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<?xml version="1.0" encoding="utf-8" ?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
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<title>Customizing LLVMC: Reference Manual</title>
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<link rel="stylesheet" href="llvm.css" type="text/css" />
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</head>
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<body>
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<div class="document" id="customizing-llvmc-reference-manual">
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<h1 class="title">Customizing LLVMC: Reference Manual</h1>
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<!-- This file was automatically generated by rst2html.
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Please do not edit directly!
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The ReST source lives in the directory 'tools/llvmc/doc'. -->
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<div class="contents topic" id="contents">
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<p class="topic-title first">Contents</p>
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<ul class="simple">
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<li><a class="reference internal" href="#introduction" id="id4">Introduction</a></li>
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<li><a class="reference internal" href="#compiling-with-llvmc" id="id5">Compiling with LLVMC</a></li>
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<li><a class="reference internal" href="#predefined-options" id="id6">Predefined options</a></li>
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<li><a class="reference internal" href="#compiling-llvmc-plugins" id="id7">Compiling LLVMC plugins</a></li>
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<li><a class="reference internal" href="#compiling-standalone-llvmc-based-drivers" id="id8">Compiling standalone LLVMC-based drivers</a></li>
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<li><a class="reference internal" href="#customizing-llvmc-the-compilation-graph" id="id9">Customizing LLVMC: the compilation graph</a></li>
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<li><a class="reference internal" href="#describing-options" id="id10">Describing options</a><ul>
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<li><a class="reference internal" href="#external-options" id="id11">External options</a></li>
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</ul>
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</li>
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<li><a class="reference internal" href="#conditional-evaluation" id="id12">Conditional evaluation</a></li>
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<li><a class="reference internal" href="#writing-a-tool-description" id="id13">Writing a tool description</a><ul>
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<li><a class="reference internal" href="#actions" id="id14">Actions</a></li>
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</ul>
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</li>
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<li><a class="reference internal" href="#language-map" id="id15">Language map</a></li>
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<li><a class="reference internal" href="#more-advanced-topics" id="id16">More advanced topics</a><ul>
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<li><a class="reference internal" href="#hooks-and-environment-variables" id="id17">Hooks and environment variables</a></li>
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<li><a class="reference internal" href="#how-plugins-are-loaded" id="id18">How plugins are loaded</a></li>
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<li><a class="reference internal" href="#debugging" id="id19">Debugging</a></li>
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<li><a class="reference internal" href="#conditioning-on-the-executable-name" id="id20">Conditioning on the executable name</a></li>
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</ul>
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</li>
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</ul>
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</div>
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<div class="doc_author">
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<p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
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</div><div class="section" id="introduction">
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<h1><a class="toc-backref" href="#id4">Introduction</a></h1>
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<p>LLVMC is a generic compiler driver, designed to be customizable and
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extensible. It plays the same role for LLVM as the <tt class="docutils literal"><span class="pre">gcc</span></tt> program
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does for GCC - LLVMC's job is essentially to transform a set of input
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files into a set of targets depending on configuration rules and user
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options. What makes LLVMC different is that these transformation rules
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are completely customizable - in fact, LLVMC knows nothing about the
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specifics of transformation (even the command-line options are mostly
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not hard-coded) and regards the transformation structure as an
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abstract graph. The structure of this graph is completely determined
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by plugins, which can be either statically or dynamically linked. This
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makes it possible to easily adapt LLVMC for other purposes - for
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example, as a build tool for game resources.</p>
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<p>Because LLVMC employs <a class="reference external" href="http://llvm.org/docs/TableGenFundamentals.html">TableGen</a> as its configuration language, you
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need to be familiar with it to customize LLVMC.</p>
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</div>
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<div class="section" id="compiling-with-llvmc">
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<h1><a class="toc-backref" href="#id5">Compiling with LLVMC</a></h1>
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<p>LLVMC tries hard to be as compatible with <tt class="docutils literal"><span class="pre">gcc</span></tt> as possible,
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although there are some small differences. Most of the time, however,
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you shouldn't be able to notice them:</p>
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<pre class="literal-block">
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$ # This works as expected:
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$ llvmc -O3 -Wall hello.cpp
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$ ./a.out
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hello
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</pre>
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<p>One nice feature of LLVMC is that one doesn't have to distinguish between
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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
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right toolchain is chosen automatically based on input language names (which
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are, in turn, determined from file extensions). If you want to force files
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ending with ".c" to compile as C++, use the <tt class="docutils literal"><span class="pre">-x</span></tt> option, just like you would
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do it with <tt class="docutils literal"><span class="pre">gcc</span></tt>:</p>
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<pre class="literal-block">
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$ # hello.c is really a C++ file
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$ llvmc -x c++ hello.c
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$ ./a.out
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hello
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</pre>
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<p>On the other hand, when using LLVMC as a linker to combine several C++
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object files you should provide the <tt class="docutils literal"><span class="pre">--linker</span></tt> option since it's
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impossible for LLVMC to choose the right linker in that case:</p>
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<pre class="literal-block">
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$ llvmc -c hello.cpp
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$ llvmc hello.o
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[A lot of link-time errors skipped]
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$ llvmc --linker=c++ hello.o
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$ ./a.out
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hello
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</pre>
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<p>By default, LLVMC uses <tt class="docutils literal"><span class="pre">llvm-gcc</span></tt> to compile the source code. It is also
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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>
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</div>
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<div class="section" id="predefined-options">
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<h1><a class="toc-backref" href="#id6">Predefined options</a></h1>
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<p>LLVMC has some built-in options that can't be overridden in the
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configuration libraries:</p>
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<ul class="simple">
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<li><tt class="docutils literal"><span class="pre">-o</span> <span class="pre">FILE</span></tt> - Output file name.</li>
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<li><tt class="docutils literal"><span class="pre">-x</span> <span class="pre">LANGUAGE</span></tt> - Specify the language of the following input files
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until the next -x option.</li>
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<li><tt class="docutils literal"><span class="pre">-load</span> <span class="pre">PLUGIN_NAME</span></tt> - Load the specified plugin DLL. Example:
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<tt class="docutils literal"><span class="pre">-load</span> <span class="pre">$LLVM_DIR/Release/lib/LLVMCSimple.so</span></tt>.</li>
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<li><tt class="docutils literal"><span class="pre">-v</span></tt> - Enable verbose mode, i.e. print out all executed commands.</li>
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<li><tt class="docutils literal"><span class="pre">--save-temps</span></tt> - Write temporary files to the current directory and do not
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delete them on exit. This option can also take an argument: the
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<tt class="docutils literal"><span class="pre">--save-temps=obj</span></tt> switch will write files into the directory specified with
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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
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both synonyms for the default behaviour.</li>
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<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
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directory is deleted on exit unless <tt class="docutils literal"><span class="pre">--save-temps</span></tt> is specified. If
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<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
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precedence.</li>
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<li><tt class="docutils literal"><span class="pre">--check-graph</span></tt> - Check the compilation for common errors like mismatched
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output/input language names, multiple default edges and cycles. Because of
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plugins, these checks can't be performed at compile-time. Exit with code zero
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if no errors were found, and return the number of found errors
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otherwise. Hidden option, useful for debugging LLVMC plugins.</li>
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<li><tt class="docutils literal"><span class="pre">--view-graph</span></tt> - Show a graphical representation of the compilation graph
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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
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option, useful for debugging LLVMC plugins.</li>
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<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
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directory with the compilation graph description in Graphviz format (identical
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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
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used to set the output file name. Hidden option, useful for debugging LLVMC
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plugins.</li>
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<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
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their standard meaning.</li>
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</ul>
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</div>
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<div class="section" id="compiling-llvmc-plugins">
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<h1><a class="toc-backref" href="#id7">Compiling LLVMC plugins</a></h1>
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<p>It's easiest to start working on your own LLVMC plugin by copying the
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skeleton project which lives under <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins/Simple</span></tt>:</p>
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<pre class="literal-block">
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$ cd $LLVMC_DIR/plugins
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$ cp -r Simple MyPlugin
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$ cd MyPlugin
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$ ls
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Makefile PluginMain.cpp Simple.td
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</pre>
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<p>As you can see, our basic plugin consists of only two files (not
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counting the build script). <tt class="docutils literal"><span class="pre">Simple.td</span></tt> contains TableGen
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description of the compilation graph; its format is documented in the
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following sections. <tt class="docutils literal"><span class="pre">PluginMain.cpp</span></tt> is just a helper file used to
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compile the auto-generated C++ code produced from TableGen source. It
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can also contain hook definitions (see <a class="reference internal" href="#hooks">below</a>).</p>
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<p>The first thing that you should do is to change the <tt class="docutils literal"><span class="pre">LLVMC_PLUGIN</span></tt>
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variable in the <tt class="docutils literal"><span class="pre">Makefile</span></tt> to avoid conflicts (since this variable
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is used to name the resulting library):</p>
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<pre class="literal-block">
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LLVMC_PLUGIN=MyPlugin
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</pre>
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<p>It is also a good idea to rename <tt class="docutils literal"><span class="pre">Simple.td</span></tt> to something less
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generic:</p>
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<pre class="literal-block">
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$ mv Simple.td MyPlugin.td
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</pre>
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<p>To build your plugin as a dynamic library, just <tt class="docutils literal"><span class="pre">cd</span></tt> to its source
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directory and run <tt class="docutils literal"><span class="pre">make</span></tt>. The resulting file will be called
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<tt class="docutils literal"><span class="pre">plugin_llvmc_$(LLVMC_PLUGIN).$(DLL_EXTENSION)</span></tt> (in our case,
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<tt class="docutils literal"><span class="pre">plugin_llvmc_MyPlugin.so</span></tt>). This library can be then loaded in with the
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<tt class="docutils literal"><span class="pre">-load</span></tt> option. Example:</p>
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<pre class="literal-block">
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$ cd $LLVMC_DIR/plugins/Simple
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$ make
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$ llvmc -load $LLVM_DIR/Release/lib/plugin_llvmc_Simple.so
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</pre>
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</div>
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<div class="section" id="compiling-standalone-llvmc-based-drivers">
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<h1><a class="toc-backref" href="#id8">Compiling standalone LLVMC-based drivers</a></h1>
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<p>By default, the <tt class="docutils literal"><span class="pre">llvmc</span></tt> executable consists of a driver core plus several
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statically linked plugins (<tt class="docutils literal"><span class="pre">Base</span></tt> and <tt class="docutils literal"><span class="pre">Clang</span></tt> at the moment). You can
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produce a standalone LLVMC-based driver executable by linking the core with your
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own plugins. The recommended way to do this is by starting with the provided
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<tt class="docutils literal"><span class="pre">Skeleton</span></tt> example (<tt class="docutils literal"><span class="pre">$LLVMC_DIR/example/Skeleton</span></tt>):</p>
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<pre class="literal-block">
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$ cd $LLVMC_DIR/example/
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$ cp -r Skeleton mydriver
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$ cd mydriver
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$ vim Makefile
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[...]
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$ make
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</pre>
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<p>If you're compiling LLVM with different source and object directories, then you
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must perform the following additional steps before running <tt class="docutils literal"><span class="pre">make</span></tt>:</p>
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<pre class="literal-block">
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# LLVMC_SRC_DIR = $LLVM_SRC_DIR/tools/llvmc/
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# LLVMC_OBJ_DIR = $LLVM_OBJ_DIR/tools/llvmc/
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$ cp $LLVMC_SRC_DIR/example/mydriver/Makefile \
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$LLVMC_OBJ_DIR/example/mydriver/
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$ cd $LLVMC_OBJ_DIR/example/mydriver
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$ make
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</pre>
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<p>Another way to do the same thing is by using the following command:</p>
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<pre class="literal-block">
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$ cd $LLVMC_DIR
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$ make LLVMC_BUILTIN_PLUGINS=MyPlugin LLVMC_BASED_DRIVER_NAME=mydriver
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</pre>
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<p>This works with both srcdir == objdir and srcdir != objdir, but assumes that the
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plugin source directory was placed under <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins</span></tt>.</p>
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<p>Sometimes, you will want a 'bare-bones' version of LLVMC that has no
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built-in plugins. It can be compiled with the following command:</p>
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<pre class="literal-block">
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$ cd $LLVMC_DIR
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$ make LLVMC_BUILTIN_PLUGINS=""
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</pre>
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</div>
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<div class="section" id="customizing-llvmc-the-compilation-graph">
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<h1><a class="toc-backref" href="#id9">Customizing LLVMC: the compilation graph</a></h1>
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<p>Each TableGen configuration file should include the common
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definitions:</p>
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<pre class="literal-block">
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include "llvm/CompilerDriver/Common.td"
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</pre>
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<p>Internally, LLVMC stores information about possible source
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transformations in form of a graph. Nodes in this graph represent
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tools, and edges between two nodes represent a transformation path. A
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special "root" node is used to mark entry points for the
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transformations. LLVMC also assigns a weight to each edge (more on
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this later) to choose between several alternative edges.</p>
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<p>The definition of the compilation graph (see file
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<tt class="docutils literal"><span class="pre">plugins/Base/Base.td</span></tt> for an example) is just a list of edges:</p>
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<pre class="literal-block">
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def CompilationGraph : CompilationGraph<[
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Edge<"root", "llvm_gcc_c">,
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Edge<"root", "llvm_gcc_assembler">,
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...
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Edge<"llvm_gcc_c", "llc">,
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Edge<"llvm_gcc_cpp", "llc">,
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...
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OptionalEdge<"llvm_gcc_c", "opt", (case (switch_on "opt"),
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(inc_weight))>,
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OptionalEdge<"llvm_gcc_cpp", "opt", (case (switch_on "opt"),
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(inc_weight))>,
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...
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OptionalEdge<"llvm_gcc_assembler", "llvm_gcc_cpp_linker",
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(case (input_languages_contain "c++"), (inc_weight),
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(or (parameter_equals "linker", "g++"),
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(parameter_equals "linker", "c++")), (inc_weight))>,
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...
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]>;
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</pre>
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<p>As you can see, the edges can be either default or optional, where
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optional edges are differentiated by an additional <tt class="docutils literal"><span class="pre">case</span></tt> expression
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used to calculate the weight of this edge. Notice also that we refer
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to tools via their names (as strings). This makes it possible to add
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edges to an existing compilation graph in plugins without having to
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know about all tool definitions used in the graph.</p>
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<p>The default edges are assigned a weight of 1, and optional edges get a
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weight of 0 + 2*N where N is the number of tests that evaluated to
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true in the <tt class="docutils literal"><span class="pre">case</span></tt> expression. It is also possible to provide an
|
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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,
|
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the weight is increased (or decreased) by the provided value instead
|
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of the default 2. It is also possible to change the default weight of
|
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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>
|
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construct.</p>
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<p>When passing an input file through the graph, LLVMC picks the edge
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with the maximum weight. To avoid ambiguity, there should be only one
|
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default edge between two nodes (with the exception of the root node,
|
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which gets a special treatment - there you are allowed to specify one
|
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default edge <em>per language</em>).</p>
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<p>When multiple plugins are loaded, their compilation graphs are merged
|
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together. Since multiple edges that have the same end nodes are not
|
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allowed (i.e. the graph is not a multigraph), an edge defined in
|
|
several plugins will be replaced by the definition from the plugin
|
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that was loaded last. Plugin load order can be controlled by using the
|
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plugin priority feature described above.</p>
|
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<p>To get a visual representation of the compilation graph (useful for
|
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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
|
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<tt class="docutils literal"><span class="pre">gsview</span></tt> installed for this to work properly.</p>
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</div>
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<div class="section" id="describing-options">
|
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<h1><a class="toc-backref" href="#id10">Describing options</a></h1>
|
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<p>Command-line options that the plugin supports are defined by using an
|
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<tt class="docutils literal"><span class="pre">OptionList</span></tt>:</p>
|
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<pre class="literal-block">
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def Options : OptionList<[
|
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(switch_option "E", (help "Help string")),
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(alias_option "quiet", "q")
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...
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]>;
|
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</pre>
|
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<p>As you can see, the option list is just a list of DAGs, where each DAG
|
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is an option description consisting of the option name and some
|
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properties. A plugin can define more than one option list (they are
|
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all merged together in the end), which can be handy if one wants to
|
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separate option groups syntactically.</p>
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<ul>
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<li><p class="first">Possible option types:</p>
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<blockquote>
|
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<ul class="simple">
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<li><tt class="docutils literal"><span class="pre">switch_option</span></tt> - a simple boolean switch without arguments, for example
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<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>
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<li><tt class="docutils literal"><span class="pre">parameter_option</span></tt> - option that takes one argument, for example
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<tt class="docutils literal"><span class="pre">-std=c99</span></tt>. It is also allowed to use spaces instead of the equality
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sign: <tt class="docutils literal"><span class="pre">-std</span> <span class="pre">c99</span></tt>. At most one occurrence is allowed.</li>
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<li><tt class="docutils literal"><span class="pre">parameter_list_option</span></tt> - same as the above, but more than one option
|
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occurrence is allowed.</li>
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<li><tt class="docutils literal"><span class="pre">prefix_option</span></tt> - same as the parameter_option, but the option name and
|
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argument do not have to be separated. Example: <tt class="docutils literal"><span class="pre">-ofile</span></tt>. This can be also
|
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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 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
|
|
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">"preprocess",</span> <span class="pre">"E")</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">zero_or_one</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">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">"foo",</span> <span class="pre">(multi_val</span>
|
|
<span class="pre">3))</span></tt>. Only list options can have this attribute; you can, however, use
|
|
the <tt class="docutils literal"><span class="pre">one_or_more</span></tt> and <tt class="docutils literal"><span class="pre">zero_or_one</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; 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 this attribute. Usage
|
|
examples: <tt class="docutils literal"><span class="pre">(switch_option</span> <span class="pre">"foo",</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">"bar",</span>
|
|
<span class="pre">(init</span> <span class="pre">"baz"))</span></tt>.</li>
|
|
<li><tt class="docutils literal"><span class="pre">extern</span></tt> - this option is defined in some other plugin, see below.</li>
|
|
</ul>
|
|
</blockquote>
|
|
</li>
|
|
</ul>
|
|
<div class="section" id="external-options">
|
|
<h2><a class="toc-backref" href="#id11">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 "E", (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="#id12">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 "-A" is provided on the
|
|
// command-line, and by 5 more if "-B" is also provided.
|
|
(case
|
|
(switch_on "A"), (inc_weight 5),
|
|
(switch_on "B"), (inc_weight 5))
|
|
|
|
|
|
// Tool command line specification
|
|
|
|
// Evaluates to "cmdline1" if the option "-A" is provided on the
|
|
// command line; to "cmdline2" if "-B" is provided;
|
|
// otherwise to "cmdline3".
|
|
|
|
(case
|
|
(switch_on "A"), "cmdline1",
|
|
(switch_on "B"), "cmdline2",
|
|
(default), "cmdline3")
|
|
</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">"B"</span></tt> switch is never checked when switch <tt class="docutils literal"><span class="pre">"A"</span></tt> is
|
|
enabled, and the whole expression always evaluates to <tt class="docutils literal"><span class="pre">"cmdline1"</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 "E"), (case (switch_on "o"), ..., (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. Example: <tt class="docutils literal"><span class="pre">(switch_on</span> <span class="pre">"opt")</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">"W",</span> <span class="pre">"all")</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">(parameter_in_list</span> <span class="pre">"l",</span> <span class="pre">"pthread")</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">"c++")</span></tt>.</li>
|
|
<li><tt class="docutils literal"><span class="pre">in_language</span></tt> - Evaluates to true if the input file language
|
|
equals 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">"c++")</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.
|
|
Example: <tt class="docutils literal"><span class="pre">(not_empty</span> <span class="pre">"o")</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.</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="#id13">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<[
|
|
(in_language "c++"),
|
|
(out_language "llvm-assembler"),
|
|
(output_suffix "bc"),
|
|
(cmd_line "llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm"),
|
|
(sink)
|
|
]>;
|
|
</pre>
|
|
<p>This defines a new tool called <tt class="docutils literal"><span class="pre">llvm_gcc_cpp</span></tt>, which is an alias for
|
|
<tt class="docutils literal"><span class="pre">llvm-g++</span></tt>. As you can see, a tool definition is just a list of
|
|
properties; most of them should be self-explanatory. The <tt class="docutils literal"><span class="pre">sink</span></tt>
|
|
property means that this tool should be passed all command-line
|
|
options that aren't mentioned in the option list.</p>
|
|
<p>The complete list of all currently implemented tool properties follows.</p>
|
|
<ul class="simple">
|
|
<li>Possible tool properties:<ul>
|
|
<li><tt class="docutils literal"><span class="pre">in_language</span></tt> - input language name. Can be either a string or a
|
|
list, in case the tool supports multiple input languages.</li>
|
|
<li><tt class="docutils literal"><span class="pre">out_language</span></tt> - output language name. Tools are not allowed to
|
|
have multiple output languages.</li>
|
|
<li><tt class="docutils literal"><span class="pre">output_suffix</span></tt> - output file suffix. Can also be changed
|
|
dynamically, see documentation on actions.</li>
|
|
<li><tt class="docutils literal"><span class="pre">cmd_line</span></tt> - the actual command used to run the tool. You can
|
|
use <tt class="docutils literal"><span class="pre">$INFILE</span></tt> and <tt class="docutils literal"><span class="pre">$OUTFILE</span></tt> variables, output redirection
|
|
with <tt class="docutils literal"><span class="pre">></span></tt>, hook invocations (<tt class="docutils literal"><span class="pre">$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 "join node" 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
|
|
below).</li>
|
|
</ul>
|
|
</li>
|
|
</ul>
|
|
<div class="section" id="actions">
|
|
<h2><a class="toc-backref" href="#id14">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>
|
|
<pre class="literal-block">
|
|
def llvm_gcc_linker : Tool<[
|
|
(in_language "object-code"),
|
|
(out_language "executable"),
|
|
(output_suffix "out"),
|
|
(cmd_line "llvm-gcc $INFILE -o $OUTFILE"),
|
|
(join),
|
|
(actions (case (not_empty "L"), (forward "L"),
|
|
(not_empty "l"), (forward "l"),
|
|
(not_empty "dummy"),
|
|
[(append_cmd "-dummy1"), (append_cmd "-dummy2")])
|
|
]>;
|
|
</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 "join" 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">"pthread"),</span> <span class="pre">(append_cmd</span>
|
|
<span class="pre">"-lpthread"))</span></tt></li>
|
|
<li><tt class="docutils literal"><span class="pre">error`</span> <span class="pre">-</span> <span class="pre">exit</span> <span class="pre">with</span> <span class="pre">error.</span>
|
|
<span class="pre">Example:</span> <span class="pre">``(error</span> <span class="pre">"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!")</span></tt>.</li>
|
|
<li><tt class="docutils literal"><span class="pre">forward</span></tt> - forward an option unchanged.
|
|
Example: <tt class="docutils literal"><span class="pre">(forward</span> <span class="pre">"Wall")</span></tt>.</li>
|
|
<li><tt class="docutils literal"><span class="pre">forward_as</span></tt> - Change the name of an option, but forward the
|
|
argument unchanged.
|
|
Example: <tt class="docutils literal"><span class="pre">(forward_as</span> <span class="pre">"O0",</span> <span class="pre">"--disable-optimization")</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">"i")</span></tt>.</li>
|
|
<li><tt class="docutils literal"><span class="pre">stop_compilation</span></tt> - stop compilation after this tool processes
|
|
its input. Used without arguments.</li>
|
|
<li><tt class="docutils literal"><span class="pre">unpack_values</span></tt> - used for for splitting and forwarding
|
|
comma-separated lists of options, e.g. <tt class="docutils literal"><span class="pre">-Wa,-foo=bar,-baz</span></tt> is
|
|
converted to <tt class="docutils literal"><span class="pre">-foo=bar</span> <span class="pre">-baz</span></tt> and appended to the tool invocation
|
|
command.
|
|
Example: <tt class="docutils literal"><span class="pre">(unpack_values</span> <span class="pre">"Wa,")</span></tt>.</li>
|
|
</ul>
|
|
</blockquote>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="section" id="language-map">
|
|
<h1><a class="toc-backref" href="#id15">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<
|
|
[LangToSuffixes<"c++", ["cc", "cp", "cxx", "cpp", "CPP", "c++", "C"]>,
|
|
LangToSuffixes<"c", ["c"]>,
|
|
...
|
|
]>;
|
|
</pre>
|
|
<p>For example, without those definitions the following command wouldn't work:</p>
|
|
<pre class="literal-block">
|
|
$ llvmc hello.cpp
|
|
llvmc: Unknown suffix: cpp
|
|
</pre>
|
|
<p>The language map entries should be added only for tools that are
|
|
linked with the root node. Since tools are not allowed to have
|
|
multiple output languages, for nodes "inside" the graph the input and
|
|
output languages should match. This is enforced at compile-time.</p>
|
|
</div>
|
|
<div class="section" id="more-advanced-topics">
|
|
<h1><a class="toc-backref" href="#id16">More advanced topics</a></h1>
|
|
<div class="section" id="hooks-and-environment-variables">
|
|
<span id="hooks"></span><h2><a class="toc-backref" href="#id17">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>
|
|
<pre class="literal-block">
|
|
(cmd_line "$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)")
|
|
</pre>
|
|
<p>To pass arguments to hooks, use the following syntax:</p>
|
|
<pre class="literal-block">
|
|
(cmd_line "$CALL(MyHook, 'Arg1', 'Arg2', 'Arg # 3')/path/to/file -o1 -o2")
|
|
</pre>
|
|
<p>It is also possible to use environment variables in the same manner:</p>
|
|
<pre class="literal-block">
|
|
(cmd_line "$ENV(VAR1)/path/to/file -o $ENV(VAR2)")
|
|
</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>
|
|
<pre class="literal-block">
|
|
(cmd_line
|
|
(case
|
|
(switch_on "E"),
|
|
"llvm-g++ -E -x c $INFILE -o $OUTFILE",
|
|
(default),
|
|
"llvm-g++ -c -x c $INFILE -o $OUTFILE -emit-llvm"))
|
|
</pre>
|
|
</div>
|
|
<div class="section" id="how-plugins-are-loaded">
|
|
<span id="priorities"></span><h2><a class="toc-backref" href="#id18">How plugins are loaded</a></h2>
|
|
<p>It is possible for LLVMC plugins to depend on each other. For example,
|
|
one can create edges between nodes defined in some other plugin. To
|
|
make this work, however, that plugin should be loaded first. To
|
|
achieve this, the concept of plugin priority was introduced. By
|
|
default, every plugin has priority zero; to specify the priority
|
|
explicitly, put the following line in your plugin's TableGen file:</p>
|
|
<pre class="literal-block">
|
|
def Priority : PluginPriority<$PRIORITY_VALUE>;
|
|
# Where PRIORITY_VALUE is some integer > 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="#id19">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>
|
|
</div>
|
|
<div class="section" id="conditioning-on-the-executable-name">
|
|
<h2><a class="toc-backref" href="#id20">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
|
|
accessible only in the C++ code (i.e. hooks). Use the following code:</p>
|
|
<pre class="literal-block">
|
|
namespace llvmc {
|
|
extern const char* ProgramName;
|
|
}
|
|
|
|
std::string MyHook() {
|
|
//...
|
|
if (strcmp(ProgramName, "mydriver") == 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>
|
|
<hr />
|
|
<address>
|
|
<a href="http://jigsaw.w3.org/css-validator/check/referer">
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|
<img src="http://jigsaw.w3.org/css-validator/images/vcss-blue"
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|
alt="Valid CSS" /></a>
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|
<a href="http://validator.w3.org/check?uri=referer">
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|
<img src="http://www.w3.org/Icons/valid-xhtml10-blue"
|
|
alt="Valid XHTML 1.0 Transitional"/></a>
|
|
|
|
<a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
|
|
<a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
|
|
|
|
Last modified: $Date$
|
|
</address></div>
|
|
</div>
|
|
</div>
|
|
</body>
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</html>
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