+<!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="LangImpl4.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 "my cool jit"
+let builder = builder ()
+let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
+</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/LLVMBuilder_8h-source.html"><tt>LLVMBuilder</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 emited
+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.
+LLVMBuilder 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 definining 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 "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 = add 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="LangImpl4.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 = mul double %a, %a
+ %multmp1 = mul double 2.000000e+00, %a
+ %multmp2 = mul double %multmp1, %b
+ %addtmp = add double %multmp, %multmp2
+ %multmp3 = mul double %b, %b
+ %addtmp4 = add 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 = add 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 = add double 4.000000e+00, 5.000000e+00
+ ret double %addtmp
+}
+
+define double @foo(double %a, double %b) {
+entry:
+ %multmp = mul double %a, %a
+ %multmp1 = mul double 2.000000e+00, %a
+ %multmp2 = mul double %multmp1, %b
+ %addtmp = add double %multmp, %multmp2
+ %multmp3 = mul double %b, %b
+ %addtmp4 = add 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 = add 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="LangImpl4.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 the_module = create_module "my cool jit"
+let builder = builder ()
+let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
+
+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 "entry" the_function in
+ position_at_end bb builder;
+
+ try
+ let ret_val = codegen_expr body in
+
+ (* Finish off the function. *)
+ let _ = build_ret ret_val builder in
+
+ (* Validate the generated code, checking for consistency. *)
+ Llvm_analysis.assert_valid_function the_function;
+
+ the_function
+ with e ->
+ delete_function the_function;
+ raise e
+</pre>
+</dd>
+
+<dt>toplevel.ml:</dt>
+<dd class="doc_code">
+<pre>
+(*===----------------------------------------------------------------------===
+ * Top-Level parsing and JIT Driver
+ *===----------------------------------------------------------------------===*)
+
+open Llvm
+
+(* top ::= definition | external | expression | ';' *)
+let rec main_loop stream =
+ match Stream.peek stream with
+ | None -> ()
+
+ (* ignore top-level semicolons. *)
+ | Some (Token.Kwd ';') ->
+ Stream.junk stream;
+ main_loop stream
+
+ | Some token ->
+ begin
+ try match token with
+ | Token.Def ->
+ let e = Parser.parse_definition stream in
+ print_endline "parsed a function definition.";
+ dump_value (Codegen.codegen_func e);
+ | Token.Extern ->
+ let e = Parser.parse_extern stream in
+ print_endline "parsed an extern.";
+ dump_value (Codegen.codegen_proto e);
+ | _ ->
+ (* Evaluate a top-level expression into an anonymous function. *)
+ let e = Parser.parse_toplevel stream in
+ print_endline "parsed a top-level expr";
+ dump_value (Codegen.codegen_func e);
+ with Stream.Error s | Codegen.Error s ->
+ (* Skip token for error recovery. *)
+ Stream.junk stream;
+ print_endline s;
+ end;
+ print_string "ready> "; flush stdout;
+ main_loop stream
+</pre>
+</dd>
+
+<dt>toy.ml:</dt>
+<dd class="doc_code">
+<pre>
+(*===----------------------------------------------------------------------===
+ * Main driver code.
+ *===----------------------------------------------------------------------===*)
+
+open Llvm
+
+let main () =
+ (* Install standard binary operators.
+ * 1 is the lowest precedence. *)
+ Hashtbl.add Parser.binop_precedence '<' 10;
+ Hashtbl.add Parser.binop_precedence '+' 20;
+ Hashtbl.add Parser.binop_precedence '-' 20;
+ Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
+
+ (* Prime the first token. *)
+ print_string "ready> "; flush stdout;
+ let stream = Lexer.lex (Stream.of_channel stdin) in
+
+ (* Run the main "interpreter loop" now. *)
+ Toplevel.main_loop stream;
+
+ (* Print out all the generated code. *)
+ dump_module Codegen.the_module
+;;
+
+main ()
+</pre>
+</dd>
+</dl>
+
+<a href="OCamlLangImpl4.html">Next: Adding JIT and Optimizer Support</a>
+</div>
+
+<!-- *********************************************************************** -->
+<hr>
+<address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+
+ <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
+ <a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a><br>
+ <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date: 2007-10-17 11:05:13 -0700 (Wed, 17 Oct 2007) $
+</address>
+</body>
+</html>
projects / oota-llvm.git / commitdiff