[llvm-commits] [llvm] r43329 - /llvm/trunk/docs/tutorial/LangImpl4.html
Chris Lattner
sabre at nondot.org
Wed Oct 24 23:23:37 PDT 2007
Author: lattner
Date: Thu Oct 25 01:23:36 2007
New Revision: 43329
URL: http://llvm.org/viewvc/llvm-project?rev=43329&view=rev
Log:
Add chapter 4, feedback appreciated.
Modified:
llvm/trunk/docs/tutorial/LangImpl4.html
Modified: llvm/trunk/docs/tutorial/LangImpl4.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl4.html?rev=43329&r1=43328&r2=43329&view=diff
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl4.html (original)
+++ llvm/trunk/docs/tutorial/LangImpl4.html Thu Oct 25 01:23:36 2007
@@ -24,22 +24,544 @@
<div class="doc_text">
<p>Welcome to part 4 of the "<a href="index.html">Implementing a language with
-LLVM</a>" tutorial.</p>
+LLVM</a>" tutorial. Parts 1-3 described the implementation of a simple language
+and included support for generating LLVM IR. This chapter describes two new
+techniques: adding optimizer support to your language, and adding JIT compiler
+support. This shows how to get nice efficient code for your language.</p>
</div>
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="basics">Code Generation setup</a></div>
+<div class="doc_section"><a name="trivialconstfold">Trivial Constant
+Folding</a></div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>
-In order to generate LLVM IR, we want some simple setup to get started. First,
-we define virtual codegen methods in each AST class:</p>
+Our demonstration for Chapter 3 is elegant and easy to extend. Unfortunately,
+it does not produce wonderful code. For example, when compiling simple code,
+we don't get obvious optimizations:</p>
<div class="doc_code">
<pre>
+ready> <b>def test(x) 1+2+x;</b>
+Read function definition:
+define double @test(double %x) {
+entry:
+ %addtmp = add double 1.000000e+00, 2.000000e+00
+ %addtmp1 = add double %addtmp, %x
+ ret double %addtmp1
+}
+</pre>
+</div>
+
+<p>This code is a very very literal transcription of the AST built by parsing
+our code, and as such, lacks optimizations like constant folding (we'd like to
+get "<tt>add x, 3.0</tt>" in the example above) as well as other more important
+optimizations. Constant folding in particular is a very common and very
+important optimization: so much so that many language implementors implement
+constant folding support in their AST representation.</p>
+
+<p>With LLVM, you don't need to. Since all calls to build LLVM IR go through
+the LLVM builder, it would be nice if the builder itself checked to see if there
+was a constant folding opportunity when you call it. If so, it could just do
+the constant fold and return the constant instead of creating an instruction.
+This is exactly what the <tt>LLVMFoldingBuilder</tt> class does. Lets make one
+change:
+
+<div class="doc_code">
+<pre>
+static LLVMFoldingBuilder Builder;
+</pre>
+</div>
+
+<p>All we did was switch from <tt>LLVMBuilder</tt> to
+<tt>LLVMFoldingBuilder</tt>. Though we change no other code, now all of our
+instructions are implicitly constant folded without us having to do anything
+about it. For example, our example above now compiles to:</p>
+
+<div class="doc_code">
+<pre>
+ready> <b>def test(x) 1+2+x;</b>
+Read function definition:
+define double @test(double %x) {
+entry:
+ %addtmp = add double 3.000000e+00, %x
+ ret double %addtmp
+}
+</pre>
+</div>
+
+<p>Well, that was easy. :) In practice, we recommend always using
+<tt>LLVMConstantBuilder</tt> when generating code like this. It has no
+"syntactic overhead" for its use (you don't have to uglify your compiler with
+constant checks everywhere) and it can dramatically reduce the amount of
+LLVM IR that is generated in some cases (particular for languages with a macro
+preprocessor or that use a lot of constants).</p>
+
+<p>On the other hand, the <tt>LLVMFoldingBuilder</tt> is limited by the fact
+that it does all of its analysis inline with the code as it is built. If you
+take a slightly more complex example:</p>
+
+<div class="doc_code">
+<pre>
+ready> <b>def test(x) (1+2+x)*(x+(1+2));</b>
+ready> Read function definition:
+define double @test(double %x) {
+entry:
+ %addtmp = add double 3.000000e+00, %x
+ %addtmp1 = add double %x, 3.000000e+00
+ %multmp = mul double %addtmp, %addtmp1
+ ret double %multmp
+}
+</pre>
+</div>
+
+<p>In this case, the LHS and RHS of the multiplication are the same value. We'd
+really like to see this generate "<tt>tmp = x+3; result = tmp*tmp;</tt>" instead
+of computing "<tt>x*3</tt>" twice.</p>
+
+<p>Unfortunately, no amount of local analysis will be able to detect and correct
+this. This requires two transformations: reassociation of expressions (to
+make the add's lexically identical) and Common Subexpression Elimination (CSE)
+to delete the redundant add instruction. Fortunately, LLVM provides a broad
+range of optimizations that you can use, in the form of "passes".</p>
+
+</div>
+
+<!-- *********************************************************************** -->
+<div class="doc_section"><a name="optimizerpasses">LLVM Optimization
+ Passes</a></div>
+<!-- *********************************************************************** -->
+
+<div class="doc_text">
+
+<p>LLVM provides many optimization passes which do many different sorts of
+things and have different tradeoffs. Unlike other systems, LLVM doesn't hold
+to the mistaken notion that one set of optimizations is right for all languages
+and for all situations. LLVM allows a compiler implementor to make complete
+decisions about what optimizations to use, in which order, and in what
+situation.</p>
+
+<p>As a concrete example, LLVM supports both "whole module" passes, which look
+across as large of body of code as they can (often a whole file, but if run
+at link time, this can be a substantial portion of the whole program). It also
+supports and includes "per-function" passes which just operate on a single
+function at a time, without looking at other functions. For more information
+on passes and how the get run, see the <a href="../WritingAnLLVMPass.html">How
+to Write a Pass</a> document.</p>
+
+<p>For Kaleidoscope, we are currently generating functions on the fly, one at
+a time, as the user types them in. We aren't shooting for the ultimate
+optimization experience in this setting, but we also want to catch the easy and
+quick stuff where possible. As such, we will choose to run a few per-function
+optimizations as the user types the function in. If we wanted to make a "static
+Kaleidoscope compiler", we would use exactly the code we have now, except that
+we would defer running the optimizer until the entire file has been parsed.</p>
+
+<p>In order to get per-function optimizations going, we need to set up a
+<a href="../WritingAnLLVMPass.html#passmanager">FunctionPassManager</a> to hold and
+organize the LLVM optimizations that we want to run. Once we have that, we can
+add a set of optimizations to run. The code looks like this:</p>
+
+<div class="doc_code">
+<pre>
+ ExistingModuleProvider OurModuleProvider(TheModule);
+ FunctionPassManager OurFPM(&OurModuleProvider);
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new TargetData(*TheExecutionEngine->getTargetData()));
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+ // Eliminate Common SubExpressions.
+ OurFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ OurFPM.add(createCFGSimplificationPass());
+
+ // Set the global so the code gen can use this.
+ TheFPM = &OurFPM;
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+</pre>
+</div>
+
+<p>This code defines two objects, a <tt>ExistingModuleProvider</tt> and a
+<tt>FunctionPassManager</tt>. The former is basically a wrapper around our
+<tt>Module</tt> that the PassManager requires. It provides certain flexibility
+that we're not going to take advantage of here, so I won't dive into what it is
+all about.</p>
+
+<p>The meat of the matter is the definition of the "<tt>OurFPM</tt>". It
+requires a pointer to the <tt>Module</tt> (through the <tt>ModuleProvider</tt>)
+to construct itself. Once it is set up, we use a series of "add" calls to add
+a bunch of LLVM passes. The first pass is basically boilerplate, it adds a pass
+so that later optimizations know how the data structures in the program are
+layed out. The "<tt>TheExecutionEngine</tt>" variable is related to the JIT,
+which we will get to in the next section.</p>
+
+<p>In this case, we choose to add 4 optimization passes. The passes we chose
+here are a pretty standard set of "cleanup" optimizations that are useful for
+a wide variety of code. I won't delve into what they do, but believe that they
+are a good starting place.</p>
+
+<p>Once the passmanager, is set up, we need to make use of it. We do this by
+running it after our newly created function is constructed (in
+<tt>FunctionAST::Codegen</tt>), but before it is returned to the client:</p>
+
+<div class="doc_code">
+<pre>
+ if (Value *RetVal = Body->Codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ // Optimize the function.
+ TheFPM->run(*TheFunction);
+
+ return TheFunction;
+ }
+</pre>
+</div>
+
+<p>As you can see, this is pretty straight-forward. The
+<tt>FunctionPassManager</tt> optimizes and updates the LLVM Function* in place,
+improving (hopefully) its body. With this in place, we can try our test above
+again:</p>
+
+<div class="doc_code">
+<pre>
+ready> <b>def test(x) (1+2+x)*(x+(1+2));</b>
+ready> Read function definition:
+define double @test(double %x) {
+entry:
+ %addtmp = add double %x, 3.000000e+00
+ %multmp = mul double %addtmp, %addtmp
+ ret double %multmp
+}
+</pre>
+</div>
+
+<p>As expected, we now get our nicely optimized code, saving a floating point
+add from the program.</p>
+
+<p>LLVM provides a wide variety of optimizations that can be used in certain
+circumstances. Unfortunately we don't have a good centralized description of
+what every pass does, but you can check out the ones that <tt>llvm-gcc</tt> or
+<tt>llvm-ld</tt> run to get started. The "<tt>opt</tt>" tool allows you to
+experiment with passes from the command line, so you can see if they do
+anything.</p>
+
+<p>Now that we have reasonable code coming out of our front-end, lets talk about
+executing it!</p>
+
+</div>
+
+<!-- *********************************************************************** -->
+<div class="doc_section"><a name="jit">Adding a JIT Compiler</a></div>
+<!-- *********************************************************************** -->
+
+<div class="doc_text">
+
+<p>Once the code is available in LLVM IR form a wide variety of tools can be
+applied to it. For example, you can run optimizations on it (as we did above),
+you can dump it out in textual or binary forms, you can compile the code to an
+assembly file (.s) for some target, or you can JIT compile it. The nice thing
+about the LLVM IR representation is that it is the common currency between many
+different parts of the compiler.
+</p>
+
+<p>In this chapter, we'll add JIT compiler support to our interpreter. The
+basic idea that we want for Kaleidoscope is to have the user enter function
+bodies as they do now, but immediately evaluate the top-level expressions they
+type in. For example, if they type in "1 + 2;", we should evaluate and print
+out 3. If they define a function, they should be able to call it from the
+command line.</p>
+
+<p>In order to do this, we first declare and initialize the JIT. This is done
+by adding a global variable and a call in <tt>main</tt>:</p>
+
+<div class="doc_code">
+<pre>
+static ExecutionEngine *TheExecutionEngine;
+...
+int main() {
+ ..
+ // Create the JIT.
+ TheExecutionEngine = ExecutionEngine::create(TheModule);
+ ..
+}
+</pre>
+</div>
+
+<p>This creates an abstract "Execution Engine" which can be either a JIT
+compiler or the LLVM interpreter. LLVM will automatically pick a JIT compiler
+for you if one is available for your platform, otherwise it will fall back to
+the interpreter.</p>
+
+<p>Once the <tt>ExecutionEngine</tt> is created, the JIT is ready to be used.
+There are a variety of APIs that are useful, but the most simple one is the
+"<tt>getPointerToFunction(F)</tt>" method. This method JIT compiles the
+specified LLVM Function and returns a function pointer to the generated machine
+code. In our case, this means that we can change the code that parses a
+top-level expression to look like this:</p>
+
+<div class="doc_code">
+<pre>
+static void HandleTopLevelExpression() {
+ // Evaluate a top level expression into an anonymous function.
+ if (FunctionAST *F = ParseTopLevelExpr()) {
+ if (Function *LF = F->Codegen()) {
+ LF->dump(); // Dump the function for exposition purposes.
+
+ // JIT the function, returning a function pointer.
+ void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
+
+ // Cast it to the right type (takes no arguments, returns a double) so we
+ // can call it as a native function.
+ double (*FP)() = (double (*)())FPtr;
+ fprintf(stderr, "Evaluated to %f\n", FP());
+ }
+</pre>
+</div>
+
+<p>Recall that we compile top-level expressions into a self-contained LLVM
+function that takes no arguments and returns the computed double. Because the
+LLVM JIT compiler matches the native platform ABI, this means that you can just
+cast the result pointer to a function pointer of that type and call it directly.
+As such, there is no difference between JIT compiled code and native machine
+code that is statically linked into your application.</p>
+
+<p>With just these two changes, lets see how Kaleidoscope works now!</p>
+
+<div class="doc_code">
+<pre>
+ready> <b>4+5;</b>
+define double @""() {
+entry:
+ ret double 9.000000e+00
+}
+
+<em>Evaluated to 9.000000</em>
+</pre>
+</div>
+
+<p>Well this looks like it is basically working. The dump of the function
+shows the "no argument function that always returns double" that we synthesize
+for each top level expression that is typed it. This demonstrates very basic
+functionality, but can we do more?</p>
+
+<div class="doc_code">
+<pre>
+ready> def testfunc(x y) x + y*2; </b>
+Read function definition:
+define double @testfunc(double %x, double %y) {
+entry:
+ %multmp = mul double %y, 2.000000e+00
+ %addtmp = add double %multmp, %x
+ ret double %addtmp
+}
+
+ready> <b>testfunc(4, 10);</b>
+define double @""() {
+entry:
+ %calltmp = call double @testfunc( double 4.000000e+00, double 1.000000e+01 )
+ ret double %calltmp
+}
+
+<em>Evaluated to 24.000000</em>
+</pre>
+</div>
+
+<p>This illustrates that we can now call user code, but it is a bit subtle what
+is going on here. Note that we only invoke the JIT on the anonymous functions
+that <em>calls testfunc</em>, but we never invoked it on <em>testfunc
+itself</em>.</p>
+
+<p>What actually happened here is that the anonymous function is
+JIT'd when requested. When the Kaleidoscope app calls through the function
+pointer that is returned, the anonymous function starts executing. It ends up
+making the call for the "testfunc" function, and ends up in a stub that invokes
+the JIT, lazily, on testfunc. Once the JIT finishes lazily compiling testfunc,
+it returns and the code reexecutes the call.</p>
+
+<p>In summary, the JIT will lazily JIT code on the fly as it is needed. The
+JIT provides a number of other more advanced interfaces for things like freeing
+allocated machine code, rejit'ing functions to update them, etc. However, even
+with this simple code, we get some surprisingly powerful capabilities - check
+this out (I removed the dump of the anonymous functions, you should get the idea
+by now :) :</p>
+
+<div class="doc_code">
+<pre>
+ready> <b>extern sin(x);</b>
+Read extern:
+declare double @sin(double)
+
+ready> <b>extern cos(x);</b>
+Read extern:
+declare double @cos(double)
+
+ready> <b>sin(1.0);</b>
+<em>Evaluated to 0.841471</em>
+ready> <b>def foo(x) sin(x)*sin(x) + cos(x)*cos(x);</b>
+Read function definition:
+define double @foo(double %x) {
+entry:
+ %calltmp = call double @sin( double %x )
+ %multmp = mul double %calltmp, %calltmp
+ %calltmp2 = call double @cos( double %x )
+ %multmp4 = mul double %calltmp2, %calltmp2
+ %addtmp = add double %multmp, %multmp4
+ ret double %addtmp
+}
+
+ready> <b>foo(4.0);</b>
+<em>Evaluated to 1.000000</em>
+</pre>
+</div>
+
+<p>Whoa, how does the JIT know about sin and cos? The answer is simple: in this
+example, the JIT started execution of a function and got to a function call. It
+realized that the function was not yet JIT compiled and invoked the standard set
+of routines to resolve the function. In this case, there is no body defined
+for the function, so the JIT ended up calling "<tt>dlsym("sin")</tt>" on itself.
+Since "<tt>sin</tt>" is defined within the JIT's address space, it simply
+patches up calls in the module to call the libm version of <tt>sin</tt>
+directly.</p>
+
+<p>The LLVM JIT provides a number of interfaces (look in the
+<tt>ExecutionEngine.h</tt> file) for controlling how unknown functions get
+resolved. It allows you to establish explicit mappings between IR objects and
+addresses (useful for LLVM global variables that you want to map to static
+tables, for example), allows you to dynamically decide on the fly based on the
+function name, and even allows you to have the JIT abort itself if any lazy
+compilation is attempted.</p>
+
+<p>This completes the JIT and optimizer chapter of the Kaleidoscope tutorial. At
+this point, we can compile a non-Turing-complete programming language, optimize
+and JIT compile it in a user-driven way. Next up we'll look into <a
+href="LangImpl5.html">extending the language with control flow constructs</a>,
+tackling some interesting LLVM IR issues along the way.</p>
+
+</div>
+
+<!-- *********************************************************************** -->
+<div class="doc_section"><a name="code">Full Code Listing</a></div>
+<!-- *********************************************************************** -->
+
+<div class="doc_text">
+
+<p>
+Here is the complete code listing for our running example, enhanced with the
+LLVM JIT and optimizer. To build this example, use:
+</p>
+
+<div class="doc_code">
+<pre>
+ # Compile
+ g++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
+ # Run
+ ./toy
+</pre>
+</div>
+
+<p>Here is the code:</p>
+
+<div class="doc_code">
+<pre>
+#include "llvm/DerivedTypes.h"
+#include "llvm/ExecutionEngine/ExecutionEngine.h"
+#include "llvm/Module.h"
+#include "llvm/ModuleProvider.h"
+#include "llvm/PassManager.h"
+#include "llvm/Analysis/Verifier.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Support/LLVMBuilder.h"
+#include <cstdio>
+#include <string>
+#include <map>
+#include <vector>
+using namespace llvm;
+
+//===----------------------------------------------------------------------===//
+// Lexer
+//===----------------------------------------------------------------------===//
+
+// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+// of these for known things.
+enum Token {
+ tok_eof = -1,
+
+ // commands
+ tok_def = -2, tok_extern = -3,
+
+ // primary
+ tok_identifier = -4, tok_number = -5,
+};
+
+static std::string IdentifierStr; // Filled in if tok_identifier
+static double NumVal; // Filled in if tok_number
+
+/// gettok - Return the next token from standard input.
+static int gettok() {
+ static int LastChar = ' ';
+
+ // Skip any whitespace.
+ while (isspace(LastChar))
+ LastChar = getchar();
+
+ if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+ IdentifierStr = LastChar;
+ while (isalnum((LastChar = getchar())))
+ IdentifierStr += LastChar;
+
+ if (IdentifierStr == "def") return tok_def;
+ if (IdentifierStr == "extern") return tok_extern;
+ return tok_identifier;
+ }
+
+ if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+ std::string NumStr;
+ do {
+ NumStr += LastChar;
+ LastChar = getchar();
+ } while (isdigit(LastChar) || LastChar == '.');
+
+ NumVal = strtod(NumStr.c_str(), 0);
+ return tok_number;
+ }
+
+ if (LastChar == '#') {
+ // Comment until end of line.
+ do LastChar = getchar();
+ while (LastChar != EOF && LastChar != '\n' & LastChar != '\r');
+
+ if (LastChar != EOF)
+ return gettok();
+ }
+
+ // Check for end of file. Don't eat the EOF.
+ if (LastChar == EOF)
+ return tok_eof;
+
+ // Otherwise, just return the character as its ascii value.
+ int ThisChar = LastChar;
+ LastChar = getchar();
+ return ThisChar;
+}
+
+//===----------------------------------------------------------------------===//
+// Abstract Syntax Tree (aka Parse Tree)
+//===----------------------------------------------------------------------===//
+
/// ExprAST - Base class for all expression nodes.
class ExprAST {
public:
@@ -51,14 +573,508 @@
class NumberExprAST : public ExprAST {
double Val;
public:
- explicit NumberExprAST(double val) : Val(val) {}
+ NumberExprAST(double val) : Val(val) {}
virtual Value *Codegen();
};
-...
-</pre>
-</div>
+/// VariableExprAST - Expression class for referencing a variable, like "a".
+class VariableExprAST : public ExprAST {
+ std::string Name;
+public:
+ VariableExprAST(const std::string &name) : Name(name) {}
+ virtual Value *Codegen();
+};
+/// BinaryExprAST - Expression class for a binary operator.
+class BinaryExprAST : public ExprAST {
+ char Op;
+ ExprAST *LHS, *RHS;
+public:
+ BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
+ : Op(op), LHS(lhs), RHS(rhs) {}
+ virtual Value *Codegen();
+};
+
+/// CallExprAST - Expression class for function calls.
+class CallExprAST : public ExprAST {
+ std::string Callee;
+ std::vector<ExprAST*> Args;
+public:
+ CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
+ : Callee(callee), Args(args) {}
+ virtual Value *Codegen();
+};
+
+/// PrototypeAST - This class represents the "prototype" for a function,
+/// which captures its argument names as well as if it is an operator.
+class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+public:
+ PrototypeAST(const std::string &name, const std::vector<std::string> &args)
+ : Name(name), Args(args) {}
+
+ Function *Codegen();
+};
+
+/// FunctionAST - This class represents a function definition itself.
+class FunctionAST {
+ PrototypeAST *Proto;
+ ExprAST *Body;
+public:
+ FunctionAST(PrototypeAST *proto, ExprAST *body)
+ : Proto(proto), Body(body) {}
+
+ Function *Codegen();
+};
+
+//===----------------------------------------------------------------------===//
+// Parser
+//===----------------------------------------------------------------------===//
+
+/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
+/// token the parser it looking at. getNextToken reads another token from the
+/// lexer and updates CurTok with its results.
+static int CurTok;
+static int getNextToken() {
+ return CurTok = gettok();
+}
+
+/// BinopPrecedence - This holds the precedence for each binary operator that is
+/// defined.
+static std::map<char, int> BinopPrecedence;
+
+/// GetTokPrecedence - Get the precedence of the pending binary operator token.
+static int GetTokPrecedence() {
+ if (!isascii(CurTok))
+ return -1;
+
+ // Make sure it's a declared binop.
+ int TokPrec = BinopPrecedence[CurTok];
+ if (TokPrec <= 0) return -1;
+ return TokPrec;
+}
+
+/// Error* - These are little helper functions for error handling.
+ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
+PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
+FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
+
+static ExprAST *ParseExpression();
+
+/// identifierexpr
+/// ::= identifer
+/// ::= identifer '(' expression* ')'
+static ExprAST *ParseIdentifierExpr() {
+ std::string IdName = IdentifierStr;
+
+ getNextToken(); // eat identifer.
+
+ if (CurTok != '(') // Simple variable ref.
+ return new VariableExprAST(IdName);
+
+ // Call.
+ getNextToken(); // eat (
+ std::vector<ExprAST*> Args;
+ while (1) {
+ ExprAST *Arg = ParseExpression();
+ if (!Arg) return 0;
+ Args.push_back(Arg);
+
+ if (CurTok == ')') break;
+
+ if (CurTok != ',')
+ return Error("Expected ')'");
+ getNextToken();
+ }
+
+ // Eat the ')'.
+ getNextToken();
+
+ return new CallExprAST(IdName, Args);
+}
+
+/// numberexpr ::= number
+static ExprAST *ParseNumberExpr() {
+ ExprAST *Result = new NumberExprAST(NumVal);
+ getNextToken(); // consume the number
+ return Result;
+}
+
+/// parenexpr ::= '(' expression ')'
+static ExprAST *ParseParenExpr() {
+ getNextToken(); // eat (.
+ ExprAST *V = ParseExpression();
+ if (!V) return 0;
+
+ if (CurTok != ')')
+ return Error("expected ')'");
+ getNextToken(); // eat ).
+ return V;
+}
+
+/// primary
+/// ::= identifierexpr
+/// ::= numberexpr
+/// ::= parenexpr
+static ExprAST *ParsePrimary() {
+ switch (CurTok) {
+ default: return Error("unknown token when expecting an expression");
+ case tok_identifier: return ParseIdentifierExpr();
+ case tok_number: return ParseNumberExpr();
+ case '(': return ParseParenExpr();
+ }
+}
+
+/// binoprhs
+/// ::= ('+' primary)*
+static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
+ // If this is a binop, find its precedence.
+ while (1) {
+ int TokPrec = GetTokPrecedence();
+
+ // If this is a binop that binds at least as tightly as the current binop,
+ // consume it, otherwise we are done.
+ if (TokPrec < ExprPrec)
+ return LHS;
+
+ // Okay, we know this is a binop.
+ int BinOp = CurTok;
+ getNextToken(); // eat binop
+
+ // Parse the primary expression after the binary operator.
+ ExprAST *RHS = ParsePrimary();
+ if (!RHS) return 0;
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+ RHS = ParseBinOpRHS(TokPrec+1, RHS);
+ if (RHS == 0) return 0;
+ }
+
+ // Merge LHS/RHS.
+ LHS = new BinaryExprAST(BinOp, LHS, RHS);
+ }
+}
+
+/// expression
+/// ::= primary binoprhs
+///
+static ExprAST *ParseExpression() {
+ ExprAST *LHS = ParsePrimary();
+ if (!LHS) return 0;
+
+ return ParseBinOpRHS(0, LHS);
+}
+
+/// prototype
+/// ::= id '(' id* ')'
+static PrototypeAST *ParsePrototype() {
+ if (CurTok != tok_identifier)
+ return ErrorP("Expected function name in prototype");
+
+ std::string FnName = IdentifierStr;
+ getNextToken();
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ return new PrototypeAST(FnName, ArgNames);
+}
+
+/// definition ::= 'def' prototype expression
+static FunctionAST *ParseDefinition() {
+ getNextToken(); // eat def.
+ PrototypeAST *Proto = ParsePrototype();
+ if (Proto == 0) return 0;
+
+ if (ExprAST *E = ParseExpression())
+ return new FunctionAST(Proto, E);
+ return 0;
+}
+
+/// toplevelexpr ::= expression
+static FunctionAST *ParseTopLevelExpr() {
+ if (ExprAST *E = ParseExpression()) {
+ // Make an anonymous proto.
+ PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
+ return new FunctionAST(Proto, E);
+ }
+ return 0;
+}
+
+/// external ::= 'extern' prototype
+static PrototypeAST *ParseExtern() {
+ getNextToken(); // eat extern.
+ return ParsePrototype();
+}
+
+//===----------------------------------------------------------------------===//
+// Code Generation
+//===----------------------------------------------------------------------===//
+
+static Module *TheModule;
+static LLVMFoldingBuilder Builder;
+static std::map<std::string, Value*> NamedValues;
+static FunctionPassManager *TheFPM;
+
+Value *ErrorV(const char *Str) { Error(Str); return 0; }
+
+Value *NumberExprAST::Codegen() {
+ return ConstantFP::get(Type::DoubleTy, APFloat(Val));
+}
+
+Value *VariableExprAST::Codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ return V ? V : ErrorV("Unknown variable name");
+}
+
+Value *BinaryExprAST::Codegen() {
+ Value *L = LHS->Codegen();
+ Value *R = RHS->Codegen();
+ if (L == 0 || R == 0) return 0;
+
+ switch (Op) {
+ case '+': return Builder.CreateAdd(L, R, "addtmp");
+ case '-': return Builder.CreateSub(L, R, "subtmp");
+ case '*': return Builder.CreateMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "multmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::DoubleTy, "booltmp");
+ default: return ErrorV("invalid binary operator");
+ }
+}
+
+Value *CallExprAST::Codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = TheModule->getFunction(Callee);
+ if (CalleeF == 0)
+ return ErrorV("Unknown function referenced");
+
+ // If argument mismatch error.
+ if (CalleeF->arg_size() != Args.size())
+ return ErrorV("Incorrect # arguments passed");
+
+ std::vector<Value*> ArgsV;
+ for (unsigned i = 0, e = Args.size(); i != e; ++i) {
+ ArgsV.push_back(Args[i]->Codegen());
+ if (ArgsV.back() == 0) return 0;
+ }
+
+ return Builder.CreateCall(CalleeF, ArgsV.begin(), ArgsV.end(), "calltmp");
+}
+
+Function *PrototypeAST::Codegen() {
+ // Make the function type: double(double,double) etc.
+ std::vector<const Type*> Doubles(Args.size(), Type::DoubleTy);
+ FunctionType *FT = FunctionType::get(Type::DoubleTy, Doubles, false);
+
+ Function *F = new Function(FT, Function::ExternalLinkage, Name, TheModule);
+
+ // If F conflicted, there was already something named 'Name'. If it has a
+ // body, don't allow redefinition or reextern.
+ if (F->getName() != Name) {
+ // Delete the one we just made and get the existing one.
+ F->eraseFromParent();
+ F = TheModule->getFunction(Name);
+
+ // If F already has a body, reject this.
+ if (!F->empty()) {
+ ErrorF("redefinition of function");
+ return 0;
+ }
+
+ // If F took a different number of args, reject.
+ if (F->arg_size() != Args.size()) {
+ ErrorF("redefinition of function with different # args");
+ return 0;
+ }
+ }
+
+ // Set names for all arguments.
+ unsigned Idx = 0;
+ for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
+ ++AI, ++Idx) {
+ AI->setName(Args[Idx]);
+
+ // Add arguments to variable symbol table.
+ NamedValues[Args[Idx]] = AI;
+ }
+
+ return F;
+}
+
+Function *FunctionAST::Codegen() {
+ NamedValues.clear();
+
+ Function *TheFunction = Proto->Codegen();
+ if (TheFunction == 0)
+ return 0;
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = new BasicBlock("entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ if (Value *RetVal = Body->Codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ // Optimize the function.
+ TheFPM->run(*TheFunction);
+
+ return TheFunction;
+ }
+
+ // Error reading body, remove function.
+ TheFunction->eraseFromParent();
+ return 0;
+}
+
+//===----------------------------------------------------------------------===//
+// Top-Level parsing and JIT Driver
+//===----------------------------------------------------------------------===//
+
+static ExecutionEngine *TheExecutionEngine;
+
+static void HandleDefinition() {
+ if (FunctionAST *F = ParseDefinition()) {
+ if (Function *LF = F->Codegen()) {
+ fprintf(stderr, "Read function definition:");
+ LF->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+}
+
+static void HandleExtern() {
+ if (PrototypeAST *P = ParseExtern()) {
+ if (Function *F = P->Codegen()) {
+ fprintf(stderr, "Read extern: ");
+ F->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+}
+
+static void HandleTopLevelExpression() {
+ // Evaluate a top level expression into an anonymous function.
+ if (FunctionAST *F = ParseTopLevelExpr()) {
+ if (Function *LF = F->Codegen()) {
+ // JIT the function, returning a function pointer.
+ void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
+
+ // Cast it to the right type (takes no arguments, returns a double) so we
+ // can call it as a native function.
+ double (*FP)() = (double (*)())FPtr;
+ fprintf(stderr, "Evaluated to %f\n", FP());
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+}
+
+/// top ::= definition | external | expression | ';'
+static void MainLoop() {
+ while (1) {
+ fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof: return;
+ case ';': getNextToken(); break; // ignore top level semicolons.
+ case tok_def: HandleDefinition(); break;
+ case tok_extern: HandleExtern(); break;
+ default: HandleTopLevelExpression(); break;
+ }
+ }
+}
+
+
+
+//===----------------------------------------------------------------------===//
+// "Library" functions that can be "extern'd" from user code.
+//===----------------------------------------------------------------------===//
+
+/// putchard - putchar that takes a double and returns 0.
+extern "C"
+double putchard(double X) {
+ putchar((char)X);
+ return 0;
+}
+
+//===----------------------------------------------------------------------===//
+// Main driver code.
+//===----------------------------------------------------------------------===//
+
+int main() {
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+ BinopPrecedence['*'] = 40; // highest.
+
+ // Prime the first token.
+ fprintf(stderr, "ready> ");
+ getNextToken();
+
+ // Make the module, which holds all the code.
+ TheModule = new Module("my cool jit");
+
+ // Create the JIT.
+ TheExecutionEngine = ExecutionEngine::create(TheModule);
+
+ {
+ ExistingModuleProvider OurModuleProvider(TheModule);
+ FunctionPassManager OurFPM(&OurModuleProvider);
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new TargetData(*TheExecutionEngine->getTargetData()));
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+ // Eliminate Common SubExpressions.
+ OurFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ OurFPM.add(createCFGSimplificationPass());
+
+ // Set the global so the code gen can use this.
+ TheFPM = &OurFPM;
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+ TheFPM = 0;
+ } // Free module provider and pass manager.
+
+
+ // Print out all of the generated code.
+ TheModule->dump();
+ return 0;
+}
+</pre>
+</div>
</div>
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