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4<html>
5<head>
6 <title>Kaleidoscope: Extending the Language: Control Flow</title>
7 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
8 <meta name="author" content="Chris Lattner">
9 <link rel="stylesheet" href="../llvm.css" type="text/css">
10</head>
11
12<body>
13
14<div class="doc_title">Kaleidoscope: Extending the Language: Control Flow</div>
15
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]16<ul>
Chris Lattner0e555b12007-11-05 20:04:56 +0000[diff] [blame]17<li><a href="index.html">Up to Tutorial Index</a></li>
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]18<li>Chapter 5
19 <ol>
20 <li><a href="#intro">Chapter 5 Introduction</a></li>
21 <li><a href="#ifthen">If/Then/Else</a>
22 <ol>
23 <li><a href="#iflexer">Lexer Extensions</a></li>
24 <li><a href="#ifast">AST Extensions</a></li>
25 <li><a href="#ifparser">Parser Extensions</a></li>
26 <li><a href="#ifir">LLVM IR</a></li>
27 <li><a href="#ifcodegen">Code Generation</a></li>
28 </ol>
29 </li>
30 <li><a href="#for">'for' Loop Expression</a>
31 <ol>
32 <li><a href="#forlexer">Lexer Extensions</a></li>
33 <li><a href="#forast">AST Extensions</a></li>
34 <li><a href="#forparser">Parser Extensions</a></li>
35 <li><a href="#forir">LLVM IR</a></li>
36 <li><a href="#forcodegen">Code Generation</a></li>
37 </ol>
38 </li>
39 <li><a href="#code">Full Code Listing</a></li>
40 </ol>
41</li>
Chris Lattner0e555b12007-11-05 20:04:56 +0000[diff] [blame]42<li><a href="LangImpl6.html">Chapter 6</a>: Extending the Language:
43User-defined Operators</li>
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]44</ul>
45
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]46<div class="doc_author">
47 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
48</div>
49
50<!-- *********************************************************************** -->
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]51<div class="doc_section"><a name="intro">Chapter 5 Introduction</a></div>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]52<!-- *********************************************************************** -->
53
54<div class="doc_text">
55
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]56<p>Welcome to Chapter 5 of the "<a href="index.html">Implementing a language
57with LLVM</a>" tutorial. Parts 1-4 described the implementation of the simple
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]58Kaleidoscope language and included support for generating LLVM IR, followed by
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]59optimizations and a JIT compiler. Unfortunately, as presented, Kaleidoscope is
60mostly useless: it has no control flow other than call and return. This means
61that you can't have conditional branches in the code, significantly limiting its
62power. In this episode of "build that compiler", we'll extend Kaleidoscope to
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]63have an if/then/else expression plus a simple 'for' loop.</p>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]64
65</div>
66
67<!-- *********************************************************************** -->
68<div class="doc_section"><a name="ifthen">If/Then/Else</a></div>
69<!-- *********************************************************************** -->
70
71<div class="doc_text">
72
73<p>
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]74Extending Kaleidoscope to support if/then/else is quite straightforward. It
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]75basically requires adding lexer support for this "new" concept to the lexer,
76parser, AST, and LLVM code emitter. This example is nice, because it shows how
77easy it is to "grow" a language over time, incrementally extending it as new
78ideas are discovered.</p>
79
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]80<p>Before we get going on "how" we add this extension, lets talk about "what" we
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]81want. The basic idea is that we want to be able to write this sort of thing:
82</p>
83
84<div class="doc_code">
85<pre>
86def fib(x)
87 if x &lt; 3 then
88 1
89 else
90 fib(x-1)+fib(x-2);
91</pre>
92</div>
93
94<p>In Kaleidoscope, every construct is an expression: there are no statements.
95As such, the if/then/else expression needs to return a value like any other.
96Since we're using a mostly functional form, we'll have it evaluate its
97conditional, then return the 'then' or 'else' value based on how the condition
98was resolved. This is very similar to the C "?:" expression.</p>
99
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]100<p>The semantics of the if/then/else expression is that it evaluates the
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]101condition to a boolean equality value: 0.0 is considered to be false and
102everything else is considered to be true.
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]103If the condition is true, the first subexpression is evaluated and returned, if
104the condition is false, the second subexpression is evaluated and returned.
105Since Kaleidoscope allows side-effects, this behavior is important to nail down.
106</p>
107
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]108<p>Now that we know what we "want", lets break this down into its constituent
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]109pieces.</p>
110
111</div>
112
113<!-- ======================================================================= -->
114<div class="doc_subsubsection"><a name="iflexer">Lexer Extensions for
115If/Then/Else</a></div>
116<!-- ======================================================================= -->
117
118
119<div class="doc_text">
120
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]121<p>The lexer extensions are straightforward. First we add new enum values
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]122for the relevant tokens:</p>
123
124<div class="doc_code">
125<pre>
126 // control
127 tok_if = -6, tok_then = -7, tok_else = -8,
128</pre>
129</div>
130
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]131<p>Once we have that, we recognize the new keywords in the lexer. This is pretty simple
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]132stuff:</p>
133
134<div class="doc_code">
135<pre>
136 ...
137 if (IdentifierStr == "def") return tok_def;
138 if (IdentifierStr == "extern") return tok_extern;
139 <b>if (IdentifierStr == "if") return tok_if;
140 if (IdentifierStr == "then") return tok_then;
141 if (IdentifierStr == "else") return tok_else;</b>
142 return tok_identifier;
143</pre>
144</div>
145
146</div>
147
148<!-- ======================================================================= -->
149<div class="doc_subsubsection"><a name="ifast">AST Extensions for
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]150 If/Then/Else</a></div>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]151<!-- ======================================================================= -->
152
153<div class="doc_text">
154
155<p>To represent the new expression we add a new AST node for it:</p>
156
157<div class="doc_code">
158<pre>
159/// IfExprAST - Expression class for if/then/else.
160class IfExprAST : public ExprAST {
161 ExprAST *Cond, *Then, *Else;
162public:
163 IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
164 : Cond(cond), Then(then), Else(_else) {}
165 virtual Value *Codegen();
166};
167</pre>
168</div>
169
170<p>The AST node just has pointers to the various subexpressions.</p>
171
172</div>
173
174<!-- ======================================================================= -->
175<div class="doc_subsubsection"><a name="ifparser">Parser Extensions for
Chris Lattner128eb862007-11-05 19:06:59 +0000[diff] [blame]176If/Then/Else</a></div>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]177<!-- ======================================================================= -->
178
179<div class="doc_text">
180
181<p>Now that we have the relevant tokens coming from the lexer and we have the
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]182AST node to build, our parsing logic is relatively straightforward. First we
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]183define a new parsing function:</p>
184
185<div class="doc_code">
186<pre>
187/// ifexpr ::= 'if' expression 'then' expression 'else' expression
188static ExprAST *ParseIfExpr() {
189 getNextToken(); // eat the if.
190
191 // condition.
192 ExprAST *Cond = ParseExpression();
193 if (!Cond) return 0;
194
195 if (CurTok != tok_then)
196 return Error("expected then");
197 getNextToken(); // eat the then
198
199 ExprAST *Then = ParseExpression();
200 if (Then == 0) return 0;
201
202 if (CurTok != tok_else)
203 return Error("expected else");
204
205 getNextToken();
206
207 ExprAST *Else = ParseExpression();
208 if (!Else) return 0;
209
210 return new IfExprAST(Cond, Then, Else);
211}
212</pre>
213</div>
214
215<p>Next we hook it up as a primary expression:</p>
216
217<div class="doc_code">
218<pre>
219static ExprAST *ParsePrimary() {
220 switch (CurTok) {
221 default: return Error("unknown token when expecting an expression");
222 case tok_identifier: return ParseIdentifierExpr();
223 case tok_number: return ParseNumberExpr();
224 case '(': return ParseParenExpr();
225 <b>case tok_if: return ParseIfExpr();</b>
226 }
227}
228</pre>
229</div>
230
231</div>
232
233<!-- ======================================================================= -->
234<div class="doc_subsubsection"><a name="ifir">LLVM IR for If/Then/Else</a></div>
235<!-- ======================================================================= -->
236
237<div class="doc_text">
238
239<p>Now that we have it parsing and building the AST, the final piece is adding
240LLVM code generation support. This is the most interesting part of the
241if/then/else example, because this is where it starts to introduce new concepts.
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]242All of the code above has been thoroughly described in previous chapters.
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]243</p>
244
245<p>To motivate the code we want to produce, lets take a look at a simple
246example. Consider:</p>
247
248<div class="doc_code">
249<pre>
250extern foo();
251extern bar();
252def baz(x) if x then foo() else bar();
253</pre>
254</div>
255
256<p>If you disable optimizations, the code you'll (soon) get from Kaleidoscope
257looks like this:</p>
258
259<div class="doc_code">
260<pre>
261declare double @foo()
262
263declare double @bar()
264
265define double @baz(double %x) {
266entry:
267 %ifcond = fcmp one double %x, 0.000000e+00
268 br i1 %ifcond, label %then, label %else
269
270then: ; preds = %entry
271 %calltmp = call double @foo()
272 br label %ifcont
273
274else: ; preds = %entry
275 %calltmp1 = call double @bar()
276 br label %ifcont
277
278ifcont: ; preds = %else, %then
279 %iftmp = phi double [ %calltmp, %then ], [ %calltmp1, %else ]
280 ret double %iftmp
281}
282</pre>
283</div>
284
285<p>To visualize the control flow graph, you can use a nifty feature of the LLVM
286'<a href="http://llvm.org/cmds/opt.html">opt</a>' tool. If you put this LLVM IR
287into "t.ll" and run "<tt>llvm-as &lt; t.ll | opt -analyze -view-cfg</tt>", <a
288href="../ProgrammersManual.html#ViewGraph">a window will pop up</a> and you'll
289see this graph:</p>
290
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]291<div style="text-align: center"><img src="LangImpl5-cfg.png" alt="Example CFG" width="423"
292height="315"></div>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]293
294<p>Another way to get this is to call "<tt>F-&gt;viewCFG()</tt>" or
295"<tt>F-&gt;viewCFGOnly()</tt>" (where F is a "<tt>Function*</tt>") either by
296inserting actual calls into the code and recompiling or by calling these in the
297debugger. LLVM has many nice features for visualizing various graphs.</p>
298
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]299<p>Getting back to the generated code, it is fairly simple: the entry block
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]300evaluates the conditional expression ("x" in our case here) and compares the
301result to 0.0 with the "<tt><a href="../LangRef.html#i_fcmp">fcmp</a> one</tt>"
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]302instruction ('one' is "Ordered and Not Equal"). Based on the result of this
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]303expression, the code jumps to either the "then" or "else" blocks, which contain
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]304the expressions for the true/false cases.</p>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]305
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]306<p>Once the then/else blocks are finished executing, they both branch back to the
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]307'ifcont' block to execute the code that happens after the if/then/else. In this
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]308case the only thing left to do is to return to the caller of the function. The
309question then becomes: how does the code know which expression to return?</p>
310
311<p>The answer to this question involves an important SSA operation: the
312<a href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Phi
313operation</a>. If you're not familiar with SSA, <a
314href="http://en.wikipedia.org/wiki/Static_single_assignment_form">the wikipedia
315article</a> is a good introduction and there are various other introductions to
316it available on your favorite search engine. The short version is that
317"execution" of the Phi operation requires "remembering" which block control came
318from. The Phi operation takes on the value corresponding to the input control
319block. In this case, if control comes in from the "then" block, it gets the
320value of "calltmp". If control comes from the "else" block, it gets the value
321of "calltmp1".</p>
322
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]323<p>At this point, you are probably starting to think "Oh no! This means my
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]324simple and elegant front-end will have to start generating SSA form in order to
325use LLVM!". Fortunately, this is not the case, and we strongly advise
326<em>not</em> implementing an SSA construction algorithm in your front-end
327unless there is an amazingly good reason to do so. In practice, there are two
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]328sorts of values that float around in code written for your average imperative
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]329programming language that might need Phi nodes:</p>
330
331<ol>
332<li>Code that involves user variables: <tt>x = 1; x = x + 1; </tt></li>
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]333<li>Values that are implicit in the structure of your AST, such as the Phi node
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]334in this case.</li>
335</ol>
336
Chris Lattnerb0f0deb2007-11-05 07:02:49 +0000[diff] [blame]337<p>In <a href="LangImpl7.html">Chapter 7</a> of this tutorial ("mutable
338variables"), we'll talk about #1
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]339in depth. For now, just believe me that you don't need SSA construction to
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]340handle this case. For #2, you have the choice of using the techniques that we will
341describe for #1, or you can insert Phi nodes directly, if convenient. In this
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]342case, it is really really easy to generate the Phi node, so we choose to do it
343directly.</p>
344
345<p>Okay, enough of the motivation and overview, lets generate code!</p>
346
347</div>
348
349<!-- ======================================================================= -->
350<div class="doc_subsubsection"><a name="ifcodegen">Code Generation for
351If/Then/Else</a></div>
352<!-- ======================================================================= -->
353
354<div class="doc_text">
355
356<p>In order to generate code for this, we implement the <tt>Codegen</tt> method
357for <tt>IfExprAST</tt>:</p>
358
359<div class="doc_code">
360<pre>
361Value *IfExprAST::Codegen() {
362 Value *CondV = Cond-&gt;Codegen();
363 if (CondV == 0) return 0;
364
365 // Convert condition to a bool by comparing equal to 0.0.
366 CondV = Builder.CreateFCmpONE(CondV,
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]367 ConstantFP::get(getGlobalContext(), APFloat(0.0)),
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]368 "ifcond");
369</pre>
370</div>
371
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]372<p>This code is straightforward and similar to what we saw before. We emit the
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]373expression for the condition, then compare that value to zero to get a truth
374value as a 1-bit (bool) value.</p>
375
376<div class="doc_code">
377<pre>
378 Function *TheFunction = Builder.GetInsertBlock()-&gt;getParent();
379
380 // Create blocks for the then and else cases. Insert the 'then' block at the
381 // end of the function.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]382 BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
383 BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
384 BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]385
386 Builder.CreateCondBr(CondV, ThenBB, ElseBB);
387</pre>
388</div>
389
390<p>This code creates the basic blocks that are related to the if/then/else
391statement, and correspond directly to the blocks in the example above. The
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]392first line gets the current Function object that is being built. It
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]393gets this by asking the builder for the current BasicBlock, and asking that
394block for its "parent" (the function it is currently embedded into).</p>
395
396<p>Once it has that, it creates three blocks. Note that it passes "TheFunction"
397into the constructor for the "then" block. This causes the constructor to
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]398automatically insert the new block into the end of the specified function. The
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]399other two blocks are created, but aren't yet inserted into the function.</p>
400
401<p>Once the blocks are created, we can emit the conditional branch that chooses
402between them. Note that creating new blocks does not implicitly affect the
Duncan Sands89f6d882008-04-13 06:22:09 +0000[diff] [blame]403IRBuilder, so it is still inserting into the block that the condition
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]404went into. Also note that it is creating a branch to the "then" block and the
405"else" block, even though the "else" block isn't inserted into the function yet.
406This is all ok: it is the standard way that LLVM supports forward
407references.</p>
408
409<div class="doc_code">
410<pre>
411 // Emit then value.
412 Builder.SetInsertPoint(ThenBB);
413
414 Value *ThenV = Then-&gt;Codegen();
415 if (ThenV == 0) return 0;
416
417 Builder.CreateBr(MergeBB);
418 // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
419 ThenBB = Builder.GetInsertBlock();
420</pre>
421</div>
422
423<p>After the conditional branch is inserted, we move the builder to start
424inserting into the "then" block. Strictly speaking, this call moves the
425insertion point to be at the end of the specified block. However, since the
426"then" block is empty, it also starts out by inserting at the beginning of the
427block. :)</p>
428
429<p>Once the insertion point is set, we recursively codegen the "then" expression
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]430from the AST. To finish off the "then" block, we create an unconditional branch
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]431to the merge block. One interesting (and very important) aspect of the LLVM IR
432is that it <a href="../LangRef.html#functionstructure">requires all basic blocks
433to be "terminated"</a> with a <a href="../LangRef.html#terminators">control flow
434instruction</a> such as return or branch. This means that all control flow,
435<em>including fall throughs</em> must be made explicit in the LLVM IR. If you
436violate this rule, the verifier will emit an error.</p>
437
438<p>The final line here is quite subtle, but is very important. The basic issue
439is that when we create the Phi node in the merge block, we need to set up the
440block/value pairs that indicate how the Phi will work. Importantly, the Phi
Chris Lattnerb5019642007-11-05 17:52:04 +0000[diff] [blame]441node expects to have an entry for each predecessor of the block in the CFG. Why
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]442then, are we getting the current block when we just set it to ThenBB 5 lines
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]443above? The problem is that the "Then" expression may actually itself change the
444block that the Builder is emitting into if, for example, it contains a nested
445"if/then/else" expression. Because calling Codegen recursively could
446arbitrarily change the notion of the current block, we are required to get an
447up-to-date value for code that will set up the Phi node.</p>
448
449<div class="doc_code">
450<pre>
451 // Emit else block.
452 TheFunction-&gt;getBasicBlockList().push_back(ElseBB);
453 Builder.SetInsertPoint(ElseBB);
454
455 Value *ElseV = Else-&gt;Codegen();
456 if (ElseV == 0) return 0;
457
458 Builder.CreateBr(MergeBB);
459 // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
460 ElseBB = Builder.GetInsertBlock();
461</pre>
462</div>
463
464<p>Code generation for the 'else' block is basically identical to codegen for
465the 'then' block. The only significant difference is the first line, which adds
466the 'else' block to the function. Recall previously that the 'else' block was
467created, but not added to the function. Now that the 'then' and 'else' blocks
468are emitted, we can finish up with the merge code:</p>
469
470<div class="doc_code">
471<pre>
472 // Emit merge block.
473 TheFunction->getBasicBlockList().push_back(MergeBB);
474 Builder.SetInsertPoint(MergeBB);
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]475 PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()),
476 "iftmp");
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]477
478 PN->addIncoming(ThenV, ThenBB);
479 PN->addIncoming(ElseV, ElseBB);
480 return PN;
481}
482</pre>
483</div>
484
485<p>The first two lines here are now familiar: the first adds the "merge" block
486to the Function object (it was previously floating, like the else block above).
487The second block changes the insertion point so that newly created code will go
488into the "merge" block. Once that is done, we need to create the PHI node and
489set up the block/value pairs for the PHI.</p>
490
491<p>Finally, the CodeGen function returns the phi node as the value computed by
492the if/then/else expression. In our example above, this returned value will
493feed into the code for the top-level function, which will create the return
494instruction.</p>
495
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]496<p>Overall, we now have the ability to execute conditional code in
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]497Kaleidoscope. With this extension, Kaleidoscope is a fairly complete language
498that can calculate a wide variety of numeric functions. Next up we'll add
499another useful expression that is familiar from non-functional languages...</p>
500
501</div>
502
503<!-- *********************************************************************** -->
504<div class="doc_section"><a name="for">'for' Loop Expression</a></div>
505<!-- *********************************************************************** -->
506
507<div class="doc_text">
508
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]509<p>Now that we know how to add basic control flow constructs to the language,
510we have the tools to add more powerful things. Lets add something more
511aggressive, a 'for' expression:</p>
512
513<div class="doc_code">
514<pre>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]515 extern putchard(char)
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]516 def printstar(n)
517 for i = 1, i &lt; n, 1.0 in
518 putchard(42); # ascii 42 = '*'
519
520 # print 100 '*' characters
521 printstar(100);
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]522</pre>
523</div>
524
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]525<p>This expression defines a new variable ("i" in this case) which iterates from
526a starting value, while the condition ("i &lt; n" in this case) is true,
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]527incrementing by an optional step value ("1.0" in this case). If the step value
528is omitted, it defaults to 1.0. While the loop is true, it executes its
529body expression. Because we don't have anything better to return, we'll just
530define the loop as always returning 0.0. In the future when we have mutable
531variables, it will get more useful.</p>
532
533<p>As before, lets talk about the changes that we need to Kaleidoscope to
534support this.</p>
535
536</div>
537
538<!-- ======================================================================= -->
539<div class="doc_subsubsection"><a name="forlexer">Lexer Extensions for
540the 'for' Loop</a></div>
541<!-- ======================================================================= -->
542
543<div class="doc_text">
544
545<p>The lexer extensions are the same sort of thing as for if/then/else:</p>
546
547<div class="doc_code">
548<pre>
549 ... in enum Token ...
550 // control
551 tok_if = -6, tok_then = -7, tok_else = -8,
552<b> tok_for = -9, tok_in = -10</b>
553
554 ... in gettok ...
555 if (IdentifierStr == "def") return tok_def;
556 if (IdentifierStr == "extern") return tok_extern;
557 if (IdentifierStr == "if") return tok_if;
558 if (IdentifierStr == "then") return tok_then;
559 if (IdentifierStr == "else") return tok_else;
560 <b>if (IdentifierStr == "for") return tok_for;
561 if (IdentifierStr == "in") return tok_in;</b>
562 return tok_identifier;
563</pre>
564</div>
565
566</div>
567
568<!-- ======================================================================= -->
569<div class="doc_subsubsection"><a name="forast">AST Extensions for
570the 'for' Loop</a></div>
571<!-- ======================================================================= -->
572
573<div class="doc_text">
574
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]575<p>The AST node is just as simple. It basically boils down to capturing
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]576the variable name and the constituent expressions in the node.</p>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]577
578<div class="doc_code">
579<pre>
580/// ForExprAST - Expression class for for/in.
581class ForExprAST : public ExprAST {
582 std::string VarName;
583 ExprAST *Start, *End, *Step, *Body;
584public:
585 ForExprAST(const std::string &amp;varname, ExprAST *start, ExprAST *end,
586 ExprAST *step, ExprAST *body)
587 : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
588 virtual Value *Codegen();
589};
590</pre>
591</div>
592
593</div>
594
595<!-- ======================================================================= -->
596<div class="doc_subsubsection"><a name="forparser">Parser Extensions for
597the 'for' Loop</a></div>
598<!-- ======================================================================= -->
599
600<div class="doc_text">
601
602<p>The parser code is also fairly standard. The only interesting thing here is
603handling of the optional step value. The parser code handles it by checking to
604see if the second comma is present. If not, it sets the step value to null in
605the AST node:</p>
606
607<div class="doc_code">
608<pre>
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]609/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]610static ExprAST *ParseForExpr() {
611 getNextToken(); // eat the for.
612
613 if (CurTok != tok_identifier)
614 return Error("expected identifier after for");
615
616 std::string IdName = IdentifierStr;
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]617 getNextToken(); // eat identifier.
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]618
619 if (CurTok != '=')
620 return Error("expected '=' after for");
621 getNextToken(); // eat '='.
622
623
624 ExprAST *Start = ParseExpression();
625 if (Start == 0) return 0;
626 if (CurTok != ',')
627 return Error("expected ',' after for start value");
628 getNextToken();
629
630 ExprAST *End = ParseExpression();
631 if (End == 0) return 0;
632
633 // The step value is optional.
634 ExprAST *Step = 0;
635 if (CurTok == ',') {
636 getNextToken();
637 Step = ParseExpression();
638 if (Step == 0) return 0;
639 }
640
641 if (CurTok != tok_in)
642 return Error("expected 'in' after for");
643 getNextToken(); // eat 'in'.
644
645 ExprAST *Body = ParseExpression();
646 if (Body == 0) return 0;
647
648 return new ForExprAST(IdName, Start, End, Step, Body);
649}
650</pre>
651</div>
652
653</div>
654
655<!-- ======================================================================= -->
656<div class="doc_subsubsection"><a name="forir">LLVM IR for
657the 'for' Loop</a></div>
658<!-- ======================================================================= -->
659
660<div class="doc_text">
661
662<p>Now we get to the good part: the LLVM IR we want to generate for this thing.
Gordon Henriksenbb310f12007-11-12 13:46:21 +0000[diff] [blame]663With the simple example above, we get this LLVM IR (note that this dump is
664generated with optimizations disabled for clarity):
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]665</p>
666
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]667<div class="doc_code">
668<pre>
669declare double @putchard(double)
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]670
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]671define double @printstar(double %n) {
672entry:
673 ; initial value = 1.0 (inlined into phi)
674 br label %loop
675
676loop: ; preds = %loop, %entry
677 %i = phi double [ 1.000000e+00, %entry ], [ %nextvar, %loop ]
678 ; body
679 %calltmp = call double @putchard( double 4.200000e+01 )
680 ; increment
681 %nextvar = add double %i, 1.000000e+00
682
683 ; termination test
Chris Lattner71155212007-11-06 01:39:12 +0000[diff] [blame]684 %cmptmp = fcmp ult double %i, %n
685 %booltmp = uitofp i1 %cmptmp to double
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]686 %loopcond = fcmp one double %booltmp, 0.000000e+00
687 br i1 %loopcond, label %loop, label %afterloop
688
689afterloop: ; preds = %loop
690 ; loop always returns 0.0
691 ret double 0.000000e+00
692}
693</pre>
694</div>
695
696<p>This loop contains all the same constructs we saw before: a phi node, several
697expressions, and some basic blocks. Lets see how this fits together.</p>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]698
699</div>
700
701<!-- ======================================================================= -->
702<div class="doc_subsubsection"><a name="forcodegen">Code Generation for
703the 'for' Loop</a></div>
704<!-- ======================================================================= -->
705
706<div class="doc_text">
707
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]708<p>The first part of Codegen is very simple: we just output the start expression
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]709for the loop value:</p>
Chris Lattnerf5234802007-10-31 06:47:39 +0000[diff] [blame]710
711<div class="doc_code">
712<pre>
713Value *ForExprAST::Codegen() {
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]714 // Emit the start code first, without 'variable' in scope.
715 Value *StartVal = Start-&gt;Codegen();
716 if (StartVal == 0) return 0;
717</pre>
718</div>
719
720<p>With this out of the way, the next step is to set up the LLVM basic block
721for the start of the loop body. In the case above, the whole loop body is one
722block, but remember that the body code itself could consist of multiple blocks
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]723(e.g. if it contains an if/then/else or a for/in expression).</p>
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]724
725<div class="doc_code">
726<pre>
727 // Make the new basic block for the loop header, inserting after current
728 // block.
729 Function *TheFunction = Builder.GetInsertBlock()-&gt;getParent();
730 BasicBlock *PreheaderBB = Builder.GetInsertBlock();
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]731 BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]732
733 // Insert an explicit fall through from the current block to the LoopBB.
734 Builder.CreateBr(LoopBB);
735</pre>
736</div>
737
738<p>This code is similar to what we saw for if/then/else. Because we will need
739it to create the Phi node, we remember the block that falls through into the
740loop. Once we have that, we create the actual block that starts the loop and
741create an unconditional branch for the fall-through between the two blocks.</p>
742
743<div class="doc_code">
744<pre>
745 // Start insertion in LoopBB.
746 Builder.SetInsertPoint(LoopBB);
747
748 // Start the PHI node with an entry for Start.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]749 PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), VarName.c_str());
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]750 Variable-&gt;addIncoming(StartVal, PreheaderBB);
751</pre>
752</div>
753
754<p>Now that the "preheader" for the loop is set up, we switch to emitting code
755for the loop body. To begin with, we move the insertion point and create the
Chris Lattner1092a962007-11-07 05:47:48 +0000[diff] [blame]756PHI node for the loop induction variable. Since we already know the incoming
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]757value for the starting value, we add it to the Phi node. Note that the Phi will
758eventually get a second value for the backedge, but we can't set it up yet
759(because it doesn't exist!).</p>
760
761<div class="doc_code">
762<pre>
763 // Within the loop, the variable is defined equal to the PHI node. If it
764 // shadows an existing variable, we have to restore it, so save it now.
765 Value *OldVal = NamedValues[VarName];
766 NamedValues[VarName] = Variable;
767
768 // Emit the body of the loop. This, like any other expr, can change the
769 // current BB. Note that we ignore the value computed by the body, but don't
770 // allow an error.
771 if (Body-&gt;Codegen() == 0)
772 return 0;
773</pre>
774</div>
775
776<p>Now the code starts to get more interesting. Our 'for' loop introduces a new
777variable to the symbol table. This means that our symbol table can now contain
778either function arguments or loop variables. To handle this, before we codegen
779the body of the loop, we add the loop variable as the current value for its
780name. Note that it is possible that there is a variable of the same name in the
781outer scope. It would be easy to make this an error (emit an error and return
782null if there is already an entry for VarName) but we choose to allow shadowing
783of variables. In order to handle this correctly, we remember the Value that
784we are potentially shadowing in <tt>OldVal</tt> (which will be null if there is
785no shadowed variable).</p>
786
787<p>Once the loop variable is set into the symbol table, the code recursively
788codegen's the body. This allows the body to use the loop variable: any
789references to it will naturally find it in the symbol table.</p>
790
791<div class="doc_code">
792<pre>
793 // Emit the step value.
794 Value *StepVal;
795 if (Step) {
796 StepVal = Step-&gt;Codegen();
797 if (StepVal == 0) return 0;
798 } else {
799 // If not specified, use 1.0.
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]800 StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]801 }
802
803 Value *NextVar = Builder.CreateAdd(Variable, StepVal, "nextvar");
804</pre>
805</div>
806
807<p>Now that the body is emitted, we compute the next value of the iteration
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]808variable by adding the step value, or 1.0 if it isn't present. '<tt>NextVar</tt>'
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]809will be the value of the loop variable on the next iteration of the loop.</p>
810
811<div class="doc_code">
812<pre>
813 // Compute the end condition.
814 Value *EndCond = End-&gt;Codegen();
815 if (EndCond == 0) return EndCond;
816
817 // Convert condition to a bool by comparing equal to 0.0.
818 EndCond = Builder.CreateFCmpONE(EndCond,
Owen Anderson6f83c9c2009-07-27 20:59:43 +0000[diff] [blame]819 ConstantFP::get(getGlobalContext(), APFloat(0.0)),
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]820 "loopcond");
821</pre>
822</div>
823
824<p>Finally, we evaluate the exit value of the loop, to determine whether the
825loop should exit. This mirrors the condition evaluation for the if/then/else
826statement.</p>
827
828<div class="doc_code">
829<pre>
830 // Create the "after loop" block and insert it.
831 BasicBlock *LoopEndBB = Builder.GetInsertBlock();
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]832 BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]833
834 // Insert the conditional branch into the end of LoopEndBB.
835 Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
836
837 // Any new code will be inserted in AfterBB.
838 Builder.SetInsertPoint(AfterBB);
839</pre>
840</div>
841
842<p>With the code for the body of the loop complete, we just need to finish up
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]843the control flow for it. This code remembers the end block (for the phi node), then creates the block for the loop exit ("afterloop"). Based on the value of the
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]844exit condition, it creates a conditional branch that chooses between executing
845the loop again and exiting the loop. Any future code is emitted in the
846"afterloop" block, so it sets the insertion position to it.</p>
847
848<div class="doc_code">
849<pre>
850 // Add a new entry to the PHI node for the backedge.
851 Variable-&gt;addIncoming(NextVar, LoopEndBB);
852
853 // Restore the unshadowed variable.
854 if (OldVal)
855 NamedValues[VarName] = OldVal;
856 else
857 NamedValues.erase(VarName);
858
859 // for expr always returns 0.0.
Owen Anderson1d0be152009-08-13 21:58:54 +0000[diff] [blame]860 return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]861}
862</pre>
863</div>
864
865<p>The final code handles various cleanups: now that we have the "NextVar"
866value, we can add the incoming value to the loop PHI node. After that, we
867remove the loop variable from the symbol table, so that it isn't in scope after
868the for loop. Finally, code generation of the for loop always returns 0.0, so
869that is what we return from <tt>ForExprAST::Codegen</tt>.</p>
870
871<p>With this, we conclude the "adding control flow to Kaleidoscope" chapter of
Chris Lattner41fcea32007-11-13 07:06:30 +0000[diff] [blame]872the tutorial. In this chapter we added two control flow constructs, and used them to motivate a couple of aspects of the LLVM IR that are important for front-end implementors
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]873to know. In the next chapter of our saga, we will get a bit crazier and add
Chris Lattner71155212007-11-06 01:39:12 +0000[diff] [blame]874<a href="LangImpl6.html">user-defined operators</a> to our poor innocent
875language.</p>
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]876
877</div>
878
879<!-- *********************************************************************** -->
880<div class="doc_section"><a name="code">Full Code Listing</a></div>
881<!-- *********************************************************************** -->
882
883<div class="doc_text">
884
885<p>
886Here is the complete code listing for our running example, enhanced with the
887if/then/else and for expressions.. To build this example, use:
888</p>
889
890<div class="doc_code">
891<pre>
892 # Compile
893 g++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
894 # Run
895 ./toy
896</pre>
897</div>
898
899<p>Here is the code:</p>
900
901<div class="doc_code">
902<pre>
903#include "llvm/DerivedTypes.h"
904#include "llvm/ExecutionEngine/ExecutionEngine.h"
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame]905#include "llvm/ExecutionEngine/Interpreter.h"
906#include "llvm/ExecutionEngine/JIT.h"
Owen Andersond1fbd142009-07-08 20:50:47 +0000[diff] [blame]907#include "llvm/LLVMContext.h"
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]908#include "llvm/Module.h"
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]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,
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1065/// which captures its name, and its argument names (thus implicitly the number
1066/// of arguments the function takes).
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1067class PrototypeAST {
1068 std::string Name;
1069 std::vector&lt;std::string&gt; Args;
1070public:
1071 PrototypeAST(const std::string &amp;name, const std::vector&lt;std::string&gt; &amp;args)
1072 : Name(name), Args(args) {}
1073
1074 Function *Codegen();
1075};
1076
1077/// FunctionAST - This class represents a function definition itself.
1078class FunctionAST {
1079 PrototypeAST *Proto;
1080 ExprAST *Body;
1081public:
1082 FunctionAST(PrototypeAST *proto, ExprAST *body)
1083 : Proto(proto), Body(body) {}
1084
1085 Function *Codegen();
1086};
1087
1088//===----------------------------------------------------------------------===//
1089// Parser
1090//===----------------------------------------------------------------------===//
1091
1092/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1093/// token the parser is looking at. getNextToken reads another token from the
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1094/// lexer and updates CurTok with its results.
1095static int CurTok;
1096static int getNextToken() {
1097 return CurTok = gettok();
1098}
1099
1100/// BinopPrecedence - This holds the precedence for each binary operator that is
1101/// defined.
1102static std::map&lt;char, int&gt; BinopPrecedence;
1103
1104/// GetTokPrecedence - Get the precedence of the pending binary operator token.
1105static int GetTokPrecedence() {
1106 if (!isascii(CurTok))
1107 return -1;
1108
1109 // Make sure it's a declared binop.
1110 int TokPrec = BinopPrecedence[CurTok];
1111 if (TokPrec &lt;= 0) return -1;
1112 return TokPrec;
1113}
1114
1115/// Error* - These are little helper functions for error handling.
1116ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
1117PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
1118FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
1119
1120static ExprAST *ParseExpression();
1121
1122/// identifierexpr
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1123/// ::= identifier
1124/// ::= identifier '(' expression* ')'
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1125static ExprAST *ParseIdentifierExpr() {
1126 std::string IdName = IdentifierStr;
1127
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1128 getNextToken(); // eat identifier.
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1129
1130 if (CurTok != '(') // Simple variable ref.
1131 return new VariableExprAST(IdName);
1132
1133 // Call.
1134 getNextToken(); // eat (
1135 std::vector&lt;ExprAST*&gt; Args;
1136 if (CurTok != ')') {
1137 while (1) {
1138 ExprAST *Arg = ParseExpression();
1139 if (!Arg) return 0;
1140 Args.push_back(Arg);
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1141
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1142 if (CurTok == ')') break;
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1143
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1144 if (CurTok != ',')
Chris Lattner6c4be9c2008-04-14 16:44:41 +0000[diff] [blame]1145 return Error("Expected ')' or ',' in argument list");
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1146 getNextToken();
1147 }
1148 }
1149
1150 // Eat the ')'.
1151 getNextToken();
1152
1153 return new CallExprAST(IdName, Args);
1154}
1155
1156/// numberexpr ::= number
1157static ExprAST *ParseNumberExpr() {
1158 ExprAST *Result = new NumberExprAST(NumVal);
1159 getNextToken(); // consume the number
1160 return Result;
1161}
1162
1163/// parenexpr ::= '(' expression ')'
1164static ExprAST *ParseParenExpr() {
1165 getNextToken(); // eat (.
1166 ExprAST *V = ParseExpression();
1167 if (!V) return 0;
1168
1169 if (CurTok != ')')
1170 return Error("expected ')'");
1171 getNextToken(); // eat ).
1172 return V;
1173}
1174
1175/// ifexpr ::= 'if' expression 'then' expression 'else' expression
1176static ExprAST *ParseIfExpr() {
1177 getNextToken(); // eat the if.
1178
1179 // condition.
1180 ExprAST *Cond = ParseExpression();
1181 if (!Cond) return 0;
1182
1183 if (CurTok != tok_then)
1184 return Error("expected then");
1185 getNextToken(); // eat the then
1186
1187 ExprAST *Then = ParseExpression();
1188 if (Then == 0) return 0;
1189
1190 if (CurTok != tok_else)
1191 return Error("expected else");
1192
1193 getNextToken();
1194
1195 ExprAST *Else = ParseExpression();
1196 if (!Else) return 0;
1197
1198 return new IfExprAST(Cond, Then, Else);
1199}
1200
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1201/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1202static ExprAST *ParseForExpr() {
1203 getNextToken(); // eat the for.
1204
1205 if (CurTok != tok_identifier)
1206 return Error("expected identifier after for");
1207
1208 std::string IdName = IdentifierStr;
Chris Lattner20a0c802007-11-05 17:54:34 +0000[diff] [blame]1209 getNextToken(); // eat identifier.
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1210
1211 if (CurTok != '=')
1212 return Error("expected '=' after for");
1213 getNextToken(); // eat '='.
1214
1215
1216 ExprAST *Start = ParseExpression();
1217 if (Start == 0) return 0;
1218 if (CurTok != ',')
1219 return Error("expected ',' after for start value");
1220 getNextToken();
1221
1222 ExprAST *End = ParseExpression();
1223 if (End == 0) return 0;
1224
1225 // The step value is optional.
1226 ExprAST *Step = 0;
1227 if (CurTok == ',') {
1228 getNextToken();
1229 Step = ParseExpression();
1230 if (Step == 0) return 0;
1231 }
1232
1233 if (CurTok != tok_in)
1234 return Error("expected 'in' after for");
1235 getNextToken(); // eat 'in'.
1236
1237 ExprAST *Body = ParseExpression();
1238 if (Body == 0) return 0;
1239
1240 return new ForExprAST(IdName, Start, End, Step, Body);
1241}
1242
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]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.
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1553 return Constant::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() {
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1658 // Evaluate a top-level expression into an anonymous function.
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]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;
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1681 case ';': getNextToken(); break; // ignore top-level semicolons.
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]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 Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1689//===----------------------------------------------------------------------===//
1690// "Library" functions that can be "extern'd" from user code.
1691//===----------------------------------------------------------------------===//
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1692
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1693/// putchard - putchar that takes a double and returns 0.
1694extern "C"
1695double putchard(double X) {
1696 putchar((char)X);
1697 return 0;
1698}
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1699
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1700//===----------------------------------------------------------------------===//
1701// Main driver code.
1702//===----------------------------------------------------------------------===//
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1703
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1704int main() {
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1705 InitializeNativeTarget();
1706 LLVMContext &amp;Context = getGlobalContext();
1707
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1708 // Install standard binary operators.
1709 // 1 is lowest precedence.
1710 BinopPrecedence['&lt;'] = 10;
1711 BinopPrecedence['+'] = 20;
1712 BinopPrecedence['-'] = 20;
1713 BinopPrecedence['*'] = 40; // highest.
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1714
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1715 // Prime the first token.
1716 fprintf(stderr, "ready&gt; ");
1717 getNextToken();
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1718
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1719 // Make the module, which holds all the code.
Erick Tryzelaarfd1ec5e2009-09-22 21:14:49 +0000[diff] [blame]1720 TheModule = new Module("my cool jit", Context);
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1721
Jeffrey Yasskinf0356fe2010-01-27 20:34:15 +0000[diff] [blame]1722 // Create the JIT. This takes ownership of the module.
1723 TheExecutionEngine = EngineBuilder(TheModule).create();
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1724
Jeffrey Yasskinf0356fe2010-01-27 20:34:15 +0000[diff] [blame]1725 FunctionPassManager OurFPM(TheModule);
Reid Kleckner60130f02009-08-26 20:58:25 +0000[diff] [blame]1726
1727 // Set up the optimizer pipeline. Start with registering info about how the
1728 // target lays out data structures.
1729 OurFPM.add(new TargetData(*TheExecutionEngine-&gt;getTargetData()));
1730 // Do simple "peephole" optimizations and bit-twiddling optzns.
1731 OurFPM.add(createInstructionCombiningPass());
1732 // Reassociate expressions.
1733 OurFPM.add(createReassociatePass());
1734 // Eliminate Common SubExpressions.
1735 OurFPM.add(createGVNPass());
1736 // Simplify the control flow graph (deleting unreachable blocks, etc).
1737 OurFPM.add(createCFGSimplificationPass());
1738
Nick Lewycky422094c2009-09-13 21:38:54 +0000[diff] [blame]1739 OurFPM.doInitialization();
1740
Reid Kleckner60130f02009-08-26 20:58:25 +0000[diff] [blame]1741 // Set the global so the code gen can use this.
1742 TheFPM = &amp;OurFPM;
1743
1744 // Run the main "interpreter loop" now.
1745 MainLoop();
1746
1747 TheFPM = 0;
1748
1749 // Print out all of the generated code.
1750 TheModule-&gt;dump();
1751
Chris Lattner6093bd52007-10-31 07:29:43 +0000[diff] [blame]1752 return 0;
1753}
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1754</pre>
1755</div>
1756
Chris Lattner729eb142008-02-10 19:11:04 +0000[diff] [blame]1757<a href="LangImpl6.html">Next: Extending the language: user-defined operators</a>
Chris Lattner602c832c2007-10-31 06:30:21 +0000[diff] [blame]1758</div>
1759
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1768 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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