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Move information on Configuration files to the ../CompilerDriver.html

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file since it doesn't belong in the man page.


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@ -55,8 +55,10 @@ is interpreted first.
=item * Configuration files are read.
Based on the options and the suffixes of the filenames presented, a set of
configuration files are read to configure the actions B<llvmc> will take
(more on this later).
configuration files are read to configure the actions B<llvmc> will take.
Configuration files are provided by either LLVM or the front end compiler tools
that B<llvmc> invokes. Users generally don't need to be concerned with the
contents of the configuration files.
=item * Determine actions to take.
@ -66,15 +68,15 @@ into a set of basic actions to be done:
=over
=item * Pre-processing: gathering/filtering compiler input
=item * Pre-processing: gathering/filtering compiler input (optional).
=item * Compilation: source language to bytecode conversion
=item * Translation: source language to bytecode conversion.
=item * Assembly: bytecode to native code conversion
=item * Assembly: bytecode to native code conversion.
=item * Optimization: conversion of bytecode to something that runs faster
=item * Optimization: conversion of bytecode to something that runs faster.
=item * Linking: combining multiple bytecodes to produce executable program
=item * Linking: combining multiple bytecodes to produce executable program.
=back
@ -372,234 +374,6 @@ the full raw code produced by the compiler will be generated.
=back
=head1 CONFIGURATION
=head2 Warning
Configuration information is relatively static for a given release of LLVM and
a front end compiler. However, the details may change from release to release.
Users are encouraged to simply use the various options of the B<llvmc> command
and ignore the configuration of the tool. These configuration files are for
compiler writers and LLVM developers. Those wishing to simply use B<llvmc>
don't need to understand this section but it may be instructive on what the tool
does.
=head2 Introduction
B<llvmc> is highly configurable both on the command line and in configuration
files. The options it understands are generic, consistent and simple by design.
Furthermore, the B<llvmc> options apply to the compilation of any LLVM enabled
programming language. To be enabled as a supported source language compiler, a
compiler writer must provide a configuration file that tells B<llvmc> how to
invoke the compiler and what its capabilities are. The purpose of the
configuration files then is to allow compiler writers to specify to B<llvmc> how
the compiler should be invoked. Users may but are not advised to alter the
compiler's B<llvmc> configuration.
Because B<llvmc> just invokes other programs, it must deal with the
available command line options for those programs regardless of whether they
were written for LLVM or not. Furthermore, not all compilation front ends will
have the same capabilities. Some front ends will simply generate LLVM assembly
code, others will be able to generate fully optimized byte code. In general,
B<llvmc> doesn't make any assumptions about the capabilities or command line
options of a sub-tool. It simply uses the details found in the configuration
files and leaves it to the compiler writer to specify the configuration
correctly.
This approach means that new compiler front ends can be up and working very
quickly. As a first cut, a front end can simply compile its source to raw
(unoptimized) bytecode or LLVM assembly and B<llvmc> can be configured to pick
up the slack (translate LLVM assembly to bytecode, optimize the bytecode,
generate native assembly, link, etc.). In fact, the front end need not use
any LLVM libraries, and it could be written in any language (instead of C++).
The configuration data will allow the full range of optimization, assembly,
and linking capabilities that LLVM provides to be added to these kinds of tools.
Enabling the rapid development of front-ends is one of the primary goals of
B<llvmc>.
As a compiler front end matures, it may utilize the LLVM libraries and tools to
more efficiently produce optimized bytecode directly in a single compilation and
optimization program. In these cases, multiple tools would not be needed and
the configuration data for the compiler would change.
Configuring B<llvmc> to the needs and capabilities of a source language compiler
is relatively straight forward. The compilation process is broken down into five
phases:
=over
=item * Pre-processing (filter and combine source files)
=item * Translation (translate source language to LLVM assembly or bytecode)
=item * Optimization (make bytecode execute quickly)
=item * Assembly (converting bytecode to object code)
=item * Linking (converting translated code to an executable)
=back
A compiler writer must provide a definition of what to do for each of these five
phases for each of the optimization levels. The specification consists simply of
prototypical command lines into which B<llvmc> can substitute command line
arguments and file names. Note that any given phase can be completely blank if
the source language's compiler combines multiple phases into a single program.
For example, quite often pre-processing, translation, and optimization are
combined into a single program. The specification for such a compiler would have
blank entries for pre-processing and translation but a full command line for
optimization.
=head2 Configuration File Types
There are two types of configuration files: the master configuration file
and the language specific configuration file.
The master configuration file contains the general configuration of B<llvmc>
itself. This includes things like the mapping between file extensions and
source languages. This mapping is needed in order to quickly read only the
applicable language-specific configuration files (avoiding reading every
configuration file for every compilation task).
Language specific configuration files tell B<llvmc> how to invoke the language's
compiler for a variety of different tasks and what other tools are needed to
I<backfill> the compiler's missing features (e.g. optimization).
Language specific configuration files are placed in directories and given
specific names to foster faster lookup. The name of a given configuration file
is the name of the source language.
=head2 Default Directory Locations
B<llvmc> will look for configuration files in two standard locations: the
LLVM installation directory (typically C</usr/local/llvm/etc>) and the user's
home directory (typically C</home/user/.llvm>). In these directories a file
named C<master> provides the master configuration for B<llvmc>. Language
specific files will have a language specific name (e.g. C++, Stacker, Scheme,
FORTRAN). When reading the configuration files, the master files are always
read first in the following order:
=over
=item 1 C<master> in LLVM installation directory
=item 2 C<master> in the user's home directory.
=back
Then, based on the command line options and the suffixes of the file names
provided on B<llvmc>'s command line, one or more language specific configuration
files are read. Only the language specific configuration files actually needed
to complete B<llvmc>'s task are read. Other language specific files will be
ignored.
Note that the user can affect this process in several ways using the various
B<--config-*> options and with the B<--x LANGUAGE> option.
Although a user I<can> override the master configuration file, this is not
advised. The capability is retained so that compiler writers can affect the
master configuration (such as adding new file suffixes) while developing a new
compiler front end since they might not have write access to the installed
master configuration.
=head2 Syntax
The syntax of the configuration files is yet to be determined. There are three
viable options:
=over
=item XML
=item Windows .ini
=item specific to B<llvmc>
=back
=head2 Master Configuration Items
=head3 Section: [lang=I<LANGUAGE>]
This section provides the master configuration data for a given language. The
language specific data will be found in a file named I<LANGUAGE>.
=over
=item C<suffix=>I<suffix>
This adds the I<suffix> specified to the list of recognized suffixes for
the I<LANGUAGE> identified in the section. As many suffixes as are commonly used
for source files for the I<LANGUAGE> should be specified.
=back
=begin html
<p>For example, the following might appear for C++:
<pre><tt>
[lang=C++]
suffix=.cpp
suffix=.cxx
suffix=.C
</tt></pre></p>
=end html
=head2 Language Specific Configuration Items
=head3 Section: [general]
=over
=item C<hasPreProcessor=yes|no>
This item specifies whether the language has a pre-processing phase or not. This
controls whether the B<-E> option works for the language or not.
=item C<output=bc|ll>
This item specifies the kind of output the language's compiler generates. The
choices are either bytecode (C<bc>) or LLVM assembly (C<ll>).
=back
=head3 Section: [-O0]
=over
=item C<preprocess=>I<commandline>
This item specifies the I<commandline> to use for pre-processing the input.
=over
Valid substitutions for this item are:
=item %in%
The input source file.
=item %out%
The output file.
=item %options%
Any pre-processing specific options (e.g. B<-I>).
=back
=item C<translate=>I<commandline>
This item specifies the I<commandline> to use for translating the source
language input into the output format given by the C<output> item.
=item C<optimize=>I<commandline>
This item specifies the I<commandline> for optimizing the translator's output.
=back
=head1 EXIT STATUS