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1094 lines
38 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<title>Kaleidoscope: Implementing code generation to LLVM IR</title>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="author" content="Chris Lattner">
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<meta name="author" content="Erick Tryzelaar">
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<link rel="stylesheet" href="../llvm.css" type="text/css">
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</head>
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<body>
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<h1>Kaleidoscope: Code generation to LLVM IR</h1>
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<ul>
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<li><a href="index.html">Up to Tutorial Index</a></li>
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<li>Chapter 3
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<ol>
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<li><a href="#intro">Chapter 3 Introduction</a></li>
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<li><a href="#basics">Code Generation Setup</a></li>
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<li><a href="#exprs">Expression Code Generation</a></li>
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<li><a href="#funcs">Function Code Generation</a></li>
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<li><a href="#driver">Driver Changes and Closing Thoughts</a></li>
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<li><a href="#code">Full Code Listing</a></li>
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</ol>
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</li>
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<li><a href="OCamlLangImpl4.html">Chapter 4</a>: Adding JIT and Optimizer
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Support</li>
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</ul>
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<div class="doc_author">
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<p>
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Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
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and <a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a>
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</p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="intro">Chapter 3 Introduction</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p>Welcome to Chapter 3 of the "<a href="index.html">Implementing a language
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with LLVM</a>" tutorial. This chapter shows you how to transform the <a
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href="OCamlLangImpl2.html">Abstract Syntax Tree</a>, built in Chapter 2, into
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LLVM IR. This will teach you a little bit about how LLVM does things, as well
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as demonstrate how easy it is to use. It's much more work to build a lexer and
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parser than it is to generate LLVM IR code. :)
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</p>
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<p><b>Please note</b>: the code in this chapter and later require LLVM 2.3 or
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LLVM SVN to work. LLVM 2.2 and before will not work with it.</p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="basics">Code Generation Setup</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p>
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In order to generate LLVM IR, we want some simple setup to get started. First
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we define virtual code generation (codegen) methods in each AST class:</p>
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<div class="doc_code">
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<pre>
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let rec codegen_expr = function
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| Ast.Number n -> ...
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| Ast.Variable name -> ...
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</pre>
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</div>
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<p>The <tt>Codegen.codegen_expr</tt> function says to emit IR for that AST node
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along with all the things it depends on, and they all return an LLVM Value
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object. "Value" is the class used to represent a "<a
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href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
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Assignment (SSA)</a> register" or "SSA value" in LLVM. The most distinct aspect
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of SSA values is that their value is computed as the related instruction
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executes, and it does not get a new value until (and if) the instruction
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re-executes. In other words, there is no way to "change" an SSA value. For
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more information, please read up on <a
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href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
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Assignment</a> - the concepts are really quite natural once you grok them.</p>
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<p>The
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second thing we want is an "Error" exception like we used for the parser, which
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will be used to report errors found during code generation (for example, use of
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an undeclared parameter):</p>
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<div class="doc_code">
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<pre>
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exception Error of string
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let context = global_context ()
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let the_module = create_module context "my cool jit"
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let builder = builder context
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let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
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let double_type = double_type context
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</pre>
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</div>
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<p>The static variables will be used during code generation.
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<tt>Codgen.the_module</tt> is the LLVM construct that contains all of the
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functions and global variables in a chunk of code. In many ways, it is the
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top-level structure that the LLVM IR uses to contain code.</p>
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<p>The <tt>Codegen.builder</tt> object is a helper object that makes it easy to
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generate LLVM instructions. Instances of the <a
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href="http://llvm.org/doxygen/IRBuilder_8h-source.html"><tt>IRBuilder</tt></a>
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class keep track of the current place to insert instructions and has methods to
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create new instructions.</p>
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<p>The <tt>Codegen.named_values</tt> map keeps track of which values are defined
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in the current scope and what their LLVM representation is. (In other words, it
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is a symbol table for the code). In this form of Kaleidoscope, the only things
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that can be referenced are function parameters. As such, function parameters
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will be in this map when generating code for their function body.</p>
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<p>
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With these basics in place, we can start talking about how to generate code for
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each expression. Note that this assumes that the <tt>Codgen.builder</tt> has
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been set up to generate code <em>into</em> something. For now, we'll assume
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that this has already been done, and we'll just use it to emit code.</p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="exprs">Expression Code Generation</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p>Generating LLVM code for expression nodes is very straightforward: less
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than 30 lines of commented code for all four of our expression nodes. First
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we'll do numeric literals:</p>
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<div class="doc_code">
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<pre>
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| Ast.Number n -> const_float double_type n
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</pre>
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</div>
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<p>In the LLVM IR, numeric constants are represented with the
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<tt>ConstantFP</tt> class, which holds the numeric value in an <tt>APFloat</tt>
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internally (<tt>APFloat</tt> has the capability of holding floating point
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constants of <em>A</em>rbitrary <em>P</em>recision). This code basically just
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creates and returns a <tt>ConstantFP</tt>. Note that in the LLVM IR
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that constants are all uniqued together and shared. For this reason, the API
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uses "the foo::get(..)" idiom instead of "new foo(..)" or "foo::Create(..)".</p>
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<div class="doc_code">
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<pre>
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| Ast.Variable name ->
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(try Hashtbl.find named_values name with
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| Not_found -> raise (Error "unknown variable name"))
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</pre>
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</div>
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<p>References to variables are also quite simple using LLVM. In the simple
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version of Kaleidoscope, we assume that the variable has already been emitted
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somewhere and its value is available. In practice, the only values that can be
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in the <tt>Codegen.named_values</tt> map are function arguments. This code
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simply checks to see that the specified name is in the map (if not, an unknown
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variable is being referenced) and returns the value for it. In future chapters,
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we'll add support for <a href="LangImpl5.html#for">loop induction variables</a>
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in the symbol table, and for <a href="LangImpl7.html#localvars">local
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variables</a>.</p>
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<div class="doc_code">
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<pre>
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| Ast.Binary (op, lhs, rhs) ->
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let lhs_val = codegen_expr lhs in
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let rhs_val = codegen_expr rhs in
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begin
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match op with
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| '+' -> build_fadd lhs_val rhs_val "addtmp" builder
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| '-' -> build_fsub lhs_val rhs_val "subtmp" builder
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| '*' -> build_fmul lhs_val rhs_val "multmp" builder
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| '<' ->
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(* Convert bool 0/1 to double 0.0 or 1.0 *)
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let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
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build_uitofp i double_type "booltmp" builder
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| _ -> raise (Error "invalid binary operator")
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end
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</pre>
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</div>
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<p>Binary operators start to get more interesting. The basic idea here is that
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we recursively emit code for the left-hand side of the expression, then the
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right-hand side, then we compute the result of the binary expression. In this
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code, we do a simple switch on the opcode to create the right LLVM instruction.
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</p>
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<p>In the example above, the LLVM builder class is starting to show its value.
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IRBuilder knows where to insert the newly created instruction, all you have to
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do is specify what instruction to create (e.g. with <tt>Llvm.create_add</tt>),
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which operands to use (<tt>lhs</tt> and <tt>rhs</tt> here) and optionally
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provide a name for the generated instruction.</p>
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<p>One nice thing about LLVM is that the name is just a hint. For instance, if
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the code above emits multiple "addtmp" variables, LLVM will automatically
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provide each one with an increasing, unique numeric suffix. Local value names
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for instructions are purely optional, but it makes it much easier to read the
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IR dumps.</p>
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<p><a href="../LangRef.html#instref">LLVM instructions</a> are constrained by
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strict rules: for example, the Left and Right operators of
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an <a href="../LangRef.html#i_add">add instruction</a> must have the same
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type, and the result type of the add must match the operand types. Because
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all values in Kaleidoscope are doubles, this makes for very simple code for add,
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sub and mul.</p>
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<p>On the other hand, LLVM specifies that the <a
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href="../LangRef.html#i_fcmp">fcmp instruction</a> always returns an 'i1' value
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(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
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a <a href="../LangRef.html#i_uitofp">uitofp instruction</a>. This instruction
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converts its input integer into a floating point value by treating the input
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as an unsigned value. In contrast, if we used the <a
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href="../LangRef.html#i_sitofp">sitofp instruction</a>, the Kaleidoscope '<'
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operator would return 0.0 and -1.0, depending on the input value.</p>
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<div class="doc_code">
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<pre>
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| Ast.Call (callee, args) ->
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(* Look up the name in the module table. *)
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let callee =
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match lookup_function callee the_module with
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| Some callee -> callee
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| None -> raise (Error "unknown function referenced")
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in
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let params = params callee in
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(* If argument mismatch error. *)
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if Array.length params == Array.length args then () else
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raise (Error "incorrect # arguments passed");
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let args = Array.map codegen_expr args in
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build_call callee args "calltmp" builder
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</pre>
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</div>
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<p>Code generation for function calls is quite straightforward with LLVM. The
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code above initially does a function name lookup in the LLVM Module's symbol
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table. Recall that the LLVM Module is the container that holds all of the
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functions we are JIT'ing. By giving each function the same name as what the
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user specifies, we can use the LLVM symbol table to resolve function names for
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us.</p>
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<p>Once we have the function to call, we recursively codegen each argument that
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is to be passed in, and create an LLVM <a href="../LangRef.html#i_call">call
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instruction</a>. Note that LLVM uses the native C calling conventions by
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default, allowing these calls to also call into standard library functions like
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"sin" and "cos", with no additional effort.</p>
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<p>This wraps up our handling of the four basic expressions that we have so far
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in Kaleidoscope. Feel free to go in and add some more. For example, by
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browsing the <a href="../LangRef.html">LLVM language reference</a> you'll find
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several other interesting instructions that are really easy to plug into our
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basic framework.</p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="funcs">Function Code Generation</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p>Code generation for prototypes and functions must handle a number of
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details, which make their code less beautiful than expression code
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generation, but allows us to illustrate some important points. First, lets
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talk about code generation for prototypes: they are used both for function
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bodies and external function declarations. The code starts with:</p>
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<div class="doc_code">
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<pre>
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let codegen_proto = function
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| Ast.Prototype (name, args) ->
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(* Make the function type: double(double,double) etc. *)
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let doubles = Array.make (Array.length args) double_type in
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let ft = function_type double_type doubles in
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let f =
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match lookup_function name the_module with
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</pre>
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</div>
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<p>This code packs a lot of power into a few lines. Note first that this
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function returns a "Function*" instead of a "Value*" (although at the moment
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they both are modeled by <tt>llvalue</tt> in ocaml). Because a "prototype"
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really talks about the external interface for a function (not the value computed
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by an expression), it makes sense for it to return the LLVM Function it
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corresponds to when codegen'd.</p>
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<p>The call to <tt>Llvm.function_type</tt> creates the <tt>Llvm.llvalue</tt>
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that should be used for a given Prototype. Since all function arguments in
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Kaleidoscope are of type double, the first line creates a vector of "N" LLVM
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double types. It then uses the <tt>Llvm.function_type</tt> method to create a
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function type that takes "N" doubles as arguments, returns one double as a
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result, and that is not vararg (that uses the function
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<tt>Llvm.var_arg_function_type</tt>). Note that Types in LLVM are uniqued just
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like <tt>Constant</tt>s are, so you don't "new" a type, you "get" it.</p>
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<p>The final line above checks if the function has already been defined in
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<tt>Codegen.the_module</tt>. If not, we will create it.</p>
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<div class="doc_code">
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<pre>
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| None -> declare_function name ft the_module
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</pre>
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</div>
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<p>This indicates the type and name to use, as well as which module to insert
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into. By default we assume a function has
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<tt>Llvm.Linkage.ExternalLinkage</tt>. "<a href="LangRef.html#linkage">external
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linkage</a>" means that the function may be defined outside the current module
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and/or that it is callable by functions outside the module. The "<tt>name</tt>"
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passed in is the name the user specified: this name is registered in
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"<tt>Codegen.the_module</tt>"s symbol table, which is used by the function call
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code above.</p>
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<p>In Kaleidoscope, I choose to allow redefinitions of functions in two cases:
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first, we want to allow 'extern'ing a function more than once, as long as the
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prototypes for the externs match (since all arguments have the same type, we
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just have to check that the number of arguments match). Second, we want to
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allow 'extern'ing a function and then defining a body for it. This is useful
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when defining mutually recursive functions.</p>
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<div class="doc_code">
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<pre>
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(* If 'f' conflicted, there was already something named 'name'. If it
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* has a body, don't allow redefinition or reextern. *)
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| Some f ->
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(* If 'f' already has a body, reject this. *)
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if Array.length (basic_blocks f) == 0 then () else
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raise (Error "redefinition of function");
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(* If 'f' took a different number of arguments, reject. *)
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if Array.length (params f) == Array.length args then () else
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raise (Error "redefinition of function with different # args");
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f
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in
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</pre>
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</div>
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<p>In order to verify the logic above, we first check to see if the pre-existing
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function is "empty". In this case, empty means that it has no basic blocks in
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it, which means it has no body. If it has no body, it is a forward
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declaration. Since we don't allow anything after a full definition of the
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function, the code rejects this case. If the previous reference to a function
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was an 'extern', we simply verify that the number of arguments for that
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definition and this one match up. If not, we emit an error.</p>
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<div class="doc_code">
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<pre>
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(* Set names for all arguments. *)
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Array.iteri (fun i a ->
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let n = args.(i) in
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set_value_name n a;
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Hashtbl.add named_values n a;
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) (params f);
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f
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</pre>
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</div>
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<p>The last bit of code for prototypes loops over all of the arguments in the
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function, setting the name of the LLVM Argument objects to match, and registering
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the arguments in the <tt>Codegen.named_values</tt> map for future use by the
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<tt>Ast.Variable</tt> variant. Once this is set up, it returns the Function
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object to the caller. Note that we don't check for conflicting
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argument names here (e.g. "extern foo(a b a)"). Doing so would be very
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straight-forward with the mechanics we have already used above.</p>
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<div class="doc_code">
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<pre>
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let codegen_func = function
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| Ast.Function (proto, body) ->
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Hashtbl.clear named_values;
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let the_function = codegen_proto proto in
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</pre>
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</div>
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<p>Code generation for function definitions starts out simply enough: we just
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codegen the prototype (Proto) and verify that it is ok. We then clear out the
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<tt>Codegen.named_values</tt> map to make sure that there isn't anything in it
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from the last function we compiled. Code generation of the prototype ensures
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that there is an LLVM Function object that is ready to go for us.</p>
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<div class="doc_code">
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<pre>
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(* Create a new basic block to start insertion into. *)
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let bb = append_block context "entry" the_function in
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position_at_end bb builder;
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try
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let ret_val = codegen_expr body in
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</pre>
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</div>
|
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<p>Now we get to the point where the <tt>Codegen.builder</tt> is set up. The
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first line creates a new
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<a href="http://en.wikipedia.org/wiki/Basic_block">basic block</a> (named
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"entry"), which is inserted into <tt>the_function</tt>. The second line then
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tells the builder that new instructions should be inserted into the end of the
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new basic block. Basic blocks in LLVM are an important part of functions that
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define the <a
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href="http://en.wikipedia.org/wiki/Control_flow_graph">Control Flow Graph</a>.
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Since we don't have any control flow, our functions will only contain one
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block at this point. We'll fix this in <a href="OCamlLangImpl5.html">Chapter
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5</a> :).</p>
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<div class="doc_code">
|
|
<pre>
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let ret_val = codegen_expr body in
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(* Finish off the function. *)
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let _ = build_ret ret_val builder in
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(* Validate the generated code, checking for consistency. *)
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Llvm_analysis.assert_valid_function the_function;
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the_function
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</pre>
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</div>
|
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<p>Once the insertion point is set up, we call the <tt>Codegen.codegen_func</tt>
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method for the root expression of the function. If no error happens, this emits
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code to compute the expression into the entry block and returns the value that
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was computed. Assuming no error, we then create an LLVM <a
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href="../LangRef.html#i_ret">ret instruction</a>, which completes the function.
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Once the function is built, we call
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<tt>Llvm_analysis.assert_valid_function</tt>, which is provided by LLVM. This
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function does a variety of consistency checks on the generated code, to
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determine if our compiler is doing everything right. Using this is important:
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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>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2><a name="driver">Driver Changes and Closing Thoughts</a></h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<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>
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2><a name="code">Full Code Listing</a></h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<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>
|
|
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|
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<address>
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<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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<a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a><br>
|
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<a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
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