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Many useful corrections resulting from Chris Lattner's review. Thanks Chris!

Browse Source 
Misha: you're next. :)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@15996 91177308-0d34-0410-b5e6-96231b3b80d8
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Reid Spencer 2004-08-22 18:06:59 +00:00
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@ -4,14 +4,6 @@
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>The LLVM Compiler Driver (llvmc)</title>
<link rel="stylesheet" href="llvm.css" type="text/css">
<style type="text/css">
TR, TD { border: 2px solid gray; padding: 4pt 4pt 2pt 2pt; }
TH { border: 2px solid gray; font-weight: bold; font-size: 105%; }
TABLE { text-align: center; border: 2px solid black;
border-collapse: collapse; margin-top: 1em; margin-left: 1em;
margin-right: 1em; margin-bottom: 1em; }
.td_left { border: 2px solid gray; text-align: left; }
</style>
<meta name="author" content="Reid Spencer">
<meta name="description"
content="A description of the use and design of the LLVM Compiler Driver.">
@ -74,8 +66,8 @@
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="purpose">Purpose</a></div>
<div class="doc_text">
<p><tt>llvmc</tt> was invented to make compilation with LLVM based compilers
easier. To accomplish this, <tt>llvmc</tt> strives to:</p>
<p><tt>llvmc</tt> was invented to make compilation of user programs with
LLVM-based tools easier. To accomplish this, <tt>llvmc</tt> strives to:</p>
<ul>
<li>Be the single point of access to most of the LLVM tool set.</li>
<li>Hide the complexities of the LLVM tools through a single interface.</li>
@ -85,7 +77,7 @@
with LLVM, because it:</p>
<ul>
<li>Makes integration of existing non-LLVM tools simple.</li>
<li>Extends the capabilities of minimal front ends by optimizing their
<li>Extends the capabilities of minimal compiler tools by optimizing their
output.</li>
<li>Reduces the number of interfaces a compiler writer must know about
before a working compiler can be completed (essentially only the VMCore
@ -112,7 +104,7 @@
<dt><b>Read Configuration Files</b></dt>
<dd>Based on the options and the suffixes of the filenames presented, a set
of configuration files are read to configure the actions <tt>llvmc</tt> will
take. Configuration files are provided by either LLVM or the front end
take. Configuration files are provided by either LLVM or the
compiler tools that <tt>llvmc</tt> invokes. These files determine what
actions <tt>llvmc</tt> will take in response to the user's request. See
the section on <a href="#configuration">configuration</a> for more details.
@ -145,11 +137,11 @@
<code>
llvmc -O2 x.c y.c z.c -o xyz</code>
<p>must produce <i>exactly</i> the same results as:</p>
<code>
<pre><tt>
llvmc -O2 x.c
llvmc -O2 y.c
llvmc -O2 z.c
llvmc -O2 x.o y.o z.o -o xyz</code>
llvmc -O2 x.o y.o z.o -o xyz</tt></pre>
<p>To accomplish this, <tt>llvmc</tt> uses a very simple goal oriented
procedure to do its work. The overall goal is to produce a functioning
executable. To accomplish this, <tt>llvmc</tt> always attempts to execute a
@ -230,7 +222,7 @@
</ul></td>
<td class="td_left"><dl>
<dt><tt>-Ox</tt>
<dd>This group of options affects the amount of optimization
<dd>This group of options controls the amount of optimization
performed.</dd>
</dl></td>
</tr>
@ -273,7 +265,7 @@
<div class="doc_text">
<p>This section of the document describes the configuration files used by
<tt>llvmc</tt>. Configuration information is relatively static for a
given release of LLVM and a front end compiler. However, the details may
given release of LLVM and a compiler tool. However, the details may
change from release to release of either. Users are encouraged to simply use
the various options of the <tt>llvmc</tt> command and ignore the configuration
of the tool. These configuration files are for compiler writers and LLVM
@ -297,32 +289,32 @@ should be invoked. Users may but are not advised to alter the compiler's
<p>Because <tt>llvmc</tt> 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
were written for LLVM or not. Furthermore, not all compiler tools will
have the same capabilities. Some compiler tools will simply generate LLVM assembly
code, others will be able to generate fully optimized byte code. In general,
<tt>llvmc</tt> 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.</p>
<p>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
<p>This approach means that new compiler tools can be up and working very
quickly. As a first cut, a tool can simply compile its source to raw
(unoptimized) bytecode or LLVM assembly and <tt>llvmc</tt> 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 <tt>llvmc</tt>.</p>
bytecode, generate native assembly, link, etc.). In fact, the compiler tools
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 <tt>llvmc</tt>.</p>
<p>As a compiler front end matures, it may utilize the LLVM libraries and tools
<p>As a compiler tool 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.</p>
<p>Configuring <tt>llvmc</tt> to the needs and capabilities of a source language
compiler is relatively straight forward. A compiler writer must provide a
compiler is relatively straight-forward. A compiler writer must provide a
definition of what to do for each of the five compilation phases for each of
the optimization levels. The specification consists simply of prototypical
command lines into which <tt>llvmc</tt> can substitute command line
@ -335,21 +327,22 @@ optimization.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="filetypes"></a>Configuration Files</div>
<div class="doc_subsection"><a name="filetypes">Configuration Files</a></div>
<div class="doc_subsubsection"><a name="filecontents">File Contents</a></div>
<div class="doc_text">
<h3>File Contents</h3>
<p>Each configuration file provides the details for a single source language
that is to be compiled. This configuration information tells <tt>llvmc</tt>
how to invoke the language's pre-processor, translator, optimizer, assembler
and linker. Note that a given source language needn't provide all these tools
as many of them exist in llvm currently.</p>
<h3>Directory Search</h3>
</div>
<div class="doc_subsubsection"><a name="dirsearch">Directory Search</a></div>
<div class="doc_text">
<p><tt>llvmc</tt> always looks for files of a specific name. It uses the
first file with the name its looking for by searching directories in the
following order:<br/>
<ol>
<li>Any directory specified by the <tt>--config-dir</tt> option will be
<li>Any directory specified by the <tt>-config-dir</tt> option will be
checked first.</li>
<li>If the environment variable LLVM_CONFIG_DIR is set, and it contains
the name of a valid directory, that directory will be searched next.</li>
@ -369,8 +362,10 @@ optimization.</p>
<p>The first file found in this search will be used. Other files with the
same name will be ignored even if they exist in one of the subsequent search
locations.</p>
</div>
<h3>File Names</h3>
<div class="doc_subsubsection"><a name="filenames">File Names</a></div>
<div class="doc_text">
<p>In the directories searched, each configuration file is given a specific
name to foster faster lookup (so llvmc doesn't have to do directory searches).
The name of a given language specific configuration file is simply the same
@ -379,11 +374,13 @@ optimization.</p>
<tt>cpp</tt>, <tt>C</tt>, or <tt>cxx</tt>. For languages that support multiple
file suffixes, multiple (probably identical) files (or symbolic links) will
need to be provided.</p>
</div>
<h3>What Gets Read</h3>
<div class="doc_subsubsection"><a name="whatgetsread">What Gets Read</a></div>
<div class="doc_text">
<p>Which configuration files are read depends on the command line options and
the suffixes of the file names provided on <tt>llvmc</tt>'s command line. Note
that the <tt>--x LANGUAGE</tt> option alters the language that <tt>llvmc</tt>
that the <tt>-x LANGUAGE</tt> option alters the language that <tt>llvmc</tt>
uses for the subsequent files on the command line. Only the configuration
files actually needed to complete <tt>llvmc</tt>'s task are read. Other
language specific files will be ignored.</p>
@ -397,7 +394,8 @@ optimization.</p>
<ul>
<li>The file encoding is ASCII.</li>
<li>The file is line oriented. There should be one configuration definition
per line. Lines are terminated by the newline character (0x0A).</li>
per line. Lines are terminated by the newline (0x0A) and/or carriage return
characters (0x0D)</li>
<li>A backslash (<tt>\</tt>) before a newline causes the newline to be
ignored. This is useful for line continuation of long definitions. A
backslash anywhere else is recognized as a backslash.</li>
@ -414,7 +412,7 @@ optimization.</p>
<li>Integers are simply sequences of digits.</li>
<li>Commands start with a program name and are followed by a sequence of
words that are passed to that program as command line arguments. Program
arguments that begin and end with the <tt>@</tt> sign will have their value
arguments that begin and end with the <tt>%</tt> sign will have their value
substituted. Program names beginning with <tt>/</tt> are considered to be
absolute. Otherwise the <tt>PATH</tt> will be applied to find the program to
execute.</li>
@ -516,8 +514,8 @@ optimization.</p>
<td><b>translator.command</b></td>
<td>command</td>
<td class="td_left">This provides the command prototype that will be used
to run the translator. Valid substitutions are <tt>@in@</tt> for the
input file and <tt>@out@</tt> for the output file.</td>
to run the translator. Valid substitutions are <tt>%in%</tt> for the
input file and <tt>%out%</tt> for the output file.</td>
<td>&lt;blank&gt;</td>
</tr>
<tr>
@ -536,7 +534,7 @@ optimization.</p>
<td><tt>false</tt></td>
</tr>
<tr>
<td><b>translator.optimizers</b></td>
<td><b>translator.optimizes</b></td>
<td>boolean</td>
<td class="td_left">Indicates that the translator also optimizes. If
this is true, then <tt>llvmc</tt> will skip the optimization phase
@ -558,8 +556,8 @@ optimization.</p>
<td><b>optimizer.command</b></td>
<td>command</td>
<td class="td_left">This provides the command prototype that will be used
to run the optimizer. Valid substitutions are <tt>@in@</tt> for the
input file and <tt>@out@</tt> for the output file.</td>
to run the optimizer. Valid substitutions are <tt>%in%</tt> for the
input file and <tt>%out%</tt> for the output file.</td>
<td>&lt;blank&gt;</td>
</tr>
<tr>
@ -600,8 +598,8 @@ optimization.</p>
<td><b>assembler.command</b></td>
<td>command</td>
<td class="td_left">This provides the command prototype that will be used
to run the assembler. Valid substitutions are <tt>@in@</tt> for the
input file and <tt>@out@</tt> for the output file.</td>
to run the assembler. Valid substitutions are <tt>%in%</tt> for the
input file and <tt>%out%</tt> for the output file.</td>
<td>&lt;blank&gt;</td>
</tr>
<tr><td colspan="4"><h4>LINKER ITEMS</h4></td></tr>
@ -659,8 +657,9 @@ optimization.</p>
<td class="td_left">Replaced with all the tool-specific arguments given
to <tt>llvmc</tt> via the <tt>-T</tt> set of options. This just allows
you to place these arguments in the correct place on the command line.
If the %args% option does not appear on your command line, then you
are explicitly disallowing the <tt>-T</tt> option for your tool.
If the <tt>%args%</tt> option does not appear on your command line,
then you are explicitly disallowing the <tt>-T</tt> option for your
tool.
</td>
<tr>
<td><tt>%in%</tt></td>
@ -729,13 +728,13 @@ optimization.</p>
-gcse -dse -scalarrepl -sccp
lang.opt3=-simplifycfg -instcombine -mem2reg -load-vn \
-gcse -dse -scalarrepl -sccp -branch-combine -adce \
-globaldce -inline -licm -pre
-globaldce -inline -licm
lang.opt4=-simplifycfg -instcombine -mem2reg -load-vn \
-gcse -dse -scalarrepl -sccp -ipconstprop \
-branch-combine -adce -globaldce -inline -licm -pre
-branch-combine -adce -globaldce -inline -licm
lang.opt5=-simplifycfg -instcombine -mem2reg --load-vn \
-gcse -dse scalarrepl -sccp -ipconstprop \
-branch-combine -adce -globaldce -inline -licm -pre \
-branch-combine -adce -globaldce -inline -licm \
-block-placement
##########################################################