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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);
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]475 PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), "iftmp");
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]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();
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]730 BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]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.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]748 PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), VarName.c_str());
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]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.
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]799 StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]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,
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]818 ConstantFP::get(getGlobalContext(), APFloat(0.0)),
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]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();
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]831 BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]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.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]859 return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]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"
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame^]904#include "llvm/ExecutionEngine/Interpreter.h"
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"
908#include "llvm/ModuleProvider.h"
909#include "llvm/PassManager.h"
910#include "llvm/Analysis/Verifier.h"
911#include "llvm/Target/TargetData.h"
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame^]912#include "llvm/Target/TargetSelect.h"
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]913#include "llvm/Transforms/Scalar.h"
Duncan Sands89f6d882008-04-13 06:22:09 +0000[diff] [blame]914#include "llvm/Support/IRBuilder.h"
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]915#include &lt;cstdio&gt;
916#include &lt;string&gt;
917#include &lt;map&gt;
918#include &lt;vector&gt;
919using namespace llvm;
920
921//===----------------------------------------------------------------------===//
922// Lexer
923//===----------------------------------------------------------------------===//
924
925// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
926// of these for known things.
927enum Token {
928 tok_eof = -1,
929
930 // commands
931 tok_def = -2, tok_extern = -3,
932
933 // primary
934 tok_identifier = -4, tok_number = -5,
935
936 // control
937 tok_if = -6, tok_then = -7, tok_else = -8,
938 tok_for = -9, tok_in = -10
939};
940
941static std::string IdentifierStr; // Filled in if tok_identifier
942static double NumVal; // Filled in if tok_number
943
944/// gettok - Return the next token from standard input.
945static int gettok() {
946 static int LastChar = ' ';
947
948 // Skip any whitespace.
949 while (isspace(LastChar))
950 LastChar = getchar();
951
952 if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
953 IdentifierStr = LastChar;
954 while (isalnum((LastChar = getchar())))
955 IdentifierStr += LastChar;
956
957 if (IdentifierStr == "def") return tok_def;
958 if (IdentifierStr == "extern") return tok_extern;
959 if (IdentifierStr == "if") return tok_if;
960 if (IdentifierStr == "then") return tok_then;
961 if (IdentifierStr == "else") return tok_else;
962 if (IdentifierStr == "for") return tok_for;
963 if (IdentifierStr == "in") return tok_in;
964 return tok_identifier;
965 }
966
967 if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
968 std::string NumStr;
969 do {
970 NumStr += LastChar;
971 LastChar = getchar();
972 } while (isdigit(LastChar) || LastChar == '.');
973
974 NumVal = strtod(NumStr.c_str(), 0);
975 return tok_number;
976 }
977
978 if (LastChar == '#') {
979 // Comment until end of line.
980 do LastChar = getchar();
Chris Lattnerc80c23f2007-12-02 22:46:01 +0000[diff] [blame]981 while (LastChar != EOF &amp;&amp; LastChar != '\n' &amp;&amp; LastChar != '\r');
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]982
983 if (LastChar != EOF)
984 return gettok();
985 }
986
987 // Check for end of file. Don't eat the EOF.
988 if (LastChar == EOF)
989 return tok_eof;
990
991 // Otherwise, just return the character as its ascii value.
992 int ThisChar = LastChar;
993 LastChar = getchar();
994 return ThisChar;
995}
996
997//===----------------------------------------------------------------------===//
998// Abstract Syntax Tree (aka Parse Tree)
999//===----------------------------------------------------------------------===//
1000
1001/// ExprAST - Base class for all expression nodes.
1002class ExprAST {
1003public:
1004 virtual ~ExprAST() {}
1005 virtual Value *Codegen() = 0;
1006};
1007
1008/// NumberExprAST - Expression class for numeric literals like "1.0".
1009class NumberExprAST : public ExprAST {
1010 double Val;
1011public:
1012 NumberExprAST(double val) : Val(val) {}
1013 virtual Value *Codegen();
1014};
1015
1016/// VariableExprAST - Expression class for referencing a variable, like "a".
1017class VariableExprAST : public ExprAST {
1018 std::string Name;
1019public:
1020 VariableExprAST(const std::string &amp;name) : Name(name) {}
1021 virtual Value *Codegen();
1022};
1023
1024/// BinaryExprAST - Expression class for a binary operator.
1025class BinaryExprAST : public ExprAST {
1026 char Op;
1027 ExprAST *LHS, *RHS;
1028public:
1029 BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
1030 : Op(op), LHS(lhs), RHS(rhs) {}
1031 virtual Value *Codegen();
1032};
1033
1034/// CallExprAST - Expression class for function calls.
1035class CallExprAST : public ExprAST {
1036 std::string Callee;
1037 std::vector&lt;ExprAST*&gt; Args;
1038public:
1039 CallExprAST(const std::string &amp;callee, std::vector&lt;ExprAST*&gt; &amp;args)
1040 : Callee(callee), Args(args) {}
1041 virtual Value *Codegen();
1042};
1043
1044/// IfExprAST - Expression class for if/then/else.
1045class IfExprAST : public ExprAST {
1046 ExprAST *Cond, *Then, *Else;
1047public:
1048 IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
1049 : Cond(cond), Then(then), Else(_else) {}
1050 virtual Value *Codegen();
1051};
1052
1053/// ForExprAST - Expression class for for/in.
1054class ForExprAST : public ExprAST {
1055 std::string VarName;
1056 ExprAST *Start, *End, *Step, *Body;
1057public:
1058 ForExprAST(const std::string &amp;varname, ExprAST *start, ExprAST *end,
1059 ExprAST *step, ExprAST *body)
1060 : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
1061 virtual Value *Codegen();
1062};
1063
1064/// PrototypeAST - This class represents the "prototype" for a function,
1065/// which captures its argument names as well as if it is an operator.
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
1092/// token the parser it looking at. getNextToken reads another token from the
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);
1140
1141 if (CurTok == ')') break;
1142
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
1242
1243/// primary
1244/// ::= identifierexpr
1245/// ::= numberexpr
1246/// ::= parenexpr
1247/// ::= ifexpr
1248/// ::= forexpr
1249static ExprAST *ParsePrimary() {
1250 switch (CurTok) {
1251 default: return Error("unknown token when expecting an expression");
1252 case tok_identifier: return ParseIdentifierExpr();
1253 case tok_number: return ParseNumberExpr();
1254 case '(': return ParseParenExpr();
1255 case tok_if: return ParseIfExpr();
1256 case tok_for: return ParseForExpr();
1257 }
1258}
1259
1260/// binoprhs
1261/// ::= ('+' primary)*
1262static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
1263 // If this is a binop, find its precedence.
1264 while (1) {
1265 int TokPrec = GetTokPrecedence();
1266
1267 // If this is a binop that binds at least as tightly as the current binop,
1268 // consume it, otherwise we are done.
1269 if (TokPrec &lt; ExprPrec)
1270 return LHS;
1271
1272 // Okay, we know this is a binop.
1273 int BinOp = CurTok;
1274 getNextToken(); // eat binop
1275
1276 // Parse the primary expression after the binary operator.
1277 ExprAST *RHS = ParsePrimary();
1278 if (!RHS) return 0;
1279
1280 // If BinOp binds less tightly with RHS than the operator after RHS, let
1281 // the pending operator take RHS as its LHS.
1282 int NextPrec = GetTokPrecedence();
1283 if (TokPrec &lt; NextPrec) {
1284 RHS = ParseBinOpRHS(TokPrec+1, RHS);
1285 if (RHS == 0) return 0;
1286 }
1287
1288 // Merge LHS/RHS.
1289 LHS = new BinaryExprAST(BinOp, LHS, RHS);
1290 }
1291}
1292
1293/// expression
1294/// ::= primary binoprhs
1295///
1296static ExprAST *ParseExpression() {
1297 ExprAST *LHS = ParsePrimary();
1298 if (!LHS) return 0;
1299
1300 return ParseBinOpRHS(0, LHS);
1301}
1302
1303/// prototype
1304/// ::= id '(' id* ')'
1305static PrototypeAST *ParsePrototype() {
1306 if (CurTok != tok_identifier)
1307 return ErrorP("Expected function name in prototype");
1308
1309 std::string FnName = IdentifierStr;
1310 getNextToken();
1311
1312 if (CurTok != '(')
1313 return ErrorP("Expected '(' in prototype");
1314
1315 std::vector&lt;std::string&gt; ArgNames;
1316 while (getNextToken() == tok_identifier)
1317 ArgNames.push_back(IdentifierStr);
1318 if (CurTok != ')')
1319 return ErrorP("Expected ')' in prototype");
1320
1321 // success.
1322 getNextToken(); // eat ')'.
1323
1324 return new PrototypeAST(FnName, ArgNames);
1325}
1326
1327/// definition ::= 'def' prototype expression
1328static FunctionAST *ParseDefinition() {
1329 getNextToken(); // eat def.
1330 PrototypeAST *Proto = ParsePrototype();
1331 if (Proto == 0) return 0;
1332
1333 if (ExprAST *E = ParseExpression())
1334 return new FunctionAST(Proto, E);
1335 return 0;
1336}
1337
1338/// toplevelexpr ::= expression
1339static FunctionAST *ParseTopLevelExpr() {
1340 if (ExprAST *E = ParseExpression()) {
1341 // Make an anonymous proto.
1342 PrototypeAST *Proto = new PrototypeAST("", std::vector&lt;std::string&gt;());
1343 return new FunctionAST(Proto, E);
1344 }
1345 return 0;
1346}
1347
1348/// external ::= 'extern' prototype
1349static PrototypeAST *ParseExtern() {
1350 getNextToken(); // eat extern.
1351 return ParsePrototype();
1352}
1353
1354//===----------------------------------------------------------------------===//
1355// Code Generation
1356//===----------------------------------------------------------------------===//
1357
1358static Module *TheModule;
Owen Andersond1fbd142009-07-08 20:50:47 +0000[diff] [blame]1359static IRBuilder&lt;&gt; Builder(getGlobalContext());
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1360static std::map&lt;std::string, Value*&gt; NamedValues;
1361static FunctionPassManager *TheFPM;
1362
1363Value *ErrorV(const char *Str) { Error(Str); return 0; }
1364
1365Value *NumberExprAST::Codegen() {
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]1366 return ConstantFP::get(getGlobalContext(), APFloat(Val));
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1367}
1368
1369Value *VariableExprAST::Codegen() {
1370 // Look this variable up in the function.
1371 Value *V = NamedValues[Name];
1372 return V ? V : ErrorV("Unknown variable name");
1373}
1374
1375Value *BinaryExprAST::Codegen() {
1376 Value *L = LHS-&gt;Codegen();
1377 Value *R = RHS-&gt;Codegen();
1378 if (L == 0 || R == 0) return 0;
1379
1380 switch (Op) {
1381 case '+': return Builder.CreateAdd(L, R, "addtmp");
1382 case '-': return Builder.CreateSub(L, R, "subtmp");
1383 case '*': return Builder.CreateMul(L, R, "multmp");
1384 case '&lt;':
Chris Lattner71155212007-11-06 01:39:12 +0000[diff] [blame]1385 L = Builder.CreateFCmpULT(L, R, "cmptmp");
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1386 // Convert bool 0/1 to double 0.0 or 1.0
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame^]1387 return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
1388 "booltmp");
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1389 default: return ErrorV("invalid binary operator");
1390 }
1391}
1392
1393Value *CallExprAST::Codegen() {
1394 // Look up the name in the global module table.
1395 Function *CalleeF = TheModule-&gt;getFunction(Callee);
1396 if (CalleeF == 0)
1397 return ErrorV("Unknown function referenced");
1398
1399 // If argument mismatch error.
1400 if (CalleeF-&gt;arg_size() != Args.size())
1401 return ErrorV("Incorrect # arguments passed");
1402
1403 std::vector&lt;Value*&gt; ArgsV;
1404 for (unsigned i = 0, e = Args.size(); i != e; ++i) {
1405 ArgsV.push_back(Args[i]-&gt;Codegen());
1406 if (ArgsV.back() == 0) return 0;
1407 }
1408
1409 return Builder.CreateCall(CalleeF, ArgsV.begin(), ArgsV.end(), "calltmp");
1410}
1411
1412Value *IfExprAST::Codegen() {
1413 Value *CondV = Cond-&gt;Codegen();
1414 if (CondV == 0) return 0;
1415
1416 // Convert condition to a bool by comparing equal to 0.0.
1417 CondV = Builder.CreateFCmpONE(CondV,
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]1418 ConstantFP::get(getGlobalContext(), APFloat(0.0)),
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1419 "ifcond");
1420
1421 Function *TheFunction = Builder.GetInsertBlock()-&gt;getParent();
1422
1423 // Create blocks for the then and else cases. Insert the 'then' block at the
1424 // end of the function.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]1425 BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
1426 BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
1427 BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1428
1429 Builder.CreateCondBr(CondV, ThenBB, ElseBB);
1430
1431 // Emit then value.
1432 Builder.SetInsertPoint(ThenBB);
1433
1434 Value *ThenV = Then-&gt;Codegen();
1435 if (ThenV == 0) return 0;
1436
1437 Builder.CreateBr(MergeBB);
1438 // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
1439 ThenBB = Builder.GetInsertBlock();
1440
1441 // Emit else block.
1442 TheFunction-&gt;getBasicBlockList().push_back(ElseBB);
1443 Builder.SetInsertPoint(ElseBB);
1444
1445 Value *ElseV = Else-&gt;Codegen();
1446 if (ElseV == 0) return 0;
1447
1448 Builder.CreateBr(MergeBB);
1449 // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
1450 ElseBB = Builder.GetInsertBlock();
1451
1452 // Emit merge block.
1453 TheFunction-&gt;getBasicBlockList().push_back(MergeBB);
1454 Builder.SetInsertPoint(MergeBB);
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame^]1455 PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()),
1456 "iftmp");
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1457
1458 PN-&gt;addIncoming(ThenV, ThenBB);
1459 PN-&gt;addIncoming(ElseV, ElseBB);
1460 return PN;
1461}
1462
1463Value *ForExprAST::Codegen() {
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1464 // Output this as:
1465 // ...
1466 // start = startexpr
1467 // goto loop
1468 // loop:
1469 // variable = phi [start, loopheader], [nextvariable, loopend]
1470 // ...
1471 // bodyexpr
1472 // ...
1473 // loopend:
1474 // step = stepexpr
1475 // nextvariable = variable + step
1476 // endcond = endexpr
1477 // br endcond, loop, endloop
1478 // outloop:
1479
1480 // Emit the start code first, without 'variable' in scope.
1481 Value *StartVal = Start-&gt;Codegen();
1482 if (StartVal == 0) return 0;
1483
1484 // Make the new basic block for the loop header, inserting after current
1485 // block.
1486 Function *TheFunction = Builder.GetInsertBlock()-&gt;getParent();
1487 BasicBlock *PreheaderBB = Builder.GetInsertBlock();
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]1488 BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1489
1490 // Insert an explicit fall through from the current block to the LoopBB.
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1491 Builder.CreateBr(LoopBB);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1492
1493 // Start insertion in LoopBB.
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1494 Builder.SetInsertPoint(LoopBB);
1495
1496 // Start the PHI node with an entry for Start.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]1497 PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), VarName.c_str());
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1498 Variable-&gt;addIncoming(StartVal, PreheaderBB);
1499
1500 // Within the loop, the variable is defined equal to the PHI node. If it
1501 // shadows an existing variable, we have to restore it, so save it now.
1502 Value *OldVal = NamedValues[VarName];
1503 NamedValues[VarName] = Variable;
1504
1505 // Emit the body of the loop. This, like any other expr, can change the
1506 // current BB. Note that we ignore the value computed by the body, but don't
1507 // allow an error.
1508 if (Body-&gt;Codegen() == 0)
1509 return 0;
1510
1511 // Emit the step value.
1512 Value *StepVal;
1513 if (Step) {
1514 StepVal = Step-&gt;Codegen();
1515 if (StepVal == 0) return 0;
1516 } else {
1517 // If not specified, use 1.0.
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]1518 StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1519 }
1520
1521 Value *NextVar = Builder.CreateAdd(Variable, StepVal, "nextvar");
1522
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1523 // Compute the end condition.
1524 Value *EndCond = End-&gt;Codegen();
1525 if (EndCond == 0) return EndCond;
1526
1527 // Convert condition to a bool by comparing equal to 0.0.
1528 EndCond = Builder.CreateFCmpONE(EndCond,
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]1529 ConstantFP::get(getGlobalContext(), APFloat(0.0)),
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1530 "loopcond");
1531
1532 // Create the "after loop" block and insert it.
1533 BasicBlock *LoopEndBB = Builder.GetInsertBlock();
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]1534 BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1535
1536 // Insert the conditional branch into the end of LoopEndBB.
1537 Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
1538
1539 // Any new code will be inserted in AfterBB.
1540 Builder.SetInsertPoint(AfterBB);
1541
1542 // Add a new entry to the PHI node for the backedge.
1543 Variable-&gt;addIncoming(NextVar, LoopEndBB);
1544
1545 // Restore the unshadowed variable.
1546 if (OldVal)
1547 NamedValues[VarName] = OldVal;
1548 else
1549 NamedValues.erase(VarName);
1550
1551
1552 // for expr always returns 0.0.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]1553 return getGlobalContext().getNullValue(Type::getDoubleTy(getGlobalContext()));
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1554}
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1555
1556Function *PrototypeAST::Codegen() {
1557 // Make the function type: double(double,double) etc.
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame^]1558 std::vector&lt;const Type*&gt; Doubles(Args.size(),
1559 Type::getDoubleTy(getGlobalContext()));
1560 FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
1561 Doubles, false);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1562
Gabor Greifdf7d2b42008-04-19 22:25:09 +0000[diff] [blame]1563 Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1564
1565 // If F conflicted, there was already something named 'Name'. If it has a
1566 // body, don't allow redefinition or reextern.
1567 if (F-&gt;getName() != Name) {
1568 // Delete the one we just made and get the existing one.
1569 F-&gt;eraseFromParent();
1570 F = TheModule-&gt;getFunction(Name);
1571
1572 // If F already has a body, reject this.
1573 if (!F-&gt;empty()) {
1574 ErrorF("redefinition of function");
1575 return 0;
1576 }
1577
1578 // If F took a different number of args, reject.
1579 if (F-&gt;arg_size() != Args.size()) {
1580 ErrorF("redefinition of function with different # args");
1581 return 0;
1582 }
1583 }
1584
1585 // Set names for all arguments.
1586 unsigned Idx = 0;
1587 for (Function::arg_iterator AI = F-&gt;arg_begin(); Idx != Args.size();
1588 ++AI, ++Idx) {
1589 AI-&gt;setName(Args[Idx]);
1590
1591 // Add arguments to variable symbol table.
1592 NamedValues[Args[Idx]] = AI;
1593 }
1594
1595 return F;
1596}
1597
1598Function *FunctionAST::Codegen() {
1599 NamedValues.clear();
1600
1601 Function *TheFunction = Proto-&gt;Codegen();
1602 if (TheFunction == 0)
1603 return 0;
1604
1605 // Create a new basic block to start insertion into.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]1606 BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1607 Builder.SetInsertPoint(BB);
1608
1609 if (Value *RetVal = Body-&gt;Codegen()) {
1610 // Finish off the function.
1611 Builder.CreateRet(RetVal);
1612
1613 // Validate the generated code, checking for consistency.
1614 verifyFunction(*TheFunction);
1615
1616 // Optimize the function.
1617 TheFPM-&gt;run(*TheFunction);
1618
1619 return TheFunction;
1620 }
1621
1622 // Error reading body, remove function.
1623 TheFunction-&gt;eraseFromParent();
1624 return 0;
1625}
1626
1627//===----------------------------------------------------------------------===//
1628// Top-Level parsing and JIT Driver
1629//===----------------------------------------------------------------------===//
1630
1631static ExecutionEngine *TheExecutionEngine;
1632
1633static void HandleDefinition() {
1634 if (FunctionAST *F = ParseDefinition()) {
1635 if (Function *LF = F-&gt;Codegen()) {
1636 fprintf(stderr, "Read function definition:");
1637 LF-&gt;dump();
1638 }
1639 } else {
1640 // Skip token for error recovery.
1641 getNextToken();
1642 }
1643}
1644
1645static void HandleExtern() {
1646 if (PrototypeAST *P = ParseExtern()) {
1647 if (Function *F = P-&gt;Codegen()) {
1648 fprintf(stderr, "Read extern: ");
1649 F-&gt;dump();
1650 }
1651 } else {
1652 // Skip token for error recovery.
1653 getNextToken();
1654 }
1655}
1656
1657static void HandleTopLevelExpression() {
1658 // Evaluate a top level expression into an anonymous function.
1659 if (FunctionAST *F = ParseTopLevelExpr()) {
1660 if (Function *LF = F-&gt;Codegen()) {
1661 // JIT the function, returning a function pointer.
1662 void *FPtr = TheExecutionEngine-&gt;getPointerToFunction(LF);
1663
1664 // Cast it to the right type (takes no arguments, returns a double) so we
1665 // can call it as a native function.
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame^]1666 double (*FP)() = (double (*)())(intptr_t)FPtr;
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1667 fprintf(stderr, "Evaluated to %f\n", FP());
1668 }
1669 } else {
1670 // Skip token for error recovery.
1671 getNextToken();
1672 }
1673}
1674
1675/// top ::= definition | external | expression | ';'
1676static void MainLoop() {
1677 while (1) {
1678 fprintf(stderr, "ready&gt; ");
1679 switch (CurTok) {
1680 case tok_eof: return;
1681 case ';': getNextToken(); break; // ignore top level semicolons.
1682 case tok_def: HandleDefinition(); break;
1683 case tok_extern: HandleExtern(); break;
1684 default: HandleTopLevelExpression(); break;
1685 }
1686 }
1687}
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]1688
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1689
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1690
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1691//===----------------------------------------------------------------------===//
1692// "Library" functions that can be "extern'd" from user code.
1693//===----------------------------------------------------------------------===//
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1694
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1695/// putchard - putchar that takes a double and returns 0.
1696extern "C"
1697double putchard(double X) {
1698 putchar((char)X);
1699 return 0;
1700}
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1701
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1702//===----------------------------------------------------------------------===//
1703// Main driver code.
1704//===----------------------------------------------------------------------===//
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1705
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1706int main() {
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.
Owen Andersond1fbd142009-07-08 20:50:47 +0000[diff] [blame]1719 TheModule = new Module("my cool jit", getGlobalContext());
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1720
Reid Kleckner60130f02009-08-26 20:58:25 +0000[diff] [blame]1721 ExistingModuleProvider *OurModuleProvider =
1722 new ExistingModuleProvider(TheModule);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1723
Reid Kleckner60130f02009-08-26 20:58:25 +0000[diff] [blame]1724 // Create the JIT. This takes ownership of the module and module provider.
1725 TheExecutionEngine = EngineBuilder(OurModuleProvider).create();
Chris Lattner515686b2008-02-05 06:18:42 +0000[diff] [blame]1726
Reid Kleckner60130f02009-08-26 20:58:25 +0000[diff] [blame]1727 FunctionPassManager OurFPM(OurModuleProvider);
1728
1729 // Set up the optimizer pipeline. Start with registering info about how the
1730 // target lays out data structures.
1731 OurFPM.add(new TargetData(*TheExecutionEngine-&gt;getTargetData()));
1732 // Do simple "peephole" optimizations and bit-twiddling optzns.
1733 OurFPM.add(createInstructionCombiningPass());
1734 // Reassociate expressions.
1735 OurFPM.add(createReassociatePass());
1736 // Eliminate Common SubExpressions.
1737 OurFPM.add(createGVNPass());
1738 // Simplify the control flow graph (deleting unreachable blocks, etc).
1739 OurFPM.add(createCFGSimplificationPass());
1740
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame^]1741 OurFPM.doInitialization();
1742
Reid Kleckner60130f02009-08-26 20:58:25 +0000[diff] [blame]1743 // Set the global so the code gen can use this.
1744 TheFPM = &amp;OurFPM;
1745
1746 // Run the main "interpreter loop" now.
1747 MainLoop();
1748
1749 TheFPM = 0;
1750
1751 // Print out all of the generated code.
1752 TheModule-&gt;dump();
1753
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1754 return 0;
1755}
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1756</pre>
1757</div>
1758
Chris Lattner729eb142008-02-10 19:11:04 +0000[diff] [blame]1759<a href="LangImpl6.html">Next: Extending the language: user-defined operators</a>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1760</div>
1761
1762<!-- *********************************************************************** -->
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1770 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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