mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-27 15:29:51 +00:00
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81800 91177308-0d34-0410-b5e6-96231b3b80d8
1570 lines
54 KiB
HTML
1570 lines
54 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
|
|
"http://www.w3.org/TR/html4/strict.dtd">
|
|
|
|
<html>
|
|
<head>
|
|
<title>Kaleidoscope: Extending the Language: Control Flow</title>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<meta name="author" content="Chris Lattner">
|
|
<meta name="author" content="Erick Tryzelaar">
|
|
<link rel="stylesheet" href="../llvm.css" type="text/css">
|
|
</head>
|
|
|
|
<body>
|
|
|
|
<div class="doc_title">Kaleidoscope: Extending the Language: Control Flow</div>
|
|
|
|
<ul>
|
|
<li><a href="index.html">Up to Tutorial Index</a></li>
|
|
<li>Chapter 5
|
|
<ol>
|
|
<li><a href="#intro">Chapter 5 Introduction</a></li>
|
|
<li><a href="#ifthen">If/Then/Else</a>
|
|
<ol>
|
|
<li><a href="#iflexer">Lexer Extensions</a></li>
|
|
<li><a href="#ifast">AST Extensions</a></li>
|
|
<li><a href="#ifparser">Parser Extensions</a></li>
|
|
<li><a href="#ifir">LLVM IR</a></li>
|
|
<li><a href="#ifcodegen">Code Generation</a></li>
|
|
</ol>
|
|
</li>
|
|
<li><a href="#for">'for' Loop Expression</a>
|
|
<ol>
|
|
<li><a href="#forlexer">Lexer Extensions</a></li>
|
|
<li><a href="#forast">AST Extensions</a></li>
|
|
<li><a href="#forparser">Parser Extensions</a></li>
|
|
<li><a href="#forir">LLVM IR</a></li>
|
|
<li><a href="#forcodegen">Code Generation</a></li>
|
|
</ol>
|
|
</li>
|
|
<li><a href="#code">Full Code Listing</a></li>
|
|
</ol>
|
|
</li>
|
|
<li><a href="OCamlLangImpl6.html">Chapter 6</a>: Extending the Language:
|
|
User-defined Operators</li>
|
|
</ul>
|
|
|
|
<div class="doc_author">
|
|
<p>
|
|
Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
|
|
and <a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a>
|
|
</p>
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"><a name="intro">Chapter 5 Introduction</a></div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>Welcome to Chapter 5 of the "<a href="index.html">Implementing a language
|
|
with LLVM</a>" tutorial. Parts 1-4 described the implementation of the simple
|
|
Kaleidoscope language and included support for generating LLVM IR, followed by
|
|
optimizations and a JIT compiler. Unfortunately, as presented, Kaleidoscope is
|
|
mostly useless: it has no control flow other than call and return. This means
|
|
that you can't have conditional branches in the code, significantly limiting its
|
|
power. In this episode of "build that compiler", we'll extend Kaleidoscope to
|
|
have an if/then/else expression plus a simple 'for' loop.</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"><a name="ifthen">If/Then/Else</a></div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>
|
|
Extending Kaleidoscope to support if/then/else is quite straightforward. It
|
|
basically requires adding lexer support for this "new" concept to the lexer,
|
|
parser, AST, and LLVM code emitter. This example is nice, because it shows how
|
|
easy it is to "grow" a language over time, incrementally extending it as new
|
|
ideas are discovered.</p>
|
|
|
|
<p>Before we get going on "how" we add this extension, lets talk about "what" we
|
|
want. The basic idea is that we want to be able to write this sort of thing:
|
|
</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
def fib(x)
|
|
if x < 3 then
|
|
1
|
|
else
|
|
fib(x-1)+fib(x-2);
|
|
</pre>
|
|
</div>
|
|
|
|
<p>In Kaleidoscope, every construct is an expression: there are no statements.
|
|
As such, the if/then/else expression needs to return a value like any other.
|
|
Since we're using a mostly functional form, we'll have it evaluate its
|
|
conditional, then return the 'then' or 'else' value based on how the condition
|
|
was resolved. This is very similar to the C "?:" expression.</p>
|
|
|
|
<p>The semantics of the if/then/else expression is that it evaluates the
|
|
condition to a boolean equality value: 0.0 is considered to be false and
|
|
everything else is considered to be true.
|
|
If the condition is true, the first subexpression is evaluated and returned, if
|
|
the condition is false, the second subexpression is evaluated and returned.
|
|
Since Kaleidoscope allows side-effects, this behavior is important to nail down.
|
|
</p>
|
|
|
|
<p>Now that we know what we "want", lets break this down into its constituent
|
|
pieces.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsubsection"><a name="iflexer">Lexer Extensions for
|
|
If/Then/Else</a></div>
|
|
<!-- ======================================================================= -->
|
|
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>The lexer extensions are straightforward. First we add new variants
|
|
for the relevant tokens:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* control *)
|
|
| If | Then | Else | For | In
|
|
</pre>
|
|
</div>
|
|
|
|
<p>Once we have that, we recognize the new keywords in the lexer. This is pretty simple
|
|
stuff:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
...
|
|
match Buffer.contents buffer with
|
|
| "def" -> [< 'Token.Def; stream >]
|
|
| "extern" -> [< 'Token.Extern; stream >]
|
|
| "if" -> [< 'Token.If; stream >]
|
|
| "then" -> [< 'Token.Then; stream >]
|
|
| "else" -> [< 'Token.Else; stream >]
|
|
| "for" -> [< 'Token.For; stream >]
|
|
| "in" -> [< 'Token.In; stream >]
|
|
| id -> [< 'Token.Ident id; stream >]
|
|
</pre>
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsubsection"><a name="ifast">AST Extensions for
|
|
If/Then/Else</a></div>
|
|
<!-- ======================================================================= -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>To represent the new expression we add a new AST variant for it:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
type expr =
|
|
...
|
|
(* variant for if/then/else. *)
|
|
| If of expr * expr * expr
|
|
</pre>
|
|
</div>
|
|
|
|
<p>The AST variant just has pointers to the various subexpressions.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsubsection"><a name="ifparser">Parser Extensions for
|
|
If/Then/Else</a></div>
|
|
<!-- ======================================================================= -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>Now that we have the relevant tokens coming from the lexer and we have the
|
|
AST node to build, our parsing logic is relatively straightforward. First we
|
|
define a new parsing function:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
let rec parse_primary = parser
|
|
...
|
|
(* ifexpr ::= 'if' expr 'then' expr 'else' expr *)
|
|
| [< 'Token.If; c=parse_expr;
|
|
'Token.Then ?? "expected 'then'"; t=parse_expr;
|
|
'Token.Else ?? "expected 'else'"; e=parse_expr >] ->
|
|
Ast.If (c, t, e)
|
|
</pre>
|
|
</div>
|
|
|
|
<p>Next we hook it up as a primary expression:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
let rec parse_primary = parser
|
|
...
|
|
(* ifexpr ::= 'if' expr 'then' expr 'else' expr *)
|
|
| [< 'Token.If; c=parse_expr;
|
|
'Token.Then ?? "expected 'then'"; t=parse_expr;
|
|
'Token.Else ?? "expected 'else'"; e=parse_expr >] ->
|
|
Ast.If (c, t, e)
|
|
</pre>
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsubsection"><a name="ifir">LLVM IR for If/Then/Else</a></div>
|
|
<!-- ======================================================================= -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>Now that we have it parsing and building the AST, the final piece is adding
|
|
LLVM code generation support. This is the most interesting part of the
|
|
if/then/else example, because this is where it starts to introduce new concepts.
|
|
All of the code above has been thoroughly described in previous chapters.
|
|
</p>
|
|
|
|
<p>To motivate the code we want to produce, lets take a look at a simple
|
|
example. Consider:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
extern foo();
|
|
extern bar();
|
|
def baz(x) if x then foo() else bar();
|
|
</pre>
|
|
</div>
|
|
|
|
<p>If you disable optimizations, the code you'll (soon) get from Kaleidoscope
|
|
looks like this:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
declare double @foo()
|
|
|
|
declare double @bar()
|
|
|
|
define double @baz(double %x) {
|
|
entry:
|
|
%ifcond = fcmp one double %x, 0.000000e+00
|
|
br i1 %ifcond, label %then, label %else
|
|
|
|
then: ; preds = %entry
|
|
%calltmp = call double @foo()
|
|
br label %ifcont
|
|
|
|
else: ; preds = %entry
|
|
%calltmp1 = call double @bar()
|
|
br label %ifcont
|
|
|
|
ifcont: ; preds = %else, %then
|
|
%iftmp = phi double [ %calltmp, %then ], [ %calltmp1, %else ]
|
|
ret double %iftmp
|
|
}
|
|
</pre>
|
|
</div>
|
|
|
|
<p>To visualize the control flow graph, you can use a nifty feature of the LLVM
|
|
'<a href="http://llvm.org/cmds/opt.html">opt</a>' tool. If you put this LLVM IR
|
|
into "t.ll" and run "<tt>llvm-as < t.ll | opt -analyze -view-cfg</tt>", <a
|
|
href="../ProgrammersManual.html#ViewGraph">a window will pop up</a> and you'll
|
|
see this graph:</p>
|
|
|
|
<div style="text-align: center"><img src="LangImpl5-cfg.png" alt="Example CFG" width="423"
|
|
height="315"></div>
|
|
|
|
<p>Another way to get this is to call "<tt>Llvm_analysis.view_function_cfg
|
|
f</tt>" or "<tt>Llvm_analysis.view_function_cfg_only f</tt>" (where <tt>f</tt>
|
|
is a "<tt>Function</tt>") either by inserting actual calls into the code and
|
|
recompiling or by calling these in the debugger. LLVM has many nice features
|
|
for visualizing various graphs.</p>
|
|
|
|
<p>Getting back to the generated code, it is fairly simple: the entry block
|
|
evaluates the conditional expression ("x" in our case here) and compares the
|
|
result to 0.0 with the "<tt><a href="../LangRef.html#i_fcmp">fcmp</a> one</tt>"
|
|
instruction ('one' is "Ordered and Not Equal"). Based on the result of this
|
|
expression, the code jumps to either the "then" or "else" blocks, which contain
|
|
the expressions for the true/false cases.</p>
|
|
|
|
<p>Once the then/else blocks are finished executing, they both branch back to the
|
|
'ifcont' block to execute the code that happens after the if/then/else. In this
|
|
case the only thing left to do is to return to the caller of the function. The
|
|
question then becomes: how does the code know which expression to return?</p>
|
|
|
|
<p>The answer to this question involves an important SSA operation: the
|
|
<a href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Phi
|
|
operation</a>. If you're not familiar with SSA, <a
|
|
href="http://en.wikipedia.org/wiki/Static_single_assignment_form">the wikipedia
|
|
article</a> is a good introduction and there are various other introductions to
|
|
it available on your favorite search engine. The short version is that
|
|
"execution" of the Phi operation requires "remembering" which block control came
|
|
from. The Phi operation takes on the value corresponding to the input control
|
|
block. In this case, if control comes in from the "then" block, it gets the
|
|
value of "calltmp". If control comes from the "else" block, it gets the value
|
|
of "calltmp1".</p>
|
|
|
|
<p>At this point, you are probably starting to think "Oh no! This means my
|
|
simple and elegant front-end will have to start generating SSA form in order to
|
|
use LLVM!". Fortunately, this is not the case, and we strongly advise
|
|
<em>not</em> implementing an SSA construction algorithm in your front-end
|
|
unless there is an amazingly good reason to do so. In practice, there are two
|
|
sorts of values that float around in code written for your average imperative
|
|
programming language that might need Phi nodes:</p>
|
|
|
|
<ol>
|
|
<li>Code that involves user variables: <tt>x = 1; x = x + 1; </tt></li>
|
|
<li>Values that are implicit in the structure of your AST, such as the Phi node
|
|
in this case.</li>
|
|
</ol>
|
|
|
|
<p>In <a href="OCamlLangImpl7.html">Chapter 7</a> of this tutorial ("mutable
|
|
variables"), we'll talk about #1
|
|
in depth. For now, just believe me that you don't need SSA construction to
|
|
handle this case. For #2, you have the choice of using the techniques that we will
|
|
describe for #1, or you can insert Phi nodes directly, if convenient. In this
|
|
case, it is really really easy to generate the Phi node, so we choose to do it
|
|
directly.</p>
|
|
|
|
<p>Okay, enough of the motivation and overview, lets generate code!</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsubsection"><a name="ifcodegen">Code Generation for
|
|
If/Then/Else</a></div>
|
|
<!-- ======================================================================= -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>In order to generate code for this, we implement the <tt>Codegen</tt> method
|
|
for <tt>IfExprAST</tt>:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
let rec codegen_expr = function
|
|
...
|
|
| Ast.If (cond, then_, else_) ->
|
|
let cond = codegen_expr cond in
|
|
|
|
(* Convert condition to a bool by comparing equal to 0.0 *)
|
|
let zero = const_float double_type 0.0 in
|
|
let cond_val = build_fcmp Fcmp.One cond zero "ifcond" builder in
|
|
</pre>
|
|
</div>
|
|
|
|
<p>This code is straightforward and similar to what we saw before. We emit the
|
|
expression for the condition, then compare that value to zero to get a truth
|
|
value as a 1-bit (bool) value.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Grab the first block so that we might later add the conditional branch
|
|
* to it at the end of the function. *)
|
|
let start_bb = insertion_block builder in
|
|
let the_function = block_parent start_bb in
|
|
|
|
let then_bb = append_block "then" the_function in
|
|
position_at_end then_bb builder;
|
|
</pre>
|
|
</div>
|
|
|
|
<p>
|
|
As opposed to the <a href="LangImpl5.html">C++ tutorial</a>, we have to build
|
|
our basic blocks bottom up since we can't have dangling BasicBlocks. We start
|
|
off by saving a pointer to the first block (which might not be the entry
|
|
block), which we'll need to build a conditional branch later. We do this by
|
|
asking the <tt>builder</tt> for the current BasicBlock. The fourth line
|
|
gets the current Function object that is being built. It gets this by the
|
|
<tt>start_bb</tt> for its "parent" (the function it is currently embedded
|
|
into).</p>
|
|
|
|
<p>Once it has that, it creates one block. It is automatically appended into
|
|
the function's list of blocks.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Emit 'then' value. *)
|
|
position_at_end then_bb builder;
|
|
let then_val = codegen_expr then_ in
|
|
|
|
(* Codegen of 'then' can change the current block, update then_bb for the
|
|
* phi. We create a new name because one is used for the phi node, and the
|
|
* other is used for the conditional branch. *)
|
|
let new_then_bb = insertion_block builder in
|
|
</pre>
|
|
</div>
|
|
|
|
<p>We move the builder to start inserting into the "then" block. Strictly
|
|
speaking, this call moves the insertion point to be at the end of the specified
|
|
block. However, since the "then" block is empty, it also starts out by
|
|
inserting at the beginning of the block. :)</p>
|
|
|
|
<p>Once the insertion point is set, we recursively codegen the "then" expression
|
|
from the AST.</p>
|
|
|
|
<p>The final line here is quite subtle, but is very important. The basic issue
|
|
is that when we create the Phi node in the merge block, we need to set up the
|
|
block/value pairs that indicate how the Phi will work. Importantly, the Phi
|
|
node expects to have an entry for each predecessor of the block in the CFG. Why
|
|
then, are we getting the current block when we just set it to ThenBB 5 lines
|
|
above? The problem is that the "Then" expression may actually itself change the
|
|
block that the Builder is emitting into if, for example, it contains a nested
|
|
"if/then/else" expression. Because calling Codegen recursively could
|
|
arbitrarily change the notion of the current block, we are required to get an
|
|
up-to-date value for code that will set up the Phi node.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Emit 'else' value. *)
|
|
let else_bb = append_block "else" the_function in
|
|
position_at_end else_bb builder;
|
|
let else_val = codegen_expr else_ in
|
|
|
|
(* Codegen of 'else' can change the current block, update else_bb for the
|
|
* phi. *)
|
|
let new_else_bb = insertion_block builder in
|
|
</pre>
|
|
</div>
|
|
|
|
<p>Code generation for the 'else' block is basically identical to codegen for
|
|
the 'then' block.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Emit merge block. *)
|
|
let merge_bb = append_block "ifcont" the_function in
|
|
position_at_end merge_bb builder;
|
|
let incoming = [(then_val, new_then_bb); (else_val, new_else_bb)] in
|
|
let phi = build_phi incoming "iftmp" builder in
|
|
</pre>
|
|
</div>
|
|
|
|
<p>The first two lines here are now familiar: the first adds the "merge" block
|
|
to the Function object. The second block changes the insertion point so that
|
|
newly created code will go into the "merge" block. Once that is done, we need
|
|
to create the PHI node and set up the block/value pairs for the PHI.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Return to the start block to add the conditional branch. *)
|
|
position_at_end start_bb builder;
|
|
ignore (build_cond_br cond_val then_bb else_bb builder);
|
|
</pre>
|
|
</div>
|
|
|
|
<p>Once the blocks are created, we can emit the conditional branch that chooses
|
|
between them. Note that creating new blocks does not implicitly affect the
|
|
IRBuilder, so it is still inserting into the block that the condition
|
|
went into. This is why we needed to save the "start" block.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Set a unconditional branch at the end of the 'then' block and the
|
|
* 'else' block to the 'merge' block. *)
|
|
position_at_end new_then_bb builder; ignore (build_br merge_bb builder);
|
|
position_at_end new_else_bb builder; ignore (build_br merge_bb builder);
|
|
|
|
(* Finally, set the builder to the end of the merge block. *)
|
|
position_at_end merge_bb builder;
|
|
|
|
phi
|
|
</pre>
|
|
</div>
|
|
|
|
<p>To finish off the blocks, we create an unconditional branch
|
|
to the merge block. One interesting (and very important) aspect of the LLVM IR
|
|
is that it <a href="../LangRef.html#functionstructure">requires all basic blocks
|
|
to be "terminated"</a> with a <a href="../LangRef.html#terminators">control flow
|
|
instruction</a> such as return or branch. This means that all control flow,
|
|
<em>including fall throughs</em> must be made explicit in the LLVM IR. If you
|
|
violate this rule, the verifier will emit an error.
|
|
|
|
<p>Finally, the CodeGen function returns the phi node as the value computed by
|
|
the if/then/else expression. In our example above, this returned value will
|
|
feed into the code for the top-level function, which will create the return
|
|
instruction.</p>
|
|
|
|
<p>Overall, we now have the ability to execute conditional code in
|
|
Kaleidoscope. With this extension, Kaleidoscope is a fairly complete language
|
|
that can calculate a wide variety of numeric functions. Next up we'll add
|
|
another useful expression that is familiar from non-functional languages...</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"><a name="for">'for' Loop Expression</a></div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>Now that we know how to add basic control flow constructs to the language,
|
|
we have the tools to add more powerful things. Lets add something more
|
|
aggressive, a 'for' expression:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
extern putchard(char);
|
|
def printstar(n)
|
|
for i = 1, i < n, 1.0 in
|
|
putchard(42); # ascii 42 = '*'
|
|
|
|
# print 100 '*' characters
|
|
printstar(100);
|
|
</pre>
|
|
</div>
|
|
|
|
<p>This expression defines a new variable ("i" in this case) which iterates from
|
|
a starting value, while the condition ("i < n" in this case) is true,
|
|
incrementing by an optional step value ("1.0" in this case). If the step value
|
|
is omitted, it defaults to 1.0. While the loop is true, it executes its
|
|
body expression. Because we don't have anything better to return, we'll just
|
|
define the loop as always returning 0.0. In the future when we have mutable
|
|
variables, it will get more useful.</p>
|
|
|
|
<p>As before, lets talk about the changes that we need to Kaleidoscope to
|
|
support this.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsubsection"><a name="forlexer">Lexer Extensions for
|
|
the 'for' Loop</a></div>
|
|
<!-- ======================================================================= -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>The lexer extensions are the same sort of thing as for if/then/else:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
... in Token.token ...
|
|
(* control *)
|
|
| If | Then | Else
|
|
<b>| For | In</b>
|
|
|
|
... in Lexer.lex_ident...
|
|
match Buffer.contents buffer with
|
|
| "def" -> [< 'Token.Def; stream >]
|
|
| "extern" -> [< 'Token.Extern; stream >]
|
|
| "if" -> [< 'Token.If; stream >]
|
|
| "then" -> [< 'Token.Then; stream >]
|
|
| "else" -> [< 'Token.Else; stream >]
|
|
<b>| "for" -> [< 'Token.For; stream >]
|
|
| "in" -> [< 'Token.In; stream >]</b>
|
|
| id -> [< 'Token.Ident id; stream >]
|
|
</pre>
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsubsection"><a name="forast">AST Extensions for
|
|
the 'for' Loop</a></div>
|
|
<!-- ======================================================================= -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>The AST variant is just as simple. It basically boils down to capturing
|
|
the variable name and the constituent expressions in the node.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
type expr =
|
|
...
|
|
(* variant for for/in. *)
|
|
| For of string * expr * expr * expr option * expr
|
|
</pre>
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsubsection"><a name="forparser">Parser Extensions for
|
|
the 'for' Loop</a></div>
|
|
<!-- ======================================================================= -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>The parser code is also fairly standard. The only interesting thing here is
|
|
handling of the optional step value. The parser code handles it by checking to
|
|
see if the second comma is present. If not, it sets the step value to null in
|
|
the AST node:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
let rec parse_primary = parser
|
|
...
|
|
(* forexpr
|
|
::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression *)
|
|
| [< 'Token.For;
|
|
'Token.Ident id ?? "expected identifier after for";
|
|
'Token.Kwd '=' ?? "expected '=' after for";
|
|
stream >] ->
|
|
begin parser
|
|
| [<
|
|
start=parse_expr;
|
|
'Token.Kwd ',' ?? "expected ',' after for";
|
|
end_=parse_expr;
|
|
stream >] ->
|
|
let step =
|
|
begin parser
|
|
| [< 'Token.Kwd ','; step=parse_expr >] -> Some step
|
|
| [< >] -> None
|
|
end stream
|
|
in
|
|
begin parser
|
|
| [< 'Token.In; body=parse_expr >] ->
|
|
Ast.For (id, start, end_, step, body)
|
|
| [< >] ->
|
|
raise (Stream.Error "expected 'in' after for")
|
|
end stream
|
|
| [< >] ->
|
|
raise (Stream.Error "expected '=' after for")
|
|
end stream
|
|
</pre>
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsubsection"><a name="forir">LLVM IR for
|
|
the 'for' Loop</a></div>
|
|
<!-- ======================================================================= -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>Now we get to the good part: the LLVM IR we want to generate for this thing.
|
|
With the simple example above, we get this LLVM IR (note that this dump is
|
|
generated with optimizations disabled for clarity):
|
|
</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
declare double @putchard(double)
|
|
|
|
define double @printstar(double %n) {
|
|
entry:
|
|
; initial value = 1.0 (inlined into phi)
|
|
br label %loop
|
|
|
|
loop: ; preds = %loop, %entry
|
|
%i = phi double [ 1.000000e+00, %entry ], [ %nextvar, %loop ]
|
|
; body
|
|
%calltmp = call double @putchard( double 4.200000e+01 )
|
|
; increment
|
|
%nextvar = add double %i, 1.000000e+00
|
|
|
|
; termination test
|
|
%cmptmp = fcmp ult double %i, %n
|
|
%booltmp = uitofp i1 %cmptmp to double
|
|
%loopcond = fcmp one double %booltmp, 0.000000e+00
|
|
br i1 %loopcond, label %loop, label %afterloop
|
|
|
|
afterloop: ; preds = %loop
|
|
; loop always returns 0.0
|
|
ret double 0.000000e+00
|
|
}
|
|
</pre>
|
|
</div>
|
|
|
|
<p>This loop contains all the same constructs we saw before: a phi node, several
|
|
expressions, and some basic blocks. Lets see how this fits together.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsubsection"><a name="forcodegen">Code Generation for
|
|
the 'for' Loop</a></div>
|
|
<!-- ======================================================================= -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>The first part of Codegen is very simple: we just output the start expression
|
|
for the loop value:</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
let rec codegen_expr = function
|
|
...
|
|
| Ast.For (var_name, start, end_, step, body) ->
|
|
(* Emit the start code first, without 'variable' in scope. *)
|
|
let start_val = codegen_expr start in
|
|
</pre>
|
|
</div>
|
|
|
|
<p>With this out of the way, the next step is to set up the LLVM basic block
|
|
for the start of the loop body. In the case above, the whole loop body is one
|
|
block, but remember that the body code itself could consist of multiple blocks
|
|
(e.g. if it contains an if/then/else or a for/in expression).</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Make the new basic block for the loop header, inserting after current
|
|
* block. *)
|
|
let preheader_bb = insertion_block builder in
|
|
let the_function = block_parent preheader_bb in
|
|
let loop_bb = append_block "loop" the_function in
|
|
|
|
(* Insert an explicit fall through from the current block to the
|
|
* loop_bb. *)
|
|
ignore (build_br loop_bb builder);
|
|
</pre>
|
|
</div>
|
|
|
|
<p>This code is similar to what we saw for if/then/else. Because we will need
|
|
it to create the Phi node, we remember the block that falls through into the
|
|
loop. Once we have that, we create the actual block that starts the loop and
|
|
create an unconditional branch for the fall-through between the two blocks.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Start insertion in loop_bb. *)
|
|
position_at_end loop_bb builder;
|
|
|
|
(* Start the PHI node with an entry for start. *)
|
|
let variable = build_phi [(start_val, preheader_bb)] var_name builder in
|
|
</pre>
|
|
</div>
|
|
|
|
<p>Now that the "preheader" for the loop is set up, we switch to emitting code
|
|
for the loop body. To begin with, we move the insertion point and create the
|
|
PHI node for the loop induction variable. Since we already know the incoming
|
|
value for the starting value, we add it to the Phi node. Note that the Phi will
|
|
eventually get a second value for the backedge, but we can't set it up yet
|
|
(because it doesn't exist!).</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Within the loop, the variable is defined equal to the PHI node. If it
|
|
* shadows an existing variable, we have to restore it, so save it
|
|
* now. *)
|
|
let old_val =
|
|
try Some (Hashtbl.find named_values var_name) with Not_found -> None
|
|
in
|
|
Hashtbl.add named_values var_name variable;
|
|
|
|
(* Emit the body of the loop. This, like any other expr, can change the
|
|
* current BB. Note that we ignore the value computed by the body, but
|
|
* don't allow an error *)
|
|
ignore (codegen_expr body);
|
|
</pre>
|
|
</div>
|
|
|
|
<p>Now the code starts to get more interesting. Our 'for' loop introduces a new
|
|
variable to the symbol table. This means that our symbol table can now contain
|
|
either function arguments or loop variables. To handle this, before we codegen
|
|
the body of the loop, we add the loop variable as the current value for its
|
|
name. Note that it is possible that there is a variable of the same name in the
|
|
outer scope. It would be easy to make this an error (emit an error and return
|
|
null if there is already an entry for VarName) but we choose to allow shadowing
|
|
of variables. In order to handle this correctly, we remember the Value that
|
|
we are potentially shadowing in <tt>old_val</tt> (which will be None if there is
|
|
no shadowed variable).</p>
|
|
|
|
<p>Once the loop variable is set into the symbol table, the code recursively
|
|
codegen's the body. This allows the body to use the loop variable: any
|
|
references to it will naturally find it in the symbol table.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Emit the step value. *)
|
|
let step_val =
|
|
match step with
|
|
| Some step -> codegen_expr step
|
|
(* If not specified, use 1.0. *)
|
|
| None -> const_float double_type 1.0
|
|
in
|
|
|
|
let next_var = build_add variable step_val "nextvar" builder in
|
|
</pre>
|
|
</div>
|
|
|
|
<p>Now that the body is emitted, we compute the next value of the iteration
|
|
variable by adding the step value, or 1.0 if it isn't present.
|
|
'<tt>next_var</tt>' will be the value of the loop variable on the next iteration
|
|
of the loop.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Compute the end condition. *)
|
|
let end_cond = codegen_expr end_ in
|
|
|
|
(* Convert condition to a bool by comparing equal to 0.0. *)
|
|
let zero = const_float double_type 0.0 in
|
|
let end_cond = build_fcmp Fcmp.One end_cond zero "loopcond" builder in
|
|
</pre>
|
|
</div>
|
|
|
|
<p>Finally, we evaluate the exit value of the loop, to determine whether the
|
|
loop should exit. This mirrors the condition evaluation for the if/then/else
|
|
statement.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Create the "after loop" block and insert it. *)
|
|
let loop_end_bb = insertion_block builder in
|
|
let after_bb = append_block "afterloop" the_function in
|
|
|
|
(* Insert the conditional branch into the end of loop_end_bb. *)
|
|
ignore (build_cond_br end_cond loop_bb after_bb builder);
|
|
|
|
(* Any new code will be inserted in after_bb. *)
|
|
position_at_end after_bb builder;
|
|
</pre>
|
|
</div>
|
|
|
|
<p>With the code for the body of the loop complete, we just need to finish up
|
|
the control flow for it. This code remembers the end block (for the phi node), then creates the block for the loop exit ("afterloop"). Based on the value of the
|
|
exit condition, it creates a conditional branch that chooses between executing
|
|
the loop again and exiting the loop. Any future code is emitted in the
|
|
"afterloop" block, so it sets the insertion position to it.</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
(* Add a new entry to the PHI node for the backedge. *)
|
|
add_incoming (next_var, loop_end_bb) variable;
|
|
|
|
(* Restore the unshadowed variable. *)
|
|
begin match old_val with
|
|
| Some old_val -> Hashtbl.add named_values var_name old_val
|
|
| None -> ()
|
|
end;
|
|
|
|
(* for expr always returns 0.0. *)
|
|
const_null double_type
|
|
</pre>
|
|
</div>
|
|
|
|
<p>The final code handles various cleanups: now that we have the
|
|
"<tt>next_var</tt>" value, we can add the incoming value to the loop PHI node.
|
|
After that, we remove the loop variable from the symbol table, so that it isn't
|
|
in scope after the for loop. Finally, code generation of the for loop always
|
|
returns 0.0, so that is what we return from <tt>Codegen.codegen_expr</tt>.</p>
|
|
|
|
<p>With this, we conclude the "adding control flow to Kaleidoscope" chapter of
|
|
the tutorial. In this chapter we added two control flow constructs, and used
|
|
them to motivate a couple of aspects of the LLVM IR that are important for
|
|
front-end implementors to know. In the next chapter of our saga, we will get
|
|
a bit crazier and add <a href="OCamlLangImpl6.html">user-defined operators</a>
|
|
to our poor innocent language.</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"><a name="code">Full Code Listing</a></div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>
|
|
Here is the complete code listing for our running example, enhanced with the
|
|
if/then/else and for expressions.. To build this example, use:
|
|
</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
# Compile
|
|
ocamlbuild toy.byte
|
|
# Run
|
|
./toy.byte
|
|
</pre>
|
|
</div>
|
|
|
|
<p>Here is the code:</p>
|
|
|
|
<dl>
|
|
<dt>_tags:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
<{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
|
|
<*.{byte,native}>: g++, use_llvm, use_llvm_analysis
|
|
<*.{byte,native}>: use_llvm_executionengine, use_llvm_target
|
|
<*.{byte,native}>: use_llvm_scalar_opts, use_bindings
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>myocamlbuild.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
open Ocamlbuild_plugin;;
|
|
|
|
ocaml_lib ~extern:true "llvm";;
|
|
ocaml_lib ~extern:true "llvm_analysis";;
|
|
ocaml_lib ~extern:true "llvm_executionengine";;
|
|
ocaml_lib ~extern:true "llvm_target";;
|
|
ocaml_lib ~extern:true "llvm_scalar_opts";;
|
|
|
|
flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);;
|
|
dep ["link"; "ocaml"; "use_bindings"] ["bindings.o"];;
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>token.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
(*===----------------------------------------------------------------------===
|
|
* Lexer Tokens
|
|
*===----------------------------------------------------------------------===*)
|
|
|
|
(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
|
|
* these others for known things. *)
|
|
type token =
|
|
(* commands *)
|
|
| Def | Extern
|
|
|
|
(* primary *)
|
|
| Ident of string | Number of float
|
|
|
|
(* unknown *)
|
|
| Kwd of char
|
|
|
|
(* control *)
|
|
| If | Then | Else
|
|
| For | In
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>lexer.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
(*===----------------------------------------------------------------------===
|
|
* Lexer
|
|
*===----------------------------------------------------------------------===*)
|
|
|
|
let rec lex = parser
|
|
(* Skip any whitespace. *)
|
|
| [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
|
|
|
|
(* identifier: [a-zA-Z][a-zA-Z0-9] *)
|
|
| [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
|
|
let buffer = Buffer.create 1 in
|
|
Buffer.add_char buffer c;
|
|
lex_ident buffer stream
|
|
|
|
(* number: [0-9.]+ *)
|
|
| [< ' ('0' .. '9' as c); stream >] ->
|
|
let buffer = Buffer.create 1 in
|
|
Buffer.add_char buffer c;
|
|
lex_number buffer stream
|
|
|
|
(* Comment until end of line. *)
|
|
| [< ' ('#'); stream >] ->
|
|
lex_comment stream
|
|
|
|
(* Otherwise, just return the character as its ascii value. *)
|
|
| [< 'c; stream >] ->
|
|
[< 'Token.Kwd c; lex stream >]
|
|
|
|
(* end of stream. *)
|
|
| [< >] -> [< >]
|
|
|
|
and lex_number buffer = parser
|
|
| [< ' ('0' .. '9' | '.' as c); stream >] ->
|
|
Buffer.add_char buffer c;
|
|
lex_number buffer stream
|
|
| [< stream=lex >] ->
|
|
[< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
|
|
|
|
and lex_ident buffer = parser
|
|
| [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
|
|
Buffer.add_char buffer c;
|
|
lex_ident buffer stream
|
|
| [< stream=lex >] ->
|
|
match Buffer.contents buffer with
|
|
| "def" -> [< 'Token.Def; stream >]
|
|
| "extern" -> [< 'Token.Extern; stream >]
|
|
| "if" -> [< 'Token.If; stream >]
|
|
| "then" -> [< 'Token.Then; stream >]
|
|
| "else" -> [< 'Token.Else; stream >]
|
|
| "for" -> [< 'Token.For; stream >]
|
|
| "in" -> [< 'Token.In; stream >]
|
|
| id -> [< 'Token.Ident id; stream >]
|
|
|
|
and lex_comment = parser
|
|
| [< ' ('\n'); stream=lex >] -> stream
|
|
| [< 'c; e=lex_comment >] -> e
|
|
| [< >] -> [< >]
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>ast.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
(*===----------------------------------------------------------------------===
|
|
* Abstract Syntax Tree (aka Parse Tree)
|
|
*===----------------------------------------------------------------------===*)
|
|
|
|
(* expr - Base type for all expression nodes. *)
|
|
type expr =
|
|
(* variant for numeric literals like "1.0". *)
|
|
| Number of float
|
|
|
|
(* variant for referencing a variable, like "a". *)
|
|
| Variable of string
|
|
|
|
(* variant for a binary operator. *)
|
|
| Binary of char * expr * expr
|
|
|
|
(* variant for function calls. *)
|
|
| Call of string * expr array
|
|
|
|
(* variant for if/then/else. *)
|
|
| If of expr * expr * expr
|
|
|
|
(* variant for for/in. *)
|
|
| For of string * expr * expr * expr option * expr
|
|
|
|
(* proto - This type represents the "prototype" for a function, which captures
|
|
* its name, and its argument names (thus implicitly the number of arguments the
|
|
* function takes). *)
|
|
type proto = Prototype of string * string array
|
|
|
|
(* func - This type represents a function definition itself. *)
|
|
type func = Function of proto * expr
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>parser.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
(*===---------------------------------------------------------------------===
|
|
* Parser
|
|
*===---------------------------------------------------------------------===*)
|
|
|
|
(* binop_precedence - This holds the precedence for each binary operator that is
|
|
* defined *)
|
|
let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
|
|
|
|
(* precedence - Get the precedence of the pending binary operator token. *)
|
|
let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
|
|
|
|
(* primary
|
|
* ::= identifier
|
|
* ::= numberexpr
|
|
* ::= parenexpr
|
|
* ::= ifexpr
|
|
* ::= forexpr *)
|
|
let rec parse_primary = parser
|
|
(* numberexpr ::= number *)
|
|
| [< 'Token.Number n >] -> Ast.Number n
|
|
|
|
(* parenexpr ::= '(' expression ')' *)
|
|
| [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
|
|
|
|
(* identifierexpr
|
|
* ::= identifier
|
|
* ::= identifier '(' argumentexpr ')' *)
|
|
| [< 'Token.Ident id; stream >] ->
|
|
let rec parse_args accumulator = parser
|
|
| [< e=parse_expr; stream >] ->
|
|
begin parser
|
|
| [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
|
|
| [< >] -> e :: accumulator
|
|
end stream
|
|
| [< >] -> accumulator
|
|
in
|
|
let rec parse_ident id = parser
|
|
(* Call. *)
|
|
| [< 'Token.Kwd '(';
|
|
args=parse_args [];
|
|
'Token.Kwd ')' ?? "expected ')'">] ->
|
|
Ast.Call (id, Array.of_list (List.rev args))
|
|
|
|
(* Simple variable ref. *)
|
|
| [< >] -> Ast.Variable id
|
|
in
|
|
parse_ident id stream
|
|
|
|
(* ifexpr ::= 'if' expr 'then' expr 'else' expr *)
|
|
| [< 'Token.If; c=parse_expr;
|
|
'Token.Then ?? "expected 'then'"; t=parse_expr;
|
|
'Token.Else ?? "expected 'else'"; e=parse_expr >] ->
|
|
Ast.If (c, t, e)
|
|
|
|
(* forexpr
|
|
::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression *)
|
|
| [< 'Token.For;
|
|
'Token.Ident id ?? "expected identifier after for";
|
|
'Token.Kwd '=' ?? "expected '=' after for";
|
|
stream >] ->
|
|
begin parser
|
|
| [<
|
|
start=parse_expr;
|
|
'Token.Kwd ',' ?? "expected ',' after for";
|
|
end_=parse_expr;
|
|
stream >] ->
|
|
let step =
|
|
begin parser
|
|
| [< 'Token.Kwd ','; step=parse_expr >] -> Some step
|
|
| [< >] -> None
|
|
end stream
|
|
in
|
|
begin parser
|
|
| [< 'Token.In; body=parse_expr >] ->
|
|
Ast.For (id, start, end_, step, body)
|
|
| [< >] ->
|
|
raise (Stream.Error "expected 'in' after for")
|
|
end stream
|
|
| [< >] ->
|
|
raise (Stream.Error "expected '=' after for")
|
|
end stream
|
|
|
|
| [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
|
|
|
|
(* binoprhs
|
|
* ::= ('+' primary)* *)
|
|
and parse_bin_rhs expr_prec lhs stream =
|
|
match Stream.peek stream with
|
|
(* If this is a binop, find its precedence. *)
|
|
| Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
|
|
let token_prec = precedence c in
|
|
|
|
(* If this is a binop that binds at least as tightly as the current binop,
|
|
* consume it, otherwise we are done. *)
|
|
if token_prec < expr_prec then lhs else begin
|
|
(* Eat the binop. *)
|
|
Stream.junk stream;
|
|
|
|
(* Parse the primary expression after the binary operator. *)
|
|
let rhs = parse_primary stream in
|
|
|
|
(* Okay, we know this is a binop. *)
|
|
let rhs =
|
|
match Stream.peek stream with
|
|
| Some (Token.Kwd c2) ->
|
|
(* If BinOp binds less tightly with rhs than the operator after
|
|
* rhs, let the pending operator take rhs as its lhs. *)
|
|
let next_prec = precedence c2 in
|
|
if token_prec < next_prec
|
|
then parse_bin_rhs (token_prec + 1) rhs stream
|
|
else rhs
|
|
| _ -> rhs
|
|
in
|
|
|
|
(* Merge lhs/rhs. *)
|
|
let lhs = Ast.Binary (c, lhs, rhs) in
|
|
parse_bin_rhs expr_prec lhs stream
|
|
end
|
|
| _ -> lhs
|
|
|
|
(* expression
|
|
* ::= primary binoprhs *)
|
|
and parse_expr = parser
|
|
| [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
|
|
|
|
(* prototype
|
|
* ::= id '(' id* ')' *)
|
|
let parse_prototype =
|
|
let rec parse_args accumulator = parser
|
|
| [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
|
|
| [< >] -> accumulator
|
|
in
|
|
|
|
parser
|
|
| [< 'Token.Ident id;
|
|
'Token.Kwd '(' ?? "expected '(' in prototype";
|
|
args=parse_args [];
|
|
'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
|
|
(* success. *)
|
|
Ast.Prototype (id, Array.of_list (List.rev args))
|
|
|
|
| [< >] ->
|
|
raise (Stream.Error "expected function name in prototype")
|
|
|
|
(* definition ::= 'def' prototype expression *)
|
|
let parse_definition = parser
|
|
| [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
|
|
Ast.Function (p, e)
|
|
|
|
(* toplevelexpr ::= expression *)
|
|
let parse_toplevel = parser
|
|
| [< e=parse_expr >] ->
|
|
(* Make an anonymous proto. *)
|
|
Ast.Function (Ast.Prototype ("", [||]), e)
|
|
|
|
(* external ::= 'extern' prototype *)
|
|
let parse_extern = parser
|
|
| [< 'Token.Extern; e=parse_prototype >] -> e
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>codegen.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
(*===----------------------------------------------------------------------===
|
|
* Code Generation
|
|
*===----------------------------------------------------------------------===*)
|
|
|
|
open Llvm
|
|
|
|
exception Error of string
|
|
|
|
let context = global_context ()
|
|
let the_module = create_module context "my cool jit"
|
|
let builder = builder context
|
|
let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
|
|
|
|
let rec codegen_expr = function
|
|
| Ast.Number n -> const_float double_type n
|
|
| Ast.Variable name ->
|
|
(try Hashtbl.find named_values name with
|
|
| Not_found -> raise (Error "unknown variable name"))
|
|
| Ast.Binary (op, lhs, rhs) ->
|
|
let lhs_val = codegen_expr lhs in
|
|
let rhs_val = codegen_expr rhs in
|
|
begin
|
|
match op with
|
|
| '+' -> build_add lhs_val rhs_val "addtmp" builder
|
|
| '-' -> build_sub lhs_val rhs_val "subtmp" builder
|
|
| '*' -> build_mul lhs_val rhs_val "multmp" builder
|
|
| '<' ->
|
|
(* Convert bool 0/1 to double 0.0 or 1.0 *)
|
|
let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
|
|
build_uitofp i double_type "booltmp" builder
|
|
| _ -> raise (Error "invalid binary operator")
|
|
end
|
|
| Ast.Call (callee, args) ->
|
|
(* Look up the name in the module table. *)
|
|
let callee =
|
|
match lookup_function callee the_module with
|
|
| Some callee -> callee
|
|
| None -> raise (Error "unknown function referenced")
|
|
in
|
|
let params = params callee in
|
|
|
|
(* If argument mismatch error. *)
|
|
if Array.length params == Array.length args then () else
|
|
raise (Error "incorrect # arguments passed");
|
|
let args = Array.map codegen_expr args in
|
|
build_call callee args "calltmp" builder
|
|
| Ast.If (cond, then_, else_) ->
|
|
let cond = codegen_expr cond in
|
|
|
|
(* Convert condition to a bool by comparing equal to 0.0 *)
|
|
let zero = const_float double_type 0.0 in
|
|
let cond_val = build_fcmp Fcmp.One cond zero "ifcond" builder in
|
|
|
|
(* Grab the first block so that we might later add the conditional branch
|
|
* to it at the end of the function. *)
|
|
let start_bb = insertion_block builder in
|
|
let the_function = block_parent start_bb in
|
|
|
|
let then_bb = append_block "then" the_function in
|
|
|
|
(* Emit 'then' value. *)
|
|
position_at_end then_bb builder;
|
|
let then_val = codegen_expr then_ in
|
|
|
|
(* Codegen of 'then' can change the current block, update then_bb for the
|
|
* phi. We create a new name because one is used for the phi node, and the
|
|
* other is used for the conditional branch. *)
|
|
let new_then_bb = insertion_block builder in
|
|
|
|
(* Emit 'else' value. *)
|
|
let else_bb = append_block "else" the_function in
|
|
position_at_end else_bb builder;
|
|
let else_val = codegen_expr else_ in
|
|
|
|
(* Codegen of 'else' can change the current block, update else_bb for the
|
|
* phi. *)
|
|
let new_else_bb = insertion_block builder in
|
|
|
|
(* Emit merge block. *)
|
|
let merge_bb = append_block "ifcont" the_function in
|
|
position_at_end merge_bb builder;
|
|
let incoming = [(then_val, new_then_bb); (else_val, new_else_bb)] in
|
|
let phi = build_phi incoming "iftmp" builder in
|
|
|
|
(* Return to the start block to add the conditional branch. *)
|
|
position_at_end start_bb builder;
|
|
ignore (build_cond_br cond_val then_bb else_bb builder);
|
|
|
|
(* Set a unconditional branch at the end of the 'then' block and the
|
|
* 'else' block to the 'merge' block. *)
|
|
position_at_end new_then_bb builder; ignore (build_br merge_bb builder);
|
|
position_at_end new_else_bb builder; ignore (build_br merge_bb builder);
|
|
|
|
(* Finally, set the builder to the end of the merge block. *)
|
|
position_at_end merge_bb builder;
|
|
|
|
phi
|
|
| Ast.For (var_name, start, end_, step, body) ->
|
|
(* Emit the start code first, without 'variable' in scope. *)
|
|
let start_val = codegen_expr start in
|
|
|
|
(* Make the new basic block for the loop header, inserting after current
|
|
* block. *)
|
|
let preheader_bb = insertion_block builder in
|
|
let the_function = block_parent preheader_bb in
|
|
let loop_bb = append_block "loop" the_function in
|
|
|
|
(* Insert an explicit fall through from the current block to the
|
|
* loop_bb. *)
|
|
ignore (build_br loop_bb builder);
|
|
|
|
(* Start insertion in loop_bb. *)
|
|
position_at_end loop_bb builder;
|
|
|
|
(* Start the PHI node with an entry for start. *)
|
|
let variable = build_phi [(start_val, preheader_bb)] var_name builder in
|
|
|
|
(* Within the loop, the variable is defined equal to the PHI node. If it
|
|
* shadows an existing variable, we have to restore it, so save it
|
|
* now. *)
|
|
let old_val =
|
|
try Some (Hashtbl.find named_values var_name) with Not_found -> None
|
|
in
|
|
Hashtbl.add named_values var_name variable;
|
|
|
|
(* Emit the body of the loop. This, like any other expr, can change the
|
|
* current BB. Note that we ignore the value computed by the body, but
|
|
* don't allow an error *)
|
|
ignore (codegen_expr body);
|
|
|
|
(* Emit the step value. *)
|
|
let step_val =
|
|
match step with
|
|
| Some step -> codegen_expr step
|
|
(* If not specified, use 1.0. *)
|
|
| None -> const_float double_type 1.0
|
|
in
|
|
|
|
let next_var = build_add variable step_val "nextvar" builder in
|
|
|
|
(* Compute the end condition. *)
|
|
let end_cond = codegen_expr end_ in
|
|
|
|
(* Convert condition to a bool by comparing equal to 0.0. *)
|
|
let zero = const_float double_type 0.0 in
|
|
let end_cond = build_fcmp Fcmp.One end_cond zero "loopcond" builder in
|
|
|
|
(* Create the "after loop" block and insert it. *)
|
|
let loop_end_bb = insertion_block builder in
|
|
let after_bb = append_block "afterloop" the_function in
|
|
|
|
(* Insert the conditional branch into the end of loop_end_bb. *)
|
|
ignore (build_cond_br end_cond loop_bb after_bb builder);
|
|
|
|
(* Any new code will be inserted in after_bb. *)
|
|
position_at_end after_bb builder;
|
|
|
|
(* Add a new entry to the PHI node for the backedge. *)
|
|
add_incoming (next_var, loop_end_bb) variable;
|
|
|
|
(* Restore the unshadowed variable. *)
|
|
begin match old_val with
|
|
| Some old_val -> Hashtbl.add named_values var_name old_val
|
|
| None -> ()
|
|
end;
|
|
|
|
(* for expr always returns 0.0. *)
|
|
const_null double_type
|
|
|
|
let codegen_proto = function
|
|
| Ast.Prototype (name, args) ->
|
|
(* Make the function type: double(double,double) etc. *)
|
|
let doubles = Array.make (Array.length args) double_type in
|
|
let ft = function_type double_type doubles in
|
|
let f =
|
|
match lookup_function name the_module with
|
|
| None -> declare_function name ft the_module
|
|
|
|
(* If 'f' conflicted, there was already something named 'name'. If it
|
|
* has a body, don't allow redefinition or reextern. *)
|
|
| Some f ->
|
|
(* If 'f' already has a body, reject this. *)
|
|
if block_begin f <> At_end f then
|
|
raise (Error "redefinition of function");
|
|
|
|
(* If 'f' took a different number of arguments, reject. *)
|
|
if element_type (type_of f) <> ft then
|
|
raise (Error "redefinition of function with different # args");
|
|
f
|
|
in
|
|
|
|
(* Set names for all arguments. *)
|
|
Array.iteri (fun i a ->
|
|
let n = args.(i) in
|
|
set_value_name n a;
|
|
Hashtbl.add named_values n a;
|
|
) (params f);
|
|
f
|
|
|
|
let codegen_func the_fpm = function
|
|
| Ast.Function (proto, body) ->
|
|
Hashtbl.clear named_values;
|
|
let the_function = codegen_proto proto in
|
|
|
|
(* Create a new basic block to start insertion into. *)
|
|
let bb = append_block "entry" the_function in
|
|
position_at_end bb builder;
|
|
|
|
try
|
|
let ret_val = codegen_expr body in
|
|
|
|
(* Finish off the function. *)
|
|
let _ = build_ret ret_val builder in
|
|
|
|
(* Validate the generated code, checking for consistency. *)
|
|
Llvm_analysis.assert_valid_function the_function;
|
|
|
|
(* Optimize the function. *)
|
|
let _ = PassManager.run_function the_function the_fpm in
|
|
|
|
the_function
|
|
with e ->
|
|
delete_function the_function;
|
|
raise e
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>toplevel.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
(*===----------------------------------------------------------------------===
|
|
* Top-Level parsing and JIT Driver
|
|
*===----------------------------------------------------------------------===*)
|
|
|
|
open Llvm
|
|
open Llvm_executionengine
|
|
|
|
(* top ::= definition | external | expression | ';' *)
|
|
let rec main_loop the_fpm the_execution_engine stream =
|
|
match Stream.peek stream with
|
|
| None -> ()
|
|
|
|
(* ignore top-level semicolons. *)
|
|
| Some (Token.Kwd ';') ->
|
|
Stream.junk stream;
|
|
main_loop the_fpm the_execution_engine stream
|
|
|
|
| Some token ->
|
|
begin
|
|
try match token with
|
|
| Token.Def ->
|
|
let e = Parser.parse_definition stream in
|
|
print_endline "parsed a function definition.";
|
|
dump_value (Codegen.codegen_func the_fpm e);
|
|
| Token.Extern ->
|
|
let e = Parser.parse_extern stream in
|
|
print_endline "parsed an extern.";
|
|
dump_value (Codegen.codegen_proto e);
|
|
| _ ->
|
|
(* Evaluate a top-level expression into an anonymous function. *)
|
|
let e = Parser.parse_toplevel stream in
|
|
print_endline "parsed a top-level expr";
|
|
let the_function = Codegen.codegen_func the_fpm e in
|
|
dump_value the_function;
|
|
|
|
(* JIT the function, returning a function pointer. *)
|
|
let result = ExecutionEngine.run_function the_function [||]
|
|
the_execution_engine in
|
|
|
|
print_string "Evaluated to ";
|
|
print_float (GenericValue.as_float double_type result);
|
|
print_newline ();
|
|
with Stream.Error s | Codegen.Error s ->
|
|
(* Skip token for error recovery. *)
|
|
Stream.junk stream;
|
|
print_endline s;
|
|
end;
|
|
print_string "ready> "; flush stdout;
|
|
main_loop the_fpm the_execution_engine stream
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>toy.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
(*===----------------------------------------------------------------------===
|
|
* Main driver code.
|
|
*===----------------------------------------------------------------------===*)
|
|
|
|
open Llvm
|
|
open Llvm_executionengine
|
|
open Llvm_target
|
|
open Llvm_scalar_opts
|
|
|
|
let main () =
|
|
ignore (initialize_native_target ());
|
|
|
|
(* Install standard binary operators.
|
|
* 1 is the lowest precedence. *)
|
|
Hashtbl.add Parser.binop_precedence '<' 10;
|
|
Hashtbl.add Parser.binop_precedence '+' 20;
|
|
Hashtbl.add Parser.binop_precedence '-' 20;
|
|
Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
|
|
|
|
(* Prime the first token. *)
|
|
print_string "ready> "; flush stdout;
|
|
let stream = Lexer.lex (Stream.of_channel stdin) in
|
|
|
|
(* Create the JIT. *)
|
|
let the_module_provider = ModuleProvider.create Codegen.the_module in
|
|
let the_execution_engine = ExecutionEngine.create the_module_provider in
|
|
let the_fpm = PassManager.create_function the_module_provider in
|
|
|
|
(* Set up the optimizer pipeline. Start with registering info about how the
|
|
* target lays out data structures. *)
|
|
TargetData.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
|
|
|
|
(* Do simple "peephole" optimizations and bit-twiddling optzn. *)
|
|
add_instruction_combining the_fpm;
|
|
|
|
(* reassociate expressions. *)
|
|
add_reassociation the_fpm;
|
|
|
|
(* Eliminate Common SubExpressions. *)
|
|
add_gvn the_fpm;
|
|
|
|
(* Simplify the control flow graph (deleting unreachable blocks, etc). *)
|
|
add_cfg_simplification the_fpm;
|
|
|
|
ignore (PassManager.initialize the_fpm);
|
|
|
|
(* Run the main "interpreter loop" now. *)
|
|
Toplevel.main_loop the_fpm the_execution_engine stream;
|
|
|
|
(* Print out all the generated code. *)
|
|
dump_module Codegen.the_module
|
|
;;
|
|
|
|
main ()
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>bindings.c</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
#include <stdio.h>
|
|
|
|
/* putchard - putchar that takes a double and returns 0. */
|
|
extern double putchard(double X) {
|
|
putchar((char)X);
|
|
return 0;
|
|
}
|
|
</pre>
|
|
</dd>
|
|
</dl>
|
|
|
|
<a href="OCamlLangImpl6.html">Next: Extending the language: user-defined
|
|
operators</a>
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<hr>
|
|
<address>
|
|
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
|
|
src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
|
|
<a href="http://validator.w3.org/check/referer"><img
|
|
src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
|
|
|
|
<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
|
|
<a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a><br>
|
|
<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
|
|
Last modified: $Date: 2007-10-17 11:05:13 -0700 (Wed, 17 Oct 2007) $
|
|
</address>
|
|
</body>
|
|
</html>
|