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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.
  15 Please do not edit directly!
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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="id8">Introduction</a></li>
  21 <li><a class="reference internal" href="#compiling-with-llvmc" id="id9">Compiling with LLVMC</a></li>
  22 <li><a class="reference internal" href="#predefined-options" id="id10">Predefined options</a></li>
  23 <li><a class="reference internal" href="#compiling-llvmc-plugins" id="id11">Compiling LLVMC plugins</a></li>
  24 <li><a class="reference internal" href="#compiling-standalone-llvmc-based-drivers" id="id12">Compiling standalone LLVMC-based drivers</a></li>
  25 <li><a class="reference internal" href="#customizing-llvmc-the-compilation-graph" id="id13">Customizing LLVMC: the compilation graph</a></li>
  26 <li><a class="reference internal" href="#describing-options" id="id14">Describing options</a><ul>
  27 <li><a class="reference internal" href="#external-options" id="id15">External options</a></li>
  28 </ul>
  29 </li>
  30 <li><a class="reference internal" href="#conditional-evaluation" id="id16">Conditional evaluation</a></li>
  31 <li><a class="reference internal" href="#writing-a-tool-description" id="id17">Writing a tool description</a><ul>
  32 <li><a class="reference internal" href="#id5" id="id18">Actions</a></li>
  33 </ul>
  34 </li>
  35 <li><a class="reference internal" href="#language-map" id="id19">Language map</a></li>
  36 <li><a class="reference internal" href="#option-preprocessor" id="id20">Option preprocessor</a></li>
  37 <li><a class="reference internal" href="#more-advanced-topics" id="id21">More advanced topics</a><ul>
  38 <li><a class="reference internal" href="#hooks-and-environment-variables" id="id22">Hooks and environment variables</a></li>
  39 <li><a class="reference internal" href="#how-plugins-are-loaded" id="id23">How plugins are loaded</a></li>
  40 <li><a class="reference internal" href="#debugging" id="id24">Debugging</a></li>
  41 <li><a class="reference internal" href="#conditioning-on-the-executable-name" id="id25">Conditioning on the executable name</a></li>
  42 </ul>
  43 </li>
  44 </ul>
  45 </div>
  46 <div class="doc_author">
  47 <p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
  48 </div><div class="section" id="introduction">
  49 <h1><a class="toc-backref" href="#id8">Introduction</a></h1>
  50 <p>LLVMC is a generic compiler driver, designed to be customizable and
  51 extensible. It plays the same role for LLVM as the <tt class="docutils literal"><span class="pre">gcc</span></tt> program
  52 does for GCC - LLVMC's job is essentially to transform a set of input
  53 files into a set of targets depending on configuration rules and user
  54 options. What makes LLVMC different is that these transformation rules
  55 are completely customizable - in fact, LLVMC knows nothing about the
  56 specifics of transformation (even the command-line options are mostly
  57 not hard-coded) and regards the transformation structure as an
  58 abstract graph. The structure of this graph is completely determined
  59 by plugins, which can be either statically or dynamically linked. This
  60 makes it possible to easily adapt LLVMC for other purposes - for
  61 example, as a build tool for game resources.</p>
  62 <p>Because LLVMC employs <a class="reference external" href="http://llvm.org/docs/TableGenFundamentals.html">TableGen</a> as its configuration language, you
  63 need to be familiar with it to customize LLVMC.</p>
  64 </div>
  65 <div class="section" id="compiling-with-llvmc">
  66 <h1><a class="toc-backref" href="#id9">Compiling with LLVMC</a></h1>
  67 <p>LLVMC tries hard to be as compatible with <tt class="docutils literal"><span class="pre">gcc</span></tt> as possible,
  68 although there are some small differences. Most of the time, however,
  69 you shouldn't be able to notice them:</p>
  70 <pre class="literal-block">
  71 $ # This works as expected:
  72 $ llvmc -O3 -Wall hello.cpp
  73 $ ./a.out
  74 hello
  75 </pre>
  76 <p>One nice feature of LLVMC is that one doesn't have to distinguish between
  77 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
  78 right toolchain is chosen automatically based on input language names (which
  79 are, in turn, determined from file extensions). If you want to force files
  80 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
  81 do it with <tt class="docutils literal"><span class="pre">gcc</span></tt>:</p>
  82 <pre class="literal-block">
  83 $ # hello.c is really a C++ file
  84 $ llvmc -x c++ hello.c
  85 $ ./a.out
  86 hello
  87 </pre>
  88 <p>On the other hand, when using LLVMC as a linker to combine several C++
  89 object files you should provide the <tt class="docutils literal"><span class="pre">--linker</span></tt> option since it's
  90 impossible for LLVMC to choose the right linker in that case:</p>
  91 <pre class="literal-block">
  92 $ llvmc -c hello.cpp
  93 $ llvmc hello.o
  94 [A lot of link-time errors skipped]
  95 $ llvmc --linker=c++ hello.o
  96 $ ./a.out
  97 hello
  98 </pre>
  99 <p>By default, LLVMC uses <tt class="docutils literal"><span class="pre">llvm-gcc</span></tt> to compile the source code. It is also
 100 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>
 101 </div>
 102 <div class="section" id="predefined-options">
 103 <h1><a class="toc-backref" href="#id10">Predefined options</a></h1>
 104 <p>LLVMC has some built-in options that can't be overridden in the
 105 configuration libraries:</p>
 106 <ul class="simple">
 107 <li><tt class="docutils literal"><span class="pre">-o</span> <span class="pre">FILE</span></tt> - Output file name.</li>
 108 <li><tt class="docutils literal"><span class="pre">-x</span> <span class="pre">LANGUAGE</span></tt> - Specify the language of the following input files
 109 until the next -x option.</li>
 110 <li><tt class="docutils literal"><span class="pre">-load</span> <span class="pre">PLUGIN_NAME</span></tt> - Load the specified plugin DLL. Example:
 111 <tt class="docutils literal"><span class="pre">-load</span> <span class="pre">$LLVM_DIR/Release/lib/LLVMCSimple.so</span></tt>.</li>
 112 <li><tt class="docutils literal"><span class="pre">-v</span></tt> - Enable verbose mode, i.e. print out all executed commands.</li>
 113 <li><tt class="docutils literal"><span class="pre">--save-temps</span></tt> - Write temporary files to the current directory and do not
 114 delete them on exit. This option can also take an argument: the
 115 <tt class="docutils literal"><span class="pre">--save-temps=obj</span></tt> switch will write files into the directory specified with
 116 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
 117 both synonyms for the default behaviour.</li>
 118 <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
 119 directory is deleted on exit unless <tt class="docutils literal"><span class="pre">--save-temps</span></tt> is specified. If
 120 <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
 121 precedence.</li>
 122 <li><tt class="docutils literal"><span class="pre">--check-graph</span></tt> - Check the compilation for common errors like mismatched
 123 output/input language names, multiple default edges and cycles. Because of
 124 plugins, these checks can't be performed at compile-time. Exit with code zero
 125 if no errors were found, and return the number of found errors
 126 otherwise. Hidden option, useful for debugging LLVMC plugins.</li>
 127 <li><tt class="docutils literal"><span class="pre">--view-graph</span></tt> - Show a graphical representation of the compilation graph
 128 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
 129 option, useful for debugging LLVMC plugins.</li>
 130 <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
 131 directory with the compilation graph description in Graphviz format (identical
 132 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
 133 used to set the output file name. Hidden option, useful for debugging LLVMC
 134 plugins.</li>
 135 <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
 136 their standard meaning.</li>
 137 </ul>
 138 </div>
 139 <div class="section" id="compiling-llvmc-plugins">
 140 <h1><a class="toc-backref" href="#id11">Compiling LLVMC plugins</a></h1>
 141 <p>It's easiest to start working on your own LLVMC plugin by copying the
 142 skeleton project which lives under <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins/Simple</span></tt>:</p>
 143 <pre class="literal-block">
 144 $ cd $LLVMC_DIR/plugins
 145 $ cp -r Simple MyPlugin
 146 $ cd MyPlugin
 147 $ ls
 148 Makefile PluginMain.cpp Simple.td
 149 </pre>
 150 <p>As you can see, our basic plugin consists of only two files (not
 151 counting the build script). <tt class="docutils literal"><span class="pre">Simple.td</span></tt> contains TableGen
 152 description of the compilation graph; its format is documented in the
 153 following sections. <tt class="docutils literal"><span class="pre">PluginMain.cpp</span></tt> is just a helper file used to
 154 compile the auto-generated C++ code produced from TableGen source. It
 155 can also contain hook definitions (see <a class="reference internal" href="#hooks">below</a>).</p>
 156 <p>The first thing that you should do is to change the <tt class="docutils literal"><span class="pre">LLVMC_PLUGIN</span></tt>
 157 variable in the <tt class="docutils literal"><span class="pre">Makefile</span></tt> to avoid conflicts (since this variable
 158 is used to name the resulting library):</p>
 159 <pre class="literal-block">
 160 LLVMC_PLUGIN=MyPlugin
 161 </pre>
 162 <p>It is also a good idea to rename <tt class="docutils literal"><span class="pre">Simple.td</span></tt> to something less
 163 generic:</p>
 164 <pre class="literal-block">
 165 $ mv Simple.td MyPlugin.td
 166 </pre>
 167 <p>To build your plugin as a dynamic library, just <tt class="docutils literal"><span class="pre">cd</span></tt> to its source
 168 directory and run <tt class="docutils literal"><span class="pre">make</span></tt>. The resulting file will be called
 169 <tt class="docutils literal"><span class="pre">plugin_llvmc_$(LLVMC_PLUGIN).$(DLL_EXTENSION)</span></tt> (in our case,
 170 <tt class="docutils literal"><span class="pre">plugin_llvmc_MyPlugin.so</span></tt>). This library can be then loaded in with the
 171 <tt class="docutils literal"><span class="pre">-load</span></tt> option. Example:</p>
 172 <pre class="literal-block">
 173 $ cd $LLVMC_DIR/plugins/Simple
 174 $ make
 175 $ llvmc -load $LLVM_DIR/Release/lib/plugin_llvmc_Simple.so
 176 </pre>
 177 </div>
 178 <div class="section" id="compiling-standalone-llvmc-based-drivers">
 179 <h1><a class="toc-backref" href="#id12">Compiling standalone LLVMC-based drivers</a></h1>
 180 <p>By default, the <tt class="docutils literal"><span class="pre">llvmc</span></tt> executable consists of a driver core plus several
 181 statically linked plugins (<tt class="docutils literal"><span class="pre">Base</span></tt> and <tt class="docutils literal"><span class="pre">Clang</span></tt> at the moment). You can
 182 produce a standalone LLVMC-based driver executable by linking the core with your
 183 own plugins. The recommended way to do this is by starting with the provided
 184 <tt class="docutils literal"><span class="pre">Skeleton</span></tt> example (<tt class="docutils literal"><span class="pre">$LLVMC_DIR/example/Skeleton</span></tt>):</p>
 185 <pre class="literal-block">
 186 $ cd $LLVMC_DIR/example/
 187 $ cp -r Skeleton mydriver
 188 $ cd mydriver
 189 $ vim Makefile
 190 [...]
 191 $ make
 192 </pre>
 193 <p>If you're compiling LLVM with different source and object directories, then you
 194 must perform the following additional steps before running <tt class="docutils literal"><span class="pre">make</span></tt>:</p>
 195 <pre class="literal-block">
 196 # LLVMC_SRC_DIR = $LLVM_SRC_DIR/tools/llvmc/
 197 # LLVMC_OBJ_DIR = $LLVM_OBJ_DIR/tools/llvmc/
 198 $ cp $LLVMC_SRC_DIR/example/mydriver/Makefile \
 199   $LLVMC_OBJ_DIR/example/mydriver/
 200 $ cd $LLVMC_OBJ_DIR/example/mydriver
 201 $ make
 202 </pre>
 203 <p>Another way to do the same thing is by using the following command:</p>
 204 <pre class="literal-block">
 205 $ cd $LLVMC_DIR
 206 $ make LLVMC_BUILTIN_PLUGINS=MyPlugin LLVMC_BASED_DRIVER_NAME=mydriver
 207 </pre>
 208 <p>This works with both srcdir == objdir and srcdir != objdir, but assumes that the
 209 plugin source directory was placed under <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins</span></tt>.</p>
 210 <p>Sometimes, you will want a 'bare-bones' version of LLVMC that has no
 211 built-in plugins. It can be compiled with the following command:</p>
 212 <pre class="literal-block">
 213 $ cd $LLVMC_DIR
 214 $ make LLVMC_BUILTIN_PLUGINS=&quot;&quot;
 215 </pre>
 216 </div>
 217 <div class="section" id="customizing-llvmc-the-compilation-graph">
 218 <h1><a class="toc-backref" href="#id13">Customizing LLVMC: the compilation graph</a></h1>
 219 <p>Each TableGen configuration file should include the common
 220 definitions:</p>
 221 <pre class="literal-block">
 222 include &quot;llvm/CompilerDriver/Common.td&quot;
 223 </pre>
 224 <p>Internally, LLVMC stores information about possible source
 225 transformations in form of a graph. Nodes in this graph represent
 226 tools, and edges between two nodes represent a transformation path. A
 227 special &quot;root&quot; node is used to mark entry points for the
 228 transformations. LLVMC also assigns a weight to each edge (more on
 229 this later) to choose between several alternative edges.</p>
 230 <p>The definition of the compilation graph (see file
 231 <tt class="docutils literal"><span class="pre">plugins/Base/Base.td</span></tt> for an example) is just a list of edges:</p>
 232 <pre class="literal-block">
 233 def CompilationGraph : CompilationGraph&lt;[
 234     Edge&lt;&quot;root&quot;, &quot;llvm_gcc_c&quot;&gt;,
 235     Edge&lt;&quot;root&quot;, &quot;llvm_gcc_assembler&quot;&gt;,
 236     ...
 237
 238     Edge&lt;&quot;llvm_gcc_c&quot;, &quot;llc&quot;&gt;,
 239     Edge&lt;&quot;llvm_gcc_cpp&quot;, &quot;llc&quot;&gt;,
 240     ...
 241
 242     OptionalEdge&lt;&quot;llvm_gcc_c&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
 243                                       (inc_weight))&gt;,
 244     OptionalEdge&lt;&quot;llvm_gcc_cpp&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
 245                                               (inc_weight))&gt;,
 246     ...
 247
 248     OptionalEdge&lt;&quot;llvm_gcc_assembler&quot;, &quot;llvm_gcc_cpp_linker&quot;,
 249         (case (input_languages_contain &quot;c++&quot;), (inc_weight),
 250               (or (parameter_equals &quot;linker&quot;, &quot;g++&quot;),
 251                   (parameter_equals &quot;linker&quot;, &quot;c++&quot;)), (inc_weight))&gt;,
 252     ...
 253
 254     ]&gt;;
 255 </pre>
 256 <p>As you can see, the edges can be either default or optional, where
 257 optional edges are differentiated by an additional <tt class="docutils literal"><span class="pre">case</span></tt> expression
 258 used to calculate the weight of this edge. Notice also that we refer
 259 to tools via their names (as strings). This makes it possible to add
 260 edges to an existing compilation graph in plugins without having to
 261 know about all tool definitions used in the graph.</p>
 262 <p>The default edges are assigned a weight of 1, and optional edges get a
 263 weight of 0 + 2*N where N is the number of tests that evaluated to
 264 true in the <tt class="docutils literal"><span class="pre">case</span></tt> expression. It is also possible to provide an
 265 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,
 266 the weight is increased (or decreased) by the provided value instead
 267 of the default 2. It is also possible to change the default weight of
 268 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>
 269 construct.</p>
 270 <p>When passing an input file through the graph, LLVMC picks the edge
 271 with the maximum weight. To avoid ambiguity, there should be only one
 272 default edge between two nodes (with the exception of the root node,
 273 which gets a special treatment - there you are allowed to specify one
 274 default edge <em>per language</em>).</p>
 275 <p>When multiple plugins are loaded, their compilation graphs are merged
 276 together. Since multiple edges that have the same end nodes are not
 277 allowed (i.e. the graph is not a multigraph), an edge defined in
 278 several plugins will be replaced by the definition from the plugin
 279 that was loaded last. Plugin load order can be controlled by using the
 280 plugin priority feature described above.</p>
 281 <p>To get a visual representation of the compilation graph (useful for
 282 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
 283 <tt class="docutils literal"><span class="pre">gsview</span></tt> installed for this to work properly.</p>
 284 </div>
 285 <div class="section" id="describing-options">
 286 <h1><a class="toc-backref" href="#id14">Describing options</a></h1>
 287 <p>Command-line options that the plugin supports are defined by using an
 288 <tt class="docutils literal"><span class="pre">OptionList</span></tt>:</p>
 289 <pre class="literal-block">
 290 def Options : OptionList&lt;[
 291 (switch_option &quot;E&quot;, (help &quot;Help string&quot;)),
 292 (alias_option &quot;quiet&quot;, &quot;q&quot;)
 293 ...
 294 ]&gt;;
 295 </pre>
 296 <p>As you can see, the option list is just a list of DAGs, where each DAG
 297 is an option description consisting of the option name and some
 298 properties. A plugin can define more than one option list (they are
 299 all merged together in the end), which can be handy if one wants to
 300 separate option groups syntactically.</p>
 301 <ul>
 302 <li><p class="first">Possible option types:</p>
 303 <blockquote>
 304 <ul class="simple">
 305 <li><tt class="docutils literal"><span class="pre">switch_option</span></tt> - a simple boolean switch without arguments, for example
 306 <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>
 307 <li><tt class="docutils literal"><span class="pre">parameter_option</span></tt> - option that takes one argument, for example
 308 <tt class="docutils literal"><span class="pre">-std=c99</span></tt>. It is also allowed to use spaces instead of the equality
 309 sign: <tt class="docutils literal"><span class="pre">-std</span> <span class="pre">c99</span></tt>. At most one occurrence is allowed.</li>
 310 <li><tt class="docutils literal"><span class="pre">parameter_list_option</span></tt> - same as the above, but more than one option
 311 occurence is allowed.</li>
 312 <li><tt class="docutils literal"><span class="pre">prefix_option</span></tt> - same as the parameter_option, but the option name and
 313 argument do not have to be separated. Example: <tt class="docutils literal"><span class="pre">-ofile</span></tt>. This can be also
 314 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
 315 (<tt class="docutils literal"><span class="pre">=file</span></tt> will be interpreted as option value). At most one occurrence is
 316 allowed.</li>
 317 <li><tt class="docutils literal"><span class="pre">prefix_list_option</span></tt> - same as the above, but more than one occurence of
 318 the option is allowed; example: <tt class="docutils literal"><span class="pre">-lm</span> <span class="pre">-lpthread</span></tt>.</li>
 319 <li><tt class="docutils literal"><span class="pre">alias_option</span></tt> - a special option type for creating aliases. Unlike other
 320 option types, aliases are not allowed to have any properties besides the
 321 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>
 322 </ul>
 323 </blockquote>
 324 </li>
 325 <li><p class="first">Possible option properties:</p>
 326 <blockquote>
 327 <ul class="simple">
 328 <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>
 329 output.</li>
 330 <li><tt class="docutils literal"><span class="pre">required</span></tt> - this option must be specified exactly once (or, in case of
 331 the list options without the <tt class="docutils literal"><span class="pre">multi_val</span></tt> property, at least
 332 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>
 333 <li><tt class="docutils literal"><span class="pre">one_or_more</span></tt> - the option must be specified at least one time. Useful
 334 only for list options in conjunction with <tt class="docutils literal"><span class="pre">multi_val</span></tt>; for ordinary lists
 335 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
 336 <tt class="docutils literal"><span class="pre">zero_or_one</span></tt>.</li>
 337 <li><tt class="docutils literal"><span class="pre">optional</span></tt> - the option can be specified zero or one times. Useful only
 338 for list options in conjunction with <tt class="docutils literal"><span class="pre">multi_val</span></tt>. Incompatible with
 339 <tt class="docutils literal"><span class="pre">required</span></tt> and <tt class="docutils literal"><span class="pre">one_or_more</span></tt>.</li>
 340 <li><tt class="docutils literal"><span class="pre">hidden</span></tt> - the description of this option will not appear in
 341 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>
 342 output).</li>
 343 <li><tt class="docutils literal"><span class="pre">really_hidden</span></tt> - the option will not be mentioned in any help
 344 output.</li>
 345 <li><tt class="docutils literal"><span class="pre">comma_separated</span></tt> - Indicates that any commas specified for an option's
 346 value should be used to split the value up into multiple values for the
 347 option. This property is valid only for list options. In conjunction with
 348 <tt class="docutils literal"><span class="pre">forward_value</span></tt> can be used to implement option forwarding in style of
 349 gcc's <tt class="docutils literal"><span class="pre">-Wa,</span></tt>.</li>
 350 <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
 351 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>
 352 <span class="pre">3))</span></tt>; the command-line syntax is '-foo a b c'. Only list options can have
 353 this attribute; you can, however, use the <tt class="docutils literal"><span class="pre">one_or_more</span></tt>, <tt class="docutils literal"><span class="pre">optional</span></tt>
 354 and <tt class="docutils literal"><span class="pre">required</span></tt> properties.</li>
 355 <li><tt class="docutils literal"><span class="pre">init</span></tt> - this option has a default value, either a string (if it is a
 356 parameter), or a boolean (if it is a switch; as in C++, boolean constants
 357 are called <tt class="docutils literal"><span class="pre">true</span></tt> and <tt class="docutils literal"><span class="pre">false</span></tt>). List options can't have <tt class="docutils literal"><span class="pre">init</span></tt>
 358 attribute.
 359 Usage examples: <tt class="docutils literal"><span class="pre">(switch_option</span> <span class="pre">&quot;foo&quot;,</span> <span class="pre">(init</span> <span class="pre">true))</span></tt>; <tt class="docutils literal"><span class="pre">(prefix_option</span>
 360 <span class="pre">&quot;bar&quot;,</span> <span class="pre">(init</span> <span class="pre">&quot;baz&quot;))</span></tt>.</li>
 361 <li><tt class="docutils literal"><span class="pre">extern</span></tt> - this option is defined in some other plugin, see <a class="reference internal" href="#extern">below</a>.</li>
 362 </ul>
 363 </blockquote>
 364 </li>
 365 </ul>
 366 <div class="section" id="external-options">
 367 <span id="extern"></span><h2><a class="toc-backref" href="#id15">External options</a></h2>
 368 <p>Sometimes, when linking several plugins together, one plugin needs to
 369 access options defined in some other plugin. Because of the way
 370 options are implemented, such options must be marked as
 371 <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
 372 for. Example:</p>
 373 <pre class="literal-block">
 374 ...
 375 (switch_option &quot;E&quot;, (extern))
 376 ...
 377 </pre>
 378 <p>If an external option has additional attributes besides 'extern', they are
 379 ignored. See also the section on plugin <a class="reference internal" href="#priorities">priorities</a>.</p>
 380 </div>
 381 </div>
 382 <div class="section" id="conditional-evaluation">
 383 <span id="case"></span><h1><a class="toc-backref" href="#id16">Conditional evaluation</a></h1>
 384 <p>The 'case' construct is the main means by which programmability is
 385 achieved in LLVMC. It can be used to calculate edge weights, program
 386 actions and modify the shell commands to be executed. The 'case'
 387 expression is designed after the similarly-named construct in
 388 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>
 389 <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
 390 are evaluated only if the corresponding tests evaluate to true.</p>
 391 <p>Examples:</p>
 392 <pre class="literal-block">
 393 // Edge weight calculation
 394
 395 // Increases edge weight by 5 if &quot;-A&quot; is provided on the
 396 // command-line, and by 5 more if &quot;-B&quot; is also provided.
 397 (case
 398     (switch_on &quot;A&quot;), (inc_weight 5),
 399     (switch_on &quot;B&quot;), (inc_weight 5))
 400
 401
 402 // Tool command line specification
 403
 404 // Evaluates to &quot;cmdline1&quot; if the option &quot;-A&quot; is provided on the
 405 // command line; to &quot;cmdline2&quot; if &quot;-B&quot; is provided;
 406 // otherwise to &quot;cmdline3&quot;.
 407
 408 (case
 409     (switch_on &quot;A&quot;), &quot;cmdline1&quot;,
 410     (switch_on &quot;B&quot;), &quot;cmdline2&quot;,
 411     (default), &quot;cmdline3&quot;)
 412 </pre>
 413 <p>Note the slight difference in 'case' expression handling in contexts
 414 of edge weights and command line specification - in the second example
 415 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
 416 enabled, and the whole expression always evaluates to <tt class="docutils literal"><span class="pre">&quot;cmdline1&quot;</span></tt> in
 417 that case.</p>
 418 <p>Case expressions can also be nested, i.e. the following is legal:</p>
 419 <pre class="literal-block">
 420 (case (switch_on &quot;E&quot;), (case (switch_on &quot;o&quot;), ..., (default), ...)
 421       (default), ...)
 422 </pre>
 423 <p>You should, however, try to avoid doing that because it hurts
 424 readability. It is usually better to split tool descriptions and/or
 425 use TableGen inheritance instead.</p>
 426 <ul class="simple">
 427 <li>Possible tests are:<ul>
 428 <li><tt class="docutils literal"><span class="pre">switch_on</span></tt> - Returns true if a given command-line switch is provided by
 429 the user. Can be given a list as argument, in that case <tt class="docutils literal"><span class="pre">(switch_on</span> <span class="pre">[&quot;foo&quot;,</span>
 430 <span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(and</span> <span class="pre">(switch_on</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(switch_on</span>
 431 <span class="pre">&quot;bar&quot;),</span> <span class="pre">(switch_on</span> <span class="pre">&quot;baz&quot;))</span></tt>.
 432 Example: <tt class="docutils literal"><span class="pre">(switch_on</span> <span class="pre">&quot;opt&quot;)</span></tt>.</li>
 433 <li><tt class="docutils literal"><span class="pre">any_switch_on</span></tt> - Given a list of switch options, returns true if any of
 434 the switches is turned on.
 435 Example: <tt class="docutils literal"><span class="pre">(any_switch_on</span> <span class="pre">[&quot;foo&quot;,</span> <span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(or</span>
 436 <span class="pre">(switch_on</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(switch_on</span> <span class="pre">&quot;bar&quot;),</span> <span class="pre">(switch_on</span> <span class="pre">&quot;baz&quot;))</span></tt>.</li>
 437 <li><tt class="docutils literal"><span class="pre">parameter_equals</span></tt> - Returns true if a command-line parameter equals
 438 a given value.
 439 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>
 440 <li><tt class="docutils literal"><span class="pre">element_in_list</span></tt> - Returns true if a command-line parameter
 441 list contains a given value.
 442 Example: <tt class="docutils literal"><span class="pre">(element_in_list</span> <span class="pre">&quot;l&quot;,</span> <span class="pre">&quot;pthread&quot;)</span></tt>.</li>
 443 <li><tt class="docutils literal"><span class="pre">input_languages_contain</span></tt> - Returns true if a given language
 444 belongs to the current input language set.
 445 Example: <tt class="docutils literal"><span class="pre">(input_languages_contain</span> <span class="pre">&quot;c++&quot;)</span></tt>.</li>
 446 <li><tt class="docutils literal"><span class="pre">in_language</span></tt> - Evaluates to true if the input file language is equal to
 447 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
 448 non-join nodes).
 449 Example: <tt class="docutils literal"><span class="pre">(in_language</span> <span class="pre">&quot;c++&quot;)</span></tt>.</li>
 450 <li><tt class="docutils literal"><span class="pre">not_empty</span></tt> - Returns true if a given option (which should be either a
 451 parameter or a parameter list) is set by the user. Like <tt class="docutils literal"><span class="pre">switch_on</span></tt>, can
 452 be also given a list as argument.
 453 Example: <tt class="docutils literal"><span class="pre">(not_empty</span> <span class="pre">&quot;o&quot;)</span></tt>.</li>
 454 <li><tt class="docutils literal"><span class="pre">any_not_empty</span></tt> - Returns true if <tt class="docutils literal"><span class="pre">not_empty</span></tt> returns true for any of
 455 the options in the list.
 456 Example: <tt class="docutils literal"><span class="pre">(any_not_empty</span> <span class="pre">[&quot;foo&quot;,</span> <span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(or</span>
 457 <span class="pre">(not_empty</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;bar&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;baz&quot;))</span></tt>.</li>
 458 <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>
 459 <span class="pre">X))</span></tt>. Provided for convenience. Can be given a list as argument.</li>
 460 <li><tt class="docutils literal"><span class="pre">any_not_empty</span></tt> - Returns true if <tt class="docutils literal"><span class="pre">not_empty</span></tt> returns true for any of
 461 the options in the list.
 462 Example: <tt class="docutils literal"><span class="pre">(any_empty</span> <span class="pre">[&quot;foo&quot;,</span> <span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(not</span> <span class="pre">(and</span>
 463 <span class="pre">(not_empty</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;bar&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;baz&quot;)))</span></tt>.</li>
 464 <li><tt class="docutils literal"><span class="pre">single_input_file</span></tt> - Returns true if there was only one input file
 465 provided on the command-line. Used without arguments:
 466 <tt class="docutils literal"><span class="pre">(single_input_file)</span></tt>.</li>
 467 <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
 468 case of zero input files is considered an error).</li>
 469 <li><tt class="docutils literal"><span class="pre">default</span></tt> - Always evaluates to true. Should always be the last
 470 test in the <tt class="docutils literal"><span class="pre">case</span></tt> expression.</li>
 471 <li><tt class="docutils literal"><span class="pre">and</span></tt> - A standard binary logical combinator that returns true iff all of
 472 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>
 473 <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
 474 encouraged.</li>
 475 <li><tt class="docutils literal"><span class="pre">or</span></tt> - A binary logical combinator that returns true iff any of its
 476 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>
 477 <li><tt class="docutils literal"><span class="pre">not</span></tt> - Standard unary logical combinator that negates its
 478 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>
 479 </ul>
 480 </li>
 481 </ul>
 482 </div>
 483 <div class="section" id="writing-a-tool-description">
 484 <h1><a class="toc-backref" href="#id17">Writing a tool description</a></h1>
 485 <p>As was said earlier, nodes in the compilation graph represent tools,
 486 which are described separately. A tool definition looks like this
 487 (taken from the <tt class="docutils literal"><span class="pre">include/llvm/CompilerDriver/Tools.td</span></tt> file):</p>
 488 <pre class="literal-block">
 489 def llvm_gcc_cpp : Tool&lt;[
 490     (in_language &quot;c++&quot;),
 491     (out_language &quot;llvm-assembler&quot;),
 492     (output_suffix &quot;bc&quot;),
 493     (cmd_line &quot;llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm&quot;),
 494     (sink)
 495     ]&gt;;
 496 </pre>
 497 <p>This defines a new tool called <tt class="docutils literal"><span class="pre">llvm_gcc_cpp</span></tt>, which is an alias for
 498 <tt class="docutils literal"><span class="pre">llvm-g++</span></tt>. As you can see, a tool definition is just a list of
 499 properties; most of them should be self-explanatory. The <tt class="docutils literal"><span class="pre">sink</span></tt>
 500 property means that this tool should be passed all command-line
 501 options that aren't mentioned in the option list.</p>
 502 <p>The complete list of all currently implemented tool properties follows.</p>
 503 <ul class="simple">
 504 <li>Possible tool properties:<ul>
 505 <li><tt class="docutils literal"><span class="pre">in_language</span></tt> - input language name. Can be either a string or a
 506 list, in case the tool supports multiple input languages.</li>
 507 <li><tt class="docutils literal"><span class="pre">out_language</span></tt> - output language name. Multiple output languages are not
 508 allowed.</li>
 509 <li><tt class="docutils literal"><span class="pre">output_suffix</span></tt> - output file suffix. Can also be changed
 510 dynamically, see documentation on actions.</li>
 511 <li><tt class="docutils literal"><span class="pre">cmd_line</span></tt> - the actual command used to run the tool. You can
 512 use <tt class="docutils literal"><span class="pre">$INFILE</span></tt> and <tt class="docutils literal"><span class="pre">$OUTFILE</span></tt> variables, output redirection
 513 with <tt class="docutils literal"><span class="pre">&gt;</span></tt>, hook invocations (<tt class="docutils literal"><span class="pre">$CALL</span></tt>), environment variables
 514 (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>
 515 <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
 516 list of input files and joins them together. Used for linkers.</li>
 517 <li><tt class="docutils literal"><span class="pre">sink</span></tt> - all command-line options that are not handled by other
 518 tools are passed to this tool.</li>
 519 <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
 520 this tool reacts on command-line options (described in more detail
 521 <a class="reference internal" href="#actions">below</a>).</li>
 522 </ul>
 523 </li>
 524 </ul>
 525 <div class="section" id="id5">
 526 <span id="actions"></span><h2><a class="toc-backref" href="#id18">Actions</a></h2>
 527 <p>A tool often needs to react to command-line options, and this is
 528 precisely what the <tt class="docutils literal"><span class="pre">actions</span></tt> property is for. The next example
 529 illustrates this feature:</p>
 530 <pre class="literal-block">
 531 def llvm_gcc_linker : Tool&lt;[
 532     (in_language &quot;object-code&quot;),
 533     (out_language &quot;executable&quot;),
 534     (output_suffix &quot;out&quot;),
 535     (cmd_line &quot;llvm-gcc $INFILE -o $OUTFILE&quot;),
 536     (join),
 537     (actions (case (not_empty &quot;L&quot;), (forward &quot;L&quot;),
 538                    (not_empty &quot;l&quot;), (forward &quot;l&quot;),
 539                    (not_empty &quot;dummy&quot;),
 540                              [(append_cmd &quot;-dummy1&quot;), (append_cmd &quot;-dummy2&quot;)])
 541     ]&gt;;
 542 </pre>
 543 <p>The <tt class="docutils literal"><span class="pre">actions</span></tt> tool property is implemented on top of the omnipresent
 544 <tt class="docutils literal"><span class="pre">case</span></tt> expression. It associates one or more different <em>actions</em>
 545 with given conditions - in the example, the actions are <tt class="docutils literal"><span class="pre">forward</span></tt>,
 546 which forwards a given option unchanged, and <tt class="docutils literal"><span class="pre">append_cmd</span></tt>, which
 547 appends a given string to the tool execution command. Multiple actions
 548 can be associated with a single condition by using a list of actions
 549 (used in the example to append some dummy options). The same <tt class="docutils literal"><span class="pre">case</span></tt>
 550 construct can also be used in the <tt class="docutils literal"><span class="pre">cmd_line</span></tt> property to modify the
 551 tool command line.</p>
 552 <p>The &quot;join&quot; property used in the example means that this tool behaves
 553 like a linker.</p>
 554 <p>The list of all possible actions follows.</p>
 555 <ul>
 556 <li><p class="first">Possible actions:</p>
 557 <blockquote>
 558 <ul class="simple">
 559 <li><tt class="docutils literal"><span class="pre">append_cmd</span></tt> - Append a string to the tool invocation command.
 560 Example: <tt class="docutils literal"><span class="pre">(case</span> <span class="pre">(switch_on</span> <span class="pre">&quot;pthread&quot;),</span> <span class="pre">(append_cmd</span> <span class="pre">&quot;-lpthread&quot;))</span></tt>.</li>
 561 <li><tt class="docutils literal"><span class="pre">error</span></tt> - Exit with error.
 562 Example: <tt class="docutils literal"><span class="pre">(error</span> <span class="pre">&quot;Mixing</span> <span class="pre">-c</span> <span class="pre">and</span> <span class="pre">-S</span> <span class="pre">is</span> <span class="pre">not</span> <span class="pre">allowed!&quot;)</span></tt>.</li>
 563 <li><tt class="docutils literal"><span class="pre">warning</span></tt> - Print a warning.
 564 Example: <tt class="docutils literal"><span class="pre">(warning</span> <span class="pre">&quot;Specifying</span> <span class="pre">both</span> <span class="pre">-O1</span> <span class="pre">and</span> <span class="pre">-O2</span> <span class="pre">is</span> <span class="pre">meaningless!&quot;)</span></tt>.</li>
 565 <li><tt class="docutils literal"><span class="pre">forward</span></tt> - Forward the option unchanged.
 566 Example: <tt class="docutils literal"><span class="pre">(forward</span> <span class="pre">&quot;Wall&quot;)</span></tt>.</li>
 567 <li><tt class="docutils literal"><span class="pre">forward_as</span></tt> - Change the option's name, but forward the argument
 568 unchanged.
 569 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>
 570 <li><tt class="docutils literal"><span class="pre">forward_value</span></tt> - Forward only option's value. Cannot be used with switch
 571 options (since they don't have values), but works fine with lists.
 572 Example: <tt class="docutils literal"><span class="pre">(forward_value</span> <span class="pre">&quot;Wa,&quot;)</span></tt>.</li>
 573 <li><tt class="docutils literal"><span class="pre">forward_transformed_value</span></tt> - As above, but applies a hook to the
 574 option's value before forwarding (see <a class="reference internal" href="#hooks">below</a>). When
 575 <tt class="docutils literal"><span class="pre">forward_transformed_value</span></tt> is applied to a list
 576 option, the hook must have signature
 577 <tt class="docutils literal"><span class="pre">std::string</span> <span class="pre">hooks::HookName</span> <span class="pre">(const</span> <span class="pre">std::vector&lt;std::string&gt;&amp;)</span></tt>.
 578 Example: <tt class="docutils literal"><span class="pre">(forward_transformed_value</span> <span class="pre">&quot;m&quot;,</span> <span class="pre">&quot;ConvertToMAttr&quot;)</span></tt>.</li>
 579 <li><tt class="docutils literal"><span class="pre">output_suffix</span></tt> - Modify the output suffix of this tool.
 580 Example: <tt class="docutils literal"><span class="pre">(output_suffix</span> <span class="pre">&quot;i&quot;)</span></tt>.</li>
 581 <li><tt class="docutils literal"><span class="pre">stop_compilation</span></tt> - Stop compilation after this tool processes its
 582 input. Used without arguments.
 583 Example: <tt class="docutils literal"><span class="pre">(stop_compilation)</span></tt>.</li>
 584 </ul>
 585 </blockquote>
 586 </li>
 587 </ul>
 588 </div>
 589 </div>
 590 <div class="section" id="language-map">
 591 <h1><a class="toc-backref" href="#id19">Language map</a></h1>
 592 <p>If you are adding support for a new language to LLVMC, you'll need to
 593 modify the language map, which defines mappings from file extensions
 594 to language names. It is used to choose the proper toolchain(s) for a
 595 given input file set. Language map definition looks like this:</p>
 596 <pre class="literal-block">
 597 def LanguageMap : LanguageMap&lt;
 598     [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;,
 599      LangToSuffixes&lt;&quot;c&quot;, [&quot;c&quot;]&gt;,
 600      ...
 601     ]&gt;;
 602 </pre>
 603 <p>For example, without those definitions the following command wouldn't work:</p>
 604 <pre class="literal-block">
 605 $ llvmc hello.cpp
 606 llvmc: Unknown suffix: cpp
 607 </pre>
 608 <p>The language map entries are needed only for the tools that are linked from the
 609 root node. Since a tool can't have multiple output languages, for inner nodes of
 610 the graph the input and output languages should match. This is enforced at
 611 compile-time.</p>
 612 </div>
 613 <div class="section" id="option-preprocessor">
 614 <h1><a class="toc-backref" href="#id20">Option preprocessor</a></h1>
 615 <p>It is sometimes useful to run error-checking code before processing the
 616 compilation graph. For example, if optimization options &quot;-O1&quot; and &quot;-O2&quot; are
 617 implemented as switches, we might want to output a warning if the user invokes
 618 the driver with both of these options enabled.</p>
 619 <p>The <tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> feature is reserved specially for these
 620 occasions. Example (adapted from the built-in Base plugin):</p>
 621 <pre class="literal-block">
 622 def Preprocess : OptionPreprocessor&lt;
 623 (case (not (any_switch_on [&quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;, &quot;O3&quot;])),
 624            (set_option &quot;O2&quot;),
 625       (and (switch_on &quot;O3&quot;), (any_switch_on [&quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;])),
 626            (unset_option [&quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;]),
 627       (and (switch_on &quot;O2&quot;), (any_switch_on [&quot;O0&quot;, &quot;O1&quot;])),
 628            (unset_option [&quot;O0&quot;, &quot;O1&quot;]),
 629       (and (switch_on &quot;O1&quot;), (switch_on &quot;O0&quot;)),
 630            (unset_option &quot;O0&quot;))
 631 &gt;;
 632 </pre>
 633 <p>Here, <tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> is used to unset all spurious <tt class="docutils literal"><span class="pre">-O</span></tt> options so
 634 that they are not forwarded to the compiler. If no optimization options are
 635 specified, <tt class="docutils literal"><span class="pre">-O2</span></tt> is enabled.</p>
 636 <p><tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> is basically a single big <tt class="docutils literal"><span class="pre">case</span></tt> expression, which is
 637 evaluated only once right after the plugin is loaded. The only allowed actions
 638 in <tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> are <tt class="docutils literal"><span class="pre">error</span></tt>, <tt class="docutils literal"><span class="pre">warning</span></tt>, and two special actions:
 639 <tt class="docutils literal"><span class="pre">unset_option</span></tt> and <tt class="docutils literal"><span class="pre">set_option</span></tt>. As their names suggest, they can be used to
 640 set or unset a given option. To set an option with <tt class="docutils literal"><span class="pre">set_option</span></tt>, use the
 641 two-argument form: <tt class="docutils literal"><span class="pre">(set_option</span> <span class="pre">&quot;parameter&quot;,</span> <span class="pre">VALUE)</span></tt>. Here, <tt class="docutils literal"><span class="pre">VALUE</span></tt> can be
 642 either a string, a string list, or a boolean constant.</p>
 643 <p>For convenience, <tt class="docutils literal"><span class="pre">set_option</span></tt> and <tt class="docutils literal"><span class="pre">unset_option</span></tt> also work on lists. That
 644 is, instead of <tt class="docutils literal"><span class="pre">[(unset_option</span> <span class="pre">&quot;A&quot;),</span> <span class="pre">(unset_option</span> <span class="pre">&quot;B&quot;)]</span></tt> you can use
 645 <tt class="docutils literal"><span class="pre">(unset_option</span> <span class="pre">[&quot;A&quot;,</span> <span class="pre">&quot;B&quot;])</span></tt>. Obviously, <tt class="docutils literal"><span class="pre">(set_option</span> <span class="pre">[&quot;A&quot;,</span> <span class="pre">&quot;B&quot;])</span></tt> is valid
 646 only if both <tt class="docutils literal"><span class="pre">A</span></tt> and <tt class="docutils literal"><span class="pre">B</span></tt> are switches.</p>
 647 </div>
 648 <div class="section" id="more-advanced-topics">
 649 <h1><a class="toc-backref" href="#id21">More advanced topics</a></h1>
 650 <div class="section" id="hooks-and-environment-variables">
 651 <span id="hooks"></span><h2><a class="toc-backref" href="#id22">Hooks and environment variables</a></h2>
 652 <p>Normally, LLVMC executes programs from the system <tt class="docutils literal"><span class="pre">PATH</span></tt>. Sometimes,
 653 this is not sufficient: for example, we may want to specify tool paths
 654 or names in the configuration file. This can be easily achieved via
 655 the hooks mechanism. To write your own hooks, just add their
 656 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
 657 your plugin directory. Hooks should live in the <tt class="docutils literal"><span class="pre">hooks</span></tt> namespace
 658 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>
 659 <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
 660 <tt class="docutils literal"><span class="pre">cmd_line</span></tt> tool property:</p>
 661 <pre class="literal-block">
 662 (cmd_line &quot;$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)&quot;)
 663 </pre>
 664 <p>To pass arguments to hooks, use the following syntax:</p>
 665 <pre class="literal-block">
 666 (cmd_line &quot;$CALL(MyHook, 'Arg1', 'Arg2', 'Arg # 3')/path/to/file -o1 -o2&quot;)
 667 </pre>
 668 <p>It is also possible to use environment variables in the same manner:</p>
 669 <pre class="literal-block">
 670 (cmd_line &quot;$ENV(VAR1)/path/to/file -o $ENV(VAR2)&quot;)
 671 </pre>
 672 <p>To change the command line string based on user-provided options use
 673 the <tt class="docutils literal"><span class="pre">case</span></tt> expression (documented <a class="reference internal" href="#case">above</a>):</p>
 674 <pre class="literal-block">
 675 (cmd_line
 676   (case
 677     (switch_on &quot;E&quot;),
 678        &quot;llvm-g++ -E -x c $INFILE -o $OUTFILE&quot;,
 679     (default),
 680        &quot;llvm-g++ -c -x c $INFILE -o $OUTFILE -emit-llvm&quot;))
 681 </pre>
 682 </div>
 683 <div class="section" id="how-plugins-are-loaded">
 684 <span id="priorities"></span><h2><a class="toc-backref" href="#id23">How plugins are loaded</a></h2>
 685 <p>It is possible for LLVMC plugins to depend on each other. For example,
 686 one can create edges between nodes defined in some other plugin. To
 687 make this work, however, that plugin should be loaded first. To
 688 achieve this, the concept of plugin priority was introduced. By
 689 default, every plugin has priority zero; to specify the priority
 690 explicitly, put the following line in your plugin's TableGen file:</p>
 691 <pre class="literal-block">
 692 def Priority : PluginPriority&lt;$PRIORITY_VALUE&gt;;
 693 # Where PRIORITY_VALUE is some integer &gt; 0
 694 </pre>
 695 <p>Plugins are loaded in order of their (increasing) priority, starting
 696 with 0. Therefore, the plugin with the highest priority value will be
 697 loaded last.</p>
 698 </div>
 699 <div class="section" id="debugging">
 700 <h2><a class="toc-backref" href="#id24">Debugging</a></h2>
 701 <p>When writing LLVMC plugins, it can be useful to get a visual view of
 702 the resulting compilation graph. This can be achieved via the command
 703 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
 704 <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
 705 creates a Graphviz source file (<tt class="docutils literal"><span class="pre">compilation-graph.dot</span></tt>) in the
 706 current directory.</p>
 707 <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
 708 compilation graph for common errors like mismatched output/input
 709 language names, multiple default edges and cycles. These checks can't
 710 be performed at compile-time because the plugins can load code
 711 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
 712 perform any compilation tasks and returns the number of encountered
 713 errors as its status code.</p>
 714 </div>
 715 <div class="section" id="conditioning-on-the-executable-name">
 716 <h2><a class="toc-backref" href="#id25">Conditioning on the executable name</a></h2>
 717 <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
 718 accessible only in the C++ code (i.e. hooks). Use the following code:</p>
 719 <pre class="literal-block">
 720 namespace llvmc {
 721 extern const char* ProgramName;
 722 }
 723
 724 namespace hooks {
 725
 726 std::string MyHook() {
 727 //...
 728 if (strcmp(ProgramName, &quot;mydriver&quot;) == 0) {
 729    //...
 730
 731 }
 732
 733 } // end namespace hooks
 734 </pre>
 735 <p>In general, you're encouraged not to make the behaviour dependent on the
 736 executable file name, and use command-line switches instead. See for example how
 737 the <tt class="docutils literal"><span class="pre">Base</span></tt> plugin behaves when it needs to choose the correct linker options
 738 (think <tt class="docutils literal"><span class="pre">g++</span></tt> vs. <tt class="docutils literal"><span class="pre">gcc</span></tt>).</p>
 739 <hr />
 740 <address>
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 747
 748 <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
 749 <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br />
 750
 751 Last modified: $Date$
 752 </address></div>
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