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14 <div class="doc_title">Kaleidoscope: Adding JIT and Optimizer Support</div>
17 <li><a href="index.html">Up to Tutorial Index</a></li>
20 <li><a href="#intro">Chapter 4 Introduction</a></li>
21 <li><a href="#trivialconstfold">Trivial Constant Folding</a></li>
22 <li><a href="#optimizerpasses">LLVM Optimization Passes</a></li>
23 <li><a href="#jit">Adding a JIT Compiler</a></li>
24 <li><a href="#code">Full Code Listing</a></li>
27 <li><a href="LangImpl5.html">Chapter 5</a>: Extending the Language: Control
31 <div class="doc_author">
32 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
35 <!-- *********************************************************************** -->
36 <div class="doc_section"><a name="intro">Chapter 4 Introduction</a></div>
37 <!-- *********************************************************************** -->
39 <div class="doc_text">
41 <p>Welcome to Chapter 4 of the "<a href="index.html">Implementing a language
42 with LLVM</a>" tutorial. Chapters 1-3 described the implementation of a simple
43 language and added support for generating LLVM IR. This chapter describes
44 two new techniques: adding optimizer support to your language, and adding JIT
45 compiler support. These additions will demonstrate how to get nice, efficient code
46 for the Kaleidoscope language.</p>
50 <!-- *********************************************************************** -->
51 <div class="doc_section"><a name="trivialconstfold">Trivial Constant
53 <!-- *********************************************************************** -->
55 <div class="doc_text">
58 Our demonstration for Chapter 3 is elegant and easy to extend. Unfortunately,
59 it does not produce wonderful code. The IRBuilder, however, does give us
60 obvious optimizations when compiling simple code:</p>
62 <div class="doc_code">
64 ready> <b>def test(x) 1+2+x;</b>
65 Read function definition:
66 define double @test(double %x) {
68 %addtmp = add double 3.000000e+00, %x
74 <p>This code is not a literal transcription of the AST built by parsing the
77 <div class="doc_code">
79 ready> <b>def test(x) 1+2+x;</b>
80 Read function definition:
81 define double @test(double %x) {
83 %addtmp = add double 2.000000e+00, 1.000000e+00
84 %addtmp1 = add double %addtmp, %x
90 <p>Constant folding, as seen above, in particular, is a very common and very
91 important optimization: so much so that many language implementors implement
92 constant folding support in their AST representation.</p>
94 <p>With LLVM, you don't need this support in the AST. Since all calls to build
95 LLVM IR go through the LLVM IR builder, the builder itself checked to see if
96 there was a constant folding opportunity when you call it. If so, it just does
97 the constant fold and return the constant instead of creating an instruction.
99 <p>Well, that was easy :). In practice, we recommend always using
100 <tt>IRBuilder</tt> when generating code like this. It has no
101 "syntactic overhead" for its use (you don't have to uglify your compiler with
102 constant checks everywhere) and it can dramatically reduce the amount of
103 LLVM IR that is generated in some cases (particular for languages with a macro
104 preprocessor or that use a lot of constants).</p>
106 <p>On the other hand, the <tt>IRBuilder</tt> is limited by the fact
107 that it does all of its analysis inline with the code as it is built. If you
108 take a slightly more complex example:</p>
110 <div class="doc_code">
112 ready> <b>def test(x) (1+2+x)*(x+(1+2));</b>
113 ready> Read function definition:
114 define double @test(double %x) {
116 %addtmp = add double 3.000000e+00, %x
117 %addtmp1 = add double %x, 3.000000e+00
118 %multmp = mul double %addtmp, %addtmp1
124 <p>In this case, the LHS and RHS of the multiplication are the same value. We'd
125 really like to see this generate "<tt>tmp = x+3; result = tmp*tmp;</tt>" instead
126 of computing "<tt>x+3</tt>" twice.</p>
128 <p>Unfortunately, no amount of local analysis will be able to detect and correct
129 this. This requires two transformations: reassociation of expressions (to
130 make the add's lexically identical) and Common Subexpression Elimination (CSE)
131 to delete the redundant add instruction. Fortunately, LLVM provides a broad
132 range of optimizations that you can use, in the form of "passes".</p>
136 <!-- *********************************************************************** -->
137 <div class="doc_section"><a name="optimizerpasses">LLVM Optimization
139 <!-- *********************************************************************** -->
141 <div class="doc_text">
143 <p>LLVM provides many optimization passes, which do many different sorts of
144 things and have different tradeoffs. Unlike other systems, LLVM doesn't hold
145 to the mistaken notion that one set of optimizations is right for all languages
146 and for all situations. LLVM allows a compiler implementor to make complete
147 decisions about what optimizations to use, in which order, and in what
150 <p>As a concrete example, LLVM supports both "whole module" passes, which look
151 across as large of body of code as they can (often a whole file, but if run
152 at link time, this can be a substantial portion of the whole program). It also
153 supports and includes "per-function" passes which just operate on a single
154 function at a time, without looking at other functions. For more information
155 on passes and how they are run, see the <a href="../WritingAnLLVMPass.html">How
156 to Write a Pass</a> document and the <a href="../Passes.html">List of LLVM
159 <p>For Kaleidoscope, we are currently generating functions on the fly, one at
160 a time, as the user types them in. We aren't shooting for the ultimate
161 optimization experience in this setting, but we also want to catch the easy and
162 quick stuff where possible. As such, we will choose to run a few per-function
163 optimizations as the user types the function in. If we wanted to make a "static
164 Kaleidoscope compiler", we would use exactly the code we have now, except that
165 we would defer running the optimizer until the entire file has been parsed.</p>
167 <p>In order to get per-function optimizations going, we need to set up a
168 <a href="../WritingAnLLVMPass.html#passmanager">FunctionPassManager</a> to hold and
169 organize the LLVM optimizations that we want to run. Once we have that, we can
170 add a set of optimizations to run. The code looks like this:</p>
172 <div class="doc_code">
174 ExistingModuleProvider OurModuleProvider(TheModule);
175 FunctionPassManager OurFPM(&OurModuleProvider);
177 // Set up the optimizer pipeline. Start with registering info about how the
178 // target lays out data structures.
179 OurFPM.add(new TargetData(*TheExecutionEngine->getTargetData()));
180 // Do simple "peephole" optimizations and bit-twiddling optzns.
181 OurFPM.add(createInstructionCombiningPass());
182 // Reassociate expressions.
183 OurFPM.add(createReassociatePass());
184 // Eliminate Common SubExpressions.
185 OurFPM.add(createGVNPass());
186 // Simplify the control flow graph (deleting unreachable blocks, etc).
187 OurFPM.add(createCFGSimplificationPass());
189 // Set the global so the code gen can use this.
190 TheFPM = &OurFPM;
192 // Run the main "interpreter loop" now.
197 <p>This code defines two objects, an <tt>ExistingModuleProvider</tt> and a
198 <tt>FunctionPassManager</tt>. The former is basically a wrapper around our
199 <tt>Module</tt> that the PassManager requires. It provides certain flexibility
200 that we're not going to take advantage of here, so I won't dive into any details
203 <p>The meat of the matter here, is the definition of "<tt>OurFPM</tt>". It
204 requires a pointer to the <tt>Module</tt> (through the <tt>ModuleProvider</tt>)
205 to construct itself. Once it is set up, we use a series of "add" calls to add
206 a bunch of LLVM passes. The first pass is basically boilerplate, it adds a pass
207 so that later optimizations know how the data structures in the program are
208 layed out. The "<tt>TheExecutionEngine</tt>" variable is related to the JIT,
209 which we will get to in the next section.</p>
211 <p>In this case, we choose to add 4 optimization passes. The passes we chose
212 here are a pretty standard set of "cleanup" optimizations that are useful for
213 a wide variety of code. I won't delve into what they do but, believe me,
214 they are a good starting place :).</p>
216 <p>Once the PassManager is set up, we need to make use of it. We do this by
217 running it after our newly created function is constructed (in
218 <tt>FunctionAST::Codegen</tt>), but before it is returned to the client:</p>
220 <div class="doc_code">
222 if (Value *RetVal = Body->Codegen()) {
223 // Finish off the function.
224 Builder.CreateRet(RetVal);
226 // Validate the generated code, checking for consistency.
227 verifyFunction(*TheFunction);
229 <b>// Optimize the function.
230 TheFPM->run(*TheFunction);</b>
237 <p>As you can see, this is pretty straightforward. The
238 <tt>FunctionPassManager</tt> optimizes and updates the LLVM Function* in place,
239 improving (hopefully) its body. With this in place, we can try our test above
242 <div class="doc_code">
244 ready> <b>def test(x) (1+2+x)*(x+(1+2));</b>
245 ready> Read function definition:
246 define double @test(double %x) {
248 %addtmp = add double %x, 3.000000e+00
249 %multmp = mul double %addtmp, %addtmp
255 <p>As expected, we now get our nicely optimized code, saving a floating point
256 add instruction from every execution of this function.</p>
258 <p>LLVM provides a wide variety of optimizations that can be used in certain
259 circumstances. Some <a href="../Passes.html">documentation about the various
260 passes</a> is available, but it isn't very complete. Another good source of
261 ideas can come from looking at the passes that <tt>llvm-gcc</tt> or
262 <tt>llvm-ld</tt> run to get started. The "<tt>opt</tt>" tool allows you to
263 experiment with passes from the command line, so you can see if they do
266 <p>Now that we have reasonable code coming out of our front-end, lets talk about
271 <!-- *********************************************************************** -->
272 <div class="doc_section"><a name="jit">Adding a JIT Compiler</a></div>
273 <!-- *********************************************************************** -->
275 <div class="doc_text">
277 <p>Code that is available in LLVM IR can have a wide variety of tools
278 applied to it. For example, you can run optimizations on it (as we did above),
279 you can dump it out in textual or binary forms, you can compile the code to an
280 assembly file (.s) for some target, or you can JIT compile it. The nice thing
281 about the LLVM IR representation is that it is the "common currency" between
282 many different parts of the compiler.
285 <p>In this section, we'll add JIT compiler support to our interpreter. The
286 basic idea that we want for Kaleidoscope is to have the user enter function
287 bodies as they do now, but immediately evaluate the top-level expressions they
288 type in. For example, if they type in "1 + 2;", we should evaluate and print
289 out 3. If they define a function, they should be able to call it from the
292 <p>In order to do this, we first declare and initialize the JIT. This is done
293 by adding a global variable and a call in <tt>main</tt>:</p>
295 <div class="doc_code">
297 <b>static ExecutionEngine *TheExecutionEngine;</b>
301 <b>// Create the JIT.
302 TheExecutionEngine = EngineBuilder(TheModule).create();</b>
308 <p>This creates an abstract "Execution Engine" which can be either a JIT
309 compiler or the LLVM interpreter. LLVM will automatically pick a JIT compiler
310 for you if one is available for your platform, otherwise it will fall back to
313 <p>Once the <tt>ExecutionEngine</tt> is created, the JIT is ready to be used.
314 There are a variety of APIs that are useful, but the simplest one is the
315 "<tt>getPointerToFunction(F)</tt>" method. This method JIT compiles the
316 specified LLVM Function and returns a function pointer to the generated machine
317 code. In our case, this means that we can change the code that parses a
318 top-level expression to look like this:</p>
320 <div class="doc_code">
322 static void HandleTopLevelExpression() {
323 // Evaluate a top level expression into an anonymous function.
324 if (FunctionAST *F = ParseTopLevelExpr()) {
325 if (Function *LF = F->Codegen()) {
326 LF->dump(); // Dump the function for exposition purposes.
328 <b>// JIT the function, returning a function pointer.
329 void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
331 // Cast it to the right type (takes no arguments, returns a double) so we
332 // can call it as a native function.
333 double (*FP)() = (double (*)())FPtr;
334 fprintf(stderr, "Evaluated to %f\n", FP());</b>
339 <p>Recall that we compile top-level expressions into a self-contained LLVM
340 function that takes no arguments and returns the computed double. Because the
341 LLVM JIT compiler matches the native platform ABI, this means that you can just
342 cast the result pointer to a function pointer of that type and call it directly.
343 This means, there is no difference between JIT compiled code and native machine
344 code that is statically linked into your application.</p>
346 <p>With just these two changes, lets see how Kaleidoscope works now!</p>
348 <div class="doc_code">
350 ready> <b>4+5;</b>
351 define double @""() {
353 ret double 9.000000e+00
356 <em>Evaluated to 9.000000</em>
360 <p>Well this looks like it is basically working. The dump of the function
361 shows the "no argument function that always returns double" that we synthesize
362 for each top level expression that is typed in. This demonstrates very basic
363 functionality, but can we do more?</p>
365 <div class="doc_code">
367 ready> <b>def testfunc(x y) x + y*2; </b>
368 Read function definition:
369 define double @testfunc(double %x, double %y) {
371 %multmp = mul double %y, 2.000000e+00
372 %addtmp = add double %multmp, %x
376 ready> <b>testfunc(4, 10);</b>
377 define double @""() {
379 %calltmp = call double @testfunc( double 4.000000e+00, double 1.000000e+01 )
383 <em>Evaluated to 24.000000</em>
387 <p>This illustrates that we can now call user code, but there is something a bit subtle
388 going on here. Note that we only invoke the JIT on the anonymous functions
389 that <em>call testfunc</em>, but we never invoked it on <em>testfunc
392 <p>What actually happened here is that the anonymous function was
393 JIT'd when requested. When the Kaleidoscope app calls through the function
394 pointer that is returned, the anonymous function starts executing. It ends up
395 making the call to the "testfunc" function, and ends up in a stub that invokes
396 the JIT, lazily, on testfunc. Once the JIT finishes lazily compiling testfunc,
397 it returns and the code re-executes the call.</p>
399 <p>In summary, the JIT will lazily JIT code, on the fly, as it is needed. The
400 JIT provides a number of other more advanced interfaces for things like freeing
401 allocated machine code, rejit'ing functions to update them, etc. However, even
402 with this simple code, we get some surprisingly powerful capabilities - check
403 this out (I removed the dump of the anonymous functions, you should get the idea
406 <div class="doc_code">
408 ready> <b>extern sin(x);</b>
410 declare double @sin(double)
412 ready> <b>extern cos(x);</b>
414 declare double @cos(double)
416 ready> <b>sin(1.0);</b>
417 <em>Evaluated to 0.841471</em>
419 ready> <b>def foo(x) sin(x)*sin(x) + cos(x)*cos(x);</b>
420 Read function definition:
421 define double @foo(double %x) {
423 %calltmp = call double @sin( double %x )
424 %multmp = mul double %calltmp, %calltmp
425 %calltmp2 = call double @cos( double %x )
426 %multmp4 = mul double %calltmp2, %calltmp2
427 %addtmp = add double %multmp, %multmp4
431 ready> <b>foo(4.0);</b>
432 <em>Evaluated to 1.000000</em>
436 <p>Whoa, how does the JIT know about sin and cos? The answer is surprisingly
438 example, the JIT started execution of a function and got to a function call. It
439 realized that the function was not yet JIT compiled and invoked the standard set
440 of routines to resolve the function. In this case, there is no body defined
441 for the function, so the JIT ended up calling "<tt>dlsym("sin")</tt>" on the
442 Kaleidoscope process itself.
443 Since "<tt>sin</tt>" is defined within the JIT's address space, it simply
444 patches up calls in the module to call the libm version of <tt>sin</tt>
447 <p>The LLVM JIT provides a number of interfaces (look in the
448 <tt>ExecutionEngine.h</tt> file) for controlling how unknown functions get
449 resolved. It allows you to establish explicit mappings between IR objects and
450 addresses (useful for LLVM global variables that you want to map to static
451 tables, for example), allows you to dynamically decide on the fly based on the
452 function name, and even allows you to have the JIT abort itself if any lazy
453 compilation is attempted.</p>
455 <p>One interesting application of this is that we can now extend the language
456 by writing arbitrary C++ code to implement operations. For example, if we add:
459 <div class="doc_code">
461 /// putchard - putchar that takes a double and returns 0.
463 double putchard(double X) {
470 <p>Now we can produce simple output to the console by using things like:
471 "<tt>extern putchard(x); putchard(120);</tt>", which prints a lowercase 'x' on
472 the console (120 is the ASCII code for 'x'). Similar code could be used to
473 implement file I/O, console input, and many other capabilities in
476 <p>This completes the JIT and optimizer chapter of the Kaleidoscope tutorial. At
477 this point, we can compile a non-Turing-complete programming language, optimize
478 and JIT compile it in a user-driven way. Next up we'll look into <a
479 href="LangImpl5.html">extending the language with control flow constructs</a>,
480 tackling some interesting LLVM IR issues along the way.</p>
484 <!-- *********************************************************************** -->
485 <div class="doc_section"><a name="code">Full Code Listing</a></div>
486 <!-- *********************************************************************** -->
488 <div class="doc_text">
491 Here is the complete code listing for our running example, enhanced with the
492 LLVM JIT and optimizer. To build this example, use:
495 <div class="doc_code">
498 g++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
505 If you are compiling this on Linux, make sure to add the "-rdynamic" option
506 as well. This makes sure that the external functions are resolved properly
509 <p>Here is the code:</p>
511 <div class="doc_code">
513 #include "llvm/DerivedTypes.h"
514 #include "llvm/ExecutionEngine/ExecutionEngine.h"
515 #include "llvm/LLVMContext.h"
516 #include "llvm/Module.h"
517 #include "llvm/ModuleProvider.h"
518 #include "llvm/PassManager.h"
519 #include "llvm/Analysis/Verifier.h"
520 #include "llvm/Target/TargetData.h"
521 #include "llvm/Transforms/Scalar.h"
522 #include "llvm/Support/IRBuilder.h"
523 #include <cstdio>
524 #include <string>
526 #include <vector>
527 using namespace llvm;
529 //===----------------------------------------------------------------------===//
531 //===----------------------------------------------------------------------===//
533 // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
534 // of these for known things.
539 tok_def = -2, tok_extern = -3,
542 tok_identifier = -4, tok_number = -5,
545 static std::string IdentifierStr; // Filled in if tok_identifier
546 static double NumVal; // Filled in if tok_number
548 /// gettok - Return the next token from standard input.
549 static int gettok() {
550 static int LastChar = ' ';
552 // Skip any whitespace.
553 while (isspace(LastChar))
554 LastChar = getchar();
556 if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
557 IdentifierStr = LastChar;
558 while (isalnum((LastChar = getchar())))
559 IdentifierStr += LastChar;
561 if (IdentifierStr == "def") return tok_def;
562 if (IdentifierStr == "extern") return tok_extern;
563 return tok_identifier;
566 if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
570 LastChar = getchar();
571 } while (isdigit(LastChar) || LastChar == '.');
573 NumVal = strtod(NumStr.c_str(), 0);
577 if (LastChar == '#') {
578 // Comment until end of line.
579 do LastChar = getchar();
580 while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
586 // Check for end of file. Don't eat the EOF.
590 // Otherwise, just return the character as its ascii value.
591 int ThisChar = LastChar;
592 LastChar = getchar();
596 //===----------------------------------------------------------------------===//
597 // Abstract Syntax Tree (aka Parse Tree)
598 //===----------------------------------------------------------------------===//
600 /// ExprAST - Base class for all expression nodes.
603 virtual ~ExprAST() {}
604 virtual Value *Codegen() = 0;
607 /// NumberExprAST - Expression class for numeric literals like "1.0".
608 class NumberExprAST : public ExprAST {
611 NumberExprAST(double val) : Val(val) {}
612 virtual Value *Codegen();
615 /// VariableExprAST - Expression class for referencing a variable, like "a".
616 class VariableExprAST : public ExprAST {
619 VariableExprAST(const std::string &name) : Name(name) {}
620 virtual Value *Codegen();
623 /// BinaryExprAST - Expression class for a binary operator.
624 class BinaryExprAST : public ExprAST {
628 BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
629 : Op(op), LHS(lhs), RHS(rhs) {}
630 virtual Value *Codegen();
633 /// CallExprAST - Expression class for function calls.
634 class CallExprAST : public ExprAST {
636 std::vector<ExprAST*> Args;
638 CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
639 : Callee(callee), Args(args) {}
640 virtual Value *Codegen();
643 /// PrototypeAST - This class represents the "prototype" for a function,
644 /// which captures its argument names as well as if it is an operator.
647 std::vector<std::string> Args;
649 PrototypeAST(const std::string &name, const std::vector<std::string> &args)
650 : Name(name), Args(args) {}
655 /// FunctionAST - This class represents a function definition itself.
660 FunctionAST(PrototypeAST *proto, ExprAST *body)
661 : Proto(proto), Body(body) {}
666 //===----------------------------------------------------------------------===//
668 //===----------------------------------------------------------------------===//
670 /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
671 /// token the parser it looking at. getNextToken reads another token from the
672 /// lexer and updates CurTok with its results.
674 static int getNextToken() {
675 return CurTok = gettok();
678 /// BinopPrecedence - This holds the precedence for each binary operator that is
680 static std::map<char, int> BinopPrecedence;
682 /// GetTokPrecedence - Get the precedence of the pending binary operator token.
683 static int GetTokPrecedence() {
684 if (!isascii(CurTok))
687 // Make sure it's a declared binop.
688 int TokPrec = BinopPrecedence[CurTok];
689 if (TokPrec <= 0) return -1;
693 /// Error* - These are little helper functions for error handling.
694 ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
695 PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
696 FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
698 static ExprAST *ParseExpression();
702 /// ::= identifier '(' expression* ')'
703 static ExprAST *ParseIdentifierExpr() {
704 std::string IdName = IdentifierStr;
706 getNextToken(); // eat identifier.
708 if (CurTok != '(') // Simple variable ref.
709 return new VariableExprAST(IdName);
712 getNextToken(); // eat (
713 std::vector<ExprAST*> Args;
716 ExprAST *Arg = ParseExpression();
720 if (CurTok == ')') break;
723 return Error("Expected ')' or ',' in argument list");
731 return new CallExprAST(IdName, Args);
734 /// numberexpr ::= number
735 static ExprAST *ParseNumberExpr() {
736 ExprAST *Result = new NumberExprAST(NumVal);
737 getNextToken(); // consume the number
741 /// parenexpr ::= '(' expression ')'
742 static ExprAST *ParseParenExpr() {
743 getNextToken(); // eat (.
744 ExprAST *V = ParseExpression();
748 return Error("expected ')'");
749 getNextToken(); // eat ).
754 /// ::= identifierexpr
757 static ExprAST *ParsePrimary() {
759 default: return Error("unknown token when expecting an expression");
760 case tok_identifier: return ParseIdentifierExpr();
761 case tok_number: return ParseNumberExpr();
762 case '(': return ParseParenExpr();
767 /// ::= ('+' primary)*
768 static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
769 // If this is a binop, find its precedence.
771 int TokPrec = GetTokPrecedence();
773 // If this is a binop that binds at least as tightly as the current binop,
774 // consume it, otherwise we are done.
775 if (TokPrec < ExprPrec)
778 // Okay, we know this is a binop.
780 getNextToken(); // eat binop
782 // Parse the primary expression after the binary operator.
783 ExprAST *RHS = ParsePrimary();
786 // If BinOp binds less tightly with RHS than the operator after RHS, let
787 // the pending operator take RHS as its LHS.
788 int NextPrec = GetTokPrecedence();
789 if (TokPrec < NextPrec) {
790 RHS = ParseBinOpRHS(TokPrec+1, RHS);
791 if (RHS == 0) return 0;
795 LHS = new BinaryExprAST(BinOp, LHS, RHS);
800 /// ::= primary binoprhs
802 static ExprAST *ParseExpression() {
803 ExprAST *LHS = ParsePrimary();
806 return ParseBinOpRHS(0, LHS);
810 /// ::= id '(' id* ')'
811 static PrototypeAST *ParsePrototype() {
812 if (CurTok != tok_identifier)
813 return ErrorP("Expected function name in prototype");
815 std::string FnName = IdentifierStr;
819 return ErrorP("Expected '(' in prototype");
821 std::vector<std::string> ArgNames;
822 while (getNextToken() == tok_identifier)
823 ArgNames.push_back(IdentifierStr);
825 return ErrorP("Expected ')' in prototype");
828 getNextToken(); // eat ')'.
830 return new PrototypeAST(FnName, ArgNames);
833 /// definition ::= 'def' prototype expression
834 static FunctionAST *ParseDefinition() {
835 getNextToken(); // eat def.
836 PrototypeAST *Proto = ParsePrototype();
837 if (Proto == 0) return 0;
839 if (ExprAST *E = ParseExpression())
840 return new FunctionAST(Proto, E);
844 /// toplevelexpr ::= expression
845 static FunctionAST *ParseTopLevelExpr() {
846 if (ExprAST *E = ParseExpression()) {
847 // Make an anonymous proto.
848 PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
849 return new FunctionAST(Proto, E);
854 /// external ::= 'extern' prototype
855 static PrototypeAST *ParseExtern() {
856 getNextToken(); // eat extern.
857 return ParsePrototype();
860 //===----------------------------------------------------------------------===//
862 //===----------------------------------------------------------------------===//
864 static Module *TheModule;
865 static IRBuilder<> Builder(getGlobalContext());
866 static std::map<std::string, Value*> NamedValues;
867 static FunctionPassManager *TheFPM;
869 Value *ErrorV(const char *Str) { Error(Str); return 0; }
871 Value *NumberExprAST::Codegen() {
872 return ConstantFP::get(getGlobalContext(), APFloat(Val));
875 Value *VariableExprAST::Codegen() {
876 // Look this variable up in the function.
877 Value *V = NamedValues[Name];
878 return V ? V : ErrorV("Unknown variable name");
881 Value *BinaryExprAST::Codegen() {
882 Value *L = LHS->Codegen();
883 Value *R = RHS->Codegen();
884 if (L == 0 || R == 0) return 0;
887 case '+': return Builder.CreateAdd(L, R, "addtmp");
888 case '-': return Builder.CreateSub(L, R, "subtmp");
889 case '*': return Builder.CreateMul(L, R, "multmp");
891 L = Builder.CreateFCmpULT(L, R, "cmptmp");
892 // Convert bool 0/1 to double 0.0 or 1.0
893 return Builder.CreateUIToFP(L, Type::DoubleTy, "booltmp");
894 default: return ErrorV("invalid binary operator");
898 Value *CallExprAST::Codegen() {
899 // Look up the name in the global module table.
900 Function *CalleeF = TheModule->getFunction(Callee);
902 return ErrorV("Unknown function referenced");
904 // If argument mismatch error.
905 if (CalleeF->arg_size() != Args.size())
906 return ErrorV("Incorrect # arguments passed");
908 std::vector<Value*> ArgsV;
909 for (unsigned i = 0, e = Args.size(); i != e; ++i) {
910 ArgsV.push_back(Args[i]->Codegen());
911 if (ArgsV.back() == 0) return 0;
914 return Builder.CreateCall(CalleeF, ArgsV.begin(), ArgsV.end(), "calltmp");
917 Function *PrototypeAST::Codegen() {
918 // Make the function type: double(double,double) etc.
919 std::vector<const Type*> Doubles(Args.size(), Type::DoubleTy);
920 FunctionType *FT = FunctionType::get(Type::DoubleTy, Doubles, false);
922 Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
924 // If F conflicted, there was already something named 'Name'. If it has a
925 // body, don't allow redefinition or reextern.
926 if (F->getName() != Name) {
927 // Delete the one we just made and get the existing one.
928 F->eraseFromParent();
929 F = TheModule->getFunction(Name);
931 // If F already has a body, reject this.
932 if (!F->empty()) {
933 ErrorF("redefinition of function");
937 // If F took a different number of args, reject.
938 if (F->arg_size() != Args.size()) {
939 ErrorF("redefinition of function with different # args");
944 // Set names for all arguments.
946 for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
948 AI->setName(Args[Idx]);
950 // Add arguments to variable symbol table.
951 NamedValues[Args[Idx]] = AI;
957 Function *FunctionAST::Codegen() {
960 Function *TheFunction = Proto->Codegen();
961 if (TheFunction == 0)
964 // Create a new basic block to start insertion into.
965 BasicBlock *BB = BasicBlock::Create("entry", TheFunction);
966 Builder.SetInsertPoint(BB);
968 if (Value *RetVal = Body->Codegen()) {
969 // Finish off the function.
970 Builder.CreateRet(RetVal);
972 // Validate the generated code, checking for consistency.
973 verifyFunction(*TheFunction);
975 // Optimize the function.
976 TheFPM->run(*TheFunction);
981 // Error reading body, remove function.
982 TheFunction->eraseFromParent();
986 //===----------------------------------------------------------------------===//
987 // Top-Level parsing and JIT Driver
988 //===----------------------------------------------------------------------===//
990 static ExecutionEngine *TheExecutionEngine;
992 static void HandleDefinition() {
993 if (FunctionAST *F = ParseDefinition()) {
994 if (Function *LF = F->Codegen()) {
995 fprintf(stderr, "Read function definition:");
999 // Skip token for error recovery.
1004 static void HandleExtern() {
1005 if (PrototypeAST *P = ParseExtern()) {
1006 if (Function *F = P->Codegen()) {
1007 fprintf(stderr, "Read extern: ");
1011 // Skip token for error recovery.
1016 static void HandleTopLevelExpression() {
1017 // Evaluate a top level expression into an anonymous function.
1018 if (FunctionAST *F = ParseTopLevelExpr()) {
1019 if (Function *LF = F->Codegen()) {
1020 // JIT the function, returning a function pointer.
1021 void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
1023 // Cast it to the right type (takes no arguments, returns a double) so we
1024 // can call it as a native function.
1025 double (*FP)() = (double (*)())FPtr;
1026 fprintf(stderr, "Evaluated to %f\n", FP());
1029 // Skip token for error recovery.
1034 /// top ::= definition | external | expression | ';'
1035 static void MainLoop() {
1037 fprintf(stderr, "ready> ");
1039 case tok_eof: return;
1040 case ';': getNextToken(); break; // ignore top level semicolons.
1041 case tok_def: HandleDefinition(); break;
1042 case tok_extern: HandleExtern(); break;
1043 default: HandleTopLevelExpression(); break;
1050 //===----------------------------------------------------------------------===//
1051 // "Library" functions that can be "extern'd" from user code.
1052 //===----------------------------------------------------------------------===//
1054 /// putchard - putchar that takes a double and returns 0.
1056 double putchard(double X) {
1061 //===----------------------------------------------------------------------===//
1062 // Main driver code.
1063 //===----------------------------------------------------------------------===//
1066 // Install standard binary operators.
1067 // 1 is lowest precedence.
1068 BinopPrecedence['<'] = 10;
1069 BinopPrecedence['+'] = 20;
1070 BinopPrecedence['-'] = 20;
1071 BinopPrecedence['*'] = 40; // highest.
1073 // Prime the first token.
1074 fprintf(stderr, "ready> ");
1077 // Make the module, which holds all the code.
1078 TheModule = new Module("my cool jit", getGlobalContext());
1081 TheExecutionEngine = EngineBuilder(TheModule).create();
1084 ExistingModuleProvider OurModuleProvider(TheModule);
1085 FunctionPassManager OurFPM(&OurModuleProvider);
1087 // Set up the optimizer pipeline. Start with registering info about how the
1088 // target lays out data structures.
1089 OurFPM.add(new TargetData(*TheExecutionEngine->getTargetData()));
1090 // Do simple "peephole" optimizations and bit-twiddling optzns.
1091 OurFPM.add(createInstructionCombiningPass());
1092 // Reassociate expressions.
1093 OurFPM.add(createReassociatePass());
1094 // Eliminate Common SubExpressions.
1095 OurFPM.add(createGVNPass());
1096 // Simplify the control flow graph (deleting unreachable blocks, etc).
1097 OurFPM.add(createCFGSimplificationPass());
1099 // Set the global so the code gen can use this.
1100 TheFPM = &OurFPM;
1102 // Run the main "interpreter loop" now.
1107 // Print out all of the generated code.
1108 TheModule->dump();
1109 } // Free module provider (and thus the module) and pass manager.
1116 <a href="LangImpl5.html">Next: Extending the language: control flow</a>
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1129 Last modified: $Date: 2007-10-17 11:05:13 -0700 (Wed, 17 Oct 2007) $