1 ===================================
2 Customizing LLVMC: Reference Manual
3 ===================================
5 This file was automatically generated by rst2html.
6 Please do not edit directly!
7 The ReST source lives in the directory 'tools/llvmc/doc'.
13 <div class="doc_author">
14 <p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
20 LLVMC is a generic compiler driver, designed to be customizable and
21 extensible. It plays the same role for LLVM as the ``gcc`` program
22 does for GCC - LLVMC's job is essentially to transform a set of input
23 files into a set of targets depending on configuration rules and user
24 options. What makes LLVMC different is that these transformation rules
25 are completely customizable - in fact, LLVMC knows nothing about the
26 specifics of transformation (even the command-line options are mostly
27 not hard-coded) and regards the transformation structure as an
28 abstract graph. The structure of this graph is completely determined
29 by plugins, which can be either statically or dynamically linked. This
30 makes it possible to easily adapt LLVMC for other purposes - for
31 example, as a build tool for game resources.
33 Because LLVMC employs TableGen_ as its configuration language, you
34 need to be familiar with it to customize LLVMC.
36 .. _TableGen: http://llvm.org/docs/TableGenFundamentals.html
42 LLVMC tries hard to be as compatible with ``gcc`` as possible,
43 although there are some small differences. Most of the time, however,
44 you shouldn't be able to notice them::
46 $ # This works as expected:
47 $ llvmc -O3 -Wall hello.cpp
51 One nice feature of LLVMC is that one doesn't have to distinguish between
52 different compilers for different languages (think ``g++`` vs. ``gcc``) - the
53 right toolchain is chosen automatically based on input language names (which
54 are, in turn, determined from file extensions). If you want to force files
55 ending with ".c" to compile as C++, use the ``-x`` option, just like you would
58 $ # hello.c is really a C++ file
59 $ llvmc -x c++ hello.c
63 On the other hand, when using LLVMC as a linker to combine several C++
64 object files you should provide the ``--linker`` option since it's
65 impossible for LLVMC to choose the right linker in that case::
69 [A lot of link-time errors skipped]
70 $ llvmc --linker=c++ hello.o
74 By default, LLVMC uses ``llvm-gcc`` to compile the source code. It is also
75 possible to choose the ``clang`` compiler with the ``-clang`` option.
81 LLVMC has some built-in options that can't be overridden in the
82 configuration libraries:
84 * ``-o FILE`` - Output file name.
86 * ``-x LANGUAGE`` - Specify the language of the following input files
87 until the next -x option.
89 * ``-load PLUGIN_NAME`` - Load the specified plugin DLL. Example:
90 ``-load $LLVM_DIR/Release/lib/LLVMCSimple.so``.
92 * ``-v`` - Enable verbose mode, i.e. print out all executed commands.
94 * ``--save-temps`` - Write temporary files to the current directory and do not
95 delete them on exit. This option can also take an argument: the
96 ``--save-temps=obj`` switch will write files into the directory specified with
97 the ``-o`` option. The ``--save-temps=cwd`` and ``--save-temps`` switches are
98 both synonyms for the default behaviour.
100 * ``--temp-dir DIRECTORY`` - Store temporary files in the given directory. This
101 directory is deleted on exit unless ``--save-temps`` is specified. If
102 ``--save-temps=obj`` is also specified, ``--temp-dir`` is given the
105 * ``--check-graph`` - Check the compilation for common errors like mismatched
106 output/input language names, multiple default edges and cycles. Because of
107 plugins, these checks can't be performed at compile-time. Exit with code zero
108 if no errors were found, and return the number of found errors
109 otherwise. Hidden option, useful for debugging LLVMC plugins.
111 * ``--view-graph`` - Show a graphical representation of the compilation graph
112 and exit. Requires that you have ``dot`` and ``gv`` programs installed. Hidden
113 option, useful for debugging LLVMC plugins.
115 * ``--write-graph`` - Write a ``compilation-graph.dot`` file in the current
116 directory with the compilation graph description in Graphviz format (identical
117 to the file used by the ``--view-graph`` option). The ``-o`` option can be
118 used to set the output file name. Hidden option, useful for debugging LLVMC
121 * ``--help``, ``--help-hidden``, ``--version`` - These options have
122 their standard meaning.
124 Compiling LLVMC plugins
125 =======================
127 It's easiest to start working on your own LLVMC plugin by copying the
128 skeleton project which lives under ``$LLVMC_DIR/plugins/Simple``::
130 $ cd $LLVMC_DIR/plugins
131 $ cp -r Simple MyPlugin
134 Makefile PluginMain.cpp Simple.td
136 As you can see, our basic plugin consists of only two files (not
137 counting the build script). ``Simple.td`` contains TableGen
138 description of the compilation graph; its format is documented in the
139 following sections. ``PluginMain.cpp`` is just a helper file used to
140 compile the auto-generated C++ code produced from TableGen source. It
141 can also contain hook definitions (see `below`__).
145 The first thing that you should do is to change the ``LLVMC_PLUGIN``
146 variable in the ``Makefile`` to avoid conflicts (since this variable
147 is used to name the resulting library)::
149 LLVMC_PLUGIN=MyPlugin
151 It is also a good idea to rename ``Simple.td`` to something less
154 $ mv Simple.td MyPlugin.td
156 To build your plugin as a dynamic library, just ``cd`` to its source
157 directory and run ``make``. The resulting file will be called
158 ``plugin_llvmc_$(LLVMC_PLUGIN).$(DLL_EXTENSION)`` (in our case,
159 ``plugin_llvmc_MyPlugin.so``). This library can be then loaded in with the
160 ``-load`` option. Example::
162 $ cd $LLVMC_DIR/plugins/Simple
164 $ llvmc -load $LLVM_DIR/Release/lib/plugin_llvmc_Simple.so
166 Compiling standalone LLVMC-based drivers
167 ========================================
169 By default, the ``llvmc`` executable consists of a driver core plus several
170 statically linked plugins (``Base`` and ``Clang`` at the moment). You can
171 produce a standalone LLVMC-based driver executable by linking the core with your
172 own plugins. The recommended way to do this is by starting with the provided
173 ``Skeleton`` example (``$LLVMC_DIR/example/Skeleton``)::
175 $ cd $LLVMC_DIR/example/
176 $ cp -r Skeleton mydriver
182 If you're compiling LLVM with different source and object directories, then you
183 must perform the following additional steps before running ``make``::
185 # LLVMC_SRC_DIR = $LLVM_SRC_DIR/tools/llvmc/
186 # LLVMC_OBJ_DIR = $LLVM_OBJ_DIR/tools/llvmc/
187 $ cp $LLVMC_SRC_DIR/example/mydriver/Makefile \
188 $LLVMC_OBJ_DIR/example/mydriver/
189 $ cd $LLVMC_OBJ_DIR/example/mydriver
192 Another way to do the same thing is by using the following command::
195 $ make LLVMC_BUILTIN_PLUGINS=MyPlugin LLVMC_BASED_DRIVER_NAME=mydriver
197 This works with both srcdir == objdir and srcdir != objdir, but assumes that the
198 plugin source directory was placed under ``$LLVMC_DIR/plugins``.
200 Sometimes, you will want a 'bare-bones' version of LLVMC that has no
201 built-in plugins. It can be compiled with the following command::
204 $ make LLVMC_BUILTIN_PLUGINS=""
207 Customizing LLVMC: the compilation graph
208 ========================================
210 Each TableGen configuration file should include the common
213 include "llvm/CompilerDriver/Common.td"
215 Internally, LLVMC stores information about possible source
216 transformations in form of a graph. Nodes in this graph represent
217 tools, and edges between two nodes represent a transformation path. A
218 special "root" node is used to mark entry points for the
219 transformations. LLVMC also assigns a weight to each edge (more on
220 this later) to choose between several alternative edges.
222 The definition of the compilation graph (see file
223 ``plugins/Base/Base.td`` for an example) is just a list of edges::
225 def CompilationGraph : CompilationGraph<[
226 Edge<"root", "llvm_gcc_c">,
227 Edge<"root", "llvm_gcc_assembler">,
230 Edge<"llvm_gcc_c", "llc">,
231 Edge<"llvm_gcc_cpp", "llc">,
234 OptionalEdge<"llvm_gcc_c", "opt", (case (switch_on "opt"),
236 OptionalEdge<"llvm_gcc_cpp", "opt", (case (switch_on "opt"),
240 OptionalEdge<"llvm_gcc_assembler", "llvm_gcc_cpp_linker",
241 (case (input_languages_contain "c++"), (inc_weight),
242 (or (parameter_equals "linker", "g++"),
243 (parameter_equals "linker", "c++")), (inc_weight))>,
248 As you can see, the edges can be either default or optional, where
249 optional edges are differentiated by an additional ``case`` expression
250 used to calculate the weight of this edge. Notice also that we refer
251 to tools via their names (as strings). This makes it possible to add
252 edges to an existing compilation graph in plugins without having to
253 know about all tool definitions used in the graph.
255 The default edges are assigned a weight of 1, and optional edges get a
256 weight of 0 + 2*N where N is the number of tests that evaluated to
257 true in the ``case`` expression. It is also possible to provide an
258 integer parameter to ``inc_weight`` and ``dec_weight`` - in this case,
259 the weight is increased (or decreased) by the provided value instead
260 of the default 2. It is also possible to change the default weight of
261 an optional edge by using the ``default`` clause of the ``case``
264 When passing an input file through the graph, LLVMC picks the edge
265 with the maximum weight. To avoid ambiguity, there should be only one
266 default edge between two nodes (with the exception of the root node,
267 which gets a special treatment - there you are allowed to specify one
268 default edge *per language*).
270 When multiple plugins are loaded, their compilation graphs are merged
271 together. Since multiple edges that have the same end nodes are not
272 allowed (i.e. the graph is not a multigraph), an edge defined in
273 several plugins will be replaced by the definition from the plugin
274 that was loaded last. Plugin load order can be controlled by using the
275 plugin priority feature described above.
277 To get a visual representation of the compilation graph (useful for
278 debugging), run ``llvmc --view-graph``. You will need ``dot`` and
279 ``gsview`` installed for this to work properly.
284 Command-line options that the plugin supports are defined by using an
287 def Options : OptionList<[
288 (switch_option "E", (help "Help string")),
289 (alias_option "quiet", "q")
293 As you can see, the option list is just a list of DAGs, where each DAG
294 is an option description consisting of the option name and some
295 properties. A plugin can define more than one option list (they are
296 all merged together in the end), which can be handy if one wants to
297 separate option groups syntactically.
299 * Possible option types:
301 - ``switch_option`` - a simple boolean switch without arguments, for example
302 ``-O2`` or ``-time``. At most one occurrence is allowed by default.
304 - ``parameter_option`` - option that takes one argument, for example
305 ``-std=c99``. It is also allowed to use spaces instead of the equality
306 sign: ``-std c99``. At most one occurrence is allowed.
308 - ``parameter_list_option`` - same as the above, but more than one option
309 occurence is allowed.
311 - ``prefix_option`` - same as the parameter_option, but the option name and
312 argument do not have to be separated. Example: ``-ofile``. This can be also
313 specified as ``-o file``; however, ``-o=file`` will be parsed incorrectly
314 (``=file`` will be interpreted as option value). At most one occurrence is
317 - ``prefix_list_option`` - same as the above, but more than one occurence of
318 the option is allowed; example: ``-lm -lpthread``.
320 - ``alias_option`` - a special option type for creating aliases. Unlike other
321 option types, aliases are not allowed to have any properties besides the
322 aliased option name. Usage example: ``(alias_option "preprocess", "E")``
324 - ``switch_list_option`` - like ``switch_option`` with the ``zero_or_more``
325 property, but remembers how many times the switch was turned on. Useful
326 mostly for forwarding. Example: when ``-foo`` is a switch option (with the
327 ``zero_or_more`` property), the command ``driver -foo -foo`` is forwarded
328 as ``some-tool -foo``, but when ``-foo`` is a switch list, the same command
329 is forwarded as ``some-tool -foo -foo``.
332 * Possible option properties:
334 - ``help`` - help string associated with this option. Used for ``--help``
337 - ``required`` - this option must be specified exactly once (or, in case of
338 the list options without the ``multi_val`` property, at least
339 once). Incompatible with ``optional`` and ``one_or_more``.
341 - ``optional`` - the option can be specified either zero times or exactly
342 once. The default for switch options. Useful only for list options in
343 conjunction with ``multi_val``. Incompatible with ``required``,
344 ``zero_or_more`` and ``one_or_more``.
346 - ``one_or_more`` - the option must be specified at least once. Can be useful
347 to allow switch options be both obligatory and be specified multiple
348 times. For list options is useful only in conjunction with ``multi_val``;
349 for ordinary it is synonymous with ``required``. Incompatible with
350 ``required``, ``optional`` and ``zero_or_more``.
352 - ``zero_or_more`` - the option can be specified zero or more times. Useful
353 to allow a single switch option to be specified more than
354 once. Incompatible with ``required``, ``optional`` and ``one_or_more``.
356 - ``hidden`` - the description of this option will not appear in
357 the ``--help`` output (but will appear in the ``--help-hidden``
360 - ``really_hidden`` - the option will not be mentioned in any help
363 - ``comma_separated`` - Indicates that any commas specified for an option's
364 value should be used to split the value up into multiple values for the
365 option. This property is valid only for list options. In conjunction with
366 ``forward_value`` can be used to implement option forwarding in style of
369 - ``multi_val n`` - this option takes *n* arguments (can be useful in some
370 special cases). Usage example: ``(parameter_list_option "foo", (multi_val
371 3))``; the command-line syntax is '-foo a b c'. Only list options can have
372 this attribute; you can, however, use the ``one_or_more``, ``optional``
373 and ``required`` properties.
375 - ``init`` - this option has a default value, either a string (if it is a
376 parameter), or a boolean (if it is a switch; as in C++, boolean constants
377 are called ``true`` and ``false``). List options can't have ``init``
379 Usage examples: ``(switch_option "foo", (init true))``; ``(prefix_option
380 "bar", (init "baz"))``.
382 - ``extern`` - this option is defined in some other plugin, see `below`__.
391 Sometimes, when linking several plugins together, one plugin needs to
392 access options defined in some other plugin. Because of the way
393 options are implemented, such options must be marked as
394 ``extern``. This is what the ``extern`` option property is
398 (switch_option "E", (extern))
401 If an external option has additional attributes besides 'extern', they are
402 ignored. See also the section on plugin `priorities`__.
408 Conditional evaluation
409 ======================
411 The 'case' construct is the main means by which programmability is
412 achieved in LLVMC. It can be used to calculate edge weights, program
413 actions and modify the shell commands to be executed. The 'case'
414 expression is designed after the similarly-named construct in
415 functional languages and takes the form ``(case (test_1), statement_1,
416 (test_2), statement_2, ... (test_N), statement_N)``. The statements
417 are evaluated only if the corresponding tests evaluate to true.
421 // Edge weight calculation
423 // Increases edge weight by 5 if "-A" is provided on the
424 // command-line, and by 5 more if "-B" is also provided.
426 (switch_on "A"), (inc_weight 5),
427 (switch_on "B"), (inc_weight 5))
430 // Tool command line specification
432 // Evaluates to "cmdline1" if the option "-A" is provided on the
433 // command line; to "cmdline2" if "-B" is provided;
434 // otherwise to "cmdline3".
437 (switch_on "A"), "cmdline1",
438 (switch_on "B"), "cmdline2",
439 (default), "cmdline3")
441 Note the slight difference in 'case' expression handling in contexts
442 of edge weights and command line specification - in the second example
443 the value of the ``"B"`` switch is never checked when switch ``"A"`` is
444 enabled, and the whole expression always evaluates to ``"cmdline1"`` in
447 Case expressions can also be nested, i.e. the following is legal::
449 (case (switch_on "E"), (case (switch_on "o"), ..., (default), ...)
452 You should, however, try to avoid doing that because it hurts
453 readability. It is usually better to split tool descriptions and/or
454 use TableGen inheritance instead.
456 * Possible tests are:
458 - ``switch_on`` - Returns true if a given command-line switch is provided by
459 the user. Can be given a list as argument, in that case ``(switch_on ["foo",
460 "bar", "baz"])`` is equivalent to ``(and (switch_on "foo"), (switch_on
461 "bar"), (switch_on "baz"))``.
462 Example: ``(switch_on "opt")``.
464 - ``any_switch_on`` - Given a list of switch options, returns true if any of
465 the switches is turned on.
466 Example: ``(any_switch_on ["foo", "bar", "baz"])`` is equivalent to ``(or
467 (switch_on "foo"), (switch_on "bar"), (switch_on "baz"))``.
469 - ``parameter_equals`` - Returns true if a command-line parameter equals
471 Example: ``(parameter_equals "W", "all")``.
473 - ``element_in_list`` - Returns true if a command-line parameter
474 list contains a given value.
475 Example: ``(element_in_list "l", "pthread")``.
477 - ``input_languages_contain`` - Returns true if a given language
478 belongs to the current input language set.
479 Example: ``(input_languages_contain "c++")``.
481 - ``in_language`` - Evaluates to true if the input file language is equal to
482 the argument. At the moment works only with ``cmd_line`` and ``actions`` (on
484 Example: ``(in_language "c++")``.
486 - ``not_empty`` - Returns true if a given option (which should be either a
487 parameter or a parameter list) is set by the user. Like ``switch_on``, can
488 be also given a list as argument.
489 Example: ``(not_empty "o")``.
491 - ``any_not_empty`` - Returns true if ``not_empty`` returns true for any of
492 the options in the list.
493 Example: ``(any_not_empty ["foo", "bar", "baz"])`` is equivalent to ``(or
494 (not_empty "foo"), (not_empty "bar"), (not_empty "baz"))``.
496 - ``empty`` - The opposite of ``not_empty``. Equivalent to ``(not (not_empty
497 X))``. Provided for convenience. Can be given a list as argument.
499 - ``any_not_empty`` - Returns true if ``not_empty`` returns true for any of
500 the options in the list.
501 Example: ``(any_empty ["foo", "bar", "baz"])`` is equivalent to ``(not (and
502 (not_empty "foo"), (not_empty "bar"), (not_empty "baz")))``.
504 - ``single_input_file`` - Returns true if there was only one input file
505 provided on the command-line. Used without arguments:
506 ``(single_input_file)``.
508 - ``multiple_input_files`` - Equivalent to ``(not (single_input_file))`` (the
509 case of zero input files is considered an error).
511 - ``default`` - Always evaluates to true. Should always be the last
512 test in the ``case`` expression.
514 - ``and`` - A standard binary logical combinator that returns true iff all of
515 its arguments return true. Used like this: ``(and (test1), (test2),
516 ... (testN))``. Nesting of ``and`` and ``or`` is allowed, but not
519 - ``or`` - A binary logical combinator that returns true iff any of its
520 arguments returns true. Example: ``(or (test1), (test2), ... (testN))``.
522 - ``not`` - Standard unary logical combinator that negates its
523 argument. Example: ``(not (or (test1), (test2), ... (testN)))``.
527 Writing a tool description
528 ==========================
530 As was said earlier, nodes in the compilation graph represent tools,
531 which are described separately. A tool definition looks like this
532 (taken from the ``include/llvm/CompilerDriver/Tools.td`` file)::
534 def llvm_gcc_cpp : Tool<[
536 (out_language "llvm-assembler"),
537 (output_suffix "bc"),
538 (cmd_line "llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm"),
542 This defines a new tool called ``llvm_gcc_cpp``, which is an alias for
543 ``llvm-g++``. As you can see, a tool definition is just a list of
544 properties; most of them should be self-explanatory. The ``sink``
545 property means that this tool should be passed all command-line
546 options that aren't mentioned in the option list.
548 The complete list of all currently implemented tool properties follows.
550 * Possible tool properties:
552 - ``in_language`` - input language name. Can be either a string or a
553 list, in case the tool supports multiple input languages.
555 - ``out_language`` - output language name. Multiple output languages are not
558 - ``output_suffix`` - output file suffix. Can also be changed
559 dynamically, see documentation on actions.
561 - ``cmd_line`` - the actual command used to run the tool. You can
562 use ``$INFILE`` and ``$OUTFILE`` variables, output redirection
563 with ``>``, hook invocations (``$CALL``), environment variables
564 (via ``$ENV``) and the ``case`` construct.
566 - ``join`` - this tool is a "join node" in the graph, i.e. it gets a
567 list of input files and joins them together. Used for linkers.
569 - ``sink`` - all command-line options that are not handled by other
570 tools are passed to this tool.
572 - ``actions`` - A single big ``case`` expression that specifies how
573 this tool reacts on command-line options (described in more detail
583 A tool often needs to react to command-line options, and this is
584 precisely what the ``actions`` property is for. The next example
585 illustrates this feature::
587 def llvm_gcc_linker : Tool<[
588 (in_language "object-code"),
589 (out_language "executable"),
590 (output_suffix "out"),
591 (cmd_line "llvm-gcc $INFILE -o $OUTFILE"),
593 (actions (case (not_empty "L"), (forward "L"),
594 (not_empty "l"), (forward "l"),
596 [(append_cmd "-dummy1"), (append_cmd "-dummy2")])
599 The ``actions`` tool property is implemented on top of the omnipresent
600 ``case`` expression. It associates one or more different *actions*
601 with given conditions - in the example, the actions are ``forward``,
602 which forwards a given option unchanged, and ``append_cmd``, which
603 appends a given string to the tool execution command. Multiple actions
604 can be associated with a single condition by using a list of actions
605 (used in the example to append some dummy options). The same ``case``
606 construct can also be used in the ``cmd_line`` property to modify the
609 The "join" property used in the example means that this tool behaves
612 The list of all possible actions follows.
616 - ``append_cmd`` - Append a string to the tool invocation command.
617 Example: ``(case (switch_on "pthread"), (append_cmd "-lpthread"))``.
619 - ``error`` - Exit with error.
620 Example: ``(error "Mixing -c and -S is not allowed!")``.
622 - ``warning`` - Print a warning.
623 Example: ``(warning "Specifying both -O1 and -O2 is meaningless!")``.
625 - ``forward`` - Forward the option unchanged.
626 Example: ``(forward "Wall")``.
628 - ``forward_as`` - Change the option's name, but forward the argument
630 Example: ``(forward_as "O0", "--disable-optimization")``.
632 - ``forward_value`` - Forward only option's value. Cannot be used with switch
633 options (since they don't have values), but works fine with lists.
634 Example: ``(forward_value "Wa,")``.
636 - ``forward_transformed_value`` - As above, but applies a hook to the
637 option's value before forwarding (see `below`__). When
638 ``forward_transformed_value`` is applied to a list
639 option, the hook must have signature
640 ``std::string hooks::HookName (const std::vector<std::string>&)``.
641 Example: ``(forward_transformed_value "m", "ConvertToMAttr")``.
645 - ``output_suffix`` - Modify the output suffix of this tool.
646 Example: ``(output_suffix "i")``.
648 - ``stop_compilation`` - Stop compilation after this tool processes its
649 input. Used without arguments.
650 Example: ``(stop_compilation)``.
656 If you are adding support for a new language to LLVMC, you'll need to
657 modify the language map, which defines mappings from file extensions
658 to language names. It is used to choose the proper toolchain(s) for a
659 given input file set. Language map definition looks like this::
661 def LanguageMap : LanguageMap<
662 [LangToSuffixes<"c++", ["cc", "cp", "cxx", "cpp", "CPP", "c++", "C"]>,
663 LangToSuffixes<"c", ["c"]>,
667 For example, without those definitions the following command wouldn't work::
670 llvmc: Unknown suffix: cpp
672 The language map entries are needed only for the tools that are linked from the
673 root node. Since a tool can't have multiple output languages, for inner nodes of
674 the graph the input and output languages should match. This is enforced at
680 It is sometimes useful to run error-checking code before processing the
681 compilation graph. For example, if optimization options "-O1" and "-O2" are
682 implemented as switches, we might want to output a warning if the user invokes
683 the driver with both of these options enabled.
685 The ``OptionPreprocessor`` feature is reserved specially for these
686 occasions. Example (adapted from the built-in Base plugin)::
689 def Preprocess : OptionPreprocessor<
690 (case (not (any_switch_on ["O0", "O1", "O2", "O3"])),
692 (and (switch_on "O3"), (any_switch_on ["O0", "O1", "O2"])),
693 (unset_option ["O0", "O1", "O2"]),
694 (and (switch_on "O2"), (any_switch_on ["O0", "O1"])),
695 (unset_option ["O0", "O1"]),
696 (and (switch_on "O1"), (switch_on "O0")),
700 Here, ``OptionPreprocessor`` is used to unset all spurious ``-O`` options so
701 that they are not forwarded to the compiler. If no optimization options are
702 specified, ``-O2`` is enabled.
704 ``OptionPreprocessor`` is basically a single big ``case`` expression, which is
705 evaluated only once right after the plugin is loaded. The only allowed actions
706 in ``OptionPreprocessor`` are ``error``, ``warning``, and two special actions:
707 ``unset_option`` and ``set_option``. As their names suggest, they can be used to
708 set or unset a given option. To set an option with ``set_option``, use the
709 two-argument form: ``(set_option "parameter", VALUE)``. Here, ``VALUE`` can be
710 either a string, a string list, or a boolean constant.
712 For convenience, ``set_option`` and ``unset_option`` also work on lists. That
713 is, instead of ``[(unset_option "A"), (unset_option "B")]`` you can use
714 ``(unset_option ["A", "B"])``. Obviously, ``(set_option ["A", "B"])`` is valid
715 only if both ``A`` and ``B`` are switches.
723 Hooks and environment variables
724 -------------------------------
726 Normally, LLVMC executes programs from the system ``PATH``. Sometimes,
727 this is not sufficient: for example, we may want to specify tool paths
728 or names in the configuration file. This can be easily achieved via
729 the hooks mechanism. To write your own hooks, just add their
730 definitions to the ``PluginMain.cpp`` or drop a ``.cpp`` file into the
731 your plugin directory. Hooks should live in the ``hooks`` namespace
732 and have the signature ``std::string hooks::MyHookName ([const char*
733 Arg0 [ const char* Arg2 [, ...]]])``. They can be used from the
734 ``cmd_line`` tool property::
736 (cmd_line "$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)")
738 To pass arguments to hooks, use the following syntax::
740 (cmd_line "$CALL(MyHook, 'Arg1', 'Arg2', 'Arg # 3')/path/to/file -o1 -o2")
742 It is also possible to use environment variables in the same manner::
744 (cmd_line "$ENV(VAR1)/path/to/file -o $ENV(VAR2)")
746 To change the command line string based on user-provided options use
747 the ``case`` expression (documented `above`__)::
752 "llvm-g++ -E -x c $INFILE -o $OUTFILE",
754 "llvm-g++ -c -x c $INFILE -o $OUTFILE -emit-llvm"))
760 How plugins are loaded
761 ----------------------
763 It is possible for LLVMC plugins to depend on each other. For example,
764 one can create edges between nodes defined in some other plugin. To
765 make this work, however, that plugin should be loaded first. To
766 achieve this, the concept of plugin priority was introduced. By
767 default, every plugin has priority zero; to specify the priority
768 explicitly, put the following line in your plugin's TableGen file::
770 def Priority : PluginPriority<$PRIORITY_VALUE>;
771 # Where PRIORITY_VALUE is some integer > 0
773 Plugins are loaded in order of their (increasing) priority, starting
774 with 0. Therefore, the plugin with the highest priority value will be
780 When writing LLVMC plugins, it can be useful to get a visual view of
781 the resulting compilation graph. This can be achieved via the command
782 line option ``--view-graph``. This command assumes that Graphviz_ and
783 Ghostview_ are installed. There is also a ``--write-graph`` option that
784 creates a Graphviz source file (``compilation-graph.dot``) in the
787 Another useful ``llvmc`` option is ``--check-graph``. It checks the
788 compilation graph for common errors like mismatched output/input
789 language names, multiple default edges and cycles. These checks can't
790 be performed at compile-time because the plugins can load code
791 dynamically. When invoked with ``--check-graph``, ``llvmc`` doesn't
792 perform any compilation tasks and returns the number of encountered
793 errors as its status code.
795 .. _Graphviz: http://www.graphviz.org/
796 .. _Ghostview: http://pages.cs.wisc.edu/~ghost/
798 Conditioning on the executable name
799 -----------------------------------
801 For now, the executable name (the value passed to the driver in ``argv[0]``) is
802 accessible only in the C++ code (i.e. hooks). Use the following code::
805 extern const char* ProgramName;
810 std::string MyHook() {
812 if (strcmp(ProgramName, "mydriver") == 0) {
817 } // end namespace hooks
819 In general, you're encouraged not to make the behaviour dependent on the
820 executable file name, and use command-line switches instead. See for example how
821 the ``Base`` plugin behaves when it needs to choose the correct linker options
822 (think ``g++`` vs. ``gcc``).
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835 <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
836 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
838 Last modified: $Date: 2008-12-11 11:34:48 -0600 (Thu, 11 Dec 2008) $