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