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  11 <div class="document" id="customizing-llvmc-reference-manual">
  12 <h1 class="title">Customizing LLVMC: Reference Manual</h1>
  13
  14 <!-- This file was automatically generated by rst2html.
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  17 <div class="contents topic" id="contents">
  18 <p class="topic-title first">Contents</p>
  19 <ul class="simple">
  20 <li><a class="reference internal" href="#introduction" id="id4">Introduction</a></li>
  21 <li><a class="reference internal" href="#compiling-with-llvmc" id="id5">Compiling with LLVMC</a></li>
  22 <li><a class="reference internal" href="#predefined-options" id="id6">Predefined options</a></li>
  23 <li><a class="reference internal" href="#compiling-llvmc-plugins" id="id7">Compiling LLVMC plugins</a></li>
  24 <li><a class="reference internal" href="#compiling-standalone-llvmc-based-drivers" id="id8">Compiling standalone LLVMC-based drivers</a></li>
  25 <li><a class="reference internal" href="#customizing-llvmc-the-compilation-graph" id="id9">Customizing LLVMC: the compilation graph</a></li>
  26 <li><a class="reference internal" href="#describing-options" id="id10">Describing options</a><ul>
  27 <li><a class="reference internal" href="#external-options" id="id11">External options</a></li>
  28 </ul>
  29 </li>
  30 <li><a class="reference internal" href="#conditional-evaluation" id="id12">Conditional evaluation</a></li>
  31 <li><a class="reference internal" href="#writing-a-tool-description" id="id13">Writing a tool description</a><ul>
  32 <li><a class="reference internal" href="#actions" id="id14">Actions</a></li>
  33 </ul>
  34 </li>
  35 <li><a class="reference internal" href="#language-map" id="id15">Language map</a></li>
  36 <li><a class="reference internal" href="#more-advanced-topics" id="id16">More advanced topics</a><ul>
  37 <li><a class="reference internal" href="#hooks-and-environment-variables" id="id17">Hooks and environment variables</a></li>
  38 <li><a class="reference internal" href="#how-plugins-are-loaded" id="id18">How plugins are loaded</a></li>
  39 <li><a class="reference internal" href="#debugging" id="id19">Debugging</a></li>
  40 <li><a class="reference internal" href="#conditioning-on-the-executable-name" id="id20">Conditioning on the executable name</a></li>
  41 </ul>
  42 </li>
  43 </ul>
  44 </div>
  45 <div class="doc_author">
  46 <p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
  47 </div><div class="section" id="introduction">
  48 <h1><a class="toc-backref" href="#id4">Introduction</a></h1>
  49 <p>LLVMC is a generic compiler driver, designed to be customizable and
  50 extensible. It plays the same role for LLVM as the <tt class="docutils literal"><span class="pre">gcc</span></tt> program
  51 does for GCC - LLVMC's job is essentially to transform a set of input
  52 files into a set of targets depending on configuration rules and user
  53 options. What makes LLVMC different is that these transformation rules
  54 are completely customizable - in fact, LLVMC knows nothing about the
  55 specifics of transformation (even the command-line options are mostly
  56 not hard-coded) and regards the transformation structure as an
  57 abstract graph. The structure of this graph is completely determined
  58 by plugins, which can be either statically or dynamically linked. This
  59 makes it possible to easily adapt LLVMC for other purposes - for
  60 example, as a build tool for game resources.</p>
  61 <p>Because LLVMC employs <a class="reference external" href="http://llvm.org/docs/TableGenFundamentals.html">TableGen</a> as its configuration language, you
  62 need to be familiar with it to customize LLVMC.</p>
  63 </div>
  64 <div class="section" id="compiling-with-llvmc">
  65 <h1><a class="toc-backref" href="#id5">Compiling with LLVMC</a></h1>
  66 <p>LLVMC tries hard to be as compatible with <tt class="docutils literal"><span class="pre">gcc</span></tt> as possible,
  67 although there are some small differences. Most of the time, however,
  68 you shouldn't be able to notice them:</p>
  69 <pre class="literal-block">
  70 $ # This works as expected:
  71 $ llvmc -O3 -Wall hello.cpp
  72 $ ./a.out
  73 hello
  74 </pre>
  75 <p>One nice feature of LLVMC is that one doesn't have to distinguish between
  76 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
  77 right toolchain is chosen automatically based on input language names (which
  78 are, in turn, determined from file extensions). If you want to force files
  79 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
  80 do it with <tt class="docutils literal"><span class="pre">gcc</span></tt>:</p>
  81 <pre class="literal-block">
  82 $ # hello.c is really a C++ file
  83 $ llvmc -x c++ hello.c
  84 $ ./a.out
  85 hello
  86 </pre>
  87 <p>On the other hand, when using LLVMC as a linker to combine several C++
  88 object files you should provide the <tt class="docutils literal"><span class="pre">--linker</span></tt> option since it's
  89 impossible for LLVMC to choose the right linker in that case:</p>
  90 <pre class="literal-block">
  91 $ llvmc -c hello.cpp
  92 $ llvmc hello.o
  93 [A lot of link-time errors skipped]
  94 $ llvmc --linker=c++ hello.o
  95 $ ./a.out
  96 hello
  97 </pre>
  98 <p>By default, LLVMC uses <tt class="docutils literal"><span class="pre">llvm-gcc</span></tt> to compile the source code. It is also
  99 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>
 100 </div>
 101 <div class="section" id="predefined-options">
 102 <h1><a class="toc-backref" href="#id6">Predefined options</a></h1>
 103 <p>LLVMC has some built-in options that can't be overridden in the
 104 configuration libraries:</p>
 105 <ul class="simple">
 106 <li><tt class="docutils literal"><span class="pre">-o</span> <span class="pre">FILE</span></tt> - Output file name.</li>
 107 <li><tt class="docutils literal"><span class="pre">-x</span> <span class="pre">LANGUAGE</span></tt> - Specify the language of the following input files
 108 until the next -x option.</li>
 109 <li><tt class="docutils literal"><span class="pre">-load</span> <span class="pre">PLUGIN_NAME</span></tt> - Load the specified plugin DLL. Example:
 110 <tt class="docutils literal"><span class="pre">-load</span> <span class="pre">$LLVM_DIR/Release/lib/LLVMCSimple.so</span></tt>.</li>
 111 <li><tt class="docutils literal"><span class="pre">-v</span></tt> - Enable verbose mode, i.e. print out all executed commands.</li>
 112 <li><tt class="docutils literal"><span class="pre">--save-temps</span></tt> - Write temporary files to the current directory and do not
 113 delete them on exit. This option can also take an argument: the
 114 <tt class="docutils literal"><span class="pre">--save-temps=obj</span></tt> switch will write files into the directory specified with
 115 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
 116 both synonyms for the default behaviour.</li>
 117 <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
 118 directory is deleted on exit unless <tt class="docutils literal"><span class="pre">--save-temps</span></tt> is specified. If
 119 <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
 120 precedence.</li>
 121 <li><tt class="docutils literal"><span class="pre">--check-graph</span></tt> - Check the compilation for common errors like mismatched
 122 output/input language names, multiple default edges and cycles. Because of
 123 plugins, these checks can't be performed at compile-time. Exit with code zero
 124 if no errors were found, and return the number of found errors
 125 otherwise. Hidden option, useful for debugging LLVMC plugins.</li>
 126 <li><tt class="docutils literal"><span class="pre">--view-graph</span></tt> - Show a graphical representation of the compilation graph
 127 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
 128 option, useful for debugging LLVMC plugins.</li>
 129 <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
 130 directory with the compilation graph description in Graphviz format (identical
 131 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
 132 used to set the output file name. Hidden option, useful for debugging LLVMC
 133 plugins.</li>
 134 <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
 135 their standard meaning.</li>
 136 </ul>
 137 </div>
 138 <div class="section" id="compiling-llvmc-plugins">
 139 <h1><a class="toc-backref" href="#id7">Compiling LLVMC plugins</a></h1>
 140 <p>It's easiest to start working on your own LLVMC plugin by copying the
 141 skeleton project which lives under <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins/Simple</span></tt>:</p>
 142 <pre class="literal-block">
 143 $ cd $LLVMC_DIR/plugins
 144 $ cp -r Simple MyPlugin
 145 $ cd MyPlugin
 146 $ ls
 147 Makefile PluginMain.cpp Simple.td
 148 </pre>
 149 <p>As you can see, our basic plugin consists of only two files (not
 150 counting the build script). <tt class="docutils literal"><span class="pre">Simple.td</span></tt> contains TableGen
 151 description of the compilation graph; its format is documented in the
 152 following sections. <tt class="docutils literal"><span class="pre">PluginMain.cpp</span></tt> is just a helper file used to
 153 compile the auto-generated C++ code produced from TableGen source. It
 154 can also contain hook definitions (see <a class="reference internal" href="#hooks">below</a>).</p>
 155 <p>The first thing that you should do is to change the <tt class="docutils literal"><span class="pre">LLVMC_PLUGIN</span></tt>
 156 variable in the <tt class="docutils literal"><span class="pre">Makefile</span></tt> to avoid conflicts (since this variable
 157 is used to name the resulting library):</p>
 158 <pre class="literal-block">
 159 LLVMC_PLUGIN=MyPlugin
 160 </pre>
 161 <p>It is also a good idea to rename <tt class="docutils literal"><span class="pre">Simple.td</span></tt> to something less
 162 generic:</p>
 163 <pre class="literal-block">
 164 $ mv Simple.td MyPlugin.td
 165 </pre>
 166 <p>To build your plugin as a dynamic library, just <tt class="docutils literal"><span class="pre">cd</span></tt> to its source
 167 directory and run <tt class="docutils literal"><span class="pre">make</span></tt>. The resulting file will be called
 168 <tt class="docutils literal"><span class="pre">plugin_llvmc_$(LLVMC_PLUGIN).$(DLL_EXTENSION)</span></tt> (in our case,
 169 <tt class="docutils literal"><span class="pre">plugin_llvmc_MyPlugin.so</span></tt>). This library can be then loaded in with the
 170 <tt class="docutils literal"><span class="pre">-load</span></tt> option. Example:</p>
 171 <pre class="literal-block">
 172 $ cd $LLVMC_DIR/plugins/Simple
 173 $ make
 174 $ llvmc -load $LLVM_DIR/Release/lib/plugin_llvmc_Simple.so
 175 </pre>
 176 </div>
 177 <div class="section" id="compiling-standalone-llvmc-based-drivers">
 178 <h1><a class="toc-backref" href="#id8">Compiling standalone LLVMC-based drivers</a></h1>
 179 <p>By default, the <tt class="docutils literal"><span class="pre">llvmc</span></tt> executable consists of a driver core plus several
 180 statically linked plugins (<tt class="docutils literal"><span class="pre">Base</span></tt> and <tt class="docutils literal"><span class="pre">Clang</span></tt> at the moment). You can
 181 produce a standalone LLVMC-based driver executable by linking the core with your
 182 own plugins. The recommended way to do this is by starting with the provided
 183 <tt class="docutils literal"><span class="pre">Skeleton</span></tt> example (<tt class="docutils literal"><span class="pre">$LLVMC_DIR/example/Skeleton</span></tt>):</p>
 184 <pre class="literal-block">
 185 $ cd $LLVMC_DIR/example/
 186 $ cp -r Skeleton mydriver
 187 $ cd mydriver
 188 $ vim Makefile
 189 [...]
 190 $ make
 191 </pre>
 192 <p>If you're compiling LLVM with different source and object directories, then you
 193 must perform the following additional steps before running <tt class="docutils literal"><span class="pre">make</span></tt>:</p>
 194 <pre class="literal-block">
 195 # LLVMC_SRC_DIR = $LLVM_SRC_DIR/tools/llvmc/
 196 # LLVMC_OBJ_DIR = $LLVM_OBJ_DIR/tools/llvmc/
 197 $ cp $LLVMC_SRC_DIR/example/mydriver/Makefile \
 198   $LLVMC_OBJ_DIR/example/mydriver/
 199 $ cd $LLVMC_OBJ_DIR/example/mydriver
 200 $ make
 201 </pre>
 202 <p>Another way to do the same thing is by using the following command:</p>
 203 <pre class="literal-block">
 204 $ cd $LLVMC_DIR
 205 $ make LLVMC_BUILTIN_PLUGINS=MyPlugin LLVMC_BASED_DRIVER_NAME=mydriver
 206 </pre>
 207 <p>This works with both srcdir == objdir and srcdir != objdir, but assumes that the
 208 plugin source directory was placed under <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins</span></tt>.</p>
 209 <p>Sometimes, you will want a 'bare-bones' version of LLVMC that has no
 210 built-in plugins. It can be compiled with the following command:</p>
 211 <pre class="literal-block">
 212 $ cd $LLVMC_DIR
 213 $ make LLVMC_BUILTIN_PLUGINS=&quot;&quot;
 214 </pre>
 215 </div>
 216 <div class="section" id="customizing-llvmc-the-compilation-graph">
 217 <h1><a class="toc-backref" href="#id9">Customizing LLVMC: the compilation graph</a></h1>
 218 <p>Each TableGen configuration file should include the common
 219 definitions:</p>
 220 <pre class="literal-block">
 221 include &quot;llvm/CompilerDriver/Common.td&quot;
 222 </pre>
 223 <p>Internally, LLVMC stores information about possible source
 224 transformations in form of a graph. Nodes in this graph represent
 225 tools, and edges between two nodes represent a transformation path. A
 226 special &quot;root&quot; node is used to mark entry points for the
 227 transformations. LLVMC also assigns a weight to each edge (more on
 228 this later) to choose between several alternative edges.</p>
 229 <p>The definition of the compilation graph (see file
 230 <tt class="docutils literal"><span class="pre">plugins/Base/Base.td</span></tt> for an example) is just a list of edges:</p>
 231 <pre class="literal-block">
 232 def CompilationGraph : CompilationGraph&lt;[
 233     Edge&lt;&quot;root&quot;, &quot;llvm_gcc_c&quot;&gt;,
 234     Edge&lt;&quot;root&quot;, &quot;llvm_gcc_assembler&quot;&gt;,
 235     ...
 236
 237     Edge&lt;&quot;llvm_gcc_c&quot;, &quot;llc&quot;&gt;,
 238     Edge&lt;&quot;llvm_gcc_cpp&quot;, &quot;llc&quot;&gt;,
 239     ...
 240
 241     OptionalEdge&lt;&quot;llvm_gcc_c&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
 242                                       (inc_weight))&gt;,
 243     OptionalEdge&lt;&quot;llvm_gcc_cpp&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
 244                                               (inc_weight))&gt;,
 245     ...
 246
 247     OptionalEdge&lt;&quot;llvm_gcc_assembler&quot;, &quot;llvm_gcc_cpp_linker&quot;,
 248         (case (input_languages_contain &quot;c++&quot;), (inc_weight),
 249               (or (parameter_equals &quot;linker&quot;, &quot;g++&quot;),
 250                   (parameter_equals &quot;linker&quot;, &quot;c++&quot;)), (inc_weight))&gt;,
 251     ...
 252
 253     ]&gt;;
 254 </pre>
 255 <p>As you can see, the edges can be either default or optional, where
 256 optional edges are differentiated by an additional <tt class="docutils literal"><span class="pre">case</span></tt> expression
 257 used to calculate the weight of this edge. Notice also that we refer
 258 to tools via their names (as strings). This makes it possible to add
 259 edges to an existing compilation graph in plugins without having to
 260 know about all tool definitions used in the graph.</p>
 261 <p>The default edges are assigned a weight of 1, and optional edges get a
 262 weight of 0 + 2*N where N is the number of tests that evaluated to
 263 true in the <tt class="docutils literal"><span class="pre">case</span></tt> expression. It is also possible to provide an
 264 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,
 265 the weight is increased (or decreased) by the provided value instead
 266 of the default 2. It is also possible to change the default weight of
 267 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>
 268 construct.</p>
 269 <p>When passing an input file through the graph, LLVMC picks the edge
 270 with the maximum weight. To avoid ambiguity, there should be only one
 271 default edge between two nodes (with the exception of the root node,
 272 which gets a special treatment - there you are allowed to specify one
 273 default edge <em>per language</em>).</p>
 274 <p>When multiple plugins are loaded, their compilation graphs are merged
 275 together. Since multiple edges that have the same end nodes are not
 276 allowed (i.e. the graph is not a multigraph), an edge defined in
 277 several plugins will be replaced by the definition from the plugin
 278 that was loaded last. Plugin load order can be controlled by using the
 279 plugin priority feature described above.</p>
 280 <p>To get a visual representation of the compilation graph (useful for
 281 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
 282 <tt class="docutils literal"><span class="pre">gsview</span></tt> installed for this to work properly.</p>
 283 </div>
 284 <div class="section" id="describing-options">
 285 <h1><a class="toc-backref" href="#id10">Describing options</a></h1>
 286 <p>Command-line options that the plugin supports are defined by using an
 287 <tt class="docutils literal"><span class="pre">OptionList</span></tt>:</p>
 288 <pre class="literal-block">
 289 def Options : OptionList&lt;[
 290 (switch_option &quot;E&quot;, (help &quot;Help string&quot;)),
 291 (alias_option &quot;quiet&quot;, &quot;q&quot;)
 292 ...
 293 ]&gt;;
 294 </pre>
 295 <p>As you can see, the option list is just a list of DAGs, where each DAG
 296 is an option description consisting of the option name and some
 297 properties. A plugin can define more than one option list (they are
 298 all merged together in the end), which can be handy if one wants to
 299 separate option groups syntactically.</p>
 300 <ul>
 301 <li><p class="first">Possible option types:</p>
 302 <blockquote>
 303 <ul class="simple">
 304 <li><tt class="docutils literal"><span class="pre">switch_option</span></tt> - a simple boolean switch without arguments, for example
 305 <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>
 306 <li><tt class="docutils literal"><span class="pre">parameter_option</span></tt> - option that takes one argument, for example
 307 <tt class="docutils literal"><span class="pre">-std=c99</span></tt>. It is also allowed to use spaces instead of the equality
 308 sign: <tt class="docutils literal"><span class="pre">-std</span> <span class="pre">c99</span></tt>. At most one occurrence is allowed.</li>
 309 <li><tt class="docutils literal"><span class="pre">parameter_list_option</span></tt> - same as the above, but more than one option
 310 occurence is allowed.</li>
 311 <li><tt class="docutils literal"><span class="pre">prefix_option</span></tt> - same as the parameter_option, but the option name and
 312 argument do not have to be separated. Example: <tt class="docutils literal"><span class="pre">-ofile</span></tt>. This can be also
 313 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
 314 (<tt class="docutils literal"><span class="pre">=file</span></tt> will be interpreted as option value). At most one occurrence is
 315 allowed.</li>
 316 <li><tt class="docutils literal"><span class="pre">prefix_list_option</span></tt> - same as the above, but more than one occurence of
 317 the option is allowed; example: <tt class="docutils literal"><span class="pre">-lm</span> <span class="pre">-lpthread</span></tt>.</li>
 318 <li><tt class="docutils literal"><span class="pre">alias_option</span></tt> - a special option type for creating aliases. Unlike other
 319 option types, aliases are not allowed to have any properties besides the
 320 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>
 321 </ul>
 322 </blockquote>
 323 </li>
 324 <li><p class="first">Possible option properties:</p>
 325 <blockquote>
 326 <ul class="simple">
 327 <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>
 328 output.</li>
 329 <li><tt class="docutils literal"><span class="pre">required</span></tt> - this option must be specified exactly once (or, in case of
 330 the list options without the <tt class="docutils literal"><span class="pre">multi_val</span></tt> property, at least
 331 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>
 332 <li><tt class="docutils literal"><span class="pre">one_or_more</span></tt> - the option must be specified at least one time. Useful
 333 only for list options in conjunction with <tt class="docutils literal"><span class="pre">multi_val</span></tt>; for ordinary lists
 334 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
 335 <tt class="docutils literal"><span class="pre">zero_or_one</span></tt>.</li>
 336 <li><tt class="docutils literal"><span class="pre">zero_or_one</span></tt> - the option can be specified zero or one times. Useful
 337 only for list options in conjunction with <tt class="docutils literal"><span class="pre">multi_val</span></tt>. Incompatible with
 338 <tt class="docutils literal"><span class="pre">required</span></tt> and <tt class="docutils literal"><span class="pre">one_or_more</span></tt>.</li>
 339 <li><tt class="docutils literal"><span class="pre">hidden</span></tt> - the description of this option will not appear in
 340 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>
 341 output).</li>
 342 <li><tt class="docutils literal"><span class="pre">really_hidden</span></tt> - the option will not be mentioned in any help
 343 output.</li>
 344 <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
 345 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>
 346 <span class="pre">3))</span></tt>. Only list options can have this attribute; you can, however, use
 347 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>
 348 <li><tt class="docutils literal"><span class="pre">init</span></tt> - this option has a default value, either a string (if it is a
 349 parameter), or a boolean (if it is a switch; boolean constants are called
 350 <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
 351 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>
 352 <span class="pre">(init</span> <span class="pre">&quot;baz&quot;))</span></tt>.</li>
 353 <li><tt class="docutils literal"><span class="pre">extern</span></tt> - this option is defined in some other plugin, see below.</li>
 354 </ul>
 355 </blockquote>
 356 </li>
 357 </ul>
 358 <div class="section" id="external-options">
 359 <h2><a class="toc-backref" href="#id11">External options</a></h2>
 360 <p>Sometimes, when linking several plugins together, one plugin needs to
 361 access options defined in some other plugin. Because of the way
 362 options are implemented, such options must be marked as
 363 <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
 364 for. Example:</p>
 365 <pre class="literal-block">
 366 ...
 367 (switch_option &quot;E&quot;, (extern))
 368 ...
 369 </pre>
 370 <p>If an external option has additional attributes besides 'extern', they are
 371 ignored. See also the section on plugin <a class="reference internal" href="#priorities">priorities</a>.</p>
 372 </div>
 373 </div>
 374 <div class="section" id="conditional-evaluation">
 375 <span id="case"></span><h1><a class="toc-backref" href="#id12">Conditional evaluation</a></h1>
 376 <p>The 'case' construct is the main means by which programmability is
 377 achieved in LLVMC. It can be used to calculate edge weights, program
 378 actions and modify the shell commands to be executed. The 'case'
 379 expression is designed after the similarly-named construct in
 380 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>
 381 <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
 382 are evaluated only if the corresponding tests evaluate to true.</p>
 383 <p>Examples:</p>
 384 <pre class="literal-block">
 385 // Edge weight calculation
 386
 387 // Increases edge weight by 5 if &quot;-A&quot; is provided on the
 388 // command-line, and by 5 more if &quot;-B&quot; is also provided.
 389 (case
 390     (switch_on &quot;A&quot;), (inc_weight 5),
 391     (switch_on &quot;B&quot;), (inc_weight 5))
 392
 393
 394 // Tool command line specification
 395
 396 // Evaluates to &quot;cmdline1&quot; if the option &quot;-A&quot; is provided on the
 397 // command line; to &quot;cmdline2&quot; if &quot;-B&quot; is provided;
 398 // otherwise to &quot;cmdline3&quot;.
 399
 400 (case
 401     (switch_on &quot;A&quot;), &quot;cmdline1&quot;,
 402     (switch_on &quot;B&quot;), &quot;cmdline2&quot;,
 403     (default), &quot;cmdline3&quot;)
 404 </pre>
 405 <p>Note the slight difference in 'case' expression handling in contexts
 406 of edge weights and command line specification - in the second example
 407 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
 408 enabled, and the whole expression always evaluates to <tt class="docutils literal"><span class="pre">&quot;cmdline1&quot;</span></tt> in
 409 that case.</p>
 410 <p>Case expressions can also be nested, i.e. the following is legal:</p>
 411 <pre class="literal-block">
 412 (case (switch_on &quot;E&quot;), (case (switch_on &quot;o&quot;), ..., (default), ...)
 413       (default), ...)
 414 </pre>
 415 <p>You should, however, try to avoid doing that because it hurts
 416 readability. It is usually better to split tool descriptions and/or
 417 use TableGen inheritance instead.</p>
 418 <ul class="simple">
 419 <li>Possible tests are:<ul>
 420 <li><tt class="docutils literal"><span class="pre">switch_on</span></tt> - Returns true if a given command-line switch is
 421 provided by the user. Example: <tt class="docutils literal"><span class="pre">(switch_on</span> <span class="pre">&quot;opt&quot;)</span></tt>.</li>
 422 <li><tt class="docutils literal"><span class="pre">parameter_equals</span></tt> - Returns true if a command-line parameter equals
 423 a given value.
 424 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>
 425 <li><tt class="docutils literal"><span class="pre">element_in_list</span></tt> - Returns true if a command-line parameter
 426 list contains a given value.
 427 Example: <tt class="docutils literal"><span class="pre">(parameter_in_list</span> <span class="pre">&quot;l&quot;,</span> <span class="pre">&quot;pthread&quot;)</span></tt>.</li>
 428 <li><tt class="docutils literal"><span class="pre">input_languages_contain</span></tt> - Returns true if a given language
 429 belongs to the current input language set.
 430 Example: <tt class="docutils literal"><span class="pre">(input_languages_contain</span> <span class="pre">&quot;c++&quot;)</span></tt>.</li>
 431 <li><tt class="docutils literal"><span class="pre">in_language</span></tt> - Evaluates to true if the input file language
 432 equals to the argument. At the moment works only with <tt class="docutils literal"><span class="pre">cmd_line</span></tt>
 433 and <tt class="docutils literal"><span class="pre">actions</span></tt> (on non-join nodes).
 434 Example: <tt class="docutils literal"><span class="pre">(in_language</span> <span class="pre">&quot;c++&quot;)</span></tt>.</li>
 435 <li><tt class="docutils literal"><span class="pre">not_empty</span></tt> - Returns true if a given option (which should be
 436 either a parameter or a parameter list) is set by the
 437 user.
 438 Example: <tt class="docutils literal"><span class="pre">(not_empty</span> <span class="pre">&quot;o&quot;)</span></tt>.</li>
 439 <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>
 440 <span class="pre">X))</span></tt>. Provided for convenience.</li>
 441 <li><tt class="docutils literal"><span class="pre">default</span></tt> - Always evaluates to true. Should always be the last
 442 test in the <tt class="docutils literal"><span class="pre">case</span></tt> expression.</li>
 443 <li><tt class="docutils literal"><span class="pre">and</span></tt> - A standard logical combinator that returns true iff all
 444 of its arguments return true. Used like this: <tt class="docutils literal"><span class="pre">(and</span> <span class="pre">(test1),</span>
 445 <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,
 446 but not encouraged.</li>
 447 <li><tt class="docutils literal"><span class="pre">or</span></tt> - Another logical combinator that returns true only if any
 448 one of its arguments returns true. Example: <tt class="docutils literal"><span class="pre">(or</span> <span class="pre">(test1),</span>
 449 <span class="pre">(test2),</span> <span class="pre">...</span> <span class="pre">(testN))</span></tt>.</li>
 450 </ul>
 451 </li>
 452 </ul>
 453 </div>
 454 <div class="section" id="writing-a-tool-description">
 455 <h1><a class="toc-backref" href="#id13">Writing a tool description</a></h1>
 456 <p>As was said earlier, nodes in the compilation graph represent tools,
 457 which are described separately. A tool definition looks like this
 458 (taken from the <tt class="docutils literal"><span class="pre">include/llvm/CompilerDriver/Tools.td</span></tt> file):</p>
 459 <pre class="literal-block">
 460 def llvm_gcc_cpp : Tool&lt;[
 461     (in_language &quot;c++&quot;),
 462     (out_language &quot;llvm-assembler&quot;),
 463     (output_suffix &quot;bc&quot;),
 464     (cmd_line &quot;llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm&quot;),
 465     (sink)
 466     ]&gt;;
 467 </pre>
 468 <p>This defines a new tool called <tt class="docutils literal"><span class="pre">llvm_gcc_cpp</span></tt>, which is an alias for
 469 <tt class="docutils literal"><span class="pre">llvm-g++</span></tt>. As you can see, a tool definition is just a list of
 470 properties; most of them should be self-explanatory. The <tt class="docutils literal"><span class="pre">sink</span></tt>
 471 property means that this tool should be passed all command-line
 472 options that aren't mentioned in the option list.</p>
 473 <p>The complete list of all currently implemented tool properties follows.</p>
 474 <ul class="simple">
 475 <li>Possible tool properties:<ul>
 476 <li><tt class="docutils literal"><span class="pre">in_language</span></tt> - input language name. Can be either a string or a
 477 list, in case the tool supports multiple input languages.</li>
 478 <li><tt class="docutils literal"><span class="pre">out_language</span></tt> - output language name. Tools are not allowed to
 479 have multiple output languages.</li>
 480 <li><tt class="docutils literal"><span class="pre">output_suffix</span></tt> - output file suffix. Can also be changed
 481 dynamically, see documentation on actions.</li>
 482 <li><tt class="docutils literal"><span class="pre">cmd_line</span></tt> - the actual command used to run the tool. You can
 483 use <tt class="docutils literal"><span class="pre">$INFILE</span></tt> and <tt class="docutils literal"><span class="pre">$OUTFILE</span></tt> variables, output redirection
 484 with <tt class="docutils literal"><span class="pre">&gt;</span></tt>, hook invocations (<tt class="docutils literal"><span class="pre">$CALL</span></tt>), environment variables
 485 (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>
 486 <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
 487 list of input files and joins them together. Used for linkers.</li>
 488 <li><tt class="docutils literal"><span class="pre">sink</span></tt> - all command-line options that are not handled by other
 489 tools are passed to this tool.</li>
 490 <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
 491 this tool reacts on command-line options (described in more detail
 492 below).</li>
 493 </ul>
 494 </li>
 495 </ul>
 496 <div class="section" id="actions">
 497 <h2><a class="toc-backref" href="#id14">Actions</a></h2>
 498 <p>A tool often needs to react to command-line options, and this is
 499 precisely what the <tt class="docutils literal"><span class="pre">actions</span></tt> property is for. The next example
 500 illustrates this feature:</p>
 501 <pre class="literal-block">
 502 def llvm_gcc_linker : Tool&lt;[
 503     (in_language &quot;object-code&quot;),
 504     (out_language &quot;executable&quot;),
 505     (output_suffix &quot;out&quot;),
 506     (cmd_line &quot;llvm-gcc $INFILE -o $OUTFILE&quot;),
 507     (join),
 508     (actions (case (not_empty &quot;L&quot;), (forward &quot;L&quot;),
 509                    (not_empty &quot;l&quot;), (forward &quot;l&quot;),
 510                    (not_empty &quot;dummy&quot;),
 511                              [(append_cmd &quot;-dummy1&quot;), (append_cmd &quot;-dummy2&quot;)])
 512     ]&gt;;
 513 </pre>
 514 <p>The <tt class="docutils literal"><span class="pre">actions</span></tt> tool property is implemented on top of the omnipresent
 515 <tt class="docutils literal"><span class="pre">case</span></tt> expression. It associates one or more different <em>actions</em>
 516 with given conditions - in the example, the actions are <tt class="docutils literal"><span class="pre">forward</span></tt>,
 517 which forwards a given option unchanged, and <tt class="docutils literal"><span class="pre">append_cmd</span></tt>, which
 518 appends a given string to the tool execution command. Multiple actions
 519 can be associated with a single condition by using a list of actions
 520 (used in the example to append some dummy options). The same <tt class="docutils literal"><span class="pre">case</span></tt>
 521 construct can also be used in the <tt class="docutils literal"><span class="pre">cmd_line</span></tt> property to modify the
 522 tool command line.</p>
 523 <p>The &quot;join&quot; property used in the example means that this tool behaves
 524 like a linker.</p>
 525 <p>The list of all possible actions follows.</p>
 526 <ul>
 527 <li><p class="first">Possible actions:</p>
 528 <blockquote>
 529 <ul class="simple">
 530 <li><tt class="docutils literal"><span class="pre">append_cmd</span></tt> - append a string to the tool invocation
 531 command.
 532 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>
 533 <span class="pre">&quot;-lpthread&quot;))</span></tt></li>
 534 <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>
 535 <span class="pre">Example:</span> <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>
 536 <li><tt class="docutils literal"><span class="pre">forward</span></tt> - forward an option unchanged.
 537 Example: <tt class="docutils literal"><span class="pre">(forward</span> <span class="pre">&quot;Wall&quot;)</span></tt>.</li>
 538 <li><tt class="docutils literal"><span class="pre">forward_as</span></tt> - Change the name of an option, but forward the
 539 argument unchanged.
 540 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>
 541 <li><tt class="docutils literal"><span class="pre">output_suffix</span></tt> - modify the output suffix of this
 542 tool.
 543 Example: <tt class="docutils literal"><span class="pre">(output_suffix</span> <span class="pre">&quot;i&quot;)</span></tt>.</li>
 544 <li><tt class="docutils literal"><span class="pre">stop_compilation</span></tt> - stop compilation after this tool processes
 545 its input. Used without arguments.</li>
 546 <li><tt class="docutils literal"><span class="pre">unpack_values</span></tt> - used for for splitting and forwarding
 547 comma-separated lists of options, e.g. <tt class="docutils literal"><span class="pre">-Wa,-foo=bar,-baz</span></tt> is
 548 converted to <tt class="docutils literal"><span class="pre">-foo=bar</span> <span class="pre">-baz</span></tt> and appended to the tool invocation
 549 command.
 550 Example: <tt class="docutils literal"><span class="pre">(unpack_values</span> <span class="pre">&quot;Wa,&quot;)</span></tt>.</li>
 551 </ul>
 552 </blockquote>
 553 </li>
 554 </ul>
 555 </div>
 556 </div>
 557 <div class="section" id="language-map">
 558 <h1><a class="toc-backref" href="#id15">Language map</a></h1>
 559 <p>If you are adding support for a new language to LLVMC, you'll need to
 560 modify the language map, which defines mappings from file extensions
 561 to language names. It is used to choose the proper toolchain(s) for a
 562 given input file set. Language map definition looks like this:</p>
 563 <pre class="literal-block">
 564 def LanguageMap : LanguageMap&lt;
 565     [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;,
 566      LangToSuffixes&lt;&quot;c&quot;, [&quot;c&quot;]&gt;,
 567      ...
 568     ]&gt;;
 569 </pre>
 570 <p>For example, without those definitions the following command wouldn't work:</p>
 571 <pre class="literal-block">
 572 $ llvmc hello.cpp
 573 llvmc: Unknown suffix: cpp
 574 </pre>
 575 <p>The language map entries should be added only for tools that are
 576 linked with the root node. Since tools are not allowed to have
 577 multiple output languages, for nodes &quot;inside&quot; the graph the input and
 578 output languages should match. This is enforced at compile-time.</p>
 579 </div>
 580 <div class="section" id="more-advanced-topics">
 581 <h1><a class="toc-backref" href="#id16">More advanced topics</a></h1>
 582 <div class="section" id="hooks-and-environment-variables">
 583 <span id="hooks"></span><h2><a class="toc-backref" href="#id17">Hooks and environment variables</a></h2>
 584 <p>Normally, LLVMC executes programs from the system <tt class="docutils literal"><span class="pre">PATH</span></tt>. Sometimes,
 585 this is not sufficient: for example, we may want to specify tool paths
 586 or names in the configuration file. This can be easily achieved via
 587 the hooks mechanism. To write your own hooks, just add their
 588 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
 589 your plugin directory. Hooks should live in the <tt class="docutils literal"><span class="pre">hooks</span></tt> namespace
 590 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>
 591 <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
 592 <tt class="docutils literal"><span class="pre">cmd_line</span></tt> tool property:</p>
 593 <pre class="literal-block">
 594 (cmd_line &quot;$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)&quot;)
 595 </pre>
 596 <p>To pass arguments to hooks, use the following syntax:</p>
 597 <pre class="literal-block">
 598 (cmd_line &quot;$CALL(MyHook, 'Arg1', 'Arg2', 'Arg # 3')/path/to/file -o1 -o2&quot;)
 599 </pre>
 600 <p>It is also possible to use environment variables in the same manner:</p>
 601 <pre class="literal-block">
 602 (cmd_line &quot;$ENV(VAR1)/path/to/file -o $ENV(VAR2)&quot;)
 603 </pre>
 604 <p>To change the command line string based on user-provided options use
 605 the <tt class="docutils literal"><span class="pre">case</span></tt> expression (documented <a class="reference internal" href="#case">above</a>):</p>
 606 <pre class="literal-block">
 607 (cmd_line
 608   (case
 609     (switch_on &quot;E&quot;),
 610        &quot;llvm-g++ -E -x c $INFILE -o $OUTFILE&quot;,
 611     (default),
 612        &quot;llvm-g++ -c -x c $INFILE -o $OUTFILE -emit-llvm&quot;))
 613 </pre>
 614 </div>
 615 <div class="section" id="how-plugins-are-loaded">
 616 <span id="priorities"></span><h2><a class="toc-backref" href="#id18">How plugins are loaded</a></h2>
 617 <p>It is possible for LLVMC plugins to depend on each other. For example,
 618 one can create edges between nodes defined in some other plugin. To
 619 make this work, however, that plugin should be loaded first. To
 620 achieve this, the concept of plugin priority was introduced. By
 621 default, every plugin has priority zero; to specify the priority
 622 explicitly, put the following line in your plugin's TableGen file:</p>
 623 <pre class="literal-block">
 624 def Priority : PluginPriority&lt;$PRIORITY_VALUE&gt;;
 625 # Where PRIORITY_VALUE is some integer &gt; 0
 626 </pre>
 627 <p>Plugins are loaded in order of their (increasing) priority, starting
 628 with 0. Therefore, the plugin with the highest priority value will be
 629 loaded last.</p>
 630 </div>
 631 <div class="section" id="debugging">
 632 <h2><a class="toc-backref" href="#id19">Debugging</a></h2>
 633 <p>When writing LLVMC plugins, it can be useful to get a visual view of
 634 the resulting compilation graph. This can be achieved via the command
 635 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
 636 <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
 637 creates a Graphviz source file (<tt class="docutils literal"><span class="pre">compilation-graph.dot</span></tt>) in the
 638 current directory.</p>
 639 <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
 640 compilation graph for common errors like mismatched output/input
 641 language names, multiple default edges and cycles. These checks can't
 642 be performed at compile-time because the plugins can load code
 643 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
 644 perform any compilation tasks and returns the number of encountered
 645 errors as its status code.</p>
 646 </div>
 647 <div class="section" id="conditioning-on-the-executable-name">
 648 <h2><a class="toc-backref" href="#id20">Conditioning on the executable name</a></h2>
 649 <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
 650 accessible only in the C++ code (i.e. hooks). Use the following code:</p>
 651 <pre class="literal-block">
 652 namespace llvmc {
 653 extern const char* ProgramName;
 654 }
 655
 656 std::string MyHook() {
 657 //...
 658 if (strcmp(ProgramName, &quot;mydriver&quot;) == 0) {
 659    //...
 660
 661 }
 662 </pre>
 663 <p>In general, you're encouraged not to make the behaviour dependent on the
 664 executable file name, and use command-line switches instead. See for example how
 665 the <tt class="docutils literal"><span class="pre">Base</span></tt> plugin behaves when it needs to choose the correct linker options
 666 (think <tt class="docutils literal"><span class="pre">g++</span></tt> vs. <tt class="docutils literal"><span class="pre">gcc</span></tt>).</p>
 667 <hr />
 668 <address>
 669 <a href="http://jigsaw.w3.org/css-validator/check/referer">
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 675
 676 <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
 677 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
 678
 679 Last modified: $Date: 2008-12-11 11:34:48 -0600 (Thu, 11 Dec 2008) $
 680 </address></div>
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