<p>Because LLVMC employs <aclass="reference"href="http://llvm.cs.uiuc.edu/docs/TableGenFundamentals.html">TableGen</a> as its configuration language, you
<p>One nice feature of LLVMC is that one doesn't have to distinguish
between different compilers for different languages (think <ttclass="docutils literal"><spanclass="pre">g++</span></tt> and
<ttclass="docutils literal"><spanclass="pre">gcc</span></tt>) - the right toolchain is chosen automatically based on input
language names (which are, in turn, determined from file
extensions). If you want to force files ending with ".c" to compile as
C++, use the <ttclass="docutils literal"><spanclass="pre">-x</span></tt> option, just like you would do it with <ttclass="docutils literal"><spanclass="pre">gcc</span></tt>:</p>
graph. Requires that you have <ttclass="docutils literal"><spanclass="pre">dot</span></tt> and <ttclass="docutils literal"><spanclass="pre">gv</span></tt> programs
installed. Hidden option, useful for debugging.</li>
<li><ttclass="docutils literal"><spanclass="pre">--write-graph</span></tt> - Write a <ttclass="docutils literal"><spanclass="pre">compilation-graph.dot</span></tt> file in the
current directory with the compilation graph description in the
Graphviz format. Hidden option, useful for debugging.</li>
<li><ttclass="docutils literal"><spanclass="pre">--save-temps</span></tt> - Write temporary files to the current directory
and do not delete them on exit. Hidden option, useful for debugging.</li>
<li><ttclass="docutils literal"><spanclass="pre">--help</span></tt>, <ttclass="docutils literal"><spanclass="pre">--help-hidden</span></tt>, <ttclass="docutils literal"><spanclass="pre">--version</span></tt> - These options have
<h1><aclass="toc-backref"href="#id8"id="customizing-llvmc-the-compilation-graph"name="customizing-llvmc-the-compilation-graph">Customizing LLVMC: the compilation graph</a></h1>
<p>The default edges are assigned a weight of 1, and optional edges get a
weight of 0 + 2*N where N is the number of tests that evaluated to
true in the <ttclass="docutils literal"><spanclass="pre">case</span></tt> expression. It is also possible to provide an
integer parameter to <ttclass="docutils literal"><spanclass="pre">inc_weight</span></tt> and <ttclass="docutils literal"><spanclass="pre">dec_weight</span></tt> - in this case,
the weight is increased (or decreased) by the provided value instead
of the default 2. It is also possible to change the default weight of
an optional edge by using the <ttclass="docutils literal"><spanclass="pre">default</span></tt> clause of the <ttclass="docutils literal"><spanclass="pre">case</span></tt>
debugging), run <ttclass="docutils literal"><spanclass="pre">llvmc</span><spanclass="pre">--view-graph</span></tt>. You will need <ttclass="docutils literal"><spanclass="pre">dot</span></tt> and
<li><ttclass="docutils literal"><spanclass="pre">switch_option</span></tt> - a simple boolean switch without arguments, for example
<ttclass="docutils literal"><spanclass="pre">-O2</span></tt> or <ttclass="docutils literal"><spanclass="pre">-time</span></tt>. At most one occurrence is allowed.</li>
<li><ttclass="docutils literal"><spanclass="pre">parameter_option</span></tt> - option that takes one argument, for example
<ttclass="docutils literal"><spanclass="pre">-std=c99</span></tt>. It is also allowed to use spaces instead of the equality
sign: <ttclass="docutils literal"><spanclass="pre">-std</span><spanclass="pre">c99</span></tt>. At most one occurrence is allowed.</li>
<li><ttclass="docutils literal"><spanclass="pre">parameter_list_option</span></tt> - same as the above, but more than one option
occurence is allowed.</li>
<li><ttclass="docutils literal"><spanclass="pre">prefix_option</span></tt> - same as the parameter_option, but the option name and
argument do not have to be separated. Example: <ttclass="docutils literal"><spanclass="pre">-ofile</span></tt>. This can be also
specified as <ttclass="docutils literal"><spanclass="pre">-o</span><spanclass="pre">file</span></tt>; however, <ttclass="docutils literal"><spanclass="pre">-o=file</span></tt> will be parsed incorrectly
(<ttclass="docutils literal"><spanclass="pre">=file</span></tt> will be interpreted as option value). At most one occurrence is
allowed.</li>
<li><ttclass="docutils literal"><spanclass="pre">prefix_list_option</span></tt> - same as the above, but more than one occurence of
the option is allowed; example: <ttclass="docutils literal"><spanclass="pre">-lm</span><spanclass="pre">-lpthread</span></tt>.</li>
<li><ttclass="docutils literal"><spanclass="pre">alias_option</span></tt> - a special option type for creating aliases. Unlike other
option types, aliases are not allowed to have any properties besides the
<li><ttclass="docutils literal"><spanclass="pre">help</span></tt> - help string associated with this option. Used for <ttclass="docutils literal"><spanclass="pre">--help</span></tt>
output.</li>
<li><ttclass="docutils literal"><spanclass="pre">required</span></tt> - this option must be specified exactly once (or, in case of
the list options without the <ttclass="docutils literal"><spanclass="pre">multi_val</span></tt> property, at least
once). Incompatible with <ttclass="docutils literal"><spanclass="pre">zero_or_one</span></tt> and <ttclass="docutils literal"><spanclass="pre">one_or_more</span></tt>.</li>
<li><ttclass="docutils literal"><spanclass="pre">one_or_more</span></tt> - the option must be specified at least one time. Useful
only for list options in conjunction with <ttclass="docutils literal"><spanclass="pre">multi_val</span></tt>; for ordinary lists
it is synonymous with <ttclass="docutils literal"><spanclass="pre">required</span></tt>. Incompatible with <ttclass="docutils literal"><spanclass="pre">required</span></tt> and
<li><ttclass="docutils literal"><spanclass="pre">hidden</span></tt> - the description of this option will not appear in
the <ttclass="docutils literal"><spanclass="pre">--help</span></tt> output (but will appear in the <ttclass="docutils literal"><spanclass="pre">--help-hidden</span></tt>
output).</li>
<li><ttclass="docutils literal"><spanclass="pre">really_hidden</span></tt> - the option will not be mentioned in any help
<li><ttclass="docutils literal"><spanclass="pre">multi_val</span><spanclass="pre">n</span></tt> - this option takes <em>n</em> arguments (can be useful in some
special cases). Usage example: <ttclass="docutils literal"><spanclass="pre">(parameter_list_option</span><spanclass="pre">"foo",</span><spanclass="pre">(multi_val</span>
<spanclass="pre">3))</span></tt>. Only list options can have this attribute; you can, however, use
the <ttclass="docutils literal"><spanclass="pre">one_or_more</span></tt> and <ttclass="docutils literal"><spanclass="pre">zero_or_one</span></tt> properties.</li>
<ttclass="docutils literal"><spanclass="pre">extern</span></tt>. This is what the <ttclass="docutils literal"><spanclass="pre">extern</span></tt> option property is
<p>The 'case' construct is the main means by which programmability is
achieved in LLVMC. It can be used to calculate edge weights, program
actions and modify the shell commands to be executed. The 'case'
expression is designed after the similarly-named construct in
functional languages and takes the form <ttclass="docutils literal"><spanclass="pre">(case</span><spanclass="pre">(test_1),</span><spanclass="pre">statement_1,</span>
<spanclass="pre">(test_2),</span><spanclass="pre">statement_2,</span><spanclass="pre">...</span><spanclass="pre">(test_N),</span><spanclass="pre">statement_N)</span></tt>. The statements
are evaluated only if the corresponding tests evaluate to true.</p>
<p>Note the slight difference in 'case' expression handling in contexts
of edge weights and command line specification - in the second example
the value of the <ttclass="docutils literal"><spanclass="pre">"B"</span></tt> switch is never checked when switch <ttclass="docutils literal"><spanclass="pre">"A"</span></tt> is
enabled, and the whole expression always evaluates to <ttclass="docutils literal"><spanclass="pre">"cmdline1"</span></tt> in
that case.</p>
<p>Case expressions can also be nested, i.e. the following is legal:</p>
<li><ttclass="docutils literal"><spanclass="pre">empty</span></tt> - The opposite of <ttclass="docutils literal"><spanclass="pre">not_empty</span></tt>. Equivalent to <ttclass="docutils literal"><spanclass="pre">(not</span><spanclass="pre">(not_empty</span>
<spanclass="pre">X))</span></tt>. Provided for convenience.</li>
<li><ttclass="docutils literal"><spanclass="pre">default</span></tt> - Always evaluates to true. Should always be the last
test in the <ttclass="docutils literal"><spanclass="pre">case</span></tt> expression.</li>
<li><ttclass="docutils literal"><spanclass="pre">and</span></tt> - A standard logical combinator that returns true iff all
of its arguments return true. Used like this: <ttclass="docutils literal"><spanclass="pre">(and</span><spanclass="pre">(test1),</span>
<spanclass="pre">(test2),</span><spanclass="pre">...</span><spanclass="pre">(testN))</span></tt>. Nesting of <ttclass="docutils literal"><spanclass="pre">and</span></tt> and <ttclass="docutils literal"><spanclass="pre">or</span></tt> is allowed,
but not encouraged.</li>
<li><ttclass="docutils literal"><spanclass="pre">or</span></tt> - Another logical combinator that returns true only if any
one of its arguments returns true. Example: <ttclass="docutils literal"><spanclass="pre">(or</span><spanclass="pre">(test1),</span>
<p>This defines a new tool called <ttclass="docutils literal"><spanclass="pre">llvm_gcc_cpp</span></tt>, which is an alias for
<ttclass="docutils literal"><spanclass="pre">llvm-g++</span></tt>. As you can see, a tool definition is just a list of
properties; most of them should be self-explanatory. The <ttclass="docutils literal"><spanclass="pre">sink</span></tt>
property means that this tool should be passed all command-line
options that aren't mentioned in the option list.</p>
<p>The complete list of all currently implemented tool properties follows.</p>
<ulclass="simple">
<li>Possible tool properties:<ul>
<li><ttclass="docutils literal"><spanclass="pre">in_language</span></tt> - input language name. Can be either a string or a
list, in case the tool supports multiple input languages.</li>
<li><ttclass="docutils literal"><spanclass="pre">out_language</span></tt> - output language name. Tools are not allowed to
have multiple output languages.</li>
<li><ttclass="docutils literal"><spanclass="pre">output_suffix</span></tt> - output file suffix. Can also be changed
dynamically, see documentation on actions.</li>
<li><ttclass="docutils literal"><spanclass="pre">cmd_line</span></tt> - the actual command used to run the tool. You can
use <ttclass="docutils literal"><spanclass="pre">$INFILE</span></tt> and <ttclass="docutils literal"><spanclass="pre">$OUTFILE</span></tt> variables, output redirection
with <ttclass="docutils literal"><spanclass="pre">></span></tt>, hook invocations (<ttclass="docutils literal"><spanclass="pre">$CALL</span></tt>), environment variables
(via <ttclass="docutils literal"><spanclass="pre">$ENV</span></tt>) and the <ttclass="docutils literal"><spanclass="pre">case</span></tt> construct.</li>
<li><ttclass="docutils literal"><spanclass="pre">join</span></tt> - this tool is a "join node" in the graph, i.e. it gets a
list of input files and joins them together. Used for linkers.</li>
<li><ttclass="docutils literal"><spanclass="pre">sink</span></tt> - all command-line options that are not handled by other
tools are passed to this tool.</li>
<li><ttclass="docutils literal"><spanclass="pre">actions</span></tt> - A single big <ttclass="docutils literal"><spanclass="pre">case</span></tt> expression that specifies how
this tool reacts on command-line options (described in more detail
<h2><aclass="toc-backref"href="#id16"id="hooks-and-environment-variables"name="hooks-and-environment-variables"><spanid="hooks"></span>Hooks and environment variables</a></h2>
this is not sufficient: for example, we may want to specify tool paths
or names in the configuration file. This can be easily achieved via
the hooks mechanism. To write your own hooks, just add their
definitions to the <ttclass="docutils literal"><spanclass="pre">PluginMain.cpp</span></tt> or drop a <ttclass="docutils literal"><spanclass="pre">.cpp</span></tt> file into the
your plugin directory. Hooks should live in the <ttclass="docutils literal"><spanclass="pre">hooks</span></tt> namespace
and have the signature <ttclass="docutils literal"><spanclass="pre">std::string</span><spanclass="pre">hooks::MyHookName</span><spanclass="pre">([const</span><spanclass="pre">char*</span>
<spanclass="pre">Arg0</span><spanclass="pre">[</span><spanclass="pre">const</span><spanclass="pre">char*</span><spanclass="pre">Arg2</span><spanclass="pre">[,</span><spanclass="pre">...]]])</span></tt>. They can be used from the
<h2><aclass="toc-backref"href="#id17"id="how-plugins-are-loaded"name="how-plugins-are-loaded"><spanid="priorities"></span>How plugins are loaded</a></h2>
line option <ttclass="docutils literal"><spanclass="pre">--view-graph</span></tt>. This command assumes that <aclass="reference"href="http://www.graphviz.org/">Graphviz</a> and
<aclass="reference"href="http://pages.cs.wisc.edu/~ghost/">Ghostview</a> are installed. There is also a <ttclass="docutils literal"><spanclass="pre">--dump-graph</span></tt> option that
creates a Graphviz source file (<ttclass="docutils literal"><spanclass="pre">compilation-graph.dot</span></tt>) in the
<p>Another useful <ttclass="docutils literal"><spanclass="pre">llvmc</span></tt> option is <ttclass="docutils literal"><spanclass="pre">--check-graph</span></tt>. It checks the
compilation graph for common errors like mismatched output/input
language names, multiple default edges and cycles. These checks can't
be performed at compile-time because the plugins can load code
dynamically. When invoked with <ttclass="docutils literal"><spanclass="pre">--check-graph</span></tt>, <ttclass="docutils literal"><spanclass="pre">llvmc</span></tt> doesn't
perform any compilation tasks and returns the number of encountered
