprSymbol && "Function not found");
+
+          // Get the symbol's address and cast it to the right type (takes no
+          // arguments, returns a double) so we can call it as a native function.
+          double (*FP)() = (double (*)())(intptr_t)ExprSymbol.getAddress();
+          fprintf(stderr, "Evaluated to %f\n", FP());
+
+          // Delete the anonymous expression module from the JIT.
+          TheJIT->removeModule(H);
+        }
+
+If parsing and codegen succeeed, the next step is to add the module containing
+the top-level expression to the JIT. We do this by calling addModule, which
+triggers code generation for all the functions in the module, and returns a
+handle that can be used to remove the module from the JIT later. Once the module
+has been added to the JIT it can no longer be modified, so we also open a new
+module to hold subsequent code by calling ``InitializeModuleAndPassManager()``.
+
+Once we've added the module to the JIT we need to get a pointer to the final
+generated code. We do this by calling the JIT's findSymbol method, and passing
+the name of the top-level expression function: ``__anon_expr``. Since we just
+added this function, we assert that findSymbol returned a result.
+
+Next, we get the in-memory address of the ``__anon_expr`` function by calling
+``getAddress()`` on the symbol. Recall that we compile top-level expressions
+into a self-contained LLVM function that takes no arguments and returns the
+computed double. Because the LLVM JIT compiler matches the native platform ABI,
+this means that you can just cast the result pointer to a function pointer of
+that type and call it directly. This means, there is no difference between JIT
+compiled code and native machine code that is statically linked into your
+application.
+
+Finally, since we don't support re-evaluation of top-level expressions, we
+remove the module from the JIT when we're done to free the associated memory.
+Recall, however, that the module we created a few lines earlier (via
+``InitializeModuleAndPassManager``) is still open and waiting for new code to be
+added.
+
+With just these two changes, let's see how Kaleidoscope works now!
+
+::
+
+    ready> 4+5;
+    Read top-level expression:
+    define double @0() {
+    entry:
+      ret double 9.000000e+00
+    }
+
+    Evaluated to 9.000000
+
+Well this looks like it is basically working. The dump of the function
+shows the "no argument function that always returns double" that we
+synthesize for each top-level expression that is typed in. This
+demonstrates very basic functionality, but can we do more?
+
+::
+
+    ready> def testfunc(x y) x + y*2;
+    Read function definition:
+    define double @testfunc(double %x, double %y) {
+    entry:
+      %multmp = fmul double %y, 2.000000e+00
+      %addtmp = fadd double %multmp, %x
+      ret double %addtmp
+    }
+
+    ready> testfunc(4, 10);
+    Read top-level expression:
+    define double @1() {
+    entry:
+      %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
+      ret double %calltmp
+    }
+
+    Evaluated to 24.000000
+
+    ready> testfunc(5, 10);
+    ready> LLVM ERROR: Program used external function 'testfunc' which could not be resolved!
+
+
+Function definitions and calls also work, but something went very wrong on that
+last line. The call looks valid, so what happened? As you may have guessed from
+the API a Module is a unit of allocation for the JIT, and testfunc was part
+of the same module that contained anonymous expression. When we removed that
+module from the JIT to free the memory for the anonymous expression, we deleted
+the definition of ``testfunc`` along with it. Then, when we tried to call
+testfunc a second time, the JIT could no longer find it.
+
+The easiest way to fix this is to put the anonymous expression in a separate
+module from the rest of the function definitions. The JIT will happily resolve
+function calls across module boundaries, as long as each of the functions called
+has a prototype, and is added to the JIT before it is called. By putting the
+anonymous expression in a different module we can delete it without affecting
+the rest of the functions.
+
+In fact, we're going to go a step further and put every function in its own
+module. Doing so allows us to exploit a useful property of the KaleidoscopeJIT
+that will make our environment more REPL-like: Functions can be added to the
+JIT more than once (unlike a module where every function must have a unique
+definition). When you look up a symbol in KaleidoscopeJIT it will always return
+the most recent definition:
+
+::
+
+    ready> def foo(x) x + 1;
+    Read function definition:
+    define double @foo(double %x) {
+    entry:
+      %addtmp = fadd double %x, 1.000000e+00
+      ret double %addtmp
+    }
+
+    ready> foo(2);
+    Evaluated to 3.000000
+
+    ready> def foo(x) x + 2;
+    define double @foo(double %x) {
+    entry:
+      %addtmp = fadd double %x, 2.000000e+00
+      ret double %addtmp
+    }
+
+    ready> foo(2);
+    Evaluated to 4.000000
+
+
+To allow each function to live in its own module we'll need a way to
+re-generate previous function declarations into each new module we open:
+
+.. code-block:: c++
+
+    static std::unique_ptr<KaleidoscopeJIT> TheJIT;
+
+    ...
+
+    Function *getFunction(std::string Name) {
+      // First, see if the function has already been added to the current module.
+      if (auto *F = TheModule->getFunction(Name))
+        return F;
+
+      // If not, check whether we can codegen the declaration from some existing
+      // prototype.
+      auto FI = FunctionProtos.find(Name);
+      if (FI != FunctionProtos.end())
+        return FI->second->codegen();
+
+      // If no existing prototype exists, return null.
+      return nullptr;
+    }
+
+    ...
+
+    Value *CallExprAST::codegen() {
+      // Look up the name in the global module table.
+      Function *CalleeF = getFunction(Callee);
+
+    ...
+
+    Function *FunctionAST::codegen() {
+      // Transfer ownership of the prototype to the FunctionProtos map, but keep a
+      // reference to it for use below.
+      auto &P = *Proto;
+      FunctionProtos[Proto->getName()] = std::move(Proto);
+      Function *TheFunction = getFunction(P.getName());
+      if (!TheFunction)
+        return nullptr;
+
+
+To enable this, we'll start by adding a new global, ``FunctionProtos``, that
+holds the most recent prototype for each function. We'll also add a convenience
+method, ``getFunction()``, to replace calls to ``TheModule->getFunction()``.
+Our convenience method searches ``TheModule`` for an existing function
+declaration, falling back to generating a new declaration from FunctionProtos if
+it doesn't find one. In ``CallExprAST::codegen()`` we just need to replace the
+call to ``TheModule->getFunction()``. In ``FunctionAST::codegen()`` we need to
+update the FunctionProtos map first, then call ``getFunction()``. With this
+done, we can always obtain a function declaration in the current module for any
+previously declared function.
+
+We also need to update HandleDefinition and HandleExtern:
+
+.. code-block:: c++
+
+    static void HandleDefinition() {
+      if (auto FnAST = ParseDefinition()) {
+        if (auto *FnIR = FnAST->codegen()) {
+          fprintf(stderr, "Read function definition:");
+          FnIR->print(errs());
+          fprintf(stderr, "\n");
+          TheJIT->addModule(std::move(TheModule));
+          InitializeModuleAndPassManager();
+        }
+      } else {
+        // Skip token for error recovery.
+         getNextToken();
+      }
+    }
+
+    static void HandleExtern() {
+      if (auto ProtoAST = ParseExtern()) {
+        if (auto *FnIR = ProtoAST->codegen()) {
+          fprintf(stderr, "Read extern: ");
+          FnIR->print(errs());
+          fprintf(stderr, "\n");
+          FunctionProtos[ProtoAST->getName()] = std::move(ProtoAST);
+        }
+      } else {
+        // Skip token for error recovery.
+        getNextToken();
+      }
+    }
+
+In HandleDefinition, we add two lines to transfer the newly defined function to
+the JIT and open a new module. In HandleExtern, we just need to add one line to
+add the prototype to FunctionProtos.
+
+With these changes made, let's try our REPL again (I removed the dump of the
+anonymous functions this time, you should get the idea by now :) :
+
+::
+
+    ready> def foo(x) x + 1;
+    ready> foo(2);
+    Evaluated to 3.000000
+
+    ready> def foo(x) x + 2;
+    ready> foo(2);
+    Evaluated to 4.000000
+
+It works!
+
+Even with this simple code, we get some surprisingly powerful capabilities -
+check this out:
+
+::
+
+    ready> extern sin(x);
+    Read extern:
+    declare double @sin(double)
+
+    ready> extern cos(x);
+    Read extern:
+    declare double @cos(double)
+
+    ready> sin(1.0);
+    Read top-level expression:
+    define double @2() {
+    entry:
+      ret double 0x3FEAED548F090CEE
+    }
+
+    Evaluated to 0.841471
+
+    ready> def foo(x) sin(x)*sin(x) + cos(x)*cos(x);
+    Read function definition:
+    define double @foo(double %x) {
+    entry:
+      %calltmp = call double @sin(double %x)
+      %multmp = fmul double %calltmp, %calltmp
+      %calltmp2 = call double @cos(double %x)
+      %multmp4 = fmul double %calltmp2, %calltmp2
+      %addtmp = fadd double %multmp, %multmp4
+      ret double %addtmp
+    }
+
+    ready> foo(4.0);
+    Read top-level expression:
+    define double @3() {
+    entry:
+      %calltmp = call double @foo(double 4.000000e+00)
+      ret double %calltmp
+    }
+
+    Evaluated to 1.000000
+
+Whoa, how does the JIT know about sin and cos? The answer is surprisingly
+simple: The KaleidoscopeJIT has a straightforward symbol resolution rule that
+it uses to find symbols that aren't available in any given module: First
+it searches all the modules that have already been added to the JIT, from the
+most recent to the oldest, to find the newest definition. If no definition is
+found inside the JIT, it falls back to calling "``dlsym("sin")``" on the
+Kaleidoscope process itself. Since "``sin``" is defined within the JIT's
+address space, it simply patches up calls in the module to call the libm
+version of ``sin`` directly. But in some cases this even goes further:
+as sin and cos are names of standard math functions, the constant folder
+will directly evaluate the function calls to the correct result when called
+with constants like in the "``sin(1.0)``" above.
+
+In the future we'll see how tweaking this symbol resolution rule can be used to
+enable all sorts of useful features, from security (restricting the set of
+symbols available to JIT'd code), to dynamic code generation based on symbol
+names, and even lazy compilation.
+
+One immediate benefit of the symbol resolution rule is that we can now extend
+the language by writing arbitrary C++ code to implement operations. For example,
+if we add:
+
+.. code-block:: c++
+
+    #ifdef _WIN32
+    #define DLLEXPORT __declspec(dllexport)
+    #else
+    #define DLLEXPORT
+    #endif
+
+    /// putchard - putchar that takes a double and returns 0.
+    extern "C" DLLEXPORT double putchard(double X) {
+      fputc((char)X, stderr);
+      return 0;
+    }
+
+Note, that for Windows we need to actually export the functions because
+the dynamic symbol loader will use GetProcAddress to find the symbols.
+
+Now we can produce simple output to the console by using things like:
+"``extern putchard(x); putchard(120);``", which prints a lowercase 'x'
+on the console (120 is the ASCII code for 'x'). Similar code could be
+used to implement file I/O, console input, and many other capabilities
+in Kaleidoscope.
+
+This completes the JIT and optimizer chapter of the Kaleidoscope
+tutorial. At this point, we can compile a non-Turing-complete
+programming language, optimize and JIT compile it in a user-driven way.
+Next up we'll look into `extending the language with control flow
+constructs <LangImpl05.html>`_, tackling some interesting LLVM IR issues
+along the way.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM JIT and optimizer. To build this example, use:
+
+.. code-block:: bash
+
+    # Compile
+    clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+    # Run
+    ./toy
+
+If you are compiling this on Linux, make sure to add the "-rdynamic"
+option as well. This makes sure that the external functions are resolved
+properly at runtime.
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter4/toy.cpp
+   :language: c++
+
+`Next: Extending the language: control flow <LangImpl05.html>`_
+
diff --git a/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl05-cfg.png b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl05-cfg.png
new file mode 100644
index 0000000..cdba92f
--- /dev/null
+++ b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl05-cfg.png
Binary files differ
diff --git a/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl05.rst b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl05.rst
new file mode 100644
index 0000000..dad2489
--- /dev/null
+++ b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl05.rst
@@ -0,0 +1,814 @@
+==================================================
+Kaleidoscope: Extending the Language: Control Flow
+==================================================
+
+.. contents::
+   :local:
+
+Chapter 5 Introduction
+======================
+
+Welcome to Chapter 5 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. Parts 1-4 described the implementation of
+the simple Kaleidoscope language and included support for generating
+LLVM IR, followed by optimizations and a JIT compiler. Unfortunately, as
+presented, Kaleidoscope is mostly useless: it has no control flow other
+than call and return. This means that you can't have conditional
+branches in the code, significantly limiting its power. In this episode
+of "build that compiler", we'll extend Kaleidoscope to have an
+if/then/else expression plus a simple 'for' loop.
+
+If/Then/Else
+============
+
+Extending Kaleidoscope to support if/then/else is quite straightforward.
+It basically requires adding support for this "new" concept to the
+lexer, parser, AST, and LLVM code emitter. This example is nice, because
+it shows how easy it is to "grow" a language over time, incrementally
+extending it as new ideas are discovered.
+
+Before we get going on "how" we add this extension, let's talk about
+"what" we want. The basic idea is that we want to be able to write this
+sort of thing:
+
+::
+
+    def fib(x)
+      if x < 3 then
+        1
+      else
+        fib(x-1)+fib(x-2);
+
+In Kaleidoscope, every construct is an expression: there are no
+statements. As such, the if/then/else expression needs to return a value
+like any other. Since we're using a mostly functional form, we'll have
+it evaluate its conditional, then return the 'then' or 'else' value
+based on how the condition was resolved. This is very similar to the C
+"?:" expression.
+
+The semantics of the if/then/else expression is that it evaluates the
+condition to a boolean equality value: 0.0 is considered to be false and
+everything else is considered to be true. If the condition is true, the
+first subexpression is evaluated and returned, if the condition is
+false, the second subexpression is evaluated and returned. Since
+Kaleidoscope allows side-effects, this behavior is important to nail
+down.
+
+Now that we know what we "want", let's break this down into its
+constituent pieces.
+
+Lexer Extensions for If/Then/Else
+---------------------------------
+
+The lexer extensions are straightforward. First we add new enum values
+for the relevant tokens:
+
+.. code-block:: c++
+
+      // control
+      tok_if = -6,
+      tok_then = -7,
+      tok_else = -8,
+
+Once we have that, we recognize the new keywords in the lexer. This is
+pretty simple stuff:
+
+.. code-block:: c++
+
+        ...
+        if (IdentifierStr == "def")
+          return tok_def;
+        if (IdentifierStr == "extern")
+          return tok_extern;
+        if (IdentifierStr == "if")
+          return tok_if;
+        if (IdentifierStr == "then")
+          return tok_then;
+        if (IdentifierStr == "else")
+          return tok_else;
+        return tok_identifier;
+
+AST Extensions for If/Then/Else
+-------------------------------
+
+To represent the new expression we add a new AST node for it:
+
+.. code-block:: c++
+
+    /// IfExprAST - Expression class for if/then/else.
+    class IfExprAST : public ExprAST {
+      std::unique_ptr<ExprAST> Cond, Then, Else;
+
+    public:
+      IfExprAST(std::unique_ptr<ExprAST> Cond, std::unique_ptr<ExprAST> Then,
+                std::unique_ptr<ExprAST> Else)
+        : Cond(std::move(Cond)), Then(std::move(Then)), Else(std::move(Else)) {}
+
+      Value *codegen() override;
+    };
+
+The AST node just has pointers to the various subexpressions.
+
+Parser Extensions for If/Then/Else
+----------------------------------
+
+Now that we have the relevant tokens coming from the lexer and we have
+the AST node to build, our parsing logic is relatively straightforward.
+First we define a new parsing function:
+
+.. code-block:: c++
+
+    /// ifexpr ::= 'if' expression 'then' expression 'else' expression
+    static std::unique_ptr<ExprAST> ParseIfExpr() {
+      getNextToken();  // eat the if.
+
+      // condition.
+      auto Cond = ParseExpression();
+      if (!Cond)
+        return nullptr;
+
+      if (CurTok != tok_then)
+        return LogError("expected then");
+      getNextToken();  // eat the then
+
+      auto Then = ParseExpression();
+      if (!Then)
+        return nullptr;
+
+      if (CurTok != tok_else)
+        return LogError("expected else");
+
+      getNextToken();
+
+      auto Else = ParseExpression();
+      if (!Else)
+        return nullptr;
+
+      return llvm::make_unique<IfExprAST>(std::move(Cond), std::move(Then),
+                                          std::move(Else));
+    }
+
+Next we hook it up as a primary expression:
+
+.. code-block:: c++
+
+    static std::unique_ptr<ExprAST> ParsePrimary() {
+      switch (CurTok) {
+      default:
+        return LogError("unknown token when expecting an expression");
+      case tok_identifier:
+        return ParseIdentifierExpr();
+      case tok_number:
+        return ParseNumberExpr();
+      case '(':
+        return ParseParenExpr();
+      case tok_if:
+        return ParseIfExpr();
+      }
+    }
+
+LLVM IR for If/Then/Else
+------------------------
+
+Now that we have it parsing and building the AST, the final piece is
+adding LLVM code generation support. This is the most interesting part
+of the if/then/else example, because this is where it starts to
+introduce new concepts. All of the code above has been thoroughly
+described in previous chapters.
+
+To motivate the code we want to produce, let's take a look at a simple
+example. Consider:
+
+::
+
+    extern foo();
+    extern bar();
+    def baz(x) if x then foo() else bar();
+
+If you disable optimizations, the code you'll (soon) get from
+Kaleidoscope looks like this:
+
+.. code-block:: llvm
+
+    declare double @foo()
+
+    declare double @bar()
+
+    define double @baz(double %x) {
+    entry:
+      %ifcond = fcmp one double %x, 0.000000e+00
+      br i1 %ifcond, label %then, label %else
+
+    then:       ; preds = %entry
+      %calltmp = call double @foo()
+      br label %ifcont
+
+    else:       ; preds = %entry
+      %calltmp1 = call double @bar()
+      br label %ifcont
+
+    ifcont:     ; preds = %else, %then
+      %iftmp = phi double [ %calltmp, %then ], [ %calltmp1, %else ]
+      ret double %iftmp
+    }
+
+To visualize the control flow graph, you can use a nifty feature of the
+LLVM '`opt <http://llvm.org/cmds/opt.html>`_' tool. If you put this LLVM
+IR into "t.ll" and run "``llvm-as < t.ll | opt -analyze -view-cfg``", `a
+window will pop up <../ProgrammersManual.html#viewing-graphs-while-debugging-code>`_ and you'll
+see this graph:
+
+.. figure:: LangImpl05-cfg.png
+   :align: center
+   :alt: Example CFG
+
+   Example CFG
+
+Another way to get this is to call "``F->viewCFG()``" or
+"``F->viewCFGOnly()``" (where F is a "``Function*``") either by
+inserting actual calls into the code and recompiling or by calling these
+in the debugger. LLVM has many nice features for visualizing various
+graphs.
+
+Getting back to the generated code, it is fairly simple: the entry block
+evaluates the conditional expression ("x" in our case here) and compares
+the result to 0.0 with the "``fcmp one``" instruction ('one' is "Ordered
+and Not Equal"). Based on the result of this expression, the code jumps
+to either the "then" or "else" blocks, which contain the expressions for
+the true/false cases.
+
+Once the then/else blocks are finished executing, they both branch back
+to the 'ifcont' block to execute the code that happens after the
+if/then/else. In this case the only thing left to do is to return to the
+caller of the function. The question then becomes: how does the code
+know which expression to return?
+
+The answer to this question involves an important SSA operation: the
+`Phi
+operation <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+If you're not familiar with SSA, `the wikipedia
+article <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+is a good introduction and there are various other introductions to it
+available on your favorite search engine. The short version is that
+"execution" of the Phi operation requires "remembering" which block
+control came from. The Phi operation takes on the value corresponding to
+the input control block. In this case, if control comes in from the
+"then" block, it gets the value of "calltmp". If control comes from the
+"else" block, it gets the value of "calltmp1".
+
+At this point, you are probably starting to think "Oh no! This means my
+simple and elegant front-end will have to start generating SSA form in
+order to use LLVM!". Fortunately, this is not the case, and we strongly
+advise *not* implementing an SSA construction algorithm in your
+front-end unless there is an amazingly good reason to do so. In
+practice, there are two sorts of values that float around in code
+written for your average imperative programming language that might need
+Phi nodes:
+
+#. Code that involves user variables: ``x = 1; x = x + 1;``
+#. Values that are implicit in the structure of your AST, such as the
+   Phi node in this case.
+
+In `Chapter 7 <LangImpl07.html>`_ of this tutorial ("mutable variables"),
+we'll talk about #1 in depth. For now, just believe me that you don't
+need SSA construction to handle this case. For #2, you have the choice
+of using the techniques that we will describe for #1, or you can insert
+Phi nodes directly, if convenient. In this case, it is really
+easy to generate the Phi node, so we choose to do it directly.
+
+Okay, enough of the motivation and overview, let's generate code!
+
+Code Generation for If/Then/Else
+--------------------------------
+
+In order to generate code for this, we implement the ``codegen`` method
+for ``IfExprAST``:
+
+.. code-block:: c++
+
+    Value *IfExprAST::codegen() {
+      Value *CondV = Cond->codegen();
+      if (!CondV)
+        return nullptr;
+
+      // Convert condition to a bool by comparing non-equal to 0.0.
+      CondV = Builder.CreateFCmpONE(
+          CondV, ConstantFP::get(TheContext, APFloat(0.0)), "ifcond");
+
+This code is straightforward and similar to what we saw before. We emit
+the expression for the condition, then compare that value to zero to get
+a truth value as a 1-bit (bool) value.
+
+.. code-block:: c++
+
+      Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+      // Create blocks for the then and else cases.  Insert the 'then' block at the
+      // end of the function.
+      BasicBlock *ThenBB =
+          BasicBlock::Create(TheContext, "then", TheFunction);
+      BasicBlock *ElseBB = BasicBlock::Create(TheContext, "else");
+      BasicBlock *MergeBB = BasicBlock::Create(TheContext, "ifcont");
+
+      Builder.CreateCondBr(CondV, ThenBB, ElseBB);
+
+This code creates the basic blocks that are related to the if/then/else
+statement, and correspond directly to the blocks in the example above.
+The first line gets the current Function object that is being built. It
+gets this by asking the builder for the current BasicBlock, and asking
+that block for its "parent" (the function it is currently embedded
+into).
+
+Once it has that, it creates three blocks. Note that it passes
+"TheFunction" into the constructor for the "then" block. This causes the
+constructor to automatically insert the new block into the end of the
+specified function. The other two blocks are created, but aren't yet
+inserted into the function.
+
+Once the blocks are created, we can emit the conditional branch that
+chooses between them. Note that creating new blocks does not implicitly
+affect the IRBuilder, so it is still inserting into the block that the
+condition went into. Also note that it is creating a branch to the
+"then" block and the "else" block, even though the "else" block isn't
+inserted into the function yet. This is all ok: it is the standard way
+that LLVM supports forward references.
+
+.. code-block:: c++
+
+      // Emit then value.
+      Builder.SetInsertPoint(ThenBB);
+
+      Value *ThenV = Then->codegen();
+      if (!ThenV)
+        return nullptr;
+
+      Builder.CreateBr(MergeBB);
+      // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
+      ThenBB = Builder.GetInsertBlock();
+
+After the conditional branch is inserted, we move the builder to start
+inserting into the "then" block. Strictly speaking, this call moves the
+insertion point to be at the end of the specified block. However, since
+the "then" block is empty, it also starts out by inserting at the
+beginning of the block. :)
+
+Once the insertion point is set, we recursively codegen the "then"
+expression from the AST. To finish off the "then" block, we create an
+unconditional branch to the merge block. One interesting (and very
+important) aspect of the LLVM IR is that it `requires all basic blocks
+to be "terminated" <../LangRef.html#functionstructure>`_ with a `control
+flow instruction <../LangRef.html#terminators>`_ such as return or
+branch. This means that all control flow, *including fall throughs* must
+be made explicit in the LLVM IR. If you violate this rule, the verifier
+will emit an error.
+
+The final line here is quite subtle, but is very important. The basic
+issue is that when we create the Phi node in the merge block, we need to
+set up the block/value pairs that indicate how the Phi will work.
+Importantly, the Phi node expects to have an entry for each predecessor
+of the block in the CFG. Why then, are we getting the current block when
+we just set it to ThenBB 5 lines above? The problem is that the "Then"
+expression may actually itself change the block that the Builder is
+emitting into if, for example, it contains a nested "if/then/else"
+expression. Because calling ``codegen()`` recursively could arbitrarily change
+the notion of the current block, we are required to get an up-to-date
+value for code that will set up the Phi node.
+
+.. code-block:: c++
+
+      // Emit else block.
+      TheFunction->getBasicBlockList().push_back(ElseBB);
+      Builder.SetInsertPoint(ElseBB);
+
+      Value *ElseV = Else->codegen();
+      if (!ElseV)
+        return nullptr;
+
+      Builder.CreateBr(MergeBB);
+      // codegen of 'Else' can change the current block, update ElseBB for the PHI.
+      ElseBB = Builder.GetInsertBlock();
+
+Code generation for the 'else' block is basically identical to codegen
+for the 'then' block. The only significant difference is the first line,
+which adds the 'else' block to the function. Recall previously that the
+'else' block was created, but not added to the function. Now that the
+'then' and 'else' blocks are emitted, we can finish up with the merge
+code:
+
+.. code-block:: c++
+
+      // Emit merge block.
+      TheFunction->getBasicBlockList().push_back(MergeBB);
+      Builder.SetInsertPoint(MergeBB);
+      PHINode *PN =
+        Builder.CreatePHI(Type::getDoubleTy(TheContext), 2, "iftmp");
+
+      PN->addIncoming(ThenV, ThenBB);
+      PN->addIncoming(ElseV, ElseBB);
+      return PN;
+    }
+
+The first two lines here are now familiar: the first adds the "merge"
+block to the Function object (it was previously floating, like the else
+block above). The second changes the insertion point so that newly
+created code will go into the "merge" block. Once that is done, we need
+to create the PHI node and set up the block/value pairs for the PHI.
+
+Finally, the CodeGen function returns the phi node as the value computed
+by the if/then/else expression. In our example above, this returned
+value will feed into the code for the top-level function, which will
+create the return instruction.
+
+Overall, we now have the ability to execute conditional code in
+Kaleidoscope. With this extension, Kaleidoscope is a fairly complete
+language that can calculate a wide variety of numeric functions. Next up
+we'll add another useful expression that is familiar from non-functional
+languages...
+
+'for' Loop Expression
+=====================
+
+Now that we know how to add basic control flow constructs to the
+language, we have the tools to add more powerful things. Let's add
+something more aggressive, a 'for' expression:
+
+::
+
+     extern putchard(char);
+     def printstar(n)
+       for i = 1, i < n, 1.0 in
+         putchard(42);  # ascii 42 = '*'
+
+     # print 100 '*' characters
+     printstar(100);
+
+This expression defines a new variable ("i" in this case) which iterates
+from a starting value, while the condition ("i < n" in this case) is
+true, incrementing by an optional step value ("1.0" in this case). If
+the step value is omitted, it defaults to 1.0. While the loop is true,
+it executes its body expression. Because we don't have anything better
+to return, we'll just define the loop as always returning 0.0. In the
+future when we have mutable variables, it will get more useful.
+
+As before, let's talk about the changes that we need to Kaleidoscope to
+support this.
+
+Lexer Extensions for the 'for' Loop
+-----------------------------------
+
+The lexer extensions are the same sort of thing as for if/then/else:
+
+.. code-block:: c++
+
+      ... in enum Token ...
+      // control
+      tok_if = -6, tok_then = -7, tok_else = -8,
+      tok_for = -9, tok_in = -10
+
+      ... in gettok ...
+      if (IdentifierStr == "def")
+        return tok_def;
+      if (IdentifierStr == "extern")
+        return tok_extern;
+      if (IdentifierStr == "if")
+        return tok_if;
+      if (IdentifierStr == "then")
+        return tok_then;
+      if (IdentifierStr == "else")
+        return tok_else;
+      if (IdentifierStr == "for")
+        return tok_for;
+      if (IdentifierStr == "in")
+        return tok_in;
+      return tok_identifier;
+
+AST Extensions for the 'for' Loop
+---------------------------------
+
+The AST node is just as simple. It basically boils down to capturing the
+variable name and the constituent expressions in the node.
+
+.. code-block:: c++
+
+    /// ForExprAST - Expression class for for/in.
+    class ForExprAST : public ExprAST {
+      std::string VarName;
+      std::unique_ptr<ExprAST> Start, End, Step, Body;
+
+    public:
+      ForExprAST(const std::string &VarName, std::unique_ptr<ExprAST> Start,
+                 std::unique_ptr<ExprAST> End, std::unique_ptr<ExprAST> Step,
+                 std::unique_ptr<ExprAST> Body)
+        : VarName(VarName), Start(std::move(Start)), End(std::move(End)),
+          Step(std::move(Step)), Body(std::move(Body)) {}
+
+      Value *codegen() override;
+    };
+
+Parser Extensions for the 'for' Loop
+------------------------------------
+
+The parser code is also fairly standard. The only interesting thing here
+is handling of the optional step value. The parser code handles it by
+checking to see if the second comma is present. If not, it sets the step
+value to null in the AST node:
+
+.. code-block:: c++
+
+    /// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
+    static std::unique_ptr<ExprAST> ParseForExpr() {
+      getNextToken();  // eat the for.
+
+      if (CurTok != tok_identifier)
+        return LogError("expected identifier after for");
+
+      std::string IdName = IdentifierStr;
+      getNextToken();  // eat identifier.
+
+      if (CurTok != '=')
+        return LogError("expected '=' after for");
+      getNextToken();  // eat '='.
+
+
+      auto Start = ParseExpression();
+      if (!Start)
+        return nullptr;
+      if (CurTok != ',')
+        return LogError("expected ',' after for start value");
+      getNextToken();
+
+      auto End = ParseExpression();
+      if (!End)
+        return nullptr;
+
+      // The step value is optional.
+      std::unique_ptr<ExprAST> Step;
+      if (CurTok == ',') {
+        getNextToken();
+        Step = ParseExpression();
+        if (!Step)
+          return nullptr;
+      }
+
+      if (CurTok != tok_in)
+        return LogError("expected 'in' after for");
+      getNextToken();  // eat 'in'.
+
+      auto Body = ParseExpression();
+      if (!Body)
+        return nullptr;
+
+      return llvm::make_unique<ForExprAST>(IdName, std::move(Start),
+                                           std::move(End), std::move(Step),
+                                           std::move(Body));
+    }
+
+And again we hook it up as a primary expression:
+
+.. code-block:: c++
+
+    static std::unique_ptr<ExprAST> ParsePrimary() {
+      switch (CurTok) {
+      default:
+        return LogError("unknown token when expecting an expression");
+      case tok_identifier:
+        return ParseIdentifierExpr();
+      case tok_number:
+        return ParseNumberExpr();
+      case '(':
+        return ParseParenExpr();
+      case tok_if:
+        return ParseIfExpr();
+      case tok_for:
+        return ParseForExpr();
+      }
+    }
+
+LLVM IR for the 'for' Loop
+--------------------------
+
+Now we get to the good part: the LLVM IR we want to generate for this
+thing. With the simple example above, we get this LLVM IR (note that
+this dump is generated with optimizations disabled for clarity):
+
+.. code-block:: llvm
+
+    declare double @putchard(double)
+
+    define double @printstar(double %n) {
+    entry:
+      ; initial value = 1.0 (inlined into phi)
+      br label %loop
+
+    loop:       ; preds = %loop, %entry
+      %i = phi double [ 1.000000e+00, %entry ], [ %nextvar, %loop ]
+      ; body
+      %calltmp = call double @putchard(double 4.200000e+01)
+      ; increment
+      %nextvar = fadd double %i, 1.000000e+00
+
+      ; termination test
+      %cmptmp = fcmp ult double %i, %n
+      %booltmp = uitofp i1 %cmptmp to double
+      %loopcond = fcmp one double %booltmp, 0.000000e+00
+      br i1 %loopcond, label %loop, label %afterloop
+
+    afterloop:      ; preds = %loop
+      ; loop always returns 0.0
+      ret double 0.000000e+00
+    }
+
+This loop contains all the same constructs we saw before: a phi node,
+several expressions, and some basic blocks. Let's see how this fits
+together.
+
+Code Generation for the 'for' Loop
+----------------------------------
+
+The first part of codegen is very simple: we just output the start
+expression for the loop value:
+
+.. code-block:: c++
+
+    Value *ForExprAST::codegen() {
+      // Emit the start code first, without 'variable' in scope.
+      Value *StartVal = Start->codegen();
+      if (!StartVal)
+        return nullptr;
+
+With this out of the way, the next step is to set up the LLVM basic
+block for the start of the loop body. In the case above, the whole loop
+body is one block, but remember that the body code itself could consist
+of multiple blocks (e.g. if it contains an if/then/else or a for/in
+expression).
+
+.. code-block:: c++
+
+      // Make the new basic block for the loop header, inserting after current
+      // block.
+      Function *TheFunction = Builder.GetInsertBlock()->getParent();
+      BasicBlock *PreheaderBB = Builder.GetInsertBlock();
+      BasicBlock *LoopBB =
+          BasicBlock::Create(TheContext, "loop", TheFunction);
+
+      // Insert an explicit fall through from the current block to the LoopBB.
+      Builder.CreateBr(LoopBB);
+
+This code is similar to what we saw for if/then/else. Because we will
+need it to create the Phi node, we remember the block that falls through
+into the loop. Once we have that, we create the actual block that starts
+the loop and create an unconditional branch for the fall-through between
+the two blocks.
+
+.. code-block:: c++
+
+      // Start insertion in LoopBB.
+      Builder.SetInsertPoint(LoopBB);
+
+      // Start the PHI node with an entry for Start.
+      PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(TheContext),
+                                            2, VarName.c_str());
+      Variable->addIncoming(StartVal, PreheaderBB);
+
+Now that the "preheader" for the loop is set up, we switch to emitting
+code for the loop body. To begin with, we move the insertion point and
+create the PHI node for the loop induction variable. Since we already
+know the incoming value for the starting value, we add it to the Phi
+node. Note that the Phi will eventually get a second value for the
+backedge, but we can't set it up yet (because it doesn't exist!).
+
+.. code-block:: c++
+
+      // Within the loop, the variable is defined equal to the PHI node.  If it
+      // shadows an existing variable, we have to restore it, so save it now.
+      Value *OldVal = NamedValues[VarName];
+      NamedValues[VarName] = Variable;
+
+      // Emit the body of the loop.  This, like any other expr, can change the
+      // current BB.  Note that we ignore the value computed by the body, but don't
+      // allow an error.
+      if (!Body->codegen())
+        return nullptr;
+
+Now the code starts to get more interesting. Our 'for' loop introduces a
+new variable to the symbol table. This means that our symbol table can
+now contain either function arguments or loop variables. To handle this,
+before we codegen the body of the loop, we add the loop variable as the
+current value for its name. Note that it is possible that there is a
+variable of the same name in the outer scope. It would be easy to make
+this an error (emit an error and return null if there is already an
+entry for VarName) but we choose to allow shadowing of variables. In
+order to handle this correctly, we remember the Value that we are
+potentially shadowing in ``OldVal`` (which will be null if there is no
+shadowed variable).
+
+Once the loop variable is set into the symbol table, the code
+recursively codegen's the body. This allows the body to use the loop
+variable: any references to it will naturally find it in the symbol
+table.
+
+.. code-block:: c++
+
+      // Emit the step value.
+      Value *StepVal = nullptr;
+      if (Step) {
+        StepVal = Step->codegen();
+        if (!StepVal)
+          return nullptr;
+      } else {
+        // If not specified, use 1.0.
+        StepVal = ConstantFP::get(TheContext, APFloat(1.0));
+      }
+
+      Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar");
+
+Now that the body is emitted, we compute the next value of the iteration
+variable by adding the step value, or 1.0 if it isn't present.
+'``NextVar``' will be the value of the loop variable on the next
+iteration of the loop.
+
+.. code-block:: c++
+
+      // Compute the end condition.
+      Value *EndCond = End->codegen();
+      if (!EndCond)
+        return nullptr;
+
+      // Convert condition to a bool by comparing non-equal to 0.0.
+      EndCond = Builder.CreateFCmpONE(
+          EndCond, ConstantFP::get(TheContext, APFloat(0.0)), "loopcond");
+
+Finally, we evaluate the exit value of the loop, to determine whether
+the loop should exit. This mirrors the condition evaluation for the
+if/then/else statement.
+
+.. code-block:: c++
+
+      // Create the "after loop" block and insert it.
+      BasicBlock *LoopEndBB = Builder.GetInsertBlock();
+      BasicBlock *AfterBB =
+          BasicBlock::Create(TheContext, "afterloop", TheFunction);
+
+      // Insert the conditional branch into the end of LoopEndBB.
+      Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
+
+      // Any new code will be inserted in AfterBB.
+      Builder.SetInsertPoint(AfterBB);
+
+With the code for the body of the loop complete, we just need to finish
+up the control flow for it. This code remembers the end block (for the
+phi node), then creates the block for the loop exit ("afterloop"). Based
+on the value of the exit condition, it creates a conditional branch that
+chooses between executing the loop again and exiting the loop. Any
+future code is emitted in the "afterloop" block, so it sets the
+insertion position to it.
+
+.. code-block:: c++
+
+      // Add a new entry to the PHI node for the backedge.
+      Variable->addIncoming(NextVar, LoopEndBB);
+
+      // Restore the unshadowed variable.
+      if (OldVal)
+        NamedValues[VarName] = OldVal;
+      else
+        NamedValues.erase(VarName);
+
+      // for expr always returns 0.0.
+      return Constant::getNullValue(Type::getDoubleTy(TheContext));
+    }
+
+The final code handles various cleanups: now that we have the "NextVar"
+value, we can add the incoming value to the loop PHI node. After that,
+we remove the loop variable from the symbol table, so that it isn't in
+scope after the for loop. Finally, code generation of the for loop
+always returns 0.0, so that is what we return from
+``ForExprAST::codegen()``.
+
+With this, we conclude the "adding control flow to Kaleidoscope" chapter
+of the tutorial. In this chapter we added two control flow constructs,
+and used them to motivate a couple of aspects of the LLVM IR that are
+important for front-end implementors to know. In the next chapter of our
+saga, we will get a bit crazier and add `user-defined
+operators <LangImpl06.html>`_ to our poor innocent language.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the if/then/else and for expressions. To build this example, use:
+
+.. code-block:: bash
+
+    # Compile
+    clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+    # Run
+    ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter5/toy.cpp
+   :language: c++
+
+`Next: Extending the language: user-defined operators <LangImpl06.html>`_
+
diff --git a/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl06.rst b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl06.rst
new file mode 100644
index 0000000..2a9f4c6
--- /dev/null
+++ b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl06.rst
@@ -0,0 +1,768 @@
+============================================================
+Kaleidoscope: Extending the Language: User-defined Operators
+============================================================
+
+.. contents::
+   :local:
+
+Chapter 6 Introduction
+======================
+
+Welcome to Chapter 6 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. At this point in our tutorial, we now
+have a fully functional language that is fairly minimal, but also
+useful. There is still one big problem with it, however. Our language
+doesn't have many useful operators (like division, logical negation, or
+even any comparisons besides less-than).
+
+This chapter of the tutorial takes a wild digression into adding
+user-defined operators to the simple and beautiful Kaleidoscope
+language. This digression now gives us a simple and ugly language in
+some ways, but also a powerful one at the same time. One of the great
+things about creating your own language is that you get to decide what
+is good or bad. In this tutorial we'll assume that it is okay to use
+this as a way to show some interesting parsing techniques.
+
+At the end of this tutorial, we'll run through an example Kaleidoscope
+application that `renders the Mandelbrot set <#kicking-the-tires>`_. This gives an
+example of what you can build with Kaleidoscope and its feature set.
+
+User-defined Operators: the Idea
+================================
+
+The "operator overloading" that we will add to Kaleidoscope is more
+general than in languages like C++. In C++, you are only allowed to
+redefine existing operators: you can't programmatically change the
+grammar, introduce new operators, change precedence levels, etc. In this
+chapter, we will add this capability to Kaleidoscope, which will let the
+user round out the set of operators that are supported.
+
+The point of going into user-defined operators in a tutorial like this
+is to show the power and flexibility of using a hand-written parser.
+Thus far, the parser we have been implementing uses recursive descent
+for most parts of the grammar and operator precedence parsing for the
+expressions. See `Chapter 2 <LangImpl02.html>`_ for details. By
+using operator precedence parsing, it is very easy to allow
+the programmer to introduce new operators into the grammar: the grammar
+is dynamically extensible as the JIT runs.
+
+The two specific features we'll add are programmable unary operators
+(right now, Kaleidoscope has no unary operators at all) as well as
+binary operators. An example of this is:
+
+::
+
+    # Logical unary not.
+    def unary!(v)
+      if v then
+        0
+      else
+        1;
+
+    # Define > with the same precedence as <.
+    def binary> 10 (LHS RHS)
+      RHS < LHS;
+
+    # Binary "logical or", (note that it does not "short circuit")
+    def binary| 5 (LHS RHS)
+      if LHS then
+        1
+      else if RHS then
+        1
+      else
+        0;
+
+    # Define = with slightly lower precedence than relationals.
+    def binary= 9 (LHS RHS)
+      !(LHS < RHS | LHS > RHS);
+
+Many languages aspire to being able to implement their standard runtime
+library in the language itself. In Kaleidoscope, we can implement
+significant parts of the language in the library!
+
+We will break down implementation of these features into two parts:
+implementing support for user-defined binary operators and adding unary
+operators.
+
+User-defined Binary Operators
+=============================
+
+Adding support for user-defined binary operators is pretty simple with
+our current framework. We'll first add support for the unary/binary
+keywords:
+
+.. code-block:: c++
+
+    enum Token {
+      ...
+      // operators
+      tok_binary = -11,
+      tok_unary = -12
+    };
+    ...
+    static int gettok() {
+    ...
+        if (IdentifierStr == "for")
+          return tok_for;
+        if (IdentifierStr == "in")
+          return tok_in;
+        if (IdentifierStr == "binary")
+          return tok_binary;
+        if (IdentifierStr == "unary")
+          return tok_unary;
+        return tok_identifier;
+
+This just adds lexer support for the unary and binary keywords, like we
+did in `previous chapters <LangImpl5.html#lexer-extensions-for-if-then-else>`_. One nice thing
+about our current AST, is that we represent binary operators with full
+generalisation by using their ASCII code as the opcode. For our extended
+operators, we'll use this same representation, so we don't need any new
+AST or parser support.
+
+On the other hand, we have to be able to represent the definitions of
+these new operators, in the "def binary\| 5" part of the function
+definition. In our grammar so far, the "name" for the function
+definition is parsed as the "prototype" production and into the
+``PrototypeAST`` AST node. To represent our new user-defined operators
+as prototypes, we have to extend the ``PrototypeAST`` AST node like
+this:
+
+.. code-block:: c++
+
+    /// PrototypeAST - This class represents the "prototype" for a function,
+    /// which captures its argument names as well as if it is an operator.
+    class PrototypeAST {
+      std::string Name;
+      std::vector<std::string> Args;
+      bool IsOperator;
+      unsigned Precedence;  // Precedence if a binary op.
+
+    public:
+      PrototypeAST(const std::string &name, std::vector<std::string> Args,
+                   bool IsOperator = false, unsigned Prec = 0)
+      : Name(name), Args(std::move(Args)), IsOperator(IsOperator),
+        Precedence(Prec) {}
+
+      Function *codegen();
+      const std::string &getName() const { return Name; }
+
+      bool isUnaryOp() const { return IsOperator && Args.size() == 1; }
+      bool isBinaryOp() const { return IsOperator && Args.size() == 2; }
+
+      char getOperatorName() const {
+        assert(isUnaryOp() || isBinaryOp());
+        return Name[Name.size() - 1];
+      }
+
+      unsigned getBinaryPrecedence() const { return Precedence; }
+    };
+
+Basically, in addition to knowing a name for the prototype, we now keep
+track of whether it was an operator, and if it was, what precedence
+level the operator is at. The precedence is only used for binary
+operators (as you'll see below, it just doesn't apply for unary
+operators). Now that we have a way to represent the prototype for a
+user-defined operator, we need to parse it:
+
+.. code-block:: c++
+
+    /// prototype
+    ///   ::= id '(' id* ')'
+    ///   ::= binary LETTER number? (id, id)
+    static std::unique_ptr<PrototypeAST> ParsePrototype() {
+      std::string FnName;
+
+      unsigned Kind = 0;  // 0 = identifier, 1 = unary, 2 = binary.
+      unsigned BinaryPrecedence = 30;
+
+      switch (CurTok) {
+      default:
+        return LogErrorP("Expected function name in prototype");
+      case tok_identifier:
+        FnName = IdentifierStr;
+        Kind = 0;
+        getNextToken();
+        break;
+      case tok_binary:
+        getNextToken();
+        if (!isascii(CurTok))
+          return LogErrorP("Expected binary operator");
+        FnName = "binary";
+        FnName += (char)CurTok;
+        Kind = 2;
+        getNextToken();
+
+        // Read the precedence if present.
+        if (CurTok == tok_number) {
+          if (NumVal < 1 || NumVal > 100)
+            return LogErrorP("Invalid precedence: must be 1..100");
+          BinaryPrecedence = (unsigned)NumVal;
+          getNextToken();
+        }
+        break;
+      }
+
+      if (CurTok != '(')
+        return LogErrorP("Expected '(' in prototype");
+
+      std::vector<std::string> ArgNames;
+      while (getNextToken() == tok_identifier)
+        ArgNames.push_back(IdentifierStr);
+      if (CurTok != ')')
+        return LogErrorP("Expected ')' in prototype");
+
+      // success.
+      getNextToken();  // eat ')'.
+
+      // Verify right number of names for operator.
+      if (Kind && ArgNames.size() != Kind)
+        return LogErrorP("Invalid number of operands for operator");
+
+      return llvm::make_unique<PrototypeAST>(FnName, std::move(ArgNames), Kind != 0,
+                                             BinaryPrecedence);
+    }
+
+This is all fairly straightforward parsing code, and we have already
+seen a lot of similar code in the past. One interesting part about the
+code above is the couple lines that set up ``FnName`` for binary
+operators. This builds names like "binary@" for a newly defined "@"
+operator. It then takes advantage of the fact that symbol names in the
+LLVM symbol table are allowed to have any character in them, including
+embedded nul characters.
+
+The next interesting thing to add, is codegen support for these binary
+operators. Given our current structure, this is a simple addition of a
+default case for our existing binary operator node:
+
+.. code-block:: c++
+
+    Value *BinaryExprAST::codegen() {
+      Value *L = LHS->codegen();
+      Value *R = RHS->codegen();
+      if (!L || !R)
+        return nullptr;
+
+      switch (Op) {
+      case '+':
+        return Builder.CreateFAdd(L, R, "addtmp");
+      case '-':
+        return Builder.CreateFSub(L, R, "subtmp");
+      case '*':
+        return Builder.CreateFMul(L, R, "multmp");
+      case '<':
+        L = Builder.CreateFCmpULT(L, R, "cmptmp");
+        // Convert bool 0/1 to double 0.0 or 1.0
+        return Builder.CreateUIToFP(L, Type::getDoubleTy(TheContext),
+                                    "booltmp");
+      default:
+        break;
+      }
+
+      // If it wasn't a builtin binary operator, it must be a user defined one. Emit
+      // a call to it.
+      Function *F = getFunction(std::string("binary") + Op);
+      assert(F && "binary operator not found!");
+
+      Value *Ops[2] = { L, R };
+      return Builder.CreateCall(F, Ops, "binop");
+    }
+
+As you can see above, the new code is actually really simple. It just
+does a lookup for the appropriate operator in the symbol table and
+generates a function call to it. Since user-defined operators are just
+built as normal functions (because the "prototype" boils down to a
+function with the right name) everything falls into place.
+
+The final piece of code we are missing, is a bit of top-level magic:
+
+.. code-block:: c++
+
+    Function *FunctionAST::codegen() {
+      // Transfer ownership of the prototype to the FunctionProtos map, but keep a
+      // reference to it for use below.
+      auto &P = *Proto;
+      FunctionProtos[Proto->getName()] = std::move(Proto);
+      Function *TheFunction = getFunction(P.getName());
+      if (!TheFunction)
+        return nullptr;
+
+      // If this is an operator, install it.
+      if (P.isBinaryOp())
+        BinopPrecedence[P.getOperatorName()] = P.getBinaryPrecedence();
+
+      // Create a new basic block to start insertion into.
+      BasicBlock *BB = BasicBlock::Create(TheContext, "entry", TheFunction);
+      ...
+
+Basically, before codegening a function, if it is a user-defined
+operator, we register it in the precedence table. This allows the binary
+operator parsing logic we already have in place to handle it. Since we
+are working on a fully-general operator precedence parser, this is all
+we need to do to "extend the grammar".
+
+Now we have useful user-defined binary operators. This builds a lot on
+the previous framework we built for other operators. Adding unary
+operators is a bit more challenging, because we don't have any framework
+for it yet - let's see what it takes.
+
+User-defined Unary Operators
+============================
+
+Since we don't currently support unary operators in the Kaleidoscope
+language, we'll need to add everything to support them. Above, we added
+simple support for the 'unary' keyword to the lexer. In addition to
+that, we need an AST node:
+
+.. code-block:: c++
+
+    /// UnaryExprAST - Expression class for a unary operator.
+    class UnaryExprAST : public ExprAST {
+      char Opcode;
+      std::unique_ptr<ExprAST> Operand;
+
+    public:
+      UnaryExprAST(char Opcode, std::unique_ptr<ExprAST> Operand)
+        : Opcode(Opcode), Operand(std::move(Operand)) {}
+
+      Value *codegen() override;
+    };
+
+This AST node is very simple and obvious by now. It directly mirrors the
+binary operator AST node, except that it only has one child. With this,
+we need to add the parsing logic. Parsing a unary operator is pretty
+simple: we'll add a new function to do it:
+
+.. code-block:: c++
+
+    /// unary
+    ///   ::= primary
+    ///   ::= '!' unary
+    static std::unique_ptr<ExprAST> ParseUnary() {
+      // If the current token is not an operator, it must be a primary expr.
+      if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
+        return ParsePrimary();
+
+      // If this is a unary operator, read it.
+      int Opc = CurTok;
+      getNextToken();
+      if (auto Operand = ParseUnary())
+        return llvm::make_unique<UnaryExprAST>(Opc, std::move(Operand));
+      return nullptr;
+    }
+
+The grammar we add is pretty straightforward here. If we see a unary
+operator when parsing a primary operator, we eat the operator as a
+prefix and parse the remaining piece as another unary operator. This
+allows us to handle multiple unary operators (e.g. "!!x"). Note that
+unary operators can't have ambiguous parses like binary operators can,
+so there is no need for precedence information.
+
+The problem with this function, is that we need to call ParseUnary from
+somewhere. To do this, we change previous callers of ParsePrimary to
+call ParseUnary instead:
+
+.. code-block:: c++
+
+    /// binoprhs
+    ///   ::= ('+' unary)*
+    static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
+                                                  std::unique_ptr<ExprAST> LHS) {
+      ...
+        // Parse the unary expression after the binary operator.
+        auto RHS = ParseUnary();
+        if (!RHS)
+          return nullptr;
+      ...
+    }
+    /// expression
+    ///   ::= unary binoprhs
+    ///
+    static std::unique_ptr<ExprAST> ParseExpression() {
+      auto LHS = ParseUnary();
+      if (!LHS)
+        return nullptr;
+
+      return ParseBinOpRHS(0, std::move(LHS));
+    }
+
+With these two simple changes, we are now able to parse unary operators
+and build the AST for them. Next up, we need to add parser support for
+prototypes, to parse the unary operator prototype. We extend the binary
+operator code above with:
+
+.. code-block:: c++
+
+    /// prototype
+    ///   ::= id '(' id* ')'
+    ///   ::= binary LETTER number? (id, id)
+    ///   ::= unary LETTER (id)
+    static std::unique_ptr<PrototypeAST> ParsePrototype() {
+      std::string FnName;
+
+      unsigned Kind = 0;  // 0 = identifier, 1 = unary, 2 = binary.
+      unsigned BinaryPrecedence = 30;
+
+      switch (CurTok) {
+      default:
+        return LogErrorP("Expected function name in prototype");
+      case tok_identifier:
+        FnName = IdentifierStr;
+        Kind = 0;
+        getNextToken();
+        break;
+      case tok_unary:
+        getNextToken();
+        if (!isascii(CurTok))
+          return LogErrorP("Expected unary operator");
+        FnName = "unary";
+        FnName += (char)CurTok;
+        Kind = 1;
+        getNextToken();
+        break;
+      case tok_binary:
+        ...
+
+As with binary operators, we name unary operators with a name that
+includes the operator character. This assists us at code generation
+time. Speaking of, the final piece we need to add is codegen support for
+unary operators. It looks like this:
+
+.. code-block:: c++
+
+    Value *UnaryExprAST::codegen() {
+      Value *OperandV = Operand->codegen();
+      if (!OperandV)
+        return nullptr;
+
+      Function *F = getFunction(std::string("unary") + Opcode);
+      if (!F)
+        return LogErrorV("Unknown unary operator");
+
+      return Builder.CreateCall(F, OperandV, "unop");
+    }
+
+This code is similar to, but simpler than, the code for binary
+operators. It is simpler primarily because it doesn't need to handle any
+predefined operators.
+
+Kicking the Tires
+=================
+
+It is somewhat hard to believe, but with a few simple extensions we've
+covered in the last chapters, we have grown a real-ish language. With
+this, we can do a lot of interesting things, including I/O, math, and a
+bunch of other things. For example, we can now add a nice sequencing
+operator (printd is defined to print out the specified value and a
+newline):
+
+::
+
+    ready> extern printd(x);
+    Read extern:
+    declare double @printd(double)
+
+    ready> def binary : 1 (x y) 0;  # Low-precedence operator that ignores operands.
+    ...
+    ready> printd(123) : printd(456) : printd(789);
+    123.000000
+    456.000000
+    789.000000
+    Evaluated to 0.000000
+
+We can also define a bunch of other "primitive" operations, such as:
+
+::
+
+    # Logical unary not.
+    def unary!(v)
+      if v then
+        0
+      else
+        1;
+
+    # Unary negate.
+    def unary-(v)
+      0-v;
+
+    # Define > with the same precedence as <.
+    def binary> 10 (LHS RHS)
+      RHS < LHS;
+
+    # Binary logical or, which does not short circuit.
+    def binary| 5 (LHS RHS)
+      if LHS then
+        1
+      else if RHS then
+        1
+      else
+        0;
+
+    # Binary logical and, which does not short circuit.
+    def binary& 6 (LHS RHS)
+      if !LHS then
+        0
+      else
+        !!RHS;
+
+    # Define = with slightly lower precedence than relationals.
+    def binary = 9 (LHS RHS)
+      !(LHS < RHS | LHS > RHS);
+
+    # Define ':' for sequencing: as a low-precedence operator that ignores operands
+    # and just returns the RHS.
+    def binary : 1 (x y) y;
+
+Given the previous if/then/else support, we can also define interesting
+functions for I/O. For example, the following prints out a character
+whose "density" reflects the value passed in: the lower the value, the
+denser the character:
+
+::
+
+    ready> extern putchard(char);
+    ...
+    ready> def printdensity(d)
+      if d > 8 then
+        putchard(32)  # ' '
+      else if d > 4 then
+        putchard(46)  # '.'
+      else if d > 2 then
+        putchard(43)  # '+'
+      else
+        putchard(42); # '*'
+    ...
+    ready> printdensity(1): printdensity(2): printdensity(3):
+           printdensity(4): printdensity(5): printdensity(9):
+           putchard(10);
+    **++.
+    Evaluated to 0.000000
+
+Based on these simple primitive operations, we can start to define more
+interesting things. For example, here's a little function that determines
+the number of iterations it takes for a certain function in the complex
+plane to diverge:
+
+::
+
+    # Determine whether the specific location diverges.
+    # Solve for z = z^2 + c in the complex plane.
+    def mandelconverger(real imag iters creal cimag)
+      if iters > 255 | (real*real + imag*imag > 4) then
+        iters
+      else
+        mandelconverger(real*real - imag*imag + creal,
+                        2*real*imag + cimag,
+                        iters+1, creal, cimag);
+
+    # Return the number of iterations required for the iteration to escape
+    def mandelconverge(real imag)
+      mandelconverger(real, imag, 0, real, imag);
+
+This "``z = z2 + c``" function is a beautiful little creature that is
+the basis for computation of the `Mandelbrot
+Set <http://en.wikipedia.org/wiki/Mandelbrot_set>`_. Our
+``mandelconverge`` function returns the number of iterations that it
+takes for a complex orbit to escape, saturating to 255. This is not a
+very useful function by itself, but if you plot its value over a
+two-dimensional plane, you can see the Mandelbrot set. Given that we are
+limited to using putchard here, our amazing graphical output is limited,
+but we can whip together something using the density plotter above:
+
+::
+
+    # Compute and plot the mandelbrot set with the specified 2 dimensional range
+    # info.
+    def mandelhelp(xmin xmax xstep   ymin ymax ystep)
+      for y = ymin, y < ymax, ystep in (
+        (for x = xmin, x < xmax, xstep in
+           printdensity(mandelconverge(x,y)))
+        : putchard(10)
+      )
+
+    # mandel - This is a convenient helper function for plotting the mandelbrot set
+    # from the specified position with the specified Magnification.
+    def mandel(realstart imagstart realmag imagmag)
+      mandelhelp(realstart, realstart+realmag*78, realmag,
+                 imagstart, imagstart+imagmag*40, imagmag);
+
+Given this, we can try plotting out the mandelbrot set! Lets try it out:
+
+::
+
+    ready> mandel(-2.3, -1.3, 0.05, 0.07);
+    *******************************+++++++++++*************************************
+    *************************+++++++++++++++++++++++*******************************
+    **********************+++++++++++++++++++++++++++++****************************
+    *******************+++++++++++++++++++++.. ...++++++++*************************
+    *****************++++++++++++++++++++++.... ...+++++++++***********************
+    ***************+++++++++++++++++++++++.....   ...+++++++++*********************
+    **************+++++++++++++++++++++++....     ....+++++++++********************
+    *************++++++++++++++++++++++......      .....++++++++*******************
+    ************+++++++++++++++++++++.......       .......+++++++******************
+    ***********+++++++++++++++++++....                ... .+++++++*****************
+    **********+++++++++++++++++.......                     .+++++++****************
+    *********++++++++++++++...........                    ...+++++++***************
+    ********++++++++++++............                      ...++++++++**************
+    ********++++++++++... ..........                        .++++++++**************
+    *******+++++++++.....                                   .+++++++++*************
+    *******++++++++......                                  ..+++++++++*************
+    *******++++++.......                                   ..+++++++++*************
+    *******+++++......                                     ..+++++++++*************
+    *******.... ....                                      ...+++++++++*************
+    *******.... .                                         ...+++++++++*************
+    *******+++++......                                    ...+++++++++*************
+    *******++++++.......                                   ..+++++++++*************
+    *******++++++++......                                   .+++++++++*************
+    *******+++++++++.....                                  ..+++++++++*************
+    ********++++++++++... ..........                        .++++++++**************
+    ********++++++++++++............                      ...++++++++**************
+    *********++++++++++++++..........                     ...+++++++***************
+    **********++++++++++++++++........                     .+++++++****************
+    **********++++++++++++++++++++....                ... ..+++++++****************
+    ***********++++++++++++++++++++++.......       .......++++++++*****************
+    ************+++++++++++++++++++++++......      ......++++++++******************
+    **************+++++++++++++++++++++++....      ....++++++++********************
+    ***************+++++++++++++++++++++++.....   ...+++++++++*********************
+    *****************++++++++++++++++++++++....  ...++++++++***********************
+    *******************+++++++++++++++++++++......++++++++*************************
+    *********************++++++++++++++++++++++.++++++++***************************
+    *************************+++++++++++++++++++++++*******************************
+    ******************************+++++++++++++************************************
+    *******************************************************************************
+    *******************************************************************************
+    *******************************************************************************
+    Evaluated to 0.000000
+    ready> mandel(-2, -1, 0.02, 0.04);
+    **************************+++++++++++++++++++++++++++++++++++++++++++++++++++++
+    ***********************++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+    *********************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.
+    *******************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++...
+    *****************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.....
+    ***************++++++++++++++++++++++++++++++++++++++++++++++++++++++++........
+    **************++++++++++++++++++++++++++++++++++++++++++++++++++++++...........
+    ************+++++++++++++++++++++++++++++++++++++++++++++++++++++..............
+    ***********++++++++++++++++++++++++++++++++++++++++++++++++++........        .
+    **********++++++++++++++++++++++++++++++++++++++++++++++.............
+    ********+++++++++++++++++++++++++++++++++++++++++++..................
+    *******+++++++++++++++++++++++++++++++++++++++.......................
+    ******+++++++++++++++++++++++++++++++++++...........................
+    *****++++++++++++++++++++++++++++++++............................
+    *****++++++++++++++++++++++++++++...............................
+    ****++++++++++++++++++++++++++......   .........................
+    ***++++++++++++++++++++++++.........     ......    ...........
+    ***++++++++++++++++++++++............
+    **+++++++++++++++++++++..............
+    **+++++++++++++++++++................
+    *++++++++++++++++++.................
+    *++++++++++++++++............ ...
+    *++++++++++++++..............
+    *+++....++++................
+    *..........  ...........
+    *
+    *..........  ...........
+    *+++....++++................
+    *++++++++++++++..............
+    *++++++++++++++++............ ...
+    *++++++++++++++++++.................
+    **+++++++++++++++++++................
+    **+++++++++++++++++++++..............
+    ***++++++++++++++++++++++............
+    ***++++++++++++++++++++++++.........     ......    ...........
+    ****++++++++++++++++++++++++++......   .........................
+    *****++++++++++++++++++++++++++++...............................
+    *****++++++++++++++++++++++++++++++++............................
+    ******+++++++++++++++++++++++++++++++++++...........................
+    *******+++++++++++++++++++++++++++++++++++++++.......................
+    ********+++++++++++++++++++++++++++++++++++++++++++..................
+    Evaluated to 0.000000
+    ready> mandel(-0.9, -1.4, 0.02, 0.03);
+    *******************************************************************************
+    *******************************************************************************
+    *******************************************************************************
+    **********+++++++++++++++++++++************************************************
+    *+++++++++++++++++++++++++++++++++++++++***************************************
+    +++++++++++++++++++++++++++++++++++++++++++++**********************************
+    ++++++++++++++++++++++++++++++++++++++++++++++++++*****************************
+    ++++++++++++++++++++++++++++++++++++++++++++++++++++++*************************
+    +++++++++++++++++++++++++++++++++++++++++++++++++++++++++**********************
+    +++++++++++++++++++++++++++++++++.........++++++++++++++++++*******************
+    +++++++++++++++++++++++++++++++....   ......+++++++++++++++++++****************
+    +++++++++++++++++++++++++++++.......  ........+++++++++++++++++++**************
+    ++++++++++++++++++++++++++++........   ........++++++++++++++++++++************
+    +++++++++++++++++++++++++++.........     ..  ...+++++++++++++++++++++**********
+    ++++++++++++++++++++++++++...........        ....++++++++++++++++++++++********
+    ++++++++++++++++++++++++.............       .......++++++++++++++++++++++******
+    +++++++++++++++++++++++.............        ........+++++++++++++++++++++++****
+    ++++++++++++++++++++++...........           ..........++++++++++++++++++++++***
+    ++++++++++++++++++++...........                .........++++++++++++++++++++++*
+    ++++++++++++++++++............                  ...........++++++++++++++++++++
+    ++++++++++++++++...............                 .............++++++++++++++++++
+    ++++++++++++++.................                 ...............++++++++++++++++
+    ++++++++++++..................                  .................++++++++++++++
+    +++++++++..................                      .................+++++++++++++
+    ++++++........        .                               .........  ..++++++++++++
+    ++............                                         ......    ....++++++++++
+    ..............                                                    ...++++++++++
+    ..............                                                    ....+++++++++
+    ..............                                                    .....++++++++
+    .............                                                    ......++++++++
+    ...........                                                     .......++++++++
+    .........                                                       ........+++++++
+    .........                                                       ........+++++++
+    .........                                                           ....+++++++
+    ........                                                             ...+++++++
+    .......                                                              ...+++++++
+                                                                        ....+++++++
+                                                                       .....+++++++
+                                                                        ....+++++++
+                                                                        ....+++++++
+                                                                        ....+++++++
+    Evaluated to 0.000000
+    ready> ^D
+
+At this point, you may be starting to realize that Kaleidoscope is a
+real and powerful language. It may not be self-similar :), but it can be
+used to plot things that are!
+
+With this, we conclude the "adding user-defined operators" chapter of
+the tutorial. We have successfully augmented our language, adding the
+ability to extend the language in the library, and we have shown how
+this can be used to build a simple but interesting end-user application
+in Kaleidoscope. At this point, Kaleidoscope can build a variety of
+applications that are functional and can call functions with
+side-effects, but it can't actually define and mutate a variable itself.
+
+Strikingly, variable mutation is an important feature of some languages,
+and it is not at all obvious how to `add support for mutable
+variables <LangImpl07.html>`_ without having to add an "SSA construction"
+phase to your front-end. In the next chapter, we will describe how you
+can add variable mutation without building SSA in your front-end.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the support for user-defined operators. To build this example, use:
+
+.. code-block:: bash
+
+    # Compile
+    clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+    # Run
+    ./toy
+
+On some platforms, you will need to specify -rdynamic or
+-Wl,--export-dynamic when linking. This ensures that symbols defined in
+the main executable are exported to the dynamic linker and so are
+available for symbol resolution at run time. This is not needed if you
+compile your support code into a shared library, although doing that
+will cause problems on Windows.
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter6/toy.cpp
+   :language: c++
+
+`Next: Extending the language: mutable variables / SSA
+construction <LangImpl07.html>`_
+
diff --git a/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl07.rst b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl07.rst
new file mode 100644
index 0000000..582645f4
--- /dev/null
+++ b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl07.rst
@@ -0,0 +1,883 @@
+=======================================================
+Kaleidoscope: Extending the Language: Mutable Variables
+=======================================================
+
+.. contents::
+   :local:
+
+Chapter 7 Introduction
+======================
+
+Welcome to Chapter 7 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. In chapters 1 through 6, we've built a
+very respectable, albeit simple, `functional programming
+language <http://en.wikipedia.org/wiki/Functional_programming>`_. In our
+journey, we learned some parsing techniques, how to build and represent
+an AST, how to build LLVM IR, and how to optimize the resultant code as
+well as JIT compile it.
+
+While Kaleidoscope is interesting as a functional language, the fact
+that it is functional makes it "too easy" to generate LLVM IR for it. In
+particular, a functional language makes it very easy to build LLVM IR
+directly in `SSA
+form <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+Since LLVM requires that the input code be in SSA form, this is a very
+nice property and it is often unclear to newcomers how to generate code
+for an imperative language with mutable variables.
+
+The short (and happy) summary of this chapter is that there is no need
+for your front-end to build SSA form: LLVM provides highly tuned and
+well tested support for this, though the way it works is a bit
+unexpected for some.
+
+Why is this a hard problem?
+===========================
+
+To understand why mutable variables cause complexities in SSA
+construction, consider this extremely simple C example:
+
+.. code-block:: c
+
+    int G, H;
+    int test(_Bool Condition) {
+      int X;
+      if (Condition)
+        X = G;
+      else
+        X = H;
+      return X;
+    }
+
+In this case, we have the variable "X", whose value depends on the path
+executed in the program. Because there are two different possible values
+for X before the return instruction, a PHI node is inserted to merge the
+two values. The LLVM IR that we want for this example looks like this:
+
+.. code-block:: llvm
+
+    @G = weak global i32 0   ; type of @G is i32*
+    @H = weak global i32 0   ; type of @H is i32*
+
+    define i32 @test(i1 %Condition) {
+    entry:
+      br i1 %Condition, label %cond_true, label %cond_false
+
+    cond_true:
+      %X.0 = load i32* @G
+      br label %cond_next
+
+    cond_false:
+      %X.1 = load i32* @H
+      br label %cond_next
+
+    cond_next:
+      %X.2 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
+      ret i32 %X.2
+    }
+
+In this example, the loads from the G and H global variables are
+explicit in the LLVM IR, and they live in the then/else branches of the
+if statement (cond\_true/cond\_false). In order to merge the incoming
+values, the X.2 phi node in the cond\_next block selects the right value
+to use based on where control flow is coming from: if control flow comes
+from the cond\_false block, X.2 gets the value of X.1. Alternatively, if
+control flow comes from cond\_true, it gets the value of X.0. The intent
+of this chapter is not to explain the details of SSA form. For more
+information, see one of the many `online
+references <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+
+The question for this article is "who places the phi nodes when lowering
+assignments to mutable variables?". The issue here is that LLVM
+*requires* that its IR be in SSA form: there is no "non-ssa" mode for
+it. However, SSA construction requires non-trivial algorithms and data
+structures, so it is inconvenient and wasteful for every front-end to
+have to reproduce this logic.
+
+Memory in LLVM
+==============
+
+The 'trick' here is that while LLVM does require all register values to
+be in SSA form, it does not require (or permit) memory objects to be in
+SSA form. In the example above, note that the loads from G and H are
+direct accesses to G and H: they are not renamed or versioned. This
+differs from some other compiler systems, which do try to version memory
+objects. In LLVM, instead of encoding dataflow analysis of memory into
+the LLVM IR, it is handled with `Analysis
+Passes <../WritingAnLLVMPass.html>`_ which are computed on demand.
+
+With this in mind, the high-level idea is that we want to make a stack
+variable (which lives in memory, because it is on the stack) for each
+mutable object in a function. To take advantage of this trick, we need
+to talk about how LLVM represents stack variables.
+
+In LLVM, all memory accesses are explicit with load/store instructions,
+and it is carefully designed not to have (or need) an "address-of"
+operator. Notice how the type of the @G/@H global variables is actually
+"i32\*" even though the variable is defined as "i32". What this means is
+that @G defines *space* for an i32 in the global data area, but its
+*name* actually refers to the address for that space. Stack variables
+work the same way, except that instead of being declared with global
+variable definitions, they are declared with the `LLVM alloca
+instruction <../LangRef.html#alloca-instruction>`_:
+
+.. code-block:: llvm
+
+    define i32 @example() {
+    entry:
+      %X = alloca i32           ; type of %X is i32*.
+      ...
+      %tmp = load i32* %X       ; load the stack value %X from the stack.
+      %tmp2 = add i32 %tmp, 1   ; increment it
+      store i32 %tmp2, i32* %X  ; store it back
+      ...
+
+This code shows an example of how you can declare and manipulate a stack
+variable in the LLVM IR. Stack memory allocated with the alloca
+instruction is fully general: you can pass the address of the stack slot
+to functions, you can store it in other variables, etc. In our example
+above, we could rewrite the example to use the alloca technique to avoid
+using a PHI node:
+
+.. code-block:: llvm
+
+    @G = weak global i32 0   ; type of @G is i32*
+    @H = weak global i32 0   ; type of @H is i32*
+
+    define i32 @test(i1 %Condition) {
+    entry:
+      %X = alloca i32           ; type of %X is i32*.
+      br i1 %Condition, label %cond_true, label %cond_false
+
+    cond_true:
+      %X.0 = load i32* @G
+      store i32 %X.0, i32* %X   ; Update X
+      br label %cond_next
+
+    cond_false:
+      %X.1 = load i32* @H
+      store i32 %X.1, i32* %X   ; Update X
+      br label %cond_next
+
+    cond_next:
+      %X.2 = load i32* %X       ; Read X
+      ret i32 %X.2
+    }
+
+With this, we have discovered a way to handle arbitrary mutable
+variables without the need to create Phi nodes at all:
+
+#. Each mutable variable becomes a stack allocation.
+#. Each read of the variable becomes a load from the stack.
+#. Each update of the variable becomes a store to the stack.
+#. Taking the address of a variable just uses the stack address
+   directly.
+
+While this solution has solved our immediate problem, it introduced
+another one: we have now apparently introduced a lot of stack traffic
+for very simple and common operations, a major performance problem.
+Fortunately for us, the LLVM optimizer has a highly-tuned optimization
+pass named "mem2reg" that handles this case, promoting allocas like this
+into SSA registers, inserting Phi nodes as appropriate. If you run this
+example through the pass, for example, you'll get:
+
+.. code-block:: bash
+
+    $ llvm-as < example.ll | opt -mem2reg | llvm-dis
+    @G = weak global i32 0
+    @H = weak global i32 0
+
+    define i32 @test(i1 %Condition) {
+    entry:
+      br i1 %Condition, label %cond_true, label %cond_false
+
+    cond_true:
+      %X.0 = load i32* @G
+      br label %cond_next
+
+    cond_false:
+      %X.1 = load i32* @H
+      br label %cond_next
+
+    cond_next:
+      %X.01 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
+      ret i32 %X.01
+    }
+
+The mem2reg pass implements the standard "iterated dominance frontier"
+algorithm for constructing SSA form and has a number of optimizations
+that speed up (very common) degenerate cases. The mem2reg optimization
+pass is the answer to dealing with mutable variables, and we highly
+recommend that you depend on it. Note that mem2reg only works on
+variables in certain circumstances:
+
+#. mem2reg is alloca-driven: it looks for allocas and if it can handle
+   them, it promotes them. It does not apply to global variables or heap
+   allocations.
+#. mem2reg only looks for alloca instructions in the entry block of the
+   function. Being in the entry block guarantees that the alloca is only
+   executed once, which makes analysis simpler.
+#. mem2reg only promotes allocas whose uses are direct loads and stores.
+   If the address of the stack object is passed to a function, or if any
+   funny pointer arithmetic is involved, the alloca will not be
+   promoted.
+#. mem2reg only works on allocas of `first
+   class <../LangRef.html#first-class-types>`_ values (such as pointers,
+   scalars and vectors), and only if the array size of the allocation is
+   1 (or missing in the .ll file). mem2reg is not capable of promoting
+   structs or arrays to registers. Note that the "sroa" pass is
+   more powerful and can promote structs, "unions", and arrays in many
+   cases.
+
+All of these properties are easy to satisfy for most imperative
+languages, and we'll illustrate it below with Kaleidoscope. The final
+question you may be asking is: should I bother with this nonsense for my
+front-end? Wouldn't it be better if I just did SSA construction
+directly, avoiding use of the mem2reg optimization pass? In short, we
+strongly recommend that you use this technique for building SSA form,
+unless there is an extremely good reason not to. Using this technique
+is:
+
+-  Proven and well tested: clang uses this technique
+   for local mutable variables. As such, the most common clients of LLVM
+   are using this to handle a bulk of their variables. You can be sure
+   that bugs are found fast and fixed early.
+-  Extremely Fast: mem2reg has a number of special cases that make it
+   fast in common cases as well as fully general. For example, it has
+   fast-paths for variables that are only used in a single block,
+   variables that only have one assignment point, good heuristics to
+   avoid insertion of unneeded phi nodes, etc.
+-  Needed for debug info generation: `Debug information in
+   LLVM <../SourceLevelDebugging.html>`_ relies on having the address of
+   the variable exposed so that debug info can be attached to it. This
+   technique dovetails very naturally with this style of debug info.
+
+If nothing else, this makes it much easier to get your front-end up and
+running, and is very simple to implement. Let's extend Kaleidoscope with
+mutable variables now!
+
+Mutable Variables in Kaleidoscope
+=================================
+
+Now that we know the sort of problem we want to tackle, let's see what
+this looks like in the context of our little Kaleidoscope language.
+We're going to add two features:
+
+#. The ability to mutate variables with the '=' operator.
+#. The ability to define new variables.
+
+While the first item is really what this is about, we only have
+variables for incoming arguments as well as for induction variables, and
+redefining those only goes so far :). Also, the ability to define new
+variables is a useful thing regardless of whether you will be mutating
+them. Here's a motivating example that shows how we could use these:
+
+::
+
+    # Define ':' for sequencing: as a low-precedence operator that ignores operands
+    # and just returns the RHS.
+    def binary : 1 (x y) y;
+
+    # Recursive fib, we could do this before.
+    def fib(x)
+      if (x < 3) then
+        1
+      else
+        fib(x-1)+fib(x-2);
+
+    # Iterative fib.
+    def fibi(x)
+      var a = 1, b = 1, c in
+      (for i = 3, i < x in
+         c = a + b :
+         a = b :
+         b = c) :
+      b;
+
+    # Call it.
+    fibi(10);
+
+In order to mutate variables, we have to change our existing variables
+to use the "alloca trick". Once we have that, we'll add our new
+operator, then extend Kaleidoscope to support new variable definitions.
+
+Adjusting Existing Variables for Mutation
+=========================================
+
+The symbol table in Kaleidoscope is managed at code generation time by
+the '``NamedValues``' map. This map currently keeps track of the LLVM
+"Value\*" that holds the double value for the named variable. In order
+to support mutation, we need to change this slightly, so that
+``NamedValues`` holds the *memory location* of the variable in question.
+Note that this change is a refactoring: it changes the structure of the
+code, but does not (by itself) change the behavior of the compiler. All
+of these changes are isolated in the Kaleidoscope code generator.
+
+At this point in Kaleidoscope's development, it only supports variables
+for two things: incoming arguments to functions and the induction
+variable of 'for' loops. For consistency, we'll allow mutation of these
+variables in addition to other user-defined variables. This means that
+these will both need memory locations.
+
+To start our transformation of Kaleidoscope, we'll change the
+NamedValues map so that it maps to AllocaInst\* instead of Value\*. Once
+we do this, the C++ compiler will tell us what parts of the code we need
+to update:
+
+.. code-block:: c++
+
+    static std::map<std::string, AllocaInst*> NamedValues;
+
+Also, since we will need to create these allocas, we'll use a helper
+function that ensures that the allocas are created in the entry block of
+the function:
+
+.. code-block:: c++
+
+    /// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of
+    /// the function.  This is used for mutable variables etc.
+    static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
+                                              const std::string &VarName) {
+      IRBuilder<> TmpB(&TheFunction->getEntryBlock(),
+                     TheFunction->getEntryBlock().begin());
+      return TmpB.CreateAlloca(Type::getDoubleTy(TheContext), 0,
+                               VarName.c_str());
+    }
+
+This funny looking code creates an IRBuilder object that is pointing at
+the first instruction (.begin()) of the entry block. It then creates an
+alloca with the expected name and returns it. Because all values in
+Kaleidoscope are doubles, there is no need to pass in a type to use.
+
+With this in place, the first functionality change we want to make belongs to
+variable references. In our new scheme, variables live on the stack, so
+code generating a reference to them actually needs to produce a load
+from the stack slot:
+
+.. code-block:: c++
+
+    Value *VariableExprAST::codegen() {
+      // Look this variable up in the function.
+      Value *V = NamedValues[Name];
+      if (!V)
+        return LogErrorV("Unknown variable name");
+
+      // Load the value.
+      return Builder.CreateLoad(V, Name.c_str());
+    }
+
+As you can see, this is pretty straightforward. Now we need to update
+the things that define the variables to set up the alloca. We'll start
+with ``ForExprAST::codegen()`` (see the `full code listing <#id1>`_ for
+the unabridged code):
+
+.. code-block:: c++
+
+      Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+      // Create an alloca for the variable in the entry block.
+      AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+
+      // Emit the start code first, without 'variable' in scope.
+      Value *StartVal = Start->codegen();
+      if (!StartVal)
+        return nullptr;
+
+      // Store the value into the alloca.
+      Builder.CreateStore(StartVal, Alloca);
+      ...
+
+      // Compute the end condition.
+      Value *EndCond = End->codegen();
+      if (!EndCond)
+        return nullptr;
+
+      // Reload, increment, and restore the alloca.  This handles the case where
+      // the body of the loop mutates the variable.
+      Value *CurVar = Builder.CreateLoad(Alloca);
+      Value *NextVar = Builder.CreateFAdd(CurVar, StepVal, "nextvar");
+      Builder.CreateStore(NextVar, Alloca);
+      ...
+
+This code is virtually identical to the code `before we allowed mutable
+variables <LangImpl5.html#code-generation-for-the-for-loop>`_. The big difference is that we
+no longer have to construct a PHI node, and we use load/store to access
+the variable as needed.
+
+To support mutable argument variables, we need to also make allocas for
+them. The code for this is also pretty simple:
+
+.. code-block:: c++
+
+    Function *FunctionAST::codegen() {
+      ...
+      Builder.SetInsertPoint(BB);
+
+      // Record the function arguments in the NamedValues map.
+      NamedValues.clear();
+      for (auto &Arg : TheFunction->args()) {
+        // Create an alloca for this variable.
+        AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, Arg.getName());
+
+        // Store the initial value into the alloca.
+        Builder.CreateStore(&Arg, Alloca);
+
+        // Add arguments to variable symbol table.
+        NamedValues[Arg.getName()] = Alloca;
+      }
+
+      if (Value *RetVal = Body->codegen()) {
+        ...
+
+For each argument, we make an alloca, store the input value to the
+function into the alloca, and register the alloca as the memory location
+for the argument. This method gets invoked by ``FunctionAST::codegen()``
+right after it sets up the entry block for the function.
+
+The final missing piece is adding the mem2reg pass, which allows us to
+get good codegen once again:
+
+.. code-block:: c++
+
+        // Promote allocas to registers.
+        TheFPM->add(createPromoteMemoryToRegisterPass());
+        // Do simple "peephole" optimizations and bit-twiddling optzns.
+        TheFPM->add(createInstructionCombiningPass());
+        // Reassociate expressions.
+        TheFPM->add(createReassociatePass());
+        ...
+
+It is interesting to see what the code looks like before and after the
+mem2reg optimization runs. For example, this is the before/after code
+for our recursive fib function. Before the optimization:
+
+.. code-block:: llvm
+
+    define double @fib(double %x) {
+    entry:
+      %x1 = alloca double
+      store double %x, double* %x1
+      %x2 = load double, double* %x1
+      %cmptmp = fcmp ult double %x2, 3.000000e+00
+      %booltmp = uitofp i1 %cmptmp to double
+      %ifcond = fcmp one double %booltmp, 0.000000e+00
+      br i1 %ifcond, label %then, label %else
+
+    then:       ; preds = %entry
+      br label %ifcont
+
+    else:       ; preds = %entry
+      %x3 = load double, double* %x1
+      %subtmp = fsub double %x3, 1.000000e+00
+      %calltmp = call double @fib(double %subtmp)
+      %x4 = load double, double* %x1
+      %subtmp5 = fsub double %x4, 2.000000e+00
+      %calltmp6 = call double @fib(double %subtmp5)
+      %addtmp = fadd double %calltmp, %calltmp6
+      br label %ifcont
+
+    ifcont:     ; preds = %else, %then
+      %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
+      ret double %iftmp
+    }
+
+Here there is only one variable (x, the input argument) but you can
+still see the extremely simple-minded code generation strategy we are
+using. In the entry block, an alloca is created, and the initial input
+value is stored into it. Each reference to the variable does a reload
+from the stack. Also, note that we didn't modify the if/then/else
+expression, so it still inserts a PHI node. While we could make an
+alloca for it, it is actually easier to create a PHI node for it, so we
+still just make the PHI.
+
+Here is the code after the mem2reg pass runs:
+
+.. code-block:: llvm
+
+    define double @fib(double %x) {
+    entry:
+      %cmptmp = fcmp ult double %x, 3.000000e+00
+      %booltmp = uitofp i1 %cmptmp to double
+      %ifcond = fcmp one double %booltmp, 0.000000e+00
+      br i1 %ifcond, label %then, label %else
+
+    then:
+      br label %ifcont
+
+    else:
+      %subtmp = fsub double %x, 1.000000e+00
+      %calltmp = call double @fib(double %subtmp)
+      %subtmp5 = fsub double %x, 2.000000e+00
+      %calltmp6 = call double @fib(double %subtmp5)
+      %addtmp = fadd double %calltmp, %calltmp6
+      br label %ifcont
+
+    ifcont:     ; preds = %else, %then
+      %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
+      ret double %iftmp
+    }
+
+This is a trivial case for mem2reg, since there are no redefinitions of
+the variable. The point of showing this is to calm your tension about
+inserting such blatent inefficiencies :).
+
+After the rest of the optimizers run, we get:
+
+.. code-block:: llvm
+
+    define double @fib(double %x) {
+    entry:
+      %cmptmp = fcmp ult double %x, 3.000000e+00
+      %booltmp = uitofp i1 %cmptmp to double
+      %ifcond = fcmp ueq double %booltmp, 0.000000e+00
+      br i1 %ifcond, label %else, label %ifcont
+
+    else:
+      %subtmp = fsub double %x, 1.000000e+00
+      %calltmp = call double @fib(double %subtmp)
+      %subtmp5 = fsub double %x, 2.000000e+00
+      %calltmp6 = call double @fib(double %subtmp5)
+      %addtmp = fadd double %calltmp, %calltmp6
+      ret double %addtmp
+
+    ifcont:
+      ret double 1.000000e+00
+    }
+
+Here we see that the simplifycfg pass decided to clone the return
+instruction into the end of the 'else' block. This allowed it to
+eliminate some branches and the PHI node.
+
+Now that all symbol table references are updated to use stack variables,
+we'll add the assignment operator.
+
+New Assignment Operator
+=======================
+
+With our current framework, adding a new assignment operator is really
+simple. We will parse it just like any other binary operator, but handle
+it internally (instead of allowing the user to define it). The first
+step is to set a precedence:
+
+.. code-block:: c++
+
+     int main() {
+       // Install standard binary operators.
+       // 1 is lowest precedence.
+       BinopPrecedence['='] = 2;
+       BinopPrecedence['<'] = 10;
+       BinopPrecedence['+'] = 20;
+       BinopPrecedence['-'] = 20;
+
+Now that the parser knows the precedence of the binary operator, it
+takes care of all the parsing and AST generation. We just need to
+implement codegen for the assignment operator. This looks like:
+
+.. code-block:: c++
+
+    Value *BinaryExprAST::codegen() {
+      // Special case '=' because we don't want to emit the LHS as an expression.
+      if (Op == '=') {
+        // Assignment requires the LHS to be an identifier.
+        VariableExprAST *LHSE = dynamic_cast<VariableExprAST*>(LHS.get());
+        if (!LHSE)
+          return LogErrorV("destination of '=' must be a variable");
+
+Unlike the rest of the binary operators, our assignment operator doesn't
+follow the "emit LHS, emit RHS, do computation" model. As such, it is
+handled as a special case before the other binary operators are handled.
+The other strange thing is that it requires the LHS to be a variable. It
+is invalid to have "(x+1) = expr" - only things like "x = expr" are
+allowed.
+
+.. code-block:: c++
+
+        // Codegen the RHS.
+        Value *Val = RHS->codegen();
+        if (!Val)
+          return nullptr;
+
+        // Look up the name.
+        Value *Variable = NamedValues[LHSE->getName()];
+        if (!Variable)
+          return LogErrorV("Unknown variable name");
+
+        Builder.CreateStore(Val, Variable);
+        return Val;
+      }
+      ...
+
+Once we have the variable, codegen'ing the assignment is
+straightforward: we emit the RHS of the assignment, create a store, and
+return the computed value. Returning a value allows for chained
+assignments like "X = (Y = Z)".
+
+Now that we have an assignment operator, we can mutate loop variables
+and arguments. For example, we can now run code like this:
+
+::
+
+    # Function to print a double.
+    extern printd(x);
+
+    # Define ':' for sequencing: as a low-precedence operator that ignores operands
+    # and just returns the RHS.
+    def binary : 1 (x y) y;
+
+    def test(x)
+      printd(x) :
+      x = 4 :
+      printd(x);
+
+    test(123);
+
+When run, this example prints "123" and then "4", showing that we did
+actually mutate the value! Okay, we have now officially implemented our
+goal: getting this to work requires SSA construction in the general
+case. However, to be really useful, we want the ability to define our
+own local variables, let's add this next!
+
+User-defined Local Variables
+============================
+
+Adding var/in is just like any other extension we made to
+Kaleidoscope: we extend the lexer, the parser, the AST and the code
+generator. The first step for adding our new 'var/in' construct is to
+extend the lexer. As before, this is pretty trivial, the code looks like
+this:
+
+.. code-block:: c++
+
+    enum Token {
+      ...
+      // var definition
+      tok_var = -13
+    ...
+    }
+    ...
+    static int gettok() {
+    ...
+        if (IdentifierStr == "in")
+          return tok_in;
+        if (IdentifierStr == "binary")
+          return tok_binary;
+        if (IdentifierStr == "unary")
+          return tok_unary;
+        if (IdentifierStr == "var")
+          return tok_var;
+        return tok_identifier;
+    ...
+
+The next step is to define the AST node that we will construct. For
+var/in, it looks like this:
+
+.. code-block:: c++
+
+    /// VarExprAST - Expression class for var/in
+    class VarExprAST : public ExprAST {
+      std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
+      std::unique_ptr<ExprAST> Body;
+
+    public:
+      VarExprAST(std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames,
+                 std::unique_ptr<ExprAST> Body)
+        : VarNames(std::move(VarNames)), Body(std::move(Body)) {}
+
+      Value *codegen() override;
+    };
+
+var/in allows a list of names to be defined all at once, and each name
+can optionally have an initializer value. As such, we capture this
+information in the VarNames vector. Also, var/in has a body, this body
+is allowed to access the variables defined by the var/in.
+
+With this in place, we can define the parser pieces. The first thing we
+do is add it as a primary expression:
+
+.. code-block:: c++
+
+    /// primary
+    ///   ::= identifierexpr
+    ///   ::= numberexpr
+    ///   ::= parenexpr
+    ///   ::= ifexpr
+    ///   ::= forexpr
+    ///   ::= varexpr
+    static std::unique_ptr<ExprAST> ParsePrimary() {
+      switch (CurTok) {
+      default:
+        return LogError("unknown token when expecting an expression");
+      case tok_identifier:
+        return ParseIdentifierExpr();
+      case tok_number:
+        return ParseNumberExpr();
+      case '(':
+        return ParseParenExpr();
+      case tok_if:
+        return ParseIfExpr();
+      case tok_for:
+        return ParseForExpr();
+      case tok_var:
+        return ParseVarExpr();
+      }
+    }
+
+Next we define ParseVarExpr:
+
+.. code-block:: c++
+
+    /// varexpr ::= 'var' identifier ('=' expression)?
+    //                    (',' identifier ('=' expression)?)* 'in' expression
+    static std::unique_ptr<ExprAST> ParseVarExpr() {
+      getNextToken();  // eat the var.
+
+      std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
+
+      // At least one variable name is required.
+      if (CurTok != tok_identifier)
+        return LogError("expected identifier after var");
+
+The first part of this code parses the list of identifier/expr pairs
+into the local ``VarNames`` vector.
+
+.. code-block:: c++
+
+      while (1) {
+        std::string Name = IdentifierStr;
+        getNextToken();  // eat identifier.
+
+        // Read the optional initializer.
+        std::unique_ptr<ExprAST> Init;
+        if (CurTok == '=') {
+          getNextToken(); // eat the '='.
+
+          Init = ParseExpression();
+          if (!Init) return nullptr;
+        }
+
+        VarNames.push_back(std::make_pair(Name, std::move(Init)));
+
+        // End of var list, exit loop.
+        if (CurTok != ',') break;
+        getNextToken(); // eat the ','.
+
+        if (CurTok != tok_identifier)
+          return LogError("expected identifier list after var");
+      }
+
+Once all the variables are parsed, we then parse the body and create the
+AST node:
+
+.. code-block:: c++
+
+      // At this point, we have to have 'in'.
+      if (CurTok != tok_in)
+        return LogError("expected 'in' keyword after 'var'");
+      getNextToken();  // eat 'in'.
+
+      auto Body = ParseExpression();
+      if (!Body)
+        return nullptr;
+
+      return llvm::make_unique<VarExprAST>(std::move(VarNames),
+                                           std::move(Body));
+    }
+
+Now that we can parse and represent the code, we need to support
+emission of LLVM IR for it. This code starts out with:
+
+.. code-block:: c++
+
+    Value *VarExprAST::codegen() {
+      std::vector<AllocaInst *> OldBindings;
+
+      Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+      // Register all variables and emit their initializer.
+      for (unsigned i = 0, e = VarNames.size(); i != e; ++i) {
+        const std::string &VarName = VarNames[i].first;
+        ExprAST *Init = VarNames[i].second.get();
+
+Basically it loops over all the variables, installing them one at a
+time. For each variable we put into the symbol table, we remember the
+previous value that we replace in OldBindings.
+
+.. code-block:: c++
+
+        // Emit the initializer before adding the variable to scope, this prevents
+        // the initializer from referencing the variable itself, and permits stuff
+        // like this:
+        //  var a = 1 in
+        //    var a = a in ...   # refers to outer 'a'.
+        Value *InitVal;
+        if (Init) {
+          InitVal = Init->codegen();
+          if (!InitVal)
+            return nullptr;
+        } else { // If not specified, use 0.0.
+          InitVal = ConstantFP::get(TheContext, APFloat(0.0));
+        }
+
+        AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+        Builder.CreateStore(InitVal, Alloca);
+
+        // Remember the old variable binding so that we can restore the binding when
+        // we unrecurse.
+        OldBindings.push_back(NamedValues[VarName]);
+
+        // Remember this binding.
+        NamedValues[VarName] = Alloca;
+      }
+
+There are more comments here than code. The basic idea is that we emit
+the initializer, create the alloca, then update the symbol table to
+point to it. Once all the variables are installed in the symbol table,
+we evaluate the body of the var/in expression:
+
+.. code-block:: c++
+
+      // Codegen the body, now that all vars are in scope.
+      Value *BodyVal = Body->codegen();
+      if (!BodyVal)
+        return nullptr;
+
+Finally, before returning, we restore the previous variable bindings:
+
+.. code-block:: c++
+
+      // Pop all our variables from scope.
+      for (unsigned i = 0, e = VarNames.size(); i != e; ++i)
+        NamedValues[VarNames[i].first] = OldBindings[i];
+
+      // Return the body computation.
+      return BodyVal;
+    }
+
+The end result of all of this is that we get properly scoped variable
+definitions, and we even (trivially) allow mutation of them :).
+
+With this, we completed what we set out to do. Our nice iterative fib
+example from the intro compiles and runs just fine. The mem2reg pass
+optimizes all of our stack variables into SSA registers, inserting PHI
+nodes where needed, and our front-end remains simple: no "iterated
+dominance frontier" computation anywhere in sight.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+mutable variables and var/in support. To build this example, use:
+
+.. code-block:: bash
+
+    # Compile
+    clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+    # Run
+    ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter7/toy.cpp
+   :language: c++
+
+`Next: Compiling to Object Code <LangImpl08.html>`_
+
diff --git a/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl08.rst b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl08.rst
new file mode 100644
index 0000000..da4e60f
--- /dev/null
+++ b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl08.rst
@@ -0,0 +1,218 @@
+========================================
+ Kaleidoscope: Compiling to Object Code
+========================================
+
+.. contents::
+   :local:
+
+Chapter 8 Introduction
+======================
+
+Welcome to Chapter 8 of the "`Implementing a language with LLVM
+<index.html>`_" tutorial. This chapter describes how to compile our
+language down to object files.
+
+Choosing a target
+=================
+
+LLVM has native support for cross-compilation. You can compile to the
+architecture of your current machine, or just as easily compile for
+other architectures. In this tutorial, we'll target the current
+machine.
+
+To specify the architecture that you want to target, we use a string
+called a "target triple". This takes the form
+``<arch><sub>-<vendor>-<sys>-<abi>`` (see the `cross compilation docs
+<http://clang.llvm.org/docs/CrossCompilation.html#target-triple>`_).
+
+As an example, we can see what clang thinks is our current target
+triple:
+
+::
+
+    $ clang --version | grep Target
+    Target: x86_64-unknown-linux-gnu
+
+Running this command may show something different on your machine as
+you might be using a different architecture or operating system to me.
+
+Fortunately, we don't need to hard-code a target triple to target the
+current machine. LLVM provides ``sys::getDefaultTargetTriple``, which
+returns the target triple of the current machine.
+
+.. code-block:: c++
+
+    auto TargetTriple = sys::getDefaultTargetTriple();
+
+LLVM doesn't require us to link in all the target
+functionality. For example, if we're just using the JIT, we don't need
+the assembly printers. Similarly, if we're only targeting certain
+architectures, we can only link in the functionality for those
+architectures.
+
+For this example, we'll initialize all the targets for emitting object
+code.
+
+.. code-block:: c++
+
+    InitializeAllTargetInfos();
+    InitializeAllTargets();
+    InitializeAllTargetMCs();
+    InitializeAllAsmParsers();
+    InitializeAllAsmPrinters();
+
+We can now use our target triple to get a ``Target``:
+
+.. code-block:: c++
+
+  std::string Error;
+  auto Target = TargetRegistry::lookupTarget(TargetTriple, Error);
+
+  // Print an error and exit if we couldn't find the requested target.
+  // This generally occurs if we've forgotten to initialise the
+  // TargetRegistry or we have a bogus target triple.
+  if (!Target) {
+    errs() << Error;
+    return 1;
+  }
+
+Target Machine
+==============
+
+We will also need a ``TargetMachine``. This class provides a complete
+machine description of the machine we're targeting. If we want to
+target a specific feature (such as SSE) or a specific CPU (such as
+Intel's Sandylake), we do so now.
+
+To see which features and CPUs that LLVM knows about, we can use
+``llc``. For example, let's look at x86:
+
+::
+
+    $ llvm-as < /dev/null | llc -march=x86 -mattr=help
+    Available CPUs for this target:
+
+      amdfam10      - Select the amdfam10 processor.
+      athlon        - Select the athlon processor.
+      athlon-4      - Select the athlon-4 processor.
+      ...
+
+    Available features for this target:
+
+      16bit-mode            - 16-bit mode (i8086).
+      32bit-mode            - 32-bit mode (80386).
+      3dnow                 - Enable 3DNow! instructions.
+      3dnowa                - Enable 3DNow! Athlon instructions.
+      ...
+
+For our example, we'll use the generic CPU without any additional
+features, options or relocation model.
+
+.. code-block:: c++
+
+  auto CPU = "generic";
+  auto Features = "";
+
+  TargetOptions opt;
+  auto RM = Optional<Reloc::Model>();
+  auto TargetMachine = Target->createTargetMachine(TargetTriple, CPU, Features, opt, RM);
+
+
+Configuring the Module
+======================
+
+We're now ready to configure our module, to specify the target and
+data layout. This isn't strictly necessary, but the `frontend
+performance guide <../Frontend/PerformanceTips.html>`_ recommends
+this. Optimizations benefit from knowing about the target and data
+layout.
+
+.. code-block:: c++
+
+  TheModule->setDataLayout(TargetMachine->createDataLayout());
+  TheModule->setTargetTriple(TargetTriple);   
+  
+Emit Object Code
+================
+
+We're ready to emit object code! Let's define where we want to write
+our file to:
+
+.. code-block:: c++
+
+  auto Filename = "output.o";
+  std::error_code EC;
+  raw_fd_ostream dest(Filename, EC, sys::fs::F_None);
+
+  if (EC) {
+    errs() << "Could not open file: " << EC.message();
+    return 1;
+  }
+
+Finally, we define a pass that emits object code, then we run that
+pass:
+
+.. code-block:: c++
+
+  legacy::PassManager pass;
+  auto FileType = TargetMachine::CGFT_ObjectFile;
+
+  if (TargetMachine->addPassesToEmitFile(pass, dest, FileType)) {
+    errs() << "TargetMachine can't emit a file of this type";
+    return 1;
+  }
+
+  pass.run(*TheModule);
+  dest.flush();
+
+Putting It All Together
+=======================
+
+Does it work? Let's give it a try. We need to compile our code, but
+note that the arguments to ``llvm-config`` are different to the previous chapters.
+
+::
+
+    $ clang++ -g -O3 toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs all` -o toy
+
+Let's run it, and define a simple ``average`` function. Press Ctrl-D
+when you're done.
+
+::
+   
+    $ ./toy
+    ready> def average(x y) (x + y) * 0.5;
+    ^D
+    Wrote output.o
+
+We have an object file! To test it, let's write a simple program and
+link it with our output. Here's the source code:
+
+.. code-block:: c++
+
+    #include <iostream>
+
+    extern "C" {
+        double average(double, double);
+    }
+
+    int main() {
+        std::cout << "average of 3.0 and 4.0: " << average(3.0, 4.0) << std::endl;
+    }
+
+We link our program to output.o and check the result is what we
+expected:
+
+::
+
+    $ clang++ main.cpp output.o -o main
+    $ ./main
+    average of 3.0 and 4.0: 3.5
+
+Full Code Listing
+=================
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter8/toy.cpp
+   :language: c++
+
+`Next: Adding Debug Information <LangImpl09.html>`_
diff --git a/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl09.rst b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl09.rst
new file mode 100644
index 0000000..d81f9fa
--- /dev/null
+++ b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl09.rst
@@ -0,0 +1,465 @@
+======================================
+Kaleidoscope: Adding Debug Information
+======================================
+
+.. contents::
+   :local:
+
+Chapter 9 Introduction
+======================
+
+Welcome to Chapter 9 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. In chapters 1 through 8, we've built a
+decent little programming language with functions and variables.
+What happens if something goes wrong though, how do you debug your
+program?
+
+Source level debugging uses formatted data that helps a debugger
+translate from binary and the state of the machine back to the
+source that the programmer wrote. In LLVM we generally use a format
+called `DWARF <http://dwarfstd.org>`_. DWARF is a compact encoding
+that represents types, source locations, and variable locations.
+
+The short summary of this chapter is that we'll go through the
+various things you have to add to a programming language to
+support debug info, and how you translate that into DWARF.
+
+Caveat: For now we can't debug via the JIT, so we'll need to compile
+our program down to something small and standalone. As part of this
+we'll make a few modifications to the running of the language and
+how programs are compiled. This means that we'll have a source file
+with a simple program written in Kaleidoscope rather than the
+interactive JIT. It does involve a limitation that we can only
+have one "top level" command at a time to reduce the number of
+changes necessary.
+
+Here's the sample program we'll be compiling:
+
+.. code-block:: python
+
+   def fib(x)
+     if x < 3 then
+       1
+     else
+       fib(x-1)+fib(x-2);
+
+   fib(10)
+
+
+Why is this a hard problem?
+===========================
+
+Debug information is a hard problem for a few different reasons - mostly
+centered around optimized code. First, optimization makes keeping source
+locations more difficult. In LLVM IR we keep the original source location
+for each IR level instruction on the instruction. Optimization passes
+should keep the source locations for newly created instructions, but merged
+instructions only get to keep a single location - this can cause jumping
+around when stepping through optimized programs. Secondly, optimization
+can move variables in ways that are either optimized out, shared in memory
+with other variables, or difficult to track. For the purposes of this
+tutorial we're going to avoid optimization (as you'll see with one of the
+next sets of patches).
+
+Ahead-of-Time Compilation Mode
+==============================
+
+To highlight only the aspects of adding debug information to a source
+language without needing to worry about the complexities of JIT debugging
+we're going to make a few changes to Kaleidoscope to support compiling
+the IR emitted by the front end into a simple standalone program that
+you can execute, debug, and see results.
+
+First we make our anonymous function that contains our top level
+statement be our "main":
+
+.. code-block:: udiff
+
+  -    auto Proto = llvm::make_unique<PrototypeAST>("", std::vector<std::string>());
+  +    auto Proto = llvm::make_unique<PrototypeAST>("main", std::vector<std::string>());
+
+just with the simple change of giving it a name.
+
+Then we're going to remove the command line code wherever it exists:
+
+.. code-block:: udiff
+
+  @@ -1129,7 +1129,6 @@ static void HandleTopLevelExpression() {
+   /// top ::= definition | external | expression | ';'
+   static void MainLoop() {
+     while (1) {
+  -    fprintf(stderr, "ready> ");
+       switch (CurTok) {
+       case tok_eof:
+         return;
+  @@ -1184,7 +1183,6 @@ int main() {
+     BinopPrecedence['*'] = 40; // highest.
+
+     // Prime the first token.
+  -  fprintf(stderr, "ready> ");
+     getNextToken();
+
+Lastly we're going to disable all of the optimization passes and the JIT so
+that the only thing that happens after we're done parsing and generating
+code is that the LLVM IR goes to standard error:
+
+.. code-block:: udiff
+
+  @@ -1108,17 +1108,8 @@ static void HandleExtern() {
+   static void HandleTopLevelExpression() {
+     // Evaluate a top-level expression into an anonymous function.
+     if (auto FnAST = ParseTopLevelExpr()) {
+  -    if (auto *FnIR = FnAST->codegen()) {
+  -      // We're just doing this to make sure it executes.
+  -      TheExecutionEngine->finalizeObject();
+  -      // JIT the function, returning a function pointer.
+  -      void *FPtr = TheExecutionEngine->getPointerToFunction(FnIR);
+  -
+  -      // Cast it to the right type (takes no arguments, returns a double) so we
+  -      // can call it as a native function.
+  -      double (*FP)() = (double (*)())(intptr_t)FPtr;
+  -      // Ignore the return value for this.
+  -      (void)FP;
+  +    if (!F->codegen()) {
+  +      fprintf(stderr, "Error generating code for top level expr");
+       }
+     } else {
+       // Skip token for error recovery.
+  @@ -1439,11 +1459,11 @@ int main() {
+     // target lays out data structures.
+     TheModule->setDataLayout(TheExecutionEngine->getDataLayout());
+     OurFPM.add(new DataLayoutPass());
+  +#if 0
+     OurFPM.add(createBasicAliasAnalysisPass());
+     // Promote allocas to registers.
+     OurFPM.add(createPromoteMemoryToRegisterPass());
+  @@ -1218,7 +1210,7 @@ int main() {
+     OurFPM.add(createGVNPass());
+     // Simplify the control flow graph (deleting unreachable blocks, etc).
+     OurFPM.add(createCFGSimplificationPass());
+  -
+  +  #endif
+     OurFPM.doInitialization();
+
+     // Set the global so the code gen can use this.
+
+This relatively small set of changes get us to the point that we can compile
+our piece of Kaleidoscope language down to an executable program via this
+command line:
+
+.. code-block:: bash
+
+  Kaleidoscope-Ch9 < fib.ks | & clang -x ir -
+
+which gives an a.out/a.exe in the current working directory.
+
+Compile Unit
+============
+
+The top level container for a section of code in DWARF is a compile unit.
+This contains the type and function data for an individual translation unit
+(read: one file of source code). So the first thing we need to do is
+construct one for our fib.ks file.
+
+DWARF Emission Setup
+====================
+
+Similar to the ``IRBuilder`` class we have a
+`DIBuilder <http://llvm.org/doxygen/classllvm_1_1DIBuilder.html>`_ class
+that helps in constructing debug metadata for an LLVM IR file. It
+corresponds 1:1 similarly to ``IRBuilder`` and LLVM IR, but with nicer names.
+Using it does require that you be more familiar with DWARF terminology than
+you needed to be with ``IRBuilder`` and ``Instruction`` names, but if you
+read through the general documentation on the
+`Metadata Format <http://llvm.org/docs/SourceLevelDebugging.html>`_ it
+should be a little more clear. We'll be using this class to construct all
+of our IR level descriptions. Construction for it takes a module so we
+need to construct it shortly after we construct our module. We've left it
+as a global static variable to make it a bit easier to use.
+
+Next we're going to create a small container to cache some of our frequent
+data. The first will be our compile unit, but we'll also write a bit of
+code for our one type since we won't have to worry about multiple typed
+expressions:
+
+.. code-block:: c++
+
+  static DIBuilder *DBuilder;
+
+  struct DebugInfo {
+    DICompileUnit *TheCU;
+    DIType *DblTy;
+
+    DIType *getDoubleTy();
+  } KSDbgInfo;
+
+  DIType *DebugInfo::getDoubleTy() {
+    if (DblTy)
+      return DblTy;
+
+    DblTy = DBuilder->createBasicType("double", 64, dwarf::DW_ATE_float);
+    return DblTy;
+  }
+
+And then later on in ``main`` when we're constructing our module:
+
+.. code-block:: c++
+
+  DBuilder = new DIBuilder(*TheModule);
+
+  KSDbgInfo.TheCU = DBuilder->createCompileUnit(
+      dwarf::DW_LANG_C, DBuilder->createFile("fib.ks", "."),
+      "Kaleidoscope Compiler", 0, "", 0);
+
+There are a couple of things to note here. First, while we're producing a
+compile unit for a language called Kaleidoscope we used the language
+constant for C. This is because a debugger wouldn't necessarily understand
+the calling conventions or default ABI for a language it doesn't recognize
+and we follow the C ABI in our LLVM code generation so it's the closest
+thing to accurate. This ensures we can actually call functions from the
+debugger and have them execute. Secondly, you'll see the "fib.ks" in the
+call to ``createCompileUnit``. This is a default hard coded value since
+we're using shell redirection to put our source into the Kaleidoscope
+compiler. In a usual front end you'd have an input file name and it would
+go there.
+
+One last thing as part of emitting debug information via DIBuilder is that
+we need to "finalize" the debug information. The reasons are part of the
+underlying API for DIBuilder, but make sure you do this near the end of
+main:
+
+.. code-block:: c++
+
+  DBuilder->finalize();
+
+before you dump out the module.
+
+Functions
+=========
+
+Now that we have our ``Compile Unit`` and our source locations, we can add
+function definitions to the debug info. So in ``PrototypeAST::codegen()`` we
+add a few lines of code to describe a context for our subprogram, in this
+case the "File", and the actual definition of the function itself.
+
+So the context:
+
+.. code-block:: c++
+
+  DIFile *Unit = DBuilder->createFile(KSDbgInfo.TheCU.getFilename(),
+                                      KSDbgInfo.TheCU.getDirectory());
+
+giving us an DIFile and asking the ``Compile Unit`` we created above for the
+directory and filename where we are currently. Then, for now, we use some
+source locations of 0 (since our AST doesn't currently have source location
+information) and construct our function definition:
+
+.. code-block:: c++
+
+  DIScope *FContext = Unit;
+  unsigned LineNo = 0;
+  unsigned ScopeLine = 0;
+  DISubprogram *SP = DBuilder->createFunction(
+      FContext, P.getName(), StringRef(), Unit, LineNo,
+      CreateFunctionType(TheFunction->arg_size(), Unit),
+      false /* internal linkage */, true /* definition */, ScopeLine,
+      DINode::FlagPrototyped, false);
+  TheFunction->setSubprogram(SP);
+
+and we now have an DISubprogram that contains a reference to all of our
+metadata for the function.
+
+Source Locations
+================
+
+The most important thing for debug information is accurate source location -
+this makes it possible to map your source code back. We have a problem though,
+Kaleidoscope really doesn't have any source location information in the lexer
+or parser so we'll need to add it.
+
+.. code-block:: c++
+
+   struct SourceLocation {
+     int Line;
+     int Col;
+   };
+   static SourceLocation CurLoc;
+   static SourceLocation LexLoc = {1, 0};
+
+   static int advance() {
+     int LastChar = getchar();
+
+     if (LastChar == '\n' || LastChar == '\r') {
+       LexLoc.Line++;
+       LexLoc.Col = 0;
+     } else
+       LexLoc.Col++;
+     return LastChar;
+   }
+
+In this set of code we've added some functionality on how to keep track of the
+line and column of the "source file". As we lex every token we set our current
+current "lexical location" to the assorted line and column for the beginning
+of the token. We do this by overriding all of the previous calls to
+``getchar()`` with our new ``advance()`` that keeps track of the information
+and then we have added to all of our AST classes a source location:
+
+.. code-block:: c++
+
+   class ExprAST {
+     SourceLocation Loc;
+
+     public:
+       ExprAST(SourceLocation Loc = CurLoc) : Loc(Loc) {}
+       virtual ~ExprAST() {}
+       virtual Value* codegen() = 0;
+       int getLine() const { return Loc.Line; }
+       int getCol() const { return Loc.Col; }
+       virtual raw_ostream &dump(raw_ostream &out, int ind) {
+         return out << ':' << getLine() << ':' << getCol() << '\n';
+       }
+
+that we pass down through when we create a new expression:
+
+.. code-block:: c++
+
+   LHS = llvm::make_unique<BinaryExprAST>(BinLoc, BinOp, std::move(LHS),
+                                          std::move(RHS));
+
+giving us locations for each of our expressions and variables.
+
+To make sure that every instruction gets proper source location information,
+we have to tell ``Builder`` whenever we're at a new source location.
+We use a small helper function for this:
+
+.. code-block:: c++
+
+  void DebugInfo::emitLocation(ExprAST *AST) {
+    DIScope *Scope;
+    if (LexicalBlocks.empty())
+      Scope = TheCU;
+    else
+      Scope = LexicalBlocks.back();
+    Builder.SetCurrentDebugLocation(
+        DebugLoc::get(AST->getLine(), AST->getCol(), Scope));
+  }
+
+This both tells the main ``IRBuilder`` where we are, but also what scope
+we're in. The scope can either be on compile-unit level or be the nearest
+enclosing lexical block like the current function.
+To represent this we create a stack of scopes:
+
+.. code-block:: c++
+
+   std::vector<DIScope *> LexicalBlocks;
+
+and push the scope (function) to the top of the stack when we start
+generating the code for each function:
+
+.. code-block:: c++
+
+  KSDbgInfo.LexicalBlocks.push_back(SP);
+
+Also, we may not forget to pop the scope back off of the scope stack at the
+end of the code generation for the function:
+
+.. code-block:: c++
+
+  // Pop off the lexical block for the function since we added it
+  // unconditionally.
+  KSDbgInfo.LexicalBlocks.pop_back();
+
+Then we make sure to emit the location every time we start to generate code
+for a new AST object:
+
+.. code-block:: c++
+
+   KSDbgInfo.emitLocation(this);
+
+Variables
+=========
+
+Now that we have functions, we need to be able to print out the variables
+we have in scope. Let's get our function arguments set up so we can get
+decent backtraces and see how our functions are being called. It isn't
+a lot of code, and we generally handle it when we're creating the
+argument allocas in ``FunctionAST::codegen``.
+
+.. code-block:: c++
+
+    // Record the function arguments in the NamedValues map.
+    NamedValues.clear();
+    unsigned ArgIdx = 0;
+    for (auto &Arg : TheFunction->args()) {
+      // Create an alloca for this variable.
+      AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, Arg.getName());
+
+      // Create a debug descriptor for the variable.
+      DILocalVariable *D = DBuilder->createParameterVariable(
+          SP, Arg.getName(), ++ArgIdx, Unit, LineNo, KSDbgInfo.getDoubleTy(),
+          true);
+
+      DBuilder->insertDeclare(Alloca, D, DBuilder->createExpression(),
+                              DebugLoc::get(LineNo, 0, SP),
+                              Builder.GetInsertBlock());
+
+      // Store the initial value into the alloca.
+      Builder.CreateStore(&Arg, Alloca);
+
+      // Add arguments to variable symbol table.
+      NamedValues[Arg.getName()] = Alloca;
+    }
+
+
+Here we're first creating the variable, giving it the scope (``SP``),
+the name, source location, type, and since it's an argument, the argument
+index. Next, we create an ``lvm.dbg.declare`` call to indicate at the IR
+level that we've got a variable in an alloca (and it gives a starting
+location for the variable), and setting a source location for the
+beginning of the scope on the declare.
+
+One interesting thing to note at this point is that various debuggers have
+assumptions based on how code and debug information was generated for them
+in the past. In this case we need to do a little bit of a hack to avoid
+generating line information for the function prologue so that the debugger
+knows to skip over those instructions when setting a breakpoint. So in
+``FunctionAST::CodeGen`` we add some more lines:
+
+.. code-block:: c++
+
+  // Unset the location for the prologue emission (leading instructions with no
+  // location in a function are considered part of the prologue and the debugger
+  // will run past them when breaking on a function)
+  KSDbgInfo.emitLocation(nullptr);
+
+and then emit a new location when we actually start generating code for the
+body of the function:
+
+.. code-block:: c++
+
+  KSDbgInfo.emitLocation(Body.get());
+
+With this we have enough debug information to set breakpoints in functions,
+print out argument variables, and call functions. Not too bad for just a
+few simple lines of code!
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+debug information. To build this example, use:
+
+.. code-block:: bash
+
+    # Compile
+    clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
+    # Run
+    ./toy
+
+Here is the code:
+
+.. literalinclude:: ../../examples/Kaleidoscope/Chapter9/toy.cpp
+   :language: c++
+
+`Next: Conclusion and other useful LLVM tidbits <LangImpl10.html>`_
+
diff --git a/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl10.rst b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl10.rst
new file mode 100644
index 0000000..b1d19c2
--- /dev/null
+++ b/llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl10.rst
@@ -0,0 +1,254 @@
+======================================================
+Kaleidoscope: Conclusion and other useful LLVM tidbits
+======================================================
+
+.. contents::
+   :local:
+
+Tutorial Conclusion
+===================
+
+Welcome to the final chapter of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. In the course of this tutorial, we have
+grown our little Kaleidoscope language from being a useless toy, to
+being a semi-interesting (but probably still useless) toy. :)
+
+It is interesting to see how far we've come, and how little code it has
+taken. We built the entire lexer, parser, AST, code generator, an
+interactive run-loop (with a JIT!), and emitted debug information in
+standalone executables - all in under 1000 lines of (non-comment/non-blank)
+code.
+
+Our little language supports a couple of interesting features: it
+supports user defined binary and unary operators, it uses JIT
+compilation for immediate evaluation, and it supports a few control flow
+constructs with SSA construction.
+
+Part of the idea of this tutorial was to show you how easy and fun it
+can be to define, build, and play with languages. Building a compiler
+need not be a scary or mystical process! Now that you've seen some of
+the basics, I strongly encourage you to take the code and hack on it.
+For example, try adding:
+
+-  **global variables** - While global variables have questional value
+   in modern software engineering, they are often useful when putting
+   together quick little hacks like the Kaleidoscope compiler itself.
+   Fortunately, our current setup makes it very easy to add global
+   variables: just have value lookup check to see if an unresolved
+   variable is in the global variable symbol table before rejecting it.
+   To create a new global variable, make an instance of the LLVM
+   ``GlobalVariable`` class.
+-  **typed variables** - Kaleidoscope currently only supports variables
+   of type double. This gives the language a very nice elegance, because
+   only supporting one type means that you never have to specify types.
+   Different languages have different ways of handling this. The easiest
+   way is to require the user to specify types for every variable
+   definition, and record the type of the variable in the symbol table
+   along with its Value\*.
+-  **arrays, structs, vectors, etc** - Once you add types, you can start
+   extending the type system in all sorts of interesting ways. Simple
+   arrays are very easy and are quite useful for many different
+   applications. Adding them is mostly an exercise in learning how the
+   LLVM `getelementptr <../LangRef.html#getelementptr-instruction>`_ instruction
+   works: it is so nifty/unconventional, it `has its own
+   FAQ <../GetElementPtr.html>`_!
+-  **standard runtime** - Our current language allows the user to access
+   arbitrary external functions, and we use it for things like "printd"
+   and "putchard". As you extend the language to add higher-level
+   constructs, often these constructs make the most sense if they are
+   lowered to calls into a language-supplied runtime. For example, if
+   you add hash tables to the language, it would probably make sense to
+   add the routines to a runtime, instead of inlining them all the way.
+-  **memory management** - Currently we can only access the stack in
+   Kaleidoscope. It would also be useful to be able to allocate heap
+   memory, either with calls to the standard libc malloc/free interface
+   or with a garbage collector. If you would like to use garbage
+   collection, note that LLVM fully supports `Accurate Garbage
+   Collection <../GarbageCollection.html>`_ including algorithms that
+   move objects and need to scan/update the stack.
+-  **exception handling support** - LLVM supports generation of `zero
+   cost exceptions <../ExceptionHandling.html>`_ which interoperate with
+   code compiled in other languages. You could also generate code by
+   implicitly making every function return an error value and checking
+   it. You could also make explicit use of setjmp/longjmp. There are
+   many different ways to go here.
+-  **object orientation, generics, database access, complex numbers,
+   geometric programming, ...** - Really, there is no end of crazy
+   features that you can add to the language.
+-  **unusual domains** - We've been talking about applying LLVM to a
+   domain that many people are interested in: building a compiler for a
+   specific language. However, there are many other domains that can use
+   compiler technology that are not typically considered. For example,
+   LLVM has been used to implement OpenGL graphics acceleration,
+   translate C++ code to ActionScript, and many other cute and clever
+   things. Maybe you will be the first to JIT compile a regular
+   expression interpreter into native code with LLVM?
+
+Have fun - try doing something crazy and unusual. Building a language
+like everyone else always has, is much less fun than trying something a
+little crazy or off the wall and seeing how it turns out. If you get
+stuck or want to talk about it, feel free to email the `llvm-dev mailing
+list <http://lists.llvm.org/mailman/listinfo/llvm-dev>`_: it has lots
+of people who are interested in languages and are often willing to help
+out.
+
+Before we end this tutorial, I want to talk about some "tips and tricks"
+for generating LLVM IR. These are some of the more subtle things that
+may not be obvious, but are very useful if you want to take advantage of
+LLVM's capabilities.
+
+Properties of the LLVM IR
+=========================
+
+We have a couple of common questions about code in the LLVM IR form -
+let's just get these out of the way right now, shall we?
+
+Target Independence
+-------------------
+
+Kaleidoscope is an example of a "portable language": any program written
+in Kaleidoscope will work the same way on any target that it runs on.
+Many other languages have this property, e.g. lisp, java, haskell,
+javascript, python, etc (note that while these languages are portable,
+not all their libraries are).
+
+One nice aspect of LLVM is that it is often capable of preserving target
+independence in the IR: you can take the LLVM IR for a
+Kaleidoscope-compiled program and run it on any target that LLVM
+supports, even emitting C code and compiling that on targets that LLVM
+doesn't support natively. You can trivially tell that the Kaleidoscope
+compiler generates target-independent code because it never queries for
+any target-specific information when generating code.
+
+The fact that LLVM provides a compact, target-independent,
+representation for code gets a lot of people excited. Unfortunately,
+these people are usually thinking about C or a language from the C
+family when they are asking questions about language portability. I say
+"unfortunately", because there is really no way to make (fully general)
+C code portable, other than shipping the source code around (and of
+course, C source code is not actually portable in general either - ever
+port a really old application from 32- to 64-bits?).
+
+The problem with C (again, in its full generality) is that it is heavily
+laden with target specific assumptions. As one simple example, the
+preprocessor often destructively removes target-independence from the
+code when it processes the input text:
+
+.. code-block:: c
+
+    #ifdef __i386__
+      int X = 1;
+    #else
+      int X = 42;
+    #endif
+
+While it is possible to engineer more and more complex solutions to
+problems like this, it cannot be solved in full generality in a way that
+is better than shipping the actual source code.
+
+That said, there are interesting subsets of C that can be made portable.
+If you are willing to fix primitive types to a fixed size (say int =
+32-bits, and long = 64-bits), don't care about ABI compatibility with
+existing binaries, and are willing to give up some other minor features,
+you can have portable code. This can make sense for specialized domains
+such as an in-kernel language.
+
+Safety Guarantees
+-----------------
+
+Many of the languages above are also "safe" languages: it is impossible
+for a program written in Java to corrupt its address space and crash the
+process (assuming the JVM has no bugs). Safety is an interesting
+property that requires a combination of language design, runtime
+support, and often operating system support.
+
+It is certainly possible to implement a safe language in LLVM, but LLVM
+IR does not itself guarantee safety. The LLVM IR allows unsafe pointer
+casts, use after free bugs, buffer over-runs, and a variety of other
+problems. Safety needs to be implemented as a layer on top of LLVM and,
+conveniently, several groups have investigated this. Ask on the `llvm-dev
+mailing list <http://lists.llvm.org/mailman/listinfo/llvm-dev>`_ if
+you are interested in more details.
+
+Language-Specific Optimizations
+-------------------------------
+
+One thing about LLVM that turns off many people is that it does not
+solve all the world's problems in one system.  One specific
+complaint is that people perceive LLVM as being incapable of performing
+high-level language-specific optimization: LLVM "loses too much
+information".  Here are a few observations about this:
+
+First, you're right that LLVM does lose information. For example, as of
+this writing, there is no way to distinguish in the LLVM IR whether an
+SSA-value came from a C "int" or a C "long" on an ILP32 machine (other
+than debug info). Both get compiled down to an 'i32' value and the
+information about what it came from is lost. The more general issue
+here, is that the LLVM type system uses "structural equivalence" instead
+of "name equivalence". Another place this surprises people is if you
+have two types in a high-level language that have the same structure
+(e.g. two different structs that have a single int field): these types
+will compile down into a single LLVM type and it will be impossible to
+tell what it came from.
+
+Second, while LLVM does lose information, LLVM is not a fixed target: we
+continue to enhance and improve it in many different ways. In addition
+to adding new features (LLVM did not always support exceptions or debug
+info), we also extend the IR to capture important information for
+optimization (e.g. whether an argument is sign or zero extended,
+information about pointers aliasing, etc). Many of the enhancements are
+user-driven: people want LLVM to include some specific feature, so they
+go ahead and extend it.
+
+Third, it is *possible and easy* to add language-specific optimizations,
+and you have a number of choices in how to do it. As one trivial
+example, it is easy to add language-specific optimization passes that
+"know" things about code compiled for a language. In the case of the C
+family, there is an optimization pass that "knows" about the standard C
+library functions. If you call "exit(0)" in main(), it knows that it is
+safe to optimize that into "return 0;" because C specifies what the
+'exit' function does.
+
+In addition to simple library knowledge, it is possible to embed a
+variety of other language-specific information into the LLVM IR. If you
+have a specific need and run into a wall, please bring the topic up on
+the llvm-dev list. At the very worst, you can always treat LLVM as if it
+were a "dumb code generator" and implement the high-level optimizations
+you desire in your front-end, on the language-specific AST.
+
+Tips and Tricks
+===============
+
+There is a variety of useful tips and tricks that you come to know after
+working on/with LLVM that aren't obvious at first glance. Instead of
+letting everyone rediscover them, this section talks about some of these
+issues.
+
+Implementing portable offsetof/sizeof
+-------------------------------------
+
+One interesting thing that comes up, if you are trying to keep the code
+generated by your compiler "target independent", is that you often need
+to know the size of some LLVM type or the offset of some field in an
+llvm structure. For example, you might need to pass the size of a type
+into a function that allocates memory.
+
+Unfortunately, this can vary widely across targets: for example the
+width of a pointer is trivially target-specific. However, there is a
+`clever way to use the getelementptr
+instruction <http://nondot.org/sabre/LLVMNotes/SizeOf-OffsetOf-VariableSizedStructs.txt>`_
+that allows you to compute this in a portable way.
+
+Garbage Collected Stack Frames
+------------------------------
+
+Some languages want to explicitly manage their stack frames, often so
+that they are garbage collected or to allow easy implementation of
+closures. There are often better ways to implement these features than
+explicit stack frames, but `LLVM does support
+them, <http://nondot.org/sabre/LLVMNotes/ExplicitlyManagedStackFrames.txt>`_
+if you want. It requires your front-end to convert the code into
+`Continuation Passing
+Style <http://en.wikipedia.org/wiki/Continuation-passing_style>`_ and
+the use of tail calls (which LLVM also supports).
+