+++ /dev/null
-<!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
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-
- <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>
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