1 ===================================
2 Customizing LLVMC: Reference Manual
3 ===================================
5 This file was automatically generated by rst2html.
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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.cs.uiuc.edu/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
52 between different compilers for different languages (think ``g++`` and
53 ``gcc``) - the right toolchain is chosen automatically based on input
54 language names (which are, in turn, determined from file
55 extensions). If you want to force files ending with ".c" to compile as
56 C++, use the ``-x`` option, just like you would do it with ``gcc``::
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
75 also possible to choose the work-in-progress ``clang`` compiler with
76 the ``-clang`` option.
82 LLVMC has some built-in options that can't be overridden in the
83 configuration libraries:
85 * ``-o FILE`` - Output file name.
87 * ``-x LANGUAGE`` - Specify the language of the following input files
88 until the next -x option.
90 * ``-load PLUGIN_NAME`` - Load the specified plugin DLL. Example:
91 ``-load $LLVM_DIR/Release/lib/LLVMCSimple.so``.
93 * ``-v`` - Enable verbose mode, i.e. print out all executed commands.
95 * ``--check-graph`` - Check the compilation for common errors like mismatched
96 output/input language names, multiple default edges and cycles. Because of
97 plugins, these checks can't be performed at compile-time. Exit with code zero
98 if no errors were found, and return the number of found errors
99 otherwise. Hidden option, useful for debugging LLVMC plugins.
101 * ``--view-graph`` - Show a graphical representation of the compilation graph
102 and exit. Requires that you have ``dot`` and ``gv`` programs installed. Hidden
103 option, useful for debugging LLVMC plugins.
105 * ``--write-graph`` - Write a ``compilation-graph.dot`` file in the current
106 directory with the compilation graph description in Graphviz format (identical
107 to the file used by the ``--view-graph`` option). The ``-o`` option can be
108 used to set the output file name. Hidden option, useful for debugging LLVMC
111 * ``--save-temps`` - Write temporary files to the current directory
112 and do not delete them on exit. Hidden option, useful for debugging.
114 * ``--help``, ``--help-hidden``, ``--version`` - These options have
115 their standard meaning.
117 Compiling LLVMC plugins
118 =======================
120 It's easiest to start working on your own LLVMC plugin by copying the
121 skeleton project which lives under ``$LLVMC_DIR/plugins/Simple``::
123 $ cd $LLVMC_DIR/plugins
124 $ cp -r Simple MyPlugin
127 Makefile PluginMain.cpp Simple.td
129 As you can see, our basic plugin consists of only two files (not
130 counting the build script). ``Simple.td`` contains TableGen
131 description of the compilation graph; its format is documented in the
132 following sections. ``PluginMain.cpp`` is just a helper file used to
133 compile the auto-generated C++ code produced from TableGen source. It
134 can also contain hook definitions (see `below`__).
138 The first thing that you should do is to change the ``LLVMC_PLUGIN``
139 variable in the ``Makefile`` to avoid conflicts (since this variable
140 is used to name the resulting library)::
142 LLVMC_PLUGIN=MyPlugin
144 It is also a good idea to rename ``Simple.td`` to something less
147 $ mv Simple.td MyPlugin.td
149 To build your plugin as a dynamic library, just ``cd`` to its source
150 directory and run ``make``. The resulting file will be called
151 ``LLVMC$(LLVMC_PLUGIN).$(DLL_EXTENSION)`` (in our case,
152 ``LLVMCMyPlugin.so``). This library can be then loaded in with the
153 ``-load`` option. Example::
155 $ cd $LLVMC_DIR/plugins/Simple
157 $ llvmc -load $LLVM_DIR/Release/lib/LLVMCSimple.so
159 Compiling standalone LLVMC-based drivers
160 ========================================
162 By default, the ``llvmc`` executable consists of a driver core plus several
163 statically linked plugins (``Base`` and ``Clang`` at the moment). You can
164 produce a standalone LLVMC-based driver executable by linking the core with your
165 own plugins. The recommended way to do this is by starting with the provided
166 ``Skeleton`` example (``$LLVMC_DIR/example/Skeleton``)::
168 $ cd $LLVMC_DIR/example/
169 $ cp -r Skeleton mydriver
175 If you're compiling LLVM with different source and object directories, then you
176 must perform the following additional steps before running ``make``::
178 # LLVMC_SRC_DIR = $LLVM_SRC_DIR/tools/llvmc/
179 # LLVMC_OBJ_DIR = $LLVM_OBJ_DIR/tools/llvmc/
180 $ cp $LLVMC_SRC_DIR/example/mydriver/Makefile \
181 $LLVMC_OBJ_DIR/example/mydriver/
182 $ cd $LLVMC_OBJ_DIR/example/mydriver
185 Another way to do the same thing is by using the following command::
188 $ make LLVMC_BUILTIN_PLUGINS=MyPlugin LLVMC_BASED_DRIVER_NAME=mydriver
190 This works with both srcdir==objdir and srcdir != objdir, but assumes that the
191 plugin source directory was placed under ``$LLVMC_DIR/plugins``.
193 Sometimes, you will want a 'bare-bones' version of LLVMC that has no
194 built-in plugins. It can be compiled with the following command::
197 $ make LLVMC_BUILTIN_PLUGINS=""
200 Customizing LLVMC: the compilation graph
201 ========================================
203 Each TableGen configuration file should include the common
206 include "llvm/CompilerDriver/Common.td"
208 Internally, LLVMC stores information about possible source
209 transformations in form of a graph. Nodes in this graph represent
210 tools, and edges between two nodes represent a transformation path. A
211 special "root" node is used to mark entry points for the
212 transformations. LLVMC also assigns a weight to each edge (more on
213 this later) to choose between several alternative edges.
215 The definition of the compilation graph (see file
216 ``plugins/Base/Base.td`` for an example) is just a list of edges::
218 def CompilationGraph : CompilationGraph<[
219 Edge<"root", "llvm_gcc_c">,
220 Edge<"root", "llvm_gcc_assembler">,
223 Edge<"llvm_gcc_c", "llc">,
224 Edge<"llvm_gcc_cpp", "llc">,
227 OptionalEdge<"llvm_gcc_c", "opt", (case (switch_on "opt"),
229 OptionalEdge<"llvm_gcc_cpp", "opt", (case (switch_on "opt"),
233 OptionalEdge<"llvm_gcc_assembler", "llvm_gcc_cpp_linker",
234 (case (input_languages_contain "c++"), (inc_weight),
235 (or (parameter_equals "linker", "g++"),
236 (parameter_equals "linker", "c++")), (inc_weight))>,
241 As you can see, the edges can be either default or optional, where
242 optional edges are differentiated by an additional ``case`` expression
243 used to calculate the weight of this edge. Notice also that we refer
244 to tools via their names (as strings). This makes it possible to add
245 edges to an existing compilation graph in plugins without having to
246 know about all tool definitions used in the graph.
248 The default edges are assigned a weight of 1, and optional edges get a
249 weight of 0 + 2*N where N is the number of tests that evaluated to
250 true in the ``case`` expression. It is also possible to provide an
251 integer parameter to ``inc_weight`` and ``dec_weight`` - in this case,
252 the weight is increased (or decreased) by the provided value instead
253 of the default 2. It is also possible to change the default weight of
254 an optional edge by using the ``default`` clause of the ``case``
257 When passing an input file through the graph, LLVMC picks the edge
258 with the maximum weight. To avoid ambiguity, there should be only one
259 default edge between two nodes (with the exception of the root node,
260 which gets a special treatment - there you are allowed to specify one
261 default edge *per language*).
263 When multiple plugins are loaded, their compilation graphs are merged
264 together. Since multiple edges that have the same end nodes are not
265 allowed (i.e. the graph is not a multigraph), an edge defined in
266 several plugins will be replaced by the definition from the plugin
267 that was loaded last. Plugin load order can be controlled by using the
268 plugin priority feature described above.
270 To get a visual representation of the compilation graph (useful for
271 debugging), run ``llvmc --view-graph``. You will need ``dot`` and
272 ``gsview`` installed for this to work properly.
277 Command-line options that the plugin supports are defined by using an
280 def Options : OptionList<[
281 (switch_option "E", (help "Help string")),
282 (alias_option "quiet", "q")
286 As you can see, the option list is just a list of DAGs, where each DAG
287 is an option description consisting of the option name and some
288 properties. A plugin can define more than one option list (they are
289 all merged together in the end), which can be handy if one wants to
290 separate option groups syntactically.
292 * Possible option types:
294 - ``switch_option`` - a simple boolean switch without arguments, for example
295 ``-O2`` or ``-time``. At most one occurrence is allowed.
297 - ``parameter_option`` - option that takes one argument, for example
298 ``-std=c99``. It is also allowed to use spaces instead of the equality
299 sign: ``-std c99``. At most one occurrence is allowed.
301 - ``parameter_list_option`` - same as the above, but more than one option
302 occurence is allowed.
304 - ``prefix_option`` - same as the parameter_option, but the option name and
305 argument do not have to be separated. Example: ``-ofile``. This can be also
306 specified as ``-o file``; however, ``-o=file`` will be parsed incorrectly
307 (``=file`` will be interpreted as option value). At most one occurrence is
310 - ``prefix_list_option`` - same as the above, but more than one occurence of
311 the option is allowed; example: ``-lm -lpthread``.
313 - ``alias_option`` - a special option type for creating aliases. Unlike other
314 option types, aliases are not allowed to have any properties besides the
315 aliased option name. Usage example: ``(alias_option "preprocess", "E")``
318 * Possible option properties:
320 - ``help`` - help string associated with this option. Used for ``--help``
323 - ``required`` - this option must be specified exactly once (or, in case of
324 the list options without the ``multi_val`` property, at least
325 once). Incompatible with ``zero_or_one`` and ``one_or_more``.
327 - ``one_or_more`` - the option must be specified at least one time. Useful
328 only for list options in conjunction with ``multi_val``; for ordinary lists
329 it is synonymous with ``required``. Incompatible with ``required`` and
332 - ``zero_or_one`` - the option can be specified zero or one times. Useful
333 only for list options in conjunction with ``multi_val``. Incompatible with
334 ``required`` and ``one_or_more``.
336 - ``hidden`` - the description of this option will not appear in
337 the ``--help`` output (but will appear in the ``--help-hidden``
340 - ``really_hidden`` - the option will not be mentioned in any help
343 - ``multi_val n`` - this option takes *n* arguments (can be useful in some
344 special cases). Usage example: ``(parameter_list_option "foo", (multi_val
345 3))``. Only list options can have this attribute; you can, however, use
346 the ``one_or_more`` and ``zero_or_one`` properties.
348 - ``extern`` - this option is defined in some other plugin, see below.
353 Sometimes, when linking several plugins together, one plugin needs to
354 access options defined in some other plugin. Because of the way
355 options are implemented, such options must be marked as
356 ``extern``. This is what the ``extern`` option property is
360 (switch_option "E", (extern))
363 See also the section on plugin `priorities`__.
369 Conditional evaluation
370 ======================
372 The 'case' construct is the main means by which programmability is
373 achieved in LLVMC. It can be used to calculate edge weights, program
374 actions and modify the shell commands to be executed. The 'case'
375 expression is designed after the similarly-named construct in
376 functional languages and takes the form ``(case (test_1), statement_1,
377 (test_2), statement_2, ... (test_N), statement_N)``. The statements
378 are evaluated only if the corresponding tests evaluate to true.
382 // Edge weight calculation
384 // Increases edge weight by 5 if "-A" is provided on the
385 // command-line, and by 5 more if "-B" is also provided.
387 (switch_on "A"), (inc_weight 5),
388 (switch_on "B"), (inc_weight 5))
391 // Tool command line specification
393 // Evaluates to "cmdline1" if the option "-A" is provided on the
394 // command line; to "cmdline2" if "-B" is provided;
395 // otherwise to "cmdline3".
398 (switch_on "A"), "cmdline1",
399 (switch_on "B"), "cmdline2",
400 (default), "cmdline3")
402 Note the slight difference in 'case' expression handling in contexts
403 of edge weights and command line specification - in the second example
404 the value of the ``"B"`` switch is never checked when switch ``"A"`` is
405 enabled, and the whole expression always evaluates to ``"cmdline1"`` in
408 Case expressions can also be nested, i.e. the following is legal::
410 (case (switch_on "E"), (case (switch_on "o"), ..., (default), ...)
413 You should, however, try to avoid doing that because it hurts
414 readability. It is usually better to split tool descriptions and/or
415 use TableGen inheritance instead.
417 * Possible tests are:
419 - ``switch_on`` - Returns true if a given command-line switch is
420 provided by the user. Example: ``(switch_on "opt")``.
422 - ``parameter_equals`` - Returns true if a command-line parameter equals
424 Example: ``(parameter_equals "W", "all")``.
426 - ``element_in_list`` - Returns true if a command-line parameter
427 list contains a given value.
428 Example: ``(parameter_in_list "l", "pthread")``.
430 - ``input_languages_contain`` - Returns true if a given language
431 belongs to the current input language set.
432 Example: ``(input_languages_contain "c++")``.
434 - ``in_language`` - Evaluates to true if the input file language
435 equals to the argument. At the moment works only with ``cmd_line``
436 and ``actions`` (on non-join nodes).
437 Example: ``(in_language "c++")``.
439 - ``not_empty`` - Returns true if a given option (which should be
440 either a parameter or a parameter list) is set by the
442 Example: ``(not_empty "o")``.
444 - ``empty`` - The opposite of ``not_empty``. Equivalent to ``(not (not_empty
445 X))``. Provided for convenience.
447 - ``default`` - Always evaluates to true. Should always be the last
448 test in the ``case`` expression.
450 - ``and`` - A standard logical combinator that returns true iff all
451 of its arguments return true. Used like this: ``(and (test1),
452 (test2), ... (testN))``. Nesting of ``and`` and ``or`` is allowed,
455 - ``or`` - Another logical combinator that returns true only if any
456 one of its arguments returns true. Example: ``(or (test1),
457 (test2), ... (testN))``.
460 Writing a tool description
461 ==========================
463 As was said earlier, nodes in the compilation graph represent tools,
464 which are described separately. A tool definition looks like this
465 (taken from the ``include/llvm/CompilerDriver/Tools.td`` file)::
467 def llvm_gcc_cpp : Tool<[
469 (out_language "llvm-assembler"),
470 (output_suffix "bc"),
471 (cmd_line "llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm"),
475 This defines a new tool called ``llvm_gcc_cpp``, which is an alias for
476 ``llvm-g++``. As you can see, a tool definition is just a list of
477 properties; most of them should be self-explanatory. The ``sink``
478 property means that this tool should be passed all command-line
479 options that aren't mentioned in the option list.
481 The complete list of all currently implemented tool properties follows.
483 * Possible tool properties:
485 - ``in_language`` - input language name. Can be either a string or a
486 list, in case the tool supports multiple input languages.
488 - ``out_language`` - output language name. Tools are not allowed to
489 have multiple output languages.
491 - ``output_suffix`` - output file suffix. Can also be changed
492 dynamically, see documentation on actions.
494 - ``cmd_line`` - the actual command used to run the tool. You can
495 use ``$INFILE`` and ``$OUTFILE`` variables, output redirection
496 with ``>``, hook invocations (``$CALL``), environment variables
497 (via ``$ENV``) and the ``case`` construct.
499 - ``join`` - this tool is a "join node" in the graph, i.e. it gets a
500 list of input files and joins them together. Used for linkers.
502 - ``sink`` - all command-line options that are not handled by other
503 tools are passed to this tool.
505 - ``actions`` - A single big ``case`` expression that specifies how
506 this tool reacts on command-line options (described in more detail
512 A tool often needs to react to command-line options, and this is
513 precisely what the ``actions`` property is for. The next example
514 illustrates this feature::
516 def llvm_gcc_linker : Tool<[
517 (in_language "object-code"),
518 (out_language "executable"),
519 (output_suffix "out"),
520 (cmd_line "llvm-gcc $INFILE -o $OUTFILE"),
522 (actions (case (not_empty "L"), (forward "L"),
523 (not_empty "l"), (forward "l"),
525 [(append_cmd "-dummy1"), (append_cmd "-dummy2")])
528 The ``actions`` tool property is implemented on top of the omnipresent
529 ``case`` expression. It associates one or more different *actions*
530 with given conditions - in the example, the actions are ``forward``,
531 which forwards a given option unchanged, and ``append_cmd``, which
532 appends a given string to the tool execution command. Multiple actions
533 can be associated with a single condition by using a list of actions
534 (used in the example to append some dummy options). The same ``case``
535 construct can also be used in the ``cmd_line`` property to modify the
538 The "join" property used in the example means that this tool behaves
541 The list of all possible actions follows.
545 - ``append_cmd`` - append a string to the tool invocation
547 Example: ``(case (switch_on "pthread"), (append_cmd
550 - ``error` - exit with error.
551 Example: ``(error "Mixing -c and -S is not allowed!")``.
553 - ``forward`` - forward an option unchanged.
554 Example: ``(forward "Wall")``.
556 - ``forward_as`` - Change the name of an option, but forward the
558 Example: ``(forward_as "O0", "--disable-optimization")``.
560 - ``output_suffix`` - modify the output suffix of this
562 Example: ``(output_suffix "i")``.
564 - ``stop_compilation`` - stop compilation after this tool processes
565 its input. Used without arguments.
567 - ``unpack_values`` - used for for splitting and forwarding
568 comma-separated lists of options, e.g. ``-Wa,-foo=bar,-baz`` is
569 converted to ``-foo=bar -baz`` and appended to the tool invocation
571 Example: ``(unpack_values "Wa,")``.
576 If you are adding support for a new language to LLVMC, you'll need to
577 modify the language map, which defines mappings from file extensions
578 to language names. It is used to choose the proper toolchain(s) for a
579 given input file set. Language map definition looks like this::
581 def LanguageMap : LanguageMap<
582 [LangToSuffixes<"c++", ["cc", "cp", "cxx", "cpp", "CPP", "c++", "C"]>,
583 LangToSuffixes<"c", ["c"]>,
587 For example, without those definitions the following command wouldn't work::
590 llvmc: Unknown suffix: cpp
592 The language map entries should be added only for tools that are
593 linked with the root node. Since tools are not allowed to have
594 multiple output languages, for nodes "inside" the graph the input and
595 output languages should match. This is enforced at compile-time.
603 Hooks and environment variables
604 -------------------------------
606 Normally, LLVMC executes programs from the system ``PATH``. Sometimes,
607 this is not sufficient: for example, we may want to specify tool paths
608 or names in the configuration file. This can be easily achieved via
609 the hooks mechanism. To write your own hooks, just add their
610 definitions to the ``PluginMain.cpp`` or drop a ``.cpp`` file into the
611 your plugin directory. Hooks should live in the ``hooks`` namespace
612 and have the signature ``std::string hooks::MyHookName ([const char*
613 Arg0 [ const char* Arg2 [, ...]]])``. They can be used from the
614 ``cmd_line`` tool property::
616 (cmd_line "$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)")
618 To pass arguments to hooks, use the following syntax::
620 (cmd_line "$CALL(MyHook, 'Arg1', 'Arg2', 'Arg # 3')/path/to/file -o1 -o2")
622 It is also possible to use environment variables in the same manner::
624 (cmd_line "$ENV(VAR1)/path/to/file -o $ENV(VAR2)")
626 To change the command line string based on user-provided options use
627 the ``case`` expression (documented `above`__)::
632 "llvm-g++ -E -x c $INFILE -o $OUTFILE",
634 "llvm-g++ -c -x c $INFILE -o $OUTFILE -emit-llvm"))
640 How plugins are loaded
641 ----------------------
643 It is possible for LLVMC plugins to depend on each other. For example,
644 one can create edges between nodes defined in some other plugin. To
645 make this work, however, that plugin should be loaded first. To
646 achieve this, the concept of plugin priority was introduced. By
647 default, every plugin has priority zero; to specify the priority
648 explicitly, put the following line in your plugin's TableGen file::
650 def Priority : PluginPriority<$PRIORITY_VALUE>;
651 # Where PRIORITY_VALUE is some integer > 0
653 Plugins are loaded in order of their (increasing) priority, starting
654 with 0. Therefore, the plugin with the highest priority value will be
660 When writing LLVMC plugins, it can be useful to get a visual view of
661 the resulting compilation graph. This can be achieved via the command
662 line option ``--view-graph``. This command assumes that Graphviz_ and
663 Ghostview_ are installed. There is also a ``--write-graph`` option that
664 creates a Graphviz source file (``compilation-graph.dot``) in the
667 Another useful ``llvmc`` option is ``--check-graph``. It checks the
668 compilation graph for common errors like mismatched output/input
669 language names, multiple default edges and cycles. These checks can't
670 be performed at compile-time because the plugins can load code
671 dynamically. When invoked with ``--check-graph``, ``llvmc`` doesn't
672 perform any compilation tasks and returns the number of encountered
673 errors as its status code.
675 .. _Graphviz: http://www.graphviz.org/
676 .. _Ghostview: http://pages.cs.wisc.edu/~ghost/
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689 <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
690 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
692 Last modified: $Date: 2008-12-11 11:34:48 -0600 (Thu, 11 Dec 2008) $