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authormike-m <mikem.llvm@gmail.com>2010-05-07 00:28:04 +0000
committermike-m <mikem.llvm@gmail.com>2010-05-07 00:28:04 +0000
commite2c3a49c8029ebd9ef530101cc24c66562e3dff5 (patch)
tree91bf9600cc8df90cf99751a8f8bafc317cffc91e /docs/CompilerDriver.html
parentc10b5afbe8138b0fdf3af4ed3e1ddf96cf3cb4cb (diff)
Revert r103213. It broke several sections of live website.
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+<?xml version="1.0" encoding="utf-8" ?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+<meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
+<title>Customizing LLVMC: Reference Manual</title>
+<link rel="stylesheet" href="llvm.css" type="text/css" />
+</head>
+<body>
+<div class="document" id="customizing-llvmc-reference-manual">
+<h1 class="title">Customizing LLVMC: Reference Manual</h1>
+
+<!-- This file was automatically generated by rst2html.
+Please do not edit directly!
+The ReST source lives in the directory 'tools/llvmc/doc'. -->
+<div class="contents topic" id="contents">
+<p class="topic-title first">Contents</p>
+<ul class="simple">
+<li><a class="reference internal" href="#introduction" id="id8">Introduction</a></li>
+<li><a class="reference internal" href="#compiling-with-llvmc" id="id9">Compiling with LLVMC</a></li>
+<li><a class="reference internal" href="#predefined-options" id="id10">Predefined options</a></li>
+<li><a class="reference internal" href="#compiling-llvmc-plugins" id="id11">Compiling LLVMC plugins</a></li>
+<li><a class="reference internal" href="#compiling-standalone-llvmc-based-drivers" id="id12">Compiling standalone LLVMC-based drivers</a></li>
+<li><a class="reference internal" href="#customizing-llvmc-the-compilation-graph" id="id13">Customizing LLVMC: the compilation graph</a></li>
+<li><a class="reference internal" href="#describing-options" id="id14">Describing options</a><ul>
+<li><a class="reference internal" href="#external-options" id="id15">External options</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#conditional-evaluation" id="id16">Conditional evaluation</a></li>
+<li><a class="reference internal" href="#writing-a-tool-description" id="id17">Writing a tool description</a><ul>
+<li><a class="reference internal" href="#id5" id="id18">Actions</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#language-map" id="id19">Language map</a></li>
+<li><a class="reference internal" href="#option-preprocessor" id="id20">Option preprocessor</a></li>
+<li><a class="reference internal" href="#more-advanced-topics" id="id21">More advanced topics</a><ul>
+<li><a class="reference internal" href="#hooks-and-environment-variables" id="id22">Hooks and environment variables</a></li>
+<li><a class="reference internal" href="#how-plugins-are-loaded" id="id23">How plugins are loaded</a></li>
+<li><a class="reference internal" href="#debugging" id="id24">Debugging</a></li>
+<li><a class="reference internal" href="#conditioning-on-the-executable-name" id="id25">Conditioning on the executable name</a></li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="doc_author">
+<p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
+</div><div class="section" id="introduction">
+<h1><a class="toc-backref" href="#id8">Introduction</a></h1>
+<p>LLVMC is a generic compiler driver, designed to be customizable and
+extensible. It plays the same role for LLVM as the <tt class="docutils literal"><span class="pre">gcc</span></tt> program
+does for GCC - LLVMC's job is essentially to transform a set of input
+files into a set of targets depending on configuration rules and user
+options. What makes LLVMC different is that these transformation rules
+are completely customizable - in fact, LLVMC knows nothing about the
+specifics of transformation (even the command-line options are mostly
+not hard-coded) and regards the transformation structure as an
+abstract graph. The structure of this graph is completely determined
+by plugins, which can be either statically or dynamically linked. This
+makes it possible to easily adapt LLVMC for other purposes - for
+example, as a build tool for game resources.</p>
+<p>Because LLVMC employs <a class="reference external" href="http://llvm.org/docs/TableGenFundamentals.html">TableGen</a> as its configuration language, you
+need to be familiar with it to customize LLVMC.</p>
+</div>
+<div class="section" id="compiling-with-llvmc">
+<h1><a class="toc-backref" href="#id9">Compiling with LLVMC</a></h1>
+<p>LLVMC tries hard to be as compatible with <tt class="docutils literal"><span class="pre">gcc</span></tt> as possible,
+although there are some small differences. Most of the time, however,
+you shouldn't be able to notice them:</p>
+<pre class="literal-block">
+$ # This works as expected:
+$ llvmc -O3 -Wall hello.cpp
+$ ./a.out
+hello
+</pre>
+<p>One nice feature of LLVMC is that one doesn't have to distinguish between
+different compilers for different languages (think <tt class="docutils literal"><span class="pre">g++</span></tt> vs. <tt class="docutils literal"><span class="pre">gcc</span></tt>) - the
+right toolchain is chosen automatically based on input language names (which
+are, in turn, determined from file extensions). If you want to force files
+ending with &quot;.c&quot; to compile as C++, use the <tt class="docutils literal"><span class="pre">-x</span></tt> option, just like you would
+do it with <tt class="docutils literal"><span class="pre">gcc</span></tt>:</p>
+<pre class="literal-block">
+$ # hello.c is really a C++ file
+$ llvmc -x c++ hello.c
+$ ./a.out
+hello
+</pre>
+<p>On the other hand, when using LLVMC as a linker to combine several C++
+object files you should provide the <tt class="docutils literal"><span class="pre">--linker</span></tt> option since it's
+impossible for LLVMC to choose the right linker in that case:</p>
+<pre class="literal-block">
+$ llvmc -c hello.cpp
+$ llvmc hello.o
+[A lot of link-time errors skipped]
+$ llvmc --linker=c++ hello.o
+$ ./a.out
+hello
+</pre>
+<p>By default, LLVMC uses <tt class="docutils literal"><span class="pre">llvm-gcc</span></tt> to compile the source code. It is also
+possible to choose the <tt class="docutils literal"><span class="pre">clang</span></tt> compiler with the <tt class="docutils literal"><span class="pre">-clang</span></tt> option.</p>
+</div>
+<div class="section" id="predefined-options">
+<h1><a class="toc-backref" href="#id10">Predefined options</a></h1>
+<p>LLVMC has some built-in options that can't be overridden in the
+configuration libraries:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">-o</span> <span class="pre">FILE</span></tt> - Output file name.</li>
+<li><tt class="docutils literal"><span class="pre">-x</span> <span class="pre">LANGUAGE</span></tt> - Specify the language of the following input files
+until the next -x option.</li>
+<li><tt class="docutils literal"><span class="pre">-load</span> <span class="pre">PLUGIN_NAME</span></tt> - Load the specified plugin DLL. Example:
+<tt class="docutils literal"><span class="pre">-load</span> <span class="pre">$LLVM_DIR/Release/lib/LLVMCSimple.so</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">-v</span></tt> - Enable verbose mode, i.e. print out all executed commands.</li>
+<li><tt class="docutils literal"><span class="pre">--save-temps</span></tt> - Write temporary files to the current directory and do not
+delete them on exit. This option can also take an argument: the
+<tt class="docutils literal"><span class="pre">--save-temps=obj</span></tt> switch will write files into the directory specified with
+the <tt class="docutils literal"><span class="pre">-o</span></tt> option. The <tt class="docutils literal"><span class="pre">--save-temps=cwd</span></tt> and <tt class="docutils literal"><span class="pre">--save-temps</span></tt> switches are
+both synonyms for the default behaviour.</li>
+<li><tt class="docutils literal"><span class="pre">--temp-dir</span> <span class="pre">DIRECTORY</span></tt> - Store temporary files in the given directory. This
+directory is deleted on exit unless <tt class="docutils literal"><span class="pre">--save-temps</span></tt> is specified. If
+<tt class="docutils literal"><span class="pre">--save-temps=obj</span></tt> is also specified, <tt class="docutils literal"><span class="pre">--temp-dir</span></tt> is given the
+precedence.</li>
+<li><tt class="docutils literal"><span class="pre">--check-graph</span></tt> - Check the compilation for common errors like mismatched
+output/input language names, multiple default edges and cycles. Because of
+plugins, these checks can't be performed at compile-time. Exit with code zero
+if no errors were found, and return the number of found errors
+otherwise. Hidden option, useful for debugging LLVMC plugins.</li>
+<li><tt class="docutils literal"><span class="pre">--view-graph</span></tt> - Show a graphical representation of the compilation graph
+and exit. Requires that you have <tt class="docutils literal"><span class="pre">dot</span></tt> and <tt class="docutils literal"><span class="pre">gv</span></tt> programs installed. Hidden
+option, useful for debugging LLVMC plugins.</li>
+<li><tt class="docutils literal"><span class="pre">--write-graph</span></tt> - Write a <tt class="docutils literal"><span class="pre">compilation-graph.dot</span></tt> file in the current
+directory with the compilation graph description in Graphviz format (identical
+to the file used by the <tt class="docutils literal"><span class="pre">--view-graph</span></tt> option). The <tt class="docutils literal"><span class="pre">-o</span></tt> option can be
+used to set the output file name. Hidden option, useful for debugging LLVMC
+plugins.</li>
+<li><tt class="docutils literal"><span class="pre">-help</span></tt>, <tt class="docutils literal"><span class="pre">-help-hidden</span></tt>, <tt class="docutils literal"><span class="pre">--version</span></tt> - These options have
+their standard meaning.</li>
+</ul>
+</div>
+<div class="section" id="compiling-llvmc-plugins">
+<h1><a class="toc-backref" href="#id11">Compiling LLVMC plugins</a></h1>
+<p>It's easiest to start working on your own LLVMC plugin by copying the
+skeleton project which lives under <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins/Simple</span></tt>:</p>
+<pre class="literal-block">
+$ cd $LLVMC_DIR/plugins
+$ cp -r Simple MyPlugin
+$ cd MyPlugin
+$ ls
+Makefile PluginMain.cpp Simple.td
+</pre>
+<p>As you can see, our basic plugin consists of only two files (not
+counting the build script). <tt class="docutils literal"><span class="pre">Simple.td</span></tt> contains TableGen
+description of the compilation graph; its format is documented in the
+following sections. <tt class="docutils literal"><span class="pre">PluginMain.cpp</span></tt> is just a helper file used to
+compile the auto-generated C++ code produced from TableGen source. It
+can also contain hook definitions (see <a class="reference internal" href="#hooks">below</a>).</p>
+<p>The first thing that you should do is to change the <tt class="docutils literal"><span class="pre">LLVMC_PLUGIN</span></tt>
+variable in the <tt class="docutils literal"><span class="pre">Makefile</span></tt> to avoid conflicts (since this variable
+is used to name the resulting library):</p>
+<pre class="literal-block">
+LLVMC_PLUGIN=MyPlugin
+</pre>
+<p>It is also a good idea to rename <tt class="docutils literal"><span class="pre">Simple.td</span></tt> to something less
+generic:</p>
+<pre class="literal-block">
+$ mv Simple.td MyPlugin.td
+</pre>
+<p>To build your plugin as a dynamic library, just <tt class="docutils literal"><span class="pre">cd</span></tt> to its source
+directory and run <tt class="docutils literal"><span class="pre">make</span></tt>. The resulting file will be called
+<tt class="docutils literal"><span class="pre">plugin_llvmc_$(LLVMC_PLUGIN).$(DLL_EXTENSION)</span></tt> (in our case,
+<tt class="docutils literal"><span class="pre">plugin_llvmc_MyPlugin.so</span></tt>). This library can be then loaded in with the
+<tt class="docutils literal"><span class="pre">-load</span></tt> option. Example:</p>
+<pre class="literal-block">
+$ cd $LLVMC_DIR/plugins/Simple
+$ make
+$ llvmc -load $LLVM_DIR/Release/lib/plugin_llvmc_Simple.so
+</pre>
+</div>
+<div class="section" id="compiling-standalone-llvmc-based-drivers">
+<h1><a class="toc-backref" href="#id12">Compiling standalone LLVMC-based drivers</a></h1>
+<p>By default, the <tt class="docutils literal"><span class="pre">llvmc</span></tt> executable consists of a driver core plus several
+statically linked plugins (<tt class="docutils literal"><span class="pre">Base</span></tt> and <tt class="docutils literal"><span class="pre">Clang</span></tt> at the moment). You can
+produce a standalone LLVMC-based driver executable by linking the core with your
+own plugins. The recommended way to do this is by starting with the provided
+<tt class="docutils literal"><span class="pre">Skeleton</span></tt> example (<tt class="docutils literal"><span class="pre">$LLVMC_DIR/example/Skeleton</span></tt>):</p>
+<pre class="literal-block">
+$ cd $LLVMC_DIR/example/
+$ cp -r Skeleton mydriver
+$ cd mydriver
+$ vim Makefile
+[...]
+$ make
+</pre>
+<p>If you're compiling LLVM with different source and object directories, then you
+must perform the following additional steps before running <tt class="docutils literal"><span class="pre">make</span></tt>:</p>
+<pre class="literal-block">
+# LLVMC_SRC_DIR = $LLVM_SRC_DIR/tools/llvmc/
+# LLVMC_OBJ_DIR = $LLVM_OBJ_DIR/tools/llvmc/
+$ cp $LLVMC_SRC_DIR/example/mydriver/Makefile \
+ $LLVMC_OBJ_DIR/example/mydriver/
+$ cd $LLVMC_OBJ_DIR/example/mydriver
+$ make
+</pre>
+<p>Another way to do the same thing is by using the following command:</p>
+<pre class="literal-block">
+$ cd $LLVMC_DIR
+$ make LLVMC_BUILTIN_PLUGINS=MyPlugin LLVMC_BASED_DRIVER_NAME=mydriver
+</pre>
+<p>This works with both srcdir == objdir and srcdir != objdir, but assumes that the
+plugin source directory was placed under <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins</span></tt>.</p>
+<p>Sometimes, you will want a 'bare-bones' version of LLVMC that has no
+built-in plugins. It can be compiled with the following command:</p>
+<pre class="literal-block">
+$ cd $LLVMC_DIR
+$ make LLVMC_BUILTIN_PLUGINS=&quot;&quot;
+</pre>
+</div>
+<div class="section" id="customizing-llvmc-the-compilation-graph">
+<h1><a class="toc-backref" href="#id13">Customizing LLVMC: the compilation graph</a></h1>
+<p>Each TableGen configuration file should include the common
+definitions:</p>
+<pre class="literal-block">
+include &quot;llvm/CompilerDriver/Common.td&quot;
+</pre>
+<p>Internally, LLVMC stores information about possible source
+transformations in form of a graph. Nodes in this graph represent
+tools, and edges between two nodes represent a transformation path. A
+special &quot;root&quot; node is used to mark entry points for the
+transformations. LLVMC also assigns a weight to each edge (more on
+this later) to choose between several alternative edges.</p>
+<p>The definition of the compilation graph (see file
+<tt class="docutils literal"><span class="pre">plugins/Base/Base.td</span></tt> for an example) is just a list of edges:</p>
+<pre class="literal-block">
+def CompilationGraph : CompilationGraph&lt;[
+ Edge&lt;&quot;root&quot;, &quot;llvm_gcc_c&quot;&gt;,
+ Edge&lt;&quot;root&quot;, &quot;llvm_gcc_assembler&quot;&gt;,
+ ...
+
+ Edge&lt;&quot;llvm_gcc_c&quot;, &quot;llc&quot;&gt;,
+ Edge&lt;&quot;llvm_gcc_cpp&quot;, &quot;llc&quot;&gt;,
+ ...
+
+ OptionalEdge&lt;&quot;llvm_gcc_c&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
+ (inc_weight))&gt;,
+ OptionalEdge&lt;&quot;llvm_gcc_cpp&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
+ (inc_weight))&gt;,
+ ...
+
+ OptionalEdge&lt;&quot;llvm_gcc_assembler&quot;, &quot;llvm_gcc_cpp_linker&quot;,
+ (case (input_languages_contain &quot;c++&quot;), (inc_weight),
+ (or (parameter_equals &quot;linker&quot;, &quot;g++&quot;),
+ (parameter_equals &quot;linker&quot;, &quot;c++&quot;)), (inc_weight))&gt;,
+ ...
+
+ ]&gt;;
+</pre>
+<p>As you can see, the edges can be either default or optional, where
+optional edges are differentiated by an additional <tt class="docutils literal"><span class="pre">case</span></tt> expression
+used to calculate the weight of this edge. Notice also that we refer
+to tools via their names (as strings). This makes it possible to add
+edges to an existing compilation graph in plugins without having to
+know about all tool definitions used in the graph.</p>
+<p>The default edges are assigned a weight of 1, and optional edges get a
+weight of 0 + 2*N where N is the number of tests that evaluated to
+true in the <tt class="docutils literal"><span class="pre">case</span></tt> expression. It is also possible to provide an
+integer parameter to <tt class="docutils literal"><span class="pre">inc_weight</span></tt> and <tt class="docutils literal"><span class="pre">dec_weight</span></tt> - in this case,
+the weight is increased (or decreased) by the provided value instead
+of the default 2. It is also possible to change the default weight of
+an optional edge by using the <tt class="docutils literal"><span class="pre">default</span></tt> clause of the <tt class="docutils literal"><span class="pre">case</span></tt>
+construct.</p>
+<p>When passing an input file through the graph, LLVMC picks the edge
+with the maximum weight. To avoid ambiguity, there should be only one
+default edge between two nodes (with the exception of the root node,
+which gets a special treatment - there you are allowed to specify one
+default edge <em>per language</em>).</p>
+<p>When multiple plugins are loaded, their compilation graphs are merged
+together. Since multiple edges that have the same end nodes are not
+allowed (i.e. the graph is not a multigraph), an edge defined in
+several plugins will be replaced by the definition from the plugin
+that was loaded last. Plugin load order can be controlled by using the
+plugin priority feature described above.</p>
+<p>To get a visual representation of the compilation graph (useful for
+debugging), run <tt class="docutils literal"><span class="pre">llvmc</span> <span class="pre">--view-graph</span></tt>. You will need <tt class="docutils literal"><span class="pre">dot</span></tt> and
+<tt class="docutils literal"><span class="pre">gsview</span></tt> installed for this to work properly.</p>
+</div>
+<div class="section" id="describing-options">
+<h1><a class="toc-backref" href="#id14">Describing options</a></h1>
+<p>Command-line options that the plugin supports are defined by using an
+<tt class="docutils literal"><span class="pre">OptionList</span></tt>:</p>
+<pre class="literal-block">
+def Options : OptionList&lt;[
+(switch_option &quot;E&quot;, (help &quot;Help string&quot;)),
+(alias_option &quot;quiet&quot;, &quot;q&quot;)
+...
+]&gt;;
+</pre>
+<p>As you can see, the option list is just a list of DAGs, where each DAG
+is an option description consisting of the option name and some
+properties. A plugin can define more than one option list (they are
+all merged together in the end), which can be handy if one wants to
+separate option groups syntactically.</p>
+<ul>
+<li><p class="first">Possible option types:</p>
+<blockquote>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">switch_option</span></tt> - a simple boolean switch without arguments, for example
+<tt class="docutils literal"><span class="pre">-O2</span></tt> or <tt class="docutils literal"><span class="pre">-time</span></tt>. At most one occurrence is allowed.</li>
+<li><tt class="docutils literal"><span class="pre">parameter_option</span></tt> - option that takes one argument, for example
+<tt class="docutils literal"><span class="pre">-std=c99</span></tt>. It is also allowed to use spaces instead of the equality
+sign: <tt class="docutils literal"><span class="pre">-std</span> <span class="pre">c99</span></tt>. At most one occurrence is allowed.</li>
+<li><tt class="docutils literal"><span class="pre">parameter_list_option</span></tt> - same as the above, but more than one option
+occurence is allowed.</li>
+<li><tt class="docutils literal"><span class="pre">prefix_option</span></tt> - same as the parameter_option, but the option name and
+argument do not have to be separated. Example: <tt class="docutils literal"><span class="pre">-ofile</span></tt>. This can be also
+specified as <tt class="docutils literal"><span class="pre">-o</span> <span class="pre">file</span></tt>; however, <tt class="docutils literal"><span class="pre">-o=file</span></tt> will be parsed incorrectly
+(<tt class="docutils literal"><span class="pre">=file</span></tt> will be interpreted as option value). At most one occurrence is
+allowed.</li>
+<li><tt class="docutils literal"><span class="pre">prefix_list_option</span></tt> - same as the above, but more than one occurence of
+the option is allowed; example: <tt class="docutils literal"><span class="pre">-lm</span> <span class="pre">-lpthread</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">alias_option</span></tt> - a special option type for creating aliases. Unlike other
+option types, aliases are not allowed to have any properties besides the
+aliased option name. Usage example: <tt class="docutils literal"><span class="pre">(alias_option</span> <span class="pre">&quot;preprocess&quot;,</span> <span class="pre">&quot;E&quot;)</span></tt></li>
+</ul>
+</blockquote>
+</li>
+<li><p class="first">Possible option properties:</p>
+<blockquote>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">help</span></tt> - help string associated with this option. Used for <tt class="docutils literal"><span class="pre">-help</span></tt>
+output.</li>
+<li><tt class="docutils literal"><span class="pre">required</span></tt> - this option must be specified exactly once (or, in case of
+the list options without the <tt class="docutils literal"><span class="pre">multi_val</span></tt> property, at least
+once). Incompatible with <tt class="docutils literal"><span class="pre">zero_or_one</span></tt> and <tt class="docutils literal"><span class="pre">one_or_more</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">one_or_more</span></tt> - the option must be specified at least one time. Useful
+only for list options in conjunction with <tt class="docutils literal"><span class="pre">multi_val</span></tt>; for ordinary lists
+it is synonymous with <tt class="docutils literal"><span class="pre">required</span></tt>. Incompatible with <tt class="docutils literal"><span class="pre">required</span></tt> and
+<tt class="docutils literal"><span class="pre">zero_or_one</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">optional</span></tt> - the option can be specified zero or one times. Useful only
+for list options in conjunction with <tt class="docutils literal"><span class="pre">multi_val</span></tt>. Incompatible with
+<tt class="docutils literal"><span class="pre">required</span></tt> and <tt class="docutils literal"><span class="pre">one_or_more</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">hidden</span></tt> - the description of this option will not appear in
+the <tt class="docutils literal"><span class="pre">-help</span></tt> output (but will appear in the <tt class="docutils literal"><span class="pre">-help-hidden</span></tt>
+output).</li>
+<li><tt class="docutils literal"><span class="pre">really_hidden</span></tt> - the option will not be mentioned in any help
+output.</li>
+<li><tt class="docutils literal"><span class="pre">comma_separated</span></tt> - Indicates that any commas specified for an option's
+value should be used to split the value up into multiple values for the
+option. This property is valid only for list options. In conjunction with
+<tt class="docutils literal"><span class="pre">forward_value</span></tt> can be used to implement option forwarding in style of
+gcc's <tt class="docutils literal"><span class="pre">-Wa,</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">multi_val</span> <span class="pre">n</span></tt> - this option takes <em>n</em> arguments (can be useful in some
+special cases). Usage example: <tt class="docutils literal"><span class="pre">(parameter_list_option</span> <span class="pre">&quot;foo&quot;,</span> <span class="pre">(multi_val</span>
+<span class="pre">3))</span></tt>; the command-line syntax is '-foo a b c'. Only list options can have
+this attribute; you can, however, use the <tt class="docutils literal"><span class="pre">one_or_more</span></tt>, <tt class="docutils literal"><span class="pre">optional</span></tt>
+and <tt class="docutils literal"><span class="pre">required</span></tt> properties.</li>
+<li><tt class="docutils literal"><span class="pre">init</span></tt> - this option has a default value, either a string (if it is a
+parameter), or a boolean (if it is a switch; as in C++, boolean constants
+are called <tt class="docutils literal"><span class="pre">true</span></tt> and <tt class="docutils literal"><span class="pre">false</span></tt>). List options can't have <tt class="docutils literal"><span class="pre">init</span></tt>
+attribute.
+Usage examples: <tt class="docutils literal"><span class="pre">(switch_option</span> <span class="pre">&quot;foo&quot;,</span> <span class="pre">(init</span> <span class="pre">true))</span></tt>; <tt class="docutils literal"><span class="pre">(prefix_option</span>
+<span class="pre">&quot;bar&quot;,</span> <span class="pre">(init</span> <span class="pre">&quot;baz&quot;))</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">extern</span></tt> - this option is defined in some other plugin, see <a class="reference internal" href="#extern">below</a>.</li>
+</ul>
+</blockquote>
+</li>
+</ul>
+<div class="section" id="external-options">
+<span id="extern"></span><h2><a class="toc-backref" href="#id15">External options</a></h2>
+<p>Sometimes, when linking several plugins together, one plugin needs to
+access options defined in some other plugin. Because of the way
+options are implemented, such options must be marked as
+<tt class="docutils literal"><span class="pre">extern</span></tt>. This is what the <tt class="docutils literal"><span class="pre">extern</span></tt> option property is
+for. Example:</p>
+<pre class="literal-block">
+...
+(switch_option &quot;E&quot;, (extern))
+...
+</pre>
+<p>If an external option has additional attributes besides 'extern', they are
+ignored. See also the section on plugin <a class="reference internal" href="#priorities">priorities</a>.</p>
+</div>
+</div>
+<div class="section" id="conditional-evaluation">
+<span id="case"></span><h1><a class="toc-backref" href="#id16">Conditional evaluation</a></h1>
+<p>The 'case' construct is the main means by which programmability is
+achieved in LLVMC. It can be used to calculate edge weights, program
+actions and modify the shell commands to be executed. The 'case'
+expression is designed after the similarly-named construct in
+functional languages and takes the form <tt class="docutils literal"><span class="pre">(case</span> <span class="pre">(test_1),</span> <span class="pre">statement_1,</span>
+<span class="pre">(test_2),</span> <span class="pre">statement_2,</span> <span class="pre">...</span> <span class="pre">(test_N),</span> <span class="pre">statement_N)</span></tt>. The statements
+are evaluated only if the corresponding tests evaluate to true.</p>
+<p>Examples:</p>
+<pre class="literal-block">
+// Edge weight calculation
+
+// Increases edge weight by 5 if &quot;-A&quot; is provided on the
+// command-line, and by 5 more if &quot;-B&quot; is also provided.
+(case
+ (switch_on &quot;A&quot;), (inc_weight 5),
+ (switch_on &quot;B&quot;), (inc_weight 5))
+
+
+// Tool command line specification
+
+// Evaluates to &quot;cmdline1&quot; if the option &quot;-A&quot; is provided on the
+// command line; to &quot;cmdline2&quot; if &quot;-B&quot; is provided;
+// otherwise to &quot;cmdline3&quot;.
+
+(case
+ (switch_on &quot;A&quot;), &quot;cmdline1&quot;,
+ (switch_on &quot;B&quot;), &quot;cmdline2&quot;,
+ (default), &quot;cmdline3&quot;)
+</pre>
+<p>Note the slight difference in 'case' expression handling in contexts
+of edge weights and command line specification - in the second example
+the value of the <tt class="docutils literal"><span class="pre">&quot;B&quot;</span></tt> switch is never checked when switch <tt class="docutils literal"><span class="pre">&quot;A&quot;</span></tt> is
+enabled, and the whole expression always evaluates to <tt class="docutils literal"><span class="pre">&quot;cmdline1&quot;</span></tt> in
+that case.</p>
+<p>Case expressions can also be nested, i.e. the following is legal:</p>
+<pre class="literal-block">
+(case (switch_on &quot;E&quot;), (case (switch_on &quot;o&quot;), ..., (default), ...)
+ (default), ...)
+</pre>
+<p>You should, however, try to avoid doing that because it hurts
+readability. It is usually better to split tool descriptions and/or
+use TableGen inheritance instead.</p>
+<ul class="simple">
+<li>Possible tests are:<ul>
+<li><tt class="docutils literal"><span class="pre">switch_on</span></tt> - Returns true if a given command-line switch is provided by
+the user. Can be given a list as argument, in that case <tt class="docutils literal"><span class="pre">(switch_on</span> <span class="pre">[&quot;foo&quot;,</span>
+<span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(and</span> <span class="pre">(switch_on</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(switch_on</span>
+<span class="pre">&quot;bar&quot;),</span> <span class="pre">(switch_on</span> <span class="pre">&quot;baz&quot;))</span></tt>.
+Example: <tt class="docutils literal"><span class="pre">(switch_on</span> <span class="pre">&quot;opt&quot;)</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">any_switch_on</span></tt> - Given a list of switch options, returns true if any of
+the switches is turned on.
+Example: <tt class="docutils literal"><span class="pre">(any_switch_on</span> <span class="pre">[&quot;foo&quot;,</span> <span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(or</span>
+<span class="pre">(switch_on</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(switch_on</span> <span class="pre">&quot;bar&quot;),</span> <span class="pre">(switch_on</span> <span class="pre">&quot;baz&quot;))</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">parameter_equals</span></tt> - Returns true if a command-line parameter equals
+a given value.
+Example: <tt class="docutils literal"><span class="pre">(parameter_equals</span> <span class="pre">&quot;W&quot;,</span> <span class="pre">&quot;all&quot;)</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">element_in_list</span></tt> - Returns true if a command-line parameter
+list contains a given value.
+Example: <tt class="docutils literal"><span class="pre">(element_in_list</span> <span class="pre">&quot;l&quot;,</span> <span class="pre">&quot;pthread&quot;)</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">input_languages_contain</span></tt> - Returns true if a given language
+belongs to the current input language set.
+Example: <tt class="docutils literal"><span class="pre">(input_languages_contain</span> <span class="pre">&quot;c++&quot;)</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">in_language</span></tt> - Evaluates to true if the input file language is equal to
+the argument. At the moment works only with <tt class="docutils literal"><span class="pre">cmd_line</span></tt> and <tt class="docutils literal"><span class="pre">actions</span></tt> (on
+non-join nodes).
+Example: <tt class="docutils literal"><span class="pre">(in_language</span> <span class="pre">&quot;c++&quot;)</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">not_empty</span></tt> - Returns true if a given option (which should be either a
+parameter or a parameter list) is set by the user. Like <tt class="docutils literal"><span class="pre">switch_on</span></tt>, can
+be also given a list as argument.
+Example: <tt class="docutils literal"><span class="pre">(not_empty</span> <span class="pre">&quot;o&quot;)</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">any_not_empty</span></tt> - Returns true if <tt class="docutils literal"><span class="pre">not_empty</span></tt> returns true for any of
+the options in the list.
+Example: <tt class="docutils literal"><span class="pre">(any_not_empty</span> <span class="pre">[&quot;foo&quot;,</span> <span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(or</span>
+<span class="pre">(not_empty</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;bar&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;baz&quot;))</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">empty</span></tt> - The opposite of <tt class="docutils literal"><span class="pre">not_empty</span></tt>. Equivalent to <tt class="docutils literal"><span class="pre">(not</span> <span class="pre">(not_empty</span>
+<span class="pre">X))</span></tt>. Provided for convenience. Can be given a list as argument.</li>
+<li><tt class="docutils literal"><span class="pre">any_not_empty</span></tt> - Returns true if <tt class="docutils literal"><span class="pre">not_empty</span></tt> returns true for any of
+the options in the list.
+Example: <tt class="docutils literal"><span class="pre">(any_empty</span> <span class="pre">[&quot;foo&quot;,</span> <span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(not</span> <span class="pre">(and</span>
+<span class="pre">(not_empty</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;bar&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;baz&quot;)))</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">single_input_file</span></tt> - Returns true if there was only one input file
+provided on the command-line. Used without arguments:
+<tt class="docutils literal"><span class="pre">(single_input_file)</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">multiple_input_files</span></tt> - Equivalent to <tt class="docutils literal"><span class="pre">(not</span> <span class="pre">(single_input_file))</span></tt> (the
+case of zero input files is considered an error).</li>
+<li><tt class="docutils literal"><span class="pre">default</span></tt> - Always evaluates to true. Should always be the last
+test in the <tt class="docutils literal"><span class="pre">case</span></tt> expression.</li>
+<li><tt class="docutils literal"><span class="pre">and</span></tt> - A standard binary logical combinator that returns true iff all of
+its arguments return true. Used like this: <tt class="docutils literal"><span class="pre">(and</span> <span class="pre">(test1),</span> <span class="pre">(test2),</span>
+<span class="pre">...</span> <span class="pre">(testN))</span></tt>. Nesting of <tt class="docutils literal"><span class="pre">and</span></tt> and <tt class="docutils literal"><span class="pre">or</span></tt> is allowed, but not
+encouraged.</li>
+<li><tt class="docutils literal"><span class="pre">or</span></tt> - A binary logical combinator that returns true iff any of its
+arguments returns true. Example: <tt class="docutils literal"><span class="pre">(or</span> <span class="pre">(test1),</span> <span class="pre">(test2),</span> <span class="pre">...</span> <span class="pre">(testN))</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">not</span></tt> - Standard unary logical combinator that negates its
+argument. Example: <tt class="docutils literal"><span class="pre">(not</span> <span class="pre">(or</span> <span class="pre">(test1),</span> <span class="pre">(test2),</span> <span class="pre">...</span> <span class="pre">(testN)))</span></tt>.</li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="writing-a-tool-description">
+<h1><a class="toc-backref" href="#id17">Writing a tool description</a></h1>
+<p>As was said earlier, nodes in the compilation graph represent tools,
+which are described separately. A tool definition looks like this
+(taken from the <tt class="docutils literal"><span class="pre">include/llvm/CompilerDriver/Tools.td</span></tt> file):</p>
+<pre class="literal-block">
+def llvm_gcc_cpp : Tool&lt;[
+ (in_language &quot;c++&quot;),
+ (out_language &quot;llvm-assembler&quot;),
+ (output_suffix &quot;bc&quot;),
+ (cmd_line &quot;llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm&quot;),
+ (sink)
+ ]&gt;;
+</pre>
+<p>This defines a new tool called <tt class="docutils literal"><span class="pre">llvm_gcc_cpp</span></tt>, which is an alias for
+<tt class="docutils literal"><span class="pre">llvm-g++</span></tt>. As you can see, a tool definition is just a list of