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  11 <div class="document" id="customizing-llvmc-reference-manual">
  12 <h1 class="title">Customizing LLVMC: Reference Manual</h1>
  13
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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="id7">Introduction</a></li>
  21 <li><a class="reference internal" href="#compiling-with-llvmc" id="id8">Compiling with <tt class="docutils literal">llvmc</tt></a></li>
  22 <li><a class="reference internal" href="#predefined-options" id="id9">Predefined options</a></li>
  23 <li><a class="reference internal" href="#compiling-llvmc-based-drivers" id="id10">Compiling LLVMC-based drivers</a></li>
  24 <li><a class="reference internal" href="#customizing-llvmc-the-compilation-graph" id="id11">Customizing LLVMC: the compilation graph</a></li>
  25 <li><a class="reference internal" href="#describing-options" id="id12">Describing options</a></li>
  26 <li><a class="reference internal" href="#conditional-evaluation" id="id13">Conditional evaluation</a></li>
  27 <li><a class="reference internal" href="#writing-a-tool-description" id="id14">Writing a tool description</a><ul>
  28 <li><a class="reference internal" href="#id4" id="id15">Actions</a></li>
  29 </ul>
  30 </li>
  31 <li><a class="reference internal" href="#language-map" id="id16">Language map</a></li>
  32 <li><a class="reference internal" href="#option-preprocessor" id="id17">Option preprocessor</a></li>
  33 <li><a class="reference internal" href="#more-advanced-topics" id="id18">More advanced topics</a><ul>
  34 <li><a class="reference internal" href="#hooks-and-environment-variables" id="id19">Hooks and environment variables</a></li>
  35 <li><a class="reference internal" href="#debugging" id="id20">Debugging</a></li>
  36 <li><a class="reference internal" href="#conditioning-on-the-executable-name" id="id21">Conditioning on the executable name</a></li>
  37 </ul>
  38 </li>
  39 </ul>
  40 </div>
  41 <div class="doc_author">
  42 <p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
  43 </div><div class="section" id="introduction">
  44 <h1><a class="toc-backref" href="#id7">Introduction</a></h1>
  45 <p>LLVMC is a generic compiler driver, designed to be customizable and
  46 extensible. It plays the same role for LLVM as the <tt class="docutils literal">gcc</tt> program does for
  47 GCC - LLVMC's job is essentially to transform a set of input files into a set of
  48 targets depending on configuration rules and user options. What makes LLVMC
  49 different is that these transformation rules are completely customizable - in
  50 fact, LLVMC knows nothing about the specifics of transformation (even the
  51 command-line options are mostly not hard-coded) and regards the transformation
  52 structure as an abstract graph. The structure of this graph is described in
  53 high-level TableGen code, from which an efficient C++ representation is
  54 automatically derived. This makes it possible to adapt LLVMC for other
  55 purposes - for example, as a build tool for game resources.</p>
  56 <p>Because LLVMC employs <a class="reference external" href="http://llvm.org/docs/TableGenFundamentals.html">TableGen</a> as its configuration language, you
  57 need to be familiar with it to customize LLVMC.</p>
  58 </div>
  59 <div class="section" id="compiling-with-llvmc">
  60 <h1><a class="toc-backref" href="#id8">Compiling with <tt class="docutils literal">llvmc</tt></a></h1>
  61 <p>LLVMC tries hard to be as compatible with <tt class="docutils literal">gcc</tt> as possible,
  62 although there are some small differences. Most of the time, however,
  63 you shouldn't be able to notice them:</p>
  64 <pre class="literal-block">
  65 $ # This works as expected:
  66 $ llvmc -O3 -Wall hello.cpp
  67 $ ./a.out
  68 hello
  69 </pre>
  70 <p>One nice feature of LLVMC is that one doesn't have to distinguish between
  71 different compilers for different languages (think <tt class="docutils literal">g++</tt> vs.  <tt class="docutils literal">gcc</tt>) - the
  72 right toolchain is chosen automatically based on input language names (which
  73 are, in turn, determined from file extensions). If you want to force files
  74 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
  75 do it with <tt class="docutils literal">gcc</tt>:</p>
  76 <pre class="literal-block">
  77 $ # hello.c is really a C++ file
  78 $ llvmc -x c++ hello.c
  79 $ ./a.out
  80 hello
  81 </pre>
  82 <p>On the other hand, when using LLVMC as a linker to combine several C++
  83 object files you should provide the <tt class="docutils literal"><span class="pre">--linker</span></tt> option since it's
  84 impossible for LLVMC to choose the right linker in that case:</p>
  85 <pre class="literal-block">
  86 $ llvmc -c hello.cpp
  87 $ llvmc hello.o
  88 [A lot of link-time errors skipped]
  89 $ llvmc --linker=c++ hello.o
  90 $ ./a.out
  91 hello
  92 </pre>
  93 <p>By default, LLVMC uses <tt class="docutils literal"><span class="pre">llvm-gcc</span></tt> to compile the source code. It is also
  94 possible to choose the <tt class="docutils literal">clang</tt> compiler with the <tt class="docutils literal"><span class="pre">-clang</span></tt> option.</p>
  95 </div>
  96 <div class="section" id="predefined-options">
  97 <h1><a class="toc-backref" href="#id9">Predefined options</a></h1>
  98 <p>LLVMC has some built-in options that can't be overridden in the TableGen code:</p>
  99 <ul class="simple">
 100 <li><tt class="docutils literal"><span class="pre">-o</span> FILE</tt> - Output file name.</li>
 101 <li><tt class="docutils literal"><span class="pre">-x</span> LANGUAGE</tt> - Specify the language of the following input files
 102 until the next -x option.</li>
 103 <li><tt class="docutils literal"><span class="pre">-v</span></tt> - Enable verbose mode, i.e. print out all executed commands.</li>
 104 <li><tt class="docutils literal"><span class="pre">--save-temps</span></tt> - Write temporary files to the current directory and do not
 105 delete them on exit. This option can also take an argument: the
 106 <tt class="docutils literal"><span class="pre">--save-temps=obj</span></tt> switch will write files into the directory specified with
 107 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
 108 both synonyms for the default behaviour.</li>
 109 <li><tt class="docutils literal"><span class="pre">--temp-dir</span> DIRECTORY</tt> - Store temporary files in the given directory. This
 110 directory is deleted on exit unless <tt class="docutils literal"><span class="pre">--save-temps</span></tt> is specified. If
 111 <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
 112 precedence.</li>
 113 <li><tt class="docutils literal"><span class="pre">--check-graph</span></tt> - Check the compilation for common errors like mismatched
 114 output/input language names, multiple default edges and cycles. Exit with code
 115 zero if no errors were found, and return the number of found errors
 116 otherwise. Hidden option, useful for debugging.</li>
 117 <li><tt class="docutils literal"><span class="pre">--view-graph</span></tt> - Show a graphical representation of the compilation graph
 118 and exit. Requires that you have <tt class="docutils literal">dot</tt> and <tt class="docutils literal">gv</tt> programs installed. Hidden
 119 option, useful for debugging.</li>
 120 <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
 121 directory with the compilation graph description in Graphviz format (identical
 122 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
 123 used to set the output file name. 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" id="compiling-llvmc-based-drivers">
 129 <h1><a class="toc-backref" href="#id10">Compiling LLVMC-based drivers</a></h1>
 130 <p>It's easiest to start working on your own LLVMC driver by copying the skeleton
 131 project which lives under <tt class="docutils literal">$LLVMC_DIR/examples/Skeleton</tt>:</p>
 132 <pre class="literal-block">
 133 $ cd $LLVMC_DIR/examples
 134 $ cp -r Skeleton MyDriver
 135 $ cd MyDriver
 136 $ ls
 137 AutoGenerated.td  Hooks.cpp  Main.cpp  Makefile
 138 </pre>
 139 <p>As you can see, our basic driver consists of only three files (not counting the
 140 build script). <tt class="docutils literal">AutoGenerated.td</tt> contains TableGen description of the
 141 compilation graph; its format is documented in the following
 142 sections. <tt class="docutils literal">Hooks.cpp</tt> is an empty file that should be used for hook
 143 definitions (see <a class="reference internal" href="#hooks">below</a>). <tt class="docutils literal">Main.cpp</tt> is just a helper used to compile the
 144 auto-generated C++ code produced from TableGen source.</p>
 145 <p>The first thing that you should do is to change the <tt class="docutils literal">LLVMC_BASED_DRIVER</tt>
 146 variable in the <tt class="docutils literal">Makefile</tt>:</p>
 147 <pre class="literal-block">
 148 LLVMC_BASED_DRIVER=MyDriver
 149 </pre>
 150 <p>It can also be a good idea to put your TableGen code into a file with a less
 151 generic name:</p>
 152 <pre class="literal-block">
 153 $ touch MyDriver.td
 154 $ vim AutoGenerated.td
 155 [...]
 156 include &quot;MyDriver.td&quot;
 157 </pre>
 158 <p>If you have more than one TableGen source file, they all should be included from
 159 <tt class="docutils literal">AutoGenerated.td</tt>, since this file is used by the build system to generate
 160 C++ code.</p>
 161 <p>To build your driver, just <tt class="docutils literal">cd</tt> to its source directory and run <tt class="docutils literal">make</tt>. The
 162 resulting executable will be put into <tt class="docutils literal"><span class="pre">$LLVM_OBJ_DIR/$(BuildMode)/bin</span></tt>.</p>
 163 <p>If you're compiling LLVM with different source and object directories, then you
 164 must perform the following additional steps before running <tt class="docutils literal">make</tt>:</p>
 165 <pre class="literal-block">
 166 # LLVMC_SRC_DIR = $LLVM_SRC_DIR/tools/llvmc/
 167 # LLVMC_OBJ_DIR = $LLVM_OBJ_DIR/tools/llvmc/
 168 $ mkdir $LLVMC_OBJ_DIR/examples/MyDriver/
 169 $ cp $LLVMC_SRC_DIR/examples/MyDriver/Makefile \
 170   $LLVMC_OBJ_DIR/examples/MyDriver/
 171 $ cd $LLVMC_OBJ_DIR/examples/MyDriver
 172 $ make
 173 </pre>
 174 </div>
 175 <div class="section" id="customizing-llvmc-the-compilation-graph">
 176 <h1><a class="toc-backref" href="#id11">Customizing LLVMC: the compilation graph</a></h1>
 177 <p>Each TableGen configuration file should include the common definitions:</p>
 178 <pre class="literal-block">
 179 include &quot;llvm/CompilerDriver/Common.td&quot;
 180 </pre>
 181 <p>Internally, LLVMC stores information about possible source transformations in
 182 form of a graph. Nodes in this graph represent tools, and edges between two
 183 nodes represent a transformation path. A special &quot;root&quot; node is used to mark
 184 entry points for the transformations. LLVMC also assigns a weight to each edge
 185 (more on this later) to choose between several alternative edges.</p>
 186 <p>The definition of the compilation graph (see file <tt class="docutils literal">llvmc/src/Base.td</tt> for an
 187 example) is just a list of edges:</p>
 188 <pre class="literal-block">
 189 def CompilationGraph : CompilationGraph&lt;[
 190     Edge&lt;&quot;root&quot;, &quot;llvm_gcc_c&quot;&gt;,
 191     Edge&lt;&quot;root&quot;, &quot;llvm_gcc_assembler&quot;&gt;,
 192     ...
 193
 194     Edge&lt;&quot;llvm_gcc_c&quot;, &quot;llc&quot;&gt;,
 195     Edge&lt;&quot;llvm_gcc_cpp&quot;, &quot;llc&quot;&gt;,
 196     ...
 197
 198     OptionalEdge&lt;&quot;llvm_gcc_c&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
 199                                       (inc_weight))&gt;,
 200     OptionalEdge&lt;&quot;llvm_gcc_cpp&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
 201                                               (inc_weight))&gt;,
 202     ...
 203
 204     OptionalEdge&lt;&quot;llvm_gcc_assembler&quot;, &quot;llvm_gcc_cpp_linker&quot;,
 205         (case (input_languages_contain &quot;c++&quot;), (inc_weight),
 206               (or (parameter_equals &quot;linker&quot;, &quot;g++&quot;),
 207                   (parameter_equals &quot;linker&quot;, &quot;c++&quot;)), (inc_weight))&gt;,
 208     ...
 209
 210     ]&gt;;
 211 </pre>
 212 <p>As you can see, the edges can be either default or optional, where optional
 213 edges are differentiated by an additional <tt class="docutils literal">case</tt> expression used to calculate
 214 the weight of this edge. Notice also that we refer to tools via their names (as
 215 strings). This makes it possible to add edges to an existing compilation graph
 216 without having to know about all tool definitions used in the graph.</p>
 217 <p>The default edges are assigned a weight of 1, and optional edges get a weight of
 218 0 + 2*N where N is the number of tests that evaluated to true in the <tt class="docutils literal">case</tt>
 219 expression. It is also possible to provide an integer parameter to
 220 <tt class="docutils literal">inc_weight</tt> and <tt class="docutils literal">dec_weight</tt> - in this case, the weight is increased (or
 221 decreased) by the provided value instead of the default 2. Default weight of an
 222 optional edge can be changed by using the <tt class="docutils literal">default</tt> clause of the <tt class="docutils literal">case</tt>
 223 construct.</p>
 224 <p>When passing an input file through the graph, LLVMC picks the edge with the
 225 maximum weight. To avoid ambiguity, there should be only one default edge
 226 between two nodes (with the exception of the root node, which gets a special
 227 treatment - there you are allowed to specify one default edge <em>per language</em>).</p>
 228 <p>When multiple compilation graphs are defined, they are merged together. Multiple
 229 edges with the same end nodes are not allowed (i.e. the graph is not a
 230 multigraph), and will lead to a compile-time error.</p>
 231 <p>To get a visual representation of the compilation graph (useful for debugging),
 232 run <tt class="docutils literal">llvmc <span class="pre">--view-graph</span></tt>. You will need <tt class="docutils literal">dot</tt> and <tt class="docutils literal">gsview</tt> installed for
 233 this to work properly.</p>
 234 </div>
 235 <div class="section" id="describing-options">
 236 <h1><a class="toc-backref" href="#id12">Describing options</a></h1>
 237 <p>Command-line options supported by the driver are defined by using an
 238 <tt class="docutils literal">OptionList</tt>:</p>
 239 <pre class="literal-block">
 240 def Options : OptionList&lt;[
 241 (switch_option &quot;E&quot;, (help &quot;Help string&quot;)),
 242 (alias_option &quot;quiet&quot;, &quot;q&quot;)
 243 ...
 244 ]&gt;;
 245 </pre>
 246 <p>As you can see, the option list is just a list of DAGs, where each DAG is an
 247 option description consisting of the option name and some properties. More than
 248 one option list can be defined (they are all merged together in the end), which
 249 can be handy if one wants to separate option groups syntactically.</p>
 250 <ul>
 251 <li><p class="first">Possible option types:</p>
 252 <blockquote>
 253 <ul class="simple">
 254 <li><tt class="docutils literal">switch_option</tt> - a simple boolean switch without arguments, for example
 255 <tt class="docutils literal"><span class="pre">-O2</span></tt> or <tt class="docutils literal"><span class="pre">-time</span></tt>. At most one occurrence is allowed by default.</li>
 256 <li><tt class="docutils literal">parameter_option</tt> - option that takes one argument, for example
 257 <tt class="docutils literal"><span class="pre">-std=c99</span></tt>. It is also allowed to use spaces instead of the equality
 258 sign: <tt class="docutils literal"><span class="pre">-std</span> c99</tt>. At most one occurrence is allowed.</li>
 259 <li><tt class="docutils literal">parameter_list_option</tt> - same as the above, but more than one option
 260 occurrence is allowed.</li>
 261 <li><tt class="docutils literal">prefix_option</tt> - same as the parameter_option, but the option name and
 262 argument do not have to be separated. Example: <tt class="docutils literal"><span class="pre">-ofile</span></tt>. This can be also
 263 specified as <tt class="docutils literal"><span class="pre">-o</span> file</tt>; however, <tt class="docutils literal"><span class="pre">-o=file</span></tt> will be parsed incorrectly
 264 (<tt class="docutils literal">=file</tt> will be interpreted as option value). At most one occurrence is
 265 allowed.</li>
 266 <li><tt class="docutils literal">prefix_list_option</tt> - same as the above, but more than one occurrence of
 267 the option is allowed; example: <tt class="docutils literal"><span class="pre">-lm</span> <span class="pre">-lpthread</span></tt>.</li>
 268 <li><tt class="docutils literal">alias_option</tt> - a special option type for creating aliases. Unlike other
 269 option types, aliases are not allowed to have any properties besides the
 270 aliased option name.
 271 Usage example: <tt class="docutils literal">(alias_option &quot;preprocess&quot;, &quot;E&quot;)</tt></li>
 272 <li><tt class="docutils literal">switch_list_option</tt> - like <tt class="docutils literal">switch_option</tt> with the <tt class="docutils literal">zero_or_more</tt>
 273 property, but remembers how many times the switch was turned on. Useful
 274 mostly for forwarding. Example: when <tt class="docutils literal"><span class="pre">-foo</span></tt> is a switch option (with the
 275 <tt class="docutils literal">zero_or_more</tt> property), the command <tt class="docutils literal">driver <span class="pre">-foo</span> <span class="pre">-foo</span></tt> is forwarded
 276 as <tt class="docutils literal"><span class="pre">some-tool</span> <span class="pre">-foo</span></tt>, but when <tt class="docutils literal"><span class="pre">-foo</span></tt> is a switch list, the same command
 277 is forwarded as <tt class="docutils literal"><span class="pre">some-tool</span> <span class="pre">-foo</span> <span class="pre">-foo</span></tt>.</li>
 278 </ul>
 279 </blockquote>
 280 </li>
 281 <li><p class="first">Possible option properties:</p>
 282 <blockquote>
 283 <ul class="simple">
 284 <li><tt class="docutils literal">help</tt> - help string associated with this option. Used for <tt class="docutils literal"><span class="pre">--help</span></tt>
 285 output.</li>
 286 <li><tt class="docutils literal">required</tt> - this option must be specified exactly once (or, in case of
 287 the list options without the <tt class="docutils literal">multi_val</tt> property, at least
 288 once). Incompatible with <tt class="docutils literal">optional</tt> and <tt class="docutils literal">one_or_more</tt>.</li>
 289 <li><tt class="docutils literal">optional</tt> - the option can be specified either zero times or exactly
 290 once. The default for switch options. Useful only for list options in
 291 conjunction with <tt class="docutils literal">multi_val</tt>. Incompatible with <tt class="docutils literal">required</tt>,
 292 <tt class="docutils literal">zero_or_more</tt> and <tt class="docutils literal">one_or_more</tt>.</li>
 293 <li><tt class="docutils literal">one_or_more</tt> - the option must be specified at least once. Can be useful
 294 to allow switch options be both obligatory and be specified multiple
 295 times. For list options is useful only in conjunction with <tt class="docutils literal">multi_val</tt>;
 296 for ordinary it is synonymous with <tt class="docutils literal">required</tt>. Incompatible with
 297 <tt class="docutils literal">required</tt>, <tt class="docutils literal">optional</tt> and <tt class="docutils literal">zero_or_more</tt>.</li>
 298 <li><tt class="docutils literal">zero_or_more</tt> - the option can be specified zero or more times. Useful
 299 to allow a single switch option to be specified more than
 300 once. Incompatible with <tt class="docutils literal">required</tt>, <tt class="docutils literal">optional</tt> and <tt class="docutils literal">one_or_more</tt>.</li>
 301 <li><tt class="docutils literal">hidden</tt> - the description of this option will not appear in
 302 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>
 303 output).</li>
 304 <li><tt class="docutils literal">really_hidden</tt> - the option will not be mentioned in any help
 305 output.</li>
 306 <li><tt class="docutils literal">comma_separated</tt> - Indicates that any commas specified for an option's
 307 value should be used to split the value up into multiple values for the
 308 option. This property is valid only for list options. In conjunction with
 309 <tt class="docutils literal">forward_value</tt> can be used to implement option forwarding in style of
 310 gcc's <tt class="docutils literal"><span class="pre">-Wa,</span></tt>.</li>
 311 <li><tt class="docutils literal">multi_val n</tt> - this option takes <em>n</em> arguments (can be useful in some
 312 special cases). Usage example: <tt class="docutils literal">(parameter_list_option &quot;foo&quot;, (multi_val
 313 3))</tt>; the command-line syntax is '-foo a b c'. Only list options can have
 314 this attribute; you can, however, use the <tt class="docutils literal">one_or_more</tt>, <tt class="docutils literal">optional</tt>
 315 and <tt class="docutils literal">required</tt> properties.</li>
 316 <li><tt class="docutils literal">init</tt> - this option has a default value, either a string (if it is a
 317 parameter), or a boolean (if it is a switch; as in C++, boolean constants
 318 are called <tt class="docutils literal">true</tt> and <tt class="docutils literal">false</tt>). List options can't have <tt class="docutils literal">init</tt>
 319 attribute.
 320 Usage examples: <tt class="docutils literal">(switch_option &quot;foo&quot;, (init true))</tt>; <tt class="docutils literal">(prefix_option
 321 &quot;bar&quot;, (init <span class="pre">&quot;baz&quot;))</span></tt>.</li>
 322 </ul>
 323 </blockquote>
 324 </li>
 325 </ul>
 326 </div>
 327 <div class="section" id="conditional-evaluation">
 328 <span id="case"></span><h1><a class="toc-backref" href="#id13">Conditional evaluation</a></h1>
 329 <p>The 'case' construct is the main means by which programmability is achieved in
 330 LLVMC. It can be used to calculate edge weights, program actions and modify the
 331 shell commands to be executed. The 'case' expression is designed after the
 332 similarly-named construct in functional languages and takes the form <tt class="docutils literal">(case
 333 (test_1), statement_1, (test_2), statement_2, ... (test_N), statement_N)</tt>. The
 334 statements are evaluated only if the corresponding tests evaluate to true.</p>
 335 <p>Examples:</p>
 336 <pre class="literal-block">
 337 // Edge weight calculation
 338
 339 // Increases edge weight by 5 if &quot;-A&quot; is provided on the
 340 // command-line, and by 5 more if &quot;-B&quot; is also provided.
 341 (case
 342     (switch_on &quot;A&quot;), (inc_weight 5),
 343     (switch_on &quot;B&quot;), (inc_weight 5))
 344
 345
 346 // Tool command line specification
 347
 348 // Evaluates to &quot;cmdline1&quot; if the option &quot;-A&quot; is provided on the
 349 // command line; to &quot;cmdline2&quot; if &quot;-B&quot; is provided;
 350 // otherwise to &quot;cmdline3&quot;.
 351
 352 (case
 353     (switch_on &quot;A&quot;), &quot;cmdline1&quot;,
 354     (switch_on &quot;B&quot;), &quot;cmdline2&quot;,
 355     (default), &quot;cmdline3&quot;)
 356 </pre>
 357 <p>Note the slight difference in 'case' expression handling in contexts of edge
 358 weights and command line specification - in the second example the value of the
 359 <tt class="docutils literal">&quot;B&quot;</tt> switch is never checked when switch <tt class="docutils literal">&quot;A&quot;</tt> is enabled, and the whole
 360 expression always evaluates to <tt class="docutils literal">&quot;cmdline1&quot;</tt> in that case.</p>
 361 <p>Case expressions can also be nested, i.e. the following is legal:</p>
 362 <pre class="literal-block">
 363 (case (switch_on &quot;E&quot;), (case (switch_on &quot;o&quot;), ..., (default), ...)
 364       (default), ...)
 365 </pre>
 366 <p>You should, however, try to avoid doing that because it hurts readability. It is
 367 usually better to split tool descriptions and/or use TableGen inheritance
 368 instead.</p>
 369 <ul class="simple">
 370 <li>Possible tests are:<ul>
 371 <li><tt class="docutils literal">switch_on</tt> - Returns true if a given command-line switch is provided by
 372 the user. Can be given multiple arguments, in that case <tt class="docutils literal">(switch_on &quot;foo&quot;,
 373 &quot;bar&quot;, &quot;baz&quot;)</tt> is equivalent to <tt class="docutils literal">(and (switch_on <span class="pre">&quot;foo&quot;),</span> (switch_on
 374 <span class="pre">&quot;bar&quot;),</span> (switch_on <span class="pre">&quot;baz&quot;))</span></tt>.
 375 Example: <tt class="docutils literal">(switch_on &quot;opt&quot;)</tt>.</li>
 376 <li><tt class="docutils literal">any_switch_on</tt> - Given a number of switch options, returns true if any of
 377 the switches is turned on.
 378 Example: <tt class="docutils literal">(any_switch_on &quot;foo&quot;, &quot;bar&quot;, &quot;baz&quot;)</tt> is equivalent to <tt class="docutils literal">(or
 379 (switch_on <span class="pre">&quot;foo&quot;),</span> (switch_on <span class="pre">&quot;bar&quot;),</span> (switch_on <span class="pre">&quot;baz&quot;))</span></tt>.</li>
 380 <li><tt class="docutils literal">parameter_equals</tt> - Returns true if a command-line parameter (first
 381 argument) equals a given value (second argument).
 382 Example: <tt class="docutils literal">(parameter_equals &quot;W&quot;, &quot;all&quot;)</tt>.</li>
 383 <li><tt class="docutils literal">element_in_list</tt> - Returns true if a command-line parameter list (first
 384 argument) contains a given value (second argument).
 385 Example: <tt class="docutils literal">(element_in_list &quot;l&quot;, &quot;pthread&quot;)</tt>.</li>
 386 <li><tt class="docutils literal">input_languages_contain</tt> - Returns true if a given language
 387 belongs to the current input language set.
 388 Example: <tt class="docutils literal">(input_languages_contain <span class="pre">&quot;c++&quot;)</span></tt>.</li>
 389 <li><tt class="docutils literal">in_language</tt> - Evaluates to true if the input file language is equal to
 390 the argument. At the moment works only with <tt class="docutils literal">command</tt> and <tt class="docutils literal">actions</tt> (on
 391 non-join nodes).
 392 Example: <tt class="docutils literal">(in_language <span class="pre">&quot;c++&quot;)</span></tt>.</li>
 393 <li><tt class="docutils literal">not_empty</tt> - Returns true if a given option (which should be either a
 394 parameter or a parameter list) is set by the user. Like <tt class="docutils literal">switch_on</tt>, can
 395 be also given multiple arguments.
 396 Examples: <tt class="docutils literal">(not_empty &quot;o&quot;)</tt>, <tt class="docutils literal">(not_empty &quot;o&quot;, &quot;l&quot;)</tt>.</li>
 397 <li><tt class="docutils literal">any_not_empty</tt> - Returns true if <tt class="docutils literal">not_empty</tt> returns true for any of
 398 the provided options.
 399 Example: <tt class="docutils literal">(any_not_empty &quot;foo&quot;, &quot;bar&quot;, &quot;baz&quot;)</tt> is equivalent to <tt class="docutils literal">(or
 400 (not_empty <span class="pre">&quot;foo&quot;),</span> (not_empty <span class="pre">&quot;bar&quot;),</span> (not_empty <span class="pre">&quot;baz&quot;))</span></tt>.</li>
 401 <li><tt class="docutils literal">empty</tt> - The opposite of <tt class="docutils literal">not_empty</tt>. Equivalent to <tt class="docutils literal">(not (not_empty
 402 X))</tt>. Can be given multiple arguments.</li>
 403 <li><tt class="docutils literal">any_not_empty</tt> - Returns true if <tt class="docutils literal">not_empty</tt> returns true for any of
 404 the provided options.
 405 Example: <tt class="docutils literal">(any_empty &quot;foo&quot;, &quot;bar&quot;, &quot;baz&quot;)</tt> is equivalent to <tt class="docutils literal">(or
 406 (not_empty <span class="pre">&quot;foo&quot;),</span> (not_empty <span class="pre">&quot;bar&quot;),</span> (not_empty <span class="pre">&quot;baz&quot;))</span></tt>.</li>
 407 <li><tt class="docutils literal">single_input_file</tt> - Returns true if there was only one input file
 408 provided on the command-line. Used without arguments:
 409 <tt class="docutils literal">(single_input_file)</tt>.</li>
 410 <li><tt class="docutils literal">multiple_input_files</tt> - Equivalent to <tt class="docutils literal">(not (single_input_file))</tt> (the
 411 case of zero input files is considered an error).</li>
 412 <li><tt class="docutils literal">default</tt> - Always evaluates to true. Should always be the last
 413 test in the <tt class="docutils literal">case</tt> expression.</li>
 414 <li><tt class="docutils literal">and</tt> - A standard logical combinator that returns true iff all of
 415 its arguments return true. Used like this: <tt class="docutils literal">(and (test1), (test2),
 416 ... (testN))</tt>. Nesting of <tt class="docutils literal">and</tt> and <tt class="docutils literal">or</tt> is allowed, but not
 417 encouraged.</li>
 418 <li><tt class="docutils literal">or</tt> - A logical combinator that returns true iff any of its arguments
 419 return true.
 420 Example: <tt class="docutils literal">(or (test1), (test2), ... (testN))</tt>.</li>
 421 <li><tt class="docutils literal">not</tt> - Standard unary logical combinator that negates its
 422 argument.
 423 Example: <tt class="docutils literal">(not (or (test1), (test2), ... <span class="pre">(testN)))</span></tt>.</li>
 424 </ul>
 425 </li>
 426 </ul>
 427 </div>
 428 <div class="section" id="writing-a-tool-description">
 429 <h1><a class="toc-backref" href="#id14">Writing a tool description</a></h1>
 430 <p>As was said earlier, nodes in the compilation graph represent tools, which are
 431 described separately. A tool definition looks like this (taken from the
 432 <tt class="docutils literal">llvmc/src/Base.td</tt> file):</p>
 433 <pre class="literal-block">
 434 def llvm_gcc_cpp : Tool&lt;[
 435     (in_language &quot;c++&quot;),
 436     (out_language &quot;llvm-assembler&quot;),
 437     (output_suffix &quot;bc&quot;),
 438     (command &quot;llvm-g++ -c -emit-llvm&quot;),
 439     (sink)
 440     ]&gt;;
 441 </pre>
 442 <p>This defines a new tool called <tt class="docutils literal">llvm_gcc_cpp</tt>, which is an alias for
 443 <tt class="docutils literal"><span class="pre">llvm-g++</span></tt>. As you can see, a tool definition is just a list of properties;
 444 most of them should be self-explanatory. The <tt class="docutils literal">sink</tt> property means that this
 445 tool should be passed all command-line options that aren't mentioned in the
 446 option list.</p>
 447 <p>The complete list of all currently implemented tool properties follows.</p>
 448 <ul class="simple">
 449 <li>Possible tool properties:<ul>
 450 <li><tt class="docutils literal">in_language</tt> - input language name. Can be given multiple arguments, in
 451 case the tool supports multiple input languages. Used for typechecking and
 452 mapping file extensions to tools.</li>
 453 <li><tt class="docutils literal">out_language</tt> - output language name. Multiple output languages are
 454 allowed. Used for typechecking the compilation graph.</li>
 455 <li><tt class="docutils literal">output_suffix</tt> - output file suffix. Can also be changed dynamically, see
 456 documentation on <a class="reference internal" href="#actions">actions</a>.</li>
 457 </ul>
 458 </li>
 459 </ul>
 460 <blockquote>
 461 <ul class="simple">
 462 <li><tt class="docutils literal">command</tt> - the actual command used to run the tool. You can use output
 463 redirection with <tt class="docutils literal">&gt;</tt>, hook invocations (<tt class="docutils literal">$CALL</tt>), environment variables
 464 (via <tt class="docutils literal">$ENV</tt>) and the <tt class="docutils literal">case</tt> construct.</li>
 465 <li><tt class="docutils literal">join</tt> - this tool is a &quot;join node&quot; in the graph, i.e. it gets a list of
 466 input files and joins them together. Used for linkers.</li>
 467 <li><tt class="docutils literal">sink</tt> - all command-line options that are not handled by other tools are
 468 passed to this tool.</li>
 469 <li><tt class="docutils literal">actions</tt> - A single big <tt class="docutils literal">case</tt> expression that specifies how this tool
 470 reacts on command-line options (described in more detail <a class="reference internal" href="#actions">below</a>).</li>
 471 </ul>
 472 </blockquote>
 473 <blockquote>
 474 <ul class="simple">
 475 <li><tt class="docutils literal">out_file_option</tt>, <tt class="docutils literal">in_file_option</tt> - Options appended to the
 476 <tt class="docutils literal">command</tt> string to designate output and input files. Default values are
 477 <tt class="docutils literal"><span class="pre">&quot;-o&quot;</span></tt> and <tt class="docutils literal">&quot;&quot;</tt>, respectively.</li>
 478 </ul>
 479 </blockquote>
 480 <div class="section" id="id4">
 481 <span id="actions"></span><h2><a class="toc-backref" href="#id15">Actions</a></h2>
 482 <p>A tool often needs to react to command-line options, and this is precisely what
 483 the <tt class="docutils literal">actions</tt> property is for. The next example illustrates this feature:</p>
 484 <pre class="literal-block">
 485 def llvm_gcc_linker : Tool&lt;[
 486     (in_language &quot;object-code&quot;),
 487     (out_language &quot;executable&quot;),
 488     (output_suffix &quot;out&quot;),
 489     (command &quot;llvm-gcc&quot;),
 490     (join),
 491     (actions (case (not_empty &quot;L&quot;), (forward &quot;L&quot;),
 492                    (not_empty &quot;l&quot;), (forward &quot;l&quot;),
 493                    (not_empty &quot;dummy&quot;),
 494                              [(append_cmd &quot;-dummy1&quot;), (append_cmd &quot;-dummy2&quot;)])
 495     ]&gt;;
 496 </pre>
 497 <p>The <tt class="docutils literal">actions</tt> tool property is implemented on top of the omnipresent <tt class="docutils literal">case</tt>
 498 expression. It associates one or more different <em>actions</em> with given
 499 conditions - in the example, the actions are <tt class="docutils literal">forward</tt>, which forwards a given
 500 option unchanged, and <tt class="docutils literal">append_cmd</tt>, which appends a given string to the tool
 501 execution command. Multiple actions can be associated with a single condition by
 502 using a list of actions (used in the example to append some dummy options). The
 503 same <tt class="docutils literal">case</tt> construct can also be used in the <tt class="docutils literal">cmd_line</tt> property to modify
 504 the tool command line.</p>
 505 <p>The &quot;join&quot; property used in the example means that this tool behaves like a
 506 linker.</p>
 507 <p>The list of all possible actions follows.</p>
 508 <ul>
 509 <li><p class="first">Possible actions:</p>
 510 <blockquote>
 511 <ul class="simple">
 512 <li><tt class="docutils literal">append_cmd</tt> - Append a string to the tool invocation command.
 513 Example: <tt class="docutils literal">(case (switch_on <span class="pre">&quot;pthread&quot;),</span> (append_cmd <span class="pre">&quot;-lpthread&quot;))</span></tt>.</li>
 514 <li><tt class="docutils literal">error</tt> - Exit with error.
 515 Example: <tt class="docutils literal">(error &quot;Mixing <span class="pre">-c</span> and <span class="pre">-S</span> is not <span class="pre">allowed!&quot;)</span></tt>.</li>
 516 <li><tt class="docutils literal">warning</tt> - Print a warning.
 517 Example: <tt class="docutils literal">(warning &quot;Specifying both <span class="pre">-O1</span> and <span class="pre">-O2</span> is <span class="pre">meaningless!&quot;)</span></tt>.</li>
 518 <li><tt class="docutils literal">forward</tt> - Forward the option unchanged.
 519 Example: <tt class="docutils literal">(forward &quot;Wall&quot;)</tt>.</li>
 520 <li><tt class="docutils literal">forward_as</tt> - Change the option's name, but forward the argument
 521 unchanged.
 522 Example: <tt class="docutils literal">(forward_as &quot;O0&quot;, <span class="pre">&quot;--disable-optimization&quot;)</span></tt>.</li>
 523 <li><tt class="docutils literal">forward_value</tt> - Forward only option's value. Cannot be used with switch
 524 options (since they don't have values), but works fine with lists.
 525 Example: <tt class="docutils literal">(forward_value <span class="pre">&quot;Wa,&quot;)</span></tt>.</li>
 526 <li><tt class="docutils literal">forward_transformed_value</tt> - As above, but applies a hook to the
 527 option's value before forwarding (see <a class="reference internal" href="#hooks">below</a>). When
 528 <tt class="docutils literal">forward_transformed_value</tt> is applied to a list
 529 option, the hook must have signature
 530 <tt class="docutils literal"><span class="pre">std::string</span> <span class="pre">hooks::HookName</span> (const <span class="pre">std::vector&lt;std::string&gt;&amp;)</span></tt>.
 531 Example: <tt class="docutils literal">(forward_transformed_value &quot;m&quot;, &quot;ConvertToMAttr&quot;)</tt>.</li>
 532 <li><tt class="docutils literal">output_suffix</tt> - Modify the output suffix of this tool.
 533 Example: <tt class="docutils literal">(output_suffix &quot;i&quot;)</tt>.</li>
 534 <li><tt class="docutils literal">stop_compilation</tt> - Stop compilation after this tool processes its
 535 input. Used without arguments.
 536 Example: <tt class="docutils literal">(stop_compilation)</tt>.</li>
 537 </ul>
 538 </blockquote>
 539 </li>
 540 </ul>
 541 </div>
 542 </div>
 543 <div class="section" id="language-map">
 544 <h1><a class="toc-backref" href="#id16">Language map</a></h1>
 545 <p>If you are adding support for a new language to LLVMC, you'll need to modify the
 546 language map, which defines mappings from file extensions to language names. It
 547 is used to choose the proper toolchain(s) for a given input file set. Language
 548 map definition looks like this:</p>
 549 <pre class="literal-block">
 550 def LanguageMap : LanguageMap&lt;
 551     [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;,
 552      LangToSuffixes&lt;&quot;c&quot;, [&quot;c&quot;]&gt;,
 553      ...
 554     ]&gt;;
 555 </pre>
 556 <p>For example, without those definitions the following command wouldn't work:</p>
 557 <pre class="literal-block">
 558 $ llvmc hello.cpp
 559 llvmc: Unknown suffix: cpp
 560 </pre>
 561 <p>The language map entries are needed only for the tools that are linked from the
 562 root node. A tool can have multiple output languages.</p>
 563 </div>
 564 <div class="section" id="option-preprocessor">
 565 <h1><a class="toc-backref" href="#id17">Option preprocessor</a></h1>
 566 <p>It is sometimes useful to run error-checking code before processing the
 567 compilation graph. For example, if optimization options &quot;-O1&quot; and &quot;-O2&quot; are
 568 implemented as switches, we might want to output a warning if the user invokes
 569 the driver with both of these options enabled.</p>
 570 <p>The <tt class="docutils literal">OptionPreprocessor</tt> feature is reserved specially for these
 571 occasions. Example (adapted from <tt class="docutils literal">llvm/src/Base.td.in</tt>):</p>
 572 <pre class="literal-block">
 573 def Preprocess : OptionPreprocessor&lt;
 574 (case (not (any_switch_on &quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;, &quot;O3&quot;)),
 575            (set_option &quot;O2&quot;),
 576       (and (switch_on &quot;O3&quot;), (any_switch_on &quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;)),
 577            (unset_option &quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;),
 578       (and (switch_on &quot;O2&quot;), (any_switch_on &quot;O0&quot;, &quot;O1&quot;)),
 579            (unset_option &quot;O0&quot;, &quot;O1&quot;),
 580       (and (switch_on &quot;O1&quot;), (switch_on &quot;O0&quot;)),
 581            (unset_option &quot;O0&quot;))
 582 &gt;;
 583 </pre>
 584 <p>Here, <tt class="docutils literal">OptionPreprocessor</tt> is used to unset all spurious <tt class="docutils literal"><span class="pre">-O</span></tt> options so
 585 that they are not forwarded to the compiler. If no optimization options are
 586 specified, <tt class="docutils literal"><span class="pre">-O2</span></tt> is enabled.</p>
 587 <p><tt class="docutils literal">OptionPreprocessor</tt> is basically a single big <tt class="docutils literal">case</tt> expression, which is
 588 evaluated only once right after the driver is started. The only allowed actions
 589 in <tt class="docutils literal">OptionPreprocessor</tt> are <tt class="docutils literal">error</tt>, <tt class="docutils literal">warning</tt>, and two special actions:
 590 <tt class="docutils literal">unset_option</tt> and <tt class="docutils literal">set_option</tt>. As their names suggest, they can be used to
 591 set or unset a given option. To set an option with <tt class="docutils literal">set_option</tt>, use the
 592 two-argument form: <tt class="docutils literal">(set_option &quot;parameter&quot;, VALUE)</tt>. Here, <tt class="docutils literal">VALUE</tt> can be
 593 either a string, a string list, or a boolean constant.</p>
 594 <p>For convenience, <tt class="docutils literal">set_option</tt> and <tt class="docutils literal">unset_option</tt> also work with multiple
 595 arguments. That is, instead of <tt class="docutils literal">[(unset_option <span class="pre">&quot;A&quot;),</span> (unset_option <span class="pre">&quot;B&quot;)]</span></tt> you
 596 can use <tt class="docutils literal">(unset_option &quot;A&quot;, &quot;B&quot;)</tt>. Obviously, <tt class="docutils literal">(set_option &quot;A&quot;, &quot;B&quot;)</tt> is
 597 only valid if both <tt class="docutils literal">A</tt> and <tt class="docutils literal">B</tt> are switches.</p>
 598 </div>
 599 <div class="section" id="more-advanced-topics">
 600 <h1><a class="toc-backref" href="#id18">More advanced topics</a></h1>
 601 <div class="section" id="hooks-and-environment-variables">
 602 <span id="hooks"></span><h2><a class="toc-backref" href="#id19">Hooks and environment variables</a></h2>
 603 <p>Normally, LLVMC searches for programs in the system <tt class="docutils literal">PATH</tt>. Sometimes, this is
 604 not sufficient: for example, we may want to specify tool paths or names in the
 605 configuration file. This can be achieved via the hooks mechanism. To write your
 606 own hooks, add their definitions to the <tt class="docutils literal">Hooks.cpp</tt> or drop a <tt class="docutils literal">.cpp</tt> file
 607 into your driver directory. Hooks should live in the <tt class="docutils literal">hooks</tt> namespace and
 608 have the signature <tt class="docutils literal"><span class="pre">std::string</span> <span class="pre">hooks::MyHookName</span> ([const char* Arg0 [ const
 609 char* Arg2 [, <span class="pre">...]]])</span></tt>. They can be used from the <tt class="docutils literal">command</tt> tool property:</p>
 610 <pre class="literal-block">
 611 (command &quot;$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)&quot;)
 612 </pre>
 613 <p>To pass arguments to hooks, use the following syntax:</p>
 614 <pre class="literal-block">
 615 (command &quot;$CALL(MyHook, 'Arg1', 'Arg2', 'Arg # 3')/path/to/file -o1 -o2&quot;)
 616 </pre>
 617 <p>It is also possible to use environment variables in the same manner:</p>
 618 <pre class="literal-block">
 619 (command &quot;$ENV(VAR1)/path/to/file -o $ENV(VAR2)&quot;)
 620 </pre>
 621 <p>To change the command line string based on user-provided options use
 622 the <tt class="docutils literal">case</tt> expression (documented <a class="reference internal" href="#case">above</a>):</p>
 623 <pre class="literal-block">
 624 (command
 625   (case
 626     (switch_on &quot;E&quot;),
 627        &quot;llvm-g++ -E -x c $INFILE -o $OUTFILE&quot;,
 628     (default),
 629        &quot;llvm-g++ -c -x c $INFILE -o $OUTFILE -emit-llvm&quot;))
 630 </pre>
 631 </div>
 632 <div class="section" id="debugging">
 633 <h2><a class="toc-backref" href="#id20">Debugging</a></h2>
 634 <p>When writing LLVMC-based drivers, it can be useful to get a visual view of the
 635 resulting compilation graph. This can be achieved via the command line option
 636 <tt class="docutils literal"><span class="pre">--view-graph</span></tt> (which assumes that <a class="reference external" href="http://www.graphviz.org/">Graphviz</a> and <a class="reference external" href="http://pages.cs.wisc.edu/~ghost/">Ghostview</a> are
 637 installed). There is also a <tt class="docutils literal"><span class="pre">--write-graph</span></tt> option that creates a Graphviz
 638 source file (<tt class="docutils literal"><span class="pre">compilation-graph.dot</span></tt>) in the current directory.</p>
 639 <p>Another useful <tt class="docutils literal">llvmc</tt> option is <tt class="docutils literal"><span class="pre">--check-graph</span></tt>. It checks the compilation
 640 graph for common errors like mismatched output/input language names, multiple
 641 default edges and cycles. When invoked with <tt class="docutils literal"><span class="pre">--check-graph</span></tt>, <tt class="docutils literal">llvmc</tt> doesn't
 642 perform any compilation tasks and returns the number of encountered errors as
 643 its status code. In the future, these checks will be performed at compile-time
 644 and this option will disappear.</p>
 645 </div>
 646 <div class="section" id="conditioning-on-the-executable-name">
 647 <h2><a class="toc-backref" href="#id21">Conditioning on the executable name</a></h2>
 648 <p>For now, the executable name (the value passed to the driver in <tt class="docutils literal">argv[0]</tt>) is
 649 accessible only in the C++ code (i.e. hooks). Use the following code:</p>
 650 <pre class="literal-block">
 651 namespace llvmc {
 652 extern const char* ProgramName;
 653 }
 654
 655 namespace hooks {
 656
 657 std::string MyHook() {
 658 //...
 659 if (strcmp(ProgramName, &quot;mydriver&quot;) == 0) {
 660    //...
 661
 662 }
 663
 664 } // end namespace hooks
 665 </pre>
 666 <p>In general, you're encouraged not to make the behaviour dependent on the
 667 executable file name, and use command-line switches instead. See for example how
 668 the <tt class="docutils literal">llvmc</tt> program behaves when it needs to choose the correct linker options
 669 (think <tt class="docutils literal">g++</tt> vs. <tt class="docutils literal">gcc</tt>).</p>
 670 <hr />
 671 <address>
 672 <a href="http://jigsaw.w3.org/css-validator/check/referer">
 673 <img src="http://jigsaw.w3.org/css-validator/images/vcss-blue"
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 677    alt="Valid XHTML 1.0 Transitional"/></a>
 678
 679 <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
 680 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
 681
 682 Last modified: $Date: 2008-12-11 11:34:48 -0600 (Thu, 11 Dec 2008) $
 683 </address></div>
 684 </div>
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