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<meta name="author" content="Reid Spencer">
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content="A description of the use and design of the LLVM Compiler Driver.">
<!-- _______________________________________________________________________ -->
<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>
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
<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.
<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
</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>
<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
<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>
-
-<p>As a compiler front end matures, it may utilize the LLVM libraries and tools
+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 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
</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>
<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
<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>
<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>
<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>
<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><blank></td>
</tr>
<tr>
<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
<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><blank></td>
</tr>
<tr>
<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><blank></td>
</tr>
<tr><td colspan="4"><h4>LINKER ITEMS</h4></td></tr>
<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>
-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
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