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======================
Tutorial - Using LLVMC
======================
..
This file was automatically generated by rst2html.
Please do not edit directly!
The ReST source lives in the directory 'tools/llvmc/doc'.
.. contents::
.. raw:: html
<div class="doc_author">
<p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
</div>
Introduction
============
LLVMC is a generic compiler driver, which plays the same role for LLVM as the
``gcc`` program does for GCC - the difference being that LLVMC is designed to be
more adaptable and easier to customize. Most of LLVMC functionality is
implemented via high-level TableGen code, from which a corresponding C++ source
file is automatically generated. This tutorial describes the basic usage and
configuration of LLVMC.
Using the ``llvmc`` program
===========================
In general, ``llvmc`` tries to be command-line compatible with ``gcc`` as much
as possible, so most of the familiar options work::
$ llvmc -O3 -Wall hello.cpp
$ ./a.out
hello
This will invoke ``llvm-g++`` under the hood (you can see which commands are
executed by using the ``-v`` option). For further help on command-line LLVMC
usage, refer to the ``llvmc --help`` output.
Using LLVMC to generate toolchain drivers
=========================================
LLVMC-based drivers are written mostly using TableGen_, so you need to be
familiar with it to get anything done.
.. _TableGen: http://llvm.org/docs/TableGenFundamentals.html
Start by compiling ``example/Simple``, which is a primitive wrapper for
``gcc``::
$ cd $LLVM_OBJ_DIR/tools/examples/Simple
$ make
$ cat > hello.c
#include <stdio.h>
int main() { printf("Hello\n"); }
$ $LLVM_BIN_DIR/Simple -v hello.c
gcc hello.c -o hello.out
$ ./hello.out
Hello
We have thus produced a simple driver called, appropriately, ``Simple``, from
the input TableGen file ``Simple.td``. The ``llvmc`` program itself is generated
using a similar process (see ``llvmc/src``). Contents of the file ``Simple.td``
look like this::
// Include common definitions
include "llvm/CompilerDriver/Common.td"
// Tool descriptions
def gcc : Tool<
[(in_language "c"),
(out_language "executable"),
(output_suffix "out"),
(command "gcc"),
(sink),
// -o is what is used by default, out_file_option here is included for
// instructive purposes.
(out_file_option "-o")
]>;
// Language map
def LanguageMap : LanguageMap<[(lang_to_suffixes "c", "c")]>;
// Compilation graph
def CompilationGraph : CompilationGraph<[(edge "root", "gcc")]>;
As you can see, this file consists of three parts: tool descriptions, language
map, and the compilation graph definition.
At the heart of LLVMC is the idea of a compilation graph: vertices in this graph
are tools, and edges represent a transformation path between two tools (for
example, assembly source produced by the compiler can be transformed into
executable code by an assembler). The compilation graph is basically a list of
edges; a special node named ``root`` is used to mark graph entry points.
Tool descriptions are represented as property lists: most properties in the
example above should be self-explanatory; the ``sink`` property means that all
options lacking an explicit description should be forwarded to this tool.
The ``LanguageMap`` associates a language name with a list of suffixes and is
used for deciding which toolchain corresponds to a given input file.
To learn more about writing your own drivers with LLVMC, refer to the reference
manual and examples in the ``examples`` directory. Of a particular interest is
the ``Skeleton`` example, which can serve as a template for your LLVMC-based
drivers.
.. raw:: html
<hr />
<address>
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<a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
<a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
Last modified: $Date: 2008-12-11 11:34:48 -0600 (Thu, 11 Dec 2008) $
</address>
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