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| author | mike-m <mikem.llvm@gmail.com> | 2010-05-07 00:28:04 +0000 |
|---|---|---|
| committer | mike-m <mikem.llvm@gmail.com> | 2010-05-07 00:28:04 +0000 |
| commit | e2c3a49c8029ebd9ef530101cc24c66562e3dff5 (patch) | |
| tree | 91bf9600cc8df90cf99751a8f8bafc317cffc91e /docs/tutorial/OCamlLangImpl4.html | |
| parent | c10b5afbe8138b0fdf3af4ed3e1ddf96cf3cb4cb (diff) | |
| download | llvm-e2c3a49c8029ebd9ef530101cc24c66562e3dff5.tar.gz llvm-e2c3a49c8029ebd9ef530101cc24c66562e3dff5.tar.bz2 llvm-e2c3a49c8029ebd9ef530101cc24c66562e3dff5.tar.xz | |
Revert r103213. It broke several sections of live website.
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diff --git a/docs/tutorial/OCamlLangImpl4.html b/docs/tutorial/OCamlLangImpl4.html new file mode 100644 index 0000000000..116c618d02 --- /dev/null +++ b/docs/tutorial/OCamlLangImpl4.html @@ -0,0 +1,1029 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> + +<html> +<head> + <title>Kaleidoscope: Adding JIT and Optimizer Support</title> + <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> + <meta name="author" content="Chris Lattner"> + <meta name="author" content="Erick Tryzelaar"> + <link rel="stylesheet" href="../llvm.css" type="text/css"> +</head> + +<body> + +<div class="doc_title">Kaleidoscope: Adding JIT and Optimizer Support</div> + +<ul> +<li><a href="index.html">Up to Tutorial Index</a></li> +<li>Chapter 4 + <ol> + <li><a href="#intro">Chapter 4 Introduction</a></li> + <li><a href="#trivialconstfold">Trivial Constant Folding</a></li> + <li><a href="#optimizerpasses">LLVM Optimization Passes</a></li> + <li><a href="#jit">Adding a JIT Compiler</a></li> + <li><a href="#code">Full Code Listing</a></li> + </ol> +</li> +<li><a href="OCamlLangImpl5.html">Chapter 5</a>: Extending the Language: Control +Flow</li> +</ul> + +<div class="doc_author"> + <p> + Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> + and <a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a> + </p> +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="intro">Chapter 4 Introduction</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>Welcome to Chapter 4 of the "<a href="index.html">Implementing a language +with LLVM</a>" tutorial. Chapters 1-3 described the implementation of a simple +language and added support for generating LLVM IR. This chapter describes +two new techniques: adding optimizer support to your language, and adding JIT +compiler support. These additions will demonstrate how to get nice, efficient code +for the Kaleidoscope language.</p> + +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="trivialconstfold">Trivial Constant +Folding</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p><b>Note:</b> the default <tt>IRBuilder</tt> now always includes the constant +folding optimisations below.<p> + +<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 = fadd double 1.000000e+00, 2.000000e+00 + %addtmp1 = fadd double %addtmp, %x + ret double %addtmp1 +} +</pre> +</div> + +<p>This code is a very, very literal transcription of the AST built by parsing +the input. As such, this transcription 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 this support in the AST. 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. + +<p>All we did was switch from <tt>LLVMBuilder</tt> to +<tt>LLVMFoldingBuilder</tt>. Though we change no other code, we now have all of our +instructions implicitly constant folded without us having to do anything +about it. For example, the input 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 = fadd double 3.000000e+00, %x + ret double %addtmp +} +</pre> +</div> + +<p>Well, that was easy :). In practice, we recommend always using +<tt>LLVMFoldingBuilder</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 = fadd double 3.000000e+00, %x + %addtmp1 = fadd double %x, 3.000000e+00 + %multmp = fmul 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 they are run, see the <a href="../WritingAnLLVMPass.html">How +to Write a Pass</a> document and the <a href="../Passes.html">List of LLVM +Passes</a>.</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">Llvm.PassManager</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> + (* Create the JIT. *) + let the_execution_engine = ExecutionEngine.create Codegen.the_module in + let the_fpm = PassManager.create_function Codegen.the_module in + + (* Set up the optimizer pipeline. Start with registering info about how the + * target lays out data structures. *) + TargetData.add (ExecutionEngine.target_data the_execution_engine) the_fpm; + + (* Do simple "peephole" optimizations and bit-twiddling optzn. *) + add_instruction_combining the_fpm; + + (* reassociate expressions. *) + add_reassociation the_fpm; + + (* Eliminate Common SubExpressions. *) + add_gvn the_fpm; + + (* Simplify the control flow graph (deleting unreachable blocks, etc). *) + add_cfg_simplification the_fpm; + + ignore (PassManager.initialize the_fpm); + + (* Run the main "interpreter loop" now. *) + Toplevel.main_loop the_fpm the_execution_engine stream; +</pre> +</div> + +<p>The meat of the matter here, is the definition of "<tt>the_fpm</tt>". It +requires a pointer to the <tt>the_module</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 laid out. The +"<tt>the_execution_engine</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 me, +they are a good starting place :).</p> + +<p>Once the <tt>Llvm.PassManager.</tt> 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>Codegen.codegen_func</tt>), but before it is returned to the client:</p> + +<div class="doc_code"> +<pre> +let codegen_func the_fpm = function + ... + try + let ret_val = codegen_expr body in + + (* Finish off the function. *) + let _ = build_ret ret_val builder in + + (* Validate the generated code, checking for consistency. *) + Llvm_analysis.assert_valid_function the_function; + + (* Optimize the function. *) + let _ = PassManager.run_function the_function the_fpm in + + the_function +</pre> +</div> + +<p>As you can see, this is pretty straightforward. The <tt>the_fpm</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 = fadd double %x, 3.000000e+00 + %multmp = fmul double %addtmp, %addtmp + ret double %multmp +} +</pre> +</div> + +<p>As expected, we now get our nicely optimized code, saving a floating point +add instruction from every execution of this function.</p> + +<p>LLVM provides a wide variety of optimizations that can be used in certain +circumstances. Some <a href="../Passes.html">documentation about the various +passes</a> is available, but it isn't very complete. Another good source of +ideas can come from looking at the passes 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>Code that is available in LLVM IR can have a wide variety of tools +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 section, 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> +... +let main () = + ... + <b>(* Create the JIT. *) + let the_execution_engine = ExecutionEngine.create Codegen.the_module in</b> + ... +</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>Llvm_executionengine.ExecutionEngine.t</tt> is created, the JIT +is ready to be used. There are a variety of APIs that are useful, but the +simplest one is the "<tt>Llvm_executionengine.ExecutionEngine.run_function</tt>" +function. 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> + (* Evaluate a top-level expression into an anonymous function. *) + let e = Parser.parse_toplevel stream in + print_endline "parsed a top-level expr"; + let the_function = Codegen.codegen_func the_fpm e in + dump_value the_function; + + (* JIT the function, returning a function pointer. *) + let result = ExecutionEngine.run_function the_function [||] + the_execution_engine in + + print_string "Evaluated to "; + print_float (GenericValue.as_float Codegen.double_type result); + print_newline (); +</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. +This means, 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 in. This demonstrates very basic +functionality, but can we do more?</p> + +<div class="doc_code"> +<pre> +ready> <b>def testfunc(x y) x + y*2; </b> +Read function definition: +define double @testfunc(double %x, double %y) { +entry: + %multmp = fmul double %y, 2.000000e+00 + %addtmp = fadd 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 there is something a bit +subtle going on here. Note that we only invoke the JIT on the anonymous +functions that <em>call testfunc</em>, but we never invoked it +on <em>testfunc</em> itself. What actually happened here is that the JIT +scanned for all non-JIT'd functions transitively called from the anonymous +function and compiled all of them before returning +from <tt>run_function</tt>.</p> + +<p>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 = fmul double %calltmp, %calltmp + %calltmp2 = call double @cos( double %x ) + %multmp4 = fmul double %calltmp2, %calltmp2 + %addtmp = fadd 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 surprisingly +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 the Kaleidoscope process 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>llvm_executionengine.mli</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 compile functions lazily the +first time they're called.</p> + +<p>One interesting application of this is that we can now extend the language +by writing arbitrary C code to implement operations. For example, if we add: +</p> + +<div class="doc_code"> +<pre> +/* putchard - putchar that takes a double and returns 0. */ +extern "C" +double putchard(double X) { + putchar((char)X); + return 0; +} +</pre> +</div> + +<p>Now we can produce simple output to the console by using things like: +"<tt>extern putchard(x); putchard(120);</tt>", which prints a lowercase 'x' on +the console (120 is the ASCII code for 'x'). Similar code could be used to +implement file I/O, console input, and many other capabilities in +Kaleidoscope.</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="OCamlLangImpl5.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 +ocamlbuild toy.byte +# Run +./toy.byte +</pre> +</div> + +<p>Here is the code:</p> + +<dl> +<dt>_tags:</dt> +<dd class="doc_code"> +<pre> +<{lexer,parser}.ml>: use_camlp4, pp(camlp4of) +<*.{byte,native}>: g++, use_llvm, use_llvm_analysis +<*.{byte,native}>: use_llvm_executionengine, use_llvm_target +<*.{byte,native}>: use_llvm_scalar_opts, use_bindings +</pre> +</dd> + +<dt>myocamlbuild.ml:</dt> +<dd class="doc_code"> +<pre> +open Ocamlbuild_plugin;; + +ocaml_lib ~extern:true "llvm";; +ocaml_lib ~extern:true "llvm_analysis";; +ocaml_lib ~extern:true "llvm_executionengine";; +ocaml_lib ~extern:true "llvm_target";; +ocaml_lib ~extern:true "llvm_scalar_opts";; + +flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);; +dep ["link"; "ocaml"; "use_bindings"] ["bindings.o"];; +</pre> +</dd> + +<dt>token.ml:</dt> +<dd class="doc_code"> +<pre> +(*===----------------------------------------------------------------------=== + * Lexer Tokens + *===----------------------------------------------------------------------===*) + +(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of + * these others for known things. *) +type token = + (* commands *) + | Def | Extern + + (* primary *) + | Ident of string | Number of float + + (* unknown *) + | Kwd of char +</pre> +</dd> + +<dt>lexer.ml:</dt> +<dd class="doc_code"> +<pre> +(*===----------------------------------------------------------------------=== + * Lexer + *===----------------------------------------------------------------------===*) + +let rec lex = parser + (* Skip any whitespace. *) + | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream + + (* identifier: [a-zA-Z][a-zA-Z0-9] *) + | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] -> + let buffer = Buffer.create 1 in + Buffer.add_char buffer c; + lex_ident buffer stream + + (* number: [0-9.]+ *) + | [< ' ('0' .. '9' as c); stream >] -> + let buffer = Buffer.create 1 in + Buffer.add_char buffer c; + lex_number buffer stream + + (* Comment until end of line. *) + | [< ' ('#'); stream >] -> + lex_comment stream + + (* Otherwise, just return the character as its ascii value. *) + | [< 'c; stream >] -> + [< 'Token.Kwd c; lex stream >] + + (* end of stream. *) + | [< >] -> [< >] + +and lex_number buffer = parser + | [< ' ('0' .. '9' | '.' as c); stream >] -> + Buffer.add_char buffer c; + lex_number buffer stream + | [< stream=lex >] -> + [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >] + +and lex_ident buffer = parser + | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] -> + Buffer.add_char buffer c; + lex_ident buffer stream + | [< stream=lex >] -> + match Buffer.contents buffer with + | "def" -> [< 'Token.Def; stream >] + | "extern" -> [< 'Token.Extern; stream >] + | id -> [< 'Token.Ident id; stream >] + +and lex_comment = parser + | [< ' ('\n'); stream=lex >] -> stream + | [< 'c; e=lex_comment >] -> e + | [< >] -> [< >] +</pre> +</dd> + +<dt>ast.ml:</dt> +<dd class="doc_code"> +<pre> +(*===----------------------------------------------------------------------=== + * Abstract Syntax Tree (aka Parse Tree) + *===----------------------------------------------------------------------===*) + +(* expr - Base type for all expression nodes. *) +type expr = + (* variant for numeric literals like "1.0". *) + | Number of float + + (* variant for referencing a variable, like "a". *) + | Variable of string + + (* variant for a binary operator. *) + | Binary of char * expr * expr + + (* variant for function calls. *) + | Call of string * expr array + +(* proto - This type represents the "prototype" for a function, which captures + * its name, and its argument names (thus implicitly the number of arguments the + * function takes). *) +type proto = Prototype of string * string array + +(* func - This type represents a function definition itself. *) +type func = Function of proto * expr +</pre> +</dd> + +<dt>parser.ml:</dt> +<dd class="doc_code"> +<pre> +(*===---------------------------------------------------------------------=== + * Parser + *===---------------------------------------------------------------------===*) + +(* binop_precedence - This holds the precedence for each binary operator that is + * defined *) +let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10 + +(* precedence - Get the precedence of the pending binary operator token. *) +let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1 + +(* primary + * ::= identifier + * ::= numberexpr + * ::= parenexpr *) +let rec parse_primary = parser + (* numberexpr ::= number *) + | [< 'Token.Number n >] -> Ast.Number n + + (* parenexpr ::= '(' expression ')' *) + | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e + + (* identifierexpr + * ::= identifier + * ::= identifier '(' argumentexpr ')' *) + | [< 'Token.Ident id; stream >] -> + let rec parse_args accumulator = parser + | [< e=parse_expr; stream >] -> + begin parser + | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e + | [< >] -> e :: accumulator + end stream + | [< >] -> accumulator + in + let rec parse_ident id = parser + (* Call. *) + | [< 'Token.Kwd '('; + args=parse_args []; + 'Token.Kwd ')' ?? "expected ')'">] -> + Ast.Call (id, Array.of_list (List.rev args)) + + (* Simple variable ref. *) + | [< >] -> Ast.Variable id + in + parse_ident id stream + + | [< >] -> raise (Stream.Error "unknown token when expecting an expression.") + +(* binoprhs + * ::= ('+' primary)* *) +and parse_bin_rhs expr_prec lhs stream = + match Stream.peek stream with + (* If this is a binop, find its precedence. *) + | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c -> + let token_prec = precedence c in + + (* If this is a binop that binds at least as tightly as the current binop, + * consume it, otherwise we are done. *) + if token_prec < expr_prec then lhs else begin + (* Eat the binop. *) + Stream.junk stream; + + (* Parse the primary expression after the binary operator. *) + let rhs = parse_primary stream in + + (* Okay, we know this is a binop. *) + let rhs = + match Stream.peek stream with + | Some (Token.Kwd c2) -> + (* If BinOp binds less tightly with rhs than the operator after + * rhs, let the pending operator take rhs as its lhs. *) + let next_prec = precedence c2 in + if token_prec < next_prec + then parse_bin_rhs (token_prec + 1) rhs stream + else rhs + | _ -> rhs + in + + (* Merge lhs/rhs. *) + let lhs = Ast.Binary (c, lhs, rhs) in + parse_bin_rhs expr_prec lhs stream + end + | _ -> lhs + +(* expression + * ::= primary binoprhs *) +and parse_expr = parser + | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream + +(* prototype + * ::= id '(' id* ')' *) +let parse_prototype = + let rec parse_args accumulator = parser + | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e + | [< >] -> accumulator + in + + parser + | [< 'Token.Ident id; + 'Token.Kwd '(' ?? "expected '(' in prototype"; + args=parse_args []; + 'Token.Kwd ')' ?? "expected ')' in prototype" >] -> + (* success. *) + Ast.Prototype (id, Array.of_list (List.rev args)) + + | [< >] -> + raise (Stream.Error "expected function name in prototype") + +(* definition ::= 'def' prototype expression *) +let parse_definition = parser + | [< 'Token.Def; p=parse_prototype; e=parse_expr >] -> + Ast.Function (p, e) + +(* toplevelexpr ::= expression *) +let parse_toplevel = parser + | [< e=parse_expr >] -> + (* Make an anonymous proto. *) + Ast.Function (Ast.Prototype ("", [||]), e) + +(* external ::= 'extern' prototype *) +let parse_extern = parser + | [< 'Token.Extern; e=parse_prototype >] -> e +</pre> +</dd> + +<dt>codegen.ml:</dt> +<dd class="doc_code"> +<pre> +(*===----------------------------------------------------------------------=== + * Code Generation + *===----------------------------------------------------------------------===*) + +open Llvm + +exception Error of string + +let context = global_context () +let the_module = create_module context "my cool jit" +let builder = builder context +let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10 +let double_type = double_type context + +let rec codegen_expr = function + | Ast.Number n -> const_float double_type n + | Ast.Variable name -> + (try Hashtbl.find named_values name with + | Not_found -> raise (Error "unknown variable name")) + | Ast.Binary (op, lhs, rhs) -> + let lhs_val = codegen_expr lhs in + let rhs_val = codegen_expr rhs in + begin + match op with + | '+' -> build_add lhs_val rhs_val "addtmp" builder + | '-' -> build_sub lhs_val rhs_val "subtmp" builder + | '*' -> build_mul lhs_val rhs_val "multmp" builder + | '<' -> + (* Convert bool 0/1 to double 0.0 or 1.0 *) + let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in + build_uitofp i double_type "booltmp" builder + | _ -> raise (Error "invalid binary operator") + end + | Ast.Call (callee, args) -> + (* Look up the name in the module table. *) + let callee = + match lookup_function callee the_module with + | Some callee -> callee + | None -> raise (Error "unknown function referenced") + in + let params = params callee in + + (* If argument mismatch error. *) + if Array.length params == Array.length args then () else + raise (Error "incorrect # arguments passed"); + let args = Array.map codegen_expr args in + build_call callee args "calltmp" builder + +let codegen_proto = function + | Ast.Prototype (name, args) -> + (* Make the function type: double(double,double) etc. *) + let doubles = Array.make (Array.length args) double_type in + let ft = function_type double_type doubles in + let f = + match lookup_function name the_module with + | None -> declare_function name ft the_module + + (* If 'f' conflicted, there was already something named 'name'. If it + * has a body, don't allow redefinition or reextern. *) + | Some f -> + (* If 'f' already has a body, reject this. *) + if block_begin f <> At_end f then + raise (Error "redefinition of function"); + + (* If 'f' took a different number of arguments, reject. *) + if element_type (type_of f) <> ft then + raise (Error "redefinition of function with different # args"); + f + in + + (* Set names for all arguments. *) + Array.iteri (fun i a -> + let n = args.(i) in + set_value_name n a; + Hashtbl.add named_values n a; + ) (params f); + f + +let codegen_func the_fpm = function + | Ast.Function (proto, body) -> + Hashtbl.clear named_values; + let the_function = codegen_proto proto in + + (* Create a new basic block to start insertion into. *) + let bb = append_block context "entry" the_function in + position_at_end bb builder; + + try + let ret_val = codegen_expr body in + + (* Finish off the function. *) + let _ = build_ret ret_val builder in + + (* Validate the generated code, checking for consistency. *) + Llvm_analysis.assert_valid_function the_function; + + (* Optimize the function. *) + let _ = PassManager.run_function the_function the_fpm in + + the_function + with e -> + delete_function the_function; + raise e +</pre> +</dd> + +<dt>toplevel.ml:</dt> +<dd class="doc_code"> +<pre> +(*===----------------------------------------------------------------------=== + * Top-Level parsing and JIT Driver + *===----------------------------------------------------------------------===*) + +open Llvm +open Llvm_executionengine + +(* top ::= definition | external | expression | ';' *) +let rec main_loop the_fpm the_execution_engine stream = + match Stream.peek stream with + | None -> () + + (* ignore top-level semicolons. *) + | Some (Token.Kwd ';') -> + Stream.junk stream; + main_loop the_fpm the_execution_engine stream + + | Some token -> + begin + try match token with + | Token.Def -> + let e = Parser.parse_definition stream in + print_endline "parsed a function definition."; + dump_value (Codegen.codegen_func the_fpm e); + | Token.Extern -> + let e = Parser.parse_extern stream in + print_endline "parsed an extern."; + dump_value (Codegen.codegen_proto e); + | _ -> + (* Evaluate a top-level expression into an anonymous function. *) + let e = Parser.parse_toplevel stream in + print_endline "parsed a top-level expr"; + let the_function = Codegen.codegen_func the_fpm e in + dump_value the_function; + + (* JIT the function, returning a function pointer. *) + let result = ExecutionEngine.run_function the_function [||] + the_execution_engine in + + print_string "Evaluated to "; + print_float (GenericValue.as_float Codegen.double_type result); + print_newline (); + with Stream.Error s | Codegen.Error s -> + (* Skip token for error recovery. *) + Stream.junk stream; + print_endline s; + end; + print_string "ready> "; flush stdout; + main_loop the_fpm the_execution_engine stream +</pre> +</dd> + +<dt>toy.ml:</dt> +<dd class="doc_code"> +<pre> +(*===----------------------------------------------------------------------=== + * Main driver code. + *===----------------------------------------------------------------------===*) + +open Llvm +open Llvm_executionengine +open Llvm_target +open Llvm_scalar_opts + +let main () = + ignore (initialize_native_target ()); + + (* Install standard binary operators. + * 1 is the lowest precedence. *) + Hashtbl.add Parser.binop_precedence '<' 10; + Hashtbl.add Parser.binop_precedence '+' 20; + Hashtbl.add Parser.binop_precedence '-' 20; + Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *) + + (* Prime the first token. *) + print_string "ready> "; flush stdout; + let stream = Lexer.lex (Stream.of_channel stdin) in + + (* Create the JIT. *) + let the_execution_engine = ExecutionEngine.create Codegen.the_module in + let the_fpm = PassManager.create_function Codegen.the_module in + + (* Set up the optimizer pipeline. Start with registering info about how the + * target lays out data structures. *) + TargetData.add (ExecutionEngine.target_data the_execution_engine) the_fpm; + + (* Do simple "peephole" optimizations and bit-twiddling optzn. *) + add_instruction_combination the_fpm; + + (* reassociate expressions. *) + add_reassociation the_fpm; + + (* Eliminate Common SubExpressions. *) + add_gvn the_fpm; + + (* Simplify the control flow graph (deleting unreachable blocks, etc). *) + add_cfg_simplification the_fpm; + + ignore (PassManager.initialize the_fpm); + + (* Run the main "interpreter loop" now. *) + Toplevel.main_loop the_fpm the_execution_engine stream; + + (* Print out all the generated code. *) + dump_module Codegen.the_module +;; + +main () +</pre> +</dd> + +<dt>bindings.c</dt> +<dd class="doc_code"> +<pre> +#include <stdio.h> + +/* putchard - putchar that takes a double and returns 0. */ +extern double putchard(double X) { + putchar((char)X); + return 0; +} +</pre> +</dd> +</dl> + +<a href="OCamlLangImpl5.html">Next: Extending the language: control flow</a> +</div> + +<!-- *********************************************************************** --> +<hr> +<address> + <a href="http://jigsaw.w3.org/css-validator/check/referer"><img + src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a> + <a href="http://validator.w3.org/check/referer"><img + src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a> + + <a href="mailto:sabre@nondot.org">Chris Lattner</a><br> + <a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a><br> + <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br> + Last modified: $Date$ +</address> +</body> +</html> |