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130 lines
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======================
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Tutorial - Using LLVMC
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======================
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..
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This file was automatically generated by rst2html.
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Please do not edit directly!
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The ReST source lives in the directory 'tools/llvmc/doc'.
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.. contents::
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.. raw:: html
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<div class="doc_author">
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<p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
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</div>
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Introduction
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============
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LLVMC is a generic compiler driver, which plays the same role for LLVM
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as the ``gcc`` program does for GCC - the difference being that LLVMC
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is designed to be more adaptable and easier to customize. Most of
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LLVMC functionality is implemented via plugins, which can be loaded
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dynamically or compiled in. This tutorial describes the basic usage
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and configuration of LLVMC.
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Compiling with LLVMC
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====================
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In general, LLVMC tries to be command-line compatible with ``gcc`` as
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much as possible, so most of the familiar options work::
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$ llvmc -O3 -Wall hello.cpp
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$ ./a.out
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hello
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This will invoke ``llvm-g++`` under the hood (you can see which
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commands are executed by using the ``-v`` option). For further help on
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command-line LLVMC usage, refer to the ``llvmc --help`` output.
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Using LLVMC to generate toolchain drivers
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=========================================
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LLVMC plugins are written mostly using TableGen_, so you need to
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be familiar with it to get anything done.
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.. _TableGen: http://llvm.org/docs/TableGenFundamentals.html
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Start by compiling ``example/Simple``, which is a primitive wrapper for
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``gcc``::
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$ cd $LLVM_DIR/tools/llvmc
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$ cp -r example/Simple plugins/Simple
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# NB: A less verbose way to compile standalone LLVMC-based drivers is
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# described in the reference manual.
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$ make LLVMC_BASED_DRIVER_NAME=mygcc LLVMC_BUILTIN_PLUGINS=Simple
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$ cat > hello.c
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[...]
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$ mygcc hello.c
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$ ./hello.out
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Hello
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Here we link our plugin with the LLVMC core statically to form an executable
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file called ``mygcc``. It is also possible to build our plugin as a dynamic
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library to be loaded by the ``llvmc`` executable (or any other LLVMC-based
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standalone driver); this is described in the reference manual.
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Contents of the file ``Simple.td`` look like this::
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// Include common definitions
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include "llvm/CompilerDriver/Common.td"
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// Tool descriptions
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def gcc : Tool<
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[(in_language "c"),
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(out_language "executable"),
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(output_suffix "out"),
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(cmd_line "gcc $INFILE -o $OUTFILE"),
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(sink)
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]>;
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// Language map
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def LanguageMap : LanguageMap<[LangToSuffixes<"c", ["c"]>]>;
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// Compilation graph
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def CompilationGraph : CompilationGraph<[Edge<"root", "gcc">]>;
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As you can see, this file consists of three parts: tool descriptions,
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language map, and the compilation graph definition.
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At the heart of LLVMC is the idea of a compilation graph: vertices in
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this graph are tools, and edges represent a transformation path
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between two tools (for example, assembly source produced by the
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compiler can be transformed into executable code by an assembler). The
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compilation graph is basically a list of edges; a special node named
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``root`` is used to mark graph entry points.
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Tool descriptions are represented as property lists: most properties
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in the example above should be self-explanatory; the ``sink`` property
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means that all options lacking an explicit description should be
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forwarded to this tool.
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The ``LanguageMap`` associates a language name with a list of suffixes
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and is used for deciding which toolchain corresponds to a given input
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file.
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To learn more about LLVMC customization, refer to the reference
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manual and plugin source code in the ``plugins`` directory.
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.. raw:: html
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<hr />
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<address>
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<a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
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<a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
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Last modified: $Date: 2008-12-11 11:34:48 -0600 (Thu, 11 Dec 2008) $
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</address>
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