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<div class="section" id="kaleidoscope-code-generation-to-llvm-ir">
<h1>3. Kaleidoscope: Code generation to LLVM IR<a class="headerlink" href="#kaleidoscope-code-generation-to-llvm-ir" title="Permalink to this headline">¶</a></h1>
<div class="contents local topic" id="contents">
<ul class="simple">
<li><a class="reference internal" href="#chapter-3-introduction" id="id1">Chapter 3 Introduction</a></li>
<li><a class="reference internal" href="#code-generation-setup" id="id2">Code Generation Setup</a></li>
<li><a class="reference internal" href="#expression-code-generation" id="id3">Expression Code Generation</a></li>
<li><a class="reference internal" href="#function-code-generation" id="id4">Function Code Generation</a></li>
<li><a class="reference internal" href="#driver-changes-and-closing-thoughts" id="id5">Driver Changes and Closing Thoughts</a></li>
<li><a class="reference internal" href="#full-code-listing" id="id6">Full Code Listing</a></li>
</ul>
</div>
<div class="section" id="chapter-3-introduction">
<h2><a class="toc-backref" href="#id1">3.1. Chapter 3 Introduction</a><a class="headerlink" href="#chapter-3-introduction" title="Permalink to this headline">¶</a></h2>
<p>Welcome to Chapter 3 of the “<a class="reference external" href="index.html">Implementing a language with
LLVM</a>” tutorial. This chapter shows you how to transform
the <a class="reference external" 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><strong>Please note</strong>: 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="section" id="code-generation-setup">
<h2><a class="toc-backref" href="#id2">3.2. Code Generation Setup</a><a class="headerlink" href="#code-generation-setup" title="Permalink to this headline">¶</a></h2>
<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="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="k">let</span> <span class="k">rec</span> <span class="n">codegen_expr</span> <span class="o">=</span> <span class="k">function</span>
<span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Number</span> <span class="n">n</span> <span class="o">-></span> <span class="o">...</span>
<span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Variable</span> <span class="n">name</span> <span class="o">-></span> <span class="o">...</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">Codegen.codegen_expr</span></code> 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 class="reference external" 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 class="reference external" 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="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="k">exception</span> <span class="nc">Error</span> <span class="k">of</span> <span class="kt">string</span>
<span class="k">let</span> <span class="n">context</span> <span class="o">=</span> <span class="n">global_context</span> <span class="bp">()</span>
<span class="k">let</span> <span class="n">the_module</span> <span class="o">=</span> <span class="n">create_module</span> <span class="n">context</span> <span class="s2">"my cool jit"</span>
<span class="k">let</span> <span class="n">builder</span> <span class="o">=</span> <span class="n">builder</span> <span class="n">context</span>
<span class="k">let</span> <span class="n">named_values</span><span class="o">:(</span><span class="kt">string</span><span class="o">,</span> <span class="n">llvalue</span><span class="o">)</span> <span class="nn">Hashtbl</span><span class="p">.</span><span class="n">t</span> <span class="o">=</span> <span class="nn">Hashtbl</span><span class="p">.</span><span class="n">create</span> <span class="mi">10</span>
<span class="k">let</span> <span class="n">double_type</span> <span class="o">=</span> <span class="n">double_type</span> <span class="n">context</span>
</pre></div>
</div>
<p>The static variables will be used during code generation.
<code class="docutils literal notranslate"><span class="pre">Codgen.the_module</span></code> 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 <code class="docutils literal notranslate"><span class="pre">Codegen.builder</span></code> object is a helper object that makes it easy to
generate LLVM instructions. Instances of the
<a class="reference external" href="http://llvm.org/doxygen/IRBuilder_8h-source.html">IRBuilder</a>
class keep track of the current place to insert instructions and has
methods to create new instructions.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">Codegen.named_values</span></code> 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
<code class="docutils literal notranslate"><span class="pre">Codgen.builder</span></code> 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="section" id="expression-code-generation">
<h2><a class="toc-backref" href="#id3">3.3. Expression Code Generation</a><a class="headerlink" href="#expression-code-generation" title="Permalink to this headline">¶</a></h2>
<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="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Number</span> <span class="n">n</span> <span class="o">-></span> <span class="n">const_float</span> <span class="n">double_type</span> <span class="n">n</span>
</pre></div>
</div>
<p>In the LLVM IR, numeric constants are represented with the
<code class="docutils literal notranslate"><span class="pre">ConstantFP</span></code> class, which holds the numeric value in an <code class="docutils literal notranslate"><span class="pre">APFloat</span></code>
internally (<code class="docutils literal notranslate"><span class="pre">APFloat</span></code> has the capability of holding floating point
constants of Arbitrary Precision). This code basically just creates
and returns a <code class="docutils literal notranslate"><span class="pre">ConstantFP</span></code>. 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="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Variable</span> <span class="n">name</span> <span class="o">-></span>
<span class="o">(</span><span class="k">try</span> <span class="nn">Hashtbl</span><span class="p">.</span><span class="n">find</span> <span class="n">named_values</span> <span class="n">name</span> <span class="k">with</span>
<span class="o">|</span> <span class="nc">Not_found</span> <span class="o">-></span> <span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"unknown variable name"</span><span class="o">))</span>
</pre></div>
</div>
<p>References to variables are also quite simple using LLVM. In the simple
version of Kaleidoscope, we assume that the variable has already been
emitted somewhere and its value is available. In practice, the only
values that can be in the <code class="docutils literal notranslate"><span class="pre">Codegen.named_values</span></code> 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 class="reference external" href="LangImpl5.html#for-loop-expression">loop
induction variables</a> in the symbol table, and for
<a class="reference external" href="LangImpl7.html#user-defined-local-variables">local variables</a>.</p>
<div class="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Binary</span> <span class="o">(</span><span class="n">op</span><span class="o">,</span> <span class="n">lhs</span><span class="o">,</span> <span class="n">rhs</span><span class="o">)</span> <span class="o">-></span>
<span class="k">let</span> <span class="n">lhs_val</span> <span class="o">=</span> <span class="n">codegen_expr</span> <span class="n">lhs</span> <span class="k">in</span>
<span class="k">let</span> <span class="n">rhs_val</span> <span class="o">=</span> <span class="n">codegen_expr</span> <span class="n">rhs</span> <span class="k">in</span>
<span class="k">begin</span>
<span class="k">match</span> <span class="n">op</span> <span class="k">with</span>
<span class="o">|</span> <span class="sc">'+'</span> <span class="o">-></span> <span class="n">build_fadd</span> <span class="n">lhs_val</span> <span class="n">rhs_val</span> <span class="s2">"addtmp"</span> <span class="n">builder</span>
<span class="o">|</span> <span class="sc">'-'</span> <span class="o">-></span> <span class="n">build_fsub</span> <span class="n">lhs_val</span> <span class="n">rhs_val</span> <span class="s2">"subtmp"</span> <span class="n">builder</span>
<span class="o">|</span> <span class="sc">'*'</span> <span class="o">-></span> <span class="n">build_fmul</span> <span class="n">lhs_val</span> <span class="n">rhs_val</span> <span class="s2">"multmp"</span> <span class="n">builder</span>
<span class="o">|</span> <span class="sc">'<'</span> <span class="o">-></span>
<span class="c">(* Convert bool 0/1 to double 0.0 or 1.0 *)</span>
<span class="k">let</span> <span class="n">i</span> <span class="o">=</span> <span class="n">build_fcmp</span> <span class="nn">Fcmp</span><span class="p">.</span><span class="nc">Ult</span> <span class="n">lhs_val</span> <span class="n">rhs_val</span> <span class="s2">"cmptmp"</span> <span class="n">builder</span> <span class="k">in</span>
<span class="n">build_uitofp</span> <span class="n">i</span> <span class="n">double_type</span> <span class="s2">"booltmp"</span> <span class="n">builder</span>
<span class="o">|</span> <span class="o">_</span> <span class="o">-></span> <span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"invalid binary operator"</span><span class="o">)</span>
<span class="k">end</span>
</pre></div>
</div>
<p>Binary operators start to get more interesting. The basic idea here is
that we recursively emit code for the left-hand side of the expression,
then the right-hand side, then we compute the result of the binary
expression. In this code, we do a simple switch on the opcode to create
the right LLVM instruction.</p>
<p>In the example above, the LLVM builder class is starting to show its
value. IRBuilder knows where to insert the newly created instruction,
all you have to do is specify what instruction to create (e.g. with
<code class="docutils literal notranslate"><span class="pre">Llvm.create_add</span></code>), which operands to use (<code class="docutils literal notranslate"><span class="pre">lhs</span></code> and <code class="docutils literal notranslate"><span class="pre">rhs</span></code> 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 class="reference external" href="../LangRef.html#instruction-reference">LLVM instructions</a> are constrained by strict
rules: for example, the Left and Right operators of an <a class="reference external" href="../LangRef.html#add-instruction">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 class="reference external" href="../LangRef.html#fcmp-instruction">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 class="reference external" href="../LangRef.html#uitofp-to-instruction">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 class="reference external" href="../LangRef.html#sitofp-to-instruction">sitofp
instruction</a>, the Kaleidoscope ‘<’ operator
would return 0.0 and -1.0, depending on the input value.</p>
<div class="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Call</span> <span class="o">(</span><span class="n">callee</span><span class="o">,</span> <span class="n">args</span><span class="o">)</span> <span class="o">-></span>
<span class="c">(* Look up the name in the module table. *)</span>
<span class="k">let</span> <span class="n">callee</span> <span class="o">=</span>
<span class="k">match</span> <span class="n">lookup_function</span> <span class="n">callee</span> <span class="n">the_module</span> <span class="k">with</span>
<span class="o">|</span> <span class="nc">Some</span> <span class="n">callee</span> <span class="o">-></span> <span class="n">callee</span>
<span class="o">|</span> <span class="nc">None</span> <span class="o">-></span> <span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"unknown function referenced"</span><span class="o">)</span>
<span class="k">in</span>
<span class="k">let</span> <span class="n">params</span> <span class="o">=</span> <span class="n">params</span> <span class="n">callee</span> <span class="k">in</span>
<span class="c">(* If argument mismatch error. *)</span>
<span class="k">if</span> <span class="nn">Array</span><span class="p">.</span><span class="n">length</span> <span class="n">params</span> <span class="o">==</span> <span class="nn">Array</span><span class="p">.</span><span class="n">length</span> <span class="n">args</span> <span class="k">then</span> <span class="bp">()</span> <span class="k">else</span>
<span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"incorrect # arguments passed"</span><span class="o">);</span>
<span class="k">let</span> <span class="n">args</span> <span class="o">=</span> <span class="nn">Array</span><span class="p">.</span><span class="n">map</span> <span class="n">codegen_expr</span> <span class="n">args</span> <span class="k">in</span>
<span class="n">build_call</span> <span class="n">callee</span> <span class="n">args</span> <span class="s2">"calltmp"</span> <span class="n">builder</span>
</pre></div>
</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 class="reference external" href="../LangRef.html#call-instruction">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 class="reference external" 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="section" id="function-code-generation">
<h2><a class="toc-backref" href="#id4">3.4. Function Code Generation</a><a class="headerlink" href="#function-code-generation" title="Permalink to this headline">¶</a></h2>
<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="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="k">let</span> <span class="n">codegen_proto</span> <span class="o">=</span> <span class="k">function</span>
<span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Prototype</span> <span class="o">(</span><span class="n">name</span><span class="o">,</span> <span class="n">args</span><span class="o">)</span> <span class="o">-></span>
<span class="c">(* Make the function type: double(double,double) etc. *)</span>
<span class="k">let</span> <span class="n">doubles</span> <span class="o">=</span> <span class="nn">Array</span><span class="p">.</span><span class="n">make</span> <span class="o">(</span><span class="nn">Array</span><span class="p">.</span><span class="n">length</span> <span class="n">args</span><span class="o">)</span> <span class="n">double_type</span> <span class="k">in</span>
<span class="k">let</span> <span class="n">ft</span> <span class="o">=</span> <span class="n">function_type</span> <span class="n">double_type</span> <span class="n">doubles</span> <span class="k">in</span>
<span class="k">let</span> <span class="n">f</span> <span class="o">=</span>
<span class="k">match</span> <span class="n">lookup_function</span> <span class="n">name</span> <span class="n">the_module</span> <span class="k">with</span>
</pre></div>
</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 <code class="docutils literal notranslate"><span class="pre">llvalue</span></code> 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 <code class="docutils literal notranslate"><span class="pre">Llvm.function_type</span></code> creates the <code class="docutils literal notranslate"><span class="pre">Llvm.llvalue</span></code> 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 <code class="docutils literal notranslate"><span class="pre">Llvm.function_type</span></code> 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
<code class="docutils literal notranslate"><span class="pre">Llvm.var_arg_function_type</span></code>). Note that Types in LLVM are uniqued
just like <code class="docutils literal notranslate"><span class="pre">Constant</span></code>’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
<code class="docutils literal notranslate"><span class="pre">Codegen.the_module</span></code>. If not, we will create it.</p>
<div class="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="o">|</span> <span class="nc">None</span> <span class="o">-></span> <span class="n">declare_function</span> <span class="n">name</span> <span class="n">ft</span> <span class="n">the_module</span>
</pre></div>
</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
<code class="docutils literal notranslate"><span class="pre">Llvm.Linkage.ExternalLinkage</span></code>. “<a class="reference external" 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 “<code class="docutils literal notranslate"><span class="pre">name</span></code>” passed in is the name the user
specified: this name is registered in “<code class="docutils literal notranslate"><span class="pre">Codegen.the_module</span></code>”s symbol
table, which is used by the function call code above.</p>
<p>In Kaleidoscope, I choose to allow redefinitions of functions in two
cases: first, we want to allow ‘extern’ing a function more than once, as
long as the prototypes for the externs match (since all arguments have
the same type, we just have to check that the number of arguments
match). Second, we want to allow ‘extern’ing a function and then
defining a body for it. This is useful when defining mutually recursive
functions.</p>
<div class="highlight-ocaml notranslate"><div class="highlight"><pre><span></span> <span class="c">(* If 'f' conflicted, there was already something named 'name'. If it</span>
<span class="c"> * has a body, don't allow redefinition or reextern. *)</span>
<span class="o">|</span> <span class="nc">Some</span> <span class="n">f</span> <span class="o">-></span>
<span class="c">(* If 'f' already has a body, reject this. *)</span>
<span class="k">if</span> <span class="nn">Array</span><span class="p">.</span><span class="n">length</span> <span class="o">(</span><span class="n">basic_blocks</span> <span class="n">f</span><span class="o">)</span> <span class="o">==</span> <span class="mi">0</span> <span class="k">then</span> <span class="bp">()</span> <span class="k">else</span>
<span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"redefinition of function"</span><span class="o">);</span>
<span class="c">(* If 'f' took a different number of arguments, reject. *)</span>
<span class="k">if</span> <span class="nn">Array</span><span class="p">.</span><span class="n">length</span> <span class="o">(</span><span class="n">params</span> <span class="n">f</span><span class="o">)</span> <span class="o">==</span> <span class="nn">Array</span><span class="p">.</span><span class="n">length</span> <span class="n">args</span> <span class="k">then</span> <span class="bp">()</span> <span class="k">else</span>
<span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"redefinition of function with different # args"</span><span class="o">);</span>
<span class="n">f</span>
<span class="k">in</span>
</pre></div>
</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="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="c">(* Set names for all arguments. *)</span>
<span class="nn">Array</span><span class="p">.</span><span class="n">iteri</span> <span class="o">(</span><span class="k">fun</span> <span class="n">i</span> <span class="n">a</span> <span class="o">-></span>
<span class="k">let</span> <span class="n">n</span> <span class="o">=</span> <span class="n">args</span><span class="o">.(</span><span class="n">i</span><span class="o">)</span> <span class="k">in</span>
<span class="n">set_value_name</span> <span class="n">n</span> <span class="n">a</span><span class="o">;</span>
<span class="nn">Hashtbl</span><span class="p">.</span><span class="n">add</span> <span class="n">named_values</span> <span class="n">n</span> <span class="n">a</span><span class="o">;</span>
<span class="o">)</span> <span class="o">(</span><span class="n">params</span> <span class="n">f</span><span class="o">);</span>
<span class="n">f</span>
</pre></div>
</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 <code class="docutils literal notranslate"><span class="pre">Codegen.named_values</span></code> map for
future use by the <code class="docutils literal notranslate"><span class="pre">Ast.Variable</span></code> 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="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="k">let</span> <span class="n">codegen_func</span> <span class="o">=</span> <span class="k">function</span>
<span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Function</span> <span class="o">(</span><span class="n">proto</span><span class="o">,</span> <span class="n">body</span><span class="o">)</span> <span class="o">-></span>
<span class="nn">Hashtbl</span><span class="p">.</span><span class="n">clear</span> <span class="n">named_values</span><span class="o">;</span>
<span class="k">let</span> <span class="n">the_function</span> <span class="o">=</span> <span class="n">codegen_proto</span> <span class="n">proto</span> <span class="k">in</span>
</pre></div>
</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 <code class="docutils literal notranslate"><span class="pre">Codegen.named_values</span></code> 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="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="c">(* Create a new basic block to start insertion into. *)</span>
<span class="k">let</span> <span class="n">bb</span> <span class="o">=</span> <span class="n">append_block</span> <span class="n">context</span> <span class="s2">"entry"</span> <span class="n">the_function</span> <span class="k">in</span>
<span class="n">position_at_end</span> <span class="n">bb</span> <span class="n">builder</span><span class="o">;</span>
<span class="k">try</span>
<span class="k">let</span> <span class="n">ret_val</span> <span class="o">=</span> <span class="n">codegen_expr</span> <span class="n">body</span> <span class="k">in</span>
</pre></div>
</div>
<p>Now we get to the point where the <code class="docutils literal notranslate"><span class="pre">Codegen.builder</span></code> is set up. The
first line creates a new <a class="reference external" href="http://en.wikipedia.org/wiki/Basic_block">basic
block</a> (named “entry”),
which is inserted into <code class="docutils literal notranslate"><span class="pre">the_function</span></code>. 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 class="reference external" 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 class="reference external" href="OCamlLangImpl5.html">Chapter 5</a> :).</p>
<div class="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="k">let</span> <span class="n">ret_val</span> <span class="o">=</span> <span class="n">codegen_expr</span> <span class="n">body</span> <span class="k">in</span>
<span class="c">(* Finish off the function. *)</span>
<span class="k">let</span> <span class="o">_</span> <span class="o">=</span> <span class="n">build_ret</span> <span class="n">ret_val</span> <span class="n">builder</span> <span class="k">in</span>
<span class="c">(* Validate the generated code, checking for consistency. *)</span>
<span class="nn">Llvm_analysis</span><span class="p">.</span><span class="n">assert_valid_function</span> <span class="n">the_function</span><span class="o">;</span>
<span class="n">the_function</span>
</pre></div>
</div>
<p>Once the insertion point is set up, we call the <code class="docutils literal notranslate"><span class="pre">Codegen.codegen_func</span></code>
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 class="reference external" href="../LangRef.html#ret-instruction">ret instruction</a>, which completes the
function. Once the function is built, we call
<code class="docutils literal notranslate"><span class="pre">Llvm_analysis.assert_valid_function</span></code>, 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="highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="n">e</span> <span class="o">-></span>
<span class="n">delete_function</span> <span class="n">the_function</span><span class="o">;</span>
<span class="k">raise</span> <span class="n">e</span>
</pre></div>
</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
<code class="docutils literal notranslate"><span class="pre">Llvm.delete_function</span></code> 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 <code class="docutils literal notranslate"><span class="pre">Codegen.codegen_proto</span></code>
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="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">extern</span> <span class="n">foo</span><span class="p">(</span><span class="n">a</span> <span class="n">b</span><span class="p">);</span> <span class="c1"># ok, defines foo.</span>
<span class="k">def</span> <span class="nf">foo</span><span class="p">(</span><span class="n">a</span> <span class="n">b</span><span class="p">)</span> <span class="n">c</span><span class="p">;</span> <span class="c1"># error, 'c' is invalid.</span>
<span class="k">def</span> <span class="nf">bar</span><span class="p">()</span> <span class="n">foo</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">);</span> <span class="c1"># error, unknown function "foo"</span>
</pre></div>
</div>
</div>
<div class="section" id="driver-changes-and-closing-thoughts">
<h2><a class="toc-backref" href="#id5">3.5. Driver Changes and Closing Thoughts</a><a class="headerlink" href="#driver-changes-and-closing-thoughts" title="Permalink to this headline">¶</a></h2>
<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 “<code class="docutils literal notranslate"><span class="pre">Toplevel.main_loop</span></code>”, 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="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ready</span><span class="o">></span> <span class="mi">4</span><span class="o">+</span><span class="mi">5</span><span class="p">;</span>
<span class="n">Read</span> <span class="n">top</span><span class="o">-</span><span class="n">level</span> <span class="n">expression</span><span class="p">:</span>
<span class="n">define</span> <span class="n">double</span> <span class="o">@</span><span class="s2">""</span><span class="p">()</span> <span class="p">{</span>
<span class="n">entry</span><span class="p">:</span>
<span class="o">%</span><span class="n">addtmp</span> <span class="o">=</span> <span class="n">fadd</span> <span class="n">double</span> <span class="mf">4.000000e+00</span><span class="p">,</span> <span class="mf">5.000000e+00</span>
<span class="n">ret</span> <span class="n">double</span> <span class="o">%</span><span class="n">addtmp</span>
<span class="p">}</span>
</pre></div>
</div>
<p>Note how the parser turns the top-level expression into anonymous
functions for us. This will be handy when we add <a class="reference external" href="OCamlLangImpl4.html#adding-a-jit-compiler">JIT
support</a> in the next chapter. Also note that
the code is very literally transcribed, no optimizations are being
performed. We will <a class="reference external" href="OCamlLangImpl4.html#trivial-constant-folding">add
optimizations</a> explicitly in the
next chapter.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ready</span><span class="o">></span> <span class="k">def</span> <span class="nf">foo</span><span class="p">(</span><span class="n">a</span> <span class="n">b</span><span class="p">)</span> <span class="n">a</span><span class="o">*</span><span class="n">a</span> <span class="o">+</span> <span class="mi">2</span><span class="o">*</span><span class="n">a</span><span class="o">*</span><span class="n">b</span> <span class="o">+</span> <span class="n">b</span><span class="o">*</span><span class="n">b</span><span class="p">;</span>
<span class="n">Read</span> <span class="n">function</span> <span class="n">definition</span><span class="p">:</span>
<span class="n">define</span> <span class="n">double</span> <span class="nd">@foo</span><span class="p">(</span><span class="n">double</span> <span class="o">%</span><span class="n">a</span><span class="p">,</span> <span class="n">double</span> <span class="o">%</span><span class="n">b</span><span class="p">)</span> <span class="p">{</span>
<span class="n">entry</span><span class="p">:</span>
<span class="o">%</span><span class="n">multmp</span> <span class="o">=</span> <span class="n">fmul</span> <span class="n">double</span> <span class="o">%</span><span class="n">a</span><span class="p">,</span> <span class="o">%</span><span class="n">a</span>
<span class="o">%</span><span class="n">multmp1</span> <span class="o">=</span> <span class="n">fmul</span> <span class="n">double</span> <span class="mf">2.000000e+00</span><span class="p">,</span> <span class="o">%</span><span class="n">a</span>
<span class="o">%</span><span class="n">multmp2</span> <span class="o">=</span> <span class="n">fmul</span> <span class="n">double</span> <span class="o">%</span><span class="n">multmp1</span><span class="p">,</span> <span class="o">%</span><span class="n">b</span>
<span class="o">%</span><span class="n">addtmp</span> <span class="o">=</span> <span class="n">fadd</span> <span class="n">double</span> <span class="o">%</span><span class="n">multmp</span><span class="p">,</span> <span class="o">%</span><span class="n">multmp2</span>
<span class="o">%</span><span class="n">multmp3</span> <span class="o">=</span> <span class="n">fmul</span> <span class="n">double</span> <span class="o">%</span><span class="n">b</span><span class="p">,</span> <span class="o">%</span><span class="n">b</span>
<span class="o">%</span><span class="n">addtmp4</span> <span class="o">=</span> <span class="n">fadd</span> <span class="n">double</span> <span class="o">%</span><span class="n">addtmp</span><span class="p">,</span> <span class="o">%</span><span class="n">multmp3</span>
<span class="n">ret</span> <span class="n">double</span> <span class="o">%</span><span class="n">addtmp4</span>
<span class="p">}</span>
</pre></div>
</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="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ready</span><span class="o">></span> <span class="k">def</span> <span class="nf">bar</span><span class="p">(</span><span class="n">a</span><span class="p">)</span> <span class="n">foo</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="mf">4.0</span><span class="p">)</span> <span class="o">+</span> <span class="n">bar</span><span class="p">(</span><span class="mi">31337</span><span class="p">);</span>
<span class="n">Read</span> <span class="n">function</span> <span class="n">definition</span><span class="p">:</span>
<span class="n">define</span> <span class="n">double</span> <span class="nd">@bar</span><span class="p">(</span><span class="n">double</span> <span class="o">%</span><span class="n">a</span><span class="p">)</span> <span class="p">{</span>
<span class="n">entry</span><span class="p">:</span>
<span class="o">%</span><span class="n">calltmp</span> <span class="o">=</span> <span class="n">call</span> <span class="n">double</span> <span class="nd">@foo</span><span class="p">(</span><span class="n">double</span> <span class="o">%</span><span class="n">a</span><span class="p">,</span> <span class="n">double</span> <span class="mf">4.000000e+00</span><span class="p">)</span>
<span class="o">%</span><span class="n">calltmp1</span> <span class="o">=</span> <span class="n">call</span> <span class="n">double</span> <span class="nd">@bar</span><span class="p">(</span><span class="n">double</span> <span class="mf">3.133700e+04</span><span class="p">)</span>
<span class="o">%</span><span class="n">addtmp</span> <span class="o">=</span> <span class="n">fadd</span> <span class="n">double</span> <span class="o">%</span><span class="n">calltmp</span><span class="p">,</span> <span class="o">%</span><span class="n">calltmp1</span>
<span class="n">ret</span> <span class="n">double</span> <span class="o">%</span><span class="n">addtmp</span>
<span class="p">}</span>
</pre></div>
</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="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ready</span><span class="o">></span> <span class="n">extern</span> <span class="n">cos</span><span class="p">(</span><span class="n">x</span><span class="p">);</span>
<span class="n">Read</span> <span class="n">extern</span><span class="p">:</span>
<span class="n">declare</span> <span class="n">double</span> <span class="nd">@cos</span><span class="p">(</span><span class="n">double</span><span class="p">)</span>
<span class="n">ready</span><span class="o">></span> <span class="n">cos</span><span class="p">(</span><span class="mf">1.234</span><span class="p">);</span>
<span class="n">Read</span> <span class="n">top</span><span class="o">-</span><span class="n">level</span> <span class="n">expression</span><span class="p">:</span>
<span class="n">define</span> <span class="n">double</span> <span class="o">@</span><span class="s2">""</span><span class="p">()</span> <span class="p">{</span>
<span class="n">entry</span><span class="p">:</span>
<span class="o">%</span><span class="n">calltmp</span> <span class="o">=</span> <span class="n">call</span> <span class="n">double</span> <span class="nd">@cos</span><span class="p">(</span><span class="n">double</span> <span class="mf">1.234000e+00</span><span class="p">)</span>
<span class="n">ret</span> <span class="n">double</span> <span class="o">%</span><span class="n">calltmp</span>
<span class="p">}</span>
</pre></div>
</div>
<p>This shows an extern for the libm “cos” function, and a call to it.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ready</span><span class="o">></span> <span class="o">^</span><span class="n">D</span>
<span class="p">;</span> <span class="n">ModuleID</span> <span class="o">=</span> <span class="s1">'my cool jit'</span>
<span class="n">define</span> <span class="n">double</span> <span class="o">@</span><span class="s2">""</span><span class="p">()</span> <span class="p">{</span>
<span class="n">entry</span><span class="p">:</span>
<span class="o">%</span><span class="n">addtmp</span> <span class="o">=</span> <span class="n">fadd</span> <span class="n">double</span> <span class="mf">4.000000e+00</span><span class="p">,</span> <span class="mf">5.000000e+00</span>
<span class="n">ret</span> <span class="n">double</span> <span class="o">%</span><span class="n">addtmp</span>
<span class="p">}</span>
<span class="n">define</span> <span class="n">double</span> <span class="nd">@foo</span><span class="p">(</span><span class="n">double</span> <span class="o">%</span><span class="n">a</span><span class="p">,</span> <span class="n">double</span> <span class="o">%</span><span class="n">b</span><span class="p">)</span> <span class="p">{</span>
<span class="n">entry</span><span class="p">:</span>
<span class="o">%</span><span class="n">multmp</span> <span class="o">=</span> <span class="n">fmul</span> <span class="n">double</span> <span class="o">%</span><span class="n">a</span><span class="p">,</span> <span class="o">%</span><span class="n">a</span>
<span class="o">%</span><span class="n">multmp1</span> <span class="o">=</span> <span class="n">fmul</span> <span class="n">double</span> <span class="mf">2.000000e+00</span><span class="p">,</span> <span class="o">%</span><span class="n">a</span>
<span class="o">%</span><span class="n">multmp2</span> <span class="o">=</span> <span class="n">fmul</span> <span class="n">double</span> <span class="o">%</span><span class="n">multmp1</span><span class="p">,</span> <span class="o">%</span><span class="n">b</span>
<span class="o">%</span><span class="n">addtmp</span> <span class="o">=</span> <span class="n">fadd</span> <span class="n">double</span> <span class="o">%</span><span class="n">multmp</span><span class="p">,</span> <span class="o">%</span><span class="n">multmp2</span>
<span class="o">%</span><span class="n">multmp3</span> <span class="o">=</span> <span class="n">fmul</span> <span class="n">double</span> <span class="o">%</span><span class="n">b</span><span class="p">,</span> <span class="o">%</span><span class="n">b</span>
<span class="o">%</span><span class="n">addtmp4</span> <span class="o">=</span> <span class="n">fadd</span> <span class="n">double</span> <span class="o">%</span><span class="n">addtmp</span><span class="p">,</span> <span class="o">%</span><span class="n">multmp3</span>
<span class="n">ret</span> <span class="n">double</span> <span class="o">%</span><span class="n">addtmp4</span>
<span class="p">}</span>
<span class="n">define</span> <span class="n">double</span> <span class="nd">@bar</span><span class="p">(</span><span class="n">double</span> <span class="o">%</span><span class="n">a</span><span class="p">)</span> <span class="p">{</span>
<span class="n">entry</span><span class="p">:</span>
<span class="o">%</span><span class="n">calltmp</span> <span class="o">=</span> <span class="n">call</span> <span class="n">double</span> <span class="nd">@foo</span><span class="p">(</span><span class="n">double</span> <span class="o">%</span><span class="n">a</span><span class="p">,</span> <span class="n">double</span> <span class="mf">4.000000e+00</span><span class="p">)</span>
<span class="o">%</span><span class="n">calltmp1</span> <span class="o">=</span> <span class="n">call</span> <span class="n">double</span> <span class="nd">@bar</span><span class="p">(</span><span class="n">double</span> <span class="mf">3.133700e+04</span><span class="p">)</span>
<span class="o">%</span><span class="n">addtmp</span> <span class="o">=</span> <span class="n">fadd</span> <span class="n">double</span> <span class="o">%</span><span class="n">calltmp</span><span class="p">,</span> <span class="o">%</span><span class="n">calltmp1</span>
<span class="n">ret</span> <span class="n">double</span> <span class="o">%</span><span class="n">addtmp</span>
<span class="p">}</span>
<span class="n">declare</span> <span class="n">double</span> <span class="nd">@cos</span><span class="p">(</span><span class="n">double</span><span class="p">)</span>
<span class="n">define</span> <span class="n">double</span> <span class="o">@</span><span class="s2">""</span><span class="p">()</span> <span class="p">{</span>
<span class="n">entry</span><span class="p">:</span>
<span class="o">%</span><span class="n">calltmp</span> <span class="o">=</span> <span class="n">call</span> <span class="n">double</span> <span class="nd">@cos</span><span class="p">(</span><span class="n">double</span> <span class="mf">1.234000e+00</span><span class="p">)</span>
<span class="n">ret</span> <span class="n">double</span> <span class="o">%</span><span class="n">calltmp</span>
<span class="p">}</span>
</pre></div>
</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 class="reference external" href="OCamlLangImpl4.html">add JIT codegen and optimizer
support</a> to this so we can actually start running
code!</p>
</div>
<div class="section" id="full-code-listing">
<h2><a class="toc-backref" href="#id6">3.6. Full Code Listing</a><a class="headerlink" href="#full-code-listing" title="Permalink to this headline">¶</a></h2>
<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 class="reference external" 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="highlight-bash notranslate"><div class="highlight"><pre><span></span><span class="c1"># Compile</span>
ocamlbuild toy.byte
<span class="c1"># Run</span>
./toy.byte
</pre></div>
</div>
<p>Here is the code:</p>
<dl class="docutils">
<dt>_tags:</dt>
<dd><div class="first last highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o"><</span><span class="p">{</span><span class="n">lexer</span><span class="p">,</span><span class="n">parser</span><span class="p">}</span><span class="o">.</span><span class="n">ml</span><span class="o">></span><span class="p">:</span> <span class="n">use_camlp4</span><span class="p">,</span> <span class="n">pp</span><span class="p">(</span><span class="n">camlp4of</span><span class="p">)</span>
<span class="o"><*.</span><span class="p">{</span><span class="n">byte</span><span class="p">,</span><span class="n">native</span><span class="p">}</span><span class="o">></span><span class="p">:</span> <span class="n">g</span><span class="o">++</span><span class="p">,</span> <span class="n">use_llvm</span><span class="p">,</span> <span class="n">use_llvm_analysis</span>
</pre></div>
</div>
</dd>
<dt>myocamlbuild.ml:</dt>
<dd><div class="first last highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="k">open</span> <span class="nc">Ocamlbuild_plugin</span><span class="o">;;</span>
<span class="n">ocaml_lib</span> <span class="o">~</span><span class="n">extern</span><span class="o">:</span><span class="bp">true</span> <span class="s2">"llvm"</span><span class="o">;;</span>
<span class="n">ocaml_lib</span> <span class="o">~</span><span class="n">extern</span><span class="o">:</span><span class="bp">true</span> <span class="s2">"llvm_analysis"</span><span class="o">;;</span>
<span class="n">flag</span> <span class="o">[</span><span class="s2">"link"</span><span class="o">;</span> <span class="s2">"ocaml"</span><span class="o">;</span> <span class="s2">"g++"</span><span class="o">]</span> <span class="o">(</span><span class="nc">S</span><span class="o">[</span><span class="nc">A</span><span class="s2">"-cc"</span><span class="o">;</span> <span class="nc">A</span><span class="s2">"g++"</span><span class="o">]);;</span>
</pre></div>
</div>
</dd>
<dt>token.ml:</dt>
<dd><div class="first last highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="c">(*===----------------------------------------------------------------------===</span>
<span class="c"> * Lexer Tokens</span>
<span class="c"> *===----------------------------------------------------------------------===*)</span>
<span class="c">(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of</span>
<span class="c"> * these others for known things. *)</span>
<span class="k">type</span> <span class="n">token</span> <span class="o">=</span>
<span class="c">(* commands *)</span>
<span class="o">|</span> <span class="nc">Def</span> <span class="o">|</span> <span class="nc">Extern</span>
<span class="c">(* primary *)</span>
<span class="o">|</span> <span class="nc">Ident</span> <span class="k">of</span> <span class="kt">string</span> <span class="o">|</span> <span class="nc">Number</span> <span class="k">of</span> <span class="kt">float</span>
<span class="c">(* unknown *)</span>
<span class="o">|</span> <span class="nc">Kwd</span> <span class="k">of</span> <span class="kt">char</span>
</pre></div>
</div>
</dd>
<dt>lexer.ml:</dt>
<dd><div class="first last highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="c">(*===----------------------------------------------------------------------===</span>
<span class="c"> * Lexer</span>
<span class="c"> *===----------------------------------------------------------------------===*)</span>
<span class="k">let</span> <span class="k">rec</span> <span class="n">lex</span> <span class="o">=</span> <span class="n">parser</span>
<span class="c">(* Skip any whitespace. *)</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">' '</span> <span class="o">|</span> <span class="sc">'\n'</span> <span class="o">|</span> <span class="sc">'\r'</span> <span class="o">|</span> <span class="sc">'\t'</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">lex</span> <span class="n">stream</span>
<span class="c">(* identifier: [a-zA-Z][a-zA-Z0-9] *)</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'A'</span> <span class="o">..</span> <span class="sc">'Z'</span> <span class="o">|</span> <span class="sc">'a'</span> <span class="o">..</span> <span class="sc">'z'</span> <span class="k">as</span> <span class="n">c</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
<span class="k">let</span> <span class="n">buffer</span> <span class="o">=</span> <span class="nn">Buffer</span><span class="p">.</span><span class="n">create</span> <span class="mi">1</span> <span class="k">in</span>
<span class="nn">Buffer</span><span class="p">.</span><span class="n">add_char</span> <span class="n">buffer</span> <span class="n">c</span><span class="o">;</span>
<span class="n">lex_ident</span> <span class="n">buffer</span> <span class="n">stream</span>
<span class="c">(* number: [0-9.]+ *)</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'0'</span> <span class="o">..</span> <span class="sc">'9'</span> <span class="k">as</span> <span class="n">c</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
<span class="k">let</span> <span class="n">buffer</span> <span class="o">=</span> <span class="nn">Buffer</span><span class="p">.</span><span class="n">create</span> <span class="mi">1</span> <span class="k">in</span>
<span class="nn">Buffer</span><span class="p">.</span><span class="n">add_char</span> <span class="n">buffer</span> <span class="n">c</span><span class="o">;</span>
<span class="n">lex_number</span> <span class="n">buffer</span> <span class="n">stream</span>
<span class="c">(* Comment until end of line. *)</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'#'</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
<span class="n">lex_comment</span> <span class="n">stream</span>
<span class="c">(* Otherwise, just return the character as its ascii value. *)</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="n">c</span><span class="o">;</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
<span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="n">c</span><span class="o">;</span> <span class="n">lex</span> <span class="n">stream</span> <span class="o">>]</span>
<span class="c">(* end of stream. *)</span>
<span class="o">|</span> <span class="o">[<</span> <span class="o">>]</span> <span class="o">-></span> <span class="o">[<</span> <span class="o">>]</span>
<span class="ow">and</span> <span class="n">lex_number</span> <span class="n">buffer</span> <span class="o">=</span> <span class="n">parser</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'0'</span> <span class="o">..</span> <span class="sc">'9'</span> <span class="o">|</span> <span class="sc">'.'</span> <span class="k">as</span> <span class="n">c</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
<span class="nn">Buffer</span><span class="p">.</span><span class="n">add_char</span> <span class="n">buffer</span> <span class="n">c</span><span class="o">;</span>
<span class="n">lex_number</span> <span class="n">buffer</span> <span class="n">stream</span>
<span class="o">|</span> <span class="o">[<</span> <span class="n">stream</span><span class="o">=</span><span class="n">lex</span> <span class="o">>]</span> <span class="o">-></span>
<span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Number</span> <span class="o">(</span><span class="n">float_of_string</span> <span class="o">(</span><span class="nn">Buffer</span><span class="p">.</span><span class="n">contents</span> <span class="n">buffer</span><span class="o">));</span> <span class="n">stream</span> <span class="o">>]</span>
<span class="ow">and</span> <span class="n">lex_ident</span> <span class="n">buffer</span> <span class="o">=</span> <span class="n">parser</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'A'</span> <span class="o">..</span> <span class="sc">'Z'</span> <span class="o">|</span> <span class="sc">'a'</span> <span class="o">..</span> <span class="sc">'z'</span> <span class="o">|</span> <span class="sc">'0'</span> <span class="o">..</span> <span class="sc">'9'</span> <span class="k">as</span> <span class="n">c</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
<span class="nn">Buffer</span><span class="p">.</span><span class="n">add_char</span> <span class="n">buffer</span> <span class="n">c</span><span class="o">;</span>
<span class="n">lex_ident</span> <span class="n">buffer</span> <span class="n">stream</span>
<span class="o">|</span> <span class="o">[<</span> <span class="n">stream</span><span class="o">=</span><span class="n">lex</span> <span class="o">>]</span> <span class="o">-></span>
<span class="k">match</span> <span class="nn">Buffer</span><span class="p">.</span><span class="n">contents</span> <span class="n">buffer</span> <span class="k">with</span>
<span class="o">|</span> <span class="s2">"def"</span> <span class="o">-></span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Def</span><span class="o">;</span> <span class="n">stream</span> <span class="o">>]</span>
<span class="o">|</span> <span class="s2">"extern"</span> <span class="o">-></span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Extern</span><span class="o">;</span> <span class="n">stream</span> <span class="o">>]</span>
<span class="o">|</span> <span class="n">id</span> <span class="o">-></span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Ident</span> <span class="n">id</span><span class="o">;</span> <span class="n">stream</span> <span class="o">>]</span>
<span class="ow">and</span> <span class="n">lex_comment</span> <span class="o">=</span> <span class="n">parser</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'\n'</span><span class="o">);</span> <span class="n">stream</span><span class="o">=</span><span class="n">lex</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">stream</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="n">c</span><span class="o">;</span> <span class="n">e</span><span class="o">=</span><span class="n">lex_comment</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">e</span>
<span class="o">|</span> <span class="o">[<</span> <span class="o">>]</span> <span class="o">-></span> <span class="o">[<</span> <span class="o">>]</span>
</pre></div>
</div>
</dd>
<dt>ast.ml:</dt>
<dd><div class="first last highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="c">(*===----------------------------------------------------------------------===</span>
<span class="c"> * Abstract Syntax Tree (aka Parse Tree)</span>
<span class="c"> *===----------------------------------------------------------------------===*)</span>
<span class="c">(* expr - Base type for all expression nodes. *)</span>
<span class="k">type</span> <span class="n">expr</span> <span class="o">=</span>
<span class="c">(* variant for numeric literals like "1.0". *)</span>
<span class="o">|</span> <span class="nc">Number</span> <span class="k">of</span> <span class="kt">float</span>
<span class="c">(* variant for referencing a variable, like "a". *)</span>
<span class="o">|</span> <span class="nc">Variable</span> <span class="k">of</span> <span class="kt">string</span>
<span class="c">(* variant for a binary operator. *)</span>
<span class="o">|</span> <span class="nc">Binary</span> <span class="k">of</span> <span class="kt">char</span> <span class="o">*</span> <span class="n">expr</span> <span class="o">*</span> <span class="n">expr</span>
<span class="c">(* variant for function calls. *)</span>
<span class="o">|</span> <span class="nc">Call</span> <span class="k">of</span> <span class="kt">string</span> <span class="o">*</span> <span class="n">expr</span> <span class="kt">array</span>
<span class="c">(* proto - This type represents the "prototype" for a function, which captures</span>
<span class="c"> * its name, and its argument names (thus implicitly the number of arguments the</span>
<span class="c"> * function takes). *)</span>
<span class="k">type</span> <span class="n">proto</span> <span class="o">=</span> <span class="nc">Prototype</span> <span class="k">of</span> <span class="kt">string</span> <span class="o">*</span> <span class="kt">string</span> <span class="kt">array</span>
<span class="c">(* func - This type represents a function definition itself. *)</span>
<span class="k">type</span> <span class="n">func</span> <span class="o">=</span> <span class="nc">Function</span> <span class="k">of</span> <span class="n">proto</span> <span class="o">*</span> <span class="n">expr</span>
</pre></div>
</div>
</dd>
<dt>parser.ml:</dt>
<dd><div class="first last highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="c">(*===---------------------------------------------------------------------===</span>
<span class="c"> * Parser</span>
<span class="c"> *===---------------------------------------------------------------------===*)</span>
<span class="c">(* binop_precedence - This holds the precedence for each binary operator that is</span>
<span class="c"> * defined *)</span>
<span class="k">let</span> <span class="n">binop_precedence</span><span class="o">:(</span><span class="kt">char</span><span class="o">,</span> <span class="kt">int</span><span class="o">)</span> <span class="nn">Hashtbl</span><span class="p">.</span><span class="n">t</span> <span class="o">=</span> <span class="nn">Hashtbl</span><span class="p">.</span><span class="n">create</span> <span class="mi">10</span>
<span class="c">(* precedence - Get the precedence of the pending binary operator token. *)</span>
<span class="k">let</span> <span class="n">precedence</span> <span class="n">c</span> <span class="o">=</span> <span class="k">try</span> <span class="nn">Hashtbl</span><span class="p">.</span><span class="n">find</span> <span class="n">binop_precedence</span> <span class="n">c</span> <span class="k">with</span> <span class="nc">Not_found</span> <span class="o">-></span> <span class="o">-</span><span class="mi">1</span>
<span class="c">(* primary</span>
<span class="c"> * ::= identifier</span>
<span class="c"> * ::= numberexpr</span>
<span class="c"> * ::= parenexpr *)</span>
<span class="k">let</span> <span class="k">rec</span> <span class="n">parse_primary</span> <span class="o">=</span> <span class="n">parser</span>
<span class="c">(* numberexpr ::= number *)</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Number</span> <span class="n">n</span> <span class="o">>]</span> <span class="o">-></span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Number</span> <span class="n">n</span>
<span class="c">(* parenexpr ::= '(' expression ')' *)</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="sc">'('</span><span class="o">;</span> <span class="n">e</span><span class="o">=</span><span class="n">parse_expr</span><span class="o">;</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="sc">')'</span> <span class="o">??</span> <span class="s2">"expected ')'"</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">e</span>
<span class="c">(* identifierexpr</span>
<span class="c"> * ::= identifier</span>
<span class="c"> * ::= identifier '(' argumentexpr ')' *)</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Ident</span> <span class="n">id</span><span class="o">;</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
<span class="k">let</span> <span class="k">rec</span> <span class="n">parse_args</span> <span class="n">accumulator</span> <span class="o">=</span> <span class="n">parser</span>
<span class="o">|</span> <span class="o">[<</span> <span class="n">e</span><span class="o">=</span><span class="n">parse_expr</span><span class="o">;</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
<span class="k">begin</span> <span class="n">parser</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="sc">','</span><span class="o">;</span> <span class="n">e</span><span class="o">=</span><span class="n">parse_args</span> <span class="o">(</span><span class="n">e</span> <span class="o">::</span> <span class="n">accumulator</span><span class="o">)</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">e</span>
<span class="o">|</span> <span class="o">[<</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">e</span> <span class="o">::</span> <span class="n">accumulator</span>
<span class="k">end</span> <span class="n">stream</span>
<span class="o">|</span> <span class="o">[<</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">accumulator</span>
<span class="k">in</span>
<span class="k">let</span> <span class="k">rec</span> <span class="n">parse_ident</span> <span class="n">id</span> <span class="o">=</span> <span class="n">parser</span>
<span class="c">(* Call. *)</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="sc">'('</span><span class="o">;</span>
<span class="n">args</span><span class="o">=</span><span class="n">parse_args</span> <span class="bp">[]</span><span class="o">;</span>
<span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="sc">')'</span> <span class="o">??</span> <span class="s2">"expected ')'"</span><span class="o">>]</span> <span class="o">-></span>
<span class="nn">Ast</span><span class="p">.</span><span class="nc">Call</span> <span class="o">(</span><span class="n">id</span><span class="o">,</span> <span class="nn">Array</span><span class="p">.</span><span class="n">of_list</span> <span class="o">(</span><span class="nn">List</span><span class="p">.</span><span class="n">rev</span> <span class="n">args</span><span class="o">))</span>
<span class="c">(* Simple variable ref. *)</span>
<span class="o">|</span> <span class="o">[<</span> <span class="o">>]</span> <span class="o">-></span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Variable</span> <span class="n">id</span>
<span class="k">in</span>
<span class="n">parse_ident</span> <span class="n">id</span> <span class="n">stream</span>
<span class="o">|</span> <span class="o">[<</span> <span class="o">>]</span> <span class="o">-></span> <span class="k">raise</span> <span class="o">(</span><span class="nn">Stream</span><span class="p">.</span><span class="nc">Error</span> <span class="s2">"unknown token when expecting an expression."</span><span class="o">)</span>
<span class="c">(* binoprhs</span>
<span class="c"> * ::= ('+' primary)* *)</span>
<span class="ow">and</span> <span class="n">parse_bin_rhs</span> <span class="n">expr_prec</span> <span class="n">lhs</span> <span class="n">stream</span> <span class="o">=</span>
<span class="k">match</span> <span class="nn">Stream</span><span class="p">.</span><span class="n">peek</span> <span class="n">stream</span> <span class="k">with</span>
<span class="c">(* If this is a binop, find its precedence. *)</span>
<span class="o">|</span> <span class="nc">Some</span> <span class="o">(</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="n">c</span><span class="o">)</span> <span class="k">when</span> <span class="nn">Hashtbl</span><span class="p">.</span><span class="n">mem</span> <span class="n">binop_precedence</span> <span class="n">c</span> <span class="o">-></span>
<span class="k">let</span> <span class="n">token_prec</span> <span class="o">=</span> <span class="n">precedence</span> <span class="n">c</span> <span class="k">in</span>
<span class="c">(* If this is a binop that binds at least as tightly as the current binop,</span>
<span class="c"> * consume it, otherwise we are done. *)</span>
<span class="k">if</span> <span class="n">token_prec</span> <span class="o"><</span> <span class="n">expr_prec</span> <span class="k">then</span> <span class="n">lhs</span> <span class="k">else</span> <span class="k">begin</span>
<span class="c">(* Eat the binop. *)</span>
<span class="nn">Stream</span><span class="p">.</span><span class="n">junk</span> <span class="n">stream</span><span class="o">;</span>
<span class="c">(* Parse the primary expression after the binary operator. *)</span>
<span class="k">let</span> <span class="n">rhs</span> <span class="o">=</span> <span class="n">parse_primary</span> <span class="n">stream</span> <span class="k">in</span>
<span class="c">(* Okay, we know this is a binop. *)</span>
<span class="k">let</span> <span class="n">rhs</span> <span class="o">=</span>
<span class="k">match</span> <span class="nn">Stream</span><span class="p">.</span><span class="n">peek</span> <span class="n">stream</span> <span class="k">with</span>
<span class="o">|</span> <span class="nc">Some</span> <span class="o">(</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="n">c2</span><span class="o">)</span> <span class="o">-></span>
<span class="c">(* If BinOp binds less tightly with rhs than the operator after</span>
<span class="c"> * rhs, let the pending operator take rhs as its lhs. *)</span>
<span class="k">let</span> <span class="n">next_prec</span> <span class="o">=</span> <span class="n">precedence</span> <span class="n">c2</span> <span class="k">in</span>
<span class="k">if</span> <span class="n">token_prec</span> <span class="o"><</span> <span class="n">next_prec</span>
<span class="k">then</span> <span class="n">parse_bin_rhs</span> <span class="o">(</span><span class="n">token_prec</span> <span class="o">+</span> <span class="mi">1</span><span class="o">)</span> <span class="n">rhs</span> <span class="n">stream</span>
<span class="k">else</span> <span class="n">rhs</span>
<span class="o">|</span> <span class="o">_</span> <span class="o">-></span> <span class="n">rhs</span>
<span class="k">in</span>
<span class="c">(* Merge lhs/rhs. *)</span>
<span class="k">let</span> <span class="n">lhs</span> <span class="o">=</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Binary</span> <span class="o">(</span><span class="n">c</span><span class="o">,</span> <span class="n">lhs</span><span class="o">,</span> <span class="n">rhs</span><span class="o">)</span> <span class="k">in</span>
<span class="n">parse_bin_rhs</span> <span class="n">expr_prec</span> <span class="n">lhs</span> <span class="n">stream</span>
<span class="k">end</span>
<span class="o">|</span> <span class="o">_</span> <span class="o">-></span> <span class="n">lhs</span>
<span class="c">(* expression</span>
<span class="c"> * ::= primary binoprhs *)</span>
<span class="ow">and</span> <span class="n">parse_expr</span> <span class="o">=</span> <span class="n">parser</span>
<span class="o">|</span> <span class="o">[<</span> <span class="n">lhs</span><span class="o">=</span><span class="n">parse_primary</span><span class="o">;</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">parse_bin_rhs</span> <span class="mi">0</span> <span class="n">lhs</span> <span class="n">stream</span>
<span class="c">(* prototype</span>
<span class="c"> * ::= id '(' id* ')' *)</span>
<span class="k">let</span> <span class="n">parse_prototype</span> <span class="o">=</span>
<span class="k">let</span> <span class="k">rec</span> <span class="n">parse_args</span> <span class="n">accumulator</span> <span class="o">=</span> <span class="n">parser</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Ident</span> <span class="n">id</span><span class="o">;</span> <span class="n">e</span><span class="o">=</span><span class="n">parse_args</span> <span class="o">(</span><span class="n">id</span><span class="o">::</span><span class="n">accumulator</span><span class="o">)</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">e</span>
<span class="o">|</span> <span class="o">[<</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">accumulator</span>
<span class="k">in</span>
<span class="n">parser</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Ident</span> <span class="n">id</span><span class="o">;</span>
<span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="sc">'('</span> <span class="o">??</span> <span class="s2">"expected '(' in prototype"</span><span class="o">;</span>
<span class="n">args</span><span class="o">=</span><span class="n">parse_args</span> <span class="bp">[]</span><span class="o">;</span>
<span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="sc">')'</span> <span class="o">??</span> <span class="s2">"expected ')' in prototype"</span> <span class="o">>]</span> <span class="o">-></span>
<span class="c">(* success. *)</span>
<span class="nn">Ast</span><span class="p">.</span><span class="nc">Prototype</span> <span class="o">(</span><span class="n">id</span><span class="o">,</span> <span class="nn">Array</span><span class="p">.</span><span class="n">of_list</span> <span class="o">(</span><span class="nn">List</span><span class="p">.</span><span class="n">rev</span> <span class="n">args</span><span class="o">))</span>
<span class="o">|</span> <span class="o">[<</span> <span class="o">>]</span> <span class="o">-></span>
<span class="k">raise</span> <span class="o">(</span><span class="nn">Stream</span><span class="p">.</span><span class="nc">Error</span> <span class="s2">"expected function name in prototype"</span><span class="o">)</span>
<span class="c">(* definition ::= 'def' prototype expression *)</span>
<span class="k">let</span> <span class="n">parse_definition</span> <span class="o">=</span> <span class="n">parser</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Def</span><span class="o">;</span> <span class="n">p</span><span class="o">=</span><span class="n">parse_prototype</span><span class="o">;</span> <span class="n">e</span><span class="o">=</span><span class="n">parse_expr</span> <span class="o">>]</span> <span class="o">-></span>
<span class="nn">Ast</span><span class="p">.</span><span class="nc">Function</span> <span class="o">(</span><span class="n">p</span><span class="o">,</span> <span class="n">e</span><span class="o">)</span>
<span class="c">(* toplevelexpr ::= expression *)</span>
<span class="k">let</span> <span class="n">parse_toplevel</span> <span class="o">=</span> <span class="n">parser</span>
<span class="o">|</span> <span class="o">[<</span> <span class="n">e</span><span class="o">=</span><span class="n">parse_expr</span> <span class="o">>]</span> <span class="o">-></span>
<span class="c">(* Make an anonymous proto. *)</span>
<span class="nn">Ast</span><span class="p">.</span><span class="nc">Function</span> <span class="o">(</span><span class="nn">Ast</span><span class="p">.</span><span class="nc">Prototype</span> <span class="o">(</span><span class="s2">""</span><span class="o">,</span> <span class="o">[||]),</span> <span class="n">e</span><span class="o">)</span>
<span class="c">(* external ::= 'extern' prototype *)</span>
<span class="k">let</span> <span class="n">parse_extern</span> <span class="o">=</span> <span class="n">parser</span>
<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Extern</span><span class="o">;</span> <span class="n">e</span><span class="o">=</span><span class="n">parse_prototype</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">e</span>
</pre></div>
</div>
</dd>
<dt>codegen.ml:</dt>
<dd><div class="first last highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="c">(*===----------------------------------------------------------------------===</span>
<span class="c"> * Code Generation</span>
<span class="c"> *===----------------------------------------------------------------------===*)</span>
<span class="k">open</span> <span class="nc">Llvm</span>
<span class="k">exception</span> <span class="nc">Error</span> <span class="k">of</span> <span class="kt">string</span>
<span class="k">let</span> <span class="n">context</span> <span class="o">=</span> <span class="n">global_context</span> <span class="bp">()</span>
<span class="k">let</span> <span class="n">the_module</span> <span class="o">=</span> <span class="n">create_module</span> <span class="n">context</span> <span class="s2">"my cool jit"</span>
<span class="k">let</span> <span class="n">builder</span> <span class="o">=</span> <span class="n">builder</span> <span class="n">context</span>
<span class="k">let</span> <span class="n">named_values</span><span class="o">:(</span><span class="kt">string</span><span class="o">,</span> <span class="n">llvalue</span><span class="o">)</span> <span class="nn">Hashtbl</span><span class="p">.</span><span class="n">t</span> <span class="o">=</span> <span class="nn">Hashtbl</span><span class="p">.</span><span class="n">create</span> <span class="mi">10</span>
<span class="k">let</span> <span class="n">double_type</span> <span class="o">=</span> <span class="n">double_type</span> <span class="n">context</span>
<span class="k">let</span> <span class="k">rec</span> <span class="n">codegen_expr</span> <span class="o">=</span> <span class="k">function</span>
<span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Number</span> <span class="n">n</span> <span class="o">-></span> <span class="n">const_float</span> <span class="n">double_type</span> <span class="n">n</span>
<span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Variable</span> <span class="n">name</span> <span class="o">-></span>
<span class="o">(</span><span class="k">try</span> <span class="nn">Hashtbl</span><span class="p">.</span><span class="n">find</span> <span class="n">named_values</span> <span class="n">name</span> <span class="k">with</span>
<span class="o">|</span> <span class="nc">Not_found</span> <span class="o">-></span> <span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"unknown variable name"</span><span class="o">))</span>
<span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Binary</span> <span class="o">(</span><span class="n">op</span><span class="o">,</span> <span class="n">lhs</span><span class="o">,</span> <span class="n">rhs</span><span class="o">)</span> <span class="o">-></span>
<span class="k">let</span> <span class="n">lhs_val</span> <span class="o">=</span> <span class="n">codegen_expr</span> <span class="n">lhs</span> <span class="k">in</span>
<span class="k">let</span> <span class="n">rhs_val</span> <span class="o">=</span> <span class="n">codegen_expr</span> <span class="n">rhs</span> <span class="k">in</span>
<span class="k">begin</span>
<span class="k">match</span> <span class="n">op</span> <span class="k">with</span>
<span class="o">|</span> <span class="sc">'+'</span> <span class="o">-></span> <span class="n">build_add</span> <span class="n">lhs_val</span> <span class="n">rhs_val</span> <span class="s2">"addtmp"</span> <span class="n">builder</span>
<span class="o">|</span> <span class="sc">'-'</span> <span class="o">-></span> <span class="n">build_sub</span> <span class="n">lhs_val</span> <span class="n">rhs_val</span> <span class="s2">"subtmp"</span> <span class="n">builder</span>
<span class="o">|</span> <span class="sc">'*'</span> <span class="o">-></span> <span class="n">build_mul</span> <span class="n">lhs_val</span> <span class="n">rhs_val</span> <span class="s2">"multmp"</span> <span class="n">builder</span>
<span class="o">|</span> <span class="sc">'<'</span> <span class="o">-></span>
<span class="c">(* Convert bool 0/1 to double 0.0 or 1.0 *)</span>
<span class="k">let</span> <span class="n">i</span> <span class="o">=</span> <span class="n">build_fcmp</span> <span class="nn">Fcmp</span><span class="p">.</span><span class="nc">Ult</span> <span class="n">lhs_val</span> <span class="n">rhs_val</span> <span class="s2">"cmptmp"</span> <span class="n">builder</span> <span class="k">in</span>
<span class="n">build_uitofp</span> <span class="n">i</span> <span class="n">double_type</span> <span class="s2">"booltmp"</span> <span class="n">builder</span>
<span class="o">|</span> <span class="o">_</span> <span class="o">-></span> <span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"invalid binary operator"</span><span class="o">)</span>
<span class="k">end</span>
<span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Call</span> <span class="o">(</span><span class="n">callee</span><span class="o">,</span> <span class="n">args</span><span class="o">)</span> <span class="o">-></span>
<span class="c">(* Look up the name in the module table. *)</span>
<span class="k">let</span> <span class="n">callee</span> <span class="o">=</span>
<span class="k">match</span> <span class="n">lookup_function</span> <span class="n">callee</span> <span class="n">the_module</span> <span class="k">with</span>
<span class="o">|</span> <span class="nc">Some</span> <span class="n">callee</span> <span class="o">-></span> <span class="n">callee</span>
<span class="o">|</span> <span class="nc">None</span> <span class="o">-></span> <span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"unknown function referenced"</span><span class="o">)</span>
<span class="k">in</span>
<span class="k">let</span> <span class="n">params</span> <span class="o">=</span> <span class="n">params</span> <span class="n">callee</span> <span class="k">in</span>
<span class="c">(* If argument mismatch error. *)</span>
<span class="k">if</span> <span class="nn">Array</span><span class="p">.</span><span class="n">length</span> <span class="n">params</span> <span class="o">==</span> <span class="nn">Array</span><span class="p">.</span><span class="n">length</span> <span class="n">args</span> <span class="k">then</span> <span class="bp">()</span> <span class="k">else</span>
<span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"incorrect # arguments passed"</span><span class="o">);</span>
<span class="k">let</span> <span class="n">args</span> <span class="o">=</span> <span class="nn">Array</span><span class="p">.</span><span class="n">map</span> <span class="n">codegen_expr</span> <span class="n">args</span> <span class="k">in</span>
<span class="n">build_call</span> <span class="n">callee</span> <span class="n">args</span> <span class="s2">"calltmp"</span> <span class="n">builder</span>
<span class="k">let</span> <span class="n">codegen_proto</span> <span class="o">=</span> <span class="k">function</span>
<span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Prototype</span> <span class="o">(</span><span class="n">name</span><span class="o">,</span> <span class="n">args</span><span class="o">)</span> <span class="o">-></span>
<span class="c">(* Make the function type: double(double,double) etc. *)</span>
<span class="k">let</span> <span class="n">doubles</span> <span class="o">=</span> <span class="nn">Array</span><span class="p">.</span><span class="n">make</span> <span class="o">(</span><span class="nn">Array</span><span class="p">.</span><span class="n">length</span> <span class="n">args</span><span class="o">)</span> <span class="n">double_type</span> <span class="k">in</span>
<span class="k">let</span> <span class="n">ft</span> <span class="o">=</span> <span class="n">function_type</span> <span class="n">double_type</span> <span class="n">doubles</span> <span class="k">in</span>
<span class="k">let</span> <span class="n">f</span> <span class="o">=</span>
<span class="k">match</span> <span class="n">lookup_function</span> <span class="n">name</span> <span class="n">the_module</span> <span class="k">with</span>
<span class="o">|</span> <span class="nc">None</span> <span class="o">-></span> <span class="n">declare_function</span> <span class="n">name</span> <span class="n">ft</span> <span class="n">the_module</span>
<span class="c">(* If 'f' conflicted, there was already something named 'name'. If it</span>
<span class="c"> * has a body, don't allow redefinition or reextern. *)</span>
<span class="o">|</span> <span class="nc">Some</span> <span class="n">f</span> <span class="o">-></span>
<span class="c">(* If 'f' already has a body, reject this. *)</span>
<span class="k">if</span> <span class="n">block_begin</span> <span class="n">f</span> <span class="o"><></span> <span class="nc">At_end</span> <span class="n">f</span> <span class="k">then</span>
<span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"redefinition of function"</span><span class="o">);</span>
<span class="c">(* If 'f' took a different number of arguments, reject. *)</span>
<span class="k">if</span> <span class="n">element_type</span> <span class="o">(</span><span class="n">type_of</span> <span class="n">f</span><span class="o">)</span> <span class="o"><></span> <span class="n">ft</span> <span class="k">then</span>
<span class="k">raise</span> <span class="o">(</span><span class="nc">Error</span> <span class="s2">"redefinition of function with different # args"</span><span class="o">);</span>
<span class="n">f</span>
<span class="k">in</span>
<span class="c">(* Set names for all arguments. *)</span>
<span class="nn">Array</span><span class="p">.</span><span class="n">iteri</span> <span class="o">(</span><span class="k">fun</span> <span class="n">i</span> <span class="n">a</span> <span class="o">-></span>
<span class="k">let</span> <span class="n">n</span> <span class="o">=</span> <span class="n">args</span><span class="o">.(</span><span class="n">i</span><span class="o">)</span> <span class="k">in</span>
<span class="n">set_value_name</span> <span class="n">n</span> <span class="n">a</span><span class="o">;</span>
<span class="nn">Hashtbl</span><span class="p">.</span><span class="n">add</span> <span class="n">named_values</span> <span class="n">n</span> <span class="n">a</span><span class="o">;</span>
<span class="o">)</span> <span class="o">(</span><span class="n">params</span> <span class="n">f</span><span class="o">);</span>
<span class="n">f</span>
<span class="k">let</span> <span class="n">codegen_func</span> <span class="o">=</span> <span class="k">function</span>
<span class="o">|</span> <span class="nn">Ast</span><span class="p">.</span><span class="nc">Function</span> <span class="o">(</span><span class="n">proto</span><span class="o">,</span> <span class="n">body</span><span class="o">)</span> <span class="o">-></span>
<span class="nn">Hashtbl</span><span class="p">.</span><span class="n">clear</span> <span class="n">named_values</span><span class="o">;</span>
<span class="k">let</span> <span class="n">the_function</span> <span class="o">=</span> <span class="n">codegen_proto</span> <span class="n">proto</span> <span class="k">in</span>
<span class="c">(* Create a new basic block to start insertion into. *)</span>
<span class="k">let</span> <span class="n">bb</span> <span class="o">=</span> <span class="n">append_block</span> <span class="n">context</span> <span class="s2">"entry"</span> <span class="n">the_function</span> <span class="k">in</span>
<span class="n">position_at_end</span> <span class="n">bb</span> <span class="n">builder</span><span class="o">;</span>
<span class="k">try</span>
<span class="k">let</span> <span class="n">ret_val</span> <span class="o">=</span> <span class="n">codegen_expr</span> <span class="n">body</span> <span class="k">in</span>
<span class="c">(* Finish off the function. *)</span>
<span class="k">let</span> <span class="o">_</span> <span class="o">=</span> <span class="n">build_ret</span> <span class="n">ret_val</span> <span class="n">builder</span> <span class="k">in</span>
<span class="c">(* Validate the generated code, checking for consistency. *)</span>
<span class="nn">Llvm_analysis</span><span class="p">.</span><span class="n">assert_valid_function</span> <span class="n">the_function</span><span class="o">;</span>
<span class="n">the_function</span>
<span class="k">with</span> <span class="n">e</span> <span class="o">-></span>
<span class="n">delete_function</span> <span class="n">the_function</span><span class="o">;</span>
<span class="k">raise</span> <span class="n">e</span>
</pre></div>
</div>
</dd>
<dt>toplevel.ml:</dt>
<dd><div class="first last highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="c">(*===----------------------------------------------------------------------===</span>
<span class="c"> * Top-Level parsing and JIT Driver</span>
<span class="c"> *===----------------------------------------------------------------------===*)</span>
<span class="k">open</span> <span class="nc">Llvm</span>
<span class="c">(* top ::= definition | external | expression | ';' *)</span>
<span class="k">let</span> <span class="k">rec</span> <span class="n">main_loop</span> <span class="n">stream</span> <span class="o">=</span>
<span class="k">match</span> <span class="nn">Stream</span><span class="p">.</span><span class="n">peek</span> <span class="n">stream</span> <span class="k">with</span>
<span class="o">|</span> <span class="nc">None</span> <span class="o">-></span> <span class="bp">()</span>
<span class="c">(* ignore top-level semicolons. *)</span>
<span class="o">|</span> <span class="nc">Some</span> <span class="o">(</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="sc">';'</span><span class="o">)</span> <span class="o">-></span>
<span class="nn">Stream</span><span class="p">.</span><span class="n">junk</span> <span class="n">stream</span><span class="o">;</span>
<span class="n">main_loop</span> <span class="n">stream</span>
<span class="o">|</span> <span class="nc">Some</span> <span class="n">token</span> <span class="o">-></span>
<span class="k">begin</span>
<span class="k">try</span> <span class="k">match</span> <span class="n">token</span> <span class="k">with</span>
<span class="o">|</span> <span class="nn">Token</span><span class="p">.</span><span class="nc">Def</span> <span class="o">-></span>
<span class="k">let</span> <span class="n">e</span> <span class="o">=</span> <span class="nn">Parser</span><span class="p">.</span><span class="n">parse_definition</span> <span class="n">stream</span> <span class="k">in</span>
<span class="n">print_endline</span> <span class="s2">"parsed a function definition."</span><span class="o">;</span>
<span class="n">dump_value</span> <span class="o">(</span><span class="nn">Codegen</span><span class="p">.</span><span class="n">codegen_func</span> <span class="n">e</span><span class="o">);</span>
<span class="o">|</span> <span class="nn">Token</span><span class="p">.</span><span class="nc">Extern</span> <span class="o">-></span>
<span class="k">let</span> <span class="n">e</span> <span class="o">=</span> <span class="nn">Parser</span><span class="p">.</span><span class="n">parse_extern</span> <span class="n">stream</span> <span class="k">in</span>
<span class="n">print_endline</span> <span class="s2">"parsed an extern."</span><span class="o">;</span>
<span class="n">dump_value</span> <span class="o">(</span><span class="nn">Codegen</span><span class="p">.</span><span class="n">codegen_proto</span> <span class="n">e</span><span class="o">);</span>
<span class="o">|</span> <span class="o">_</span> <span class="o">-></span>
<span class="c">(* Evaluate a top-level expression into an anonymous function. *)</span>
<span class="k">let</span> <span class="n">e</span> <span class="o">=</span> <span class="nn">Parser</span><span class="p">.</span><span class="n">parse_toplevel</span> <span class="n">stream</span> <span class="k">in</span>
<span class="n">print_endline</span> <span class="s2">"parsed a top-level expr"</span><span class="o">;</span>
<span class="n">dump_value</span> <span class="o">(</span><span class="nn">Codegen</span><span class="p">.</span><span class="n">codegen_func</span> <span class="n">e</span><span class="o">);</span>
<span class="k">with</span> <span class="nn">Stream</span><span class="p">.</span><span class="nc">Error</span> <span class="n">s</span> <span class="o">|</span> <span class="nn">Codegen</span><span class="p">.</span><span class="nc">Error</span> <span class="n">s</span> <span class="o">-></span>
<span class="c">(* Skip token for error recovery. *)</span>
<span class="nn">Stream</span><span class="p">.</span><span class="n">junk</span> <span class="n">stream</span><span class="o">;</span>
<span class="n">print_endline</span> <span class="n">s</span><span class="o">;</span>
<span class="k">end</span><span class="o">;</span>
<span class="n">print_string</span> <span class="s2">"ready> "</span><span class="o">;</span> <span class="n">flush</span> <span class="n">stdout</span><span class="o">;</span>
<span class="n">main_loop</span> <span class="n">stream</span>
</pre></div>
</div>
</dd>
<dt>toy.ml:</dt>
<dd><div class="first last highlight-ocaml notranslate"><div class="highlight"><pre><span></span><span class="c">(*===----------------------------------------------------------------------===</span>
<span class="c"> * Main driver code.</span>
<span class="c"> *===----------------------------------------------------------------------===*)</span>
<span class="k">open</span> <span class="nc">Llvm</span>
<span class="k">let</span> <span class="n">main</span> <span class="bp">()</span> <span class="o">=</span>
<span class="c">(* Install standard binary operators.</span>
<span class="c"> * 1 is the lowest precedence. *)</span>
<span class="nn">Hashtbl</span><span class="p">.</span><span class="n">add</span> <span class="nn">Parser</span><span class="p">.</span><span class="n">binop_precedence</span> <span class="sc">'<'</span> <span class="mi">10</span><span class="o">;</span>
<span class="nn">Hashtbl</span><span class="p">.</span><span class="n">add</span> <span class="nn">Parser</span><span class="p">.</span><span class="n">binop_precedence</span> <span class="sc">'+'</span> <span class="mi">20</span><span class="o">;</span>
<span class="nn">Hashtbl</span><span class="p">.</span><span class="n">add</span> <span class="nn">Parser</span><span class="p">.</span><span class="n">binop_precedence</span> <span class="sc">'-'</span> <span class="mi">20</span><span class="o">;</span>
<span class="nn">Hashtbl</span><span class="p">.</span><span class="n">add</span> <span class="nn">Parser</span><span class="p">.</span><span class="n">binop_precedence</span> <span class="sc">'*'</span> <span class="mi">40</span><span class="o">;</span> <span class="c">(* highest. *)</span>
<span class="c">(* Prime the first token. *)</span>
<span class="n">print_string</span> <span class="s2">"ready> "</span><span class="o">;</span> <span class="n">flush</span> <span class="n">stdout</span><span class="o">;</span>
<span class="k">let</span> <span class="n">stream</span> <span class="o">=</span> <span class="nn">Lexer</span><span class="p">.</span><span class="n">lex</span> <span class="o">(</span><span class="nn">Stream</span><span class="p">.</span><span class="n">of_channel</span> <span class="n">stdin</span><span class="o">)</span> <span class="k">in</span>
<span class="c">(* Run the main "interpreter loop" now. *)</span>
<span class="nn">Toplevel</span><span class="p">.</span><span class="n">main_loop</span> <span class="n">stream</span><span class="o">;</span>
<span class="c">(* Print out all the generated code. *)</span>
<span class="n">dump_module</span> <span class="nn">Codegen</span><span class="p">.</span><span class="n">the_module</span>
<span class="o">;;</span>
<span class="n">main</span> <span class="bp">()</span>
</pre></div>
</div>
</dd>
</dl>
<p><a class="reference external" href="OCamlLangImpl4.html">Next: Adding JIT and Optimizer Support</a></p>
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