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  11 <div class="document" id="customizing-llvmc-reference-manual">
  12 <h1 class="title">Customizing LLVMC: Reference Manual</h1>
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  16 <div class="contents topic">
  17 <p class="topic-title first"><a id="contents" name="contents">Contents</a></p>
  18 <ul class="simple">
  19 <li><a class="reference" href="#introduction" id="id4" name="id4">Introduction</a></li>
  20 <li><a class="reference" href="#compiling-with-llvmc" id="id5" name="id5">Compiling with LLVMC</a></li>
  21 <li><a class="reference" href="#predefined-options" id="id6" name="id6">Predefined options</a></li>
  22 <li><a class="reference" href="#compiling-llvmc-plugins" id="id7" name="id7">Compiling LLVMC plugins</a></li>
  23 <li><a class="reference" href="#customizing-llvmc-the-compilation-graph" id="id8" name="id8">Customizing LLVMC: the compilation graph</a></li>
  24 <li><a class="reference" href="#describing-options" id="id9" name="id9">Describing options</a><ul>
  25 <li><a class="reference" href="#external-options" id="id10" name="id10">External options</a></li>
  26 </ul>
  27 </li>
  28 <li><a class="reference" href="#conditional-evaluation" id="id11" name="id11">Conditional evaluation</a></li>
  29 <li><a class="reference" href="#writing-a-tool-description" id="id12" name="id12">Writing a tool description</a><ul>
  30 <li><a class="reference" href="#actions" id="id13" name="id13">Actions</a></li>
  31 </ul>
  32 </li>
  33 <li><a class="reference" href="#language-map" id="id14" name="id14">Language map</a></li>
  34 <li><a class="reference" href="#more-advanced-topics" id="id15" name="id15">More advanced topics</a><ul>
  35 <li><a class="reference" href="#hooks-and-environment-variables" id="id16" name="id16">Hooks and environment variables</a></li>
  36 <li><a class="reference" href="#how-plugins-are-loaded" id="id17" name="id17">How plugins are loaded</a></li>
  37 <li><a class="reference" href="#debugging" id="id18" name="id18">Debugging</a></li>
  38 </ul>
  39 </li>
  40 </ul>
  41 </div>
  42 <div class="doc_author">
  43 <p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
  44 </div><div class="section">
  45 <h1><a class="toc-backref" href="#id4" id="introduction" name="introduction">Introduction</a></h1>
  46 <p>LLVMC is a generic compiler driver, designed to be customizable and
  47 extensible. It plays the same role for LLVM as the <tt class="docutils literal"><span class="pre">gcc</span></tt> program
  48 does for GCC - LLVMC's job is essentially to transform a set of input
  49 files into a set of targets depending on configuration rules and user
  50 options. What makes LLVMC different is that these transformation rules
  51 are completely customizable - in fact, LLVMC knows nothing about the
  52 specifics of transformation (even the command-line options are mostly
  53 not hard-coded) and regards the transformation structure as an
  54 abstract graph. The structure of this graph is completely determined
  55 by plugins, which can be either statically or dynamically linked. This
  56 makes it possible to easily adapt LLVMC for other purposes - for
  57 example, as a build tool for game resources.</p>
  58 <p>Because LLVMC employs <a class="reference" href="http://llvm.cs.uiuc.edu/docs/TableGenFundamentals.html">TableGen</a> as its configuration language, you
  59 need to be familiar with it to customize LLVMC.</p>
  60 </div>
  61 <div class="section">
  62 <h1><a class="toc-backref" href="#id5" id="compiling-with-llvmc" name="compiling-with-llvmc">Compiling with LLVMC</a></h1>
  63 <p>LLVMC tries hard to be as compatible with <tt class="docutils literal"><span class="pre">gcc</span></tt> as possible,
  64 although there are some small differences. Most of the time, however,
  65 you shouldn't be able to notice them:</p>
  66 <pre class="literal-block">
  67 $ # This works as expected:
  68 $ llvmc -O3 -Wall hello.cpp
  69 $ ./a.out
  70 hello
  71 </pre>
  72 <p>One nice feature of LLVMC is that one doesn't have to distinguish
  73 between different compilers for different languages (think <tt class="docutils literal"><span class="pre">g++</span></tt> and
  74 <tt class="docutils literal"><span class="pre">gcc</span></tt>) - the right toolchain is chosen automatically based on input
  75 language names (which are, in turn, determined from file
  76 extensions). If you want to force files ending with &quot;.c&quot; to compile as
  77 C++, use the <tt class="docutils literal"><span class="pre">-x</span></tt> option, just like you would do it with <tt class="docutils literal"><span class="pre">gcc</span></tt>:</p>
  78 <pre class="literal-block">
  79 $ # hello.c is really a C++ file
  80 $ llvmc -x c++ hello.c
  81 $ ./a.out
  82 hello
  83 </pre>
  84 <p>On the other hand, when using LLVMC as a linker to combine several C++
  85 object files you should provide the <tt class="docutils literal"><span class="pre">--linker</span></tt> option since it's
  86 impossible for LLVMC to choose the right linker in that case:</p>
  87 <pre class="literal-block">
  88 $ llvmc -c hello.cpp
  89 $ llvmc hello.o
  90 [A lot of link-time errors skipped]
  91 $ llvmc --linker=c++ hello.o
  92 $ ./a.out
  93 hello
  94 </pre>
  95 <p>By default, LLVMC uses <tt class="docutils literal"><span class="pre">llvm-gcc</span></tt> to compile the source code. It is
  96 also possible to choose the work-in-progress <tt class="docutils literal"><span class="pre">clang</span></tt> compiler with
  97 the <tt class="docutils literal"><span class="pre">-clang</span></tt> option.</p>
  98 </div>
  99 <div class="section">
 100 <h1><a class="toc-backref" href="#id6" id="predefined-options" name="predefined-options">Predefined options</a></h1>
 101 <p>LLVMC has some built-in options that can't be overridden in the
 102 configuration libraries:</p>
 103 <ul class="simple">
 104 <li><tt class="docutils literal"><span class="pre">-o</span> <span class="pre">FILE</span></tt> - Output file name.</li>
 105 <li><tt class="docutils literal"><span class="pre">-x</span> <span class="pre">LANGUAGE</span></tt> - Specify the language of the following input files
 106 until the next -x option.</li>
 107 <li><tt class="docutils literal"><span class="pre">-load</span> <span class="pre">PLUGIN_NAME</span></tt> - Load the specified plugin DLL. Example:
 108 <tt class="docutils literal"><span class="pre">-load</span> <span class="pre">$LLVM_DIR/Release/lib/LLVMCSimple.so</span></tt>.</li>
 109 <li><tt class="docutils literal"><span class="pre">-v</span></tt> - Enable verbose mode, i.e. print out all executed commands.</li>
 110 <li><tt class="docutils literal"><span class="pre">--check-graph</span></tt> - Check the compilation for common errors like mismatched
 111 output/input language names, multiple default edges and cycles. Because of
 112 plugins, these checks can't be performed at compile-time. Exit with code zero if
 113 no errors were found, and return the number of found errors otherwise. Hidden
 114 option, useful for debugging LLVMC plugins.</li>
 115 <li><tt class="docutils literal"><span class="pre">--view-graph</span></tt> - Show a graphical representation of the compilation graph
 116 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
 117 option, useful for debugging LLVMC plugins.</li>
 118 <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
 119 directory with the compilation graph description in Graphviz format (identical
 120 to the file used by the <tt class="docutils literal"><span class="pre">--view-graph</span></tt> option). The <tt class="docutils literal"><span class="pre">-o</span></tt> option can be used
 121 to set the output file name. Hidden option, useful for debugging LLVMC plugins.</li>
 122 <li><tt class="docutils literal"><span class="pre">--save-temps</span></tt> - Write temporary files to the current directory
 123 and do not delete them on exit. Hidden option, useful for debugging.</li>
 124 <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
 125 their standard meaning.</li>
 126 </ul>
 127 </div>
 128 <div class="section">
 129 <h1><a class="toc-backref" href="#id7" id="compiling-llvmc-plugins" name="compiling-llvmc-plugins">Compiling LLVMC plugins</a></h1>
 130 <p>It's easiest to start working on your own LLVMC plugin by copying the
 131 skeleton project which lives under <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins/Simple</span></tt>:</p>
 132 <pre class="literal-block">
 133 $ cd $LLVMC_DIR/plugins
 134 $ cp -r Simple MyPlugin
 135 $ cd MyPlugin
 136 $ ls
 137 Makefile PluginMain.cpp Simple.td
 138 </pre>
 139 <p>As you can see, our basic plugin consists of only two files (not
 140 counting the build script). <tt class="docutils literal"><span class="pre">Simple.td</span></tt> contains TableGen
 141 description of the compilation graph; its format is documented in the
 142 following sections. <tt class="docutils literal"><span class="pre">PluginMain.cpp</span></tt> is just a helper file used to
 143 compile the auto-generated C++ code produced from TableGen source. It
 144 can also contain hook definitions (see <a class="reference" href="#hooks">below</a>).</p>
 145 <p>The first thing that you should do is to change the <tt class="docutils literal"><span class="pre">LLVMC_PLUGIN</span></tt>
 146 variable in the <tt class="docutils literal"><span class="pre">Makefile</span></tt> to avoid conflicts (since this variable
 147 is used to name the resulting library):</p>
 148 <pre class="literal-block">
 149 LLVMC_PLUGIN=MyPlugin
 150 </pre>
 151 <p>It is also a good idea to rename <tt class="docutils literal"><span class="pre">Simple.td</span></tt> to something less
 152 generic:</p>
 153 <pre class="literal-block">
 154 $ mv Simple.td MyPlugin.td
 155 </pre>
 156 <p>Note that the plugin source directory must be placed under
 157 <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins</span></tt> to make use of the existing build
 158 infrastructure. To build a version of the LLVMC executable called
 159 <tt class="docutils literal"><span class="pre">mydriver</span></tt> with your plugin compiled in, use the following command:</p>
 160 <pre class="literal-block">
 161 $ cd $LLVMC_DIR
 162 $ make BUILTIN_PLUGINS=MyPlugin DRIVER_NAME=mydriver
 163 </pre>
 164 <p>To build your plugin as a dynamic library, just <tt class="docutils literal"><span class="pre">cd</span></tt> to its source
 165 directory and run <tt class="docutils literal"><span class="pre">make</span></tt>. The resulting file will be called
 166 <tt class="docutils literal"><span class="pre">LLVMC$(LLVMC_PLUGIN).$(DLL_EXTENSION)</span></tt> (in our case,
 167 <tt class="docutils literal"><span class="pre">LLVMCMyPlugin.so</span></tt>). This library can be then loaded in with the
 168 <tt class="docutils literal"><span class="pre">-load</span></tt> option. Example:</p>
 169 <pre class="literal-block">
 170 $ cd $LLVMC_DIR/plugins/Simple
 171 $ make
 172 $ llvmc -load $LLVM_DIR/Release/lib/LLVMCSimple.so
 173 </pre>
 174 <p>Sometimes, you will want a 'bare-bones' version of LLVMC that has no
 175 built-in plugins. It can be compiled with the following command:</p>
 176 <pre class="literal-block">
 177 $ cd $LLVMC_DIR
 178 $ make BUILTIN_PLUGINS=&quot;&quot;
 179 </pre>
 180 </div>
 181 <div class="section">
 182 <h1><a class="toc-backref" href="#id8" id="customizing-llvmc-the-compilation-graph" name="customizing-llvmc-the-compilation-graph">Customizing LLVMC: the compilation graph</a></h1>
 183 <p>Each TableGen configuration file should include the common
 184 definitions:</p>
 185 <pre class="literal-block">
 186 include &quot;llvm/CompilerDriver/Common.td&quot;
 187 </pre>
 188 <p>Internally, LLVMC stores information about possible source
 189 transformations in form of a graph. Nodes in this graph represent
 190 tools, and edges between two nodes represent a transformation path. A
 191 special &quot;root&quot; node is used to mark entry points for the
 192 transformations. LLVMC also assigns a weight to each edge (more on
 193 this later) to choose between several alternative edges.</p>
 194 <p>The definition of the compilation graph (see file
 195 <tt class="docutils literal"><span class="pre">plugins/Base/Base.td</span></tt> for an example) is just a list of edges:</p>
 196 <pre class="literal-block">
 197 def CompilationGraph : CompilationGraph&lt;[
 198     Edge&lt;&quot;root&quot;, &quot;llvm_gcc_c&quot;&gt;,
 199     Edge&lt;&quot;root&quot;, &quot;llvm_gcc_assembler&quot;&gt;,
 200     ...
 201
 202     Edge&lt;&quot;llvm_gcc_c&quot;, &quot;llc&quot;&gt;,
 203     Edge&lt;&quot;llvm_gcc_cpp&quot;, &quot;llc&quot;&gt;,
 204     ...
 205
 206     OptionalEdge&lt;&quot;llvm_gcc_c&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
 207                                       (inc_weight))&gt;,
 208     OptionalEdge&lt;&quot;llvm_gcc_cpp&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
 209                                               (inc_weight))&gt;,
 210     ...
 211
 212     OptionalEdge&lt;&quot;llvm_gcc_assembler&quot;, &quot;llvm_gcc_cpp_linker&quot;,
 213         (case (input_languages_contain &quot;c++&quot;), (inc_weight),
 214               (or (parameter_equals &quot;linker&quot;, &quot;g++&quot;),
 215                   (parameter_equals &quot;linker&quot;, &quot;c++&quot;)), (inc_weight))&gt;,
 216     ...
 217
 218     ]&gt;;
 219 </pre>
 220 <p>As you can see, the edges can be either default or optional, where
 221 optional edges are differentiated by an additional <tt class="docutils literal"><span class="pre">case</span></tt> expression
 222 used to calculate the weight of this edge. Notice also that we refer
 223 to tools via their names (as strings). This makes it possible to add
 224 edges to an existing compilation graph in plugins without having to
 225 know about all tool definitions used in the graph.</p>
 226 <p>The default edges are assigned a weight of 1, and optional edges get a
 227 weight of 0 + 2*N where N is the number of tests that evaluated to
 228 true in the <tt class="docutils literal"><span class="pre">case</span></tt> expression. It is also possible to provide an
 229 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,
 230 the weight is increased (or decreased) by the provided value instead
 231 of the default 2. It is also possible to change the default weight of
 232 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>
 233 construct.</p>
 234 <p>When passing an input file through the graph, LLVMC picks the edge
 235 with the maximum weight. To avoid ambiguity, there should be only one
 236 default edge between two nodes (with the exception of the root node,
 237 which gets a special treatment - there you are allowed to specify one
 238 default edge <em>per language</em>).</p>
 239 <p>When multiple plugins are loaded, their compilation graphs are merged
 240 together. Since multiple edges that have the same end nodes are not
 241 allowed (i.e. the graph is not a multigraph), an edge defined in
 242 several plugins will be replaced by the definition from the plugin
 243 that was loaded last. Plugin load order can be controlled by using the
 244 plugin priority feature described above.</p>
 245 <p>To get a visual representation of the compilation graph (useful for
 246 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
 247 <tt class="docutils literal"><span class="pre">gsview</span></tt> installed for this to work properly.</p>
 248 </div>
 249 <div class="section">
 250 <h1><a class="toc-backref" href="#id9" id="describing-options" name="describing-options">Describing options</a></h1>
 251 <p>Command-line options that the plugin supports are defined by using an
 252 <tt class="docutils literal"><span class="pre">OptionList</span></tt>:</p>
 253 <pre class="literal-block">
 254 def Options : OptionList&lt;[
 255 (switch_option &quot;E&quot;, (help &quot;Help string&quot;)),
 256 (alias_option &quot;quiet&quot;, &quot;q&quot;)
 257 ...
 258 ]&gt;;
 259 </pre>
 260 <p>As you can see, the option list is just a list of DAGs, where each DAG
 261 is an option description consisting of the option name and some
 262 properties. A plugin can define more than one option list (they are
 263 all merged together in the end), which can be handy if one wants to
 264 separate option groups syntactically.</p>
 265 <ul>
 266 <li><p class="first">Possible option types:</p>
 267 <blockquote>
 268 <ul class="simple">
 269 <li><tt class="docutils literal"><span class="pre">switch_option</span></tt> - a simple boolean switch without arguments, for example
 270 <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>
 271 <li><tt class="docutils literal"><span class="pre">parameter_option</span></tt> - option that takes one argument, for example
 272 <tt class="docutils literal"><span class="pre">-std=c99</span></tt>. It is also allowed to use spaces instead of the equality
 273 sign: <tt class="docutils literal"><span class="pre">-std</span> <span class="pre">c99</span></tt>. At most one occurrence is allowed.</li>
 274 <li><tt class="docutils literal"><span class="pre">parameter_list_option</span></tt> - same as the above, but more than one option
 275 occurence is allowed.</li>
 276 <li><tt class="docutils literal"><span class="pre">prefix_option</span></tt> - same as the parameter_option, but the option name and
 277 argument do not have to be separated. Example: <tt class="docutils literal"><span class="pre">-ofile</span></tt>. This can be also
 278 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
 279 (<tt class="docutils literal"><span class="pre">=file</span></tt> will be interpreted as option value). At most one occurrence is
 280 allowed.</li>
 281 <li><tt class="docutils literal"><span class="pre">prefix_list_option</span></tt> - same as the above, but more than one occurence of
 282 the option is allowed; example: <tt class="docutils literal"><span class="pre">-lm</span> <span class="pre">-lpthread</span></tt>.</li>
 283 <li><tt class="docutils literal"><span class="pre">alias_option</span></tt> - a special option type for creating aliases. Unlike other
 284 option types, aliases are not allowed to have any properties besides the
 285 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>
 286 </ul>
 287 </blockquote>
 288 </li>
 289 <li><p class="first">Possible option properties:</p>
 290 <blockquote>
 291 <ul class="simple">
 292 <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>
 293 output.</li>
 294 <li><tt class="docutils literal"><span class="pre">required</span></tt> - this option must be specified exactly once (or, in case of
 295 the list options without the <tt class="docutils literal"><span class="pre">multi_val</span></tt> property, at least
 296 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>
 297 <li><tt class="docutils literal"><span class="pre">one_or_more</span></tt> - the option must be specified at least one time. Useful
 298 only for list options in conjunction with <tt class="docutils literal"><span class="pre">multi_val</span></tt>; for ordinary lists
 299 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
 300 <tt class="docutils literal"><span class="pre">zero_or_one</span></tt>.</li>
 301 <li><tt class="docutils literal"><span class="pre">zero_or_one</span></tt> - the option can be specified zero or one times. Useful
 302 only for list options in conjunction with <tt class="docutils literal"><span class="pre">multi_val</span></tt>. Incompatible with
 303 <tt class="docutils literal"><span class="pre">required</span></tt> and <tt class="docutils literal"><span class="pre">one_or_more</span></tt>.</li>
 304 <li><tt class="docutils literal"><span class="pre">hidden</span></tt> - the description of this option will not appear in
 305 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>
 306 output).</li>
 307 <li><tt class="docutils literal"><span class="pre">really_hidden</span></tt> - the option will not be mentioned in any help
 308 output.</li>
 309 <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
 310 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>
 311 <span class="pre">3))</span></tt>. Only list options can have this attribute; you can, however, use
 312 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>
 313 <li><tt class="docutils literal"><span class="pre">extern</span></tt> - this option is defined in some other plugin, see below.</li>
 314 </ul>
 315 </blockquote>
 316 </li>
 317 </ul>
 318 <div class="section">
 319 <h2><a class="toc-backref" href="#id10" id="external-options" name="external-options">External options</a></h2>
 320 <p>Sometimes, when linking several plugins together, one plugin needs to
 321 access options defined in some other plugin. Because of the way
 322 options are implemented, such options must be marked as
 323 <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
 324 for. Example:</p>
 325 <pre class="literal-block">
 326 ...
 327 (switch_option &quot;E&quot;, (extern))
 328 ...
 329 </pre>
 330 <p>See also the section on plugin <a class="reference" href="#priorities">priorities</a>.</p>
 331 </div>
 332 </div>
 333 <div class="section">
 334 <h1><a class="toc-backref" href="#id11" id="conditional-evaluation" name="conditional-evaluation"><span id="case"></span>Conditional evaluation</a></h1>
 335 <p>The 'case' construct is the main means by which programmability is
 336 achieved in LLVMC. It can be used to calculate edge weights, program
 337 actions and modify the shell commands to be executed. The 'case'
 338 expression is designed after the similarly-named construct in
 339 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>
 340 <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
 341 are evaluated only if the corresponding tests evaluate to true.</p>
 342 <p>Examples:</p>
 343 <pre class="literal-block">
 344 // Edge weight calculation
 345
 346 // Increases edge weight by 5 if &quot;-A&quot; is provided on the
 347 // command-line, and by 5 more if &quot;-B&quot; is also provided.
 348 (case
 349     (switch_on &quot;A&quot;), (inc_weight 5),
 350     (switch_on &quot;B&quot;), (inc_weight 5))
 351
 352
 353 // Tool command line specification
 354
 355 // Evaluates to &quot;cmdline1&quot; if the option &quot;-A&quot; is provided on the
 356 // command line; to &quot;cmdline2&quot; if &quot;-B&quot; is provided;
 357 // otherwise to &quot;cmdline3&quot;.
 358
 359 (case
 360     (switch_on &quot;A&quot;), &quot;cmdline1&quot;,
 361     (switch_on &quot;B&quot;), &quot;cmdline2&quot;,
 362     (default), &quot;cmdline3&quot;)
 363 </pre>
 364 <p>Note the slight difference in 'case' expression handling in contexts
 365 of edge weights and command line specification - in the second example
 366 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
 367 enabled, and the whole expression always evaluates to <tt class="docutils literal"><span class="pre">&quot;cmdline1&quot;</span></tt> in
 368 that case.</p>
 369 <p>Case expressions can also be nested, i.e. the following is legal:</p>
 370 <pre class="literal-block">
 371 (case (switch_on &quot;E&quot;), (case (switch_on &quot;o&quot;), ..., (default), ...)
 372       (default), ...)
 373 </pre>
 374 <p>You should, however, try to avoid doing that because it hurts
 375 readability. It is usually better to split tool descriptions and/or
 376 use TableGen inheritance instead.</p>
 377 <ul class="simple">
 378 <li>Possible tests are:<ul>
 379 <li><tt class="docutils literal"><span class="pre">switch_on</span></tt> - Returns true if a given command-line switch is
 380 provided by the user. Example: <tt class="docutils literal"><span class="pre">(switch_on</span> <span class="pre">&quot;opt&quot;)</span></tt>.</li>
 381 <li><tt class="docutils literal"><span class="pre">parameter_equals</span></tt> - Returns true if a command-line parameter equals
 382 a given value.
 383 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>
 384 <li><tt class="docutils literal"><span class="pre">element_in_list</span></tt> - Returns true if a command-line parameter
 385 list contains a given value.
 386 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>
 387 <li><tt class="docutils literal"><span class="pre">input_languages_contain</span></tt> - Returns true if a given language
 388 belongs to the current input language set.
 389 Example: <tt class="docutils literal"><span class="pre">(input_languages_contain</span> <span class="pre">&quot;c++&quot;)</span></tt>.</li>
 390 <li><tt class="docutils literal"><span class="pre">in_language</span></tt> - Evaluates to true if the input file language
 391 equals to the argument. At the moment works only with <tt class="docutils literal"><span class="pre">cmd_line</span></tt>
 392 and <tt class="docutils literal"><span class="pre">actions</span></tt> (on non-join nodes).
 393 Example: <tt class="docutils literal"><span class="pre">(in_language</span> <span class="pre">&quot;c++&quot;)</span></tt>.</li>
 394 <li><tt class="docutils literal"><span class="pre">not_empty</span></tt> - Returns true if a given option (which should be
 395 either a parameter or a parameter list) is set by the
 396 user.
 397 Example: <tt class="docutils literal"><span class="pre">(not_empty</span> <span class="pre">&quot;o&quot;)</span></tt>.</li>
 398 <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>
 399 <span class="pre">X))</span></tt>. Provided for convenience.</li>
 400 <li><tt class="docutils literal"><span class="pre">default</span></tt> - Always evaluates to true. Should always be the last
 401 test in the <tt class="docutils literal"><span class="pre">case</span></tt> expression.</li>
 402 <li><tt class="docutils literal"><span class="pre">and</span></tt> - A standard logical combinator that returns true iff all
 403 of its arguments return true. Used like this: <tt class="docutils literal"><span class="pre">(and</span> <span class="pre">(test1),</span>
 404 <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,
 405 but not encouraged.</li>
 406 <li><tt class="docutils literal"><span class="pre">or</span></tt> - Another logical combinator that returns true only if any
 407 one of its arguments returns true. Example: <tt class="docutils literal"><span class="pre">(or</span> <span class="pre">(test1),</span>
 408 <span class="pre">(test2),</span> <span class="pre">...</span> <span class="pre">(testN))</span></tt>.</li>
 409 </ul>
 410 </li>
 411 </ul>
 412 </div>
 413 <div class="section">
 414 <h1><a class="toc-backref" href="#id12" id="writing-a-tool-description" name="writing-a-tool-description">Writing a tool description</a></h1>
 415 <p>As was said earlier, nodes in the compilation graph represent tools,
 416 which are described separately. A tool definition looks like this
 417 (taken from the <tt class="docutils literal"><span class="pre">include/llvm/CompilerDriver/Tools.td</span></tt> file):</p>
 418 <pre class="literal-block">
 419 def llvm_gcc_cpp : Tool&lt;[
 420     (in_language &quot;c++&quot;),
 421     (out_language &quot;llvm-assembler&quot;),
 422     (output_suffix &quot;bc&quot;),
 423     (cmd_line &quot;llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm&quot;),
 424     (sink)
 425     ]&gt;;
 426 </pre>
 427 <p>This defines a new tool called <tt class="docutils literal"><span class="pre">llvm_gcc_cpp</span></tt>, which is an alias for
 428 <tt class="docutils literal"><span class="pre">llvm-g++</span></tt>. As you can see, a tool definition is just a list of
 429 properties; most of them should be self-explanatory. The <tt class="docutils literal"><span class="pre">sink</span></tt>
 430 property means that this tool should be passed all command-line
 431 options that aren't mentioned in the option list.</p>
 432 <p>The complete list of all currently implemented tool properties follows.</p>
 433 <ul class="simple">
 434 <li>Possible tool properties:<ul>
 435 <li><tt class="docutils literal"><span class="pre">in_language</span></tt> - input language name. Can be either a string or a
 436 list, in case the tool supports multiple input languages.</li>
 437 <li><tt class="docutils literal"><span class="pre">out_language</span></tt> - output language name. Tools are not allowed to
 438 have multiple output languages.</li>
 439 <li><tt class="docutils literal"><span class="pre">output_suffix</span></tt> - output file suffix. Can also be changed
 440 dynamically, see documentation on actions.</li>
 441 <li><tt class="docutils literal"><span class="pre">cmd_line</span></tt> - the actual command used to run the tool. You can
 442 use <tt class="docutils literal"><span class="pre">$INFILE</span></tt> and <tt class="docutils literal"><span class="pre">$OUTFILE</span></tt> variables, output redirection
 443 with <tt class="docutils literal"><span class="pre">&gt;</span></tt>, hook invocations (<tt class="docutils literal"><span class="pre">$CALL</span></tt>), environment variables
 444 (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>
 445 <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
 446 list of input files and joins them together. Used for linkers.</li>
 447 <li><tt class="docutils literal"><span class="pre">sink</span></tt> - all command-line options that are not handled by other
 448 tools are passed to this tool.</li>
 449 <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
 450 this tool reacts on command-line options (described in more detail
 451 below).</li>
 452 </ul>
 453 </li>
 454 </ul>
 455 <div class="section">
 456 <h2><a class="toc-backref" href="#id13" id="actions" name="actions">Actions</a></h2>
 457 <p>A tool often needs to react to command-line options, and this is
 458 precisely what the <tt class="docutils literal"><span class="pre">actions</span></tt> property is for. The next example
 459 illustrates this feature:</p>
 460 <pre class="literal-block">
 461 def llvm_gcc_linker : Tool&lt;[
 462     (in_language &quot;object-code&quot;),
 463     (out_language &quot;executable&quot;),
 464     (output_suffix &quot;out&quot;),
 465     (cmd_line &quot;llvm-gcc $INFILE -o $OUTFILE&quot;),
 466     (join),
 467     (actions (case (not_empty &quot;L&quot;), (forward &quot;L&quot;),
 468                    (not_empty &quot;l&quot;), (forward &quot;l&quot;),
 469                    (not_empty &quot;dummy&quot;),
 470                              [(append_cmd &quot;-dummy1&quot;), (append_cmd &quot;-dummy2&quot;)])
 471     ]&gt;;
 472 </pre>
 473 <p>The <tt class="docutils literal"><span class="pre">actions</span></tt> tool property is implemented on top of the omnipresent
 474 <tt class="docutils literal"><span class="pre">case</span></tt> expression. It associates one or more different <em>actions</em>
 475 with given conditions - in the example, the actions are <tt class="docutils literal"><span class="pre">forward</span></tt>,
 476 which forwards a given option unchanged, and <tt class="docutils literal"><span class="pre">append_cmd</span></tt>, which
 477 appends a given string to the tool execution command. Multiple actions
 478 can be associated with a single condition by using a list of actions
 479 (used in the example to append some dummy options). The same <tt class="docutils literal"><span class="pre">case</span></tt>
 480 construct can also be used in the <tt class="docutils literal"><span class="pre">cmd_line</span></tt> property to modify the
 481 tool command line.</p>
 482 <p>The &quot;join&quot; property used in the example means that this tool behaves
 483 like a linker.</p>
 484 <p>The list of all possible actions follows.</p>
 485 <ul>
 486 <li><p class="first">Possible actions:</p>
 487 <blockquote>
 488 <ul class="simple">
 489 <li><tt class="docutils literal"><span class="pre">append_cmd</span></tt> - append a string to the tool invocation
 490 command.
 491 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>
 492 <span class="pre">&quot;-lpthread&quot;))</span></tt></li>
 493 <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>
 494 <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>
 495 <li><tt class="docutils literal"><span class="pre">forward</span></tt> - forward an option unchanged.
 496 Example: <tt class="docutils literal"><span class="pre">(forward</span> <span class="pre">&quot;Wall&quot;)</span></tt>.</li>
 497 <li><tt class="docutils literal"><span class="pre">forward_as</span></tt> - Change the name of an option, but forward the
 498 argument unchanged.
 499 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>
 500 <li><tt class="docutils literal"><span class="pre">output_suffix</span></tt> - modify the output suffix of this
 501 tool.
 502 Example: <tt class="docutils literal"><span class="pre">(output_suffix</span> <span class="pre">&quot;i&quot;)</span></tt>.</li>
 503 <li><tt class="docutils literal"><span class="pre">stop_compilation</span></tt> - stop compilation after this tool processes
 504 its input. Used without arguments.</li>
 505 <li><tt class="docutils literal"><span class="pre">unpack_values</span></tt> - used for for splitting and forwarding
 506 comma-separated lists of options, e.g. <tt class="docutils literal"><span class="pre">-Wa,-foo=bar,-baz</span></tt> is
 507 converted to <tt class="docutils literal"><span class="pre">-foo=bar</span> <span class="pre">-baz</span></tt> and appended to the tool invocation
 508 command.
 509 Example: <tt class="docutils literal"><span class="pre">(unpack_values</span> <span class="pre">&quot;Wa,&quot;)</span></tt>.</li>
 510 </ul>
 511 </blockquote>
 512 </li>
 513 </ul>
 514 </div>
 515 </div>
 516 <div class="section">
 517 <h1><a class="toc-backref" href="#id14" id="language-map" name="language-map">Language map</a></h1>
 518 <p>If you are adding support for a new language to LLVMC, you'll need to
 519 modify the language map, which defines mappings from file extensions
 520 to language names. It is used to choose the proper toolchain(s) for a
 521 given input file set. Language map definition looks like this:</p>
 522 <pre class="literal-block">
 523 def LanguageMap : LanguageMap&lt;
 524     [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;,
 525      LangToSuffixes&lt;&quot;c&quot;, [&quot;c&quot;]&gt;,
 526      ...
 527     ]&gt;;
 528 </pre>
 529 <p>For example, without those definitions the following command wouldn't work:</p>
 530 <pre class="literal-block">
 531 $ llvmc hello.cpp
 532 llvmc: Unknown suffix: cpp
 533 </pre>
 534 <p>The language map entries should be added only for tools that are
 535 linked with the root node. Since tools are not allowed to have
 536 multiple output languages, for nodes &quot;inside&quot; the graph the input and
 537 output languages should match. This is enforced at compile-time.</p>
 538 </div>
 539 <div class="section">
 540 <h1><a class="toc-backref" href="#id15" id="more-advanced-topics" name="more-advanced-topics">More advanced topics</a></h1>
 541 <div class="section">
 542 <h2><a class="toc-backref" href="#id16" id="hooks-and-environment-variables" name="hooks-and-environment-variables"><span id="hooks"></span>Hooks and environment variables</a></h2>
 543 <p>Normally, LLVMC executes programs from the system <tt class="docutils literal"><span class="pre">PATH</span></tt>. Sometimes,
 544 this is not sufficient: for example, we may want to specify tool paths
 545 or names in the configuration file. This can be easily achieved via
 546 the hooks mechanism. To write your own hooks, just add their
 547 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
 548 your plugin directory. Hooks should live in the <tt class="docutils literal"><span class="pre">hooks</span></tt> namespace
 549 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>
 550 <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
 551 <tt class="docutils literal"><span class="pre">cmd_line</span></tt> tool property:</p>
 552 <pre class="literal-block">
 553 (cmd_line &quot;$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)&quot;)
 554 </pre>
 555 <p>To pass arguments to hooks, use the following syntax:</p>
 556 <pre class="literal-block">
 557 (cmd_line &quot;$CALL(MyHook, 'Arg1', 'Arg2', 'Arg # 3')/path/to/file -o1 -o2&quot;)
 558 </pre>
 559 <p>It is also possible to use environment variables in the same manner:</p>
 560 <pre class="literal-block">
 561 (cmd_line &quot;$ENV(VAR1)/path/to/file -o $ENV(VAR2)&quot;)
 562 </pre>
 563 <p>To change the command line string based on user-provided options use
 564 the <tt class="docutils literal"><span class="pre">case</span></tt> expression (documented <a class="reference" href="#case">above</a>):</p>
 565 <pre class="literal-block">
 566 (cmd_line
 567   (case
 568     (switch_on &quot;E&quot;),
 569        &quot;llvm-g++ -E -x c $INFILE -o $OUTFILE&quot;,
 570     (default),
 571        &quot;llvm-g++ -c -x c $INFILE -o $OUTFILE -emit-llvm&quot;))
 572 </pre>
 573 </div>
 574 <div class="section">
 575 <h2><a class="toc-backref" href="#id17" id="how-plugins-are-loaded" name="how-plugins-are-loaded"><span id="priorities"></span>How plugins are loaded</a></h2>
 576 <p>It is possible for LLVMC plugins to depend on each other. For example,
 577 one can create edges between nodes defined in some other plugin. To
 578 make this work, however, that plugin should be loaded first. To
 579 achieve this, the concept of plugin priority was introduced. By
 580 default, every plugin has priority zero; to specify the priority
 581 explicitly, put the following line in your plugin's TableGen file:</p>
 582 <pre class="literal-block">
 583 def Priority : PluginPriority&lt;$PRIORITY_VALUE&gt;;
 584 # Where PRIORITY_VALUE is some integer &gt; 0
 585 </pre>
 586 <p>Plugins are loaded in order of their (increasing) priority, starting
 587 with 0. Therefore, the plugin with the highest priority value will be
 588 loaded last.</p>
 589 </div>
 590 <div class="section">
 591 <h2><a class="toc-backref" href="#id18" id="debugging" name="debugging">Debugging</a></h2>
 592 <p>When writing LLVMC plugins, it can be useful to get a visual view of
 593 the resulting compilation graph. This can be achieved via the command
 594 line option <tt class="docutils literal"><span class="pre">--view-graph</span></tt>. This command assumes that <a class="reference" href="http://www.graphviz.org/">Graphviz</a> and
 595 <a class="reference" 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
 596 creates a Graphviz source file (<tt class="docutils literal"><span class="pre">compilation-graph.dot</span></tt>) in the
 597 current directory.</p>
 598 <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
 599 compilation graph for common errors like mismatched output/input
 600 language names, multiple default edges and cycles. These checks can't
 601 be performed at compile-time because the plugins can load code
 602 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
 603 perform any compilation tasks and returns the number of encountered
 604 errors as its status code.</p>
 605 <hr />
 606 <address>
 607 <a href="http://jigsaw.w3.org/css-validator/check/referer">
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 612    alt="Valid XHTML 1.0 Transitional"/></a>
 613
 614 <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
 615 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
 616
 617 Last modified: $Date: 2008-12-11 11:34:48 -0600 (Thu, 11 Dec 2008) $
 618 </address></div>
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