docs: Sphinxify `docs/tutorial/`
Sorry for the massive commit, but I just wanted to knock this one down
and it is really straightforward.
There are still a couple trivial (i.e. not related to the content)
things left to fix:
- Use of raw HTML links where :doc:`...` and :ref:`...` could be used
instead. If you are a newbie and want to help fix this it would make
for some good bite-sized patches; more experienced developers should
be focusing on adding new content (to this tutorial or elsewhere, but
please _do not_ waste your time on formatting when there is such dire
need for documentation (see docs/SphinxQuickstartTemplate.rst to get
started writing)).
- Highlighting of the kaleidoscope code blocks (currently left as bare
`::`). I will be working on writing a custom Pygments highlighter for
this, mostly as training for maintaining the `llvm` code-block's lexer
in-tree. I want to do this because I am extremely unhappy with how it
just "gives up" on the slightest deviation from the expected syntax
and leaves the whole code-block un-highlighted.
More generally I am looking at writing some Sphinx extensions and
keeping them in-tree as well, to support common use cases that
currently have no good solution (like "monospace text inside a link").
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169343 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/tutorial/LangImpl4.rst b/docs/tutorial/LangImpl4.rst
new file mode 100644
index 0000000..8484c57
--- /dev/null
+++ b/docs/tutorial/LangImpl4.rst
@@ -0,0 +1,1063 @@
+==============================================
+Kaleidoscope: Adding JIT and Optimizer Support
+==============================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre@nondot.org>`_
+
+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
+========================
+
+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#passmanager>`_ 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. The code looks like
+this:
+
+.. code-block:: c++
+
+ FunctionPassManager OurFPM(TheModule);
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
+ // Provide basic AliasAnalysis support for GVN.
+ OurFPM.add(createBasicAliasAnalysisPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+ // Eliminate Common SubExpressions.
+ OurFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ OurFPM.add(createCFGSimplificationPass());
+
+ OurFPM.doInitialization();
+
+ // Set the global so the code gen can use this.
+ TheFPM = &OurFPM;
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+This code defines a ``FunctionPassManager``, "``OurFPM``". It requires a
+pointer to the ``Module`` to construct itself. Once it is set up, we use
+a series of "add" calls to add a bunch of LLVM passes. The first pass is
+basically boilerplate, it adds a pass so that later optimizations know
+how the data structures in the program are laid out. The
+"``TheExecutionEngine``" variable is related to the JIT, which we will
+get to in the next section.
+
+In this case, we choose to add 4 optimization passes. The passes we
+chose 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, lets 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 declare and initialize the JIT. This is
+done by adding a global variable and a call in ``main``:
+
+.. code-block:: c++
+
+ static ExecutionEngine *TheExecutionEngine;
+ ...
+ int main() {
+ ..
+ // Create the JIT. This takes ownership of the module.
+ TheExecutionEngine = EngineBuilder(TheModule).create();
+ ..
+ }
+
+This creates an abstract "Execution Engine" which can be either a JIT
+compiler or the LLVM interpreter. LLVM will automatically pick a JIT
+compiler for you if one is available for your platform, otherwise it
+will fall back to the interpreter.
+
+Once the ``ExecutionEngine`` is created, the JIT is ready to be used.
+There are a variety of APIs that are useful, but the simplest one is the
+"``getPointerToFunction(F)``" method. This method JIT compiles the
+specified LLVM Function and returns a function pointer to the generated
+machine code. In our case, this means that we can change the code that
+parses a top-level expression to look like this:
+
+.. code-block:: c++
+
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (FunctionAST *F = ParseTopLevelExpr()) {
+ if (Function *LF = F->Codegen()) {
+ LF->dump(); // Dump the function for exposition purposes.
+
+ // JIT the function, returning a function pointer.
+ void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
+
+ // 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;
+ fprintf(stderr, "Evaluated to %f\n", FP());
+ }
+
+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.
+
+With just these two changes, lets 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
+
+This illustrates that we can now call user code, but there is something
+a bit subtle going on here. Note that we only invoke the JIT on the
+anonymous functions that *call testfunc*, but we never invoked it on
+*testfunc* itself. What actually happened here is that the JIT scanned
+for all non-JIT'd functions transitively called from the anonymous
+function and compiled all of them before returning from
+``getPointerToFunction()``.
+
+The JIT provides a number of other more advanced interfaces for things
+like freeing allocated machine code, rejit'ing functions to update them,
+etc. However, even with this simple code, we get some surprisingly
+powerful capabilities - check this out (I removed the dump of the
+anonymous functions, you should get the idea by now :) :
+
+::
+
+ 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: in this example, the JIT started execution of a
+function and got to a function call. It realized that the function was
+not yet JIT compiled and invoked the standard set of routines to resolve
+the function. In this case, there is no body defined for the function,
+so the JIT ended up 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.
+
+The LLVM JIT provides a number of interfaces (look in the
+``ExecutionEngine.h`` file) for controlling how unknown functions get
+resolved. It allows you to establish explicit mappings between IR
+objects and addresses (useful for LLVM global variables that you want to
+map to static tables, for example), allows you to dynamically decide on
+the fly based on the function name, and even allows you to have the JIT
+compile functions lazily the first time they're called.
+
+One interesting application of this is that we can now extend the
+language by writing arbitrary C++ code to implement operations. For
+example, if we add:
+
+.. code-block:: c++
+
+ /// putchard - putchar that takes a double and returns 0.
+ extern "C"
+ double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+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 <LangImpl5.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 --cppflags --ldflags --libs core jit 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:
+
+.. code-block:: c++
+
+ #include "llvm/DerivedTypes.h"
+ #include "llvm/ExecutionEngine/ExecutionEngine.h"
+ #include "llvm/ExecutionEngine/JIT.h"
+ #include "llvm/IRBuilder.h"
+ #include "llvm/LLVMContext.h"
+ #include "llvm/Module.h"
+ #include "llvm/PassManager.h"
+ #include "llvm/Analysis/Verifier.h"
+ #include "llvm/Analysis/Passes.h"
+ #include "llvm/DataLayout.h"
+ #include "llvm/Transforms/Scalar.h"
+ #include "llvm/Support/TargetSelect.h"
+ #include <cstdio>
+ #include <string>
+ #include <map>
+ #include <vector>
+ using namespace llvm;
+
+ //===----------------------------------------------------------------------===//
+ // Lexer
+ //===----------------------------------------------------------------------===//
+
+ // 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
+
+ /// gettok - Return the next token from standard input.
+ static int gettok() {
+ static int LastChar = ' ';
+
+ // Skip any whitespace.
+ while (isspace(LastChar))
+ LastChar = getchar();
+
+ 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;
+ }
+
+ 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;
+ }
+
+ if (LastChar == '#') {
+ // Comment until end of line.
+ do LastChar = getchar();
+ while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+ if (LastChar != EOF)
+ return gettok();
+ }
+
+ // 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;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Abstract Syntax Tree (aka Parse Tree)
+ //===----------------------------------------------------------------------===//
+
+ /// 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();
+ };
+
+ /// VariableExprAST - Expression class for referencing a variable, like "a".
+ class VariableExprAST : public ExprAST {
+ std::string Name;
+ public:
+ VariableExprAST(const std::string &name) : Name(name) {}
+ virtual Value *Codegen();
+ };
+
+ /// BinaryExprAST - Expression class for a binary operator.
+ class BinaryExprAST : public ExprAST {
+ char Op;
+ ExprAST *LHS, *RHS;
+ public:
+ BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
+ : Op(op), LHS(lhs), RHS(rhs) {}
+ virtual Value *Codegen();
+ };
+
+ /// CallExprAST - Expression class for function calls.
+ class CallExprAST : public ExprAST {
+ std::string Callee;
+ std::vector<ExprAST*> Args;
+ public:
+ CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
+ : Callee(callee), Args(args) {}
+ virtual Value *Codegen();
+ };
+
+ /// 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, const std::vector<std::string> &args)
+ : Name(name), Args(args) {}
+
+ Function *Codegen();
+ };
+
+ /// FunctionAST - This class represents a function definition itself.
+ class FunctionAST {
+ PrototypeAST *Proto;
+ ExprAST *Body;
+ public:
+ FunctionAST(PrototypeAST *proto, ExprAST *body)
+ : Proto(proto), Body(body) {}
+
+ Function *Codegen();
+ };
+
+ //===----------------------------------------------------------------------===//
+ // Parser
+ //===----------------------------------------------------------------------===//
+
+ /// 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();
+ }
+
+ /// 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;
+ }
+
+ /// Error* - These are little helper functions for error handling.
+ ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
+ PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
+ FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
+
+ static ExprAST *ParseExpression();
+
+ /// identifierexpr
+ /// ::= identifier
+ /// ::= identifier '(' expression* ')'
+ static ExprAST *ParseIdentifierExpr() {
+ std::string IdName = IdentifierStr;
+
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '(') // Simple variable ref.
+ return new VariableExprAST(IdName);
+
+ // Call.
+ getNextToken(); // eat (
+ std::vector<ExprAST*> Args;
+ if (CurTok != ')') {
+ while (1) {
+ ExprAST *Arg = ParseExpression();
+ if (!Arg) return 0;
+ Args.push_back(Arg);
+
+ if (CurTok == ')') break;
+
+ if (CurTok != ',')
+ return Error("Expected ')' or ',' in argument list");
+ getNextToken();
+ }
+ }
+
+ // Eat the ')'.
+ getNextToken();
+
+ return new CallExprAST(IdName, Args);
+ }
+
+ /// numberexpr ::= number
+ static ExprAST *ParseNumberExpr() {
+ ExprAST *Result = new NumberExprAST(NumVal);
+ getNextToken(); // consume the number
+ return Result;
+ }
+
+ /// parenexpr ::= '(' expression ')'
+ static ExprAST *ParseParenExpr() {
+ getNextToken(); // eat (.
+ ExprAST *V = ParseExpression();
+ if (!V) return 0;
+
+ if (CurTok != ')')
+ return Error("expected ')'");
+ getNextToken(); // eat ).
+ return V;
+ }
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ static ExprAST *ParsePrimary() {
+ switch (CurTok) {
+ default: return Error("unknown token when expecting an expression");
+ case tok_identifier: return ParseIdentifierExpr();
+ case tok_number: return ParseNumberExpr();
+ case '(': return ParseParenExpr();
+ }
+ }
+
+ /// binoprhs
+ /// ::= ('+' primary)*
+ static ExprAST *ParseBinOpRHS(int ExprPrec, 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;
+
+ // Okay, we know this is a binop.
+ int BinOp = CurTok;
+ getNextToken(); // eat binop
+
+ // Parse the primary expression after the binary operator.
+ ExprAST *RHS = ParsePrimary();
+ if (!RHS) return 0;
+
+ // 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, RHS);
+ if (RHS == 0) return 0;
+ }
+
+ // Merge LHS/RHS.
+ LHS = new BinaryExprAST(BinOp, LHS, RHS);
+ }
+ }
+
+ /// expression
+ /// ::= primary binoprhs
+ ///
+ static ExprAST *ParseExpression() {
+ ExprAST *LHS = ParsePrimary();
+ if (!LHS) return 0;
+
+ return ParseBinOpRHS(0, LHS);
+ }
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ static PrototypeAST *ParsePrototype() {
+ if (CurTok != tok_identifier)
+ return ErrorP("Expected function name in prototype");
+
+ std::string FnName = IdentifierStr;
+ getNextToken();
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ return new PrototypeAST(FnName, ArgNames);
+ }
+
+ /// definition ::= 'def' prototype expression
+ static FunctionAST *ParseDefinition() {
+ getNextToken(); // eat def.
+ PrototypeAST *Proto = ParsePrototype();
+ if (Proto == 0) return 0;
+
+ if (ExprAST *E = ParseExpression())
+ return new FunctionAST(Proto, E);
+ return 0;
+ }
+
+ /// toplevelexpr ::= expression
+ static FunctionAST *ParseTopLevelExpr() {
+ if (ExprAST *E = ParseExpression()) {
+ // Make an anonymous proto.
+ PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
+ return new FunctionAST(Proto, E);
+ }
+ return 0;
+ }
+
+ /// external ::= 'extern' prototype
+ static PrototypeAST *ParseExtern() {
+ getNextToken(); // eat extern.
+ return ParsePrototype();
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Code Generation
+ //===----------------------------------------------------------------------===//
+
+ static Module *TheModule;
+ static IRBuilder<> Builder(getGlobalContext());
+ static std::map<std::string, Value*> NamedValues;
+ static FunctionPassManager *TheFPM;
+
+ Value *ErrorV(const char *Str) { Error(Str); return 0; }
+
+ Value *NumberExprAST::Codegen() {
+ return ConstantFP::get(getGlobalContext(), APFloat(Val));
+ }
+
+ Value *VariableExprAST::Codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ return V ? V : ErrorV("Unknown variable name");
+ }
+
+ Value *BinaryExprAST::Codegen() {
+ Value *L = LHS->Codegen();
+ Value *R = RHS->Codegen();
+ if (L == 0 || R == 0) return 0;
+
+ 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(getGlobalContext()),
+ "booltmp");
+ default: return ErrorV("invalid binary operator");
+ }
+ }
+
+ Value *CallExprAST::Codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = TheModule->getFunction(Callee);
+ if (CalleeF == 0)
+ return ErrorV("Unknown function referenced");
+
+ // If argument mismatch error.
+ if (CalleeF->arg_size() != Args.size())
+ return ErrorV("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() == 0) return 0;
+ }
+
+ return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+ }
+
+ Function *PrototypeAST::Codegen() {
+ // Make the function type: double(double,double) etc.
+ std::vector<Type*> Doubles(Args.size(),
+ Type::getDoubleTy(getGlobalContext()));
+ FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
+ Doubles, false);
+
+ Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
+
+ // If F conflicted, there was already something named 'Name'. If it has a
+ // body, don't allow redefinition or reextern.
+ if (F->getName() != Name) {
+ // Delete the one we just made and get the existing one.
+ F->eraseFromParent();
+ F = TheModule->getFunction(Name);
+
+ // If F already has a body, reject this.
+ if (!F->empty()) {
+ ErrorF("redefinition of function");
+ return 0;
+ }
+
+ // If F took a different number of args, reject.
+ if (F->arg_size() != Args.size()) {
+ ErrorF("redefinition of function with different # args");
+ return 0;
+ }
+ }
+
+ // Set names for all arguments.
+ unsigned Idx = 0;
+ for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
+ ++AI, ++Idx) {
+ AI->setName(Args[Idx]);
+
+ // Add arguments to variable symbol table.
+ NamedValues[Args[Idx]] = AI;
+ }
+
+ return F;
+ }
+
+ Function *FunctionAST::Codegen() {
+ NamedValues.clear();
+
+ Function *TheFunction = Proto->Codegen();
+ if (TheFunction == 0)
+ return 0;
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ 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;
+ }
+
+ // Error reading body, remove function.
+ TheFunction->eraseFromParent();
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Top-Level parsing and JIT Driver
+ //===----------------------------------------------------------------------===//
+
+ static ExecutionEngine *TheExecutionEngine;
+
+ static void HandleDefinition() {
+ if (FunctionAST *F = ParseDefinition()) {
+ if (Function *LF = F->Codegen()) {
+ fprintf(stderr, "Read function definition:");
+ LF->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleExtern() {
+ if (PrototypeAST *P = ParseExtern()) {
+ if (Function *F = P->Codegen()) {
+ fprintf(stderr, "Read extern: ");
+ F->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (FunctionAST *F = ParseTopLevelExpr()) {
+ if (Function *LF = F->Codegen()) {
+ fprintf(stderr, "Read top-level expression:");
+ LF->dump();
+
+ // JIT the function, returning a function pointer.
+ void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
+
+ // 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;
+ fprintf(stderr, "Evaluated to %f\n", FP());
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof: return;
+ case ';': getNextToken(); break; // ignore top-level semicolons.
+ case tok_def: HandleDefinition(); break;
+ case tok_extern: HandleExtern(); break;
+ default: HandleTopLevelExpression(); break;
+ }
+ }
+ }
+
+ //===----------------------------------------------------------------------===//
+ // "Library" functions that can be "extern'd" from user code.
+ //===----------------------------------------------------------------------===//
+
+ /// putchard - putchar that takes a double and returns 0.
+ extern "C"
+ double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Main driver code.
+ //===----------------------------------------------------------------------===//
+
+ int main() {
+ InitializeNativeTarget();
+ LLVMContext &Context = getGlobalContext();
+
+ // 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();
+
+ // Make the module, which holds all the code.
+ TheModule = new Module("my cool jit", Context);
+
+ // Create the JIT. This takes ownership of the module.
+ std::string ErrStr;
+ TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create();
+ if (!TheExecutionEngine) {
+ fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str());
+ exit(1);
+ }
+
+ FunctionPassManager OurFPM(TheModule);
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
+ // Provide basic AliasAnalysis support for GVN.
+ OurFPM.add(createBasicAliasAnalysisPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+ // Eliminate Common SubExpressions.
+ OurFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ OurFPM.add(createCFGSimplificationPass());
+
+ OurFPM.doInitialization();
+
+ // Set the global so the code gen can use this.
+ TheFPM = &OurFPM;
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+ TheFPM = 0;
+
+ // Print out all of the generated code.
+ TheModule->dump();
+
+ return 0;
+ }
+
+`Next: Extending the language: control flow <LangImpl5.html>`_
+