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Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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4<html>
5<head>
6 <title>Kaleidoscope: Extending the Language: Control Flow</title>
7 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
8 <meta name="author" content="Chris Lattner">
9 <link rel="stylesheet" href="../llvm.css" type="text/css">
10</head>
11
12<body>
13
14<div class="doc_title">Kaleidoscope: Extending the Language: Control Flow</div>
15
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]16<ul>
Chris Lattner0e555b12007-11-05 20:04:56 +0000[diff] [blame]17<li><a href="index.html">Up to Tutorial Index</a></li>
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]18<li>Chapter 5
19 <ol>
20 <li><a href="#intro">Chapter 5 Introduction</a></li>
21 <li><a href="#ifthen">If/Then/Else</a>
22 <ol>
23 <li><a href="#iflexer">Lexer Extensions</a></li>
24 <li><a href="#ifast">AST Extensions</a></li>
25 <li><a href="#ifparser">Parser Extensions</a></li>
26 <li><a href="#ifir">LLVM IR</a></li>
27 <li><a href="#ifcodegen">Code Generation</a></li>
28 </ol>
29 </li>
30 <li><a href="#for">'for' Loop Expression</a>
31 <ol>
32 <li><a href="#forlexer">Lexer Extensions</a></li>
33 <li><a href="#forast">AST Extensions</a></li>
34 <li><a href="#forparser">Parser Extensions</a></li>
35 <li><a href="#forir">LLVM IR</a></li>
36 <li><a href="#forcodegen">Code Generation</a></li>
37 </ol>
38 </li>
39 <li><a href="#code">Full Code Listing</a></li>
40 </ol>
41</li>
Chris Lattner0e555b12007-11-05 20:04:56 +0000[diff] [blame]42<li><a href="LangImpl6.html">Chapter 6</a>: Extending the Language:
43User-defined Operators</li>
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]44</ul>
45
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]46<div class="doc_author">
47 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
48</div>
49
50<!-- *********************************************************************** -->
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]51<div class="doc_section"><a name="intro">Chapter 5 Introduction</a></div>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]52<!-- *********************************************************************** -->
53
54<div class="doc_text">
55
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]56<p>Welcome to Chapter 5 of the "<a href="index.html">Implementing a language
57with LLVM</a>" tutorial. Parts 1-4 described the implementation of the simple
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]58Kaleidoscope language and included support for generating LLVM IR, followed by
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]59optimizations and a JIT compiler. Unfortunately, as presented, Kaleidoscope is
60mostly useless: it has no control flow other than call and return. This means
61that you can't have conditional branches in the code, significantly limiting its
62power. In this episode of "build that compiler", we'll extend Kaleidoscope to
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]63have an if/then/else expression plus a simple 'for' loop.</p>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]64
65</div>
66
67<!-- *********************************************************************** -->
68<div class="doc_section"><a name="ifthen">If/Then/Else</a></div>
69<!-- *********************************************************************** -->
70
71<div class="doc_text">
72
73<p>
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]74Extending Kaleidoscope to support if/then/else is quite straightforward. It
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]75basically requires adding lexer support for this "new" concept to the lexer,
76parser, AST, and LLVM code emitter. This example is nice, because it shows how
77easy it is to "grow" a language over time, incrementally extending it as new
78ideas are discovered.</p>
79
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]80<p>Before we get going on "how" we add this extension, lets talk about "what" we
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]81want. The basic idea is that we want to be able to write this sort of thing:
82</p>
83
84<div class="doc_code">
85<pre>
86def fib(x)
87 if x &lt; 3 then
88 1
89 else
90 fib(x-1)+fib(x-2);
91</pre>
92</div>
93
94<p>In Kaleidoscope, every construct is an expression: there are no statements.
95As such, the if/then/else expression needs to return a value like any other.
96Since we're using a mostly functional form, we'll have it evaluate its
97conditional, then return the 'then' or 'else' value based on how the condition
98was resolved. This is very similar to the C "?:" expression.</p>
99
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]100<p>The semantics of the if/then/else expression is that it evaluates the
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]101condition to a boolean equality value: 0.0 is considered to be false and
102everything else is considered to be true.
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]103If the condition is true, the first subexpression is evaluated and returned, if
104the condition is false, the second subexpression is evaluated and returned.
105Since Kaleidoscope allows side-effects, this behavior is important to nail down.
106</p>
107
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]108<p>Now that we know what we "want", lets break this down into its constituent
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]109pieces.</p>
110
111</div>
112
113<!-- ======================================================================= -->
114<div class="doc_subsubsection"><a name="iflexer">Lexer Extensions for
115If/Then/Else</a></div>
116<!-- ======================================================================= -->
117
118
119<div class="doc_text">
120
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]121<p>The lexer extensions are straightforward. First we add new enum values
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]122for the relevant tokens:</p>
123
124<div class="doc_code">
125<pre>
126 // control
127 tok_if = -6, tok_then = -7, tok_else = -8,
128</pre>
129</div>
130
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]131<p>Once we have that, we recognize the new keywords in the lexer. This is pretty simple
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]132stuff:</p>
133
134<div class="doc_code">
135<pre>
136 ...
137 if (IdentifierStr == "def") return tok_def;
138 if (IdentifierStr == "extern") return tok_extern;
139 <b>if (IdentifierStr == "if") return tok_if;
140 if (IdentifierStr == "then") return tok_then;
141 if (IdentifierStr == "else") return tok_else;</b>
142 return tok_identifier;
143</pre>
144</div>
145
146</div>
147
148<!-- ======================================================================= -->
149<div class="doc_subsubsection"><a name="ifast">AST Extensions for
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]150 If/Then/Else</a></div>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]151<!-- ======================================================================= -->
152
153<div class="doc_text">
154
155<p>To represent the new expression we add a new AST node for it:</p>
156
157<div class="doc_code">
158<pre>
159/// IfExprAST - Expression class for if/then/else.
160class IfExprAST : public ExprAST {
161 ExprAST *Cond, *Then, *Else;
162public:
163 IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
164 : Cond(cond), Then(then), Else(_else) {}
165 virtual Value *Codegen();
166};
167</pre>
168</div>
169
170<p>The AST node just has pointers to the various subexpressions.</p>
171
172</div>
173
174<!-- ======================================================================= -->
175<div class="doc_subsubsection"><a name="ifparser">Parser Extensions for
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]176If/Then/Else</a></div>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]177<!-- ======================================================================= -->
178
179<div class="doc_text">
180
181<p>Now that we have the relevant tokens coming from the lexer and we have the
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]182AST node to build, our parsing logic is relatively straightforward. First we
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]183define a new parsing function:</p>
184
185<div class="doc_code">
186<pre>
187/// ifexpr ::= 'if' expression 'then' expression 'else' expression
188static ExprAST *ParseIfExpr() {
189 getNextToken(); // eat the if.
190
191 // condition.
192 ExprAST *Cond = ParseExpression();
193 if (!Cond) return 0;
194
195 if (CurTok != tok_then)
196 return Error("expected then");
197 getNextToken(); // eat the then
198
199 ExprAST *Then = ParseExpression();
200 if (Then == 0) return 0;
201
202 if (CurTok != tok_else)
203 return Error("expected else");
204
205 getNextToken();
206
207 ExprAST *Else = ParseExpression();
208 if (!Else) return 0;
209
210 return new IfExprAST(Cond, Then, Else);
211}
212</pre>
213</div>
214
215<p>Next we hook it up as a primary expression:</p>
216
217<div class="doc_code">
218<pre>
219static ExprAST *ParsePrimary() {
220 switch (CurTok) {
221 default: return Error("unknown token when expecting an expression");
222 case tok_identifier: return ParseIdentifierExpr();
223 case tok_number: return ParseNumberExpr();
224 case '(': return ParseParenExpr();
225 <b>case tok_if: return ParseIfExpr();</b>
226 }
227}
228</pre>
229</div>
230
231</div>
232
233<!-- ======================================================================= -->
234<div class="doc_subsubsection"><a name="ifir">LLVM IR for If/Then/Else</a></div>
235<!-- ======================================================================= -->
236
237<div class="doc_text">
238
239<p>Now that we have it parsing and building the AST, the final piece is adding
240LLVM code generation support. This is the most interesting part of the
241if/then/else example, because this is where it starts to introduce new concepts.
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]242All of the code above has been thoroughly described in previous chapters.
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]243</p>
244
245<p>To motivate the code we want to produce, lets take a look at a simple
246example. Consider:</p>
247
248<div class="doc_code">
249<pre>
250extern foo();
251extern bar();
252def baz(x) if x then foo() else bar();
253</pre>
254</div>
255
256<p>If you disable optimizations, the code you'll (soon) get from Kaleidoscope
257looks like this:</p>
258
259<div class="doc_code">
260<pre>
261declare double @foo()
262
263declare double @bar()
264
265define double @baz(double %x) {
266entry:
267 %ifcond = fcmp one double %x, 0.000000e+00
268 br i1 %ifcond, label %then, label %else
269
270then: ; preds = %entry
271 %calltmp = call double @foo()
272 br label %ifcont
273
274else: ; preds = %entry
275 %calltmp1 = call double @bar()
276 br label %ifcont
277
278ifcont: ; preds = %else, %then
279 %iftmp = phi double [ %calltmp, %then ], [ %calltmp1, %else ]
280 ret double %iftmp
281}
282</pre>
283</div>
284
285<p>To visualize the control flow graph, you can use a nifty feature of the LLVM
286'<a href="http://llvm.org/cmds/opt.html">opt</a>' tool. If you put this LLVM IR
287into "t.ll" and run "<tt>llvm-as &lt; t.ll | opt -analyze -view-cfg</tt>", <a
288href="../ProgrammersManual.html#ViewGraph">a window will pop up</a> and you'll
289see this graph:</p>
290
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]291<div style="text-align: center"><img src="LangImpl5-cfg.png" alt="Example CFG" width="423"
292height="315"></div>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]293
294<p>Another way to get this is to call "<tt>F-&gt;viewCFG()</tt>" or
295"<tt>F-&gt;viewCFGOnly()</tt>" (where F is a "<tt>Function*</tt>") either by
296inserting actual calls into the code and recompiling or by calling these in the
297debugger. LLVM has many nice features for visualizing various graphs.</p>
298
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]299<p>Getting back to the generated code, it is fairly simple: the entry block
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]300evaluates the conditional expression ("x" in our case here) and compares the
301result to 0.0 with the "<tt><a href="../LangRef.html#i_fcmp">fcmp</a> one</tt>"
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]302instruction ('one' is "Ordered and Not Equal"). Based on the result of this
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]303expression, the code jumps to either the "then" or "else" blocks, which contain
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]304the expressions for the true/false cases.</p>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]305
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]306<p>Once the then/else blocks are finished executing, they both branch back to the
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]307'ifcont' block to execute the code that happens after the if/then/else. In this
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]308case the only thing left to do is to return to the caller of the function. The
309question then becomes: how does the code know which expression to return?</p>
310
311<p>The answer to this question involves an important SSA operation: the
312<a href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Phi
313operation</a>. If you're not familiar with SSA, <a
314href="http://en.wikipedia.org/wiki/Static_single_assignment_form">the wikipedia
315article</a> is a good introduction and there are various other introductions to
316it available on your favorite search engine. The short version is that
317"execution" of the Phi operation requires "remembering" which block control came
318from. The Phi operation takes on the value corresponding to the input control
319block. In this case, if control comes in from the "then" block, it gets the
320value of "calltmp". If control comes from the "else" block, it gets the value
321of "calltmp1".</p>
322
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]323<p>At this point, you are probably starting to think "Oh no! This means my
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]324simple and elegant front-end will have to start generating SSA form in order to
325use LLVM!". Fortunately, this is not the case, and we strongly advise
326<em>not</em> implementing an SSA construction algorithm in your front-end
327unless there is an amazingly good reason to do so. In practice, there are two
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]328sorts of values that float around in code written for your average imperative
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]329programming language that might need Phi nodes:</p>
330
331<ol>
332<li>Code that involves user variables: <tt>x = 1; x = x + 1; </tt></li>
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]333<li>Values that are implicit in the structure of your AST, such as the Phi node
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]334in this case.</li>
335</ol>
336
Chris Lattnerb0f0deb2007-11-05 07:02:49 +0000[diff] [blame]337<p>In <a href="LangImpl7.html">Chapter 7</a> of this tutorial ("mutable
338variables"), we'll talk about #1
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]339in depth. For now, just believe me that you don't need SSA construction to
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]340handle this case. For #2, you have the choice of using the techniques that we will
341describe for #1, or you can insert Phi nodes directly, if convenient. In this
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]342case, it is really really easy to generate the Phi node, so we choose to do it
343directly.</p>
344
345<p>Okay, enough of the motivation and overview, lets generate code!</p>
346
347</div>
348
349<!-- ======================================================================= -->
350<div class="doc_subsubsection"><a name="ifcodegen">Code Generation for
351If/Then/Else</a></div>
352<!-- ======================================================================= -->
353
354<div class="doc_text">
355
356<p>In order to generate code for this, we implement the <tt>Codegen</tt> method
357for <tt>IfExprAST</tt>:</p>
358
359<div class="doc_code">
360<pre>
361Value *IfExprAST::Codegen() {
362 Value *CondV = Cond-&gt;Codegen();
363 if (CondV == 0) return 0;
364
365 // Convert condition to a bool by comparing equal to 0.0.
366 CondV = Builder.CreateFCmpONE(CondV,
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]367 ConstantFP::get(getGlobalContext(), APFloat(0.0)),
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]368 "ifcond");
369</pre>
370</div>
371
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]372<p>This code is straightforward and similar to what we saw before. We emit the
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]373expression for the condition, then compare that value to zero to get a truth
374value as a 1-bit (bool) value.</p>
375
376<div class="doc_code">
377<pre>
378 Function *TheFunction = Builder.GetInsertBlock()-&gt;getParent();
379
380 // Create blocks for the then and else cases. Insert the 'then' block at the
381 // end of the function.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]382 BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
383 BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
384 BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]385
386 Builder.CreateCondBr(CondV, ThenBB, ElseBB);
387</pre>
388</div>
389
390<p>This code creates the basic blocks that are related to the if/then/else
391statement, and correspond directly to the blocks in the example above. The
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]392first line gets the current Function object that is being built. It
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]393gets this by asking the builder for the current BasicBlock, and asking that
394block for its "parent" (the function it is currently embedded into).</p>
395
396<p>Once it has that, it creates three blocks. Note that it passes "TheFunction"
397into the constructor for the "then" block. This causes the constructor to
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]398automatically insert the new block into the end of the specified function. The
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]399other two blocks are created, but aren't yet inserted into the function.</p>
400
401<p>Once the blocks are created, we can emit the conditional branch that chooses
402between them. Note that creating new blocks does not implicitly affect the
Duncan Sands89f6d882008-04-13 06:22:09 +0000[diff] [blame]403IRBuilder, so it is still inserting into the block that the condition
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]404went into. Also note that it is creating a branch to the "then" block and the
405"else" block, even though the "else" block isn't inserted into the function yet.
406This is all ok: it is the standard way that LLVM supports forward
407references.</p>
408
409<div class="doc_code">
410<pre>
411 // Emit then value.
412 Builder.SetInsertPoint(ThenBB);
413
414 Value *ThenV = Then-&gt;Codegen();
415 if (ThenV == 0) return 0;
416
417 Builder.CreateBr(MergeBB);
418 // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
419 ThenBB = Builder.GetInsertBlock();
420</pre>
421</div>
422
423<p>After the conditional branch is inserted, we move the builder to start
424inserting into the "then" block. Strictly speaking, this call moves the
425insertion point to be at the end of the specified block. However, since the
426"then" block is empty, it also starts out by inserting at the beginning of the
427block. :)</p>
428
429<p>Once the insertion point is set, we recursively codegen the "then" expression
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]430from the AST. To finish off the "then" block, we create an unconditional branch
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]431to the merge block. One interesting (and very important) aspect of the LLVM IR
432is that it <a href="../LangRef.html#functionstructure">requires all basic blocks
433to be "terminated"</a> with a <a href="../LangRef.html#terminators">control flow
434instruction</a> such as return or branch. This means that all control flow,
435<em>including fall throughs</em> must be made explicit in the LLVM IR. If you
436violate this rule, the verifier will emit an error.</p>
437
438<p>The final line here is quite subtle, but is very important. The basic issue
439is that when we create the Phi node in the merge block, we need to set up the
440block/value pairs that indicate how the Phi will work. Importantly, the Phi
Chris Lattnerb5019642007-11-05 17:52:04 +0000[diff] [blame]441node expects to have an entry for each predecessor of the block in the CFG. Why
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]442then, are we getting the current block when we just set it to ThenBB 5 lines
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]443above? The problem is that the "Then" expression may actually itself change the
444block that the Builder is emitting into if, for example, it contains a nested
445"if/then/else" expression. Because calling Codegen recursively could
446arbitrarily change the notion of the current block, we are required to get an
447up-to-date value for code that will set up the Phi node.</p>
448
449<div class="doc_code">
450<pre>
451 // Emit else block.
452 TheFunction-&gt;getBasicBlockList().push_back(ElseBB);
453 Builder.SetInsertPoint(ElseBB);
454
455 Value *ElseV = Else-&gt;Codegen();
456 if (ElseV == 0) return 0;
457
458 Builder.CreateBr(MergeBB);
459 // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
460 ElseBB = Builder.GetInsertBlock();
461</pre>
462</div>
463
464<p>Code generation for the 'else' block is basically identical to codegen for
465the 'then' block. The only significant difference is the first line, which adds
466the 'else' block to the function. Recall previously that the 'else' block was
467created, but not added to the function. Now that the 'then' and 'else' blocks
468are emitted, we can finish up with the merge code:</p>
469
470<div class="doc_code">
471<pre>
472 // Emit merge block.
473 TheFunction->getBasicBlockList().push_back(MergeBB);
474 Builder.SetInsertPoint(MergeBB);
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]475 PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()),
476 "iftmp");
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]477
478 PN->addIncoming(ThenV, ThenBB);
479 PN->addIncoming(ElseV, ElseBB);
480 return PN;
481}
482</pre>
483</div>
484
485<p>The first two lines here are now familiar: the first adds the "merge" block
486to the Function object (it was previously floating, like the else block above).
487The second block changes the insertion point so that newly created code will go
488into the "merge" block. Once that is done, we need to create the PHI node and
489set up the block/value pairs for the PHI.</p>
490
491<p>Finally, the CodeGen function returns the phi node as the value computed by
492the if/then/else expression. In our example above, this returned value will
493feed into the code for the top-level function, which will create the return
494instruction.</p>
495
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]496<p>Overall, we now have the ability to execute conditional code in
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]497Kaleidoscope. With this extension, Kaleidoscope is a fairly complete language
498that can calculate a wide variety of numeric functions. Next up we'll add
499another useful expression that is familiar from non-functional languages...</p>
500
501</div>
502
503<!-- *********************************************************************** -->
504<div class="doc_section"><a name="for">'for' Loop Expression</a></div>
505<!-- *********************************************************************** -->
506
507<div class="doc_text">
508
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]509<p>Now that we know how to add basic control flow constructs to the language,
510we have the tools to add more powerful things. Lets add something more
511aggressive, a 'for' expression:</p>
512
513<div class="doc_code">
514<pre>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]515 extern putchard(char)
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]516 def printstar(n)
517 for i = 1, i &lt; n, 1.0 in
518 putchard(42); # ascii 42 = '*'
519
520 # print 100 '*' characters
521 printstar(100);
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]522</pre>
523</div>
524
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]525<p>This expression defines a new variable ("i" in this case) which iterates from
526a starting value, while the condition ("i &lt; n" in this case) is true,
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]527incrementing by an optional step value ("1.0" in this case). If the step value
528is omitted, it defaults to 1.0. While the loop is true, it executes its
529body expression. Because we don't have anything better to return, we'll just
530define the loop as always returning 0.0. In the future when we have mutable
531variables, it will get more useful.</p>
532
533<p>As before, lets talk about the changes that we need to Kaleidoscope to
534support this.</p>
535
536</div>
537
538<!-- ======================================================================= -->
539<div class="doc_subsubsection"><a name="forlexer">Lexer Extensions for
540the 'for' Loop</a></div>
541<!-- ======================================================================= -->
542
543<div class="doc_text">
544
545<p>The lexer extensions are the same sort of thing as for if/then/else:</p>
546
547<div class="doc_code">
548<pre>
549 ... in enum Token ...
550 // control
551 tok_if = -6, tok_then = -7, tok_else = -8,
552<b> tok_for = -9, tok_in = -10</b>
553
554 ... in gettok ...
555 if (IdentifierStr == "def") return tok_def;
556 if (IdentifierStr == "extern") return tok_extern;
557 if (IdentifierStr == "if") return tok_if;
558 if (IdentifierStr == "then") return tok_then;
559 if (IdentifierStr == "else") return tok_else;
560 <b>if (IdentifierStr == "for") return tok_for;
561 if (IdentifierStr == "in") return tok_in;</b>
562 return tok_identifier;
563</pre>
564</div>
565
566</div>
567
568<!-- ======================================================================= -->
569<div class="doc_subsubsection"><a name="forast">AST Extensions for
570the 'for' Loop</a></div>
571<!-- ======================================================================= -->
572
573<div class="doc_text">
574
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]575<p>The AST node is just as simple. It basically boils down to capturing
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]576the variable name and the constituent expressions in the node.</p>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]577
578<div class="doc_code">
579<pre>
580/// ForExprAST - Expression class for for/in.
581class ForExprAST : public ExprAST {
582 std::string VarName;
583 ExprAST *Start, *End, *Step, *Body;
584public:
585 ForExprAST(const std::string &amp;varname, ExprAST *start, ExprAST *end,
586 ExprAST *step, ExprAST *body)
587 : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
588 virtual Value *Codegen();
589};
590</pre>
591</div>
592
593</div>
594
595<!-- ======================================================================= -->
596<div class="doc_subsubsection"><a name="forparser">Parser Extensions for
597the 'for' Loop</a></div>
598<!-- ======================================================================= -->
599
600<div class="doc_text">
601
602<p>The parser code is also fairly standard. The only interesting thing here is
603handling of the optional step value. The parser code handles it by checking to
604see if the second comma is present. If not, it sets the step value to null in
605the AST node:</p>
606
607<div class="doc_code">
608<pre>
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]609/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]610static ExprAST *ParseForExpr() {
611 getNextToken(); // eat the for.
612
613 if (CurTok != tok_identifier)
614 return Error("expected identifier after for");
615
616 std::string IdName = IdentifierStr;
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]617 getNextToken(); // eat identifier.
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]618
619 if (CurTok != '=')
620 return Error("expected '=' after for");
621 getNextToken(); // eat '='.
622
623
624 ExprAST *Start = ParseExpression();
625 if (Start == 0) return 0;
626 if (CurTok != ',')
627 return Error("expected ',' after for start value");
628 getNextToken();
629
630 ExprAST *End = ParseExpression();
631 if (End == 0) return 0;
632
633 // The step value is optional.
634 ExprAST *Step = 0;
635 if (CurTok == ',') {
636 getNextToken();
637 Step = ParseExpression();
638 if (Step == 0) return 0;
639 }
640
641 if (CurTok != tok_in)
642 return Error("expected 'in' after for");
643 getNextToken(); // eat 'in'.
644
645 ExprAST *Body = ParseExpression();
646 if (Body == 0) return 0;
647
648 return new ForExprAST(IdName, Start, End, Step, Body);
649}
650</pre>
651</div>
652
653</div>
654
655<!-- ======================================================================= -->
656<div class="doc_subsubsection"><a name="forir">LLVM IR for
657the 'for' Loop</a></div>
658<!-- ======================================================================= -->
659
660<div class="doc_text">
661
662<p>Now we get to the good part: the LLVM IR we want to generate for this thing.
Gordon Henriksenbb310f12007-11-12 13:46:21 +0000[diff] [blame]663With the simple example above, we get this LLVM IR (note that this dump is
664generated with optimizations disabled for clarity):
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]665</p>
666
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]667<div class="doc_code">
668<pre>
669declare double @putchard(double)
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]670
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]671define double @printstar(double %n) {
672entry:
673 ; initial value = 1.0 (inlined into phi)
674 br label %loop
675
676loop: ; preds = %loop, %entry
677 %i = phi double [ 1.000000e+00, %entry ], [ %nextvar, %loop ]
678 ; body
679 %calltmp = call double @putchard( double 4.200000e+01 )
680 ; increment
Dan Gohmana9445e12010-03-02 01:11:08 +0000[diff] [blame]681 %nextvar = fadd double %i, 1.000000e+00
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]682
683 ; termination test
Chris Lattner71155212007-11-06 01:39:12 +0000[diff] [blame]684 %cmptmp = fcmp ult double %i, %n
685 %booltmp = uitofp i1 %cmptmp to double
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]686 %loopcond = fcmp one double %booltmp, 0.000000e+00
687 br i1 %loopcond, label %loop, label %afterloop
688
689afterloop: ; preds = %loop
690 ; loop always returns 0.0
691 ret double 0.000000e+00
692}
693</pre>
694</div>
695
696<p>This loop contains all the same constructs we saw before: a phi node, several
697expressions, and some basic blocks. Lets see how this fits together.</p>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]698
699</div>
700
701<!-- ======================================================================= -->
702<div class="doc_subsubsection"><a name="forcodegen">Code Generation for
703the 'for' Loop</a></div>
704<!-- ======================================================================= -->
705
706<div class="doc_text">
707
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]708<p>The first part of Codegen is very simple: we just output the start expression
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]709for the loop value:</p>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]710
711<div class="doc_code">
712<pre>
713Value *ForExprAST::Codegen() {
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]714 // Emit the start code first, without 'variable' in scope.
715 Value *StartVal = Start-&gt;Codegen();
716 if (StartVal == 0) return 0;
717</pre>
718</div>
719
720<p>With this out of the way, the next step is to set up the LLVM basic block
721for the start of the loop body. In the case above, the whole loop body is one
722block, but remember that the body code itself could consist of multiple blocks
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]723(e.g. if it contains an if/then/else or a for/in expression).</p>
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]724
725<div class="doc_code">
726<pre>
727 // Make the new basic block for the loop header, inserting after current
728 // block.
729 Function *TheFunction = Builder.GetInsertBlock()-&gt;getParent();
730 BasicBlock *PreheaderBB = Builder.GetInsertBlock();
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]731 BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]732
733 // Insert an explicit fall through from the current block to the LoopBB.
734 Builder.CreateBr(LoopBB);
735</pre>
736</div>
737
738<p>This code is similar to what we saw for if/then/else. Because we will need
739it to create the Phi node, we remember the block that falls through into the
740loop. Once we have that, we create the actual block that starts the loop and
741create an unconditional branch for the fall-through between the two blocks.</p>
742
743<div class="doc_code">
744<pre>
745 // Start insertion in LoopBB.
746 Builder.SetInsertPoint(LoopBB);
747
748 // Start the PHI node with an entry for Start.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]749 PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), VarName.c_str());
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]750 Variable-&gt;addIncoming(StartVal, PreheaderBB);
751</pre>
752</div>
753
754<p>Now that the "preheader" for the loop is set up, we switch to emitting code
755for the loop body. To begin with, we move the insertion point and create the
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]756PHI node for the loop induction variable. Since we already know the incoming
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]757value for the starting value, we add it to the Phi node. Note that the Phi will
758eventually get a second value for the backedge, but we can't set it up yet
759(because it doesn't exist!).</p>
760
761<div class="doc_code">
762<pre>
763 // Within the loop, the variable is defined equal to the PHI node. If it
764 // shadows an existing variable, we have to restore it, so save it now.
765 Value *OldVal = NamedValues[VarName];
766 NamedValues[VarName] = Variable;
767
768 // Emit the body of the loop. This, like any other expr, can change the
769 // current BB. Note that we ignore the value computed by the body, but don't
770 // allow an error.
771 if (Body-&gt;Codegen() == 0)
772 return 0;
773</pre>
774</div>
775
776<p>Now the code starts to get more interesting. Our 'for' loop introduces a new
777variable to the symbol table. This means that our symbol table can now contain
778either function arguments or loop variables. To handle this, before we codegen
779the body of the loop, we add the loop variable as the current value for its
780name. Note that it is possible that there is a variable of the same name in the
781outer scope. It would be easy to make this an error (emit an error and return
782null if there is already an entry for VarName) but we choose to allow shadowing
783of variables. In order to handle this correctly, we remember the Value that
784we are potentially shadowing in <tt>OldVal</tt> (which will be null if there is
785no shadowed variable).</p>
786
787<p>Once the loop variable is set into the symbol table, the code recursively
788codegen's the body. This allows the body to use the loop variable: any
789references to it will naturally find it in the symbol table.</p>
790
791<div class="doc_code">
792<pre>
793 // Emit the step value.
794 Value *StepVal;
795 if (Step) {
796 StepVal = Step-&gt;Codegen();
797 if (StepVal == 0) return 0;
798 } else {
799 // If not specified, use 1.0.
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]800 StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]801 }
802
803 Value *NextVar = Builder.CreateAdd(Variable, StepVal, "nextvar");
804</pre>
805</div>
806
807<p>Now that the body is emitted, we compute the next value of the iteration
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]808variable by adding the step value, or 1.0 if it isn't present. '<tt>NextVar</tt>'
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]809will be the value of the loop variable on the next iteration of the loop.</p>
810
811<div class="doc_code">
812<pre>
813 // Compute the end condition.
814 Value *EndCond = End-&gt;Codegen();
815 if (EndCond == 0) return EndCond;
816
817 // Convert condition to a bool by comparing equal to 0.0.
818 EndCond = Builder.CreateFCmpONE(EndCond,
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]819 ConstantFP::get(getGlobalContext(), APFloat(0.0)),
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]820 "loopcond");
821</pre>
822</div>
823
824<p>Finally, we evaluate the exit value of the loop, to determine whether the
825loop should exit. This mirrors the condition evaluation for the if/then/else
826statement.</p>
827
828<div class="doc_code">
829<pre>
830 // Create the "after loop" block and insert it.
831 BasicBlock *LoopEndBB = Builder.GetInsertBlock();
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]832 BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]833
834 // Insert the conditional branch into the end of LoopEndBB.
835 Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
836
837 // Any new code will be inserted in AfterBB.
838 Builder.SetInsertPoint(AfterBB);
839</pre>
840</div>
841
842<p>With the code for the body of the loop complete, we just need to finish up
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]843the 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
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]844exit condition, it creates a conditional branch that chooses between executing
845the loop again and exiting the loop. Any future code is emitted in the
846"afterloop" block, so it sets the insertion position to it.</p>
847
848<div class="doc_code">
849<pre>
850 // Add a new entry to the PHI node for the backedge.
851 Variable-&gt;addIncoming(NextVar, LoopEndBB);
852
853 // Restore the unshadowed variable.
854 if (OldVal)
855 NamedValues[VarName] = OldVal;
856 else
857 NamedValues.erase(VarName);
858
859 // for expr always returns 0.0.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]860 return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]861}
862</pre>
863</div>
864
865<p>The final code handles various cleanups: now that we have the "NextVar"
866value, we can add the incoming value to the loop PHI node. After that, we
867remove the loop variable from the symbol table, so that it isn't in scope after
868the for loop. Finally, code generation of the for loop always returns 0.0, so
869that is what we return from <tt>ForExprAST::Codegen</tt>.</p>
870
871<p>With this, we conclude the "adding control flow to Kaleidoscope" chapter of
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]872the 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
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]873to know. In the next chapter of our saga, we will get a bit crazier and add
Chris Lattner71155212007-11-06 01:39:12 +0000[diff] [blame]874<a href="LangImpl6.html">user-defined operators</a> to our poor innocent
875language.</p>
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]876
877</div>
878
879<!-- *********************************************************************** -->
880<div class="doc_section"><a name="code">Full Code Listing</a></div>
881<!-- *********************************************************************** -->
882
883<div class="doc_text">
884
885<p>
886Here is the complete code listing for our running example, enhanced with the
887if/then/else and for expressions.. To build this example, use:
888</p>
889
890<div class="doc_code">
891<pre>
892 # Compile
893 g++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
894 # Run
895 ./toy
896</pre>
897</div>
898
899<p>Here is the code:</p>
900
901<div class="doc_code">
902<pre>
903#include "llvm/DerivedTypes.h"
904#include "llvm/ExecutionEngine/ExecutionEngine.h"
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame]905#include "llvm/ExecutionEngine/JIT.h"
Owen Andersond1fbd142009-07-08 20:50:47 +0000[diff] [blame]906#include "llvm/LLVMContext.h"
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]907#include "llvm/Module.h"
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]908#include "llvm/PassManager.h"
909#include "llvm/Analysis/Verifier.h"
910#include "llvm/Target/TargetData.h"
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame]911#include "llvm/Target/TargetSelect.h"
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]912#include "llvm/Transforms/Scalar.h"
Duncan Sands89f6d882008-04-13 06:22:09 +0000[diff] [blame]913#include "llvm/Support/IRBuilder.h"
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]914#include &lt;cstdio&gt;
915#include &lt;string&gt;
916#include &lt;map&gt;
917#include &lt;vector&gt;
918using namespace llvm;
919
920//===----------------------------------------------------------------------===//
921// Lexer
922//===----------------------------------------------------------------------===//
923
924// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
925// of these for known things.
926enum Token {
927 tok_eof = -1,
928
929 // commands
930 tok_def = -2, tok_extern = -3,
931
932 // primary
933 tok_identifier = -4, tok_number = -5,
934
935 // control
936 tok_if = -6, tok_then = -7, tok_else = -8,
937 tok_for = -9, tok_in = -10
938};
939
940static std::string IdentifierStr; // Filled in if tok_identifier
941static double NumVal; // Filled in if tok_number
942
943/// gettok - Return the next token from standard input.
944static int gettok() {
945 static int LastChar = ' ';
946
947 // Skip any whitespace.
948 while (isspace(LastChar))
949 LastChar = getchar();
950
951 if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
952 IdentifierStr = LastChar;
953 while (isalnum((LastChar = getchar())))
954 IdentifierStr += LastChar;
955
956 if (IdentifierStr == "def") return tok_def;
957 if (IdentifierStr == "extern") return tok_extern;
958 if (IdentifierStr == "if") return tok_if;
959 if (IdentifierStr == "then") return tok_then;
960 if (IdentifierStr == "else") return tok_else;
961 if (IdentifierStr == "for") return tok_for;
962 if (IdentifierStr == "in") return tok_in;
963 return tok_identifier;
964 }
965
966 if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
967 std::string NumStr;
968 do {
969 NumStr += LastChar;
970 LastChar = getchar();
971 } while (isdigit(LastChar) || LastChar == '.');
972
973 NumVal = strtod(NumStr.c_str(), 0);
974 return tok_number;
975 }
976
977 if (LastChar == '#') {
978 // Comment until end of line.
979 do LastChar = getchar();
Chris Lattnerc80c23f2007-12-02 22:46:01 +0000[diff] [blame]980 while (LastChar != EOF &amp;&amp; LastChar != '\n' &amp;&amp; LastChar != '\r');
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]981
982 if (LastChar != EOF)
983 return gettok();
984 }
985
986 // Check for end of file. Don't eat the EOF.
987 if (LastChar == EOF)
988 return tok_eof;
989
990 // Otherwise, just return the character as its ascii value.
991 int ThisChar = LastChar;
992 LastChar = getchar();
993 return ThisChar;
994}
995
996//===----------------------------------------------------------------------===//
997// Abstract Syntax Tree (aka Parse Tree)
998//===----------------------------------------------------------------------===//
999
1000/// ExprAST - Base class for all expression nodes.
1001class ExprAST {
1002public:
1003 virtual ~ExprAST() {}
1004 virtual Value *Codegen() = 0;
1005};
1006
1007/// NumberExprAST - Expression class for numeric literals like "1.0".
1008class NumberExprAST : public ExprAST {
1009 double Val;
1010public:
1011 NumberExprAST(double val) : Val(val) {}
1012 virtual Value *Codegen();
1013};
1014
1015/// VariableExprAST - Expression class for referencing a variable, like "a".
1016class VariableExprAST : public ExprAST {
1017 std::string Name;
1018public:
1019 VariableExprAST(const std::string &amp;name) : Name(name) {}
1020 virtual Value *Codegen();
1021};
1022
1023/// BinaryExprAST - Expression class for a binary operator.
1024class BinaryExprAST : public ExprAST {
1025 char Op;
1026 ExprAST *LHS, *RHS;
1027public:
1028 BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
1029 : Op(op), LHS(lhs), RHS(rhs) {}
1030 virtual Value *Codegen();
1031};
1032
1033/// CallExprAST - Expression class for function calls.
1034class CallExprAST : public ExprAST {
1035 std::string Callee;
1036 std::vector&lt;ExprAST*&gt; Args;
1037public:
1038 CallExprAST(const std::string &amp;callee, std::vector&lt;ExprAST*&gt; &amp;args)
1039 : Callee(callee), Args(args) {}
1040 virtual Value *Codegen();
1041};
1042
1043/// IfExprAST - Expression class for if/then/else.
1044class IfExprAST : public ExprAST {
1045 ExprAST *Cond, *Then, *Else;
1046public:
1047 IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
1048 : Cond(cond), Then(then), Else(_else) {}
1049 virtual Value *Codegen();
1050};
1051
1052/// ForExprAST - Expression class for for/in.
1053class ForExprAST : public ExprAST {
1054 std::string VarName;
1055 ExprAST *Start, *End, *Step, *Body;
1056public:
1057 ForExprAST(const std::string &amp;varname, ExprAST *start, ExprAST *end,
1058 ExprAST *step, ExprAST *body)
1059 : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
1060 virtual Value *Codegen();
1061};
1062
1063/// PrototypeAST - This class represents the "prototype" for a function,
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1064/// which captures its name, and its argument names (thus implicitly the number
1065/// of arguments the function takes).
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1066class PrototypeAST {
1067 std::string Name;
1068 std::vector&lt;std::string&gt; Args;
1069public:
1070 PrototypeAST(const std::string &amp;name, const std::vector&lt;std::string&gt; &amp;args)
1071 : Name(name), Args(args) {}
1072
1073 Function *Codegen();
1074};
1075
1076/// FunctionAST - This class represents a function definition itself.
1077class FunctionAST {
1078 PrototypeAST *Proto;
1079 ExprAST *Body;
1080public:
1081 FunctionAST(PrototypeAST *proto, ExprAST *body)
1082 : Proto(proto), Body(body) {}
1083
1084 Function *Codegen();
1085};
1086
1087//===----------------------------------------------------------------------===//
1088// Parser
1089//===----------------------------------------------------------------------===//
1090
1091/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1092/// token the parser is looking at. getNextToken reads another token from the
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1093/// lexer and updates CurTok with its results.
1094static int CurTok;
1095static int getNextToken() {
1096 return CurTok = gettok();
1097}
1098
1099/// BinopPrecedence - This holds the precedence for each binary operator that is
1100/// defined.
1101static std::map&lt;char, int&gt; BinopPrecedence;
1102
1103/// GetTokPrecedence - Get the precedence of the pending binary operator token.
1104static int GetTokPrecedence() {
1105 if (!isascii(CurTok))
1106 return -1;
1107
1108 // Make sure it's a declared binop.
1109 int TokPrec = BinopPrecedence[CurTok];
1110 if (TokPrec &lt;= 0) return -1;
1111 return TokPrec;
1112}
1113
1114/// Error* - These are little helper functions for error handling.
1115ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
1116PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
1117FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
1118
1119static ExprAST *ParseExpression();
1120
1121/// identifierexpr
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1122/// ::= identifier
1123/// ::= identifier '(' expression* ')'
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1124static ExprAST *ParseIdentifierExpr() {
1125 std::string IdName = IdentifierStr;
1126
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1127 getNextToken(); // eat identifier.
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1128
1129 if (CurTok != '(') // Simple variable ref.
1130 return new VariableExprAST(IdName);
1131
1132 // Call.
1133 getNextToken(); // eat (
1134 std::vector&lt;ExprAST*&gt; Args;
1135 if (CurTok != ')') {
1136 while (1) {
1137 ExprAST *Arg = ParseExpression();
1138 if (!Arg) return 0;
1139 Args.push_back(Arg);
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1140
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1141 if (CurTok == ')') break;
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1142
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1143 if (CurTok != ',')
Chris Lattner6c4be9c2008-04-14 16:44:41 +0000[diff] [blame]1144 return Error("Expected ')' or ',' in argument list");
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1145 getNextToken();
1146 }
1147 }
1148
1149 // Eat the ')'.
1150 getNextToken();
1151
1152 return new CallExprAST(IdName, Args);
1153}
1154
1155/// numberexpr ::= number
1156static ExprAST *ParseNumberExpr() {
1157 ExprAST *Result = new NumberExprAST(NumVal);
1158 getNextToken(); // consume the number
1159 return Result;
1160}
1161
1162/// parenexpr ::= '(' expression ')'
1163static ExprAST *ParseParenExpr() {
1164 getNextToken(); // eat (.
1165 ExprAST *V = ParseExpression();
1166 if (!V) return 0;
1167
1168 if (CurTok != ')')
1169 return Error("expected ')'");
1170 getNextToken(); // eat ).
1171 return V;
1172}
1173
1174/// ifexpr ::= 'if' expression 'then' expression 'else' expression
1175static ExprAST *ParseIfExpr() {
1176 getNextToken(); // eat the if.
1177
1178 // condition.
1179 ExprAST *Cond = ParseExpression();
1180 if (!Cond) return 0;
1181
1182 if (CurTok != tok_then)
1183 return Error("expected then");
1184 getNextToken(); // eat the then
1185
1186 ExprAST *Then = ParseExpression();
1187 if (Then == 0) return 0;
1188
1189 if (CurTok != tok_else)
1190 return Error("expected else");
1191
1192 getNextToken();
1193
1194 ExprAST *Else = ParseExpression();
1195 if (!Else) return 0;
1196
1197 return new IfExprAST(Cond, Then, Else);
1198}
1199
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1200/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1201static ExprAST *ParseForExpr() {
1202 getNextToken(); // eat the for.
1203
1204 if (CurTok != tok_identifier)
1205 return Error("expected identifier after for");
1206
1207 std::string IdName = IdentifierStr;
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1208 getNextToken(); // eat identifier.
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1209
1210 if (CurTok != '=')
1211 return Error("expected '=' after for");
1212 getNextToken(); // eat '='.
1213
1214
1215 ExprAST *Start = ParseExpression();
1216 if (Start == 0) return 0;
1217 if (CurTok != ',')
1218 return Error("expected ',' after for start value");
1219 getNextToken();
1220
1221 ExprAST *End = ParseExpression();
1222 if (End == 0) return 0;
1223
1224 // The step value is optional.
1225 ExprAST *Step = 0;
1226 if (CurTok == ',') {
1227 getNextToken();
1228 Step = ParseExpression();
1229 if (Step == 0) return 0;
1230 }
1231
1232 if (CurTok != tok_in)
1233 return Error("expected 'in' after for");
1234 getNextToken(); // eat 'in'.
1235
1236 ExprAST *Body = ParseExpression();
1237 if (Body == 0) return 0;
1238
1239 return new ForExprAST(IdName, Start, End, Step, Body);
1240}
1241
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1242/// primary
1243/// ::= identifierexpr
1244/// ::= numberexpr
1245/// ::= parenexpr
1246/// ::= ifexpr
1247/// ::= forexpr
1248static ExprAST *ParsePrimary() {
1249 switch (CurTok) {
1250 default: return Error("unknown token when expecting an expression");
1251 case tok_identifier: return ParseIdentifierExpr();
1252 case tok_number: return ParseNumberExpr();
1253 case '(': return ParseParenExpr();
1254 case tok_if: return ParseIfExpr();
1255 case tok_for: return ParseForExpr();
1256 }
1257}
1258
1259/// binoprhs
1260/// ::= ('+' primary)*
1261static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
1262 // If this is a binop, find its precedence.
1263 while (1) {
1264 int TokPrec = GetTokPrecedence();
1265
1266 // If this is a binop that binds at least as tightly as the current binop,
1267 // consume it, otherwise we are done.
1268 if (TokPrec &lt; ExprPrec)
1269 return LHS;
1270
1271 // Okay, we know this is a binop.
1272 int BinOp = CurTok;
1273 getNextToken(); // eat binop
1274
1275 // Parse the primary expression after the binary operator.
1276 ExprAST *RHS = ParsePrimary();
1277 if (!RHS) return 0;
1278
1279 // If BinOp binds less tightly with RHS than the operator after RHS, let
1280 // the pending operator take RHS as its LHS.
1281 int NextPrec = GetTokPrecedence();
1282 if (TokPrec &lt; NextPrec) {
1283 RHS = ParseBinOpRHS(TokPrec+1, RHS);
1284 if (RHS == 0) return 0;
1285 }
1286
1287 // Merge LHS/RHS.
1288 LHS = new BinaryExprAST(BinOp, LHS, RHS);
1289 }
1290}
1291
1292/// expression
1293/// ::= primary binoprhs
1294///
1295static ExprAST *ParseExpression() {
1296 ExprAST *LHS = ParsePrimary();
1297 if (!LHS) return 0;
1298
1299 return ParseBinOpRHS(0, LHS);
1300}
1301
1302/// prototype
1303/// ::= id '(' id* ')'
1304static PrototypeAST *ParsePrototype() {
1305 if (CurTok != tok_identifier)
1306 return ErrorP("Expected function name in prototype");
1307
1308 std::string FnName = IdentifierStr;
1309 getNextToken();
1310
1311 if (CurTok != '(')
1312 return ErrorP("Expected '(' in prototype");
1313
1314 std::vector&lt;std::string&gt; ArgNames;
1315 while (getNextToken() == tok_identifier)
1316 ArgNames.push_back(IdentifierStr);
1317 if (CurTok != ')')
1318 return ErrorP("Expected ')' in prototype");
1319
1320 // success.
1321 getNextToken(); // eat ')'.
1322
1323 return new PrototypeAST(FnName, ArgNames);
1324}
1325
1326/// definition ::= 'def' prototype expression
1327static FunctionAST *ParseDefinition() {
1328 getNextToken(); // eat def.
1329 PrototypeAST *Proto = ParsePrototype();
1330 if (Proto == 0) return 0;
1331
1332 if (ExprAST *E = ParseExpression())
1333 return new FunctionAST(Proto, E);
1334 return 0;
1335}
1336
1337/// toplevelexpr ::= expression
1338static FunctionAST *ParseTopLevelExpr() {
1339 if (ExprAST *E = ParseExpression()) {
1340 // Make an anonymous proto.
1341 PrototypeAST *Proto = new PrototypeAST("", std::vector&lt;std::string&gt;());
1342 return new FunctionAST(Proto, E);
1343 }
1344 return 0;
1345}
1346
1347/// external ::= 'extern' prototype
1348static PrototypeAST *ParseExtern() {
1349 getNextToken(); // eat extern.
1350 return ParsePrototype();
1351}
1352
1353//===----------------------------------------------------------------------===//
1354// Code Generation
1355//===----------------------------------------------------------------------===//
1356
1357static Module *TheModule;
Owen Andersond1fbd142009-07-08 20:50:47 +0000[diff] [blame]1358static IRBuilder&lt;&gt; Builder(getGlobalContext());
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1359static std::map&lt;std::string, Value*&gt; NamedValues;
1360static FunctionPassManager *TheFPM;
1361
1362Value *ErrorV(const char *Str) { Error(Str); return 0; }
1363
1364Value *NumberExprAST::Codegen() {
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]1365 return ConstantFP::get(getGlobalContext(), APFloat(Val));
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1366}
1367
1368Value *VariableExprAST::Codegen() {
1369 // Look this variable up in the function.
1370 Value *V = NamedValues[Name];
1371 return V ? V : ErrorV("Unknown variable name");
1372}
1373
1374Value *BinaryExprAST::Codegen() {
1375 Value *L = LHS-&gt;Codegen();
1376 Value *R = RHS-&gt;Codegen();
1377 if (L == 0 || R == 0) return 0;
1378
1379 switch (Op) {
1380 case '+': return Builder.CreateAdd(L, R, "addtmp");
1381 case '-': return Builder.CreateSub(L, R, "subtmp");
1382 case '*': return Builder.CreateMul(L, R, "multmp");
1383 case '&lt;':
Chris Lattner71155212007-11-06 01:39:12 +0000[diff] [blame]1384 L = Builder.CreateFCmpULT(L, R, "cmptmp");
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1385 // Convert bool 0/1 to double 0.0 or 1.0
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame]1386 return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
1387 "booltmp");
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1388 default: return ErrorV("invalid binary operator");
1389 }
1390}
1391
1392Value *CallExprAST::Codegen() {
1393 // Look up the name in the global module table.
1394 Function *CalleeF = TheModule-&gt;getFunction(Callee);
1395 if (CalleeF == 0)
1396 return ErrorV("Unknown function referenced");
1397
1398 // If argument mismatch error.
1399 if (CalleeF-&gt;arg_size() != Args.size())
1400 return ErrorV("Incorrect # arguments passed");
1401
1402 std::vector&lt;Value*&gt; ArgsV;
1403 for (unsigned i = 0, e = Args.size(); i != e; ++i) {
1404 ArgsV.push_back(Args[i]-&gt;Codegen());
1405 if (ArgsV.back() == 0) return 0;
1406 }
1407
1408 return Builder.CreateCall(CalleeF, ArgsV.begin(), ArgsV.end(), "calltmp");
1409}
1410
1411Value *IfExprAST::Codegen() {
1412 Value *CondV = Cond-&gt;Codegen();
1413 if (CondV == 0) return 0;
1414
1415 // Convert condition to a bool by comparing equal to 0.0.
1416 CondV = Builder.CreateFCmpONE(CondV,
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]1417 ConstantFP::get(getGlobalContext(), APFloat(0.0)),
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1418 "ifcond");
1419
1420 Function *TheFunction = Builder.GetInsertBlock()-&gt;getParent();
1421
1422 // Create blocks for the then and else cases. Insert the 'then' block at the
1423 // end of the function.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]1424 BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
1425 BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
1426 BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1427
1428 Builder.CreateCondBr(CondV, ThenBB, ElseBB);
1429
1430 // Emit then value.
1431 Builder.SetInsertPoint(ThenBB);
1432
1433 Value *ThenV = Then-&gt;Codegen();
1434 if (ThenV == 0) return 0;
1435
1436 Builder.CreateBr(MergeBB);
1437 // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
1438 ThenBB = Builder.GetInsertBlock();
1439
1440 // Emit else block.
1441 TheFunction-&gt;getBasicBlockList().push_back(ElseBB);
1442 Builder.SetInsertPoint(ElseBB);
1443
1444 Value *ElseV = Else-&gt;Codegen();
1445 if (ElseV == 0) return 0;
1446
1447 Builder.CreateBr(MergeBB);
1448 // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
1449 ElseBB = Builder.GetInsertBlock();
1450
1451 // Emit merge block.
1452 TheFunction-&gt;getBasicBlockList().push_back(MergeBB);
1453 Builder.SetInsertPoint(MergeBB);
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame]1454 PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()),
1455 "iftmp");
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1456
1457 PN-&gt;addIncoming(ThenV, ThenBB);
1458 PN-&gt;addIncoming(ElseV, ElseBB);
1459 return PN;
1460}
1461
1462Value *ForExprAST::Codegen() {
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1463 // Output this as:
1464 // ...
1465 // start = startexpr
1466 // goto loop
1467 // loop:
1468 // variable = phi [start, loopheader], [nextvariable, loopend]
1469 // ...
1470 // bodyexpr
1471 // ...
1472 // loopend:
1473 // step = stepexpr
1474 // nextvariable = variable + step
1475 // endcond = endexpr
1476 // br endcond, loop, endloop
1477 // outloop:
1478
1479 // Emit the start code first, without 'variable' in scope.
1480 Value *StartVal = Start-&gt;Codegen();
1481 if (StartVal == 0) return 0;
1482
1483 // Make the new basic block for the loop header, inserting after current
1484 // block.
1485 Function *TheFunction = Builder.GetInsertBlock()-&gt;getParent();
1486 BasicBlock *PreheaderBB = Builder.GetInsertBlock();
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]1487 BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1488
1489 // Insert an explicit fall through from the current block to the LoopBB.
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1490 Builder.CreateBr(LoopBB);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1491
1492 // Start insertion in LoopBB.
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1493 Builder.SetInsertPoint(LoopBB);
1494
1495 // Start the PHI node with an entry for Start.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]1496 PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), VarName.c_str());
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1497 Variable-&gt;addIncoming(StartVal, PreheaderBB);
1498
1499 // Within the loop, the variable is defined equal to the PHI node. If it
1500 // shadows an existing variable, we have to restore it, so save it now.
1501 Value *OldVal = NamedValues[VarName];
1502 NamedValues[VarName] = Variable;
1503
1504 // Emit the body of the loop. This, like any other expr, can change the
1505 // current BB. Note that we ignore the value computed by the body, but don't
1506 // allow an error.
1507 if (Body-&gt;Codegen() == 0)
1508 return 0;
1509
1510 // Emit the step value.
1511 Value *StepVal;
1512 if (Step) {
1513 StepVal = Step-&gt;Codegen();
1514 if (StepVal == 0) return 0;
1515 } else {
1516 // If not specified, use 1.0.
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]1517 StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1518 }
1519
1520 Value *NextVar = Builder.CreateAdd(Variable, StepVal, "nextvar");
1521
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1522 // Compute the end condition.
1523 Value *EndCond = End-&gt;Codegen();
1524 if (EndCond == 0) return EndCond;
1525
1526 // Convert condition to a bool by comparing equal to 0.0.
1527 EndCond = Builder.CreateFCmpONE(EndCond,
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]1528 ConstantFP::get(getGlobalContext(), APFloat(0.0)),
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1529 "loopcond");
1530
1531 // Create the "after loop" block and insert it.
1532 BasicBlock *LoopEndBB = Builder.GetInsertBlock();
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]1533 BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1534
1535 // Insert the conditional branch into the end of LoopEndBB.
1536 Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
1537
1538 // Any new code will be inserted in AfterBB.
1539 Builder.SetInsertPoint(AfterBB);
1540
1541 // Add a new entry to the PHI node for the backedge.
1542 Variable-&gt;addIncoming(NextVar, LoopEndBB);
1543
1544 // Restore the unshadowed variable.
1545 if (OldVal)
1546 NamedValues[VarName] = OldVal;
1547 else
1548 NamedValues.erase(VarName);
1549
1550
1551 // for expr always returns 0.0.
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1552 return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1553}
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1554
1555Function *PrototypeAST::Codegen() {
1556 // Make the function type: double(double,double) etc.
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame]1557 std::vector&lt;const Type*&gt; Doubles(Args.size(),
1558 Type::getDoubleTy(getGlobalContext()));
1559 FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
1560 Doubles, false);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1561
Gabor Greifdf7d2b42008-04-19 22:25:09 +0000[diff] [blame]1562 Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1563
1564 // If F conflicted, there was already something named 'Name'. If it has a
1565 // body, don't allow redefinition or reextern.
1566 if (F-&gt;getName() != Name) {
1567 // Delete the one we just made and get the existing one.
1568 F-&gt;eraseFromParent();
1569 F = TheModule-&gt;getFunction(Name);
1570
1571 // If F already has a body, reject this.
1572 if (!F-&gt;empty()) {
1573 ErrorF("redefinition of function");
1574 return 0;
1575 }
1576
1577 // If F took a different number of args, reject.
1578 if (F-&gt;arg_size() != Args.size()) {
1579 ErrorF("redefinition of function with different # args");
1580 return 0;
1581 }
1582 }
1583
1584 // Set names for all arguments.
1585 unsigned Idx = 0;
1586 for (Function::arg_iterator AI = F-&gt;arg_begin(); Idx != Args.size();
1587 ++AI, ++Idx) {
1588 AI-&gt;setName(Args[Idx]);
1589
1590 // Add arguments to variable symbol table.
1591 NamedValues[Args[Idx]] = AI;
1592 }
1593
1594 return F;
1595}
1596
1597Function *FunctionAST::Codegen() {
1598 NamedValues.clear();
1599
1600 Function *TheFunction = Proto-&gt;Codegen();
1601 if (TheFunction == 0)
1602 return 0;
1603
1604 // Create a new basic block to start insertion into.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]1605 BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1606 Builder.SetInsertPoint(BB);
1607
1608 if (Value *RetVal = Body-&gt;Codegen()) {
1609 // Finish off the function.
1610 Builder.CreateRet(RetVal);
1611
1612 // Validate the generated code, checking for consistency.
1613 verifyFunction(*TheFunction);
1614
1615 // Optimize the function.
1616 TheFPM-&gt;run(*TheFunction);
1617
1618 return TheFunction;
1619 }
1620
1621 // Error reading body, remove function.
1622 TheFunction-&gt;eraseFromParent();
1623 return 0;
1624}
1625
1626//===----------------------------------------------------------------------===//
1627// Top-Level parsing and JIT Driver
1628//===----------------------------------------------------------------------===//
1629
1630static ExecutionEngine *TheExecutionEngine;
1631
1632static void HandleDefinition() {
1633 if (FunctionAST *F = ParseDefinition()) {
1634 if (Function *LF = F-&gt;Codegen()) {
1635 fprintf(stderr, "Read function definition:");
1636 LF-&gt;dump();
1637 }
1638 } else {
1639 // Skip token for error recovery.
1640 getNextToken();
1641 }
1642}
1643
1644static void HandleExtern() {
1645 if (PrototypeAST *P = ParseExtern()) {
1646 if (Function *F = P-&gt;Codegen()) {
1647 fprintf(stderr, "Read extern: ");
1648 F-&gt;dump();
1649 }
1650 } else {
1651 // Skip token for error recovery.
1652 getNextToken();
1653 }
1654}
1655
1656static void HandleTopLevelExpression() {
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1657 // Evaluate a top-level expression into an anonymous function.
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1658 if (FunctionAST *F = ParseTopLevelExpr()) {
1659 if (Function *LF = F-&gt;Codegen()) {
1660 // JIT the function, returning a function pointer.
1661 void *FPtr = TheExecutionEngine-&gt;getPointerToFunction(LF);
1662
1663 // Cast it to the right type (takes no arguments, returns a double) so we
1664 // can call it as a native function.
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame]1665 double (*FP)() = (double (*)())(intptr_t)FPtr;
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1666 fprintf(stderr, "Evaluated to %f\n", FP());
1667 }
1668 } else {
1669 // Skip token for error recovery.
1670 getNextToken();
1671 }
1672}
1673
1674/// top ::= definition | external | expression | ';'
1675static void MainLoop() {
1676 while (1) {
1677 fprintf(stderr, "ready&gt; ");
1678 switch (CurTok) {
1679 case tok_eof: return;
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1680 case ';': getNextToken(); break; // ignore top-level semicolons.
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1681 case tok_def: HandleDefinition(); break;
1682 case tok_extern: HandleExtern(); break;
1683 default: HandleTopLevelExpression(); break;
1684 }
1685 }
1686}
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1687
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1688//===----------------------------------------------------------------------===//
1689// "Library" functions that can be "extern'd" from user code.
1690//===----------------------------------------------------------------------===//
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1691
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1692/// putchard - putchar that takes a double and returns 0.
1693extern "C"
1694double putchard(double X) {
1695 putchar((char)X);
1696 return 0;
1697}
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1698
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1699//===----------------------------------------------------------------------===//
1700// Main driver code.
1701//===----------------------------------------------------------------------===//
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1702
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1703int main() {
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1704 InitializeNativeTarget();
1705 LLVMContext &amp;Context = getGlobalContext();
1706
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1707 // Install standard binary operators.
1708 // 1 is lowest precedence.
1709 BinopPrecedence['&lt;'] = 10;
1710 BinopPrecedence['+'] = 20;
1711 BinopPrecedence['-'] = 20;
1712 BinopPrecedence['*'] = 40; // highest.
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1713
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1714 // Prime the first token.
1715 fprintf(stderr, "ready&gt; ");
1716 getNextToken();
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1717
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1718 // Make the module, which holds all the code.
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1719 TheModule = new Module("my cool jit", Context);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1720
Jeffrey Yasskinf0356fe2010-01-27 20:34:15 +0000[diff] [blame]1721 // Create the JIT. This takes ownership of the module.
Jeffrey Yasskin42fc5582010-02-11 19:15:20 +0000[diff] [blame]1722 std::string ErrStr;
1723 TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create();
1724 if (!TheExecutionEngine) {
1725 fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str());
1726 exit(1);
1727 }
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1728
Jeffrey Yasskinf0356fe2010-01-27 20:34:15 +0000[diff] [blame]1729 FunctionPassManager OurFPM(TheModule);
Reid Kleckner60130f02009-08-26 20:58:25 +0000[diff] [blame]1730
1731 // Set up the optimizer pipeline. Start with registering info about how the
1732 // target lays out data structures.
1733 OurFPM.add(new TargetData(*TheExecutionEngine-&gt;getTargetData()));
1734 // Do simple "peephole" optimizations and bit-twiddling optzns.
1735 OurFPM.add(createInstructionCombiningPass());
1736 // Reassociate expressions.
1737 OurFPM.add(createReassociatePass());
1738 // Eliminate Common SubExpressions.
1739 OurFPM.add(createGVNPass());
1740 // Simplify the control flow graph (deleting unreachable blocks, etc).
1741 OurFPM.add(createCFGSimplificationPass());
1742
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame]1743 OurFPM.doInitialization();
1744
Reid Kleckner60130f02009-08-26 20:58:25 +0000[diff] [blame]1745 // Set the global so the code gen can use this.
1746 TheFPM = &amp;OurFPM;
1747
1748 // Run the main "interpreter loop" now.
1749 MainLoop();
1750
1751 TheFPM = 0;
1752
1753 // Print out all of the generated code.
1754 TheModule-&gt;dump();
1755
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1756 return 0;
1757}
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1758</pre>
1759</div>
1760
Chris Lattner729eb142008-02-10 19:11:04 +0000[diff] [blame]1761<a href="LangImpl6.html">Next: Extending the language: user-defined operators</a>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1762</div>
1763
1764<!-- *********************************************************************** -->
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1772 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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Dan Gohman523e3922010-02-03 17:27:31 +0000[diff] [blame]1774 Last modified: $Date$
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