From 2b066988909948dc3d53d01760bc2d71d32f3feb Mon Sep 17 00:00:00 2001
From: dim <dim@FreeBSD.org>
Date: Mon, 2 May 2011 19:34:44 +0000
Subject: Vendor import of llvm trunk r130700:
 http://llvm.org/svn/llvm-project/llvm/trunk@130700

---
 docs/CompilerDriver.html | 771 +++++++++++++++++++++--------------------------
 1 file changed, 351 insertions(+), 420 deletions(-)

(limited to 'docs/CompilerDriver.html')
diff --git a/docs/CompilerDriver.html b/docs/CompilerDriver.html
index c63e174..03db3a0 100644
--- a/docs/CompilerDriver.html
+++ b/docs/CompilerDriver.html
@@ -3,7 +3,7 @@
 <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/" />
+<meta name="generator" content="Docutils 0.6: http://docutils.sourceforge.net/" />
 <title>Customizing LLVMC: Reference Manual</title>
 <link rel="stylesheet" href="llvm.css" type="text/css" />
 </head>
@@ -17,28 +17,23 @@ 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>
+<li><a class="reference internal" href="#introduction" id="id7">Introduction</a></li>
+<li><a class="reference internal" href="#compiling-with-llvmc" id="id8">Compiling with <tt class="docutils literal">llvmc</tt></a></li>
+<li><a class="reference internal" href="#predefined-options" id="id9">Predefined options</a></li>
+<li><a class="reference internal" href="#compiling-llvmc-based-drivers" id="id10">Compiling LLVMC-based drivers</a></li>
+<li><a class="reference internal" href="#customizing-llvmc-the-compilation-graph" id="id11">Customizing LLVMC: the compilation graph</a></li>
+<li><a class="reference internal" href="#describing-options" id="id12">Describing options</a></li>
+<li><a class="reference internal" href="#conditional-evaluation" id="id13">Conditional evaluation</a></li>
+<li><a class="reference internal" href="#writing-a-tool-description" id="id14">Writing a tool description</a><ul>
+<li><a class="reference internal" href="#id4" id="id15">Actions</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>
+<li><a class="reference internal" href="#language-map" id="id16">Language map</a></li>
+<li><a class="reference internal" href="#option-preprocessor" id="id17">Option preprocessor</a></li>
+<li><a class="reference internal" href="#more-advanced-topics" id="id18">More advanced topics</a><ul>
+<li><a class="reference internal" href="#hooks-and-environment-variables" id="id19">Hooks and environment variables</a></li>
+<li><a class="reference internal" href="#debugging" id="id20">Debugging</a></li>
+<li><a class="reference internal" href="#conditioning-on-the-executable-name" id="id21">Conditioning on the executable name</a></li>
 </ul>
 </li>
 </ul>
@@ -46,25 +41,24 @@ The ReST source lives in the directory 'tools/llvmc/doc'. -->
 <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>
+<h1><a class="toc-backref" href="#id7">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>
+extensible. It plays the same role for LLVM as the <tt class="docutils literal">gcc</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 described in
+high-level TableGen code, from which an efficient C++ representation is
+automatically derived. This makes it possible to 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,
+<h1><a class="toc-backref" href="#id8">Compiling with <tt class="docutils literal">llvmc</tt></a></h1>
+<p>LLVMC tries hard to be as compatible with <tt class="docutils literal">gcc</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">
@@ -74,11 +68,11 @@ $ ./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
+different compilers for different languages (think <tt class="docutils literal">g++</tt> vs.  <tt class="docutils literal">gcc</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>
+do it with <tt class="docutils literal">gcc</tt>:</p>
 <pre class="literal-block">
 $ # hello.c is really a C++ file
 $ llvmc -x c++ hello.c
@@ -97,138 +91,100 @@ $ ./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>
+possible to choose the <tt class="docutils literal">clang</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>
+<h1><a class="toc-backref" href="#id9">Predefined options</a></h1>
+<p>LLVMC has some built-in options that can't be overridden in the TableGen code:</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
+<li><tt class="docutils literal"><span class="pre">-o</span> FILE</tt> - Output file name.</li>
+<li><tt class="docutils literal"><span class="pre">-x</span> LANGUAGE</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
+<li><tt class="docutils literal"><span class="pre">--temp-dir</span> DIRECTORY</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>
+output/input language names, multiple default edges and cycles. Exit with code
+zero if no errors were found, and return the number of found errors
+otherwise. Hidden option, useful for debugging.</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>
+and exit. Requires that you have <tt class="docutils literal">dot</tt> and <tt class="docutils literal">gv</tt> programs installed. Hidden
+option, useful for debugging.</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
+used to set the output file name. Hidden option, useful for debugging.</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>
+<div class="section" id="compiling-llvmc-based-drivers">
+<h1><a class="toc-backref" href="#id10">Compiling LLVMC-based drivers</a></h1>
+<p>It's easiest to start working on your own LLVMC driver by copying the skeleton
+project which lives under <tt class="docutils literal">$LLVMC_DIR/examples/Skeleton</tt>:</p>
 <pre class="literal-block">
-$ cd $LLVMC_DIR/plugins
-$ cp -r Simple MyPlugin
-$ cd MyPlugin
+$ cd $LLVMC_DIR/examples
+$ cp -r Skeleton MyDriver
+$ cd MyDriver
 $ 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
+AutoGenerated.td  Hooks.cpp  Main.cpp  Makefile
 </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>
+<p>As you can see, our basic driver consists of only three files (not counting the
+build script). <tt class="docutils literal">AutoGenerated.td</tt> contains TableGen description of the
+compilation graph; its format is documented in the following
+sections. <tt class="docutils literal">Hooks.cpp</tt> is an empty file that should be used for hook
+definitions (see <a class="reference internal" href="#hooks">below</a>). <tt class="docutils literal">Main.cpp</tt> is just a helper used to compile the
+auto-generated C++ code produced from TableGen source.</p>
+<p>The first thing that you should do is to change the <tt class="docutils literal">LLVMC_BASED_DRIVER</tt>
+variable in the <tt class="docutils literal">Makefile</tt>:</p>
 <pre class="literal-block">
-$ mv Simple.td MyPlugin.td
+LLVMC_BASED_DRIVER=MyDriver
 </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>
+<p>It can also be a good idea to put your TableGen code into a file with a less
+generic name:</p>
 <pre class="literal-block">
-$ cd $LLVMC_DIR/example/
-$ cp -r Skeleton mydriver
-$ cd mydriver
-$ vim Makefile
+$ touch MyDriver.td
+$ vim AutoGenerated.td
 [...]
-$ make
+include &quot;MyDriver.td&quot;
 </pre>
+<p>If you have more than one TableGen source file, they all should be included from
+<tt class="docutils literal">AutoGenerated.td</tt>, since this file is used by the build system to generate
+C++ code.</p>
+<p>To build your driver, just <tt class="docutils literal">cd</tt> to its source directory and run <tt class="docutils literal">make</tt>. The
+resulting executable will be put into <tt class="docutils literal"><span class="pre">$LLVM_OBJ_DIR/$(BuildMode)/bin</span></tt>.</p>
 <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>
+must perform the following additional steps before running <tt class="docutils literal">make</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 $LLVMC_OBJ_DIR/example/mydriver
+$ mkdir $LLVMC_OBJ_DIR/examples/MyDriver/
+$ cp $LLVMC_SRC_DIR/examples/MyDriver/Makefile \
+  $LLVMC_OBJ_DIR/examples/MyDriver/
+$ cd $LLVMC_OBJ_DIR/examples/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>
+<h1><a class="toc-backref" href="#id11">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>
+<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">llvmc/src/Base.td</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;,
@@ -253,39 +209,33 @@ def CompilationGraph : CompilationGraph&lt;[
 
     ]&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>
+<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">case</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
+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">case</tt>
+expression. It is also possible to provide an integer parameter to
+<tt class="docutils literal">inc_weight</tt> and <tt class="docutils literal">dec_weight</tt> - in this case, the weight is increased (or
+decreased) by the provided value instead of the default 2. Default weight of an
+optional edge can be changed by using the <tt class="docutils literal">default</tt> clause of the <tt class="docutils literal">case</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>
+<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 compilation graphs are defined, they are merged together. Multiple
+edges with the same end nodes are not allowed (i.e. the graph is not a
+multigraph), and will lead to a compile-time error.</p>
+<p>To get a visual representation of the compilation graph (useful for debugging),
+run <tt class="docutils literal">llvmc <span class="pre">--view-graph</span></tt>. You will need <tt class="docutils literal">dot</tt> and <tt class="docutils literal">gsview</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>
+<h1><a class="toc-backref" href="#id12">Describing options</a></h1>
+<p>Command-line options supported by the driver are defined by using an
+<tt class="docutils literal">OptionList</tt>:</p>
 <pre class="literal-block">
 def Options : OptionList&lt;[
 (switch_option &quot;E&quot;, (help &quot;Help string&quot;)),
@@ -293,101 +243,95 @@ def Options : OptionList&lt;[
 ...
 ]&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>
+<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. More than
+one option list can be defined (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
+<li><tt class="docutils literal">switch_option</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 by default.</li>
+<li><tt class="docutils literal">parameter_option</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
+sign: <tt class="docutils literal"><span class="pre">-std</span> c99</tt>. At most one occurrence is allowed.</li>
+<li><tt class="docutils literal">parameter_list_option</tt> - same as the above, but more than one option
+occurrence is allowed.</li>
+<li><tt class="docutils literal">prefix_option</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
+specified as <tt class="docutils literal"><span class="pre">-o</span> file</tt>; however, <tt class="docutils literal"><span class="pre">-o=file</span></tt> will be parsed incorrectly
+(<tt class="docutils literal">=file</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
+<li><tt class="docutils literal">prefix_list_option</tt> - same as the above, but more than one occurrence 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
+<li><tt class="docutils literal">alias_option</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>
+aliased option name.
+Usage example: <tt class="docutils literal">(alias_option &quot;preprocess&quot;, &quot;E&quot;)</tt></li>
+<li><tt class="docutils literal">switch_list_option</tt> - like <tt class="docutils literal">switch_option</tt> with the <tt class="docutils literal">zero_or_more</tt>
+property, but remembers how many times the switch was turned on. Useful
+mostly for forwarding. Example: when <tt class="docutils literal"><span class="pre">-foo</span></tt> is a switch option (with the
+<tt class="docutils literal">zero_or_more</tt> property), the command <tt class="docutils literal">driver <span class="pre">-foo</span> <span class="pre">-foo</span></tt> is forwarded
+as <tt class="docutils literal"><span class="pre">some-tool</span> <span class="pre">-foo</span></tt>, but when <tt class="docutils literal"><span class="pre">-foo</span></tt> is a switch list, the same command
+is forwarded as <tt class="docutils literal"><span class="pre">some-tool</span> <span class="pre">-foo</span> <span class="pre">-foo</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>
+<li><tt class="docutils literal">help</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>
+<li><tt class="docutils literal">required</tt> - this option must be specified exactly once (or, in case of
+the list options without the <tt class="docutils literal">multi_val</tt> property, at least
+once). Incompatible with <tt class="docutils literal">optional</tt> and <tt class="docutils literal">one_or_more</tt>.</li>
+<li><tt class="docutils literal">optional</tt> - the option can be specified either zero times or exactly
+once. The default for switch options. Useful only for list options in
+conjunction with <tt class="docutils literal">multi_val</tt>. Incompatible with <tt class="docutils literal">required</tt>,
+<tt class="docutils literal">zero_or_more</tt> and <tt class="docutils literal">one_or_more</tt>.</li>
+<li><tt class="docutils literal">one_or_more</tt> - the option must be specified at least once. Can be useful
+to allow switch options be both obligatory and be specified multiple
+times. For list options is useful only in conjunction with <tt class="docutils literal">multi_val</tt>;
+for ordinary it is synonymous with <tt class="docutils literal">required</tt>. Incompatible with
+<tt class="docutils literal">required</tt>, <tt class="docutils literal">optional</tt> and <tt class="docutils literal">zero_or_more</tt>.</li>
+<li><tt class="docutils literal">zero_or_more</tt> - the option can be specified zero or more times. Useful
+to allow a single switch option to be specified more than
+once. Incompatible with <tt class="docutils literal">required</tt>, <tt class="docutils literal">optional</tt> and <tt class="docutils literal">one_or_more</tt>.</li>
+<li><tt class="docutils literal">hidden</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
+<li><tt class="docutils literal">really_hidden</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
+<li><tt class="docutils literal">comma_separated</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
+<tt class="docutils literal">forward_value</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
+<li><tt class="docutils literal">multi_val n</tt> - this option takes <em>n</em> arguments (can be useful in some
+special cases). Usage example: <tt class="docutils literal">(parameter_list_option &quot;foo&quot;, (multi_val
+3))</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">one_or_more</tt>, <tt class="docutils literal">optional</tt>
+and <tt class="docutils literal">required</tt> properties.</li>
+<li><tt class="docutils literal">init</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>
+are called <tt class="docutils literal">true</tt> and <tt class="docutils literal">false</tt>). List options can't have <tt class="docutils literal">init</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>
+Usage examples: <tt class="docutils literal">(switch_option &quot;foo&quot;, (init true))</tt>; <tt class="docutils literal">(prefix_option
+&quot;bar&quot;, (init <span class="pre">&quot;baz&quot;))</span></tt>.</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>
+<span id="case"></span><h1><a class="toc-backref" href="#id13">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">(case
+(test_1), statement_1, (test_2), statement_2, ... (test_N), statement_N)</tt>. The
+statements are evaluated only if the corresponding tests evaluate to true.</p>
 <p>Examples:</p>
 <pre class="literal-block">
 // Edge weight calculation
@@ -410,129 +354,139 @@ are evaluated only if the corresponding tests evaluate to true.</p>
     (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>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">&quot;B&quot;</tt> switch is never checked when switch <tt class="docutils literal">&quot;A&quot;</tt> is enabled, and the whole
+expression always evaluates to <tt class="docutils literal">&quot;cmdline1&quot;</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>
+<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
+<li><tt class="docutils literal">switch_on</tt> - Returns true if a given command-line switch is provided by
+the user. Can be given multiple arguments, in that case <tt class="docutils literal">(switch_on &quot;foo&quot;,
+&quot;bar&quot;, &quot;baz&quot;)</tt> is equivalent to <tt class="docutils literal">(and (switch_on <span class="pre">&quot;foo&quot;),</span> (switch_on
+<span class="pre">&quot;bar&quot;),</span> (switch_on <span class="pre">&quot;baz&quot;))</span></tt>.
+Example: <tt class="docutils literal">(switch_on &quot;opt&quot;)</tt>.</li>
+<li><tt class="docutils literal">any_switch_on</tt> - Given a number 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
+Example: <tt class="docutils literal">(any_switch_on &quot;foo&quot;, &quot;bar&quot;, &quot;baz&quot;)</tt> is equivalent to <tt class="docutils literal">(or
+(switch_on <span class="pre">&quot;foo&quot;),</span> (switch_on <span class="pre">&quot;bar&quot;),</span> (switch_on <span class="pre">&quot;baz&quot;))</span></tt>.</li>
+<li><tt class="docutils literal">parameter_equals</tt> - Returns true if a command-line parameter (first
+argument) equals a given value (second argument).
+Example: <tt class="docutils literal">(parameter_equals &quot;W&quot;, &quot;all&quot;)</tt>.</li>
+<li><tt class="docutils literal">element_in_list</tt> - Returns true if a command-line parameter list (first
+argument) contains a given value (second argument).
+Example: <tt class="docutils literal">(element_in_list &quot;l&quot;, &quot;pthread&quot;)</tt>.</li>
+<li><tt class="docutils literal">input_languages_contain</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
+Example: <tt class="docutils literal">(input_languages_contain <span class="pre">&quot;c++&quot;)</span></tt>.</li>
+<li><tt class="docutils literal">in_language</tt> - Evaluates to true if the input file language is equal to
+the argument. At the moment works only with <tt class="docutils literal">command</tt> and <tt class="docutils literal">actions</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
+Example: <tt class="docutils literal">(in_language <span class="pre">&quot;c++&quot;)</span></tt>.</li>
+<li><tt class="docutils literal">not_empty</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">switch_on</tt>, can
+be also given multiple arguments.
+Examples: <tt class="docutils literal">(not_empty &quot;o&quot;)</tt>, <tt class="docutils literal">(not_empty &quot;o&quot;, &quot;l&quot;)</tt>.</li>
+<li><tt class="docutils literal">any_not_empty</tt> - Returns true if <tt class="docutils literal">not_empty</tt> returns true for any of
+the provided options.
+Example: <tt class="docutils literal">(any_not_empty &quot;foo&quot;, &quot;bar&quot;, &quot;baz&quot;)</tt> is equivalent to <tt class="docutils literal">(or
+(not_empty <span class="pre">&quot;foo&quot;),</span> (not_empty <span class="pre">&quot;bar&quot;),</span> (not_empty <span class="pre">&quot;baz&quot;))</span></tt>.</li>
+<li><tt class="docutils literal">empty</tt> - The opposite of <tt class="docutils literal">not_empty</tt>. Equivalent to <tt class="docutils literal">(not (not_empty
+X))</tt>. Can be given multiple arguments.</li>
+<li><tt class="docutils literal">any_not_empty</tt> - Returns true if <tt class="docutils literal">not_empty</tt> returns true for any of
+the provided options.
+Example: <tt class="docutils literal">(any_empty &quot;foo&quot;, &quot;bar&quot;, &quot;baz&quot;)</tt> is equivalent to <tt class="docutils literal">(or
+(not_empty <span class="pre">&quot;foo&quot;),</span> (not_empty <span class="pre">&quot;bar&quot;),</span> (not_empty <span class="pre">&quot;baz&quot;))</span></tt>.</li>
+<li><tt class="docutils literal">single_input_file</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
+<tt class="docutils literal">(single_input_file)</tt>.</li>
+<li><tt class="docutils literal">multiple_input_files</tt> - Equivalent to <tt class="docutils literal">(not (single_input_file))</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
+<li><tt class="docutils literal">default</tt> - Always evaluates to true. Should always be the last
+test in the <tt class="docutils literal">case</tt> expression.</li>
+<li><tt class="docutils literal">and</tt> - A standard logical combinator that returns true iff all of
+its arguments return true. Used like this: <tt class="docutils literal">(and (test1), (test2),
+... (testN))</tt>. Nesting of <tt class="docutils literal">and</tt> and <tt class="docutils literal">or</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>
+<li><tt class="docutils literal">or</tt> - A logical combinator that returns true iff any of its arguments
+return true.
+Example: <tt class="docutils literal">(or (test1), (test2), ... (testN))</tt>.</li>
+<li><tt class="docutils literal">not</tt> - Standard unary logical combinator that negates its
+argument.
+Example: <tt class="docutils literal">(not (or (test1), (test2), ... <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>
+<h1><a class="toc-backref" href="#id14">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">llvmc/src/Base.td</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 $OUTFILE -emit-llvm&quot;),
+    (command &quot;llvm-g++ -c -emit-llvm&quot;),
     (sink)
     ]&gt;;
 </pre>
-<p>This defines a new tool called <tt class="docutils literal"><span class="pre">llvm_gcc_cpp</span></tt>, which is an alias for
-<tt class="docutils literal"><span class="pre">llvm-g++</span></tt>. As you can see, a tool definition is just a list of
-properties; most of them should be self-explanatory. The <tt class="docutils literal"><span class="pre">sink</span></tt>
-property means that this tool should be passed all command-line
-options that aren't mentioned in the option list.</p>
+<p>This defines a new tool called <tt class="docutils literal">llvm_gcc_cpp</tt>, which is an alias for
+<tt class="docutils literal"><span class="pre">llvm-g++</span></tt>. As you can see, a tool definition is just a list of properties;
+most of them should be self-explanatory. The <tt class="docutils literal">sink</tt> property means that this
+tool should be passed all command-line options that aren't mentioned in the
+option list.</p>
 <p>The complete list of all currently implemented tool properties follows.</p>
 <ul class="simple">
 <li>Possible tool properties:<ul>
-<li><tt class="docutils literal"><span class="pre">in_language</span></tt> - input language name. Can be either a string or a
-list, in case the tool supports multiple input languages.</li>
-<li><tt class="docutils literal"><span class="pre">out_language</span></tt> - output language name. Multiple output languages are not
-allowed.</li>
-<li><tt class="docutils literal"><span class="pre">output_suffix</span></tt> - output file suffix. Can also be changed
-dynamically, see documentation on actions.</li>
-<li><tt class="docutils literal"><span class="pre">cmd_line</span></tt> - the actual command used to run the tool. You can
-use <tt class="docutils literal"><span class="pre">$INFILE</span></tt> and <tt class="docutils literal"><span class="pre">$OUTFILE</span></tt> variables, output redirection
-with <tt class="docutils literal"><span class="pre">&gt;</span></tt>, hook invocations (<tt class="docutils literal"><span class="pre">$CALL</span></tt>), environment variables
-(via <tt class="docutils literal"><span class="pre">$ENV</span></tt>) and the <tt class="docutils literal"><span class="pre">case</span></tt> construct.</li>
-<li><tt class="docutils literal"><span class="pre">join</span></tt> - this tool is a &quot;join node&quot; in the graph, i.e. it gets a
-list of input files and joins them together. Used for linkers.</li>
-<li><tt class="docutils literal"><span class="pre">sink</span></tt> - all command-line options that are not handled by other
-tools are passed to this tool.</li>
-<li><tt class="docutils literal"><span class="pre">actions</span></tt> - A single big <tt class="docutils literal"><span class="pre">case</span></tt> expression that specifies how
-this tool reacts on command-line options (described in more detail
-<a class="reference internal" href="#actions">below</a>).</li>
+<li><tt class="docutils literal">in_language</tt> - input language name. Can be given multiple arguments, in
+case the tool supports multiple input languages. Used for typechecking and
+mapping file extensions to tools.</li>
+<li><tt class="docutils literal">out_language</tt> - output language name. Multiple output languages are
+allowed. Used for typechecking the compilation graph.</li>
+<li><tt class="docutils literal">output_suffix</tt> - output file suffix. Can also be changed dynamically, see
+documentation on <a class="reference internal" href="#actions">actions</a>.</li>
 </ul>
 </li>
 </ul>
-<div class="section" id="id5">
-<span id="actions"></span><h2><a class="toc-backref" href="#id18">Actions</a></h2>
-<p>A tool often needs to react to command-line options, and this is
-precisely what the <tt class="docutils literal"><span class="pre">actions</span></tt> property is for. The next example
-illustrates this feature:</p>
+<blockquote>
+<ul class="simple">
+<li><tt class="docutils literal">command</tt> - the actual command used to run the tool. You can use output
+redirection with <tt class="docutils literal">&gt;</tt>, hook invocations (<tt class="docutils literal">$CALL</tt>), environment variables
+(via <tt class="docutils literal">$ENV</tt>) and the <tt class="docutils literal">case</tt> construct.</li>
+<li><tt class="docutils literal">join</tt> - this tool is a &quot;join node&quot; in the graph, i.e. it gets a list of
+input files and joins them together. Used for linkers.</li>
+<li><tt class="docutils literal">sink</tt> - all command-line options that are not handled by other tools are
+passed to this tool.</li>
+<li><tt class="docutils literal">actions</tt> - A single big <tt class="docutils literal">case</tt> expression that specifies how this tool
+reacts on command-line options (described in more detail <a class="reference internal" href="#actions">below</a>).</li>
+</ul>
+</blockquote>
+<blockquote>
+<ul class="simple">
+<li><tt class="docutils literal">out_file_option</tt>, <tt class="docutils literal">in_file_option</tt> - Options appended to the
+<tt class="docutils literal">command</tt> string to designate output and input files. Default values are
+<tt class="docutils literal"><span class="pre">&quot;-o&quot;</span></tt> and <tt class="docutils literal">&quot;&quot;</tt>, respectively.</li>
+</ul>
+</blockquote>
+<div class="section" id="id4">
+<span id="actions"></span><h2><a class="toc-backref" href="#id15">Actions</a></h2>
+<p>A tool often needs to react to command-line options, and this is precisely what
+the <tt class="docutils literal">actions</tt> property is for. The next example illustrates this feature:</p>
 <pre class="literal-block">
 def llvm_gcc_linker : Tool&lt;[
     (in_language &quot;object-code&quot;),
     (out_language &quot;executable&quot;),
     (output_suffix &quot;out&quot;),
-    (cmd_line &quot;llvm-gcc $INFILE -o $OUTFILE&quot;),
+    (command &quot;llvm-gcc&quot;),
     (join),
     (actions (case (not_empty &quot;L&quot;), (forward &quot;L&quot;),
                    (not_empty &quot;l&quot;), (forward &quot;l&quot;),
@@ -540,47 +494,46 @@ def llvm_gcc_linker : Tool&lt;[
                              [(append_cmd &quot;-dummy1&quot;), (append_cmd &quot;-dummy2&quot;)])
     ]&gt;;
 </pre>
-<p>The <tt class="docutils literal"><span class="pre">actions</span></tt> tool property is implemented on top of the omnipresent
-<tt class="docutils literal"><span class="pre">case</span></tt> expression. It associates one or more different <em>actions</em>
-with given conditions - in the example, the actions are <tt class="docutils literal"><span class="pre">forward</span></tt>,
-which forwards a given option unchanged, and <tt class="docutils literal"><span class="pre">append_cmd</span></tt>, which
-appends a given string to the tool execution command. Multiple actions
-can be associated with a single condition by using a list of actions
-(used in the example to append some dummy options). The same <tt class="docutils literal"><span class="pre">case</span></tt>
-construct can also be used in the <tt class="docutils literal"><span class="pre">cmd_line</span></tt> property to modify the
-tool command line.</p>
-<p>The &quot;join&quot; property used in the example means that this tool behaves
-like a linker.</p>
+<p>The <tt class="docutils literal">actions</tt> tool property is implemented on top of the omnipresent <tt class="docutils literal">case</tt>
+expression. It associates one or more different <em>actions</em> with given
+conditions - in the example, the actions are <tt class="docutils literal">forward</tt>, which forwards a given
+option unchanged, and <tt class="docutils literal">append_cmd</tt>, which appends a given string to the tool
+execution command. Multiple actions can be associated with a single condition by
+using a list of actions (used in the example to append some dummy options). The
+same <tt class="docutils literal">case</tt> construct can also be used in the <tt class="docutils literal">cmd_line</tt> property to modify
+the tool command line.</p>
+<p>The &quot;join&quot; property used in the example means that this tool behaves like a
+linker.</p>
 <p>The list of all possible actions follows.</p>
 <ul>
 <li><p class="first">Possible actions:</p>
 <blockquote>
 <ul class="simple">
-<li><tt class="docutils literal"><span class="pre">append_cmd</span></tt> - Append a string to the tool invocation command.
-Example: <tt class="docutils literal"><span class="pre">(case</span> <span class="pre">(switch_on</span> <span class="pre">&quot;pthread&quot;),</span> <span class="pre">(append_cmd</span> <span class="pre">&quot;-lpthread&quot;))</span></tt>.</li>
-<li><tt class="docutils literal"><span class="pre">error</span></tt> - Exit with error.
-Example: <tt class="docutils literal"><span class="pre">(error</span> <span class="pre">&quot;Mixing</span> <span class="pre">-c</span> <span class="pre">and</span> <span class="pre">-S</span> <span class="pre">is</span> <span class="pre">not</span> <span class="pre">allowed!&quot;)</span></tt>.</li>
-<li><tt class="docutils literal"><span class="pre">warning</span></tt> - Print a warning.
-Example: <tt class="docutils literal"><span class="pre">(warning</span> <span class="pre">&quot;Specifying</span> <span class="pre">both</span> <span class="pre">-O1</span> <span class="pre">and</span> <span class="pre">-O2</span> <span class="pre">is</span> <span class="pre">meaningless!&quot;)</span></tt>.</li>
-<li><tt class="docutils literal"><span class="pre">forward</span></tt> - Forward the option unchanged.
-Example: <tt class="docutils literal"><span class="pre">(forward</span> <span class="pre">&quot;Wall&quot;)</span></tt>.</li>
-<li><tt class="docutils literal"><span class="pre">forward_as</span></tt> - Change the option's name, but forward the argument
+<li><tt class="docutils literal">append_cmd</tt> - Append a string to the tool invocation command.
+Example: <tt class="docutils literal">(case (switch_on <span class="pre">&quot;pthread&quot;),</span> (append_cmd <span class="pre">&quot;-lpthread&quot;))</span></tt>.</li>
+<li><tt class="docutils literal">error</tt> - Exit with error.
+Example: <tt class="docutils literal">(error &quot;Mixing <span class="pre">-c</span> and <span class="pre">-S</span> is not <span class="pre">allowed!&quot;)</span></tt>.</li>
+<li><tt class="docutils literal">warning</tt> - Print a warning.
+Example: <tt class="docutils literal">(warning &quot;Specifying both <span class="pre">-O1</span> and <span class="pre">-O2</span> is <span class="pre">meaningless!&quot;)</span></tt>.</li>
+<li><tt class="docutils literal">forward</tt> - Forward the option unchanged.
+Example: <tt class="docutils literal">(forward &quot;Wall&quot;)</tt>.</li>
+<li><tt class="docutils literal">forward_as</tt> - Change the option's name, but forward the argument
 unchanged.
-Example: <tt class="docutils literal"><span class="pre">(forward_as</span> <span class="pre">&quot;O0&quot;,</span> <span class="pre">&quot;--disable-optimization&quot;)</span></tt>.</li>
-<li><tt class="docutils literal"><span class="pre">forward_value</span></tt> - Forward only option's value. Cannot be used with switch
+Example: <tt class="docutils literal">(forward_as &quot;O0&quot;, <span class="pre">&quot;--disable-optimization&quot;)</span></tt>.</li>
+<li><tt class="docutils literal">forward_value</tt> - Forward only option's value. Cannot be used with switch
 options (since they don't have values), but works fine with lists.
-Example: <tt class="docutils literal"><span class="pre">(forward_value</span> <span class="pre">&quot;Wa,&quot;)</span></tt>.</li>
-<li><tt class="docutils literal"><span class="pre">forward_transformed_value</span></tt> - As above, but applies a hook to the
+Example: <tt class="docutils literal">(forward_value <span class="pre">&quot;Wa,&quot;)</span></tt>.</li>
+<li><tt class="docutils literal">forward_transformed_value</tt> - As above, but applies a hook to the
 option's value before forwarding (see <a class="reference internal" href="#hooks">below</a>). When
-<tt class="docutils literal"><span class="pre">forward_transformed_value</span></tt> is applied to a list
+<tt class="docutils literal">forward_transformed_value</tt> is applied to a list
 option, the hook must have signature
-<tt class="docutils literal"><span class="pre">std::string</span> <span class="pre">hooks::HookName</span> <span class="pre">(const</span> <span class="pre">std::vector&lt;std::string&gt;&amp;)</span></tt>.
-Example: <tt class="docutils literal"><span class="pre">(forward_transformed_value</span> <span class="pre">&quot;m&quot;,</span> <span class="pre">&quot;ConvertToMAttr&quot;)</span></tt>.</li>
-<li><tt class="docutils literal"><span class="pre">output_suffix</span></tt> - Modify the output suffix of this tool.
-Example: <tt class="docutils literal"><span class="pre">(output_suffix</span> <span class="pre">&quot;i&quot;)</span></tt>.</li>
-<li><tt class="docutils literal"><span class="pre">stop_compilation</span></tt> - Stop compilation after this tool processes its
+<tt class="docutils literal"><span class="pre">std::string</span> <span class="pre">hooks::HookName</span> (const <span class="pre">std::vector&lt;std::string&gt;&amp;)</span></tt>.
+Example: <tt class="docutils literal">(forward_transformed_value &quot;m&quot;, &quot;ConvertToMAttr&quot;)</tt>.</li>
+<li><tt class="docutils literal">output_suffix</tt> - Modify the output suffix of this tool.
+Example: <tt class="docutils literal">(output_suffix &quot;i&quot;)</tt>.</li>
+<li><tt class="docutils literal">stop_compilation</tt> - Stop compilation after this tool processes its
 input. Used without arguments.
-Example: <tt class="docutils literal"><span class="pre">(stop_compilation)</span></tt>.</li>
+Example: <tt class="docutils literal">(stop_compilation)</tt>.</li>
 </ul>
 </blockquote>
 </li>
@@ -588,11 +541,11 @@ Example: <tt class="docutils literal"><span class="pre">(stop_compilation)</span
 </div>
 </div>
 <div class="section" id="language-map">
-<h1><a class="toc-backref" href="#id19">Language map</a></h1>
-<p>If you are adding support for a new language to LLVMC, you'll need to
-modify the language map, which defines mappings from file extensions
-to language names. It is used to choose the proper toolchain(s) for a
-given input file set. Language map definition looks like this:</p>
+<h1><a class="toc-backref" href="#id16">Language map</a></h1>
+<p>If you are adding support for a new language to LLVMC, you'll need to modify the
+language map, which defines mappings from file extensions to language names. It
+is used to choose the proper toolchain(s) for a given input file set. Language
+map definition looks like this:</p>
 <pre class="literal-block">
 def LanguageMap : LanguageMap&lt;
     [LangToSuffixes&lt;&quot;c++&quot;, [&quot;cc&quot;, &quot;cp&quot;, &quot;cxx&quot;, &quot;cpp&quot;, &quot;CPP&quot;, &quot;c++&quot;, &quot;C&quot;]&gt;,
@@ -606,73 +559,69 @@ $ llvmc hello.cpp
 llvmc: Unknown suffix: cpp
 </pre>
 <p>The language map entries are needed only for the tools that are linked from the
-root node. Since a tool can't have multiple output languages, for inner nodes of
-the graph the input and output languages should match. This is enforced at
-compile-time.</p>
+root node. A tool can have multiple output languages.</p>
 </div>
 <div class="section" id="option-preprocessor">
-<h1><a class="toc-backref" href="#id20">Option preprocessor</a></h1>
+<h1><a class="toc-backref" href="#id17">Option preprocessor</a></h1>
 <p>It is sometimes useful to run error-checking code before processing the
 compilation graph. For example, if optimization options &quot;-O1&quot; and &quot;-O2&quot; are
 implemented as switches, we might want to output a warning if the user invokes
 the driver with both of these options enabled.</p>
-<p>The <tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> feature is reserved specially for these
-occasions. Example (adapted from the built-in Base plugin):</p>
+<p>The <tt class="docutils literal">OptionPreprocessor</tt> feature is reserved specially for these
+occasions. Example (adapted from <tt class="docutils literal">llvm/src/Base.td.in</tt>):</p>
 <pre class="literal-block">
 def Preprocess : OptionPreprocessor&lt;
-(case (not (any_switch_on [&quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;, &quot;O3&quot;])),
+(case (not (any_switch_on &quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;, &quot;O3&quot;)),
            (set_option &quot;O2&quot;),
-      (and (switch_on &quot;O3&quot;), (any_switch_on [&quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;])),
-           (unset_option [&quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;]),
-      (and (switch_on &quot;O2&quot;), (any_switch_on [&quot;O0&quot;, &quot;O1&quot;])),
-           (unset_option [&quot;O0&quot;, &quot;O1&quot;]),
+      (and (switch_on &quot;O3&quot;), (any_switch_on &quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;)),
+           (unset_option &quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;),
+      (and (switch_on &quot;O2&quot;), (any_switch_on &quot;O0&quot;, &quot;O1&quot;)),
+           (unset_option &quot;O0&quot;, &quot;O1&quot;),
       (and (switch_on &quot;O1&quot;), (switch_on &quot;O0&quot;)),
            (unset_option &quot;O0&quot;))
 &gt;;
 </pre>
-<p>Here, <tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> is used to unset all spurious <tt class="docutils literal"><span class="pre">-O</span></tt> options so
+<p>Here, <tt class="docutils literal">OptionPreprocessor</tt> is used to unset all spurious <tt class="docutils literal"><span class="pre">-O</span></tt> options so
 that they are not forwarded to the compiler. If no optimization options are
 specified, <tt class="docutils literal"><span class="pre">-O2</span></tt> is enabled.</p>
-<p><tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> is basically a single big <tt class="docutils literal"><span class="pre">case</span></tt> expression, which is
-evaluated only once right after the plugin is loaded. The only allowed actions
-in <tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> are <tt class="docutils literal"><span class="pre">error</span></tt>, <tt class="docutils literal"><span class="pre">warning</span></tt>, and two special actions:
-<tt class="docutils literal"><span class="pre">unset_option</span></tt> and <tt class="docutils literal"><span class="pre">set_option</span></tt>. As their names suggest, they can be used to
-set or unset a given option. To set an option with <tt class="docutils literal"><span class="pre">set_option</span></tt>, use the
-two-argument form: <tt class="docutils literal"><span class="pre">(set_option</span> <span class="pre">&quot;parameter&quot;,</span> <span class="pre">VALUE)</span></tt>. Here, <tt class="docutils literal"><span class="pre">VALUE</span></tt> can be
+<p><tt class="docutils literal">OptionPreprocessor</tt> is basically a single big <tt class="docutils literal">case</tt> expression, which is
+evaluated only once right after the driver is started. The only allowed actions
+in <tt class="docutils literal">OptionPreprocessor</tt> are <tt class="docutils literal">error</tt>, <tt class="docutils literal">warning</tt>, and two special actions:
+<tt class="docutils literal">unset_option</tt> and <tt class="docutils literal">set_option</tt>. As their names suggest, they can be used to
+set or unset a given option. To set an option with <tt class="docutils literal">set_option</tt>, use the
+two-argument form: <tt class="docutils literal">(set_option &quot;parameter&quot;, VALUE)</tt>. Here, <tt class="docutils literal">VALUE</tt> can be
 either a string, a string list, or a boolean constant.</p>
-<p>For convenience, <tt class="docutils literal"><span class="pre">set_option</span></tt> and <tt class="docutils literal"><span class="pre">unset_option</span></tt> also work on lists. That
-is, instead of <tt class="docutils literal"><span class="pre">[(unset_option</span> <span class="pre">&quot;A&quot;),</span> <span class="pre">(unset_option</span> <span class="pre">&quot;B&quot;)]</span></tt> you can use
-<tt class="docutils literal"><span class="pre">(unset_option</span> <span class="pre">[&quot;A&quot;,</span> <span class="pre">&quot;B&quot;])</span></tt>. Obviously, <tt class="docutils literal"><span class="pre">(set_option</span> <span class="pre">[&quot;A&quot;,</span> <span class="pre">&quot;B&quot;])</span></tt> is valid
-only if both <tt class="docutils literal"><span class="pre">A</span></tt> and <tt class="docutils literal"><span class="pre">B</span></tt> are switches.</p>
+<p>For convenience, <tt class="docutils literal">set_option</tt> and <tt class="docutils literal">unset_option</tt> also work with multiple
+arguments. That is, instead of <tt class="docutils literal">[(unset_option <span class="pre">&quot;A&quot;),</span> (unset_option <span class="pre">&quot;B&quot;)]</span></tt> you
+can use <tt class="docutils literal">(unset_option &quot;A&quot;, &quot;B&quot;)</tt>. Obviously, <tt class="docutils literal">(set_option &quot;A&quot;, &quot;B&quot;)</tt> is
+only valid if both <tt class="docutils literal">A</tt> and <tt class="docutils literal">B</tt> are switches.</p>
 </div>
 <div class="section" id="more-advanced-topics">
-<h1><a class="toc-backref" href="#id21">More advanced topics</a></h1>
+<h1><a class="toc-backref" href="#id18">More advanced topics</a></h1>
 <div class="section" id="hooks-and-environment-variables">
-<span id="hooks"></span><h2><a class="toc-backref" href="#id22">Hooks and environment variables</a></h2>
-<p>Normally, LLVMC executes programs from the system <tt class="docutils literal"><span class="pre">PATH</span></tt>. Sometimes,
-this is not sufficient: for example, we may want to specify tool paths
-or names in the configuration file. This can be easily achieved via
-the hooks mechanism. To write your own hooks, just add their
-definitions to the <tt class="docutils literal"><span class="pre">PluginMain.cpp</span></tt> or drop a <tt class="docutils literal"><span class="pre">.cpp</span></tt> file into the
-your plugin directory. Hooks should live in the <tt class="docutils literal"><span class="pre">hooks</span></tt> namespace
-and have the signature <tt class="docutils literal"><span class="pre">std::string</span> <span class="pre">hooks::MyHookName</span> <span class="pre">([const</span> <span class="pre">char*</span>
-<span class="pre">Arg0</span> <span class="pre">[</span> <span class="pre">const</span> <span class="pre">char*</span> <span class="pre">Arg2</span> <span class="pre">[,</span> <span class="pre">...]]])</span></tt>. They can be used from the
-<tt class="docutils literal"><span class="pre">cmd_line</span></tt> tool property:</p>
+<span id="hooks"></span><h2><a class="toc-backref" href="#id19">Hooks and environment variables</a></h2>
+<p>Normally, LLVMC searches for programs in the system <tt class="docutils literal">PATH</tt>. Sometimes, this is
+not sufficient: for example, we may want to specify tool paths or names in the
+configuration file. This can be achieved via the hooks mechanism. To write your
+own hooks, add their definitions to the <tt class="docutils literal">Hooks.cpp</tt> or drop a <tt class="docutils literal">.cpp</tt> file
+into your driver directory. Hooks should live in the <tt class="docutils literal">hooks</tt> namespace and
+have the signature <tt class="docutils literal"><span class="pre">std::string</span> <span class="pre">hooks::MyHookName</span> ([const char* Arg0 [ const
+char* Arg2 [, <span class="pre">...]]])</span></tt>. They can be used from the <tt class="docutils literal">command</tt> tool property:</p>
 <pre class="literal-block">
-(cmd_line &quot;$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)&quot;)
+(command &quot;$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)&quot;)
 </pre>
 <p>To pass arguments to hooks, use the following syntax:</p>
 <pre class="literal-block">
-(cmd_line &quot;$CALL(MyHook, 'Arg1', 'Arg2', 'Arg # 3')/path/to/file -o1 -o2&quot;)
+(command &quot;$CALL(MyHook, 'Arg1', 'Arg2', 'Arg # 3')/path/to/file -o1 -o2&quot;)
 </pre>
 <p>It is also possible to use environment variables in the same manner:</p>
 <pre class="literal-block">
-(cmd_line &quot;$ENV(VAR1)/path/to/file -o $ENV(VAR2)&quot;)
+(command &quot;$ENV(VAR1)/path/to/file -o $ENV(VAR2)&quot;)
 </pre>
 <p>To change the command line string based on user-provided options use
-the <tt class="docutils literal"><span class="pre">case</span></tt> expression (documented <a class="reference internal" href="#case">above</a>):</p>
+the <tt class="docutils literal">case</tt> expression (documented <a class="reference internal" href="#case">above</a>):</p>
 <pre class="literal-block">
-(cmd_line
+(command
   (case
     (switch_on &quot;E&quot;),
        &quot;llvm-g++ -E -x c $INFILE -o $OUTFILE&quot;,
@@ -680,41 +629,23 @@ the <tt class="docutils literal"><span class="pre">case</span></tt> expression (
        &quot;llvm-g++ -c -x c $INFILE -o $OUTFILE -emit-llvm&quot;))
 </pre>
 </div>
-<div class="section" id="how-plugins-are-loaded">
-<span id="priorities"></span><h2><a class="toc-backref" href="#id23">How plugins are loaded</a></h2>
-<p>It is possible for LLVMC plugins to depend on each other. For example,
-one can create edges between nodes defined in some other plugin. To
-make this work, however, that plugin should be loaded first. To
-achieve this, the concept of plugin priority was introduced. By
-default, every plugin has priority zero; to specify the priority
-explicitly, put the following line in your plugin's TableGen file:</p>
-<pre class="literal-block">
-def Priority : PluginPriority&lt;$PRIORITY_VALUE&gt;;
-# Where PRIORITY_VALUE is some integer &gt; 0
-</pre>
-<p>Plugins are loaded in order of their (increasing) priority, starting
-with 0. Therefore, the plugin with the highest priority value will be
-loaded last.</p>
-</div>
 <div class="section" id="debugging">
-<h2><a class="toc-backref" href="#id24">Debugging</a></h2>
-<p>When writing LLVMC plugins, it can be useful to get a visual view of
-the resulting compilation graph. This can be achieved via the command
-line option <tt class="docutils literal"><span class="pre">--view-graph</span></tt>. This command assumes that <a class="reference external" href="http://www.graphviz.org/">Graphviz</a> and
-<a class="reference external" href="http://pages.cs.wisc.edu/~ghost/">Ghostview</a> are installed. There is also a <tt class="docutils literal"><span class="pre">--write-graph</span></tt> option that
-creates a Graphviz source file (<tt class="docutils literal"><span class="pre">compilation-graph.dot</span></tt>) in the
-current directory.</p>
-<p>Another useful <tt class="docutils literal"><span class="pre">llvmc</span></tt> option is <tt class="docutils literal"><span class="pre">--check-graph</span></tt>. It checks the
-compilation graph for common errors like mismatched output/input
-language names, multiple default edges and cycles. These checks can't
-be performed at compile-time because the plugins can load code
-dynamically. When invoked with <tt class="docutils literal"><span class="pre">--check-graph</span></tt>, <tt class="docutils literal"><span class="pre">llvmc</span></tt> doesn't
-perform any compilation tasks and returns the number of encountered
-errors as its status code.</p>
+<h2><a class="toc-backref" href="#id20">Debugging</a></h2>
+<p>When writing LLVMC-based drivers, it can be useful to get a visual view of the
+resulting compilation graph. This can be achieved via the command line option
+<tt class="docutils literal"><span class="pre">--view-graph</span></tt> (which assumes that <a class="reference external" href="http://www.graphviz.org/">Graphviz</a> and <a class="reference external" href="http://pages.cs.wisc.edu/~ghost/">Ghostview</a> are
+installed). There is also a <tt class="docutils literal"><span class="pre">--write-graph</span></tt> option that creates a Graphviz
+source file (<tt class="docutils literal"><span class="pre">compilation-graph.dot</span></tt>) in the current directory.</p>
+<p>Another useful <tt class="docutils literal">llvmc</tt> option is <tt class="docutils literal"><span class="pre">--check-graph</span></tt>. It checks the compilation
+graph for common errors like mismatched output/input language names, multiple
+default edges and cycles. When invoked with <tt class="docutils literal"><span class="pre">--check-graph</span></tt>, <tt class="docutils literal">llvmc</tt> doesn't
+perform any compilation tasks and returns the number of encountered errors as
+its status code. In the future, these checks will be performed at compile-time
+and this option will disappear.</p>
 </div>
 <div class="section" id="conditioning-on-the-executable-name">
-<h2><a class="toc-backref" href="#id25">Conditioning on the executable name</a></h2>
-<p>For now, the executable name (the value passed to the driver in <tt class="docutils literal"><span class="pre">argv[0]</span></tt>) is
+<h2><a class="toc-backref" href="#id21">Conditioning on the executable name</a></h2>
+<p>For now, the executable name (the value passed to the driver in <tt class="docutils literal">argv[0]</tt>) is
 accessible only in the C++ code (i.e. hooks). Use the following code:</p>
 <pre class="literal-block">
 namespace llvmc {
@@ -734,8 +665,8 @@ if (strcmp(ProgramName, &quot;mydriver&quot;) == 0) {
 </pre>
 <p>In general, you're encouraged not to make the behaviour dependent on the
 executable file name, and use command-line switches instead. See for example how
-the <tt class="docutils literal"><span class="pre">Base</span></tt> plugin behaves when it needs to choose the correct linker options
-(think <tt class="docutils literal"><span class="pre">g++</span></tt> vs. <tt class="docutils literal"><span class="pre">gcc</span></tt>).</p>
+the <tt class="docutils literal">llvmc</tt> program behaves when it needs to choose the correct linker options
+(think <tt class="docutils literal">g++</tt> vs. <tt class="docutils literal">gcc</tt>).</p>
 <hr />
 <address>
 <a href="http://jigsaw.w3.org/css-validator/check/referer">
@@ -748,7 +679,7 @@ the <tt class="docutils literal"><span class="pre">Base</span></tt> plugin behav
 <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
 
-Last modified: $Date: 2010-05-07 02:28:04 +0200 (Fri, 07 May 2010) $
+Last modified: $Date: 2011-04-24 16:17:37 +0200 (Sun, 24 Apr 2011) $
 </address></div>
 </div>
 </div>
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