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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
291<center><img src="LangImpl5-cfg.png" alt="Example CFG" width="423"
292height="315"></center>
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,
367 ConstantFP::get(Type::DoubleTy, APFloat(0.0)),
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.
382 BasicBlock *ThenBB = new BasicBlock("then", TheFunction);
383 BasicBlock *ElseBB = new BasicBlock("else");
384 BasicBlock *MergeBB = new BasicBlock("ifcont");
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
403LLVMBuilder, so it is still inserting into the block that the condition
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);
475 PHINode *PN = Builder.CreatePHI(Type::DoubleTy, "iftmp");
476
477 PN->addIncoming(ThenV, ThenBB);
478 PN->addIncoming(ElseV, ElseBB);
479 return PN;
480}
481</pre>
482</div>
483
484<p>The first two lines here are now familiar: the first adds the "merge" block
485to the Function object (it was previously floating, like the else block above).
486The second block changes the insertion point so that newly created code will go
487into the "merge" block. Once that is done, we need to create the PHI node and
488set up the block/value pairs for the PHI.</p>
489
490<p>Finally, the CodeGen function returns the phi node as the value computed by
491the if/then/else expression. In our example above, this returned value will
492feed into the code for the top-level function, which will create the return
493instruction.</p>
494
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]495<p>Overall, we now have the ability to execute conditional code in
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]496Kaleidoscope. With this extension, Kaleidoscope is a fairly complete language
497that can calculate a wide variety of numeric functions. Next up we'll add
498another useful expression that is familiar from non-functional languages...</p>
499
500</div>
501
502<!-- *********************************************************************** -->
503<div class="doc_section"><a name="for">'for' Loop Expression</a></div>
504<!-- *********************************************************************** -->
505
506<div class="doc_text">
507
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]508<p>Now that we know how to add basic control flow constructs to the language,
509we have the tools to add more powerful things. Lets add something more
510aggressive, a 'for' expression:</p>
511
512<div class="doc_code">
513<pre>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]514 extern putchard(char)
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]515 def printstar(n)
516 for i = 1, i &lt; n, 1.0 in
517 putchard(42); # ascii 42 = '*'
518
519 # print 100 '*' characters
520 printstar(100);
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]521</pre>
522</div>
523
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]524<p>This expression defines a new variable ("i" in this case) which iterates from
525a starting value, while the condition ("i &lt; n" in this case) is true,
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]526incrementing by an optional step value ("1.0" in this case). If the step value
527is omitted, it defaults to 1.0. While the loop is true, it executes its
528body expression. Because we don't have anything better to return, we'll just
529define the loop as always returning 0.0. In the future when we have mutable
530variables, it will get more useful.</p>
531
532<p>As before, lets talk about the changes that we need to Kaleidoscope to
533support this.</p>
534
535</div>
536
537<!-- ======================================================================= -->
538<div class="doc_subsubsection"><a name="forlexer">Lexer Extensions for
539the 'for' Loop</a></div>
540<!-- ======================================================================= -->
541
542<div class="doc_text">
543
544<p>The lexer extensions are the same sort of thing as for if/then/else:</p>
545
546<div class="doc_code">
547<pre>
548 ... in enum Token ...
549 // control
550 tok_if = -6, tok_then = -7, tok_else = -8,
551<b> tok_for = -9, tok_in = -10</b>
552
553 ... in gettok ...
554 if (IdentifierStr == "def") return tok_def;
555 if (IdentifierStr == "extern") return tok_extern;
556 if (IdentifierStr == "if") return tok_if;
557 if (IdentifierStr == "then") return tok_then;
558 if (IdentifierStr == "else") return tok_else;
559 <b>if (IdentifierStr == "for") return tok_for;
560 if (IdentifierStr == "in") return tok_in;</b>
561 return tok_identifier;
562</pre>
563</div>
564
565</div>
566
567<!-- ======================================================================= -->
568<div class="doc_subsubsection"><a name="forast">AST Extensions for
569the 'for' Loop</a></div>
570<!-- ======================================================================= -->
571
572<div class="doc_text">
573
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]574<p>The AST node is just as simple. It basically boils down to capturing
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]575the variable name and the constituent expressions in the node.</p>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]576
577<div class="doc_code">
578<pre>
579/// ForExprAST - Expression class for for/in.
580class ForExprAST : public ExprAST {
581 std::string VarName;
582 ExprAST *Start, *End, *Step, *Body;
583public:
584 ForExprAST(const std::string &amp;varname, ExprAST *start, ExprAST *end,
585 ExprAST *step, ExprAST *body)
586 : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
587 virtual Value *Codegen();
588};
589</pre>
590</div>
591
592</div>
593
594<!-- ======================================================================= -->
595<div class="doc_subsubsection"><a name="forparser">Parser Extensions for
596the 'for' Loop</a></div>
597<!-- ======================================================================= -->
598
599<div class="doc_text">
600
601<p>The parser code is also fairly standard. The only interesting thing here is
602handling of the optional step value. The parser code handles it by checking to
603see if the second comma is present. If not, it sets the step value to null in
604the AST node:</p>
605
606<div class="doc_code">
607<pre>
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]608/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]609static ExprAST *ParseForExpr() {
610 getNextToken(); // eat the for.
611
612 if (CurTok != tok_identifier)
613 return Error("expected identifier after for");
614
615 std::string IdName = IdentifierStr;
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]616 getNextToken(); // eat identifier.
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]617
618 if (CurTok != '=')
619 return Error("expected '=' after for");
620 getNextToken(); // eat '='.
621
622
623 ExprAST *Start = ParseExpression();
624 if (Start == 0) return 0;
625 if (CurTok != ',')
626 return Error("expected ',' after for start value");
627 getNextToken();
628
629 ExprAST *End = ParseExpression();
630 if (End == 0) return 0;
631
632 // The step value is optional.
633 ExprAST *Step = 0;
634 if (CurTok == ',') {
635 getNextToken();
636 Step = ParseExpression();
637 if (Step == 0) return 0;
638 }
639
640 if (CurTok != tok_in)
641 return Error("expected 'in' after for");
642 getNextToken(); // eat 'in'.
643
644 ExprAST *Body = ParseExpression();
645 if (Body == 0) return 0;
646
647 return new ForExprAST(IdName, Start, End, Step, Body);
648}
649</pre>
650</div>
651
652</div>
653
654<!-- ======================================================================= -->
655<div class="doc_subsubsection"><a name="forir">LLVM IR for
656the 'for' Loop</a></div>
657<!-- ======================================================================= -->
658
659<div class="doc_text">
660
661<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]662With the simple example above, we get this LLVM IR (note that this dump is
663generated with optimizations disabled for clarity):
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]664</p>
665
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]666<div class="doc_code">
667<pre>
668declare double @putchard(double)
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]669
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]670define double @printstar(double %n) {
671entry:
672 ; initial value = 1.0 (inlined into phi)
673 br label %loop
674
675loop: ; preds = %loop, %entry
676 %i = phi double [ 1.000000e+00, %entry ], [ %nextvar, %loop ]
677 ; body
678 %calltmp = call double @putchard( double 4.200000e+01 )
679 ; increment
680 %nextvar = add double %i, 1.000000e+00
681
682 ; termination test
Chris Lattner71155212007-11-06 01:39:12 +0000[diff] [blame]683 %cmptmp = fcmp ult double %i, %n
684 %booltmp = uitofp i1 %cmptmp to double
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]685 %loopcond = fcmp one double %booltmp, 0.000000e+00
686 br i1 %loopcond, label %loop, label %afterloop
687
688afterloop: ; preds = %loop
689 ; loop always returns 0.0
690 ret double 0.000000e+00
691}
692</pre>
693</div>
694
695<p>This loop contains all the same constructs we saw before: a phi node, several
696expressions, and some basic blocks. Lets see how this fits together.</p>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]697
698</div>
699
700<!-- ======================================================================= -->
701<div class="doc_subsubsection"><a name="forcodegen">Code Generation for
702the 'for' Loop</a></div>
703<!-- ======================================================================= -->
704
705<div class="doc_text">
706
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]707<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]708for the loop value:</p>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]709
710<div class="doc_code">
711<pre>
712Value *ForExprAST::Codegen() {
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]713 // Emit the start code first, without 'variable' in scope.
714 Value *StartVal = Start-&gt;Codegen();
715 if (StartVal == 0) return 0;
716</pre>
717</div>
718
719<p>With this out of the way, the next step is to set up the LLVM basic block
720for the start of the loop body. In the case above, the whole loop body is one
721block, but remember that the body code itself could consist of multiple blocks
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]722(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]723
724<div class="doc_code">
725<pre>
726 // Make the new basic block for the loop header, inserting after current
727 // block.
728 Function *TheFunction = Builder.GetInsertBlock()-&gt;getParent();
729 BasicBlock *PreheaderBB = Builder.GetInsertBlock();
730 BasicBlock *LoopBB = new BasicBlock("loop", TheFunction);
731
732 // Insert an explicit fall through from the current block to the LoopBB.
733 Builder.CreateBr(LoopBB);
734</pre>
735</div>
736
737<p>This code is similar to what we saw for if/then/else. Because we will need
738it to create the Phi node, we remember the block that falls through into the
739loop. Once we have that, we create the actual block that starts the loop and
740create an unconditional branch for the fall-through between the two blocks.</p>
741
742<div class="doc_code">
743<pre>
744 // Start insertion in LoopBB.
745 Builder.SetInsertPoint(LoopBB);
746
747 // Start the PHI node with an entry for Start.
748 PHINode *Variable = Builder.CreatePHI(Type::DoubleTy, VarName.c_str());
749 Variable-&gt;addIncoming(StartVal, PreheaderBB);
750</pre>
751</div>
752
753<p>Now that the "preheader" for the loop is set up, we switch to emitting code
754for the loop body. To begin with, we move the insertion point and create the
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]755PHI node for the loop induction variable. Since we already know the incoming
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]756value for the starting value, we add it to the Phi node. Note that the Phi will
757eventually get a second value for the backedge, but we can't set it up yet
758(because it doesn't exist!).</p>
759
760<div class="doc_code">
761<pre>
762 // Within the loop, the variable is defined equal to the PHI node. If it
763 // shadows an existing variable, we have to restore it, so save it now.
764 Value *OldVal = NamedValues[VarName];
765 NamedValues[VarName] = Variable;
766
767 // Emit the body of the loop. This, like any other expr, can change the
768 // current BB. Note that we ignore the value computed by the body, but don't
769 // allow an error.
770 if (Body-&gt;Codegen() == 0)
771 return 0;
772</pre>
773</div>
774
775<p>Now the code starts to get more interesting. Our 'for' loop introduces a new
776variable to the symbol table. This means that our symbol table can now contain
777either function arguments or loop variables. To handle this, before we codegen
778the body of the loop, we add the loop variable as the current value for its
779name. Note that it is possible that there is a variable of the same name in the
780outer scope. It would be easy to make this an error (emit an error and return
781null if there is already an entry for VarName) but we choose to allow shadowing
782of variables. In order to handle this correctly, we remember the Value that
783we are potentially shadowing in <tt>OldVal</tt> (which will be null if there is
784no shadowed variable).</p>
785
786<p>Once the loop variable is set into the symbol table, the code recursively
787codegen's the body. This allows the body to use the loop variable: any
788references to it will naturally find it in the symbol table.</p>
789
790<div class="doc_code">
791<pre>
792 // Emit the step value.
793 Value *StepVal;
794 if (Step) {
795 StepVal = Step-&gt;Codegen();
796 if (StepVal == 0) return 0;
797 } else {
798 // If not specified, use 1.0.
799 StepVal = ConstantFP::get(Type::DoubleTy, APFloat(1.0));
800 }
801
802 Value *NextVar = Builder.CreateAdd(Variable, StepVal, "nextvar");
803</pre>
804</div>
805
806<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]807variable 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]808will be the value of the loop variable on the next iteration of the loop.</p>
809
810<div class="doc_code">
811<pre>
812 // Compute the end condition.
813 Value *EndCond = End-&gt;Codegen();
814 if (EndCond == 0) return EndCond;
815
816 // Convert condition to a bool by comparing equal to 0.0.
817 EndCond = Builder.CreateFCmpONE(EndCond,
818 ConstantFP::get(Type::DoubleTy, APFloat(0.0)),
819 "loopcond");
820</pre>
821</div>
822
823<p>Finally, we evaluate the exit value of the loop, to determine whether the
824loop should exit. This mirrors the condition evaluation for the if/then/else
825statement.</p>
826
827<div class="doc_code">
828<pre>
829 // Create the "after loop" block and insert it.
830 BasicBlock *LoopEndBB = Builder.GetInsertBlock();
831 BasicBlock *AfterBB = new BasicBlock("afterloop", TheFunction);
832
833 // Insert the conditional branch into the end of LoopEndBB.
834 Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
835
836 // Any new code will be inserted in AfterBB.
837 Builder.SetInsertPoint(AfterBB);
838</pre>
839</div>
840
841<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]842the 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]843exit condition, it creates a conditional branch that chooses between executing
844the loop again and exiting the loop. Any future code is emitted in the
845"afterloop" block, so it sets the insertion position to it.</p>
846
847<div class="doc_code">
848<pre>
849 // Add a new entry to the PHI node for the backedge.
850 Variable-&gt;addIncoming(NextVar, LoopEndBB);
851
852 // Restore the unshadowed variable.
853 if (OldVal)
854 NamedValues[VarName] = OldVal;
855 else
856 NamedValues.erase(VarName);
857
858 // for expr always returns 0.0.
859 return Constant::getNullValue(Type::DoubleTy);
860}
861</pre>
862</div>
863
864<p>The final code handles various cleanups: now that we have the "NextVar"
865value, we can add the incoming value to the loop PHI node. After that, we
866remove the loop variable from the symbol table, so that it isn't in scope after
867the for loop. Finally, code generation of the for loop always returns 0.0, so
868that is what we return from <tt>ForExprAST::Codegen</tt>.</p>
869
870<p>With this, we conclude the "adding control flow to Kaleidoscope" chapter of
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]871the 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]872to 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]873<a href="LangImpl6.html">user-defined operators</a> to our poor innocent
874language.</p>
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]875
876</div>
877
878<!-- *********************************************************************** -->
879<div class="doc_section"><a name="code">Full Code Listing</a></div>
880<!-- *********************************************************************** -->
881
882<div class="doc_text">
883
884<p>
885Here is the complete code listing for our running example, enhanced with the
886if/then/else and for expressions.. To build this example, use:
887</p>
888
889<div class="doc_code">
890<pre>
891 # Compile
892 g++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
893 # Run
894 ./toy
895</pre>
896</div>
897
898<p>Here is the code:</p>
899
900<div class="doc_code">
901<pre>
902#include "llvm/DerivedTypes.h"
903#include "llvm/ExecutionEngine/ExecutionEngine.h"
904#include "llvm/Module.h"
905#include "llvm/ModuleProvider.h"
906#include "llvm/PassManager.h"
907#include "llvm/Analysis/Verifier.h"
908#include "llvm/Target/TargetData.h"
909#include "llvm/Transforms/Scalar.h"
910#include "llvm/Support/LLVMBuilder.h"
911#include &lt;cstdio&gt;
912#include &lt;string&gt;
913#include &lt;map&gt;
914#include &lt;vector&gt;
915using namespace llvm;
916
917//===----------------------------------------------------------------------===//
918// Lexer
919//===----------------------------------------------------------------------===//
920
921// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
922// of these for known things.
923enum Token {
924 tok_eof = -1,
925
926 // commands
927 tok_def = -2, tok_extern = -3,
928
929 // primary
930 tok_identifier = -4, tok_number = -5,
931
932 // control
933 tok_if = -6, tok_then = -7, tok_else = -8,
934 tok_for = -9, tok_in = -10
935};
936
937static std::string IdentifierStr; // Filled in if tok_identifier
938static double NumVal; // Filled in if tok_number
939
940/// gettok - Return the next token from standard input.
941static int gettok() {
942 static int LastChar = ' ';
943
944 // Skip any whitespace.
945 while (isspace(LastChar))
946 LastChar = getchar();
947
948 if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
949 IdentifierStr = LastChar;
950 while (isalnum((LastChar = getchar())))
951 IdentifierStr += LastChar;
952
953 if (IdentifierStr == "def") return tok_def;
954 if (IdentifierStr == "extern") return tok_extern;
955 if (IdentifierStr == "if") return tok_if;
956 if (IdentifierStr == "then") return tok_then;
957 if (IdentifierStr == "else") return tok_else;
958 if (IdentifierStr == "for") return tok_for;
959 if (IdentifierStr == "in") return tok_in;
960 return tok_identifier;
961 }
962
963 if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
964 std::string NumStr;
965 do {
966 NumStr += LastChar;
967 LastChar = getchar();
968 } while (isdigit(LastChar) || LastChar == '.');
969
970 NumVal = strtod(NumStr.c_str(), 0);
971 return tok_number;
972 }
973
974 if (LastChar == '#') {
975 // Comment until end of line.
976 do LastChar = getchar();
Chris Lattnerc80c23f2007-12-02 22:46:01 +0000[diff] [blame]977 while (LastChar != EOF &amp;&amp; LastChar != '\n' &amp;&amp; LastChar != '\r');
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]978
979 if (LastChar != EOF)
980 return gettok();
981 }
982
983 // Check for end of file. Don't eat the EOF.
984 if (LastChar == EOF)
985 return tok_eof;
986
987 // Otherwise, just return the character as its ascii value.
988 int ThisChar = LastChar;
989 LastChar = getchar();
990 return ThisChar;
991}
992
993//===----------------------------------------------------------------------===//
994// Abstract Syntax Tree (aka Parse Tree)
995//===----------------------------------------------------------------------===//
996
997/// ExprAST - Base class for all expression nodes.
998class ExprAST {
999public:
1000 virtual ~ExprAST() {}
1001 virtual Value *Codegen() = 0;
1002};
1003
1004/// NumberExprAST - Expression class for numeric literals like "1.0".
1005class NumberExprAST : public ExprAST {
1006 double Val;
1007public:
1008 NumberExprAST(double val) : Val(val) {}
1009 virtual Value *Codegen();
1010};
1011
1012/// VariableExprAST - Expression class for referencing a variable, like "a".
1013class VariableExprAST : public ExprAST {
1014 std::string Name;
1015public:
1016 VariableExprAST(const std::string &amp;name) : Name(name) {}
1017 virtual Value *Codegen();
1018};
1019
1020/// BinaryExprAST - Expression class for a binary operator.
1021class BinaryExprAST : public ExprAST {
1022 char Op;
1023 ExprAST *LHS, *RHS;
1024public:
1025 BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
1026 : Op(op), LHS(lhs), RHS(rhs) {}
1027 virtual Value *Codegen();
1028};
1029
1030/// CallExprAST - Expression class for function calls.
1031class CallExprAST : public ExprAST {
1032 std::string Callee;
1033 std::vector&lt;ExprAST*&gt; Args;
1034public:
1035 CallExprAST(const std::string &amp;callee, std::vector&lt;ExprAST*&gt; &amp;args)
1036 : Callee(callee), Args(args) {}
1037 virtual Value *Codegen();
1038};
1039
1040/// IfExprAST - Expression class for if/then/else.
1041class IfExprAST : public ExprAST {
1042 ExprAST *Cond, *Then, *Else;
1043public:
1044 IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
1045 : Cond(cond), Then(then), Else(_else) {}
1046 virtual Value *Codegen();
1047};
1048
1049/// ForExprAST - Expression class for for/in.
1050class ForExprAST : public ExprAST {
1051 std::string VarName;
1052 ExprAST *Start, *End, *Step, *Body;
1053public:
1054 ForExprAST(const std::string &amp;varname, ExprAST *start, ExprAST *end,
1055 ExprAST *step, ExprAST *body)
1056 : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
1057 virtual Value *Codegen();
1058};
1059
1060/// PrototypeAST - This class represents the "prototype" for a function,
1061/// which captures its argument names as well as if it is an operator.
1062class PrototypeAST {
1063 std::string Name;
1064 std::vector&lt;std::string&gt; Args;
1065public:
1066 PrototypeAST(const std::string &amp;name, const std::vector&lt;std::string&gt; &amp;args)
1067 : Name(name), Args(args) {}
1068
1069 Function *Codegen();
1070};
1071
1072/// FunctionAST - This class represents a function definition itself.
1073class FunctionAST {
1074 PrototypeAST *Proto;
1075 ExprAST *Body;
1076public:
1077 FunctionAST(PrototypeAST *proto, ExprAST *body)
1078 : Proto(proto), Body(body) {}
1079
1080 Function *Codegen();
1081};
1082
1083//===----------------------------------------------------------------------===//
1084// Parser
1085//===----------------------------------------------------------------------===//
1086
1087/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
1088/// token the parser it looking at. getNextToken reads another token from the
1089/// lexer and updates CurTok with its results.
1090static int CurTok;
1091static int getNextToken() {
1092 return CurTok = gettok();
1093}
1094
1095/// BinopPrecedence - This holds the precedence for each binary operator that is
1096/// defined.
1097static std::map&lt;char, int&gt; BinopPrecedence;
1098
1099/// GetTokPrecedence - Get the precedence of the pending binary operator token.
1100static int GetTokPrecedence() {
1101 if (!isascii(CurTok))
1102 return -1;
1103
1104 // Make sure it's a declared binop.
1105 int TokPrec = BinopPrecedence[CurTok];
1106 if (TokPrec &lt;= 0) return -1;
1107 return TokPrec;
1108}
1109
1110/// Error* - These are little helper functions for error handling.
1111ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
1112PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
1113FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
1114
1115static ExprAST *ParseExpression();
1116
1117/// identifierexpr
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1118/// ::= identifier
1119/// ::= identifier '(' expression* ')'
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1120static ExprAST *ParseIdentifierExpr() {
1121 std::string IdName = IdentifierStr;
1122
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1123 getNextToken(); // eat identifier.
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1124
1125 if (CurTok != '(') // Simple variable ref.
1126 return new VariableExprAST(IdName);
1127
1128 // Call.
1129 getNextToken(); // eat (
1130 std::vector&lt;ExprAST*&gt; Args;
1131 if (CurTok != ')') {
1132 while (1) {
1133 ExprAST *Arg = ParseExpression();
1134 if (!Arg) return 0;
1135 Args.push_back(Arg);
1136
1137 if (CurTok == ')') break;
1138
1139 if (CurTok != ',')
1140 return Error("Expected ')'");
1141 getNextToken();
1142 }
1143 }
1144
1145 // Eat the ')'.
1146 getNextToken();
1147
1148 return new CallExprAST(IdName, Args);
1149}
1150
1151/// numberexpr ::= number
1152static ExprAST *ParseNumberExpr() {
1153 ExprAST *Result = new NumberExprAST(NumVal);
1154 getNextToken(); // consume the number
1155 return Result;
1156}
1157
1158/// parenexpr ::= '(' expression ')'
1159static ExprAST *ParseParenExpr() {
1160 getNextToken(); // eat (.
1161 ExprAST *V = ParseExpression();
1162 if (!V) return 0;
1163
1164 if (CurTok != ')')
1165 return Error("expected ')'");
1166 getNextToken(); // eat ).
1167 return V;
1168}
1169
1170/// ifexpr ::= 'if' expression 'then' expression 'else' expression
1171static ExprAST *ParseIfExpr() {
1172 getNextToken(); // eat the if.
1173
1174 // condition.
1175 ExprAST *Cond = ParseExpression();
1176 if (!Cond) return 0;
1177
1178 if (CurTok != tok_then)
1179 return Error("expected then");
1180 getNextToken(); // eat the then
1181
1182 ExprAST *Then = ParseExpression();
1183 if (Then == 0) return 0;
1184
1185 if (CurTok != tok_else)
1186 return Error("expected else");
1187
1188 getNextToken();
1189
1190 ExprAST *Else = ParseExpression();
1191 if (!Else) return 0;
1192
1193 return new IfExprAST(Cond, Then, Else);
1194}
1195
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1196/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1197static ExprAST *ParseForExpr() {
1198 getNextToken(); // eat the for.
1199
1200 if (CurTok != tok_identifier)
1201 return Error("expected identifier after for");
1202
1203 std::string IdName = IdentifierStr;
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1204 getNextToken(); // eat identifier.
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1205
1206 if (CurTok != '=')
1207 return Error("expected '=' after for");
1208 getNextToken(); // eat '='.
1209
1210
1211 ExprAST *Start = ParseExpression();
1212 if (Start == 0) return 0;
1213 if (CurTok != ',')
1214 return Error("expected ',' after for start value");
1215 getNextToken();
1216
1217 ExprAST *End = ParseExpression();
1218 if (End == 0) return 0;
1219
1220 // The step value is optional.
1221 ExprAST *Step = 0;
1222 if (CurTok == ',') {
1223 getNextToken();
1224 Step = ParseExpression();
1225 if (Step == 0) return 0;
1226 }
1227
1228 if (CurTok != tok_in)
1229 return Error("expected 'in' after for");
1230 getNextToken(); // eat 'in'.
1231
1232 ExprAST *Body = ParseExpression();
1233 if (Body == 0) return 0;
1234
1235 return new ForExprAST(IdName, Start, End, Step, Body);
1236}
1237
1238
1239/// primary
1240/// ::= identifierexpr
1241/// ::= numberexpr
1242/// ::= parenexpr
1243/// ::= ifexpr
1244/// ::= forexpr
1245static ExprAST *ParsePrimary() {
1246 switch (CurTok) {
1247 default: return Error("unknown token when expecting an expression");
1248 case tok_identifier: return ParseIdentifierExpr();
1249 case tok_number: return ParseNumberExpr();
1250 case '(': return ParseParenExpr();
1251 case tok_if: return ParseIfExpr();
1252 case tok_for: return ParseForExpr();
1253 }
1254}
1255
1256/// binoprhs
1257/// ::= ('+' primary)*
1258static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
1259 // If this is a binop, find its precedence.
1260 while (1) {
1261 int TokPrec = GetTokPrecedence();
1262
1263 // If this is a binop that binds at least as tightly as the current binop,
1264 // consume it, otherwise we are done.
1265 if (TokPrec &lt; ExprPrec)
1266 return LHS;
1267
1268 // Okay, we know this is a binop.
1269 int BinOp = CurTok;
1270 getNextToken(); // eat binop
1271
1272 // Parse the primary expression after the binary operator.
1273 ExprAST *RHS = ParsePrimary();
1274 if (!RHS) return 0;
1275
1276 // If BinOp binds less tightly with RHS than the operator after RHS, let
1277 // the pending operator take RHS as its LHS.
1278 int NextPrec = GetTokPrecedence();
1279 if (TokPrec &lt; NextPrec) {
1280 RHS = ParseBinOpRHS(TokPrec+1, RHS);
1281 if (RHS == 0) return 0;
1282 }
1283
1284 // Merge LHS/RHS.
1285 LHS = new BinaryExprAST(BinOp, LHS, RHS);
1286 }
1287}
1288
1289/// expression
1290/// ::= primary binoprhs
1291///
1292static ExprAST *ParseExpression() {
1293 ExprAST *LHS = ParsePrimary();
1294 if (!LHS) return 0;
1295
1296 return ParseBinOpRHS(0, LHS);
1297}
1298
1299/// prototype
1300/// ::= id '(' id* ')'
1301static PrototypeAST *ParsePrototype() {
1302 if (CurTok != tok_identifier)
1303 return ErrorP("Expected function name in prototype");
1304
1305 std::string FnName = IdentifierStr;
1306 getNextToken();
1307
1308 if (CurTok != '(')
1309 return ErrorP("Expected '(' in prototype");
1310
1311 std::vector&lt;std::string&gt; ArgNames;
1312 while (getNextToken() == tok_identifier)
1313 ArgNames.push_back(IdentifierStr);
1314 if (CurTok != ')')
1315 return ErrorP("Expected ')' in prototype");
1316
1317 // success.
1318 getNextToken(); // eat ')'.
1319
1320 return new PrototypeAST(FnName, ArgNames);
1321}
1322
1323/// definition ::= 'def' prototype expression
1324static FunctionAST *ParseDefinition() {
1325 getNextToken(); // eat def.
1326 PrototypeAST *Proto = ParsePrototype();
1327 if (Proto == 0) return 0;
1328
1329 if (ExprAST *E = ParseExpression())
1330 return new FunctionAST(Proto, E);
1331 return 0;
1332}
1333
1334/// toplevelexpr ::= expression
1335static FunctionAST *ParseTopLevelExpr() {
1336 if (ExprAST *E = ParseExpression()) {
1337 // Make an anonymous proto.
1338 PrototypeAST *Proto = new PrototypeAST("", std::vector&lt;std::string&gt;());
1339 return new FunctionAST(Proto, E);
1340 }
1341 return 0;
1342}
1343
1344/// external ::= 'extern' prototype
1345static PrototypeAST *ParseExtern() {
1346 getNextToken(); // eat extern.
1347 return ParsePrototype();
1348}
1349
1350//===----------------------------------------------------------------------===//
1351// Code Generation
1352//===----------------------------------------------------------------------===//
1353
1354static Module *TheModule;
1355static LLVMFoldingBuilder Builder;
1356static std::map&lt;std::string, Value*&gt; NamedValues;
1357static FunctionPassManager *TheFPM;
1358
1359Value *ErrorV(const char *Str) { Error(Str); return 0; }
1360
1361Value *NumberExprAST::Codegen() {
1362 return ConstantFP::get(Type::DoubleTy, APFloat(Val));
1363}
1364
1365Value *VariableExprAST::Codegen() {
1366 // Look this variable up in the function.
1367 Value *V = NamedValues[Name];
1368 return V ? V : ErrorV("Unknown variable name");
1369}
1370
1371Value *BinaryExprAST::Codegen() {
1372 Value *L = LHS-&gt;Codegen();
1373 Value *R = RHS-&gt;Codegen();
1374 if (L == 0 || R == 0) return 0;
1375
1376 switch (Op) {
1377 case '+': return Builder.CreateAdd(L, R, "addtmp");
1378 case '-': return Builder.CreateSub(L, R, "subtmp");
1379 case '*': return Builder.CreateMul(L, R, "multmp");
1380 case '&lt;':
Chris Lattner71155212007-11-06 01:39:12 +0000[diff] [blame]1381 L = Builder.CreateFCmpULT(L, R, "cmptmp");
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1382 // Convert bool 0/1 to double 0.0 or 1.0
1383 return Builder.CreateUIToFP(L, Type::DoubleTy, "booltmp");
1384 default: return ErrorV("invalid binary operator");
1385 }
1386}
1387
1388Value *CallExprAST::Codegen() {
1389 // Look up the name in the global module table.
1390 Function *CalleeF = TheModule-&gt;getFunction(Callee);
1391 if (CalleeF == 0)
1392 return ErrorV("Unknown function referenced");
1393
1394 // If argument mismatch error.
1395 if (CalleeF-&gt;arg_size() != Args.size())
1396 return ErrorV("Incorrect # arguments passed");
1397
1398 std::vector&lt;Value*&gt; ArgsV;
1399 for (unsigned i = 0, e = Args.size(); i != e; ++i) {
1400 ArgsV.push_back(Args[i]-&gt;Codegen());
1401 if (ArgsV.back() == 0) return 0;
1402 }
1403
1404 return Builder.CreateCall(CalleeF, ArgsV.begin(), ArgsV.end(), "calltmp");
1405}
1406
1407Value *IfExprAST::Codegen() {
1408 Value *CondV = Cond-&gt;Codegen();
1409 if (CondV == 0) return 0;
1410
1411 // Convert condition to a bool by comparing equal to 0.0.
1412 CondV = Builder.CreateFCmpONE(CondV,
1413 ConstantFP::get(Type::DoubleTy, APFloat(0.0)),
1414 "ifcond");
1415
1416 Function *TheFunction = Builder.GetInsertBlock()-&gt;getParent();
1417
1418 // Create blocks for the then and else cases. Insert the 'then' block at the
1419 // end of the function.
1420 BasicBlock *ThenBB = new BasicBlock("then", TheFunction);
1421 BasicBlock *ElseBB = new BasicBlock("else");
1422 BasicBlock *MergeBB = new BasicBlock("ifcont");
1423
1424 Builder.CreateCondBr(CondV, ThenBB, ElseBB);
1425
1426 // Emit then value.
1427 Builder.SetInsertPoint(ThenBB);
1428
1429 Value *ThenV = Then-&gt;Codegen();
1430 if (ThenV == 0) return 0;
1431
1432 Builder.CreateBr(MergeBB);
1433 // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
1434 ThenBB = Builder.GetInsertBlock();
1435
1436 // Emit else block.
1437 TheFunction-&gt;getBasicBlockList().push_back(ElseBB);
1438 Builder.SetInsertPoint(ElseBB);
1439
1440 Value *ElseV = Else-&gt;Codegen();
1441 if (ElseV == 0) return 0;
1442
1443 Builder.CreateBr(MergeBB);
1444 // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
1445 ElseBB = Builder.GetInsertBlock();
1446
1447 // Emit merge block.
1448 TheFunction-&gt;getBasicBlockList().push_back(MergeBB);
1449 Builder.SetInsertPoint(MergeBB);
1450 PHINode *PN = Builder.CreatePHI(Type::DoubleTy, "iftmp");
1451
1452 PN-&gt;addIncoming(ThenV, ThenBB);
1453 PN-&gt;addIncoming(ElseV, ElseBB);
1454 return PN;
1455}
1456
1457Value *ForExprAST::Codegen() {
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1458 // Output this as:
1459 // ...
1460 // start = startexpr
1461 // goto loop
1462 // loop:
1463 // variable = phi [start, loopheader], [nextvariable, loopend]
1464 // ...
1465 // bodyexpr
1466 // ...
1467 // loopend:
1468 // step = stepexpr
1469 // nextvariable = variable + step
1470 // endcond = endexpr
1471 // br endcond, loop, endloop
1472 // outloop:
1473
1474 // Emit the start code first, without 'variable' in scope.
1475 Value *StartVal = Start-&gt;Codegen();
1476 if (StartVal == 0) return 0;
1477
1478 // Make the new basic block for the loop header, inserting after current
1479 // block.
1480 Function *TheFunction = Builder.GetInsertBlock()-&gt;getParent();
1481 BasicBlock *PreheaderBB = Builder.GetInsertBlock();
1482 BasicBlock *LoopBB = new BasicBlock("loop", TheFunction);
1483
1484 // Insert an explicit fall through from the current block to the LoopBB.
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1485 Builder.CreateBr(LoopBB);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1486
1487 // Start insertion in LoopBB.
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1488 Builder.SetInsertPoint(LoopBB);
1489
1490 // Start the PHI node with an entry for Start.
1491 PHINode *Variable = Builder.CreatePHI(Type::DoubleTy, VarName.c_str());
1492 Variable-&gt;addIncoming(StartVal, PreheaderBB);
1493
1494 // Within the loop, the variable is defined equal to the PHI node. If it
1495 // shadows an existing variable, we have to restore it, so save it now.
1496 Value *OldVal = NamedValues[VarName];
1497 NamedValues[VarName] = Variable;
1498
1499 // Emit the body of the loop. This, like any other expr, can change the
1500 // current BB. Note that we ignore the value computed by the body, but don't
1501 // allow an error.
1502 if (Body-&gt;Codegen() == 0)
1503 return 0;
1504
1505 // Emit the step value.
1506 Value *StepVal;
1507 if (Step) {
1508 StepVal = Step-&gt;Codegen();
1509 if (StepVal == 0) return 0;
1510 } else {
1511 // If not specified, use 1.0.
1512 StepVal = ConstantFP::get(Type::DoubleTy, APFloat(1.0));
1513 }
1514
1515 Value *NextVar = Builder.CreateAdd(Variable, StepVal, "nextvar");
1516
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1517 // Compute the end condition.
1518 Value *EndCond = End-&gt;Codegen();
1519 if (EndCond == 0) return EndCond;
1520
1521 // Convert condition to a bool by comparing equal to 0.0.
1522 EndCond = Builder.CreateFCmpONE(EndCond,
1523 ConstantFP::get(Type::DoubleTy, APFloat(0.0)),
1524 "loopcond");
1525
1526 // Create the "after loop" block and insert it.
1527 BasicBlock *LoopEndBB = Builder.GetInsertBlock();
1528 BasicBlock *AfterBB = new BasicBlock("afterloop", TheFunction);
1529
1530 // Insert the conditional branch into the end of LoopEndBB.
1531 Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
1532
1533 // Any new code will be inserted in AfterBB.
1534 Builder.SetInsertPoint(AfterBB);
1535
1536 // Add a new entry to the PHI node for the backedge.
1537 Variable-&gt;addIncoming(NextVar, LoopEndBB);
1538
1539 // Restore the unshadowed variable.
1540 if (OldVal)
1541 NamedValues[VarName] = OldVal;
1542 else
1543 NamedValues.erase(VarName);
1544
1545
1546 // for expr always returns 0.0.
1547 return Constant::getNullValue(Type::DoubleTy);
1548}
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1549
1550Function *PrototypeAST::Codegen() {
1551 // Make the function type: double(double,double) etc.
1552 std::vector&lt;const Type*&gt; Doubles(Args.size(), Type::DoubleTy);
1553 FunctionType *FT = FunctionType::get(Type::DoubleTy, Doubles, false);
1554
1555 Function *F = new Function(FT, Function::ExternalLinkage, Name, TheModule);
1556
1557 // If F conflicted, there was already something named 'Name'. If it has a
1558 // body, don't allow redefinition or reextern.
1559 if (F-&gt;getName() != Name) {
1560 // Delete the one we just made and get the existing one.
1561 F-&gt;eraseFromParent();
1562 F = TheModule-&gt;getFunction(Name);
1563
1564 // If F already has a body, reject this.
1565 if (!F-&gt;empty()) {
1566 ErrorF("redefinition of function");
1567 return 0;
1568 }
1569
1570 // If F took a different number of args, reject.
1571 if (F-&gt;arg_size() != Args.size()) {
1572 ErrorF("redefinition of function with different # args");
1573 return 0;
1574 }
1575 }
1576
1577 // Set names for all arguments.
1578 unsigned Idx = 0;
1579 for (Function::arg_iterator AI = F-&gt;arg_begin(); Idx != Args.size();
1580 ++AI, ++Idx) {
1581 AI-&gt;setName(Args[Idx]);
1582
1583 // Add arguments to variable symbol table.
1584 NamedValues[Args[Idx]] = AI;
1585 }
1586
1587 return F;
1588}
1589
1590Function *FunctionAST::Codegen() {
1591 NamedValues.clear();
1592
1593 Function *TheFunction = Proto-&gt;Codegen();
1594 if (TheFunction == 0)
1595 return 0;
1596
1597 // Create a new basic block to start insertion into.
1598 BasicBlock *BB = new BasicBlock("entry", TheFunction);
1599 Builder.SetInsertPoint(BB);
1600
1601 if (Value *RetVal = Body-&gt;Codegen()) {
1602 // Finish off the function.
1603 Builder.CreateRet(RetVal);
1604
1605 // Validate the generated code, checking for consistency.
1606 verifyFunction(*TheFunction);
1607
1608 // Optimize the function.
1609 TheFPM-&gt;run(*TheFunction);
1610
1611 return TheFunction;
1612 }
1613
1614 // Error reading body, remove function.
1615 TheFunction-&gt;eraseFromParent();
1616 return 0;
1617}
1618
1619//===----------------------------------------------------------------------===//
1620// Top-Level parsing and JIT Driver
1621//===----------------------------------------------------------------------===//
1622
1623static ExecutionEngine *TheExecutionEngine;
1624
1625static void HandleDefinition() {
1626 if (FunctionAST *F = ParseDefinition()) {
1627 if (Function *LF = F-&gt;Codegen()) {
1628 fprintf(stderr, "Read function definition:");
1629 LF-&gt;dump();
1630 }
1631 } else {
1632 // Skip token for error recovery.
1633 getNextToken();
1634 }
1635}
1636
1637static void HandleExtern() {
1638 if (PrototypeAST *P = ParseExtern()) {
1639 if (Function *F = P-&gt;Codegen()) {
1640 fprintf(stderr, "Read extern: ");
1641 F-&gt;dump();
1642 }
1643 } else {
1644 // Skip token for error recovery.
1645 getNextToken();
1646 }
1647}
1648
1649static void HandleTopLevelExpression() {
1650 // Evaluate a top level expression into an anonymous function.
1651 if (FunctionAST *F = ParseTopLevelExpr()) {
1652 if (Function *LF = F-&gt;Codegen()) {
1653 // JIT the function, returning a function pointer.
1654 void *FPtr = TheExecutionEngine-&gt;getPointerToFunction(LF);
1655
1656 // Cast it to the right type (takes no arguments, returns a double) so we
1657 // can call it as a native function.
1658 double (*FP)() = (double (*)())FPtr;
1659 fprintf(stderr, "Evaluated to %f\n", FP());
1660 }
1661 } else {
1662 // Skip token for error recovery.
1663 getNextToken();
1664 }
1665}
1666
1667/// top ::= definition | external | expression | ';'
1668static void MainLoop() {
1669 while (1) {
1670 fprintf(stderr, "ready&gt; ");
1671 switch (CurTok) {
1672 case tok_eof: return;
1673 case ';': getNextToken(); break; // ignore top level semicolons.
1674 case tok_def: HandleDefinition(); break;
1675 case tok_extern: HandleExtern(); break;
1676 default: HandleTopLevelExpression(); break;
1677 }
1678 }
1679}
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1680
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1681
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1682
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1683//===----------------------------------------------------------------------===//
1684// "Library" functions that can be "extern'd" from user code.
1685//===----------------------------------------------------------------------===//
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1686
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1687/// putchard - putchar that takes a double and returns 0.
1688extern "C"
1689double putchard(double X) {
1690 putchar((char)X);
1691 return 0;
1692}
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1693
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1694//===----------------------------------------------------------------------===//
1695// Main driver code.
1696//===----------------------------------------------------------------------===//
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1697
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1698int main() {
1699 // Install standard binary operators.
1700 // 1 is lowest precedence.
1701 BinopPrecedence['&lt;'] = 10;
1702 BinopPrecedence['+'] = 20;
1703 BinopPrecedence['-'] = 20;
1704 BinopPrecedence['*'] = 40; // highest.
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1705
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1706 // Prime the first token.
1707 fprintf(stderr, "ready&gt; ");
1708 getNextToken();
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1709
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1710 // Make the module, which holds all the code.
1711 TheModule = new Module("my cool jit");
1712
1713 // Create the JIT.
1714 TheExecutionEngine = ExecutionEngine::create(TheModule);
1715
1716 {
1717 ExistingModuleProvider OurModuleProvider(TheModule);
1718 FunctionPassManager OurFPM(&amp;OurModuleProvider);
1719
1720 // Set up the optimizer pipeline. Start with registering info about how the
1721 // target lays out data structures.
1722 OurFPM.add(new TargetData(*TheExecutionEngine-&gt;getTargetData()));
1723 // Do simple "peephole" optimizations and bit-twiddling optzns.
1724 OurFPM.add(createInstructionCombiningPass());
1725 // Reassociate expressions.
1726 OurFPM.add(createReassociatePass());
1727 // Eliminate Common SubExpressions.
1728 OurFPM.add(createGVNPass());
1729 // Simplify the control flow graph (deleting unreachable blocks, etc).
1730 OurFPM.add(createCFGSimplificationPass());
1731 // Set the global so the code gen can use this.
1732 TheFPM = &amp;OurFPM;
1733
1734 // Run the main "interpreter loop" now.
1735 MainLoop();
1736
1737 TheFPM = 0;
Chris Lattner515686b2008-02-05 06:18:42 +0000[diff] [blame]1738
1739 // Print out all of the generated code.
1740 TheModule-&gt;dump();
1741 } // Free module provider (and thus the module) and pass manager.
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1742
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1743 return 0;
1744}
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1745</pre>
1746</div>
1747
Chris Lattner729eb142008-02-10 19:11:04 +0000[diff] [blame^]1748<a href="LangImpl6.html">Next: Extending the language: user-defined operators</a>
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