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128 lines
4.3 KiB
ReStructuredText
======================
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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 as the
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``gcc`` program does for GCC - the difference being that LLVMC is designed to be
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more adaptable and easier to customize. Most of LLVMC functionality is
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implemented via high-level TableGen code, from which a corresponding C++ source
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file is automatically generated. This tutorial describes the basic usage and
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configuration of LLVMC.
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Using the ``llvmc`` program
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===========================
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In general, ``llvmc`` tries to be command-line compatible with ``gcc`` as much
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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 commands are
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executed by using the ``-v`` option). For further help on command-line LLVMC
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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-based drivers are written mostly using TableGen_, so you need to be
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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 $LLVM_OBJ_DIR/tools/examples/Simple
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$ make
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$ cat > hello.c
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#include <stdio.h>
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int main() { printf("Hello\n"); }
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$ $LLVM_BIN_DIR/Simple -v hello.c
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gcc hello.c -o hello.out
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$ ./hello.out
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Hello
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We have thus produced a simple driver called, appropriately, ``Simple``, from
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the input TableGen file ``Simple.td``. The ``llvmc`` program itself is generated
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using a similar process (see ``llvmc/src``). Contents of the file ``Simple.td``
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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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(command "gcc"),
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(sink),
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// -o is what is used by default, out_file_option here is included for
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// instructive purposes.
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(out_file_option "-o")
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]>;
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// Language map
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def LanguageMap : LanguageMap<[(lang_to_suffixes "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, language
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map, and the compilation graph definition.
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At the heart of LLVMC is the idea of a compilation graph: vertices in this graph
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are tools, and edges represent a transformation path between two tools (for
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example, assembly source produced by the compiler can be transformed into
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executable code by an assembler). The compilation graph is basically a list of
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edges; a special node named ``root`` is used to mark graph entry points.
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Tool descriptions are represented as property lists: most properties in the
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example above should be self-explanatory; the ``sink`` property means that all
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options lacking an explicit description should be forwarded to this tool.
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The ``LanguageMap`` associates a language name with a list of suffixes and is
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used for deciding which toolchain corresponds to a given input file.
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To learn more about writing your own drivers with LLVMC, refer to the reference
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manual and examples in the ``examples`` directory. Of a particular interest is
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the ``Skeleton`` example, which can serve as a template for your LLVMC-based
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drivers.
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.. raw:: html
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<hr />
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<address>
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<a href="http://jigsaw.w3.org/css-validator/check/referer">
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<img src="http://jigsaw.w3.org/css-validator/images/vcss-blue"
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alt="Valid CSS" /></a>
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<a href="http://validator.w3.org/check?uri=referer">
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<img src="http://www.w3.org/Icons/valid-xhtml10-blue"
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alt="Valid XHTML 1.0 Transitional"/></a>
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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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