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11<div class="document" id="customizing-llvmc-reference-manual">
12<h1 class="title">Customizing LLVMC: Reference Manual</h1>
13
14<!-- This file was automatically generated by rst2html.
15Please do not edit directly!
16The ReST source lives in the directory 'tools/llvmc/doc'. -->
17<div class="contents topic" id="contents">
18<p class="topic-title first">Contents</p>
19<ul class="simple">
20<li><a class="reference internal" href="#introduction" id="id8">Introduction</a></li>
21<li><a class="reference internal" href="#compiling-with-llvmc" id="id9">Compiling with LLVMC</a></li>
22<li><a class="reference internal" href="#predefined-options" id="id10">Predefined options</a></li>
23<li><a class="reference internal" href="#compiling-llvmc-plugins" id="id11">Compiling LLVMC plugins</a></li>
24<li><a class="reference internal" href="#compiling-standalone-llvmc-based-drivers" id="id12">Compiling standalone LLVMC-based drivers</a></li>
25<li><a class="reference internal" href="#customizing-llvmc-the-compilation-graph" id="id13">Customizing LLVMC: the compilation graph</a></li>
26<li><a class="reference internal" href="#describing-options" id="id14">Describing options</a><ul>
27<li><a class="reference internal" href="#external-options" id="id15">External options</a></li>
28</ul>
29</li>
30<li><a class="reference internal" href="#conditional-evaluation" id="id16">Conditional evaluation</a></li>
31<li><a class="reference internal" href="#writing-a-tool-description" id="id17">Writing a tool description</a><ul>
32<li><a class="reference internal" href="#id5" id="id18">Actions</a></li>
33</ul>
34</li>
35<li><a class="reference internal" href="#language-map" id="id19">Language map</a></li>
36<li><a class="reference internal" href="#option-preprocessor" id="id20">Option preprocessor</a></li>
37<li><a class="reference internal" href="#more-advanced-topics" id="id21">More advanced topics</a><ul>
38<li><a class="reference internal" href="#hooks-and-environment-variables" id="id22">Hooks and environment variables</a></li>
39<li><a class="reference internal" href="#how-plugins-are-loaded" id="id23">How plugins are loaded</a></li>
40<li><a class="reference internal" href="#debugging" id="id24">Debugging</a></li>
41<li><a class="reference internal" href="#conditioning-on-the-executable-name" id="id25">Conditioning on the executable name</a></li>
42</ul>
43</li>
44</ul>
45</div>
46<div class="doc_author">
47<p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
48</div><div class="section" id="introduction">
49<h1><a class="toc-backref" href="#id8">Introduction</a></h1>
50<p>LLVMC is a generic compiler driver, designed to be customizable and
51extensible. It plays the same role for LLVM as the <tt class="docutils literal"><span class="pre">gcc</span></tt> program
52does for GCC - LLVMC's job is essentially to transform a set of input
53files into a set of targets depending on configuration rules and user
54options. What makes LLVMC different is that these transformation rules
55are completely customizable - in fact, LLVMC knows nothing about the
56specifics of transformation (even the command-line options are mostly
57not hard-coded) and regards the transformation structure as an
58abstract graph. The structure of this graph is completely determined
59by plugins, which can be either statically or dynamically linked. This
60makes it possible to easily adapt LLVMC for other purposes - for
61example, as a build tool for game resources.</p>
62<p>Because LLVMC employs <a class="reference external" href="http://llvm.org/docs/TableGenFundamentals.html">TableGen</a> as its configuration language, you
63need to be familiar with it to customize LLVMC.</p>
64</div>
65<div class="section" id="compiling-with-llvmc">
66<h1><a class="toc-backref" href="#id9">Compiling with LLVMC</a></h1>
67<p>LLVMC tries hard to be as compatible with <tt class="docutils literal"><span class="pre">gcc</span></tt> as possible,
68although there are some small differences. Most of the time, however,
69you shouldn't be able to notice them:</p>
70<pre class="literal-block">
71$ # This works as expected:
72$ llvmc -O3 -Wall hello.cpp
73$ ./a.out
74hello
75</pre>
76<p>One nice feature of LLVMC is that one doesn't have to distinguish between
77different compilers for different languages (think <tt class="docutils literal"><span class="pre">g++</span></tt> vs. <tt class="docutils literal"><span class="pre">gcc</span></tt>) - the
78right toolchain is chosen automatically based on input language names (which
79are, in turn, determined from file extensions). If you want to force files
80ending 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
81do it with <tt class="docutils literal"><span class="pre">gcc</span></tt>:</p>
82<pre class="literal-block">
83$ # hello.c is really a C++ file
84$ llvmc -x c++ hello.c
85$ ./a.out
86hello
87</pre>
88<p>On the other hand, when using LLVMC as a linker to combine several C++
89object files you should provide the <tt class="docutils literal"><span class="pre">--linker</span></tt> option since it's
90impossible for LLVMC to choose the right linker in that case:</p>
91<pre class="literal-block">
92$ llvmc -c hello.cpp
93$ llvmc hello.o
94[A lot of link-time errors skipped]
95$ llvmc --linker=c++ hello.o
96$ ./a.out
97hello
98</pre>
99<p>By default, LLVMC uses <tt class="docutils literal"><span class="pre">llvm-gcc</span></tt> to compile the source code. It is also
100possible to choose the <tt class="docutils literal"><span class="pre">clang</span></tt> compiler with the <tt class="docutils literal"><span class="pre">-clang</span></tt> option.</p>
101</div>
102<div class="section" id="predefined-options">
103<h1><a class="toc-backref" href="#id10">Predefined options</a></h1>
104<p>LLVMC has some built-in options that can't be overridden in the
105configuration libraries:</p>
106<ul class="simple">
107<li><tt class="docutils literal"><span class="pre">-o</span> <span class="pre">FILE</span></tt> - Output file name.</li>
108<li><tt class="docutils literal"><span class="pre">-x</span> <span class="pre">LANGUAGE</span></tt> - Specify the language of the following input files
109until the next -x option.</li>
110<li><tt class="docutils literal"><span class="pre">-load</span> <span class="pre">PLUGIN_NAME</span></tt> - Load the specified plugin DLL. Example:
111<tt class="docutils literal"><span class="pre">-load</span> <span class="pre">$LLVM_DIR/Release/lib/LLVMCSimple.so</span></tt>.</li>
112<li><tt class="docutils literal"><span class="pre">-v</span></tt> - Enable verbose mode, i.e. print out all executed commands.</li>
113<li><tt class="docutils literal"><span class="pre">--save-temps</span></tt> - Write temporary files to the current directory and do not
114delete them on exit. This option can also take an argument: the
115<tt class="docutils literal"><span class="pre">--save-temps=obj</span></tt> switch will write files into the directory specified with
116the <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
117both synonyms for the default behaviour.</li>
118<li><tt class="docutils literal"><span class="pre">--temp-dir</span> <span class="pre">DIRECTORY</span></tt> - Store temporary files in the given directory. This
119directory is deleted on exit unless <tt class="docutils literal"><span class="pre">--save-temps</span></tt> is specified. If
120<tt class="docutils literal"><span class="pre">--save-temps=obj</span></tt> is also specified, <tt class="docutils literal"><span class="pre">--temp-dir</span></tt> is given the
121precedence.</li>
122<li><tt class="docutils literal"><span class="pre">--check-graph</span></tt> - Check the compilation for common errors like mismatched
123output/input language names, multiple default edges and cycles. Because of
124plugins, these checks can't be performed at compile-time. Exit with code zero
125if no errors were found, and return the number of found errors
126otherwise. Hidden option, useful for debugging LLVMC plugins.</li>
127<li><tt class="docutils literal"><span class="pre">--view-graph</span></tt> - Show a graphical representation of the compilation graph
128and 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
129option, useful for debugging LLVMC plugins.</li>
130<li><tt class="docutils literal"><span class="pre">--write-graph</span></tt> - Write a <tt class="docutils literal"><span class="pre">compilation-graph.dot</span></tt> file in the current
131directory with the compilation graph description in Graphviz format (identical
132to 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
133used to set the output file name. Hidden option, useful for debugging LLVMC
134plugins.</li>
135<li><tt class="docutils literal"><span class="pre">--help</span></tt>, <tt class="docutils literal"><span class="pre">--help-hidden</span></tt>, <tt class="docutils literal"><span class="pre">--version</span></tt> - These options have
136their standard meaning.</li>
137</ul>
138</div>
139<div class="section" id="compiling-llvmc-plugins">
140<h1><a class="toc-backref" href="#id11">Compiling LLVMC plugins</a></h1>
141<p>It's easiest to start working on your own LLVMC plugin by copying the
142skeleton project which lives under <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins/Simple</span></tt>:</p>
143<pre class="literal-block">
144$ cd $LLVMC_DIR/plugins
145$ cp -r Simple MyPlugin
146$ cd MyPlugin
147$ ls
148Makefile PluginMain.cpp Simple.td
149</pre>
150<p>As you can see, our basic plugin consists of only two files (not
151counting the build script). <tt class="docutils literal"><span class="pre">Simple.td</span></tt> contains TableGen
152description of the compilation graph; its format is documented in the
153following sections. <tt class="docutils literal"><span class="pre">PluginMain.cpp</span></tt> is just a helper file used to
154compile the auto-generated C++ code produced from TableGen source. It
155can also contain hook definitions (see <a class="reference internal" href="#hooks">below</a>).</p>
156<p>The first thing that you should do is to change the <tt class="docutils literal"><span class="pre">LLVMC_PLUGIN</span></tt>
157variable in the <tt class="docutils literal"><span class="pre">Makefile</span></tt> to avoid conflicts (since this variable
158is used to name the resulting library):</p>
159<pre class="literal-block">
160LLVMC_PLUGIN=MyPlugin
161</pre>
162<p>It is also a good idea to rename <tt class="docutils literal"><span class="pre">Simple.td</span></tt> to something less
163generic:</p>
164<pre class="literal-block">
165$ mv Simple.td MyPlugin.td
166</pre>
167<p>To build your plugin as a dynamic library, just <tt class="docutils literal"><span class="pre">cd</span></tt> to its source
168directory and run <tt class="docutils literal"><span class="pre">make</span></tt>. The resulting file will be called
169<tt class="docutils literal"><span class="pre">plugin_llvmc_$(LLVMC_PLUGIN).$(DLL_EXTENSION)</span></tt> (in our case,
170<tt class="docutils literal"><span class="pre">plugin_llvmc_MyPlugin.so</span></tt>). This library can be then loaded in with the
171<tt class="docutils literal"><span class="pre">-load</span></tt> option. Example:</p>
172<pre class="literal-block">
173$ cd $LLVMC_DIR/plugins/Simple
174$ make
175$ llvmc -load $LLVM_DIR/Release/lib/plugin_llvmc_Simple.so
176</pre>
177</div>
178<div class="section" id="compiling-standalone-llvmc-based-drivers">
179<h1><a class="toc-backref" href="#id12">Compiling standalone LLVMC-based drivers</a></h1>
180<p>By default, the <tt class="docutils literal"><span class="pre">llvmc</span></tt> executable consists of a driver core plus several
181statically linked plugins (<tt class="docutils literal"><span class="pre">Base</span></tt> and <tt class="docutils literal"><span class="pre">Clang</span></tt> at the moment). You can
182produce a standalone LLVMC-based driver executable by linking the core with your
183own plugins. The recommended way to do this is by starting with the provided
184<tt class="docutils literal"><span class="pre">Skeleton</span></tt> example (<tt class="docutils literal"><span class="pre">$LLVMC_DIR/example/Skeleton</span></tt>):</p>
185<pre class="literal-block">
186$ cd $LLVMC_DIR/example/
187$ cp -r Skeleton mydriver
188$ cd mydriver
189$ vim Makefile
190[...]
191$ make
192</pre>
193<p>If you're compiling LLVM with different source and object directories, then you
194must perform the following additional steps before running <tt class="docutils literal"><span class="pre">make</span></tt>:</p>
195<pre class="literal-block">
196# LLVMC_SRC_DIR = $LLVM_SRC_DIR/tools/llvmc/
197# LLVMC_OBJ_DIR = $LLVM_OBJ_DIR/tools/llvmc/
198$ cp $LLVMC_SRC_DIR/example/mydriver/Makefile \
199 $LLVMC_OBJ_DIR/example/mydriver/
200$ cd $LLVMC_OBJ_DIR/example/mydriver
201$ make
202</pre>
203<p>Another way to do the same thing is by using the following command:</p>
204<pre class="literal-block">
205$ cd $LLVMC_DIR
206$ make LLVMC_BUILTIN_PLUGINS=MyPlugin LLVMC_BASED_DRIVER_NAME=mydriver
207</pre>
208<p>This works with both srcdir == objdir and srcdir != objdir, but assumes that the
209plugin source directory was placed under <tt class="docutils literal"><span class="pre">$LLVMC_DIR/plugins</span></tt>.</p>
210<p>Sometimes, you will want a 'bare-bones' version of LLVMC that has no
211built-in plugins. It can be compiled with the following command:</p>
212<pre class="literal-block">
213$ cd $LLVMC_DIR
214$ make LLVMC_BUILTIN_PLUGINS=&quot;&quot;
215</pre>
216</div>
217<div class="section" id="customizing-llvmc-the-compilation-graph">
218<h1><a class="toc-backref" href="#id13">Customizing LLVMC: the compilation graph</a></h1>
219<p>Each TableGen configuration file should include the common
220definitions:</p>
221<pre class="literal-block">
222include &quot;llvm/CompilerDriver/Common.td&quot;
223</pre>
224<p>Internally, LLVMC stores information about possible source
225transformations in form of a graph. Nodes in this graph represent
226tools, and edges between two nodes represent a transformation path. A
227special &quot;root&quot; node is used to mark entry points for the
228transformations. LLVMC also assigns a weight to each edge (more on
229this later) to choose between several alternative edges.</p>
230<p>The definition of the compilation graph (see file
231<tt class="docutils literal"><span class="pre">plugins/Base/Base.td</span></tt> for an example) is just a list of edges:</p>
232<pre class="literal-block">
233def CompilationGraph : CompilationGraph&lt;[
234 Edge&lt;&quot;root&quot;, &quot;llvm_gcc_c&quot;&gt;,
235 Edge&lt;&quot;root&quot;, &quot;llvm_gcc_assembler&quot;&gt;,
236 ...
237
238 Edge&lt;&quot;llvm_gcc_c&quot;, &quot;llc&quot;&gt;,
239 Edge&lt;&quot;llvm_gcc_cpp&quot;, &quot;llc&quot;&gt;,
240 ...
241
242 OptionalEdge&lt;&quot;llvm_gcc_c&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
243 (inc_weight))&gt;,
244 OptionalEdge&lt;&quot;llvm_gcc_cpp&quot;, &quot;opt&quot;, (case (switch_on &quot;opt&quot;),
245 (inc_weight))&gt;,
246 ...
247
248 OptionalEdge&lt;&quot;llvm_gcc_assembler&quot;, &quot;llvm_gcc_cpp_linker&quot;,
249 (case (input_languages_contain &quot;c++&quot;), (inc_weight),
250 (or (parameter_equals &quot;linker&quot;, &quot;g++&quot;),
251 (parameter_equals &quot;linker&quot;, &quot;c++&quot;)), (inc_weight))&gt;,
252 ...
253
254 ]&gt;;
255</pre>
256<p>As you can see, the edges can be either default or optional, where
257optional edges are differentiated by an additional <tt class="docutils literal"><span class="pre">case</span></tt> expression
258used to calculate the weight of this edge. Notice also that we refer
259to tools via their names (as strings). This makes it possible to add
260edges to an existing compilation graph in plugins without having to
261know about all tool definitions used in the graph.</p>
262<p>The default edges are assigned a weight of 1, and optional edges get a
263weight of 0 + 2*N where N is the number of tests that evaluated to
264true in the <tt class="docutils literal"><span class="pre">case</span></tt> expression. It is also possible to provide an
265integer 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,
266the weight is increased (or decreased) by the provided value instead
267of the default 2. It is also possible to change the default weight of
268an 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>
269construct.</p>
270<p>When passing an input file through the graph, LLVMC picks the edge
271with the maximum weight. To avoid ambiguity, there should be only one
272default edge between two nodes (with the exception of the root node,
273which gets a special treatment - there you are allowed to specify one
274default edge <em>per language</em>).</p>
275<p>When multiple plugins are loaded, their compilation graphs are merged
276together. Since multiple edges that have the same end nodes are not
277allowed (i.e. the graph is not a multigraph), an edge defined in
278several plugins will be replaced by the definition from the plugin
279that was loaded last. Plugin load order can be controlled by using the
280plugin priority feature described above.</p>
281<p>To get a visual representation of the compilation graph (useful for
282debugging), run <tt class="docutils literal"><span class="pre">llvmc</span> <span class="pre">--view-graph</span></tt>. You will need <tt class="docutils literal"><span class="pre">dot</span></tt> and
283<tt class="docutils literal"><span class="pre">gsview</span></tt> installed for this to work properly.</p>
284</div>
285<div class="section" id="describing-options">
286<h1><a class="toc-backref" href="#id14">Describing options</a></h1>
287<p>Command-line options that the plugin supports are defined by using an
288<tt class="docutils literal"><span class="pre">OptionList</span></tt>:</p>
289<pre class="literal-block">
290def Options : OptionList&lt;[
291(switch_option &quot;E&quot;, (help &quot;Help string&quot;)),
292(alias_option &quot;quiet&quot;, &quot;q&quot;)
293...
294]&gt;;
295</pre>
296<p>As you can see, the option list is just a list of DAGs, where each DAG
297is an option description consisting of the option name and some
298properties. A plugin can define more than one option list (they are
299all merged together in the end), which can be handy if one wants to
300separate option groups syntactically.</p>
301<ul>
302<li><p class="first">Possible option types:</p>
303<blockquote>
304<ul class="simple">
305<li><tt class="docutils literal"><span class="pre">switch_option</span></tt> - a simple boolean switch without arguments, for example
306<tt class="docutils literal"><span class="pre">-O2</span></tt> or <tt class="docutils literal"><span class="pre">-time</span></tt>. At most one occurrence is allowed.</li>
307<li><tt class="docutils literal"><span class="pre">parameter_option</span></tt> - option that takes one argument, for example
308<tt class="docutils literal"><span class="pre">-std=c99</span></tt>. It is also allowed to use spaces instead of the equality
309sign: <tt class="docutils literal"><span class="pre">-std</span> <span class="pre">c99</span></tt>. At most one occurrence is allowed.</li>
310<li><tt class="docutils literal"><span class="pre">parameter_list_option</span></tt> - same as the above, but more than one option
311occurence is allowed.</li>
312<li><tt class="docutils literal"><span class="pre">prefix_option</span></tt> - same as the parameter_option, but the option name and
313argument do not have to be separated. Example: <tt class="docutils literal"><span class="pre">-ofile</span></tt>. This can be also
314specified as <tt class="docutils literal"><span class="pre">-o</span> <span class="pre">file</span></tt>; however, <tt class="docutils literal"><span class="pre">-o=file</span></tt> will be parsed incorrectly
315(<tt class="docutils literal"><span class="pre">=file</span></tt> will be interpreted as option value). At most one occurrence is
316allowed.</li>
317<li><tt class="docutils literal"><span class="pre">prefix_list_option</span></tt> - same as the above, but more than one occurence of
318the option is allowed; example: <tt class="docutils literal"><span class="pre">-lm</span> <span class="pre">-lpthread</span></tt>.</li>
319<li><tt class="docutils literal"><span class="pre">alias_option</span></tt> - a special option type for creating aliases. Unlike other
320option types, aliases are not allowed to have any properties besides the
321aliased option name. Usage example: <tt class="docutils literal"><span class="pre">(alias_option</span> <span class="pre">&quot;preprocess&quot;,</span> <span class="pre">&quot;E&quot;)</span></tt></li>
322</ul>
323</blockquote>
324</li>
325<li><p class="first">Possible option properties:</p>
326<blockquote>
327<ul class="simple">
328<li><tt class="docutils literal"><span class="pre">help</span></tt> - help string associated with this option. Used for <tt class="docutils literal"><span class="pre">--help</span></tt>
329output.</li>
330<li><tt class="docutils literal"><span class="pre">required</span></tt> - this option must be specified exactly once (or, in case of
331the list options without the <tt class="docutils literal"><span class="pre">multi_val</span></tt> property, at least
332once). Incompatible with <tt class="docutils literal"><span class="pre">zero_or_one</span></tt> and <tt class="docutils literal"><span class="pre">one_or_more</span></tt>.</li>
333<li><tt class="docutils literal"><span class="pre">one_or_more</span></tt> - the option must be specified at least one time. Useful
334only for list options in conjunction with <tt class="docutils literal"><span class="pre">multi_val</span></tt>; for ordinary lists
335it is synonymous with <tt class="docutils literal"><span class="pre">required</span></tt>. Incompatible with <tt class="docutils literal"><span class="pre">required</span></tt> and
336<tt class="docutils literal"><span class="pre">zero_or_one</span></tt>.</li>
337<li><tt class="docutils literal"><span class="pre">optional</span></tt> - the option can be specified zero or one times. Useful only
338for list options in conjunction with <tt class="docutils literal"><span class="pre">multi_val</span></tt>. Incompatible with
339<tt class="docutils literal"><span class="pre">required</span></tt> and <tt class="docutils literal"><span class="pre">one_or_more</span></tt>.</li>
340<li><tt class="docutils literal"><span class="pre">hidden</span></tt> - the description of this option will not appear in
341the <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>
342output).</li>
343<li><tt class="docutils literal"><span class="pre">really_hidden</span></tt> - the option will not be mentioned in any help
344output.</li>
345<li><tt class="docutils literal"><span class="pre">comma_separated</span></tt> - Indicates that any commas specified for an option's
346value should be used to split the value up into multiple values for the
347option. This property is valid only for list options. In conjunction with
348<tt class="docutils literal"><span class="pre">forward_value</span></tt> can be used to implement option forwarding in style of
349gcc's <tt class="docutils literal"><span class="pre">-Wa,</span></tt>.</li>
350<li><tt class="docutils literal"><span class="pre">multi_val</span> <span class="pre">n</span></tt> - this option takes <em>n</em> arguments (can be useful in some
351special cases). Usage example: <tt class="docutils literal"><span class="pre">(parameter_list_option</span> <span class="pre">&quot;foo&quot;,</span> <span class="pre">(multi_val</span>
352<span class="pre">3))</span></tt>; the command-line syntax is '-foo a b c'. Only list options can have
353this attribute; you can, however, use the <tt class="docutils literal"><span class="pre">one_or_more</span></tt>, <tt class="docutils literal"><span class="pre">optional</span></tt>
354and <tt class="docutils literal"><span class="pre">required</span></tt> properties.</li>
355<li><tt class="docutils literal"><span class="pre">init</span></tt> - this option has a default value, either a string (if it is a
356parameter), or a boolean (if it is a switch; as in C++, boolean constants
357are called <tt class="docutils literal"><span class="pre">true</span></tt> and <tt class="docutils literal"><span class="pre">false</span></tt>). List options can't have <tt class="docutils literal"><span class="pre">init</span></tt>
358attribute.
359Usage examples: <tt class="docutils literal"><span class="pre">(switch_option</span> <span class="pre">&quot;foo&quot;,</span> <span class="pre">(init</span> <span class="pre">true))</span></tt>; <tt class="docutils literal"><span class="pre">(prefix_option</span>
360<span class="pre">&quot;bar&quot;,</span> <span class="pre">(init</span> <span class="pre">&quot;baz&quot;))</span></tt>.</li>
361<li><tt class="docutils literal"><span class="pre">extern</span></tt> - this option is defined in some other plugin, see <a class="reference internal" href="#extern">below</a>.</li>
362</ul>
363</blockquote>
364</li>
365</ul>
366<div class="section" id="external-options">
367<span id="extern"></span><h2><a class="toc-backref" href="#id15">External options</a></h2>
368<p>Sometimes, when linking several plugins together, one plugin needs to
369access options defined in some other plugin. Because of the way
370options are implemented, such options must be marked as
371<tt class="docutils literal"><span class="pre">extern</span></tt>. This is what the <tt class="docutils literal"><span class="pre">extern</span></tt> option property is
372for. Example:</p>
373<pre class="literal-block">
374...
375(switch_option &quot;E&quot;, (extern))
376...
377</pre>
378<p>If an external option has additional attributes besides 'extern', they are
379ignored. See also the section on plugin <a class="reference internal" href="#priorities">priorities</a>.</p>
380</div>
381</div>
382<div class="section" id="conditional-evaluation">
383<span id="case"></span><h1><a class="toc-backref" href="#id16">Conditional evaluation</a></h1>
384<p>The 'case' construct is the main means by which programmability is
385achieved in LLVMC. It can be used to calculate edge weights, program
386actions and modify the shell commands to be executed. The 'case'
387expression is designed after the similarly-named construct in
388functional languages and takes the form <tt class="docutils literal"><span class="pre">(case</span> <span class="pre">(test_1),</span> <span class="pre">statement_1,</span>
389<span class="pre">(test_2),</span> <span class="pre">statement_2,</span> <span class="pre">...</span> <span class="pre">(test_N),</span> <span class="pre">statement_N)</span></tt>. The statements
390are evaluated only if the corresponding tests evaluate to true.</p>
391<p>Examples:</p>
392<pre class="literal-block">
393// Edge weight calculation
394
395// Increases edge weight by 5 if &quot;-A&quot; is provided on the
396// command-line, and by 5 more if &quot;-B&quot; is also provided.
397(case
398 (switch_on &quot;A&quot;), (inc_weight 5),
399 (switch_on &quot;B&quot;), (inc_weight 5))
400
401
402// Tool command line specification
403
404// Evaluates to &quot;cmdline1&quot; if the option &quot;-A&quot; is provided on the
405// command line; to &quot;cmdline2&quot; if &quot;-B&quot; is provided;
406// otherwise to &quot;cmdline3&quot;.
407
408(case
409 (switch_on &quot;A&quot;), &quot;cmdline1&quot;,
410 (switch_on &quot;B&quot;), &quot;cmdline2&quot;,
411 (default), &quot;cmdline3&quot;)
412</pre>
413<p>Note the slight difference in 'case' expression handling in contexts
414of edge weights and command line specification - in the second example
415the 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
416enabled, and the whole expression always evaluates to <tt class="docutils literal"><span class="pre">&quot;cmdline1&quot;</span></tt> in
417that case.</p>
418<p>Case expressions can also be nested, i.e. the following is legal:</p>
419<pre class="literal-block">
420(case (switch_on &quot;E&quot;), (case (switch_on &quot;o&quot;), ..., (default), ...)
421 (default), ...)
422</pre>
423<p>You should, however, try to avoid doing that because it hurts
424readability. It is usually better to split tool descriptions and/or
425use TableGen inheritance instead.</p>
426<ul class="simple">
427<li>Possible tests are:<ul>
428<li><tt class="docutils literal"><span class="pre">switch_on</span></tt> - Returns true if a given command-line switch is provided by
429the user. Can be given a list as argument, in that case <tt class="docutils literal"><span class="pre">(switch_on</span> <span class="pre">[&quot;foo&quot;,</span>
430<span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(and</span> <span class="pre">(switch_on</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(switch_on</span>
431<span class="pre">&quot;bar&quot;),</span> <span class="pre">(switch_on</span> <span class="pre">&quot;baz&quot;))</span></tt>.
432Example: <tt class="docutils literal"><span class="pre">(switch_on</span> <span class="pre">&quot;opt&quot;)</span></tt>.</li>
433<li><tt class="docutils literal"><span class="pre">any_switch_on</span></tt> - Given a list of switch options, returns true if any of
434the switches is turned on.
435Example: <tt class="docutils literal"><span class="pre">(any_switch_on</span> <span class="pre">[&quot;foo&quot;,</span> <span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(or</span>
436<span class="pre">(switch_on</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(switch_on</span> <span class="pre">&quot;bar&quot;),</span> <span class="pre">(switch_on</span> <span class="pre">&quot;baz&quot;))</span></tt>.</li>
437<li><tt class="docutils literal"><span class="pre">parameter_equals</span></tt> - Returns true if a command-line parameter equals
438a given value.
439Example: <tt class="docutils literal"><span class="pre">(parameter_equals</span> <span class="pre">&quot;W&quot;,</span> <span class="pre">&quot;all&quot;)</span></tt>.</li>
440<li><tt class="docutils literal"><span class="pre">element_in_list</span></tt> - Returns true if a command-line parameter
441list contains a given value.
442Example: <tt class="docutils literal"><span class="pre">(element_in_list</span> <span class="pre">&quot;l&quot;,</span> <span class="pre">&quot;pthread&quot;)</span></tt>.</li>
443<li><tt class="docutils literal"><span class="pre">input_languages_contain</span></tt> - Returns true if a given language
444belongs to the current input language set.
445Example: <tt class="docutils literal"><span class="pre">(input_languages_contain</span> <span class="pre">&quot;c++&quot;)</span></tt>.</li>
446<li><tt class="docutils literal"><span class="pre">in_language</span></tt> - Evaluates to true if the input file language is equal to
447the argument. At the moment works only with <tt class="docutils literal"><span class="pre">cmd_line</span></tt> and <tt class="docutils literal"><span class="pre">actions</span></tt> (on
448non-join nodes).
449Example: <tt class="docutils literal"><span class="pre">(in_language</span> <span class="pre">&quot;c++&quot;)</span></tt>.</li>
450<li><tt class="docutils literal"><span class="pre">not_empty</span></tt> - Returns true if a given option (which should be either a
451parameter or a parameter list) is set by the user. Like <tt class="docutils literal"><span class="pre">switch_on</span></tt>, can
452be also given a list as argument.
453Example: <tt class="docutils literal"><span class="pre">(not_empty</span> <span class="pre">&quot;o&quot;)</span></tt>.</li>
454<li><tt class="docutils literal"><span class="pre">any_not_empty</span></tt> - Returns true if <tt class="docutils literal"><span class="pre">not_empty</span></tt> returns true for any of
455the options in the list.
456Example: <tt class="docutils literal"><span class="pre">(any_not_empty</span> <span class="pre">[&quot;foo&quot;,</span> <span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(or</span>
457<span class="pre">(not_empty</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;bar&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;baz&quot;))</span></tt>.</li>
458<li><tt class="docutils literal"><span class="pre">empty</span></tt> - The opposite of <tt class="docutils literal"><span class="pre">not_empty</span></tt>. Equivalent to <tt class="docutils literal"><span class="pre">(not</span> <span class="pre">(not_empty</span>
459<span class="pre">X))</span></tt>. Provided for convenience. Can be given a list as argument.</li>
460<li><tt class="docutils literal"><span class="pre">any_not_empty</span></tt> - Returns true if <tt class="docutils literal"><span class="pre">not_empty</span></tt> returns true for any of
461the options in the list.
462Example: <tt class="docutils literal"><span class="pre">(any_empty</span> <span class="pre">[&quot;foo&quot;,</span> <span class="pre">&quot;bar&quot;,</span> <span class="pre">&quot;baz&quot;])</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(not</span> <span class="pre">(and</span>
463<span class="pre">(not_empty</span> <span class="pre">&quot;foo&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;bar&quot;),</span> <span class="pre">(not_empty</span> <span class="pre">&quot;baz&quot;)))</span></tt>.</li>
464<li><tt class="docutils literal"><span class="pre">single_input_file</span></tt> - Returns true if there was only one input file
465provided on the command-line. Used without arguments:
466<tt class="docutils literal"><span class="pre">(single_input_file)</span></tt>.</li>
467<li><tt class="docutils literal"><span class="pre">multiple_input_files</span></tt> - Equivalent to <tt class="docutils literal"><span class="pre">(not</span> <span class="pre">(single_input_file))</span></tt> (the
468case of zero input files is considered an error).</li>
469<li><tt class="docutils literal"><span class="pre">default</span></tt> - Always evaluates to true. Should always be the last
470test in the <tt class="docutils literal"><span class="pre">case</span></tt> expression.</li>
471<li><tt class="docutils literal"><span class="pre">and</span></tt> - A standard binary logical combinator that returns true iff all of
472its arguments return true. Used like this: <tt class="docutils literal"><span class="pre">(and</span> <span class="pre">(test1),</span> <span class="pre">(test2),</span>
473<span class="pre">...</span> <span class="pre">(testN))</span></tt>. Nesting of <tt class="docutils literal"><span class="pre">and</span></tt> and <tt class="docutils literal"><span class="pre">or</span></tt> is allowed, but not
474encouraged.</li>
475<li><tt class="docutils literal"><span class="pre">or</span></tt> - A binary logical combinator that returns true iff any of its
476arguments returns true. Example: <tt class="docutils literal"><span class="pre">(or</span> <span class="pre">(test1),</span> <span class="pre">(test2),</span> <span class="pre">...</span> <span class="pre">(testN))</span></tt>.</li>
477<li><tt class="docutils literal"><span class="pre">not</span></tt> - Standard unary logical combinator that negates its
478argument. Example: <tt class="docutils literal"><span class="pre">(not</span> <span class="pre">(or</span> <span class="pre">(test1),</span> <span class="pre">(test2),</span> <span class="pre">...</span> <span class="pre">(testN)))</span></tt>.</li>
479</ul>
480</li>
481</ul>
482</div>
483<div class="section" id="writing-a-tool-description">
484<h1><a class="toc-backref" href="#id17">Writing a tool description</a></h1>
485<p>As was said earlier, nodes in the compilation graph represent tools,
486which are described separately. A tool definition looks like this
487(taken from the <tt class="docutils literal"><span class="pre">include/llvm/CompilerDriver/Tools.td</span></tt> file):</p>
488<pre class="literal-block">
489def llvm_gcc_cpp : Tool&lt;[
490 (in_language &quot;c++&quot;),
491 (out_language &quot;llvm-assembler&quot;),
492 (output_suffix &quot;bc&quot;),
493 (cmd_line &quot;llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm&quot;),
494 (sink)
495 ]&gt;;
496</pre>
497<p>This defines a new tool called <tt class="docutils literal"><span class="pre">llvm_gcc_cpp</span></tt>, which is an alias for
498<tt class="docutils literal"><span class="pre">llvm-g++</span></tt>. As you can see, a tool definition is just a list of
499properties; most of them should be self-explanatory. The <tt class="docutils literal"><span class="pre">sink</span></tt>
500property means that this tool should be passed all command-line
501options that aren't mentioned in the option list.</p>
502<p>The complete list of all currently implemented tool properties follows.</p>
503<ul class="simple">
504<li>Possible tool properties:<ul>
505<li><tt class="docutils literal"><span class="pre">in_language</span></tt> - input language name. Can be either a string or a
506list, in case the tool supports multiple input languages.</li>
507<li><tt class="docutils literal"><span class="pre">out_language</span></tt> - output language name. Multiple output languages are not
508allowed.</li>
509<li><tt class="docutils literal"><span class="pre">output_suffix</span></tt> - output file suffix. Can also be changed
510dynamically, see documentation on actions.</li>
511<li><tt class="docutils literal"><span class="pre">cmd_line</span></tt> - the actual command used to run the tool. You can
512use <tt class="docutils literal"><span class="pre">$INFILE</span></tt> and <tt class="docutils literal"><span class="pre">$OUTFILE</span></tt> variables, output redirection
513with <tt class="docutils literal"><span class="pre">&gt;</span></tt>, hook invocations (<tt class="docutils literal"><span class="pre">$CALL</span></tt>), environment variables
514(via <tt class="docutils literal"><span class="pre">$ENV</span></tt>) and the <tt class="docutils literal"><span class="pre">case</span></tt> construct.</li>
515<li><tt class="docutils literal"><span class="pre">join</span></tt> - this tool is a &quot;join node&quot; in the graph, i.e. it gets a
516list of input files and joins them together. Used for linkers.</li>
517<li><tt class="docutils literal"><span class="pre">sink</span></tt> - all command-line options that are not handled by other
518tools are passed to this tool.</li>
519<li><tt class="docutils literal"><span class="pre">actions</span></tt> - A single big <tt class="docutils literal"><span class="pre">case</span></tt> expression that specifies how
520this tool reacts on command-line options (described in more detail
521<a class="reference internal" href="#actions">below</a>).</li>
522</ul>
523</li>
524</ul>
525<div class="section" id="id5">
526<span id="actions"></span><h2><a class="toc-backref" href="#id18">Actions</a></h2>
527<p>A tool often needs to react to command-line options, and this is
528precisely what the <tt class="docutils literal"><span class="pre">actions</span></tt> property is for. The next example
529illustrates this feature:</p>
530<pre class="literal-block">
531def llvm_gcc_linker : Tool&lt;[
532 (in_language &quot;object-code&quot;),
533 (out_language &quot;executable&quot;),
534 (output_suffix &quot;out&quot;),
535 (cmd_line &quot;llvm-gcc $INFILE -o $OUTFILE&quot;),
536 (join),
537 (actions (case (not_empty &quot;L&quot;), (forward &quot;L&quot;),
538 (not_empty &quot;l&quot;), (forward &quot;l&quot;),
539 (not_empty &quot;dummy&quot;),
540 [(append_cmd &quot;-dummy1&quot;), (append_cmd &quot;-dummy2&quot;)])
541 ]&gt;;
542</pre>
543<p>The <tt class="docutils literal"><span class="pre">actions</span></tt> tool property is implemented on top of the omnipresent
544<tt class="docutils literal"><span class="pre">case</span></tt> expression. It associates one or more different <em>actions</em>
545with given conditions - in the example, the actions are <tt class="docutils literal"><span class="pre">forward</span></tt>,
546which forwards a given option unchanged, and <tt class="docutils literal"><span class="pre">append_cmd</span></tt>, which
547appends a given string to the tool execution command. Multiple actions
548can be associated with a single condition by using a list of actions
549(used in the example to append some dummy options). The same <tt class="docutils literal"><span class="pre">case</span></tt>
550construct can also be used in the <tt class="docutils literal"><span class="pre">cmd_line</span></tt> property to modify the
551tool command line.</p>
552<p>The &quot;join&quot; property used in the example means that this tool behaves
553like a linker.</p>
554<p>The list of all possible actions follows.</p>
555<ul>
556<li><p class="first">Possible actions:</p>
557<blockquote>
558<ul class="simple">
559<li><tt class="docutils literal"><span class="pre">append_cmd</span></tt> - Append a string to the tool invocation command.
560Example: <tt class="docutils literal"><span class="pre">(case</span> <span class="pre">(switch_on</span> <span class="pre">&quot;pthread&quot;),</span> <span class="pre">(append_cmd</span> <span class="pre">&quot;-lpthread&quot;))</span></tt>.</li>
561<li><tt class="docutils literal"><span class="pre">error</span></tt> - Exit with error.
562Example: <tt class="docutils literal"><span class="pre">(error</span> <span class="pre">&quot;Mixing</span> <span class="pre">-c</span> <span class="pre">and</span> <span class="pre">-S</span> <span class="pre">is</span> <span class="pre">not</span> <span class="pre">allowed!&quot;)</span></tt>.</li>
563<li><tt class="docutils literal"><span class="pre">warning</span></tt> - Print a warning.
564Example: <tt class="docutils literal"><span class="pre">(warning</span> <span class="pre">&quot;Specifying</span> <span class="pre">both</span> <span class="pre">-O1</span> <span class="pre">and</span> <span class="pre">-O2</span> <span class="pre">is</span> <span class="pre">meaningless!&quot;)</span></tt>.</li>
565<li><tt class="docutils literal"><span class="pre">forward</span></tt> - Forward the option unchanged.
566Example: <tt class="docutils literal"><span class="pre">(forward</span> <span class="pre">&quot;Wall&quot;)</span></tt>.</li>
567<li><tt class="docutils literal"><span class="pre">forward_as</span></tt> - Change the option's name, but forward the argument
568unchanged.
569Example: <tt class="docutils literal"><span class="pre">(forward_as</span> <span class="pre">&quot;O0&quot;,</span> <span class="pre">&quot;--disable-optimization&quot;)</span></tt>.</li>
570<li><tt class="docutils literal"><span class="pre">forward_value</span></tt> - Forward only option's value. Cannot be used with switch
571options (since they don't have values), but works fine with lists.
572Example: <tt class="docutils literal"><span class="pre">(forward_value</span> <span class="pre">&quot;Wa,&quot;)</span></tt>.</li>
573<li><tt class="docutils literal"><span class="pre">forward_transformed_value</span></tt> - As above, but applies a hook to the
574option's value before forwarding (see <a class="reference internal" href="#hooks">below</a>). When
575<tt class="docutils literal"><span class="pre">forward_transformed_value</span></tt> is applied to a list
576option, the hook must have signature
577<tt class="docutils literal"><span class="pre">std::string</span> <span class="pre">hooks::HookName</span> <span class="pre">(const</span> <span class="pre">std::vector&lt;std::string&gt;&amp;)</span></tt>.
578Example: <tt class="docutils literal"><span class="pre">(forward_transformed_value</span> <span class="pre">&quot;m&quot;,</span> <span class="pre">&quot;ConvertToMAttr&quot;)</span></tt>.</li>
579<li><tt class="docutils literal"><span class="pre">output_suffix</span></tt> - Modify the output suffix of this tool.
580Example: <tt class="docutils literal"><span class="pre">(output_suffix</span> <span class="pre">&quot;i&quot;)</span></tt>.</li>
581<li><tt class="docutils literal"><span class="pre">stop_compilation</span></tt> - Stop compilation after this tool processes its
582input. Used without arguments.
583Example: <tt class="docutils literal"><span class="pre">(stop_compilation)</span></tt>.</li>
584</ul>
585</blockquote>
586</li>
587</ul>
588</div>
589</div>
590<div class="section" id="language-map">
591<h1><a class="toc-backref" href="#id19">Language map</a></h1>
592<p>If you are adding support for a new language to LLVMC, you'll need to
593modify the language map, which defines mappings from file extensions
594to language names. It is used to choose the proper toolchain(s) for a
595given input file set. Language map definition looks like this:</p>
596<pre class="literal-block">
597def LanguageMap : LanguageMap&lt;
598 [LangToSuffixes&lt;&quot;c++&quot;, [&quot;cc&quot;, &quot;cp&quot;, &quot;cxx&quot;, &quot;cpp&quot;, &quot;CPP&quot;, &quot;c++&quot;, &quot;C&quot;]&gt;,
599 LangToSuffixes&lt;&quot;c&quot;, [&quot;c&quot;]&gt;,
600 ...
601 ]&gt;;
602</pre>
603<p>For example, without those definitions the following command wouldn't work:</p>
604<pre class="literal-block">
605$ llvmc hello.cpp
606llvmc: Unknown suffix: cpp
607</pre>
608<p>The language map entries are needed only for the tools that are linked from the
609root node. Since a tool can't have multiple output languages, for inner nodes of
610the graph the input and output languages should match. This is enforced at
611compile-time.</p>
612</div>
613<div class="section" id="option-preprocessor">
614<h1><a class="toc-backref" href="#id20">Option preprocessor</a></h1>
615<p>It is sometimes useful to run error-checking code before processing the
616compilation graph. For example, if optimization options &quot;-O1&quot; and &quot;-O2&quot; are
617implemented as switches, we might want to output a warning if the user invokes
618the driver with both of these options enabled.</p>
619<p>The <tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> feature is reserved specially for these
620occasions. Example (adapted from the built-in Base plugin):</p>
621<pre class="literal-block">
622def Preprocess : OptionPreprocessor&lt;
623(case (not (any_switch_on [&quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;, &quot;O3&quot;])),
624 (set_option &quot;O2&quot;),
625 (and (switch_on &quot;O3&quot;), (any_switch_on [&quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;])),
626 (unset_option [&quot;O0&quot;, &quot;O1&quot;, &quot;O2&quot;]),
627 (and (switch_on &quot;O2&quot;), (any_switch_on [&quot;O0&quot;, &quot;O1&quot;])),
628 (unset_option [&quot;O0&quot;, &quot;O1&quot;]),
629 (and (switch_on &quot;O1&quot;), (switch_on &quot;O0&quot;)),
630 (unset_option &quot;O0&quot;))
631&gt;;
632</pre>
633<p>Here, <tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> is used to unset all spurious <tt class="docutils literal"><span class="pre">-O</span></tt> options so
634that they are not forwarded to the compiler. If no optimization options are
635specified, <tt class="docutils literal"><span class="pre">-O2</span></tt> is enabled.</p>
636<p><tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> is basically a single big <tt class="docutils literal"><span class="pre">case</span></tt> expression, which is
637evaluated only once right after the plugin is loaded. The only allowed actions
638in <tt class="docutils literal"><span class="pre">OptionPreprocessor</span></tt> are <tt class="docutils literal"><span class="pre">error</span></tt>, <tt class="docutils literal"><span class="pre">warning</span></tt>, and two special actions:
639<tt class="docutils literal"><span class="pre">unset_option</span></tt> and <tt class="docutils literal"><span class="pre">set_option</span></tt>. As their names suggest, they can be used to
640set or unset a given option. To set an option with <tt class="docutils literal"><span class="pre">set_option</span></tt>, use the
641two-argument form: <tt class="docutils literal"><span class="pre">(set_option</span> <span class="pre">&quot;parameter&quot;,</span> <span class="pre">VALUE)</span></tt>. Here, <tt class="docutils literal"><span class="pre">VALUE</span></tt> can be
642either a string, a string list, or a boolean constant.</p>
643<p>For convenience, <tt class="docutils literal"><span class="pre">set_option</span></tt> and <tt class="docutils literal"><span class="pre">unset_option</span></tt> also work on lists. That
644is, instead of <tt class="docutils literal"><span class="pre">[(unset_option</span> <span class="pre">&quot;A&quot;),</span> <span class="pre">(unset_option</span> <span class="pre">&quot;B&quot;)]</span></tt> you can use
645<tt class="docutils literal"><span class="pre">(unset_option</span> <span class="pre">[&quot;A&quot;,</span> <span class="pre">&quot;B&quot;])</span></tt>. Obviously, <tt class="docutils literal"><span class="pre">(set_option</span> <span class="pre">[&quot;A&quot;,</span> <span class="pre">&quot;B&quot;])</span></tt> is valid
646only if both <tt class="docutils literal"><span class="pre">A</span></tt> and <tt class="docutils literal"><span class="pre">B</span></tt> are switches.</p>
647</div>
648<div class="section" id="more-advanced-topics">
649<h1><a class="toc-backref" href="#id21">More advanced topics</a></h1>
650<div class="section" id="hooks-and-environment-variables">
651<span id="hooks"></span><h2><a class="toc-backref" href="#id22">Hooks and environment variables</a></h2>
652<p>Normally, LLVMC executes programs from the system <tt class="docutils literal"><span class="pre">PATH</span></tt>. Sometimes,
653this is not sufficient: for example, we may want to specify tool paths
654or names in the configuration file. This can be easily achieved via
655the hooks mechanism. To write your own hooks, just add their
656definitions 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
657your plugin directory. Hooks should live in the <tt class="docutils literal"><span class="pre">hooks</span></tt> namespace
658and have the signature <tt class="docutils literal"><span class="pre">std::string</span> <span class="pre">hooks::MyHookName</span> <span class="pre">([const</span> <span class="pre">char*</span>
659<span class="pre">Arg0</span> <span class="pre">[</span> <span class="pre">const</span> <span class="pre">char*</span> <span class="pre">Arg2</span> <span class="pre">[,</span> <span class="pre">...]]])</span></tt>. They can be used from the
660<tt class="docutils literal"><span class="pre">cmd_line</span></tt> tool property:</p>
661<pre class="literal-block">
662(cmd_line &quot;$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)&quot;)
663</pre>
664<p>To pass arguments to hooks, use the following syntax:</p>
665<pre class="literal-block">
666(cmd_line &quot;$CALL(MyHook, 'Arg1', 'Arg2', 'Arg # 3')/path/to/file -o1 -o2&quot;)
667</pre>
668<p>It is also possible to use environment variables in the same manner:</p>
669<pre class="literal-block">
670(cmd_line &quot;$ENV(VAR1)/path/to/file -o $ENV(VAR2)&quot;)
671</pre>
672<p>To change the command line string based on user-provided options use
673the <tt class="docutils literal"><span class="pre">case</span></tt> expression (documented <a class="reference internal" href="#case">above</a>):</p>
674<pre class="literal-block">
675(cmd_line
676 (case
677 (switch_on &quot;E&quot;),
678 &quot;llvm-g++ -E -x c $INFILE -o $OUTFILE&quot;,
679 (default),
680 &quot;llvm-g++ -c -x c $INFILE -o $OUTFILE -emit-llvm&quot;))
681</pre>
682</div>
683<div class="section" id="how-plugins-are-loaded">
684<span id="priorities"></span><h2><a class="toc-backref" href="#id23">How plugins are loaded</a></h2>
685<p>It is possible for LLVMC plugins to depend on each other. For example,
686one can create edges between nodes defined in some other plugin. To
687make this work, however, that plugin should be loaded first. To
688achieve this, the concept of plugin priority was introduced. By
689default, every plugin has priority zero; to specify the priority
690explicitly, put the following line in your plugin's TableGen file:</p>
691<pre class="literal-block">
692def Priority : PluginPriority&lt;$PRIORITY_VALUE&gt;;
693# Where PRIORITY_VALUE is some integer &gt; 0
694</pre>
695<p>Plugins are loaded in order of their (increasing) priority, starting
696with 0. Therefore, the plugin with the highest priority value will be
697loaded last.</p>
698</div>
699<div class="section" id="debugging">
700<h2><a class="toc-backref" href="#id24">Debugging</a></h2>
701<p>When writing LLVMC plugins, it can be useful to get a visual view of
702the resulting compilation graph. This can be achieved via the command
703line option <tt class="docutils literal"><span class="pre">--view-graph</span></tt>. This command assumes that <a class="reference external" href="http://www.graphviz.org/">Graphviz</a> and
704<a class="reference external" href="http://pages.cs.wisc.edu/~ghost/">Ghostview</a> are installed. There is also a <tt class="docutils literal"><span class="pre">--write-graph</span></tt> option that
705creates a Graphviz source file (<tt class="docutils literal"><span class="pre">compilation-graph.dot</span></tt>) in the
706current directory.</p>
707<p>Another useful <tt class="docutils literal"><span class="pre">llvmc</span></tt> option is <tt class="docutils literal"><span class="pre">--check-graph</span></tt>. It checks the
708compilation graph for common errors like mismatched output/input
709language names, multiple default edges and cycles. These checks can't
710be performed at compile-time because the plugins can load code
711dynamically. 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
712perform any compilation tasks and returns the number of encountered
713errors as its status code.</p>
714</div>
715<div class="section" id="conditioning-on-the-executable-name">
716<h2><a class="toc-backref" href="#id25">Conditioning on the executable name</a></h2>
717<p>For now, the executable name (the value passed to the driver in <tt class="docutils literal"><span class="pre">argv[0]</span></tt>) is
718accessible only in the C++ code (i.e. hooks). Use the following code:</p>
719<pre class="literal-block">
720namespace llvmc {
721extern const char* ProgramName;
722}
723
724namespace hooks {
725
726std::string MyHook() {
727//...
728if (strcmp(ProgramName, &quot;mydriver&quot;) == 0) {
729 //...
730
731}
732
733} // end namespace hooks
734</pre>
735<p>In general, you're encouraged not to make the behaviour dependent on the
736executable file name, and use command-line switches instead. See for example how
737the <tt class="docutils literal"><span class="pre">Base</span></tt> plugin behaves when it needs to choose the correct linker options
738(think <tt class="docutils literal"><span class="pre">g++</span></tt> vs. <tt class="docutils literal"><span class="pre">gcc</span></tt>).</p>
739<hr />
740<address>
741<a href="http://jigsaw.w3.org/css-validator/check/referer">
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746 alt="Valid XHTML 1.0 Transitional"/></a>
747
748<a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
749<a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
750
751Last modified: $Date: 2009-12-23 04:49:51 -0800 (Wed, 23 Dec 2009) $
752</address></div>
753</div>
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