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1027 lines
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1027 lines
35 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<title>Kaleidoscope: Adding JIT and Optimizer Support</title>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="author" content="Chris Lattner">
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<meta name="author" content="Erick Tryzelaar">
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<link rel="stylesheet" href="../_static/llvm.css" type="text/css">
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</head>
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<body>
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<h1>Kaleidoscope: Adding JIT and Optimizer Support</h1>
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<ul>
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<li><a href="index.html">Up to Tutorial Index</a></li>
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<li>Chapter 4
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<ol>
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<li><a href="#intro">Chapter 4 Introduction</a></li>
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<li><a href="#trivialconstfold">Trivial Constant Folding</a></li>
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<li><a href="#optimizerpasses">LLVM Optimization Passes</a></li>
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<li><a href="#jit">Adding a JIT Compiler</a></li>
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<li><a href="#code">Full Code Listing</a></li>
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</ol>
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</li>
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<li><a href="OCamlLangImpl5.html">Chapter 5</a>: Extending the Language: Control
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Flow</li>
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</ul>
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<div class="doc_author">
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<p>
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Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
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and <a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a>
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</p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="intro">Chapter 4 Introduction</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p>Welcome to Chapter 4 of the "<a href="index.html">Implementing a language
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with LLVM</a>" tutorial. Chapters 1-3 described the implementation of a simple
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language and added support for generating LLVM IR. This chapter describes
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two new techniques: adding optimizer support to your language, and adding JIT
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compiler support. These additions will demonstrate how to get nice, efficient code
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for the Kaleidoscope language.</p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="trivialconstfold">Trivial Constant Folding</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p><b>Note:</b> the default <tt>IRBuilder</tt> now always includes the constant
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folding optimisations below.<p>
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<p>
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Our demonstration for Chapter 3 is elegant and easy to extend. Unfortunately,
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it does not produce wonderful code. For example, when compiling simple code,
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we don't get obvious optimizations:</p>
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<div class="doc_code">
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<pre>
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ready> <b>def test(x) 1+2+x;</b>
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Read function definition:
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define double @test(double %x) {
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entry:
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%addtmp = fadd double 1.000000e+00, 2.000000e+00
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%addtmp1 = fadd double %addtmp, %x
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ret double %addtmp1
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}
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</pre>
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</div>
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<p>This code is a very, very literal transcription of the AST built by parsing
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the input. As such, this transcription lacks optimizations like constant folding
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(we'd like to get "<tt>add x, 3.0</tt>" in the example above) as well as other
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more important optimizations. Constant folding, in particular, is a very common
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and very important optimization: so much so that many language implementors
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implement constant folding support in their AST representation.</p>
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<p>With LLVM, you don't need this support in the AST. Since all calls to build
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LLVM IR go through the LLVM builder, it would be nice if the builder itself
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checked to see if there was a constant folding opportunity when you call it.
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If so, it could just do the constant fold and return the constant instead of
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creating an instruction. This is exactly what the <tt>LLVMFoldingBuilder</tt>
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class does.
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<p>All we did was switch from <tt>LLVMBuilder</tt> to
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<tt>LLVMFoldingBuilder</tt>. Though we change no other code, we now have all of our
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instructions implicitly constant folded without us having to do anything
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about it. For example, the input above now compiles to:</p>
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<div class="doc_code">
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<pre>
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ready> <b>def test(x) 1+2+x;</b>
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Read function definition:
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define double @test(double %x) {
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entry:
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%addtmp = fadd double 3.000000e+00, %x
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ret double %addtmp
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}
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</pre>
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</div>
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<p>Well, that was easy :). In practice, we recommend always using
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<tt>LLVMFoldingBuilder</tt> when generating code like this. It has no
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"syntactic overhead" for its use (you don't have to uglify your compiler with
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constant checks everywhere) and it can dramatically reduce the amount of
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LLVM IR that is generated in some cases (particular for languages with a macro
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preprocessor or that use a lot of constants).</p>
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<p>On the other hand, the <tt>LLVMFoldingBuilder</tt> is limited by the fact
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that it does all of its analysis inline with the code as it is built. If you
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take a slightly more complex example:</p>
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<div class="doc_code">
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<pre>
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ready> <b>def test(x) (1+2+x)*(x+(1+2));</b>
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ready> Read function definition:
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define double @test(double %x) {
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entry:
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%addtmp = fadd double 3.000000e+00, %x
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%addtmp1 = fadd double %x, 3.000000e+00
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%multmp = fmul double %addtmp, %addtmp1
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ret double %multmp
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}
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</pre>
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</div>
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<p>In this case, the LHS and RHS of the multiplication are the same value. We'd
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really like to see this generate "<tt>tmp = x+3; result = tmp*tmp;</tt>" instead
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of computing "<tt>x*3</tt>" twice.</p>
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<p>Unfortunately, no amount of local analysis will be able to detect and correct
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this. This requires two transformations: reassociation of expressions (to
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make the add's lexically identical) and Common Subexpression Elimination (CSE)
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to delete the redundant add instruction. Fortunately, LLVM provides a broad
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range of optimizations that you can use, in the form of "passes".</p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="optimizerpasses">LLVM Optimization Passes</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p>LLVM provides many optimization passes, which do many different sorts of
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things and have different tradeoffs. Unlike other systems, LLVM doesn't hold
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to the mistaken notion that one set of optimizations is right for all languages
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and for all situations. LLVM allows a compiler implementor to make complete
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decisions about what optimizations to use, in which order, and in what
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situation.</p>
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<p>As a concrete example, LLVM supports both "whole module" passes, which look
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across as large of body of code as they can (often a whole file, but if run
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at link time, this can be a substantial portion of the whole program). It also
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supports and includes "per-function" passes which just operate on a single
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function at a time, without looking at other functions. For more information
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on passes and how they are run, see the <a href="../WritingAnLLVMPass.html">How
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to Write a Pass</a> document and the <a href="../Passes.html">List of LLVM
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Passes</a>.</p>
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<p>For Kaleidoscope, we are currently generating functions on the fly, one at
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a time, as the user types them in. We aren't shooting for the ultimate
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optimization experience in this setting, but we also want to catch the easy and
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quick stuff where possible. As such, we will choose to run a few per-function
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optimizations as the user types the function in. If we wanted to make a "static
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Kaleidoscope compiler", we would use exactly the code we have now, except that
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we would defer running the optimizer until the entire file has been parsed.</p>
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<p>In order to get per-function optimizations going, we need to set up a
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<a href="../WritingAnLLVMPass.html#passmanager">Llvm.PassManager</a> to hold and
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organize the LLVM optimizations that we want to run. Once we have that, we can
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add a set of optimizations to run. The code looks like this:</p>
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<div class="doc_code">
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<pre>
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(* Create the JIT. *)
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let the_execution_engine = ExecutionEngine.create Codegen.the_module in
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let the_fpm = PassManager.create_function Codegen.the_module in
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(* Set up the optimizer pipeline. Start with registering info about how the
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* target lays out data structures. *)
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TargetData.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
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(* Do simple "peephole" optimizations and bit-twiddling optzn. *)
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add_instruction_combining the_fpm;
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(* reassociate expressions. *)
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add_reassociation the_fpm;
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(* Eliminate Common SubExpressions. *)
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add_gvn the_fpm;
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(* Simplify the control flow graph (deleting unreachable blocks, etc). *)
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add_cfg_simplification the_fpm;
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ignore (PassManager.initialize the_fpm);
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(* Run the main "interpreter loop" now. *)
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Toplevel.main_loop the_fpm the_execution_engine stream;
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</pre>
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</div>
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<p>The meat of the matter here, is the definition of "<tt>the_fpm</tt>". It
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requires a pointer to the <tt>the_module</tt> to construct itself. Once it is
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set up, we use a series of "add" calls to add a bunch of LLVM passes. The
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first pass is basically boilerplate, it adds a pass so that later optimizations
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know how the data structures in the program are laid out. The
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"<tt>the_execution_engine</tt>" variable is related to the JIT, which we will
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get to in the next section.</p>
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<p>In this case, we choose to add 4 optimization passes. The passes we chose
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here are a pretty standard set of "cleanup" optimizations that are useful for
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a wide variety of code. I won't delve into what they do but, believe me,
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they are a good starting place :).</p>
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<p>Once the <tt>Llvm.PassManager.</tt> is set up, we need to make use of it.
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We do this by running it after our newly created function is constructed (in
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<tt>Codegen.codegen_func</tt>), but before it is returned to the client:</p>
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<div class="doc_code">
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<pre>
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let codegen_func the_fpm = function
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...
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try
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let ret_val = codegen_expr body in
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(* Finish off the function. *)
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let _ = build_ret ret_val builder in
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(* Validate the generated code, checking for consistency. *)
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Llvm_analysis.assert_valid_function the_function;
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(* Optimize the function. *)
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let _ = PassManager.run_function the_function the_fpm in
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the_function
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</pre>
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</div>
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<p>As you can see, this is pretty straightforward. The <tt>the_fpm</tt>
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optimizes and updates the LLVM Function* in place, improving (hopefully) its
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body. With this in place, we can try our test above again:</p>
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<div class="doc_code">
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<pre>
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ready> <b>def test(x) (1+2+x)*(x+(1+2));</b>
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ready> Read function definition:
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define double @test(double %x) {
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entry:
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%addtmp = fadd double %x, 3.000000e+00
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%multmp = fmul double %addtmp, %addtmp
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ret double %multmp
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}
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</pre>
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</div>
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<p>As expected, we now get our nicely optimized code, saving a floating point
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add instruction from every execution of this function.</p>
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<p>LLVM provides a wide variety of optimizations that can be used in certain
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circumstances. Some <a href="../Passes.html">documentation about the various
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passes</a> is available, but it isn't very complete. Another good source of
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ideas can come from looking at the passes that <tt>Clang</tt> runs to get
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started. The "<tt>opt</tt>" tool allows you to experiment with passes from the
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command line, so you can see if they do anything.</p>
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<p>Now that we have reasonable code coming out of our front-end, lets talk about
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executing it!</p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="jit">Adding a JIT Compiler</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p>Code that is available in LLVM IR can have a wide variety of tools
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applied to it. For example, you can run optimizations on it (as we did above),
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you can dump it out in textual or binary forms, you can compile the code to an
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assembly file (.s) for some target, or you can JIT compile it. The nice thing
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about the LLVM IR representation is that it is the "common currency" between
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many different parts of the compiler.
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</p>
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<p>In this section, we'll add JIT compiler support to our interpreter. The
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basic idea that we want for Kaleidoscope is to have the user enter function
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bodies as they do now, but immediately evaluate the top-level expressions they
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type in. For example, if they type in "1 + 2;", we should evaluate and print
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out 3. If they define a function, they should be able to call it from the
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command line.</p>
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<p>In order to do this, we first declare and initialize the JIT. This is done
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by adding a global variable and a call in <tt>main</tt>:</p>
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<div class="doc_code">
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<pre>
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...
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let main () =
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...
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<b>(* Create the JIT. *)
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let the_execution_engine = ExecutionEngine.create Codegen.the_module in</b>
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...
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</pre>
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</div>
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<p>This creates an abstract "Execution Engine" which can be either a JIT
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compiler or the LLVM interpreter. LLVM will automatically pick a JIT compiler
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for you if one is available for your platform, otherwise it will fall back to
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the interpreter.</p>
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<p>Once the <tt>Llvm_executionengine.ExecutionEngine.t</tt> is created, the JIT
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is ready to be used. There are a variety of APIs that are useful, but the
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simplest one is the "<tt>Llvm_executionengine.ExecutionEngine.run_function</tt>"
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function. This method JIT compiles the specified LLVM Function and returns a
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function pointer to the generated machine code. In our case, this means that we
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can change the code that parses a top-level expression to look like this:</p>
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<div class="doc_code">
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<pre>
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(* Evaluate a top-level expression into an anonymous function. *)
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let e = Parser.parse_toplevel stream in
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print_endline "parsed a top-level expr";
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let the_function = Codegen.codegen_func the_fpm e in
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dump_value the_function;
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(* JIT the function, returning a function pointer. *)
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let result = ExecutionEngine.run_function the_function [||]
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the_execution_engine in
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print_string "Evaluated to ";
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print_float (GenericValue.as_float Codegen.double_type result);
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print_newline ();
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</pre>
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</div>
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<p>Recall that we compile top-level expressions into a self-contained LLVM
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function that takes no arguments and returns the computed double. Because the
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LLVM JIT compiler matches the native platform ABI, this means that you can just
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cast the result pointer to a function pointer of that type and call it directly.
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This means, there is no difference between JIT compiled code and native machine
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code that is statically linked into your application.</p>
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<p>With just these two changes, lets see how Kaleidoscope works now!</p>
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<div class="doc_code">
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<pre>
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ready> <b>4+5;</b>
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define double @""() {
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entry:
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ret double 9.000000e+00
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}
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<em>Evaluated to 9.000000</em>
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</pre>
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</div>
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<p>Well this looks like it is basically working. The dump of the function
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shows the "no argument function that always returns double" that we synthesize
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for each top level expression that is typed in. This demonstrates very basic
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functionality, but can we do more?</p>
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<div class="doc_code">
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<pre>
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ready> <b>def testfunc(x y) x + y*2; </b>
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Read function definition:
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define double @testfunc(double %x, double %y) {
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entry:
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%multmp = fmul double %y, 2.000000e+00
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%addtmp = fadd double %multmp, %x
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ret double %addtmp
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}
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ready> <b>testfunc(4, 10);</b>
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define double @""() {
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entry:
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%calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
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ret double %calltmp
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}
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<em>Evaluated to 24.000000</em>
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</pre>
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</div>
|
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<p>This illustrates that we can now call user code, but there is something a bit
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subtle going on here. Note that we only invoke the JIT on the anonymous
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functions that <em>call testfunc</em>, but we never invoked it
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on <em>testfunc</em> itself. What actually happened here is that the JIT
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scanned for all non-JIT'd functions transitively called from the anonymous
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function and compiled all of them before returning
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from <tt>run_function</tt>.</p>
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<p>The JIT provides a number of other more advanced interfaces for things like
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freeing allocated machine code, rejit'ing functions to update them, etc.
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However, even with this simple code, we get some surprisingly powerful
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capabilities - check this out (I removed the dump of the anonymous functions,
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you should get the idea by now :) :</p>
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<div class="doc_code">
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<pre>
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ready> <b>extern sin(x);</b>
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Read extern:
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declare double @sin(double)
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ready> <b>extern cos(x);</b>
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Read extern:
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declare double @cos(double)
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ready> <b>sin(1.0);</b>
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<em>Evaluated to 0.841471</em>
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ready> <b>def foo(x) sin(x)*sin(x) + cos(x)*cos(x);</b>
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Read function definition:
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define double @foo(double %x) {
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entry:
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%calltmp = call double @sin(double %x)
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%multmp = fmul double %calltmp, %calltmp
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%calltmp2 = call double @cos(double %x)
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%multmp4 = fmul double %calltmp2, %calltmp2
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%addtmp = fadd double %multmp, %multmp4
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ret double %addtmp
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}
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ready> <b>foo(4.0);</b>
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<em>Evaluated to 1.000000</em>
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</pre>
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</div>
|
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<p>Whoa, how does the JIT know about sin and cos? The answer is surprisingly
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simple: in this example, the JIT started execution of a function and got to a
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function call. It realized that the function was not yet JIT compiled and
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invoked the standard set of routines to resolve the function. In this case,
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there is no body defined for the function, so the JIT ended up calling
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"<tt>dlsym("sin")</tt>" on the Kaleidoscope process itself. Since
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"<tt>sin</tt>" is defined within the JIT's address space, it simply patches up
|
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calls in the module to call the libm version of <tt>sin</tt> directly.</p>
|
|
|
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<p>The LLVM JIT provides a number of interfaces (look in the
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<tt>llvm_executionengine.mli</tt> file) for controlling how unknown functions
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get resolved. It allows you to establish explicit mappings between IR objects
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|
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 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:
|
|
</p>
|
|
|
|
<div class="doc_code">
|
|
<pre>
|
|
/* putchard - putchar that takes a double and returns 0. */
|
|
extern "C"
|
|
double putchard(double X) {
|
|
putchar((char)X);
|
|
return 0;
|
|
}
|
|
</pre>
|
|
</div>
|
|
|
|
<p>Now we can produce simple output to the console by using things like:
|
|
"<tt>extern putchard(x); putchard(120);</tt>", which prints a lowercase 'x' on
|
|
the console (120 is the ASCII code for 'x'). Similar code could be used to
|
|
implement file I/O, console input, and many other capabilities in
|
|
Kaleidoscope.</p>
|
|
|
|
<p>This completes the JIT and optimizer chapter of the Kaleidoscope tutorial. At
|
|
this point, we can compile a non-Turing-complete programming language, optimize
|
|
and JIT compile it in a user-driven way. Next up we'll look into <a
|
|
href="OCamlLangImpl5.html">extending the language with control flow
|
|
constructs</a>, tackling some interesting LLVM IR issues along the way.</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2><a name="code">Full Code Listing</a></h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<p>
|
|
Here is the complete code listing for our running example, enhanced with the
|
|
LLVM JIT and optimizer. 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
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>lexer.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
(*===----------------------------------------------------------------------===
|
|
* Lexer
|
|
*===----------------------------------------------------------------------===*)
|
|
|
|
let rec lex = parser
|
|
(* Skip any whitespace. *)
|
|
| [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
|
|
|
|
(* identifier: [a-zA-Z][a-zA-Z0-9] *)
|
|
| [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
|
|
let buffer = Buffer.create 1 in
|
|
Buffer.add_char buffer c;
|
|
lex_ident buffer stream
|
|
|
|
(* number: [0-9.]+ *)
|
|
| [< ' ('0' .. '9' as c); stream >] ->
|
|
let buffer = Buffer.create 1 in
|
|
Buffer.add_char buffer c;
|
|
lex_number buffer stream
|
|
|
|
(* Comment until end of line. *)
|
|
| [< ' ('#'); stream >] ->
|
|
lex_comment stream
|
|
|
|
(* Otherwise, just return the character as its ascii value. *)
|
|
| [< 'c; stream >] ->
|
|
[< 'Token.Kwd c; lex stream >]
|
|
|
|
(* end of stream. *)
|
|
| [< >] -> [< >]
|
|
|
|
and lex_number buffer = parser
|
|
| [< ' ('0' .. '9' | '.' as c); stream >] ->
|
|
Buffer.add_char buffer c;
|
|
lex_number buffer stream
|
|
| [< stream=lex >] ->
|
|
[< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
|
|
|
|
and lex_ident buffer = parser
|
|
| [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
|
|
Buffer.add_char buffer c;
|
|
lex_ident buffer stream
|
|
| [< stream=lex >] ->
|
|
match Buffer.contents buffer with
|
|
| "def" -> [< 'Token.Def; stream >]
|
|
| "extern" -> [< 'Token.Extern; stream >]
|
|
| id -> [< 'Token.Ident id; stream >]
|
|
|
|
and lex_comment = parser
|
|
| [< ' ('\n'); stream=lex >] -> stream
|
|
| [< 'c; e=lex_comment >] -> e
|
|
| [< >] -> [< >]
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>ast.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
(*===----------------------------------------------------------------------===
|
|
* Abstract Syntax Tree (aka Parse Tree)
|
|
*===----------------------------------------------------------------------===*)
|
|
|
|
(* expr - Base type for all expression nodes. *)
|
|
type expr =
|
|
(* variant for numeric literals like "1.0". *)
|
|
| Number of float
|
|
|
|
(* variant for referencing a variable, like "a". *)
|
|
| Variable of string
|
|
|
|
(* variant for a binary operator. *)
|
|
| Binary of char * expr * expr
|
|
|
|
(* variant for function calls. *)
|
|
| Call of string * expr array
|
|
|
|
(* proto - This type represents the "prototype" for a function, which captures
|
|
* its name, and its argument names (thus implicitly the number of arguments the
|
|
* function takes). *)
|
|
type proto = Prototype of string * string array
|
|
|
|
(* func - This type represents a function definition itself. *)
|
|
type func = Function of proto * expr
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>parser.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
(*===---------------------------------------------------------------------===
|
|
* Parser
|
|
*===---------------------------------------------------------------------===*)
|
|
|
|
(* binop_precedence - This holds the precedence for each binary operator that is
|
|
* defined *)
|
|
let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
|
|
|
|
(* precedence - Get the precedence of the pending binary operator token. *)
|
|
let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
|
|
|
|
(* primary
|
|
* ::= identifier
|
|
* ::= numberexpr
|
|
* ::= parenexpr *)
|
|
let rec parse_primary = parser
|
|
(* numberexpr ::= number *)
|
|
| [< 'Token.Number n >] -> Ast.Number n
|
|
|
|
(* parenexpr ::= '(' expression ')' *)
|
|
| [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
|
|
|
|
(* identifierexpr
|
|
* ::= identifier
|
|
* ::= identifier '(' argumentexpr ')' *)
|
|
| [< 'Token.Ident id; stream >] ->
|
|
let rec parse_args accumulator = parser
|
|
| [< e=parse_expr; stream >] ->
|
|
begin parser
|
|
| [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
|
|
| [< >] -> e :: accumulator
|
|
end stream
|
|
| [< >] -> accumulator
|
|
in
|
|
let rec parse_ident id = parser
|
|
(* Call. *)
|
|
| [< 'Token.Kwd '(';
|
|
args=parse_args [];
|
|
'Token.Kwd ')' ?? "expected ')'">] ->
|
|
Ast.Call (id, Array.of_list (List.rev args))
|
|
|
|
(* Simple variable ref. *)
|
|
| [< >] -> Ast.Variable id
|
|
in
|
|
parse_ident id stream
|
|
|
|
| [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
|
|
|
|
(* binoprhs
|
|
* ::= ('+' primary)* *)
|
|
and parse_bin_rhs expr_prec lhs stream =
|
|
match Stream.peek stream with
|
|
(* If this is a binop, find its precedence. *)
|
|
| Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
|
|
let token_prec = precedence c in
|
|
|
|
(* If this is a binop that binds at least as tightly as the current binop,
|
|
* consume it, otherwise we are done. *)
|
|
if token_prec < expr_prec then lhs else begin
|
|
(* Eat the binop. *)
|
|
Stream.junk stream;
|
|
|
|
(* Parse the primary expression after the binary operator. *)
|
|
let rhs = parse_primary stream in
|
|
|
|
(* Okay, we know this is a binop. *)
|
|
let rhs =
|
|
match Stream.peek stream with
|
|
| Some (Token.Kwd c2) ->
|
|
(* If BinOp binds less tightly with rhs than the operator after
|
|
* rhs, let the pending operator take rhs as its lhs. *)
|
|
let next_prec = precedence c2 in
|
|
if token_prec < next_prec
|
|
then parse_bin_rhs (token_prec + 1) rhs stream
|
|
else rhs
|
|
| _ -> rhs
|
|
in
|
|
|
|
(* Merge lhs/rhs. *)
|
|
let lhs = Ast.Binary (c, lhs, rhs) in
|
|
parse_bin_rhs expr_prec lhs stream
|
|
end
|
|
| _ -> lhs
|
|
|
|
(* expression
|
|
* ::= primary binoprhs *)
|
|
and parse_expr = parser
|
|
| [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
|
|
|
|
(* prototype
|
|
* ::= id '(' id* ')' *)
|
|
let parse_prototype =
|
|
let rec parse_args accumulator = parser
|
|
| [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
|
|
| [< >] -> accumulator
|
|
in
|
|
|
|
parser
|
|
| [< 'Token.Ident id;
|
|
'Token.Kwd '(' ?? "expected '(' in prototype";
|
|
args=parse_args [];
|
|
'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
|
|
(* success. *)
|
|
Ast.Prototype (id, Array.of_list (List.rev args))
|
|
|
|
| [< >] ->
|
|
raise (Stream.Error "expected function name in prototype")
|
|
|
|
(* definition ::= 'def' prototype expression *)
|
|
let parse_definition = parser
|
|
| [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
|
|
Ast.Function (p, e)
|
|
|
|
(* toplevelexpr ::= expression *)
|
|
let parse_toplevel = parser
|
|
| [< e=parse_expr >] ->
|
|
(* Make an anonymous proto. *)
|
|
Ast.Function (Ast.Prototype ("", [||]), e)
|
|
|
|
(* external ::= 'extern' prototype *)
|
|
let parse_extern = parser
|
|
| [< 'Token.Extern; e=parse_prototype >] -> e
|
|
</pre>
|
|
</dd>
|
|
|
|
<dt>codegen.ml:</dt>
|
|
<dd class="doc_code">
|
|
<pre>
|
|
(*===----------------------------------------------------------------------===
|
|
* Code Generation
|
|
*===----------------------------------------------------------------------===*)
|
|
|
|
open Llvm
|
|
|
|
exception Error of string
|
|
|
|
let context = global_context ()
|
|
let the_module = create_module context "my cool jit"
|
|
let builder = builder context
|
|
let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
|
|
let double_type = double_type context
|
|
|
|
let rec codegen_expr = function
|
|
| Ast.Number n -> const_float double_type n
|
|
| Ast.Variable name ->
|
|
(try Hashtbl.find named_values name with
|
|
| Not_found -> raise (Error "unknown variable name"))
|
|
| Ast.Binary (op, lhs, rhs) ->
|
|
let lhs_val = codegen_expr lhs in
|
|
let rhs_val = codegen_expr rhs in
|
|
begin
|
|
match op with
|
|
| '+' -> build_add lhs_val rhs_val "addtmp" builder
|
|
| '-' -> build_sub lhs_val rhs_val "subtmp" builder
|
|
| '*' -> build_mul lhs_val rhs_val "multmp" builder
|
|
| '<' ->
|
|
(* Convert bool 0/1 to double 0.0 or 1.0 *)
|
|
let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
|
|
build_uitofp i double_type "booltmp" builder
|
|
| _ -> raise (Error "invalid binary operator")
|
|
end
|
|
| Ast.Call (callee, args) ->
|
|
(* Look up the name in the module table. *)
|
|
let callee =
|
|
match lookup_function callee the_module with
|
|
| Some callee -> callee
|
|
| None -> raise (Error "unknown function referenced")
|
|
in
|
|
let params = params callee in
|
|
|
|
(* If argument mismatch error. *)
|
|
if Array.length params == Array.length args then () else
|
|
raise (Error "incorrect # arguments passed");
|
|
let args = Array.map codegen_expr args in
|
|
build_call callee args "calltmp" builder
|
|
|
|
let codegen_proto = function
|
|
| Ast.Prototype (name, args) ->
|
|
(* Make the function type: double(double,double) etc. *)
|
|
let doubles = Array.make (Array.length args) double_type in
|
|
let ft = function_type double_type doubles in
|
|
let f =
|
|
match lookup_function name the_module with
|
|
| None -> declare_function name ft the_module
|
|
|
|
(* If 'f' conflicted, there was already something named 'name'. If it
|
|
* has a body, don't allow redefinition or reextern. *)
|
|
| Some f ->
|
|
(* If 'f' already has a body, reject this. *)
|
|
if block_begin f <> At_end f then
|
|
raise (Error "redefinition of function");
|
|
|
|
(* If 'f' took a different number of arguments, reject. *)
|
|
if element_type (type_of f) <> ft then
|
|
raise (Error "redefinition of function with different # args");
|
|
f
|
|
in
|
|
|
|
(* Set names for all arguments. *)
|
|
Array.iteri (fun i a ->
|
|
let n = args.(i) in
|
|
set_value_name n a;
|
|
Hashtbl.add named_values n a;
|
|
) (params f);
|
|
f
|
|
|
|
let codegen_func 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 context "entry" the_function in
|
|
position_at_end bb builder;
|
|
|
|
try
|
|
let ret_val = codegen_expr body in
|
|
|
|
(* Finish off the function. *)
|
|
let _ = build_ret ret_val builder in
|
|
|
|
(* Validate the generated code, checking for consistency. *)
|
|
Llvm_analysis.assert_valid_function the_function;
|
|
|
|
(* 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 Codegen.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_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_combination 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="OCamlLangImpl5.html">Next: Extending the language: control flow</a>
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</div>
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<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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<a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a><br>
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<a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
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Last modified: $Date$
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