<body>
-<div class="doc_title">Kaleidoscope: Adding JIT and Optimizer Support</div>
+<h1>Kaleidoscope: Adding JIT and Optimizer Support</h1>
<ul>
<li><a href="index.html">Up to Tutorial Index</a></li>
</div>
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="intro">Chapter 4 Introduction</a></div>
+<h2><a name="intro">Chapter 4 Introduction</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>Welcome to Chapter 4 of the "<a href="index.html">Implementing a language
with LLVM</a>" tutorial. Chapters 1-3 described the implementation of a simple
</div>
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="trivialconstfold">Trivial Constant
-Folding</a></div>
+<h2><a name="trivialconstfold">Trivial Constant Folding</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p><b>Note:</b> the default <tt>IRBuilder</tt> now always includes the constant
folding optimisations below.<p>
Read function definition:
define double @test(double %x) {
entry:
- %addtmp = add double 1.000000e+00, 2.000000e+00
- %addtmp1 = add double %addtmp, %x
+ %addtmp = fadd double 1.000000e+00, 2.000000e+00
+ %addtmp1 = fadd double %addtmp, %x
ret double %addtmp1
}
</pre>
Read function definition:
define double @test(double %x) {
entry:
- %addtmp = add double 3.000000e+00, %x
+ %addtmp = fadd double 3.000000e+00, %x
ret double %addtmp
}
</pre>
ready> Read function definition:
define double @test(double %x) {
entry:
- %addtmp = add double 3.000000e+00, %x
- %addtmp1 = add double %x, 3.000000e+00
- %multmp = mul double %addtmp, %addtmp1
+ %addtmp = fadd double 3.000000e+00, %x
+ %addtmp1 = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp1
ret double %multmp
}
</pre>
</div>
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="optimizerpasses">LLVM Optimization
- Passes</a></div>
+<h2><a name="optimizerpasses">LLVM Optimization Passes</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>LLVM provides many optimization passes, which do many different sorts of
things and have different tradeoffs. Unlike other systems, LLVM doesn't hold
<div class="doc_code">
<pre>
(* 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
+ let the_execution_engine = ExecutionEngine.create Codegen.the_module in
+ let the_fpm = PassManager.create_function Codegen.the_module in
(* Set up the optimizer pipeline. Start with registering info about how the
* target lays out data structures. *)
</pre>
</div>
-<p>This code defines two values, an <tt>Llvm.llmoduleprovider</tt> and a
-<tt>Llvm.PassManager.t</tt>. The former is basically a wrapper around our
-<tt>Llvm.llmodule</tt> that the <tt>Llvm.PassManager.t</tt> requires. It
-provides certain flexibility that we're not going to take advantage of here,
-so I won't dive into any details about it.</p>
-
<p>The meat of the matter here, is the definition of "<tt>the_fpm</tt>". It
-requires a pointer to the <tt>the_module</tt> (through the
-<tt>the_module_provider</tt>) to construct itself. Once it is set up, we use a
-series of "add" calls to add a bunch of LLVM passes. The first pass is
-basically boilerplate, it adds a pass so that later optimizations know how the
-data structures in the program are layed out. The
+requires a pointer to the <tt>the_module</tt> to construct itself. Once it is
+set up, we use a series of "add" calls to add a bunch of LLVM passes. The
+first pass is basically boilerplate, it adds a pass so that later optimizations
+know how the data structures in the program are laid out. The
"<tt>the_execution_engine</tt>" variable is related to the JIT, which we will
get to in the next section.</p>
ready> Read function definition:
define double @test(double %x) {
entry:
- %addtmp = add double %x, 3.000000e+00
- %multmp = mul double %addtmp, %addtmp
+ %addtmp = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp
ret double %multmp
}
</pre>
<p>LLVM provides a wide variety of optimizations that can be used in certain
circumstances. Some <a href="../Passes.html">documentation about the various
passes</a> is available, but it isn't very complete. Another good source of
-ideas can come from looking at the passes that <tt>llvm-gcc</tt> or
-<tt>llvm-ld</tt> run to get started. The "<tt>opt</tt>" tool allows you to
-experiment with passes from the command line, so you can see if they do
-anything.</p>
+ideas can come from looking at the passes that <tt>Clang</tt> runs to get
+started. The "<tt>opt</tt>" tool allows you to experiment with passes from the
+command line, so you can see if they do anything.</p>
<p>Now that we have reasonable code coming out of our front-end, lets talk about
executing it!</p>
</div>
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="jit">Adding a JIT Compiler</a></div>
+<h2><a name="jit">Adding a JIT Compiler</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>Code that is available in LLVM IR can have a wide variety of tools
applied to it. For example, you can run optimizations on it (as we did above),
let main () =
...
<b>(* Create the JIT. *)
- let the_module_provider = ModuleProvider.create Codegen.the_module in
- let the_execution_engine = ExecutionEngine.create the_module_provider in</b>
+ let the_execution_engine = ExecutionEngine.create Codegen.the_module in</b>
...
</pre>
</div>
the_execution_engine in
print_string "Evaluated to ";
- print_float (GenericValue.as_float double_type result);
+ print_float (GenericValue.as_float Codegen.double_type result);
print_newline ();
</pre>
</div>
Read function definition:
define double @testfunc(double %x, double %y) {
entry:
- %multmp = mul double %y, 2.000000e+00
- %addtmp = add double %multmp, %x
+ %multmp = fmul double %y, 2.000000e+00
+ %addtmp = fadd double %multmp, %x
ret double %addtmp
}
ready> <b>testfunc(4, 10);</b>
define double @""() {
entry:
- %calltmp = call double @testfunc( double 4.000000e+00, double 1.000000e+01 )
+ %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
ret double %calltmp
}
<p>This illustrates that we can now call user code, but there is something a bit
subtle going on here. Note that we only invoke the JIT on the anonymous
-functions that <em>call testfunc</em>, but we never invoked it on <em>testfunc
-</em>itself.</p>
-
-<p>What actually happened here is that the anonymous function was JIT'd when
-requested. When the Kaleidoscope app calls through the function pointer that is
-returned, the anonymous function starts executing. It ends up making the call
-to the "testfunc" function, and ends up in a stub that invokes the JIT, lazily,
-on testfunc. Once the JIT finishes lazily compiling testfunc,
-it returns and the code re-executes the call.</p>
-
-<p>In summary, the JIT will lazily JIT code, on the fly, as it is needed. The
-JIT provides a number of other more advanced interfaces for things like freeing
-allocated machine code, rejit'ing functions to update them, etc. However, even
-with this simple code, we get some surprisingly powerful capabilities - check
-this out (I removed the dump of the anonymous functions, you should get the idea
-by now :) :</p>
+functions that <em>call testfunc</em>, but we never invoked it
+on <em>testfunc</em> itself. What actually happened here is that the JIT
+scanned for all non-JIT'd functions transitively called from the anonymous
+function and compiled all of them before returning
+from <tt>run_function</tt>.</p>
+
+<p>The JIT provides a number of other more advanced interfaces for things like
+freeing allocated machine code, rejit'ing functions to update them, etc.
+However, even with this simple code, we get some surprisingly powerful
+capabilities - check this out (I removed the dump of the anonymous functions,
+you should get the idea by now :) :</p>
<div class="doc_code">
<pre>
Read function definition:
define double @foo(double %x) {
entry:
- %calltmp = call double @sin( double %x )
- %multmp = mul double %calltmp, %calltmp
- %calltmp2 = call double @cos( double %x )
- %multmp4 = mul double %calltmp2, %calltmp2
- %addtmp = add double %multmp, %multmp4
+ %calltmp = call double @sin(double %x)
+ %multmp = fmul double %calltmp, %calltmp
+ %calltmp2 = call double @cos(double %x)
+ %multmp4 = fmul double %calltmp2, %calltmp2
+ %addtmp = fadd double %multmp, %multmp4
ret double %addtmp
}
get resolved. It allows you to establish explicit mappings between IR objects
and addresses (useful for LLVM global variables that you want to map to static
tables, for example), allows you to dynamically decide on the fly based on the
-function name, and even allows you to have the JIT abort itself if any lazy
-compilation is attempted.</p>
+function name, and even allows you to have the JIT compile functions lazily the
+first time they're called.</p>
<p>One interesting application of this is that we can now extend the language
by writing arbitrary C code to implement operations. For example, if we add:
</div>
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="code">Full Code Listing</a></div>
+<h2><a name="code">Full Code Listing</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>
Here is the complete code listing for our running example, enhanced with the
let the_module = create_module context "my cool jit"
let builder = builder context
let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
+let double_type = double_type context
let rec codegen_expr = function
| Ast.Number n -> const_float double_type n
let the_function = codegen_proto proto in
(* Create a new basic block to start insertion into. *)
- let bb = append_block "entry" the_function in
+ let bb = append_block context "entry" the_function in
position_at_end bb builder;
try
the_execution_engine in
print_string "Evaluated to ";
- print_float (GenericValue.as_float double_type result);
+ print_float (GenericValue.as_float Codegen.double_type result);
print_newline ();
with Stream.Error s | Codegen.Error s ->
(* Skip token for error recovery. *)
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
+ let the_execution_engine = ExecutionEngine.create Codegen.the_module in
+ let the_fpm = PassManager.create_function Codegen.the_module 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;
+ add_instruction_combination the_fpm;
(* reassociate expressions. *)
add_reassociation the_fpm;
<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) $
+ <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date$
</address>
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