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4 <html>
5 <head>
10 </head>
12 <body>
16 <ul>
19 <ol>
26 </ol>
27 </li>
29 Support</li>
30 </ul>
34 </div>
36 <!-- *********************************************************************** -->
38 <!-- *********************************************************************** -->
45 This will teach you a little bit about how LLVM does things, as well as
46 demonstrate how easy it is to use. It's much more work to build a lexer and
47 parser than it is to generate LLVM IR code. :)
48 </p>
51 later. LLVM 2.1 and before will not work with it. Also note that you need
52 to use a version of this tutorial that matches your LLVM release: If you are
53 using an official LLVM release, use the version of the documentation included
57 </div>
59 <!-- *********************************************************************** -->
61 <!-- *********************************************************************** -->
65 <p>
66 In order to generate LLVM IR, we want some simple setup to get started. First
67 we define virtual code generation (codegen) methods in each AST class:</p>
70 <pre>
71 /// ExprAST - Base class for all expression nodes.
72 class ExprAST {
73 public:
74 virtual ~ExprAST() {}
76 };
78 /// NumberExprAST - Expression class for numeric literals like "1.0".
79 class NumberExprAST : public ExprAST {
80 double Val;
81 public:
82 explicit NumberExprAST(double val) : Val(val) {}
84 };
85 ...
86 </pre>
87 </div>
89 <p>The Codegen() method says to emit IR for that AST node along with all the things it
90 depends on, and they all return an LLVM Value object.
94 of SSA values is that their value is computed as the related instruction
95 executes, and it does not get a new value until (and if) the instruction
96 re-executes. In other words, there is no way to "change" an SSA value. For
97 more information, please read up on <a
101 <p>Note that instead of adding virtual methods to the ExprAST class hierarchy,
102 it could also make sense to use a <a
104 other way to model this. Again, this tutorial won't dwell on good software
105 engineering practices: for our purposes, adding a virtual method is
106 simplest.</p>
108 <p>The
109 second thing we want is an "Error" method like we used for the parser, which will
110 be used to report errors found during code generation (for example, use of an
111 undeclared parameter):</p>
114 <pre>
115 Value *ErrorV(const char *Str) { Error(Str); return 0; }
117 static Module *TheModule;
118 static IRBuilder<> Builder(getGlobalContext());
120 </pre>
121 </div>
124 is the LLVM construct that contains all of the functions and global variables in
125 a chunk of code. In many ways, it is the top-level structure that the LLVM IR
126 uses to contain code.</p>
129 LLVM instructions. Instances of the <a
131 class template keep track of the current place to insert instructions and has
132 methods to create new instructions.</p>
135 current scope and what their LLVM representation is. (In other words, it is a
136 symbol table for the code). In this form of Kaleidoscope, the only things that
137 can be referenced are function parameters. As such, function parameters will
138 be in this map when generating code for their function body.</p>
140 <p>
141 With these basics in place, we can start talking about how to generate code for
144 has already been done, and we'll just use it to emit code.
145 </p>
147 </div>
149 <!-- *********************************************************************** -->
151 <!-- *********************************************************************** -->
155 <p>Generating LLVM code for expression nodes is very straightforward: less
156 than 45 lines of commented code for all four of our expression nodes. First
157 we'll do numeric literals:</p>
160 <pre>
161 Value *NumberExprAST::Codegen() {
162 return ConstantFP::get(getGlobalContext(), APFloat(Val));
163 }
164 </pre>
165 </div>
167 <p>In the LLVM IR, numeric constants are represented with the
172 that constants are all uniqued together and shared. For this reason, the API
176 <pre>
177 Value *VariableExprAST::Codegen() {
178 // Look this variable up in the function.
179 Value *V = NamedValues[Name];
180 return V ? V : ErrorV("Unknown variable name");
181 }
182 </pre>
183 </div>
185 <p>References to variables are also quite simple using LLVM. In the simple version
186 of Kaleidoscope, we assume that the variable has already been emited somewhere
187 and its value is available. In practice, the only values that can be in the
189 code simply checks to see that the specified name is in the map (if not, an
190 unknown variable is being referenced) and returns the value for it. In future
196 <pre>
197 Value *BinaryExprAST::Codegen() {
198 Value *L = LHS->Codegen();
199 Value *R = RHS->Codegen();
202 switch (Op) {
203 case '+': return Builder.CreateAdd(L, R, "addtmp");
204 case '-': return Builder.CreateSub(L, R, "subtmp");
205 case '*': return Builder.CreateMul(L, R, "multmp");
206 case '<':
207 L = Builder.CreateFCmpULT(L, R, "cmptmp");
209 return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
210 "booltmp");
211 default: return ErrorV("invalid binary operator");
212 }
213 }
214 </pre>
215 </div>
217 <p>Binary operators start to get more interesting. The basic idea here is that
218 we recursively emit code for the left-hand side of the expression, then the
219 right-hand side, then we compute the result of the binary expression. In this
220 code, we do a simple switch on the opcode to create the right LLVM instruction.
221 </p>
223 <p>In the example above, the LLVM builder class is starting to show its value.
224 IRBuilder knows where to insert the newly created instruction, all you have to
227 for the generated instruction.</p>
229 <p>One nice thing about LLVM is that the name is just a hint. For instance, if
230 the code above emits multiple "addtmp" variables, LLVM will automatically
231 provide each one with an increasing, unique numeric suffix. Local value names
232 for instructions are purely optional, but it makes it much easier to read the
233 IR dumps.</p>
236 strict rules: for example, the Left and Right operators of
238 type, and the result type of the add must match the operand types. Because
239 all values in Kaleidoscope are doubles, this makes for very simple code for add,
240 sub and mul.</p>
244 (a one bit integer). The problem with this is that Kaleidoscope wants the value to be a 0.0 or 1.0 value. In order to get these semantics, we combine the fcmp instruction with
246 converts its input integer into a floating point value by treating the input
247 as an unsigned value. In contrast, if we used the <a
252 <pre>
253 Value *CallExprAST::Codegen() {
254 // Look up the name in the global module table.
255 Function *CalleeF = TheModule->getFunction(Callee);
256 if (CalleeF == 0)
257 return ErrorV("Unknown function referenced");
259 // If argument mismatch error.
260 if (CalleeF->arg_size() != Args.size())
261 return ErrorV("Incorrect # arguments passed");
264 for (unsigned i = 0, e = Args.size(); i != e; ++i) {
265 ArgsV.push_back(Args[i]->Codegen());
267 }
269 return Builder.CreateCall(CalleeF, ArgsV.begin(), ArgsV.end(), "calltmp");
270 }
271 </pre>
272 </div>
274 <p>Code generation for function calls is quite straightforward with LLVM. The
275 code above initially does a function name lookup in the LLVM Module's symbol
276 table. Recall that the LLVM Module is the container that holds all of the
277 functions we are JIT'ing. By giving each function the same name as what the
278 user specifies, we can use the LLVM symbol table to resolve function names for
279 us.</p>
281 <p>Once we have the function to call, we recursively codegen each argument that
283 instruction</a>. Note that LLVM uses the native C calling conventions by
284 default, allowing these calls to also call into standard library functions like
287 <p>This wraps up our handling of the four basic expressions that we have so far
288 in Kaleidoscope. Feel free to go in and add some more. For example, by
290 several other interesting instructions that are really easy to plug into our
291 basic framework.</p>
293 </div>
295 <!-- *********************************************************************** -->
297 <!-- *********************************************************************** -->
301 <p>Code generation for prototypes and functions must handle a number of
302 details, which make their code less beautiful than expression code
303 generation, but allows us to illustrate some important points. First, lets
304 talk about code generation for prototypes: they are used both for function
305 bodies and external function declarations. The code starts with:</p>
308 <pre>
309 Function *PrototypeAST::Codegen() {
310 // Make the function type: double(double,double) etc.
312 Type::getDoubleTy(getGlobalContext()));
313 FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
314 Doubles, false);
316 Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
317 </pre>
318 </div>
320 <p>This code packs a lot of power into a few lines. Note first that this
322 really talks about the external interface for a function (not the value computed
323 by an expression), it makes sense for it to return the LLVM Function it
324 corresponds to when codegen'd.</p>
328 function arguments in Kaleidoscope are of type double, the first line creates
330 method to create a function type that takes "N" doubles as arguments, returns
331 one double as a result, and that is not vararg (the false parameter indicates
332 this). Note that Types in LLVM are uniqued just like Constants are, so you
335 <p>The final line above actually creates the function that the prototype will
336 correspond to. This indicates the type, linkage and name to use, as well as which
338 means that the function may be defined outside the current module and/or that it
339 is callable by functions outside the module. The Name passed in is the name the
340 user specified: since "<tt>TheModule</tt>" is specified, this name is registered
341 in "<tt>TheModule</tt>"s symbol table, which is used by the function call code
342 above.</p>
345 <pre>
346 // If F conflicted, there was already something named 'Name'. If it has a
347 // body, don't allow redefinition or reextern.
348 if (F->getName() != Name) {
349 // Delete the one we just made and get the existing one.
350 F->eraseFromParent();
351 F = TheModule->getFunction(Name);
352 </pre>
353 </div>
355 <p>The Module symbol table works just like the Function symbol table when it
356 comes to name conflicts: if a new function is created with a name was previously
357 added to the symbol table, it will get implicitly renamed when added to the
358 Module. The code above exploits this fact to determine if there was a previous
359 definition of this function.</p>
361 <p>In Kaleidoscope, I choose to allow redefinitions of functions in two cases:
362 first, we want to allow 'extern'ing a function more than once, as long as the
363 prototypes for the externs match (since all arguments have the same type, we
364 just have to check that the number of arguments match). Second, we want to
365 allow 'extern'ing a function and then definining a body for it. This is useful
366 when defining mutually recursive functions.</p>
368 <p>In order to implement this, the code above first checks to see if there is
369 a collision on the name of the function. If so, it deletes the function we just
373 unlinks the object from its parent (e.g. a Function from a Module) and returns
377 <pre>
378 // If F already has a body, reject this.
379 if (!F->empty()) {
380 ErrorF("redefinition of function");
381 return 0;
382 }
384 // If F took a different number of args, reject.
385 if (F->arg_size() != Args.size()) {
386 ErrorF("redefinition of function with different # args");
387 return 0;
388 }
389 }
390 </pre>
391 </div>
393 <p>In order to verify the logic above, we first check to see if the pre-existing
394 function is "empty". In this case, empty means that it has no basic blocks in
395 it, which means it has no body. If it has no body, it is a forward
396 declaration. Since we don't allow anything after a full definition of the
397 function, the code rejects this case. If the previous reference to a function
398 was an 'extern', we simply verify that the number of arguments for that
399 definition and this one match up. If not, we emit an error.</p>
402 <pre>
403 // Set names for all arguments.
404 unsigned Idx = 0;
405 for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
406 ++AI, ++Idx) {
407 AI->setName(Args[Idx]);
409 // Add arguments to variable symbol table.
410 NamedValues[Args[Idx]] = AI;
411 }
412 return F;
413 }
414 </pre>
415 </div>
417 <p>The last bit of code for prototypes loops over all of the arguments in the
418 function, setting the name of the LLVM Argument objects to match, and registering
421 object to the caller. Note that we don't check for conflicting
422 argument names here (e.g. "extern foo(a b a)"). Doing so would be very
423 straight-forward with the mechanics we have already used above.</p>
426 <pre>
427 Function *FunctionAST::Codegen() {
428 NamedValues.clear();
430 Function *TheFunction = Proto->Codegen();
431 if (TheFunction == 0)
432 return 0;
433 </pre>
434 </div>
436 <p>Code generation for function definitions starts out simply enough: we just
437 codegen the prototype (Proto) and verify that it is ok. We then clear out the
439 last function we compiled. Code generation of the prototype ensures that there
440 is an LLVM Function object that is ready to go for us.</p>
443 <pre>
444 // Create a new basic block to start insertion into.
445 BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
446 Builder.SetInsertPoint(BB);
448 if (Value *RetVal = Body->Codegen()) {
449 </pre>
450 </div>
455 second line then tells the builder that new instructions should be inserted into
456 the end of the new basic block. Basic blocks in LLVM are an important part
457 of functions that define the <a
459 Since we don't have any control flow, our functions will only contain one
463 <pre>
464 if (Value *RetVal = Body->Codegen()) {
465 // Finish off the function.
466 Builder.CreateRet(RetVal);
468 // Validate the generated code, checking for consistency.
469 verifyFunction(*TheFunction);
470 return TheFunction;
471 }
472 </pre>
473 </div>
476 the root expression of the function. If no error happens, this emits code to
477 compute the expression into the entry block and returns the value that was
478 computed. Assuming no error, we then create an LLVM <a
481 is provided by LLVM. This function does a variety of consistency checks on the
482 generated code, to determine if our compiler is doing everything right. Using
483 this is important: it can catch a lot of bugs. Once the function is finished
484 and validated, we return it.</p>
487 <pre>
488 // Error reading body, remove function.
489 TheFunction->eraseFromParent();
490 return 0;
491 }
492 </pre>
493 </div>
495 <p>The only piece left here is handling of the error case. For simplicity, we
496 handle this by merely deleting the function we produced with the
498 that they incorrectly typed in before: if we didn't delete it, it would live in
499 the symbol table, with a body, preventing future redefinition.</p>
502 can return a previously defined forward declaration, our code can actually delete
503 a forward declaration. There are a number of ways to fix this bug, see what you
504 can come up with! Here is a testcase:</p>
507 <pre>
508 extern foo(a b); # ok, defines foo.
509 def foo(a b) c; # error, 'c' is invalid.
511 </pre>
512 </div>
514 </div>
516 <!-- *********************************************************************** -->
518 Closing Thoughts</a></div>
519 <!-- *********************************************************************** -->
523 <p>
524 For now, code generation to LLVM doesn't really get us much, except that we can
525 look at the pretty IR calls. The sample code inserts calls to Codegen into the
527 dumps out the LLVM IR. This gives a nice way to look at the LLVM IR for simple
528 functions. For example:
529 </p>
532 <pre>
534 Read top-level expression:
535 define double @""() {
536 entry:
538 ret double %addtmp
539 }
540 </pre>
541 </div>
543 <p>Note how the parser turns the top-level expression into anonymous functions
545 support</a> in the next chapter. Also note that the code is very literally
546 transcribed, no optimizations are being performed. We will
548 the next chapter.</p>
551 <pre>
553 Read function definition:
554 define double @foo(double %a, double %b) {
555 entry:
556 %multmp = mul double %a, %a
557 %multmp1 = mul double 2.000000e+00, %a
558 %multmp2 = mul double %multmp1, %b
559 %addtmp = add double %multmp, %multmp2
560 %multmp3 = mul double %b, %b
561 %addtmp4 = add double %addtmp, %multmp3
562 ret double %addtmp4
563 }
564 </pre>
565 </div>
567 <p>This shows some simple arithmetic. Notice the striking similarity to the
568 LLVM builder calls that we use to create the instructions.</p>
571 <pre>
573 Read function definition:
574 define double @bar(double %a) {
575 entry:
576 %calltmp = call double @foo( double %a, double 4.000000e+00 )
577 %calltmp1 = call double @bar( double 3.133700e+04 )
578 %addtmp = add double %calltmp, %calltmp1
579 ret double %addtmp
580 }
581 </pre>
582 </div>
584 <p>This shows some function calls. Note that this function will take a long
585 time to execute if you call it. In the future we'll add conditional control
586 flow to actually make recursion useful :).</p>
589 <pre>
591 Read extern:
592 declare double @cos(double)
595 Read top-level expression:
596 define double @""() {
597 entry:
598 %calltmp = call double @cos( double 1.234000e+00 )
599 ret double %calltmp
600 }
601 </pre>
602 </div>
608 <pre>
610 ; ModuleID = 'my cool jit'
612 define double @""() {
613 entry:
615 ret double %addtmp
616 }
618 define double @foo(double %a, double %b) {
619 entry:
620 %multmp = mul double %a, %a
621 %multmp1 = mul double 2.000000e+00, %a
622 %multmp2 = mul double %multmp1, %b
623 %addtmp = add double %multmp, %multmp2
624 %multmp3 = mul double %b, %b
625 %addtmp4 = add double %addtmp, %multmp3
626 ret double %addtmp4
627 }
629 define double @bar(double %a) {
630 entry:
631 %calltmp = call double @foo( double %a, double 4.000000e+00 )
632 %calltmp1 = call double @bar( double 3.133700e+04 )
633 %addtmp = add double %calltmp, %calltmp1
634 ret double %addtmp
635 }
637 declare double @cos(double)
639 define double @""() {
640 entry:
641 %calltmp = call double @cos( double 1.234000e+00 )
642 ret double %calltmp
643 }
644 </pre>
645 </div>
647 <p>When you quit the current demo, it dumps out the IR for the entire module
648 generated. Here you can see the big picture with all the functions referencing
649 each other.</p>
651 <p>This wraps up the third chapter of the Kaleidoscope tutorial. Up next, we'll
655 </div>
658 <!-- *********************************************************************** -->
660 <!-- *********************************************************************** -->
664 <p>
665 Here is the complete code listing for our running example, enhanced with the
666 LLVM code generator. Because this uses the LLVM libraries, we need to link
667 them in. To do this, we use the <a
669 our makefile/command line about which options to use:</p>
672 <pre>
673 # Compile
674 g++ -g -O3 toy.cpp `llvm-config --cppflags --ldflags --libs core` -o toy
675 # Run
676 ./toy
677 </pre>
678 </div>
683 <pre>
684 // To build this:
685 // See example below.
687 #include "llvm/DerivedTypes.h"
688 #include "llvm/LLVMContext.h"
689 #include "llvm/Module.h"
690 #include "llvm/Analysis/Verifier.h"
691 #include "llvm/Support/IRBuilder.h"
696 using namespace llvm;
698 //===----------------------------------------------------------------------===//
699 // Lexer
700 //===----------------------------------------------------------------------===//
703 // of these for known things.
704 enum Token {
705 tok_eof = -1,
707 // commands
710 // primary
712 };
714 static std::string IdentifierStr; // Filled in if tok_identifier
715 static double NumVal; // Filled in if tok_number
717 /// gettok - Return the next token from standard input.
718 static int gettok() {
719 static int LastChar = ' ';
721 // Skip any whitespace.
722 while (isspace(LastChar))
723 LastChar = getchar();
725 if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
726 IdentifierStr = LastChar;
727 while (isalnum((LastChar = getchar())))
728 IdentifierStr += LastChar;
730 if (IdentifierStr == "def") return tok_def;
731 if (IdentifierStr == "extern") return tok_extern;
732 return tok_identifier;
733 }
736 std::string NumStr;
737 do {
738 NumStr += LastChar;
739 LastChar = getchar();
740 } while (isdigit(LastChar) || LastChar == '.');
742 NumVal = strtod(NumStr.c_str(), 0);
743 return tok_number;
744 }
746 if (LastChar == '#') {
747 // Comment until end of line.
748 do LastChar = getchar();
751 if (LastChar != EOF)
752 return gettok();
753 }
755 // Check for end of file. Don't eat the EOF.
756 if (LastChar == EOF)
757 return tok_eof;
759 // Otherwise, just return the character as its ascii value.
760 int ThisChar = LastChar;
761 LastChar = getchar();
762 return ThisChar;
763 }
765 //===----------------------------------------------------------------------===//
766 // Abstract Syntax Tree (aka Parse Tree)
767 //===----------------------------------------------------------------------===//
769 /// ExprAST - Base class for all expression nodes.
770 class ExprAST {
771 public:
772 virtual ~ExprAST() {}
773 virtual Value *Codegen() = 0;
774 };
776 /// NumberExprAST - Expression class for numeric literals like "1.0".
777 class NumberExprAST : public ExprAST {
778 double Val;
779 public:
780 explicit NumberExprAST(double val) : Val(val) {}
781 virtual Value *Codegen();
782 };
784 /// VariableExprAST - Expression class for referencing a variable, like "a".
785 class VariableExprAST : public ExprAST {
786 std::string Name;
787 public:
788 explicit VariableExprAST(const std::string &name) : Name(name) {}
789 virtual Value *Codegen();
790 };
792 /// BinaryExprAST - Expression class for a binary operator.
793 class BinaryExprAST : public ExprAST {
794 char Op;
795 ExprAST *LHS, *RHS;
796 public:
797 BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
798 : Op(op), LHS(lhs), RHS(rhs) {}
799 virtual Value *Codegen();
800 };
802 /// CallExprAST - Expression class for function calls.
803 class CallExprAST : public ExprAST {
804 std::string Callee;
806 public:
808 : Callee(callee), Args(args) {}
809 virtual Value *Codegen();
810 };
812 /// PrototypeAST - This class represents the "prototype" for a function,
813 /// which captures its argument names as well as if it is an operator.
814 class PrototypeAST {
815 std::string Name;
817 public:
819 : Name(name), Args(args) {}
821 Function *Codegen();
822 };
824 /// FunctionAST - This class represents a function definition itself.
825 class FunctionAST {
826 PrototypeAST *Proto;
827 ExprAST *Body;
828 public:
829 FunctionAST(PrototypeAST *proto, ExprAST *body)
830 : Proto(proto), Body(body) {}
832 Function *Codegen();
833 };
835 //===----------------------------------------------------------------------===//
836 // Parser
837 //===----------------------------------------------------------------------===//
839 /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
840 /// token the parser it looking at. getNextToken reads another token from the
841 /// lexer and updates CurTok with its results.
842 static int CurTok;
843 static int getNextToken() {
844 return CurTok = gettok();
845 }
847 /// BinopPrecedence - This holds the precedence for each binary operator that is
848 /// defined.
851 /// GetTokPrecedence - Get the precedence of the pending binary operator token.
852 static int GetTokPrecedence() {
853 if (!isascii(CurTok))
854 return -1;
856 // Make sure it's a declared binop.
857 int TokPrec = BinopPrecedence[CurTok];
859 return TokPrec;
860 }
862 /// Error* - These are little helper functions for error handling.
864 PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
865 FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
867 static ExprAST *ParseExpression();
869 /// identifierexpr
870 /// ::= identifier
871 /// ::= identifier '(' expression* ')'
872 static ExprAST *ParseIdentifierExpr() {
873 std::string IdName = IdentifierStr;
875 getNextToken(); // eat identifier.
877 if (CurTok != '(') // Simple variable ref.
878 return new VariableExprAST(IdName);
880 // Call.
881 getNextToken(); // eat (
883 if (CurTok != ')') {
884 while (1) {
885 ExprAST *Arg = ParseExpression();
886 if (!Arg) return 0;
887 Args.push_back(Arg);
889 if (CurTok == ')') break;
891 if (CurTok != ',')
892 return Error("Expected ')' or ',' in argument list");
893 getNextToken();
894 }
895 }
897 // Eat the ')'.
898 getNextToken();
900 return new CallExprAST(IdName, Args);
901 }
903 /// numberexpr ::= number
904 static ExprAST *ParseNumberExpr() {
905 ExprAST *Result = new NumberExprAST(NumVal);
906 getNextToken(); // consume the number
907 return Result;
908 }
910 /// parenexpr ::= '(' expression ')'
911 static ExprAST *ParseParenExpr() {
912 getNextToken(); // eat (.
913 ExprAST *V = ParseExpression();
914 if (!V) return 0;
916 if (CurTok != ')')
917 return Error("expected ')'");
918 getNextToken(); // eat ).
919 return V;
920 }
922 /// primary
923 /// ::= identifierexpr
924 /// ::= numberexpr
925 /// ::= parenexpr
926 static ExprAST *ParsePrimary() {
927 switch (CurTok) {
928 default: return Error("unknown token when expecting an expression");
929 case tok_identifier: return ParseIdentifierExpr();
930 case tok_number: return ParseNumberExpr();
931 case '(': return ParseParenExpr();
932 }
933 }
935 /// binoprhs
936 /// ::= ('+' primary)*
937 static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
938 // If this is a binop, find its precedence.
939 while (1) {
940 int TokPrec = GetTokPrecedence();
942 // If this is a binop that binds at least as tightly as the current binop,
943 // consume it, otherwise we are done.
944 if (TokPrec < ExprPrec)
945 return LHS;
947 // Okay, we know this is a binop.
948 int BinOp = CurTok;
949 getNextToken(); // eat binop
951 // Parse the primary expression after the binary operator.
952 ExprAST *RHS = ParsePrimary();
953 if (!RHS) return 0;
955 // If BinOp binds less tightly with RHS than the operator after RHS, let
956 // the pending operator take RHS as its LHS.
957 int NextPrec = GetTokPrecedence();
958 if (TokPrec < NextPrec) {
959 RHS = ParseBinOpRHS(TokPrec+1, RHS);
961 }
963 // Merge LHS/RHS.
964 LHS = new BinaryExprAST(BinOp, LHS, RHS);
965 }
966 }
968 /// expression
969 /// ::= primary binoprhs
970 ///
971 static ExprAST *ParseExpression() {
972 ExprAST *LHS = ParsePrimary();
973 if (!LHS) return 0;
975 return ParseBinOpRHS(0, LHS);
976 }
978 /// prototype
979 /// ::= id '(' id* ')'
980 static PrototypeAST *ParsePrototype() {
981 if (CurTok != tok_identifier)
982 return ErrorP("Expected function name in prototype");
984 std::string FnName = IdentifierStr;
985 getNextToken();
987 if (CurTok != '(')
988 return ErrorP("Expected '(' in prototype");
991 while (getNextToken() == tok_identifier)
992 ArgNames.push_back(IdentifierStr);
993 if (CurTok != ')')
994 return ErrorP("Expected ')' in prototype");
996 // success.
997 getNextToken(); // eat ')'.
999 return new PrototypeAST(FnName, ArgNames);
1000 }
1002 /// definition ::= 'def' prototype expression
1003 static FunctionAST *ParseDefinition() {
1004 getNextToken(); // eat def.
1005 PrototypeAST *Proto = ParsePrototype();
1008 if (ExprAST *E = ParseExpression())
1009 return new FunctionAST(Proto, E);
1010 return 0;
1011 }
1013 /// toplevelexpr ::= expression
1014 static FunctionAST *ParseTopLevelExpr() {
1015 if (ExprAST *E = ParseExpression()) {
1016 // Make an anonymous proto.
1018 return new FunctionAST(Proto, E);
1019 }
1020 return 0;
1021 }
1023 /// external ::= 'extern' prototype
1024 static PrototypeAST *ParseExtern() {
1025 getNextToken(); // eat extern.
1026 return ParsePrototype();
1027 }
1029 //===----------------------------------------------------------------------===//
1030 // Code Generation
1031 //===----------------------------------------------------------------------===//
1033 static Module *TheModule;
1034 static IRBuilder<> Builder(getGlobalContext());
1037 Value *ErrorV(const char *Str) { Error(Str); return 0; }
1039 Value *NumberExprAST::Codegen() {
1040 return ConstantFP::get(getGlobalContext(), APFloat(Val));
1041 }
1043 Value *VariableExprAST::Codegen() {
1044 // Look this variable up in the function.
1045 Value *V = NamedValues[Name];
1046 return V ? V : ErrorV("Unknown variable name");
1047 }
1049 Value *BinaryExprAST::Codegen() {
1050 Value *L = LHS->Codegen();
1051 Value *R = RHS->Codegen();
1054 switch (Op) {
1055 case '+': return Builder.CreateAdd(L, R, "addtmp");
1056 case '-': return Builder.CreateSub(L, R, "subtmp");
1057 case '*': return Builder.CreateMul(L, R, "multmp");
1058 case '<':
1059 L = Builder.CreateFCmpULT(L, R, "cmptmp");
1061 return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()), "booltmp");
1062 default: return ErrorV("invalid binary operator");
1063 }
1064 }
1066 Value *CallExprAST::Codegen() {
1067 // Look up the name in the global module table.
1068 Function *CalleeF = TheModule->getFunction(Callee);
1069 if (CalleeF == 0)
1070 return ErrorV("Unknown function referenced");
1072 // If argument mismatch error.
1073 if (CalleeF->arg_size() != Args.size())
1074 return ErrorV("Incorrect # arguments passed");
1077 for (unsigned i = 0, e = Args.size(); i != e; ++i) {
1078 ArgsV.push_back(Args[i]->Codegen());
1080 }
1082 return Builder.CreateCall(CalleeF, ArgsV.begin(), ArgsV.end(), "calltmp");
1083 }
1085 Function *PrototypeAST::Codegen() {
1086 // Make the function type: double(double,double) etc.
1088 Type::getDoubleTy(getGlobalContext()));
1089 FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
1090 Doubles, false);
1092 Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
1094 // If F conflicted, there was already something named 'Name'. If it has a
1095 // body, don't allow redefinition or reextern.
1096 if (F->getName() != Name) {
1097 // Delete the one we just made and get the existing one.
1098 F->eraseFromParent();
1099 F = TheModule->getFunction(Name);
1101 // If F already has a body, reject this.
1102 if (!F->empty()) {
1103 ErrorF("redefinition of function");
1104 return 0;
1105 }
1107 // If F took a different number of args, reject.
1108 if (F->arg_size() != Args.size()) {
1109 ErrorF("redefinition of function with different # args");
1110 return 0;
1111 }
1112 }
1114 // Set names for all arguments.
1115 unsigned Idx = 0;
1116 for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
1117 ++AI, ++Idx) {
1118 AI->setName(Args[Idx]);
1120 // Add arguments to variable symbol table.
1121 NamedValues[Args[Idx]] = AI;
1122 }
1124 return F;
1125 }
1127 Function *FunctionAST::Codegen() {
1128 NamedValues.clear();
1130 Function *TheFunction = Proto->Codegen();
1131 if (TheFunction == 0)
1132 return 0;
1134 // Create a new basic block to start insertion into.
1135 BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
1136 Builder.SetInsertPoint(BB);
1138 if (Value *RetVal = Body->Codegen()) {
1139 // Finish off the function.
1140 Builder.CreateRet(RetVal);
1142 // Validate the generated code, checking for consistency.
1143 verifyFunction(*TheFunction);
1144 return TheFunction;
1145 }
1147 // Error reading body, remove function.
1148 TheFunction->eraseFromParent();
1149 return 0;
1150 }
1152 //===----------------------------------------------------------------------===//
1153 // Top-Level parsing and JIT Driver
1154 //===----------------------------------------------------------------------===//
1156 static void HandleDefinition() {
1157 if (FunctionAST *F = ParseDefinition()) {
1158 if (Function *LF = F->Codegen()) {
1159 fprintf(stderr, "Read function definition:");
1160 LF->dump();
1161 }
1162 } else {
1163 // Skip token for error recovery.
1164 getNextToken();
1165 }
1166 }
1168 static void HandleExtern() {
1169 if (PrototypeAST *P = ParseExtern()) {
1170 if (Function *F = P->Codegen()) {
1171 fprintf(stderr, "Read extern: ");
1172 F->dump();
1173 }
1174 } else {
1175 // Skip token for error recovery.
1176 getNextToken();
1177 }
1178 }
1180 static void HandleTopLevelExpression() {
1181 // Evaluate a top level expression into an anonymous function.
1182 if (FunctionAST *F = ParseTopLevelExpr()) {
1183 if (Function *LF = F->Codegen()) {
1184 fprintf(stderr, "Read top-level expression:");
1185 LF->dump();
1186 }
1187 } else {
1188 // Skip token for error recovery.
1189 getNextToken();
1190 }
1191 }
1193 /// top ::= definition | external | expression | ';'
1194 static void MainLoop() {
1195 while (1) {
1196 fprintf(stderr, "ready> ");
1197 switch (CurTok) {
1198 case tok_eof: return;
1199 case ';': getNextToken(); break; // ignore top level semicolons.
1200 case tok_def: HandleDefinition(); break;
1201 case tok_extern: HandleExtern(); break;
1202 default: HandleTopLevelExpression(); break;
1203 }
1204 }
1205 }
1209 //===----------------------------------------------------------------------===//
1211 //===----------------------------------------------------------------------===//
1213 /// putchard - putchar that takes a double and returns 0.
1214 extern "C"
1215 double putchard(double X) {
1216 putchar((char)X);
1217 return 0;
1218 }
1220 //===----------------------------------------------------------------------===//
1221 // Main driver code.
1222 //===----------------------------------------------------------------------===//
1224 int main() {
1225 TheModule = new Module("my cool jit", getGlobalContext());
1227 // Install standard binary operators.
1228 // 1 is lowest precedence.
1230 BinopPrecedence['+'] = 20;
1231 BinopPrecedence['-'] = 20;
1232 BinopPrecedence['*'] = 40; // highest.
1234 // Prime the first token.
1235 fprintf(stderr, "ready> ");
1236 getNextToken();
1238 MainLoop();
1239 TheModule->dump();
1240 return 0;
1241 }
1242 </pre>
1243 </div>
1245 </div>
1247 <!-- *********************************************************************** -->
1248 <hr>
1249 <address>
1258 </address>
1259 </body>
1260 </html>