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916 lines
34 KiB
ReStructuredText
==============================================
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Kaleidoscope: Adding JIT and Optimizer Support
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==============================================
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.. contents::
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:local:
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Chapter 4 Introduction
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======================
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Welcome to Chapter 4 of the "`Implementing a language with
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LLVM <index.html>`_" tutorial. Chapters 1-3 described the implementation
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of a simple language and added support for generating LLVM IR. This
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chapter describes two new techniques: adding optimizer support to your
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language, and adding JIT compiler support. These additions will
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demonstrate how to get nice, efficient code for the Kaleidoscope
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language.
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Trivial Constant Folding
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========================
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**Note:** the default ``IRBuilder`` now always includes the constant
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folding optimisations below.
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Our demonstration for Chapter 3 is elegant and easy to extend.
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Unfortunately, it does not produce wonderful code. For example, when
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compiling simple code, we don't get obvious optimizations:
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::
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ready> def test(x) 1+2+x;
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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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This code is a very, very literal transcription of the AST built by
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parsing the input. As such, this transcription lacks optimizations like
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constant folding (we'd like to get "``add x, 3.0``" in the example
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above) as well as other more important optimizations. Constant folding,
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in particular, is a very common and very important optimization: so much
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so that many language implementors implement constant folding support in
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their AST representation.
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With LLVM, you don't need this support in the AST. Since all calls to
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build LLVM IR go through the LLVM builder, it would be nice if the
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builder itself checked to see if there was a constant folding
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opportunity when you call it. If so, it could just do the constant fold
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and return the constant instead of creating an instruction. This is
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exactly what the ``LLVMFoldingBuilder`` class does.
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All we did was switch from ``LLVMBuilder`` to ``LLVMFoldingBuilder``.
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Though we change no other code, we now have all of our instructions
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implicitly constant folded without us having to do anything about it.
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For example, the input above now compiles to:
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::
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ready> def test(x) 1+2+x;
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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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Well, that was easy :). In practice, we recommend always using
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``LLVMFoldingBuilder`` 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
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with constant checks everywhere) and it can dramatically reduce the
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amount of LLVM IR that is generated in some cases (particular for
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languages with a macro preprocessor or that use a lot of constants).
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On the other hand, the ``LLVMFoldingBuilder`` 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
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you take a slightly more complex example:
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::
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ready> def test(x) (1+2+x)*(x+(1+2));
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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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In this case, the LHS and RHS of the multiplication are the same value.
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We'd really like to see this generate "``tmp = x+3; result = tmp*tmp;``"
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instead of computing "``x*3``" twice.
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Unfortunately, no amount of local analysis will be able to detect and
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correct this. This requires two transformations: reassociation of
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expressions (to make the add's lexically identical) and Common
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Subexpression Elimination (CSE) to delete the redundant add instruction.
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Fortunately, LLVM provides a broad range of optimizations that you can
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use, in the form of "passes".
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LLVM Optimization Passes
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========================
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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
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hold to the mistaken notion that one set of optimizations is right for
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all languages and for all situations. LLVM allows a compiler implementor
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to make complete decisions about what optimizations to use, in which
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order, and in what situation.
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As a concrete example, LLVM supports both "whole module" passes, which
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look across as large of body of code as they can (often a whole file,
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but if run at link time, this can be a substantial portion of the whole
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program). It also supports and includes "per-function" passes which just
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operate on a single function at a time, without looking at other
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functions. For more information on passes and how they are run, see the
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`How to Write a Pass <../WritingAnLLVMPass.html>`_ document and the
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`List of LLVM Passes <../Passes.html>`_.
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For Kaleidoscope, we are currently generating functions on the fly, one
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at a time, as the user types them in. We aren't shooting for the
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ultimate optimization experience in this setting, but we also want to
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catch the easy and quick stuff where possible. As such, we will choose
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to run a few per-function optimizations as the user types the function
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in. If we wanted to make a "static Kaleidoscope compiler", we would use
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exactly the code we have now, except that we would defer running the
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optimizer until the entire file has been parsed.
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In order to get per-function optimizations going, we need to set up a
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`Llvm.PassManager <../WritingAnLLVMPass.html#passmanager>`_ to hold and
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organize the LLVM optimizations that we want to run. Once we have that,
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we can add a set of optimizations to run. The code looks like this:
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.. code-block:: ocaml
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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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DataLayout.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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The meat of the matter here, is the definition of "``the_fpm``". It
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requires a pointer to the ``the_module`` 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.
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The first pass is basically boilerplate, it adds a pass so that later
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optimizations know how the data structures in the program are laid out.
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The "``the_execution_engine``" variable is related to the JIT, which we
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will get to in the next section.
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In this case, we choose to add 4 optimization passes. The passes we
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chose here are a pretty standard set of "cleanup" optimizations that are
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useful for a wide variety of code. I won't delve into what they do but,
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believe me, they are a good starting place :).
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Once the ``Llvm.PassManager.`` is set up, we need to make use of it. We
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do this by running it after our newly created function is constructed
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(in ``Codegen.codegen_func``), but before it is returned to the client:
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.. code-block:: ocaml
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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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As you can see, this is pretty straightforward. The ``the_fpm``
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optimizes and updates the LLVM Function\* in place, improving
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(hopefully) its body. With this in place, we can try our test above
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again:
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::
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ready> def test(x) (1+2+x)*(x+(1+2));
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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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As expected, we now get our nicely optimized code, saving a floating
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point add instruction from every execution of this function.
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LLVM provides a wide variety of optimizations that can be used in
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certain circumstances. Some `documentation about the various
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passes <../Passes.html>`_ is available, but it isn't very complete.
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Another good source of ideas can come from looking at the passes that
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``Clang`` runs to get started. The "``opt``" tool allows you to
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experiment with passes from the command line, so you can see if they do
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anything.
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Now that we have reasonable code coming out of our front-end, lets talk
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about executing it!
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Adding a JIT Compiler
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=====================
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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
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above), you can dump it out in textual or binary forms, you can compile
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the code to an assembly file (.s) for some target, or you can JIT
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compile it. The nice thing about the LLVM IR representation is that it
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is the "common currency" between many different parts of the compiler.
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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
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function bodies as they do now, but immediately evaluate the top-level
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expressions they type in. For example, if they type in "1 + 2;", we
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should evaluate and print out 3. If they define a function, they should
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be able to call it from the command line.
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In order to do this, we first declare and initialize the JIT. This is
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done by adding a global variable and a call in ``main``:
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.. code-block:: ocaml
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...
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let main () =
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...
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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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...
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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
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compiler for you if one is available for your platform, otherwise it
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will fall back to the interpreter.
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Once the ``Llvm_executionengine.ExecutionEngine.t`` is created, the JIT
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is ready to be used. There are a variety of APIs that are useful, but
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the simplest one is the
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"``Llvm_executionengine.ExecutionEngine.run_function``" function. This
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method JIT compiles the specified LLVM Function and returns a function
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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
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this:
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.. code-block:: ocaml
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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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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.
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Because the LLVM JIT compiler matches the native platform ABI, this
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means that you can just cast the result pointer to a function pointer of
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that type and call it directly. This means, there is no difference
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between JIT compiled code and native machine code that is statically
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linked into your application.
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With just these two changes, lets see how Kaleidoscope works now!
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::
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ready> 4+5;
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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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Evaluated to 9.000000
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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
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synthesize for each top level expression that is typed in. This
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demonstrates very basic functionality, but can we do more?
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::
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ready> def testfunc(x y) x + y*2;
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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> testfunc(4, 10);
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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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Evaluated to 24.000000
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This illustrates that we can now call user code, but there is something
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a bit subtle going on here. Note that we only invoke the JIT on the
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anonymous functions that *call testfunc*, but we never invoked it on
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*testfunc* itself. What actually happened here is that the JIT scanned
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for all non-JIT'd functions transitively called from the anonymous
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function and compiled all of them before returning from
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``run_function``.
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The JIT provides a number of other more advanced interfaces for things
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like freeing allocated machine code, rejit'ing functions to update them,
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etc. However, even with this simple code, we get some surprisingly
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powerful capabilities - check this out (I removed the dump of the
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anonymous functions, you should get the idea by now :) :
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::
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ready> extern sin(x);
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Read extern:
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declare double @sin(double)
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ready> extern cos(x);
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Read extern:
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declare double @cos(double)
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ready> sin(1.0);
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Evaluated to 0.841471
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ready> def foo(x) sin(x)*sin(x) + cos(x)*cos(x);
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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> foo(4.0);
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Evaluated to 1.000000
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Whoa, how does the JIT know about sin and cos? The answer is
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surprisingly simple: in this example, the JIT started execution of a
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function and got to a function call. It realized that the function was
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not yet JIT compiled and invoked the standard set of routines to resolve
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the function. In this case, there is no body defined for the function,
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so the JIT ended up calling "``dlsym("sin")``" on the Kaleidoscope
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process itself. Since "``sin``" is defined within the JIT's address
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space, it simply patches up calls in the module to call the libm version
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of ``sin`` directly.
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The LLVM JIT provides a number of interfaces (look in the
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``llvm_executionengine.mli`` file) for controlling how unknown functions
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get resolved. It allows you to establish explicit mappings between IR
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objects and addresses (useful for LLVM global variables that you want to
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map to static tables, for example), allows you to dynamically decide on
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the fly based on the function name, and even allows you to have the JIT
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compile functions lazily the first time they're called.
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One interesting application of this is that we can now extend the
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language by writing arbitrary C code to implement operations. For
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example, if we add:
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.. code-block:: c++
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/* putchard - putchar that takes a double and returns 0. */
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extern "C"
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double putchard(double X) {
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putchar((char)X);
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return 0;
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}
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Now we can produce simple output to the console by using things like:
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"``extern putchard(x); putchard(120);``", which prints a lowercase 'x'
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on the console (120 is the ASCII code for 'x'). Similar code could be
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used to implement file I/O, console input, and many other capabilities
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in Kaleidoscope.
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This completes the JIT and optimizer chapter of the Kaleidoscope
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tutorial. At this point, we can compile a non-Turing-complete
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programming language, optimize and JIT compile it in a user-driven way.
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Next up we'll look into `extending the language with control flow
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|
constructs <OCamlLangImpl5.html>`_, tackling some interesting LLVM IR
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issues along the way.
|
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|
Full Code Listing
|
|
=================
|
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Here is the complete code listing for our running example, enhanced with
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the LLVM JIT and optimizer. To build this example, use:
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.. code-block:: bash
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# Compile
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ocamlbuild toy.byte
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# Run
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./toy.byte
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Here is the code:
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\_tags:
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::
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<{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
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<*.{byte,native}>: g++, use_llvm, use_llvm_analysis
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<*.{byte,native}>: use_llvm_executionengine, use_llvm_target
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<*.{byte,native}>: use_llvm_scalar_opts, use_bindings
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myocamlbuild.ml:
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|
.. code-block:: ocaml
|
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open Ocamlbuild_plugin;;
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ocaml_lib ~extern:true "llvm";;
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ocaml_lib ~extern:true "llvm_analysis";;
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ocaml_lib ~extern:true "llvm_executionengine";;
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|
ocaml_lib ~extern:true "llvm_target";;
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ocaml_lib ~extern:true "llvm_scalar_opts";;
|
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flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);;
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dep ["link"; "ocaml"; "use_bindings"] ["bindings.o"];;
|
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|
token.ml:
|
|
.. code-block:: ocaml
|
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(*===----------------------------------------------------------------------===
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* Lexer Tokens
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*===----------------------------------------------------------------------===*)
|
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(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
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* these others for known things. *)
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type token =
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(* commands *)
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| Def | Extern
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(* primary *)
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| Ident of string | Number of float
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(* unknown *)
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| Kwd of char
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lexer.ml:
|
|
.. code-block:: ocaml
|
|
|
|
(*===----------------------------------------------------------------------===
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* Lexer
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*===----------------------------------------------------------------------===*)
|
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let rec lex = parser
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(* Skip any whitespace. *)
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| [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
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(* identifier: [a-zA-Z][a-zA-Z0-9] *)
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|
| [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
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let buffer = Buffer.create 1 in
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Buffer.add_char buffer c;
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lex_ident buffer stream
|
|
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|
(* 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
|
|
| [< >] -> [< >]
|
|
|
|
ast.ml:
|
|
.. code-block:: ocaml
|
|
|
|
(*===----------------------------------------------------------------------===
|
|
* 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
|
|
|
|
parser.ml:
|
|
.. code-block:: ocaml
|
|
|
|
(*===---------------------------------------------------------------------===
|
|
* 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
|
|
|
|
codegen.ml:
|
|
.. code-block:: ocaml
|
|
|
|
(*===----------------------------------------------------------------------===
|
|
* 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
|
|
|
|
toplevel.ml:
|
|
.. code-block:: ocaml
|
|
|
|
(*===----------------------------------------------------------------------===
|
|
* 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
|
|
|
|
toy.ml:
|
|
.. code-block:: ocaml
|
|
|
|
(*===----------------------------------------------------------------------===
|
|
* 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. *)
|
|
DataLayout.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 ()
|
|
|
|
bindings.c
|
|
.. code-block:: c
|
|
|
|
#include <stdio.h>
|
|
|
|
/* putchard - putchar that takes a double and returns 0. */
|
|
extern double putchard(double X) {
|
|
putchar((char)X);
|
|
return 0;
|
|
}
|
|
|
|
`Next: Extending the language: control flow <OCamlLangImpl5.html>`_
|
|
|