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diff --git a/docs/tutorial/OCamlLangImpl3.html b/docs/tutorial/OCamlLangImpl3.html new file mode 100644 index 0000000000..febd7f528c --- /dev/null +++ b/docs/tutorial/OCamlLangImpl3.html @@ -0,0 +1,1093 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> + +<html> +<head> + <title>Kaleidoscope: Implementing code generation to LLVM IR</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: Code generation to LLVM IR</div> + +<ul> +<li><a href="index.html">Up to Tutorial Index</a></li> +<li>Chapter 3 + <ol> + <li><a href="#intro">Chapter 3 Introduction</a></li> + <li><a href="#basics">Code Generation Setup</a></li> + <li><a href="#exprs">Expression Code Generation</a></li> + <li><a href="#funcs">Function Code Generation</a></li> + <li><a href="#driver">Driver Changes and Closing Thoughts</a></li> + <li><a href="#code">Full Code Listing</a></li> + </ol> +</li> +<li><a href="OCamlLangImpl4.html">Chapter 4</a>: Adding JIT and Optimizer +Support</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 3 Introduction</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>Welcome to Chapter 3 of the "<a href="index.html">Implementing a language +with LLVM</a>" tutorial. This chapter shows you how to transform the <a +href="OCamlLangImpl2.html">Abstract Syntax Tree</a>, built in Chapter 2, into +LLVM IR. This will teach you a little bit about how LLVM does things, as well +as demonstrate how easy it is to use. It's much more work to build a lexer and +parser than it is to generate LLVM IR code. :) +</p> + +<p><b>Please note</b>: the code in this chapter and later require LLVM 2.3 or +LLVM SVN to work. LLVM 2.2 and before will not work with it.</p> + +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="basics">Code Generation Setup</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 code generation (codegen) methods in each AST class:</p> + +<div class="doc_code"> +<pre> +let rec codegen_expr = function + | Ast.Number n -> ... + | Ast.Variable name -> ... +</pre> +</div> + +<p>The <tt>Codegen.codegen_expr</tt> function says to emit IR for that AST node +along with all the things it depends on, and they all return an LLVM Value +object. "Value" is the class used to represent a "<a +href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single +Assignment (SSA)</a> register" or "SSA value" in LLVM. The most distinct aspect +of SSA values is that their value is computed as the related instruction +executes, and it does not get a new value until (and if) the instruction +re-executes. In other words, there is no way to "change" an SSA value. For +more information, please read up on <a +href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single +Assignment</a> - the concepts are really quite natural once you grok them.</p> + +<p>The +second thing we want is an "Error" exception like we used for the parser, which +will be used to report errors found during code generation (for example, use of +an undeclared parameter):</p> + +<div class="doc_code"> +<pre> +exception Error of string + +let the_module = create_module (global_context ()) "my cool jit" +let builder = builder (global_context ()) +let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10 +let double_type = double_type context +</pre> +</div> + +<p>The static variables will be used during code generation. +<tt>Codgen.the_module</tt> is the LLVM construct that contains all of the +functions and global variables in a chunk of code. In many ways, it is the +top-level structure that the LLVM IR uses to contain code.</p> + +<p>The <tt>Codegen.builder</tt> object is a helper object that makes it easy to +generate LLVM instructions. Instances of the <a +href="http://llvm.org/doxygen/IRBuilder_8h-source.html"><tt>IRBuilder</tt></a> +class keep track of the current place to insert instructions and has methods to +create new instructions.</p> + +<p>The <tt>Codegen.named_values</tt> map keeps track of which values are defined +in the current scope and what their LLVM representation is. (In other words, it +is a symbol table for the code). In this form of Kaleidoscope, the only things +that can be referenced are function parameters. As such, function parameters +will be in this map when generating code for their function body.</p> + +<p> +With these basics in place, we can start talking about how to generate code for +each expression. Note that this assumes that the <tt>Codgen.builder</tt> has +been set up to generate code <em>into</em> something. For now, we'll assume +that this has already been done, and we'll just use it to emit code.</p> + +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="exprs">Expression Code Generation</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>Generating LLVM code for expression nodes is very straightforward: less +than 30 lines of commented code for all four of our expression nodes. First +we'll do numeric literals:</p> + +<div class="doc_code"> +<pre> + | Ast.Number n -> const_float double_type n +</pre> +</div> + +<p>In the LLVM IR, numeric constants are represented with the +<tt>ConstantFP</tt> class, which holds the numeric value in an <tt>APFloat</tt> +internally (<tt>APFloat</tt> has the capability of holding floating point +constants of <em>A</em>rbitrary <em>P</em>recision). This code basically just +creates and returns a <tt>ConstantFP</tt>. Note that in the LLVM IR +that constants are all uniqued together and shared. For this reason, the API +uses "the foo::get(..)" idiom instead of "new foo(..)" or "foo::Create(..)".</p> + +<div class="doc_code"> +<pre> + | Ast.Variable name -> + (try Hashtbl.find named_values name with + | Not_found -> raise (Error "unknown variable name")) +</pre> +</div> + +<p>References to variables are also quite simple using LLVM. In the simple +version of Kaleidoscope, we assume that the variable has already been emitted +somewhere and its value is available. In practice, the only values that can be +in the <tt>Codegen.named_values</tt> map are function arguments. This code +simply checks to see that the specified name is in the map (if not, an unknown +variable is being referenced) and returns the value for it. In future chapters, +we'll add support for <a href="LangImpl5.html#for">loop induction variables</a> +in the symbol table, and for <a href="LangImpl7.html#localvars">local +variables</a>.</p> + +<div class="doc_code"> +<pre> + | 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 +</pre> +</div> + +<p>Binary operators start to get more interesting. The basic idea here is that +we recursively emit code for the left-hand side of the expression, then the +right-hand side, then we compute the result of the binary expression. In this +code, we do a simple switch on the opcode to create the right LLVM instruction. +</p> + +<p>In the example above, the LLVM builder class is starting to show its value. +IRBuilder knows where to insert the newly created instruction, all you have to +do is specify what instruction to create (e.g. with <tt>Llvm.create_add</tt>), +which operands to use (<tt>lhs</tt> and <tt>rhs</tt> here) and optionally +provide a name for the generated instruction.</p> + +<p>One nice thing about LLVM is that the name is just a hint. For instance, if +the code above emits multiple "addtmp" variables, LLVM will automatically +provide each one with an increasing, unique numeric suffix. Local value names +for instructions are purely optional, but it makes it much easier to read the +IR dumps.</p> + +<p><a href="../LangRef.html#instref">LLVM instructions</a> are constrained by +strict rules: for example, the Left and Right operators of +an <a href="../LangRef.html#i_add">add instruction</a> must have the same +type, and the result type of the add must match the operand types. Because +all values in Kaleidoscope are doubles, this makes for very simple code for add, +sub and mul.</p> + +<p>On the other hand, LLVM specifies that the <a +href="../LangRef.html#i_fcmp">fcmp instruction</a> always returns an 'i1' value +(a one bit integer). The problem with this is that Kaleidoscope wants the value to be a 0.0 or 1.0 value. In order to get these semantics, we combine the fcmp instruction with +a <a href="../LangRef.html#i_uitofp">uitofp instruction</a>. This instruction +converts its input integer into a floating point value by treating the input +as an unsigned value. In contrast, if we used the <a +href="../LangRef.html#i_sitofp">sitofp instruction</a>, the Kaleidoscope '<' +operator would return 0.0 and -1.0, depending on the input value.</p> + +<div class="doc_code"> +<pre> + | 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 +</pre> +</div> + +<p>Code generation for function calls is quite straightforward with LLVM. The +code above initially does a function name lookup in the LLVM Module's symbol +table. Recall that the LLVM Module is the container that holds all of the +functions we are JIT'ing. By giving each function the same name as what the +user specifies, we can use the LLVM symbol table to resolve function names for +us.</p> + +<p>Once we have the function to call, we recursively codegen each argument that +is to be passed in, and create an LLVM <a href="../LangRef.html#i_call">call +instruction</a>. Note that LLVM uses the native C calling conventions by +default, allowing these calls to also call into standard library functions like +"sin" and "cos", with no additional effort.</p> + +<p>This wraps up our handling of the four basic expressions that we have so far +in Kaleidoscope. Feel free to go in and add some more. For example, by +browsing the <a href="../LangRef.html">LLVM language reference</a> you'll find +several other interesting instructions that are really easy to plug into our +basic framework.</p> + +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="funcs">Function Code Generation</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>Code generation for prototypes and functions must handle a number of +details, which make their code less beautiful than expression code +generation, but allows us to illustrate some important points. First, lets +talk about code generation for prototypes: they are used both for function +bodies and external function declarations. The code starts with:</p> + +<div class="doc_code"> +<pre> +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 +</pre> +</div> + +<p>This code packs a lot of power into a few lines. Note first that this +function returns a "Function*" instead of a "Value*" (although at the moment +they both are modeled by <tt>llvalue</tt> in ocaml). Because a "prototype" +really talks about the external interface for a function (not the value computed +by an expression), it makes sense for it to return the LLVM Function it +corresponds to when codegen'd.</p> + +<p>The call to <tt>Llvm.function_type</tt> creates the <tt>Llvm.llvalue</tt> +that should be used for a given Prototype. Since all function arguments in +Kaleidoscope are of type double, the first line creates a vector of "N" LLVM +double types. It then uses the <tt>Llvm.function_type</tt> method to create a +function type that takes "N" doubles as arguments, returns one double as a +result, and that is not vararg (that uses the function +<tt>Llvm.var_arg_function_type</tt>). Note that Types in LLVM are uniqued just +like <tt>Constant</tt>s are, so you don't "new" a type, you "get" it.</p> + +<p>The final line above checks if the function has already been defined in +<tt>Codegen.the_module</tt>. If not, we will create it.</p> + +<div class="doc_code"> +<pre> + | None -> declare_function name ft the_module +</pre> +</div> + +<p>This indicates the type and name to use, as well as which module to insert +into. By default we assume a function has +<tt>Llvm.Linkage.ExternalLinkage</tt>. "<a href="LangRef.html#linkage">external +linkage</a>" means that the function may be defined outside the current module +and/or that it is callable by functions outside the module. The "<tt>name</tt>" +passed in is the name the user specified: this name is registered in +"<tt>Codegen.the_module</tt>"s symbol table, which is used by the function call +code above.</p> + +<p>In Kaleidoscope, I choose to allow redefinitions of functions in two cases: +first, we want to allow 'extern'ing a function more than once, as long as the +prototypes for the externs match (since all arguments have the same type, we +just have to check that the number of arguments match). Second, we want to +allow 'extern'ing a function and then defining a body for it. This is useful +when defining mutually recursive functions.</p> + +<div class="doc_code"> +<pre> + (* 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 Array.length (basic_blocks f) == 0 then () else + raise (Error "redefinition of function"); + + (* If 'f' took a different number of arguments, reject. *) + if Array.length (params f) == Array.length args then () else + raise (Error "redefinition of function with different # args"); + f + in +</pre> +</div> + +<p>In order to verify the logic above, we first check to see if the pre-existing +function is "empty". In this case, empty means that it has no basic blocks in +it, which means it has no body. If it has no body, it is a forward +declaration. Since we don't allow anything after a full definition of the +function, the code rejects this case. If the previous reference to a function +was an 'extern', we simply verify that the number of arguments for that +definition and this one match up. If not, we emit an error.</p> + +<div class="doc_code"> +<pre> + (* 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 +</pre> +</div> + +<p>The last bit of code for prototypes loops over all of the arguments in the +function, setting the name of the LLVM Argument objects to match, and registering +the arguments in the <tt>Codegen.named_values</tt> map for future use by the +<tt>Ast.Variable</tt> variant. Once this is set up, it returns the Function +object to the caller. Note that we don't check for conflicting +argument names here (e.g. "extern foo(a b a)"). Doing so would be very +straight-forward with the mechanics we have already used above.</p> + +<div class="doc_code"> +<pre> +let codegen_func = function + | Ast.Function (proto, body) -> + Hashtbl.clear named_values; + let the_function = codegen_proto proto in +</pre> +</div> + +<p>Code generation for function definitions starts out simply enough: we just +codegen the prototype (Proto) and verify that it is ok. We then clear out the +<tt>Codegen.named_values</tt> map to make sure that there isn't anything in it +from the last function we compiled. Code generation of the prototype ensures +that there is an LLVM Function object that is ready to go for us.</p> + +<div class="doc_code"> +<pre> + (* 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 +</pre> +</div> + +<p>Now we get to the point where the <tt>Codegen.builder</tt> is set up. The +first line creates a new +<a href="http://en.wikipedia.org/wiki/Basic_block">basic block</a> (named +"entry"), which is inserted into <tt>the_function</tt>. The second line then +tells the builder that new instructions should be inserted into the end of the +new basic block. Basic blocks in LLVM are an important part of functions that +define the <a +href="http://en.wikipedia.org/wiki/Control_flow_graph">Control Flow Graph</a>. +Since we don't have any control flow, our functions will only contain one +block at this point. We'll fix this in <a href="OCamlLangImpl5.html">Chapter +5</a> :).</p> + +<div class="doc_code"> +<pre> + 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; + + the_function +</pre> +</div> + +<p>Once the insertion point is set up, we call the <tt>Codegen.codegen_func</tt> +method for the root expression of the function. If no error happens, this emits +code to compute the expression into the entry block and returns the value that +was computed. Assuming no error, we then create an LLVM <a +href="../LangRef.html#i_ret">ret instruction</a>, which completes the function. +Once the function is built, we call +<tt>Llvm_analysis.assert_valid_function</tt>, which is provided by LLVM. This +function does a variety of consistency checks on the generated code, to +determine if our compiler is doing everything right. Using this is important: +it can catch a lot of bugs. Once the function is finished and validated, we +return it.</p> + +<div class="doc_code"> +<pre> + with e -> + delete_function the_function; + raise e +</pre> +</div> + +<p>The only piece left here is handling of the error case. For simplicity, we +handle this by merely deleting the function we produced with the +<tt>Llvm.delete_function</tt> method. This allows the user to redefine a +function that they incorrectly typed in before: if we didn't delete it, it +would live in the symbol table, with a body, preventing future redefinition.</p> + +<p>This code does have a bug, though. Since the <tt>Codegen.codegen_proto</tt> +can return a previously defined forward declaration, our code can actually delete +a forward declaration. There are a number of ways to fix this bug, see what you +can come up with! Here is a testcase:</p> + +<div class="doc_code"> +<pre> +extern foo(a b); # ok, defines foo. +def foo(a b) c; # error, 'c' is invalid. +def bar() foo(1, 2); # error, unknown function "foo" +</pre> +</div> + +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="driver">Driver Changes and +Closing Thoughts</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p> +For now, code generation to LLVM doesn't really get us much, except that we can +look at the pretty IR calls. The sample code inserts calls to Codegen into the +"<tt>Toplevel.main_loop</tt>", and then dumps out the LLVM IR. This gives a +nice way to look at the LLVM IR for simple functions. For example: +</p> + +<div class="doc_code"> +<pre> +ready> <b>4+5</b>; +Read top-level expression: +define double @""() { +entry: + %addtmp = fadd double 4.000000e+00, 5.000000e+00 + ret double %addtmp +} +</pre> +</div> + +<p>Note how the parser turns the top-level expression into anonymous functions +for us. This will be handy when we add <a href="OCamlLangImpl4.html#jit">JIT +support</a> in the next chapter. Also note that the code is very literally +transcribed, no optimizations are being performed. We will +<a href="OCamlLangImpl4.html#trivialconstfold">add optimizations</a> explicitly +in the next chapter.</p> + +<div class="doc_code"> +<pre> +ready> <b>def foo(a b) a*a + 2*a*b + b*b;</b> +Read function definition: +define double @foo(double %a, double %b) { +entry: + %multmp = fmul double %a, %a + %multmp1 = fmul double 2.000000e+00, %a + %multmp2 = fmul double %multmp1, %b + %addtmp = fadd double %multmp, %multmp2 + %multmp3 = fmul double %b, %b + %addtmp4 = fadd double %addtmp, %multmp3 + ret double %addtmp4 +} +</pre> +</div> + +<p>This shows some simple arithmetic. Notice the striking similarity to the +LLVM builder calls that we use to create the instructions.</p> + +<div class="doc_code"> +<pre> +ready> <b>def bar(a) foo(a, 4.0) + bar(31337);</b> +Read function definition: +define double @bar(double %a) { +entry: + %calltmp = call double @foo( double %a, double 4.000000e+00 ) + %calltmp1 = call double @bar( double 3.133700e+04 ) + %addtmp = fadd double %calltmp, %calltmp1 + ret double %addtmp +} +</pre> +</div> + +<p>This shows some function calls. Note that this function will take a long +time to execute if you call it. In the future we'll add conditional control +flow to actually make recursion useful :).</p> + +<div class="doc_code"> +<pre> +ready> <b>extern cos(x);</b> +Read extern: +declare double @cos(double) + +ready> <b>cos(1.234);</b> +Read top-level expression: +define double @""() { +entry: + %calltmp = call double @cos( double 1.234000e+00 ) + ret double %calltmp +} +</pre> +</div> + +<p>This shows an extern for the libm "cos" function, and a call to it.</p> + + +<div class="doc_code"> +<pre> +ready> <b>^D</b> +; ModuleID = 'my cool jit' + +define double @""() { +entry: + %addtmp = fadd double 4.000000e+00, 5.000000e+00 + ret double %addtmp +} + +define double @foo(double %a, double %b) { +entry: + %multmp = fmul double %a, %a + %multmp1 = fmul double 2.000000e+00, %a + %multmp2 = fmul double %multmp1, %b + %addtmp = fadd double %multmp, %multmp2 + %multmp3 = fmul double %b, %b + %addtmp4 = fadd double %addtmp, %multmp3 + ret double %addtmp4 +} + +define double @bar(double %a) { +entry: + %calltmp = call double @foo( double %a, double 4.000000e+00 ) + %calltmp1 = call double @bar( double 3.133700e+04 ) + %addtmp = fadd double %calltmp, %calltmp1 + ret double %addtmp +} + +declare double @cos(double) + +define double @""() { +entry: + %calltmp = call double @cos( double 1.234000e+00 ) + ret double %calltmp +} +</pre> +</div> + +<p>When you quit the current demo, it dumps out the IR for the entire module +generated. Here you can see the big picture with all the functions referencing +each other.</p> + +<p>This wraps up the third chapter of the Kaleidoscope tutorial. Up next, we'll +describe how to <a href="OCamlLangImpl4.html">add JIT codegen and optimizer +support</a> to this so we can actually start running code!</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 code generator. Because this uses the LLVM libraries, we need to link +them in. To do this, we use the <a +href="http://llvm.org/cmds/llvm-config.html">llvm-config</a> tool to inform +our makefile/command line about which options to 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 +</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";; + +flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);; +</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 = 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; + + 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 + +(* top ::= definition | external | expression | ';' *) +let rec main_loop stream = + match Stream.peek stream with + | None -> () + + (* ignore top-level semicolons. *) + | Some (Token.Kwd ';') -> + Stream.junk stream; + main_loop 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 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"; + dump_value (Codegen.codegen_func e); + 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 stream +</pre> +</dd> + +<dt>toy.ml:</dt> +<dd class="doc_code"> +<pre> +(*===----------------------------------------------------------------------=== + * Main driver code. + *===----------------------------------------------------------------------===*) + +open Llvm + +let main () = + (* 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 + + (* Run the main "interpreter loop" now. *) + Toplevel.main_loop stream; + + (* Print out all the generated code. *) + dump_module Codegen.the_module +;; + +main () +</pre> +</dd> +</dl> + +<a href="OCamlLangImpl4.html">Next: Adding JIT and Optimizer Support</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> |