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5 <head>
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12 <body>
16 <ul>
19 <ol>
22 <ol>
28 </ol>
29 </li>
31 <ol>
37 </ol>
38 </li>
40 </ol>
41 </li>
43 User-defined Operators</li>
44 </ul>
48 </div>
50 <!-- *********************************************************************** -->
52 <!-- *********************************************************************** -->
58 Kaleidoscope language and included support for generating LLVM IR, followed by
59 optimizations and a JIT compiler. Unfortunately, as presented, Kaleidoscope is
60 mostly useless: it has no control flow other than call and return. This means
61 that you can't have conditional branches in the code, significantly limiting its
62 power. In this episode of "build that compiler", we'll extend Kaleidoscope to
63 have an if/then/else expression plus a simple 'for' loop.</p>
65 </div>
67 <!-- *********************************************************************** -->
69 <!-- *********************************************************************** -->
73 <p>
74 Extending Kaleidoscope to support if/then/else is quite straightforward. It
75 basically requires adding lexer support for this "new" concept to the lexer,
76 parser, AST, and LLVM code emitter. This example is nice, because it shows how
77 easy it is to "grow" a language over time, incrementally extending it as new
78 ideas are discovered.</p>
81 want. The basic idea is that we want to be able to write this sort of thing:
82 </p>
85 <pre>
86 def fib(x)
88 1
89 else
91 </pre>
92 </div>
94 <p>In Kaleidoscope, every construct is an expression: there are no statements.
95 As such, the if/then/else expression needs to return a value like any other.
96 Since we're using a mostly functional form, we'll have it evaluate its
97 conditional, then return the 'then' or 'else' value based on how the condition
100 <p>The semantics of the if/then/else expression is that it evaluates the
101 condition to a boolean equality value: 0.0 is considered to be false and
102 everything else is considered to be true.
103 If the condition is true, the first subexpression is evaluated and returned, if
104 the condition is false, the second subexpression is evaluated and returned.
105 Since Kaleidoscope allows side-effects, this behavior is important to nail down.
106 </p>
109 pieces.</p>
111 </div>
113 <!-- ======================================================================= -->
115 If/Then/Else</a></div>
116 <!-- ======================================================================= -->
121 <p>The lexer extensions are straightforward. First we add new enum values
122 for the relevant tokens:</p>
125 <pre>
126 // control
128 </pre>
129 </div>
131 <p>Once we have that, we recognize the new keywords in the lexer. This is pretty simple
132 stuff:</p>
135 <pre>
136 ...
137 if (IdentifierStr == "def") return tok_def;
138 if (IdentifierStr == "extern") return tok_extern;
140 if (IdentifierStr == "then") return tok_then;
142 return tok_identifier;
143 </pre>
144 </div>
146 </div>
148 <!-- ======================================================================= -->
150 If/Then/Else</a></div>
151 <!-- ======================================================================= -->
158 <pre>
159 /// IfExprAST - Expression class for if/then/else.
160 class IfExprAST : public ExprAST {
161 ExprAST *Cond, *Then, *Else;
162 public:
163 IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
164 : Cond(cond), Then(then), Else(_else) {}
165 virtual Value *Codegen();
166 };
167 </pre>
168 </div>
172 </div>
174 <!-- ======================================================================= -->
176 If/Then/Else</a></div>
177 <!-- ======================================================================= -->
181 <p>Now that we have the relevant tokens coming from the lexer and we have the
182 AST node to build, our parsing logic is relatively straightforward. First we
183 define a new parsing function:</p>
186 <pre>
187 /// ifexpr ::= 'if' expression 'then' expression 'else' expression
188 static ExprAST *ParseIfExpr() {
189 getNextToken(); // eat the if.
191 // condition.
192 ExprAST *Cond = ParseExpression();
193 if (!Cond) return 0;
195 if (CurTok != tok_then)
196 return Error("expected then");
197 getNextToken(); // eat the then
199 ExprAST *Then = ParseExpression();
202 if (CurTok != tok_else)
203 return Error("expected else");
205 getNextToken();
207 ExprAST *Else = ParseExpression();
208 if (!Else) return 0;
210 return new IfExprAST(Cond, Then, Else);
211 }
212 </pre>
213 </div>
218 <pre>
219 static 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();
226 }
227 }
228 </pre>
229 </div>
231 </div>
233 <!-- ======================================================================= -->
235 <!-- ======================================================================= -->
239 <p>Now that we have it parsing and building the AST, the final piece is adding
240 LLVM code generation support. This is the most interesting part of the
241 if/then/else example, because this is where it starts to introduce new concepts.
242 All of the code above has been thoroughly described in previous chapters.
243 </p>
245 <p>To motivate the code we want to produce, lets take a look at a simple
246 example. Consider:</p>
249 <pre>
250 extern foo();
251 extern bar();
252 def baz(x) if x then foo() else bar();
253 </pre>
254 </div>
256 <p>If you disable optimizations, the code you'll (soon) get from Kaleidoscope
257 looks like this:</p>
260 <pre>
261 declare double @foo()
263 declare double @bar()
265 define double @baz(double %x) {
266 entry:
267 %ifcond = fcmp one double %x, 0.000000e+00
268 br i1 %ifcond, label %then, label %else
270 then: ; preds = %entry
271 %calltmp = call double @foo()
272 br label %ifcont
274 else: ; preds = %entry
275 %calltmp1 = call double @bar()
276 br label %ifcont
278 ifcont: ; preds = %else, %then
279 %iftmp = phi double [ %calltmp, %then ], [ %calltmp1, %else ]
280 ret double %iftmp
281 }
282 </pre>
283 </div>
285 <p>To visualize the control flow graph, you can use a nifty feature of the LLVM
289 see this graph:</p>
296 inserting actual calls into the code and recompiling or by calling these in the
297 debugger. LLVM has many nice features for visualizing various graphs.</p>
299 <p>Getting back to the generated code, it is fairly simple: the entry block
300 evaluates the conditional expression ("x" in our case here) and compares the
302 instruction ('one' is "Ordered and Not Equal"). Based on the result of this
304 the expressions for the true/false cases.</p>
306 <p>Once the then/else blocks are finished executing, they both branch back to the
307 'ifcont' block to execute the code that happens after the if/then/else. In this
308 case the only thing left to do is to return to the caller of the function. The
309 question then becomes: how does the code know which expression to return?</p>
311 <p>The answer to this question involves an important SSA operation: the
315 article</a> is a good introduction and there are various other introductions to
316 it available on your favorite search engine. The short version is that
318 from. The Phi operation takes on the value corresponding to the input control
319 block. In this case, if control comes in from the "then" block, it gets the
324 simple and elegant front-end will have to start generating SSA form in order to
325 use LLVM!". Fortunately, this is not the case, and we strongly advise
327 unless there is an amazingly good reason to do so. In practice, there are two
328 sorts of values that float around in code written for your average imperative
329 programming language that might need Phi nodes:</p>
331 <ol>
333 <li>Values that are implicit in the structure of your AST, such as the Phi node
334 in this case.</li>
335 </ol>
339 in depth. For now, just believe me that you don't need SSA construction to
340 handle this case. For #2, you have the choice of using the techniques that we will
341 describe for #1, or you can insert Phi nodes directly, if convenient. In this
342 case, it is really really easy to generate the Phi node, so we choose to do it
343 directly.</p>
347 </div>
349 <!-- ======================================================================= -->
351 If/Then/Else</a></div>
352 <!-- ======================================================================= -->
360 <pre>
361 Value *IfExprAST::Codegen() {
362 Value *CondV = Cond->Codegen();
365 // Convert condition to a bool by comparing equal to 0.0.
366 CondV = Builder.CreateFCmpONE(CondV,
367 ConstantFP::get(APFloat(0.0)),
368 "ifcond");
369 </pre>
370 </div>
372 <p>This code is straightforward and similar to what we saw before. We emit the
373 expression for the condition, then compare that value to zero to get a truth
377 <pre>
378 Function *TheFunction = Builder.GetInsertBlock()->getParent();
380 // Create blocks for the then and else cases. Insert the 'then' block at the
381 // end of the function.
382 BasicBlock *ThenBB = BasicBlock::Create("then", TheFunction);
383 BasicBlock *ElseBB = BasicBlock::Create("else");
384 BasicBlock *MergeBB = BasicBlock::Create("ifcont");
386 Builder.CreateCondBr(CondV, ThenBB, ElseBB);
387 </pre>
388 </div>
390 <p>This code creates the basic blocks that are related to the if/then/else
391 statement, and correspond directly to the blocks in the example above. The
392 first line gets the current Function object that is being built. It
393 gets this by asking the builder for the current BasicBlock, and asking that
397 into the constructor for the "then" block. This causes the constructor to
398 automatically insert the new block into the end of the specified function. The
399 other two blocks are created, but aren't yet inserted into the function.</p>
401 <p>Once the blocks are created, we can emit the conditional branch that chooses
402 between them. Note that creating new blocks does not implicitly affect the
403 IRBuilder, so it is still inserting into the block that the condition
404 went into. Also note that it is creating a branch to the "then" block and the
406 This is all ok: it is the standard way that LLVM supports forward
407 references.</p>
410 <pre>
411 // Emit then value.
412 Builder.SetInsertPoint(ThenBB);
414 Value *ThenV = Then->Codegen();
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>
423 <p>After the conditional branch is inserted, we move the builder to start
424 inserting into the "then" block. Strictly speaking, this call moves the
425 insertion 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
427 block. :)</p>
430 from the AST. To finish off the "then" block, we create an unconditional branch
431 to the merge block. One interesting (and very important) aspect of the LLVM IR
434 instruction</a> such as return or branch. This means that all control flow,
436 violate this rule, the verifier will emit an error.</p>
438 <p>The final line here is quite subtle, but is very important. The basic issue
439 is that when we create the Phi node in the merge block, we need to set up the
440 block/value pairs that indicate how the Phi will work. Importantly, the Phi
441 node expects to have an entry for each predecessor of the block in the CFG. Why
442 then, are we getting the current block when we just set it to ThenBB 5 lines
443 above? The problem is that the "Then" expression may actually itself change the
444 block that the Builder is emitting into if, for example, it contains a nested
445 "if/then/else" expression. Because calling Codegen recursively could
446 arbitrarily change the notion of the current block, we are required to get an
447 up-to-date value for code that will set up the Phi node.</p>
450 <pre>
451 // Emit else block.
452 TheFunction->getBasicBlockList().push_back(ElseBB);
453 Builder.SetInsertPoint(ElseBB);
455 Value *ElseV = Else->Codegen();
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>
464 <p>Code generation for the 'else' block is basically identical to codegen for
465 the 'then' block. The only significant difference is the first line, which adds
466 the 'else' block to the function. Recall previously that the 'else' block was
467 created, but not added to the function. Now that the 'then' and 'else' blocks
468 are emitted, we can finish up with the merge code:</p>
471 <pre>
472 // Emit merge block.
473 TheFunction->getBasicBlockList().push_back(MergeBB);
474 Builder.SetInsertPoint(MergeBB);
475 PHINode *PN = Builder.CreatePHI(Type::DoubleTy, "iftmp");
477 PN->addIncoming(ThenV, ThenBB);
478 PN->addIncoming(ElseV, ElseBB);
479 return PN;
480 }
481 </pre>
482 </div>
485 to the Function object (it was previously floating, like the else block above).
486 The second block changes the insertion point so that newly created code will go
487 into the "merge" block. Once that is done, we need to create the PHI node and
488 set up the block/value pairs for the PHI.</p>
490 <p>Finally, the CodeGen function returns the phi node as the value computed by
491 the if/then/else expression. In our example above, this returned value will
492 feed into the code for the top-level function, which will create the return
493 instruction.</p>
495 <p>Overall, we now have the ability to execute conditional code in
496 Kaleidoscope. With this extension, Kaleidoscope is a fairly complete language
497 that can calculate a wide variety of numeric functions. Next up we'll add
498 another useful expression that is familiar from non-functional languages...</p>
500 </div>
502 <!-- *********************************************************************** -->
504 <!-- *********************************************************************** -->
508 <p>Now that we know how to add basic control flow constructs to the language,
509 we have the tools to add more powerful things. Lets add something more
510 aggressive, a 'for' expression:</p>
513 <pre>
514 extern putchard(char)
515 def printstar(n)
519 # print 100 '*' characters
520 printstar(100);
521 </pre>
522 </div>
525 a starting value, while the condition ("i < n" in this case) is true,
526 incrementing by an optional step value ("1.0" in this case). If the step value
527 is omitted, it defaults to 1.0. While the loop is true, it executes its
528 body expression. Because we don't have anything better to return, we'll just
529 define the loop as always returning 0.0. In the future when we have mutable
530 variables, it will get more useful.</p>
532 <p>As before, lets talk about the changes that we need to Kaleidoscope to
533 support this.</p>
535 </div>
537 <!-- ======================================================================= -->
539 the 'for' Loop</a></div>
540 <!-- ======================================================================= -->
547 <pre>
548 ... in enum Token ...
549 // control
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;
561 return tok_identifier;
562 </pre>
563 </div>
565 </div>
567 <!-- ======================================================================= -->
569 the 'for' Loop</a></div>
570 <!-- ======================================================================= -->
574 <p>The AST node is just as simple. It basically boils down to capturing
575 the variable name and the constituent expressions in the node.</p>
578 <pre>
579 /// ForExprAST - Expression class for for/in.
580 class ForExprAST : public ExprAST {
581 std::string VarName;
582 ExprAST *Start, *End, *Step, *Body;
583 public:
584 ForExprAST(const std::string &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>
592 </div>
594 <!-- ======================================================================= -->
596 the 'for' Loop</a></div>
597 <!-- ======================================================================= -->
601 <p>The parser code is also fairly standard. The only interesting thing here is
602 handling of the optional step value. The parser code handles it by checking to
603 see if the second comma is present. If not, it sets the step value to null in
604 the AST node:</p>
607 <pre>
608 /// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
609 static ExprAST *ParseForExpr() {
610 getNextToken(); // eat the for.
612 if (CurTok != tok_identifier)
613 return Error("expected identifier after for");
615 std::string IdName = IdentifierStr;
616 getNextToken(); // eat identifier.
618 if (CurTok != '=')
619 return Error("expected '=' after for");
620 getNextToken(); // eat '='.
623 ExprAST *Start = ParseExpression();
625 if (CurTok != ',')
626 return Error("expected ',' after for start value");
627 getNextToken();
629 ExprAST *End = ParseExpression();
632 // The step value is optional.
633 ExprAST *Step = 0;
634 if (CurTok == ',') {
635 getNextToken();
636 Step = ParseExpression();
638 }
640 if (CurTok != tok_in)
641 return Error("expected 'in' after for");
642 getNextToken(); // eat 'in'.
644 ExprAST *Body = ParseExpression();
647 return new ForExprAST(IdName, Start, End, Step, Body);
648 }
649 </pre>
650 </div>
652 </div>
654 <!-- ======================================================================= -->
656 the 'for' Loop</a></div>
657 <!-- ======================================================================= -->
661 <p>Now we get to the good part: the LLVM IR we want to generate for this thing.
662 With the simple example above, we get this LLVM IR (note that this dump is
663 generated with optimizations disabled for clarity):
664 </p>
667 <pre>
668 declare double @putchard(double)
670 define double @printstar(double %n) {
671 entry:
672 ; initial value = 1.0 (inlined into phi)
673 br label %loop
675 loop: ; 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
682 ; termination test
683 %cmptmp = fcmp ult double %i, %n
684 %booltmp = uitofp i1 %cmptmp to double
685 %loopcond = fcmp one double %booltmp, 0.000000e+00
686 br i1 %loopcond, label %loop, label %afterloop
688 afterloop: ; preds = %loop
689 ; loop always returns 0.0
690 ret double 0.000000e+00
691 }
692 </pre>
693 </div>
695 <p>This loop contains all the same constructs we saw before: a phi node, several
696 expressions, and some basic blocks. Lets see how this fits together.</p>
698 </div>
700 <!-- ======================================================================= -->
702 the 'for' Loop</a></div>
703 <!-- ======================================================================= -->
707 <p>The first part of Codegen is very simple: we just output the start expression
708 for the loop value:</p>
711 <pre>
712 Value *ForExprAST::Codegen() {
713 // Emit the start code first, without 'variable' in scope.
714 Value *StartVal = Start->Codegen();
716 </pre>
717 </div>
719 <p>With this out of the way, the next step is to set up the LLVM basic block
720 for the start of the loop body. In the case above, the whole loop body is one
721 block, but remember that the body code itself could consist of multiple blocks
722 (e.g. if it contains an if/then/else or a for/in expression).</p>
725 <pre>
726 // Make the new basic block for the loop header, inserting after current
727 // block.
728 Function *TheFunction = Builder.GetInsertBlock()->getParent();
729 BasicBlock *PreheaderBB = Builder.GetInsertBlock();
730 BasicBlock *LoopBB = BasicBlock::Create("loop", TheFunction);
732 // Insert an explicit fall through from the current block to the LoopBB.
733 Builder.CreateBr(LoopBB);
734 </pre>
735 </div>
737 <p>This code is similar to what we saw for if/then/else. Because we will need
738 it to create the Phi node, we remember the block that falls through into the
739 loop. Once we have that, we create the actual block that starts the loop and
740 create an unconditional branch for the fall-through between the two blocks.</p>
743 <pre>
744 // Start insertion in LoopBB.
745 Builder.SetInsertPoint(LoopBB);
747 // Start the PHI node with an entry for Start.
748 PHINode *Variable = Builder.CreatePHI(Type::DoubleTy, VarName.c_str());
749 Variable->addIncoming(StartVal, PreheaderBB);
750 </pre>
751 </div>
754 for the loop body. To begin with, we move the insertion point and create the
755 PHI node for the loop induction variable. Since we already know the incoming
756 value for the starting value, we add it to the Phi node. Note that the Phi will
757 eventually get a second value for the backedge, but we can't set it up yet
758 (because it doesn't exist!).</p>
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;
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.
771 return 0;
772 </pre>
773 </div>
775 <p>Now the code starts to get more interesting. Our 'for' loop introduces a new
776 variable to the symbol table. This means that our symbol table can now contain
777 either function arguments or loop variables. To handle this, before we codegen
778 the body of the loop, we add the loop variable as the current value for its
779 name. Note that it is possible that there is a variable of the same name in the
780 outer scope. It would be easy to make this an error (emit an error and return
781 null if there is already an entry for VarName) but we choose to allow shadowing
782 of variables. In order to handle this correctly, we remember the Value that
784 no shadowed variable).</p>
786 <p>Once the loop variable is set into the symbol table, the code recursively
787 codegen's the body. This allows the body to use the loop variable: any
788 references to it will naturally find it in the symbol table.</p>
791 <pre>
792 // Emit the step value.
793 Value *StepVal;
794 if (Step) {
795 StepVal = Step->Codegen();
797 } else {
798 // If not specified, use 1.0.
799 StepVal = ConstantFP::get(APFloat(1.0));
800 }
802 Value *NextVar = Builder.CreateAdd(Variable, StepVal, "nextvar");
803 </pre>
804 </div>
806 <p>Now that the body is emitted, we compute the next value of the iteration
808 will be the value of the loop variable on the next iteration of the loop.</p>
811 <pre>
812 // Compute the end condition.
813 Value *EndCond = End->Codegen();
814 if (EndCond == 0) return EndCond;
816 // Convert condition to a bool by comparing equal to 0.0.
817 EndCond = Builder.CreateFCmpONE(EndCond,
818 ConstantFP::get(APFloat(0.0)),
819 "loopcond");
820 </pre>
821 </div>
823 <p>Finally, we evaluate the exit value of the loop, to determine whether the
824 loop should exit. This mirrors the condition evaluation for the if/then/else
825 statement.</p>
828 <pre>
829 // Create the "after loop" block and insert it.
830 BasicBlock *LoopEndBB = Builder.GetInsertBlock();
831 BasicBlock *AfterBB = BasicBlock::Create("afterloop", TheFunction);
833 // Insert the conditional branch into the end of LoopEndBB.
834 Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
836 // Any new code will be inserted in AfterBB.
837 Builder.SetInsertPoint(AfterBB);
838 </pre>
839 </div>
841 <p>With the code for the body of the loop complete, we just need to finish up
842 the 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
843 exit condition, it creates a conditional branch that chooses between executing
844 the loop again and exiting the loop. Any future code is emitted in the
848 <pre>
849 // Add a new entry to the PHI node for the backedge.
850 Variable->addIncoming(NextVar, LoopEndBB);
852 // Restore the unshadowed variable.
853 if (OldVal)
854 NamedValues[VarName] = OldVal;
855 else
856 NamedValues.erase(VarName);
858 // for expr always returns 0.0.
859 return Constant::getNullValue(Type::DoubleTy);
860 }
861 </pre>
862 </div>
865 value, we can add the incoming value to the loop PHI node. After that, we
866 remove the loop variable from the symbol table, so that it isn't in scope after
867 the for loop. Finally, code generation of the for loop always returns 0.0, so
871 the 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
872 to know. In the next chapter of our saga, we will get a bit crazier and add
874 language.</p>
876 </div>
878 <!-- *********************************************************************** -->
880 <!-- *********************************************************************** -->
884 <p>
885 Here is the complete code listing for our running example, enhanced with the
886 if/then/else and for expressions.. To build this example, use:
887 </p>
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>
901 <pre>
902 #include "llvm/DerivedTypes.h"
903 #include "llvm/ExecutionEngine/ExecutionEngine.h"
904 #include "llvm/Module.h"
905 #include "llvm/ModuleProvider.h"
906 #include "llvm/PassManager.h"
907 #include "llvm/Analysis/Verifier.h"
908 #include "llvm/Target/TargetData.h"
909 #include "llvm/Transforms/Scalar.h"
910 #include "llvm/Support/IRBuilder.h"
915 using namespace llvm;
917 //===----------------------------------------------------------------------===//
918 // Lexer
919 //===----------------------------------------------------------------------===//
922 // of these for known things.
923 enum Token {
924 tok_eof = -1,
926 // commands
929 // primary
932 // control
935 };
937 static std::string IdentifierStr; // Filled in if tok_identifier
938 static double NumVal; // Filled in if tok_number
940 /// gettok - Return the next token from standard input.
941 static int gettok() {
942 static int LastChar = ' ';
944 // Skip any whitespace.
945 while (isspace(LastChar))
946 LastChar = getchar();
948 if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
949 IdentifierStr = LastChar;
950 while (isalnum((LastChar = getchar())))
951 IdentifierStr += LastChar;
953 if (IdentifierStr == "def") return tok_def;
954 if (IdentifierStr == "extern") return tok_extern;
955 if (IdentifierStr == "if") return tok_if;
956 if (IdentifierStr == "then") return tok_then;
957 if (IdentifierStr == "else") return tok_else;
958 if (IdentifierStr == "for") return tok_for;
959 if (IdentifierStr == "in") return tok_in;
960 return tok_identifier;
961 }
964 std::string NumStr;
965 do {
966 NumStr += LastChar;
967 LastChar = getchar();
968 } while (isdigit(LastChar) || LastChar == '.');
970 NumVal = strtod(NumStr.c_str(), 0);
971 return tok_number;
972 }
974 if (LastChar == '#') {
975 // Comment until end of line.
976 do LastChar = getchar();
979 if (LastChar != EOF)
980 return gettok();
981 }
983 // Check for end of file. Don't eat the EOF.
984 if (LastChar == EOF)
985 return tok_eof;
987 // Otherwise, just return the character as its ascii value.
988 int ThisChar = LastChar;
989 LastChar = getchar();
990 return ThisChar;
991 }
993 //===----------------------------------------------------------------------===//
994 // Abstract Syntax Tree (aka Parse Tree)
995 //===----------------------------------------------------------------------===//
997 /// ExprAST - Base class for all expression nodes.
998 class ExprAST {
999 public:
1000 virtual ~ExprAST() {}
1001 virtual Value *Codegen() = 0;
1002 };
1004 /// NumberExprAST - Expression class for numeric literals like "1.0".
1005 class NumberExprAST : public ExprAST {
1006 double Val;
1007 public:
1008 NumberExprAST(double val) : Val(val) {}
1009 virtual Value *Codegen();
1010 };
1012 /// VariableExprAST - Expression class for referencing a variable, like "a".
1013 class VariableExprAST : public ExprAST {
1014 std::string Name;
1015 public:
1016 VariableExprAST(const std::string &name) : Name(name) {}
1017 virtual Value *Codegen();
1018 };
1020 /// BinaryExprAST - Expression class for a binary operator.
1021 class BinaryExprAST : public ExprAST {
1022 char Op;
1023 ExprAST *LHS, *RHS;
1024 public:
1025 BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
1026 : Op(op), LHS(lhs), RHS(rhs) {}
1027 virtual Value *Codegen();
1028 };
1030 /// CallExprAST - Expression class for function calls.
1031 class CallExprAST : public ExprAST {
1032 std::string Callee;
1034 public:
1036 : Callee(callee), Args(args) {}
1037 virtual Value *Codegen();
1038 };
1040 /// IfExprAST - Expression class for if/then/else.
1041 class IfExprAST : public ExprAST {
1042 ExprAST *Cond, *Then, *Else;
1043 public:
1044 IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
1045 : Cond(cond), Then(then), Else(_else) {}
1046 virtual Value *Codegen();
1047 };
1049 /// ForExprAST - Expression class for for/in.
1050 class ForExprAST : public ExprAST {
1051 std::string VarName;
1052 ExprAST *Start, *End, *Step, *Body;
1053 public:
1054 ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end,
1055 ExprAST *step, ExprAST *body)
1056 : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
1057 virtual Value *Codegen();
1058 };
1060 /// PrototypeAST - This class represents the "prototype" for a function,
1061 /// which captures its argument names as well as if it is an operator.
1062 class PrototypeAST {
1063 std::string Name;
1065 public:
1067 : Name(name), Args(args) {}
1069 Function *Codegen();
1070 };
1072 /// FunctionAST - This class represents a function definition itself.
1073 class FunctionAST {
1074 PrototypeAST *Proto;
1075 ExprAST *Body;
1076 public:
1077 FunctionAST(PrototypeAST *proto, ExprAST *body)
1078 : Proto(proto), Body(body) {}
1080 Function *Codegen();
1081 };
1083 //===----------------------------------------------------------------------===//
1084 // Parser
1085 //===----------------------------------------------------------------------===//
1087 /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
1088 /// token the parser it looking at. getNextToken reads another token from the
1089 /// lexer and updates CurTok with its results.
1090 static int CurTok;
1091 static int getNextToken() {
1092 return CurTok = gettok();
1093 }
1095 /// BinopPrecedence - This holds the precedence for each binary operator that is
1096 /// defined.
1099 /// GetTokPrecedence - Get the precedence of the pending binary operator token.
1100 static int GetTokPrecedence() {
1101 if (!isascii(CurTok))
1102 return -1;
1104 // Make sure it's a declared binop.
1105 int TokPrec = BinopPrecedence[CurTok];
1107 return TokPrec;
1108 }
1110 /// Error* - These are little helper functions for error handling.
1112 PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
1113 FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
1115 static ExprAST *ParseExpression();
1117 /// identifierexpr
1118 /// ::= identifier
1119 /// ::= identifier '(' expression* ')'
1120 static ExprAST *ParseIdentifierExpr() {
1121 std::string IdName = IdentifierStr;
1123 getNextToken(); // eat identifier.
1125 if (CurTok != '(') // Simple variable ref.
1126 return new VariableExprAST(IdName);
1128 // Call.
1129 getNextToken(); // eat (
1131 if (CurTok != ')') {
1132 while (1) {
1133 ExprAST *Arg = ParseExpression();
1134 if (!Arg) return 0;
1135 Args.push_back(Arg);
1137 if (CurTok == ')') break;
1139 if (CurTok != ',')
1140 return Error("Expected ')' or ',' in argument list");
1141 getNextToken();
1142 }
1143 }
1145 // Eat the ')'.
1146 getNextToken();
1148 return new CallExprAST(IdName, Args);
1149 }
1151 /// numberexpr ::= number
1152 static ExprAST *ParseNumberExpr() {
1153 ExprAST *Result = new NumberExprAST(NumVal);
1154 getNextToken(); // consume the number
1155 return Result;
1156 }
1158 /// parenexpr ::= '(' expression ')'
1159 static ExprAST *ParseParenExpr() {
1160 getNextToken(); // eat (.
1161 ExprAST *V = ParseExpression();
1162 if (!V) return 0;
1164 if (CurTok != ')')
1165 return Error("expected ')'");
1166 getNextToken(); // eat ).
1167 return V;
1168 }
1170 /// ifexpr ::= 'if' expression 'then' expression 'else' expression
1171 static ExprAST *ParseIfExpr() {
1172 getNextToken(); // eat the if.
1174 // condition.
1175 ExprAST *Cond = ParseExpression();
1176 if (!Cond) return 0;
1178 if (CurTok != tok_then)
1179 return Error("expected then");
1180 getNextToken(); // eat the then
1182 ExprAST *Then = ParseExpression();
1185 if (CurTok != tok_else)
1186 return Error("expected else");
1188 getNextToken();
1190 ExprAST *Else = ParseExpression();
1191 if (!Else) return 0;
1193 return new IfExprAST(Cond, Then, Else);
1194 }
1196 /// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
1197 static ExprAST *ParseForExpr() {
1198 getNextToken(); // eat the for.
1200 if (CurTok != tok_identifier)
1201 return Error("expected identifier after for");
1203 std::string IdName = IdentifierStr;
1204 getNextToken(); // eat identifier.
1206 if (CurTok != '=')
1207 return Error("expected '=' after for");
1208 getNextToken(); // eat '='.
1211 ExprAST *Start = ParseExpression();
1213 if (CurTok != ',')
1214 return Error("expected ',' after for start value");
1215 getNextToken();
1217 ExprAST *End = ParseExpression();
1220 // The step value is optional.
1221 ExprAST *Step = 0;
1222 if (CurTok == ',') {
1223 getNextToken();
1224 Step = ParseExpression();
1226 }
1228 if (CurTok != tok_in)
1229 return Error("expected 'in' after for");
1230 getNextToken(); // eat 'in'.
1232 ExprAST *Body = ParseExpression();
1235 return new ForExprAST(IdName, Start, End, Step, Body);
1236 }
1239 /// primary
1240 /// ::= identifierexpr
1241 /// ::= numberexpr
1242 /// ::= parenexpr
1243 /// ::= ifexpr
1244 /// ::= forexpr
1245 static ExprAST *ParsePrimary() {
1246 switch (CurTok) {
1247 default: return Error("unknown token when expecting an expression");
1248 case tok_identifier: return ParseIdentifierExpr();
1249 case tok_number: return ParseNumberExpr();
1250 case '(': return ParseParenExpr();
1251 case tok_if: return ParseIfExpr();
1252 case tok_for: return ParseForExpr();
1253 }
1254 }
1256 /// binoprhs
1257 /// ::= ('+' primary)*
1258 static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
1259 // If this is a binop, find its precedence.
1260 while (1) {
1261 int TokPrec = GetTokPrecedence();
1263 // If this is a binop that binds at least as tightly as the current binop,
1264 // consume it, otherwise we are done.
1265 if (TokPrec < ExprPrec)
1266 return LHS;
1268 // Okay, we know this is a binop.
1269 int BinOp = CurTok;
1270 getNextToken(); // eat binop
1272 // Parse the primary expression after the binary operator.
1273 ExprAST *RHS = ParsePrimary();
1274 if (!RHS) return 0;
1276 // If BinOp binds less tightly with RHS than the operator after RHS, let
1277 // the pending operator take RHS as its LHS.
1278 int NextPrec = GetTokPrecedence();
1279 if (TokPrec < NextPrec) {
1280 RHS = ParseBinOpRHS(TokPrec+1, RHS);
1282 }
1284 // Merge LHS/RHS.
1285 LHS = new BinaryExprAST(BinOp, LHS, RHS);
1286 }
1287 }
1289 /// expression
1290 /// ::= primary binoprhs
1291 ///
1292 static ExprAST *ParseExpression() {
1293 ExprAST *LHS = ParsePrimary();
1294 if (!LHS) return 0;
1296 return ParseBinOpRHS(0, LHS);
1297 }
1299 /// prototype
1300 /// ::= id '(' id* ')'
1301 static PrototypeAST *ParsePrototype() {
1302 if (CurTok != tok_identifier)
1303 return ErrorP("Expected function name in prototype");
1305 std::string FnName = IdentifierStr;
1306 getNextToken();
1308 if (CurTok != '(')
1309 return ErrorP("Expected '(' in prototype");
1312 while (getNextToken() == tok_identifier)
1313 ArgNames.push_back(IdentifierStr);
1314 if (CurTok != ')')
1315 return ErrorP("Expected ')' in prototype");
1317 // success.
1318 getNextToken(); // eat ')'.
1320 return new PrototypeAST(FnName, ArgNames);
1321 }
1323 /// definition ::= 'def' prototype expression
1324 static FunctionAST *ParseDefinition() {
1325 getNextToken(); // eat def.
1326 PrototypeAST *Proto = ParsePrototype();
1329 if (ExprAST *E = ParseExpression())
1330 return new FunctionAST(Proto, E);
1331 return 0;
1332 }
1334 /// toplevelexpr ::= expression
1335 static FunctionAST *ParseTopLevelExpr() {
1336 if (ExprAST *E = ParseExpression()) {
1337 // Make an anonymous proto.
1339 return new FunctionAST(Proto, E);
1340 }
1341 return 0;
1342 }
1344 /// external ::= 'extern' prototype
1345 static PrototypeAST *ParseExtern() {
1346 getNextToken(); // eat extern.
1347 return ParsePrototype();
1348 }
1350 //===----------------------------------------------------------------------===//
1351 // Code Generation
1352 //===----------------------------------------------------------------------===//
1354 static Module *TheModule;
1355 static IRBuilder<> Builder;
1357 static FunctionPassManager *TheFPM;
1359 Value *ErrorV(const char *Str) { Error(Str); return 0; }
1361 Value *NumberExprAST::Codegen() {
1362 return ConstantFP::get(APFloat(Val));
1363 }
1365 Value *VariableExprAST::Codegen() {
1366 // Look this variable up in the function.
1367 Value *V = NamedValues[Name];
1368 return V ? V : ErrorV("Unknown variable name");
1369 }
1371 Value *BinaryExprAST::Codegen() {
1372 Value *L = LHS->Codegen();
1373 Value *R = RHS->Codegen();
1376 switch (Op) {
1377 case '+': return Builder.CreateAdd(L, R, "addtmp");
1378 case '-': return Builder.CreateSub(L, R, "subtmp");
1379 case '*': return Builder.CreateMul(L, R, "multmp");
1380 case '<':
1381 L = Builder.CreateFCmpULT(L, R, "cmptmp");
1383 return Builder.CreateUIToFP(L, Type::DoubleTy, "booltmp");
1384 default: return ErrorV("invalid binary operator");
1385 }
1386 }
1388 Value *CallExprAST::Codegen() {
1389 // Look up the name in the global module table.
1390 Function *CalleeF = TheModule->getFunction(Callee);
1391 if (CalleeF == 0)
1392 return ErrorV("Unknown function referenced");
1394 // If argument mismatch error.
1395 if (CalleeF->arg_size() != Args.size())
1396 return ErrorV("Incorrect # arguments passed");
1399 for (unsigned i = 0, e = Args.size(); i != e; ++i) {
1400 ArgsV.push_back(Args[i]->Codegen());
1402 }
1404 return Builder.CreateCall(CalleeF, ArgsV.begin(), ArgsV.end(), "calltmp");
1405 }
1407 Value *IfExprAST::Codegen() {
1408 Value *CondV = Cond->Codegen();
1411 // Convert condition to a bool by comparing equal to 0.0.
1412 CondV = Builder.CreateFCmpONE(CondV,
1413 ConstantFP::get(APFloat(0.0)),
1414 "ifcond");
1416 Function *TheFunction = Builder.GetInsertBlock()->getParent();
1418 // Create blocks for the then and else cases. Insert the 'then' block at the
1419 // end of the function.
1420 BasicBlock *ThenBB = BasicBlock::Create("then", TheFunction);
1421 BasicBlock *ElseBB = BasicBlock::Create("else");
1422 BasicBlock *MergeBB = BasicBlock::Create("ifcont");
1424 Builder.CreateCondBr(CondV, ThenBB, ElseBB);
1426 // Emit then value.
1427 Builder.SetInsertPoint(ThenBB);
1429 Value *ThenV = Then->Codegen();
1432 Builder.CreateBr(MergeBB);
1433 // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
1434 ThenBB = Builder.GetInsertBlock();
1436 // Emit else block.
1437 TheFunction->getBasicBlockList().push_back(ElseBB);
1438 Builder.SetInsertPoint(ElseBB);
1440 Value *ElseV = Else->Codegen();
1443 Builder.CreateBr(MergeBB);
1444 // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
1445 ElseBB = Builder.GetInsertBlock();
1447 // Emit merge block.
1448 TheFunction->getBasicBlockList().push_back(MergeBB);
1449 Builder.SetInsertPoint(MergeBB);
1450 PHINode *PN = Builder.CreatePHI(Type::DoubleTy, "iftmp");
1452 PN->addIncoming(ThenV, ThenBB);
1453 PN->addIncoming(ElseV, ElseBB);
1454 return PN;
1455 }
1457 Value *ForExprAST::Codegen() {
1458 // Output this as:
1459 // ...
1460 // start = startexpr
1461 // goto loop
1462 // loop:
1463 // variable = phi [start, loopheader], [nextvariable, loopend]
1464 // ...
1465 // bodyexpr
1466 // ...
1467 // loopend:
1468 // step = stepexpr
1469 // nextvariable = variable + step
1470 // endcond = endexpr
1471 // br endcond, loop, endloop
1472 // outloop:
1474 // Emit the start code first, without 'variable' in scope.
1475 Value *StartVal = Start->Codegen();
1478 // Make the new basic block for the loop header, inserting after current
1479 // block.
1480 Function *TheFunction = Builder.GetInsertBlock()->getParent();
1481 BasicBlock *PreheaderBB = Builder.GetInsertBlock();
1482 BasicBlock *LoopBB = BasicBlock::Create("loop", TheFunction);
1484 // Insert an explicit fall through from the current block to the LoopBB.
1485 Builder.CreateBr(LoopBB);
1487 // Start insertion in LoopBB.
1488 Builder.SetInsertPoint(LoopBB);
1490 // Start the PHI node with an entry for Start.
1491 PHINode *Variable = Builder.CreatePHI(Type::DoubleTy, VarName.c_str());
1492 Variable->addIncoming(StartVal, PreheaderBB);
1494 // Within the loop, the variable is defined equal to the PHI node. If it
1495 // shadows an existing variable, we have to restore it, so save it now.
1496 Value *OldVal = NamedValues[VarName];
1497 NamedValues[VarName] = Variable;
1499 // Emit the body of the loop. This, like any other expr, can change the
1500 // current BB. Note that we ignore the value computed by the body, but don't
1501 // allow an error.
1503 return 0;
1505 // Emit the step value.
1506 Value *StepVal;
1507 if (Step) {
1508 StepVal = Step->Codegen();
1510 } else {
1511 // If not specified, use 1.0.
1512 StepVal = ConstantFP::get(APFloat(1.0));
1513 }
1515 Value *NextVar = Builder.CreateAdd(Variable, StepVal, "nextvar");
1517 // Compute the end condition.
1518 Value *EndCond = End->Codegen();
1519 if (EndCond == 0) return EndCond;
1521 // Convert condition to a bool by comparing equal to 0.0.
1522 EndCond = Builder.CreateFCmpONE(EndCond,
1523 ConstantFP::get(APFloat(0.0)),
1524 "loopcond");
1526 // Create the "after loop" block and insert it.
1527 BasicBlock *LoopEndBB = Builder.GetInsertBlock();
1528 BasicBlock *AfterBB = BasicBlock::Create("afterloop", TheFunction);
1530 // Insert the conditional branch into the end of LoopEndBB.
1531 Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
1533 // Any new code will be inserted in AfterBB.
1534 Builder.SetInsertPoint(AfterBB);
1536 // Add a new entry to the PHI node for the backedge.
1537 Variable->addIncoming(NextVar, LoopEndBB);
1539 // Restore the unshadowed variable.
1540 if (OldVal)
1541 NamedValues[VarName] = OldVal;
1542 else
1543 NamedValues.erase(VarName);
1546 // for expr always returns 0.0.
1547 return Constant::getNullValue(Type::DoubleTy);
1548 }
1550 Function *PrototypeAST::Codegen() {
1551 // Make the function type: double(double,double) etc.
1553 FunctionType *FT = FunctionType::get(Type::DoubleTy, Doubles, false);
1555 Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
1557 // If F conflicted, there was already something named 'Name'. If it has a
1558 // body, don't allow redefinition or reextern.
1559 if (F->getName() != Name) {
1560 // Delete the one we just made and get the existing one.
1561 F->eraseFromParent();
1562 F = TheModule->getFunction(Name);
1564 // If F already has a body, reject this.
1565 if (!F->empty()) {
1566 ErrorF("redefinition of function");
1567 return 0;
1568 }
1570 // If F took a different number of args, reject.
1571 if (F->arg_size() != Args.size()) {
1572 ErrorF("redefinition of function with different # args");
1573 return 0;
1574 }
1575 }
1577 // Set names for all arguments.
1578 unsigned Idx = 0;
1579 for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
1580 ++AI, ++Idx) {
1581 AI->setName(Args[Idx]);
1583 // Add arguments to variable symbol table.
1584 NamedValues[Args[Idx]] = AI;
1585 }
1587 return F;
1588 }
1590 Function *FunctionAST::Codegen() {
1591 NamedValues.clear();
1593 Function *TheFunction = Proto->Codegen();
1594 if (TheFunction == 0)
1595 return 0;
1597 // Create a new basic block to start insertion into.
1598 BasicBlock *BB = BasicBlock::Create("entry", TheFunction);
1599 Builder.SetInsertPoint(BB);
1601 if (Value *RetVal = Body->Codegen()) {
1602 // Finish off the function.
1603 Builder.CreateRet(RetVal);
1605 // Validate the generated code, checking for consistency.
1606 verifyFunction(*TheFunction);
1608 // Optimize the function.
1609 TheFPM->run(*TheFunction);
1611 return TheFunction;
1612 }
1614 // Error reading body, remove function.
1615 TheFunction->eraseFromParent();
1616 return 0;
1617 }
1619 //===----------------------------------------------------------------------===//
1620 // Top-Level parsing and JIT Driver
1621 //===----------------------------------------------------------------------===//
1623 static ExecutionEngine *TheExecutionEngine;
1625 static void HandleDefinition() {
1626 if (FunctionAST *F = ParseDefinition()) {
1627 if (Function *LF = F->Codegen()) {
1628 fprintf(stderr, "Read function definition:");
1629 LF->dump();
1630 }
1631 } else {
1632 // Skip token for error recovery.
1633 getNextToken();
1634 }
1635 }
1637 static void HandleExtern() {
1638 if (PrototypeAST *P = ParseExtern()) {
1639 if (Function *F = P->Codegen()) {
1640 fprintf(stderr, "Read extern: ");
1641 F->dump();
1642 }
1643 } else {
1644 // Skip token for error recovery.
1645 getNextToken();
1646 }
1647 }
1649 static void HandleTopLevelExpression() {
1650 // Evaluate a top level expression into an anonymous function.
1651 if (FunctionAST *F = ParseTopLevelExpr()) {
1652 if (Function *LF = F->Codegen()) {
1653 // JIT the function, returning a function pointer.
1654 void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
1656 // Cast it to the right type (takes no arguments, returns a double) so we
1657 // can call it as a native function.
1658 double (*FP)() = (double (*)())FPtr;
1659 fprintf(stderr, "Evaluated to %f\n", FP());
1660 }
1661 } else {
1662 // Skip token for error recovery.
1663 getNextToken();
1664 }
1665 }
1667 /// top ::= definition | external | expression | ';'
1668 static void MainLoop() {
1669 while (1) {
1670 fprintf(stderr, "ready> ");
1671 switch (CurTok) {
1672 case tok_eof: return;
1673 case ';': getNextToken(); break; // ignore top level semicolons.
1674 case tok_def: HandleDefinition(); break;
1675 case tok_extern: HandleExtern(); break;
1676 default: HandleTopLevelExpression(); break;
1677 }
1678 }
1679 }
1683 //===----------------------------------------------------------------------===//
1685 //===----------------------------------------------------------------------===//
1687 /// putchard - putchar that takes a double and returns 0.
1688 extern "C"
1689 double putchard(double X) {
1690 putchar((char)X);
1691 return 0;
1692 }
1694 //===----------------------------------------------------------------------===//
1695 // Main driver code.
1696 //===----------------------------------------------------------------------===//
1698 int main() {
1699 // Install standard binary operators.
1700 // 1 is lowest precedence.
1702 BinopPrecedence['+'] = 20;
1703 BinopPrecedence['-'] = 20;
1704 BinopPrecedence['*'] = 40; // highest.
1706 // Prime the first token.
1707 fprintf(stderr, "ready> ");
1708 getNextToken();
1710 // Make the module, which holds all the code.
1711 TheModule = new Module("my cool jit");
1713 // Create the JIT.
1714 TheExecutionEngine = ExecutionEngine::create(TheModule);
1716 {
1717 ExistingModuleProvider OurModuleProvider(TheModule);
1718 FunctionPassManager OurFPM(&OurModuleProvider);
1720 // Set up the optimizer pipeline. Start with registering info about how the
1721 // target lays out data structures.
1722 OurFPM.add(new TargetData(*TheExecutionEngine->getTargetData()));
1723 // Do simple "peephole" optimizations and bit-twiddling optzns.
1724 OurFPM.add(createInstructionCombiningPass());
1725 // Reassociate expressions.
1726 OurFPM.add(createReassociatePass());
1727 // Eliminate Common SubExpressions.
1728 OurFPM.add(createGVNPass());
1729 // Simplify the control flow graph (deleting unreachable blocks, etc).
1730 OurFPM.add(createCFGSimplificationPass());
1731 // Set the global so the code gen can use this.
1732 TheFPM = &OurFPM;
1734 // Run the main "interpreter loop" now.
1735 MainLoop();
1737 TheFPM = 0;
1739 // Print out all of the generated code.
1740 TheModule->dump();
1741 } // Free module provider (and thus the module) and pass manager.
1743 return 0;
1744 }
1745 </pre>
1746 </div>
1749 </div>
1751 <!-- *********************************************************************** -->
1752 <hr>
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1762 </address>
1763 </body>
1764 </html>