1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
6 <title>Kaleidoscope: Implementing code generation to LLVM IR</title>
7 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
8 <meta name="author" content="Chris Lattner">
9 <link rel="stylesheet" href="../llvm.css" type="text/css">
14 <div class="doc_title">Kaleidoscope: Code generation to LLVM IR</div>
19 <li><a href="#intro">Chapter 3 Introduction</a></li>
20 <li><a href="#basics">Code Generation setup</a></li>
21 <li><a href="#exprs">Expression Code Generation</a></li>
22 <li><a href="#funcs">Function Code Generation</a></li>
23 <li><a href="#driver">Driver Changes and Closing Thoughts</a></li>
24 <li><a href="#code">Full Code Listing</a></li>
29 <div class="doc_author">
30 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
33 <!-- *********************************************************************** -->
34 <div class="doc_section"><a name="intro">Chapter 3 Introduction</a></div>
35 <!-- *********************************************************************** -->
37 <div class="doc_text">
39 <p>Welcome to Chapter 3 of the "<a href="index.html">Implementing a language
40 with LLVM</a>" tutorial. This chapter shows you how to transform the <a
41 href="LangImpl2.html">Abstract Syntax Tree built in Chapter 2</a> into LLVM IR.
42 This will teach you a little bit about how LLVM does things, as well as
43 demonstrate how easy it is to use. It's much more work to build a lexer and
44 parser than it is to generate LLVM IR code.
49 <!-- *********************************************************************** -->
50 <div class="doc_section"><a name="basics">Code Generation setup</a></div>
51 <!-- *********************************************************************** -->
53 <div class="doc_text">
56 In order to generate LLVM IR, we want some simple setup to get started. First,
57 we define virtual codegen methods in each AST class:</p>
59 <div class="doc_code">
61 /// ExprAST - Base class for all expression nodes.
65 virtual Value *Codegen() = 0;
68 /// NumberExprAST - Expression class for numeric literals like "1.0".
69 class NumberExprAST : public ExprAST {
72 explicit NumberExprAST(double val) : Val(val) {}
73 virtual Value *Codegen();
79 <p>The Codegen() method says to emit IR for that AST node and all things it
80 depends on, and they all return an LLVM Value object.
81 "Value" is the class used to represent a "<a
82 href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
83 Assignment (SSA)</a> register" or "SSA value" in LLVM. The most distinct aspect
84 of SSA values is that their value is computed as the related instruction
85 executes, and it does not get a new value until (and if) the instruction
86 re-executes. In order words, there is no way to "change" an SSA value. For
87 more information, please read up on <a
88 href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
89 Assignment</a> - the concepts are really quite natural once you grok them.</p>
92 second thing we want is an "Error" method like we used for parser, which will
93 be used to report errors found during code generation (for example, use of an
94 undeclared parameter):</p>
96 <div class="doc_code">
98 Value *ErrorV(const char *Str) { Error(Str); return 0; }
100 static Module *TheModule;
101 static LLVMBuilder Builder;
102 static std::map<std::string, Value*> NamedValues;
106 <p>The static variables will be used during code generation. <tt>TheModule</tt>
107 is the LLVM construct that contains all of the functions and global variables in
108 a chunk of code. In many ways, it is the top-level structure that the LLVM IR
109 uses to contain code.</p>
111 <p>The <tt>Builder</tt> object is a helper object that makes it easy to generate
112 LLVM instructions. Instances of the <a
113 href="http://llvm.org/doxygen/LLVMBuilder_8h-source.html"><tt>LLVMBuilder</tt>
114 class</a> keeps track of the current place to
115 insert instructions and has methods to create new instructions.</p>
117 <p>The <tt>NamedValues</tt> map keeps track of which values are defined in the
118 current scope and what their LLVM representation is. In this form of
119 Kaleidoscope, the only things that can be referenced are function parameters.
120 As such, function parameters will be in this map when generating code for their
124 With these basics in place, we can start talking about how to generate code for
125 each expression. Note that this assumes that the <tt>Builder</tt> has been set
126 up to generate code <em>into</em> something. For now, we'll assume that this
127 has already been done, and we'll just use it to emit code.
132 <!-- *********************************************************************** -->
133 <div class="doc_section"><a name="exprs">Expression Code Generation</a></div>
134 <!-- *********************************************************************** -->
136 <div class="doc_text">
138 <p>Generating LLVM code for expression nodes is very straight-forward: less
139 than 45 lines of commented code for all four of our expression nodes. First,
140 we'll do numeric literals:</p>
142 <div class="doc_code">
144 Value *NumberExprAST::Codegen() {
145 return ConstantFP::get(Type::DoubleTy, APFloat(Val));
150 <p>In the LLVM IR, numeric constants are represented with the
151 <tt>ConstantFP</tt> class, which holds the numeric value in an <tt>APFloat</tt>
152 internally (<tt>APFloat</tt> has the capability of holding floating point
153 constants of <em>A</em>rbitrary <em>P</em>recision). This code basically just
154 creates and returns a <tt>ConstantFP</tt>. Note that in the LLVM IR
155 that constants are all uniqued together and shared. For this reason, the API
156 uses "the foo::get(..)" idiom instead of "new foo(..)" or "foo::create(..).</p>
158 <div class="doc_code">
160 Value *VariableExprAST::Codegen() {
161 // Look this variable up in the function.
162 Value *V = NamedValues[Name];
163 return V ? V : ErrorV("Unknown variable name");
168 <p>References to variables is also quite simple here. In the simple version
169 of Kaleidoscope, we assume that the variable has already been emited somewhere
170 and its value is available. In practice, the only values that can be in the
171 <tt>NamedValues</tt> map are function arguments. This
172 code simply checks to see that the specified name is in the map (if not, an
173 unknown variable is being referenced) and returns the value for it.</p>
175 <div class="doc_code">
177 Value *BinaryExprAST::Codegen() {
178 Value *L = LHS->Codegen();
179 Value *R = RHS->Codegen();
180 if (L == 0 || R == 0) return 0;
183 case '+': return Builder.CreateAdd(L, R, "addtmp");
184 case '-': return Builder.CreateSub(L, R, "subtmp");
185 case '*': return Builder.CreateMul(L, R, "multmp");
187 L = Builder.CreateFCmpULT(L, R, "multmp");
188 // Convert bool 0/1 to double 0.0 or 1.0
189 return Builder.CreateUIToFP(L, Type::DoubleTy, "booltmp");
190 default: return ErrorV("invalid binary operator");
196 <p>Binary operators start to get more interesting. The basic idea here is that
197 we recursively emit code for the left-hand side of the expression, then the
198 right-hand side, then we compute the result of the binary expression. In this
199 code, we do a simple switch on the opcode to create the right LLVM instruction.
202 <p>In this example, the LLVM builder class is starting to show its value.
203 Because it knows where to insert the newly created instruction, you just have to
204 specificy what instruction to create (e.g. with <tt>CreateAdd</tt>), which
205 operands to use (<tt>L</tt> and <tt>R</tt> here) and optionally provide a name
206 for the generated instruction. One nice thing about LLVM is that the name is
207 just a hint: if there are multiple additions in a single function, the first
208 will be named "addtmp" and the second will be "autorenamed" by adding a suffix,
209 giving it a name like "addtmp42". Local value names for instructions are purely
210 optional, but it makes it much easier to read the IR dumps.</p>
212 <p><a href="../LangRef.html#instref">LLVM instructions</a> are constrained to
213 have very strict type properties: for example, the Left and Right operators of
214 an <a href="../LangRef.html#i_add">add instruction</a> have to have the same
215 type, and that the result of the add matches the operands. Because all values
216 in Kaleidoscope are doubles, this makes for very simple code for add, sub and
219 <p>On the other hand, LLVM specifies that the <a
220 href="../LangRef.html#i_fcmp">fcmp instruction</a> always returns an 'i1' value
221 (a one bit integer). However, Kaleidoscope wants the value to be a 0.0 or 1.0
222 value. In order to get these semantics, we combine the fcmp instruction with
223 a <a href="../LangRef.html#i_uitofp">uitofp instruction</a>. This instruction
224 converts its input integer into a floating point value by treating the input
225 as an unsigned value. In contrast, if we used the <a
226 href="../LangRef.html#i_sitofp">sitofp instruction</a>, the Kaleidoscope '<'
227 operator would return 0.0 and -1.0, depending on the input value.</p>
229 <div class="doc_code">
231 Value *CallExprAST::Codegen() {
232 // Look up the name in the global module table.
233 Function *CalleeF = TheModule->getFunction(Callee);
235 return ErrorV("Unknown function referenced");
237 // If argument mismatch error.
238 if (CalleeF->arg_size() != Args.size())
239 return ErrorV("Incorrect # arguments passed");
241 std::vector<Value*> ArgsV;
242 for (unsigned i = 0, e = Args.size(); i != e; ++i) {
243 ArgsV.push_back(Args[i]->Codegen());
244 if (ArgsV.back() == 0) return 0;
247 return Builder.CreateCall(CalleeF, ArgsV.begin(), ArgsV.end(), "calltmp");
252 <p>Code generation for function calls is quite straight-forward with LLVM. The
253 code above first looks the name of the function up in the LLVM Module's symbol
254 table. Recall that the LLVM Module is the container that holds all of the
255 functions we are JIT'ing. By giving each function the same name as what the
256 user specifies, we can use the LLVM symbol table to resolve function names for
259 <p>Once we have the function to call, we recursively codegen each argument that
260 is to be passed in, and create an LLVM <a href="../LangRef.html#i_call">call
261 instruction</a>. Note that LLVM uses the native C calling conventions by
262 default, allowing these calls to call into standard library functions like
263 "sin" and "cos" with no additional effort.</p>
265 <p>This wraps up our handling of the four basic expressions that we have so far
266 in Kaleidoscope. Feel free to go in and add some more. For example, by
267 browsing the <a href="../LangRef.html">LLVM language reference</a> you'll find
268 several other interesting instructions that are really easy to plug into our
273 <!-- *********************************************************************** -->
274 <div class="doc_section"><a name="funcs">Function Code Generation</a></div>
275 <!-- *********************************************************************** -->
277 <div class="doc_text">
279 <p>Code generation for prototypes and functions has to handle a number of
280 details, which make their code less beautiful and elegant than expression code
281 generation, but they illustrate some important points. First, lets talk about
282 code generation for prototypes: this is used both for function bodies as well
283 as external function declarations. The code starts with:</p>
285 <div class="doc_code">
287 Function *PrototypeAST::Codegen() {
288 // Make the function type: double(double,double) etc.
289 std::vector<const Type*> Doubles(Args.size(), Type::DoubleTy);
290 FunctionType *FT = FunctionType::get(Type::DoubleTy, Doubles, false);
292 Function *F = new Function(FT, Function::ExternalLinkage, Name, TheModule);
296 <p>This code packs a lot of power into a few lines. The first step is to create
297 the <tt>FunctionType</tt> that should be used for a given Prototype. Since all
298 function arguments in Kaleidoscope are of type double, the first line creates
299 a vector of "N" LLVM Double types. It then uses the <tt>FunctionType::get</tt>
300 method to create a function type that takes "N" doubles as arguments, returns
301 one double as a result, and that is not vararg (the false parameter indicates
302 this). Note that Types in LLVM are uniqued just like Constants are, so you
303 don't "new" a type, you "get" it.</p>
305 <p>The final line above actually creates the function that the prototype will
306 correspond to. This indicates which type, linkage, and name to use, and which
307 module to insert into. "<a href="LangRef.html#linkage">external linkage</a>"
308 means that the function may be defined outside the current module and/or that it
309 is callable by functions outside the module. The Name passed in is the name the
310 user specified: since "<tt>TheModule</tt>" is specified, this name is registered
311 in "<tt>TheModule</tt>"s symbol table, which is used by the function call code
314 <div class="doc_code">
316 // If F conflicted, there was already something named 'Name'. If it has a
317 // body, don't allow redefinition or reextern.
318 if (F->getName() != Name) {
319 // Delete the one we just made and get the existing one.
320 F->eraseFromParent();
321 F = TheModule->getFunction(Name);
325 <p>The Module symbol table works just like the Function symbol table when it
326 comes to name conflicts: if a new function is created with a name was previously
327 added to the symbol table, it will get implicitly renamed when added to the
328 Module. The code above exploits this fact to tell if there was a previous
329 definition of this function.</p>
331 <p>In Kaleidoscope, I choose to allow redefinitions of functions in two cases:
332 first, we want to allow 'extern'ing a function more than once, so long as the
333 prototypes for the externs match (since all arguments have the same type, we
334 just have to check that the number of arguments match). Second, we want to
335 allow 'extern'ing a function and then definining a body for it. This is useful
336 when defining mutually recursive functions.</p>
338 <p>In order to implement this, the code above first checks to see if there is
339 a collision on the name of the function. If so, it deletes the function we just
340 created (by calling <tt>eraseFromParent</tt>) and then calling
341 <tt>getFunction</tt> to get the existing function with the specified name. Note
342 that many APIs in LLVM have "erase" forms and "remove" forms. The "remove" form
343 unlinks the object from its parent (e.g. a Function from a Module) and returns
344 it. The "erase" form unlinks the object and then deletes it.</p>
346 <div class="doc_code">
348 // If F already has a body, reject this.
349 if (!F->empty()) {
350 ErrorF("redefinition of function");
354 // If F took a different number of args, reject.
355 if (F->arg_size() != Args.size()) {
356 ErrorF("redefinition of function with different # args");
363 <p>In order to verify the logic above, we first check to see if the preexisting
364 function is "empty". In this case, empty means that it has no basic blocks in
365 it, which means it has no body. If it has no body, this means its a forward
366 declaration. Since we don't allow anything after a full definition of the
367 function, the code rejects this case. If the previous reference to a function
368 was an 'extern', we simply verify that the number of arguments for that
369 definition and this one match up. If not, we emit an error.</p>
371 <div class="doc_code">
373 // Set names for all arguments.
375 for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
377 AI->setName(Args[Idx]);
379 // Add arguments to variable symbol table.
380 NamedValues[Args[Idx]] = AI;
387 <p>The last bit of code for prototypes loops over all of the arguments in the
388 function, setting the name of the LLVM Argument objects to match and registering
389 the arguments in the <tt>NamedValues</tt> map for future use by the
390 <tt>VariableExprAST</tt> AST node. Once this is set up, it returns the Function
391 object to the caller. Note that we don't check for conflicting
392 argument names here (e.g. "extern foo(a b a)"). Doing so would be very
393 straight-forward.</p>
395 <div class="doc_code">
397 Function *FunctionAST::Codegen() {
400 Function *TheFunction = Proto->Codegen();
401 if (TheFunction == 0)
406 <p>Code generation for function definitions starts out simply enough: first we
407 codegen the prototype and verify that it is ok. We also clear out the
408 <tt>NamedValues</tt> map to make sure that there isn't anything in it from the
409 last function we compiled.</p>
411 <div class="doc_code">
413 // Create a new basic block to start insertion into.
414 BasicBlock *BB = new BasicBlock("entry", TheFunction);
415 Builder.SetInsertPoint(BB);
417 if (Value *RetVal = Body->Codegen()) {
421 <p>Now we get to the point where the <tt>Builder</tt> is set up. The first
422 line creates a new <a href="http://en.wikipedia.org/wiki/Basic_block">basic
423 block</a> (named "entry"), which is inserted into <tt>TheFunction</tt>. The
424 second line then tells the builder that new instructions should be inserted into
425 the end of the new basic block. Basic blocks in LLVM are an important part
426 of functions that define the <a
427 href="http://en.wikipedia.org/wiki/Control_flow_graph">Control Flow Graph</a>.
428 Since we don't have any control flow, our functions will only contain one
429 block so far. We'll fix this in a future installment :).</p>
431 <div class="doc_code">
433 if (Value *RetVal = Body->Codegen()) {
434 // Finish off the function.
435 Builder.CreateRet(RetVal);
437 // Validate the generated code, checking for consistency.
438 verifyFunction(*TheFunction);
444 <p>Once the insertion point is set up, we call the <tt>CodeGen()</tt> method for
445 the root expression of the function. If no error happens, this emits code to
446 compute the expression into the entry block and returns the value that was
447 computed. Assuming no error, we then create an LLVM <a
448 href="../LangRef.html#i_ret">ret instruction</a>, which completes the function.
449 Once the function is built, we call the <tt>verifyFunction</tt> function, which
450 is provided by LLVM. This function does a variety of consistency checks on the
451 generated code, to determine if our compiler is doing everything right. Using
452 this is important: it can catch a lot of bugs. Once the function is finished
453 and validated, we return it.</p>
455 <div class="doc_code">
457 // Error reading body, remove function.
458 TheFunction->eraseFromParent();
464 <p>The only piece left here is handling of the error case. For simplicity, we
465 simply handle this by deleting the function we produced with the
466 <tt>eraseFromParent</tt> method. This allows the user to redefine a function
467 that they incorrectly typed in before: if we didn't delete it, it would live in
468 the symbol table, with a body, preventing future redefinition.</p>
470 <p>This code does have a bug though. Since the <tt>PrototypeAST::Codegen</tt>
471 can return a previously defined forward declaration, this can actually delete
472 a forward declaration. There are a number of ways to fix this bug, see what you
473 can come up with! Here is a testcase:</p>
475 <div class="doc_code">
477 extern foo(a b); # ok, defines foo.
478 def foo(a b) c; # error, 'c' is invalid.
479 def bar() foo(1, 2); # error, unknown function "foo"
485 <!-- *********************************************************************** -->
486 <div class="doc_section"><a name="driver">Driver Changes and
487 Closing Thoughts</a></div>
488 <!-- *********************************************************************** -->
490 <div class="doc_text">
493 For now, code generation to LLVM doesn't really get us much, except that we can
494 look at the pretty IR calls. The sample code inserts calls to Codegen into the
495 "<tt>HandleDefinition</tt>", "<tt>HandleExtern</tt>" etc functions, and then
496 dumps out the LLVM IR. This gives a nice way to look at the LLVM IR for simple
497 functions. For example:
500 <div class="doc_code">
503 ready> Read top-level expression:
504 define double @""() {
506 %addtmp = add double 4.000000e+00, 5.000000e+00
512 <p>Note how the parser turns the top-level expression into anonymous functions
513 for us. This will be handy when we add JIT support in the next chapter. Also
514 note that the code is very literally transcribed, no optimizations are being
515 performed. We will add optimizations explicitly in the next chapter.</p>
517 <div class="doc_code">
519 ready> <b>def foo(a b) a*a + 2*a*b + b*b;</b>
520 ready> Read function definition:
521 define double @foo(double %a, double %b) {
523 %multmp = mul double %a, %a
524 %multmp1 = mul double 2.000000e+00, %a
525 %multmp2 = mul double %multmp1, %b
526 %addtmp = add double %multmp, %multmp2
527 %multmp3 = mul double %b, %b
528 %addtmp4 = add double %addtmp, %multmp3
534 <p>This shows some simple arithmetic. Notice the striking similarity to the
535 LLVM builder calls that we use to create the instructions.</p>
537 <div class="doc_code">
539 ready> <b>def bar(a) foo(a, 4.0) + bar(31337);</b>
540 ready> Read function definition:
541 define double @bar(double %a) {
543 %calltmp = call double @foo( double %a, double 4.000000e+00 )
544 %calltmp1 = call double @bar( double 3.133700e+04 )
545 %addtmp = add double %calltmp, %calltmp1
551 <p>This shows some function calls. Note that this function will take a long
552 time to execute if you call it. In the future we'll add conditional control
553 flow to make recursion actually be useful :).</p>
555 <div class="doc_code">
557 ready> <b>extern cos(x);</b>
558 ready> Read extern:
559 declare double @cos(double)
561 ready> <b>cos(1.234);</b>
562 ready> Read top-level expression:
563 define double @""() {
565 %calltmp = call double @cos( double 1.234000e+00 )
571 <p>This shows an extern for the libm "cos" function, and a call to it.</p>
574 <div class="doc_code">
577 ; ModuleID = 'my cool jit'
579 define double @""() {
581 %addtmp = add double 4.000000e+00, 5.000000e+00
585 define double @foo(double %a, double %b) {
587 %multmp = mul double %a, %a
588 %multmp1 = mul double 2.000000e+00, %a
589 %multmp2 = mul double %multmp1, %b
590 %addtmp = add double %multmp, %multmp2
591 %multmp3 = mul double %b, %b
592 %addtmp4 = add double %addtmp, %multmp3
596 define double @bar(double %a) {
598 %calltmp = call double @foo( double %a, double 4.000000e+00 )
599 %calltmp1 = call double @bar( double 3.133700e+04 )
600 %addtmp = add double %calltmp, %calltmp1
604 declare double @cos(double)
606 define double @""() {
608 %calltmp = call double @cos( double 1.234000e+00 )
614 <p>When you quit the current demo, it dumps out the IR for the entire module
615 generated. Here you can see the big picture with all the functions referencing
618 <p>This wraps up this chapter of the Kaleidoscope tutorial. Up next we'll
619 describe how to <a href="LangImpl4.html">add JIT codegen and optimizer
620 support</a> to this so we can actually start running code!</p>
625 <!-- *********************************************************************** -->
626 <div class="doc_section"><a name="code">Full Code Listing</a></div>
627 <!-- *********************************************************************** -->
629 <div class="doc_text">
632 Here is the complete code listing for our running example, enhanced with the
633 LLVM code generator. Because this uses the LLVM libraries, we need to link
634 them in. To do this, we use the <a
635 href="http://llvm.org/cmds/llvm-config.html">llvm-config</a> tool to inform
636 our makefile/command line about which options to use:</p>
638 <div class="doc_code">
641 g++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core` -o toy
647 <p>Here is the code:</p>
649 <div class="doc_code">
652 // See example below.
654 #include "llvm/DerivedTypes.h"
655 #include "llvm/Module.h"
656 #include "llvm/Analysis/Verifier.h"
657 #include "llvm/Support/LLVMBuilder.h"
658 #include <cstdio>
659 #include <string>
661 #include <vector>
662 using namespace llvm;
664 //===----------------------------------------------------------------------===//
666 //===----------------------------------------------------------------------===//
668 // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
669 // of these for known things.
674 tok_def = -2, tok_extern = -3,
677 tok_identifier = -4, tok_number = -5,
680 static std::string IdentifierStr; // Filled in if tok_identifier
681 static double NumVal; // Filled in if tok_number
683 /// gettok - Return the next token from standard input.
684 static int gettok() {
685 static int LastChar = ' ';
687 // Skip any whitespace.
688 while (isspace(LastChar))
689 LastChar = getchar();
691 if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
692 IdentifierStr = LastChar;
693 while (isalnum((LastChar = getchar())))
694 IdentifierStr += LastChar;
696 if (IdentifierStr == "def") return tok_def;
697 if (IdentifierStr == "extern") return tok_extern;
698 return tok_identifier;
701 if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
705 LastChar = getchar();
706 } while (isdigit(LastChar) || LastChar == '.');
708 NumVal = strtod(NumStr.c_str(), 0);
712 if (LastChar == '#') {
713 // Comment until end of line.
714 do LastChar = getchar();
715 while (LastChar != EOF && LastChar != '\n' & LastChar != '\r');
721 // Check for end of file. Don't eat the EOF.
725 // Otherwise, just return the character as its ascii value.
726 int ThisChar = LastChar;
727 LastChar = getchar();
731 //===----------------------------------------------------------------------===//
732 // Abstract Syntax Tree (aka Parse Tree)
733 //===----------------------------------------------------------------------===//
735 /// ExprAST - Base class for all expression nodes.
738 virtual ~ExprAST() {}
739 virtual Value *Codegen() = 0;
742 /// NumberExprAST - Expression class for numeric literals like "1.0".
743 class NumberExprAST : public ExprAST {
746 explicit NumberExprAST(double val) : Val(val) {}
747 virtual Value *Codegen();
750 /// VariableExprAST - Expression class for referencing a variable, like "a".
751 class VariableExprAST : public ExprAST {
754 explicit VariableExprAST(const std::string &name) : Name(name) {}
755 virtual Value *Codegen();
758 /// BinaryExprAST - Expression class for a binary operator.
759 class BinaryExprAST : public ExprAST {
763 BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
764 : Op(op), LHS(lhs), RHS(rhs) {}
765 virtual Value *Codegen();
768 /// CallExprAST - Expression class for function calls.
769 class CallExprAST : public ExprAST {
771 std::vector<ExprAST*> Args;
773 CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
774 : Callee(callee), Args(args) {}
775 virtual Value *Codegen();
778 /// PrototypeAST - This class represents the "prototype" for a function,
779 /// which captures its argument names as well as if it is an operator.
782 std::vector<std::string> Args;
784 PrototypeAST(const std::string &name, const std::vector<std::string> &args)
785 : Name(name), Args(args) {}
790 /// FunctionAST - This class represents a function definition itself.
795 FunctionAST(PrototypeAST *proto, ExprAST *body)
796 : Proto(proto), Body(body) {}
801 //===----------------------------------------------------------------------===//
803 //===----------------------------------------------------------------------===//
805 /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
806 /// token the parser it looking at. getNextToken reads another token from the
807 /// lexer and updates CurTok with its results.
809 static int getNextToken() {
810 return CurTok = gettok();
813 /// BinopPrecedence - This holds the precedence for each binary operator that is
815 static std::map<char, int> BinopPrecedence;
817 /// GetTokPrecedence - Get the precedence of the pending binary operator token.
818 static int GetTokPrecedence() {
819 if (!isascii(CurTok))
822 // Make sure it's a declared binop.
823 int TokPrec = BinopPrecedence[CurTok];
824 if (TokPrec <= 0) return -1;
828 /// Error* - These are little helper functions for error handling.
829 ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
830 PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
831 FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
833 static ExprAST *ParseExpression();
837 /// ::= identifier '(' expression* ')'
838 static ExprAST *ParseIdentifierExpr() {
839 std::string IdName = IdentifierStr;
841 getNextToken(); // eat identifier.
843 if (CurTok != '(') // Simple variable ref.
844 return new VariableExprAST(IdName);
847 getNextToken(); // eat (
848 std::vector<ExprAST*> Args;
850 ExprAST *Arg = ParseExpression();
854 if (CurTok == ')') break;
857 return Error("Expected ')'");
864 return new CallExprAST(IdName, Args);
867 /// numberexpr ::= number
868 static ExprAST *ParseNumberExpr() {
869 ExprAST *Result = new NumberExprAST(NumVal);
870 getNextToken(); // consume the number
874 /// parenexpr ::= '(' expression ')'
875 static ExprAST *ParseParenExpr() {
876 getNextToken(); // eat (.
877 ExprAST *V = ParseExpression();
881 return Error("expected ')'");
882 getNextToken(); // eat ).
887 /// ::= identifierexpr
890 static ExprAST *ParsePrimary() {
892 default: return Error("unknown token when expecting an expression");
893 case tok_identifier: return ParseIdentifierExpr();
894 case tok_number: return ParseNumberExpr();
895 case '(': return ParseParenExpr();
900 /// ::= ('+' primary)*
901 static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
902 // If this is a binop, find its precedence.
904 int TokPrec = GetTokPrecedence();
906 // If this is a binop that binds at least as tightly as the current binop,
907 // consume it, otherwise we are done.
908 if (TokPrec < ExprPrec)
911 // Okay, we know this is a binop.
913 getNextToken(); // eat binop
915 // Parse the primary expression after the binary operator.
916 ExprAST *RHS = ParsePrimary();
919 // If BinOp binds less tightly with RHS than the operator after RHS, let
920 // the pending operator take RHS as its LHS.
921 int NextPrec = GetTokPrecedence();
922 if (TokPrec < NextPrec) {
923 RHS = ParseBinOpRHS(TokPrec+1, RHS);
924 if (RHS == 0) return 0;
928 LHS = new BinaryExprAST(BinOp, LHS, RHS);
933 /// ::= primary binoprhs
935 static ExprAST *ParseExpression() {
936 ExprAST *LHS = ParsePrimary();
939 return ParseBinOpRHS(0, LHS);
943 /// ::= id '(' id* ')'
944 static PrototypeAST *ParsePrototype() {
945 if (CurTok != tok_identifier)
946 return ErrorP("Expected function name in prototype");
948 std::string FnName = IdentifierStr;
952 return ErrorP("Expected '(' in prototype");
954 std::vector<std::string> ArgNames;
955 while (getNextToken() == tok_identifier)
956 ArgNames.push_back(IdentifierStr);
958 return ErrorP("Expected ')' in prototype");
961 getNextToken(); // eat ')'.
963 return new PrototypeAST(FnName, ArgNames);
966 /// definition ::= 'def' prototype expression
967 static FunctionAST *ParseDefinition() {
968 getNextToken(); // eat def.
969 PrototypeAST *Proto = ParsePrototype();
970 if (Proto == 0) return 0;
972 if (ExprAST *E = ParseExpression())
973 return new FunctionAST(Proto, E);
977 /// toplevelexpr ::= expression
978 static FunctionAST *ParseTopLevelExpr() {
979 if (ExprAST *E = ParseExpression()) {
980 // Make an anonymous proto.
981 PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
982 return new FunctionAST(Proto, E);
987 /// external ::= 'extern' prototype
988 static PrototypeAST *ParseExtern() {
989 getNextToken(); // eat extern.
990 return ParsePrototype();
993 //===----------------------------------------------------------------------===//
995 //===----------------------------------------------------------------------===//
997 static Module *TheModule;
998 static LLVMBuilder Builder;
999 static std::map<std::string, Value*> NamedValues;
1001 Value *ErrorV(const char *Str) { Error(Str); return 0; }
1003 Value *NumberExprAST::Codegen() {
1004 return ConstantFP::get(Type::DoubleTy, APFloat(Val));
1007 Value *VariableExprAST::Codegen() {
1008 // Look this variable up in the function.
1009 Value *V = NamedValues[Name];
1010 return V ? V : ErrorV("Unknown variable name");
1013 Value *BinaryExprAST::Codegen() {
1014 Value *L = LHS->Codegen();
1015 Value *R = RHS->Codegen();
1016 if (L == 0 || R == 0) return 0;
1019 case '+': return Builder.CreateAdd(L, R, "addtmp");
1020 case '-': return Builder.CreateSub(L, R, "subtmp");
1021 case '*': return Builder.CreateMul(L, R, "multmp");
1023 L = Builder.CreateFCmpULT(L, R, "multmp");
1024 // Convert bool 0/1 to double 0.0 or 1.0
1025 return Builder.CreateUIToFP(L, Type::DoubleTy, "booltmp");
1026 default: return ErrorV("invalid binary operator");
1030 Value *CallExprAST::Codegen() {
1031 // Look up the name in the global module table.
1032 Function *CalleeF = TheModule->getFunction(Callee);
1034 return ErrorV("Unknown function referenced");
1036 // If argument mismatch error.
1037 if (CalleeF->arg_size() != Args.size())
1038 return ErrorV("Incorrect # arguments passed");
1040 std::vector<Value*> ArgsV;
1041 for (unsigned i = 0, e = Args.size(); i != e; ++i) {
1042 ArgsV.push_back(Args[i]->Codegen());
1043 if (ArgsV.back() == 0) return 0;
1046 return Builder.CreateCall(CalleeF, ArgsV.begin(), ArgsV.end(), "calltmp");
1049 Function *PrototypeAST::Codegen() {
1050 // Make the function type: double(double,double) etc.
1051 std::vector<const Type*> Doubles(Args.size(), Type::DoubleTy);
1052 FunctionType *FT = FunctionType::get(Type::DoubleTy, Doubles, false);
1054 Function *F = new Function(FT, Function::ExternalLinkage, Name, TheModule);
1056 // If F conflicted, there was already something named 'Name'. If it has a
1057 // body, don't allow redefinition or reextern.
1058 if (F->getName() != Name) {
1059 // Delete the one we just made and get the existing one.
1060 F->eraseFromParent();
1061 F = TheModule->getFunction(Name);
1063 // If F already has a body, reject this.
1064 if (!F->empty()) {
1065 ErrorF("redefinition of function");
1069 // If F took a different number of args, reject.
1070 if (F->arg_size() != Args.size()) {
1071 ErrorF("redefinition of function with different # args");
1076 // Set names for all arguments.
1078 for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
1080 AI->setName(Args[Idx]);
1082 // Add arguments to variable symbol table.
1083 NamedValues[Args[Idx]] = AI;
1089 Function *FunctionAST::Codegen() {
1090 NamedValues.clear();
1092 Function *TheFunction = Proto->Codegen();
1093 if (TheFunction == 0)
1096 // Create a new basic block to start insertion into.
1097 BasicBlock *BB = new BasicBlock("entry", TheFunction);
1098 Builder.SetInsertPoint(BB);
1100 if (Value *RetVal = Body->Codegen()) {
1101 // Finish off the function.
1102 Builder.CreateRet(RetVal);
1104 // Validate the generated code, checking for consistency.
1105 verifyFunction(*TheFunction);
1109 // Error reading body, remove function.
1110 TheFunction->eraseFromParent();
1114 //===----------------------------------------------------------------------===//
1115 // Top-Level parsing and JIT Driver
1116 //===----------------------------------------------------------------------===//
1118 static void HandleDefinition() {
1119 if (FunctionAST *F = ParseDefinition()) {
1120 if (Function *LF = F->Codegen()) {
1121 fprintf(stderr, "Read function definition:");
1125 // Skip token for error recovery.
1130 static void HandleExtern() {
1131 if (PrototypeAST *P = ParseExtern()) {
1132 if (Function *F = P->Codegen()) {
1133 fprintf(stderr, "Read extern: ");
1137 // Skip token for error recovery.
1142 static void HandleTopLevelExpression() {
1143 // Evaluate a top level expression into an anonymous function.
1144 if (FunctionAST *F = ParseTopLevelExpr()) {
1145 if (Function *LF = F->Codegen()) {
1146 fprintf(stderr, "Read top-level expression:");
1150 // Skip token for error recovery.
1155 /// top ::= definition | external | expression | ';'
1156 static void MainLoop() {
1158 fprintf(stderr, "ready> ");
1160 case tok_eof: return;
1161 case ';': getNextToken(); break; // ignore top level semicolons.
1162 case tok_def: HandleDefinition(); break;
1163 case tok_extern: HandleExtern(); break;
1164 default: HandleTopLevelExpression(); break;
1171 //===----------------------------------------------------------------------===//
1172 // "Library" functions that can be "extern'd" from user code.
1173 //===----------------------------------------------------------------------===//
1175 /// putchard - putchar that takes a double and returns 0.
1177 double putchard(double X) {
1182 //===----------------------------------------------------------------------===//
1183 // Main driver code.
1184 //===----------------------------------------------------------------------===//
1187 TheModule = new Module("my cool jit");
1189 // Install standard binary operators.
1190 // 1 is lowest precedence.
1191 BinopPrecedence['<'] = 10;
1192 BinopPrecedence['+'] = 20;
1193 BinopPrecedence['-'] = 20;
1194 BinopPrecedence['*'] = 40; // highest.
1196 // Prime the first token.
1197 fprintf(stderr, "ready> ");
1201 TheModule->dump();
1208 <!-- *********************************************************************** -->
1211 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1212 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
1213 <a href="http://validator.w3.org/check/referer"><img
1214 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
1216 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1217 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
1218 Last modified: $Date: 2007-10-17 11:05:13 -0700 (Wed, 17 Oct 2007) $