diff --git a/llvm/docs/CompilerDriver.html b/llvm/docs/CompilerDriver.html index ece0de4044b3..2eb452af0fe3 100644 --- a/llvm/docs/CompilerDriver.html +++ b/llvm/docs/CompilerDriver.html @@ -3,20 +3,22 @@
- +Note: This document is a work-in-progress. Additions and clarifications - are welcome.
-Author: | +Mikhail Glushenkov <foldr@codedegers.com> |
---|
LLVMC is a generic compiler driver, designed to be customizable and extensible. It plays the same role for LLVM as the gcc program does for GCC - LLVMC's job is essentially to transform a set of input @@ -25,34 +27,46 @@ options. What makes LLVMC different is that these transformation rules are completely customizable - in fact, LLVMC knows nothing about the specifics of transformation (even the command-line options are mostly not hard-coded) and regards the transformation structure as an -abstract graph. This makes it possible to adapt LLVMC for other -purposes - for example, as a build tool for game resources.
-Because LLVMC employs TableGen [1] as its configuration language, you +abstract graph. The structure of this graph is completely determined +by plugins, which can be either statically or dynamically linked. This +makes it possible to easily adapt LLVMC for other purposes - for +example, as a build tool for game resources.
+Because LLVMC employs TableGen [1] as its configuration language, you need to be familiar with it to customize LLVMC.
LLVMC tries hard to be as compatible with gcc as possible, although there are some small differences. Most of the time, however, you shouldn't be able to notice them:
$ # This works as expected: -$ llvmc2 -O3 -Wall hello.cpp +$ llvmc -O3 -Wall hello.cpp $ ./a.out hello@@ -63,8 +77,8 @@ 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 -x option, just like you would do it with gcc:
-$ llvmc2 -x c hello.cpp -$ # hello.cpp is really a C file +$ # hello.c is really a C++ file +$ llvmc -x c++ hello.c $ ./a.out hello@@ -72,25 +86,30 @@ hello object files you should provide the --linker option since it's impossible for LLVMC to choose the right linker in that case:
-$ llvmc2 -c hello.cpp -$ llvmc2 hello.o +$ llvmc -c hello.cpp +$ llvmc hello.o [A lot of link-time errors skipped] -$ llvmc2 --linker=c++ hello.o +$ llvmc --linker=c++ hello.o $ ./a.out hello+
By default, LLVMC uses llvm-gcc to compile the source code. It is +also possible to choose the work-in-progress clang compiler with +the -clang option.
LLVMC has some built-in options that can't be overridden in the -configuration files:
+configuration libraries:At the time of writing LLVMC does not support on-the-fly reloading of -configuration, so to customize LLVMC you'll have to recompile the -source code (which lives under $LLVM_DIR/tools/llvmc2). The -default configuration files are Common.td (contains common -definitions, don't forget to include it in your configuration -files), Tools.td (tool descriptions) and Graph.td (compilation -graph definition).
-To compile LLVMC with your own configuration file (say,``MyGraph.td``), -run make like this:
+It's easiest to start working on your own LLVMC plugin by copying the +skeleton project which lives under $LLVMC_DIR/plugins/Simple:
-$ cd $LLVM_DIR/tools/llvmc2 -$ make GRAPH=MyGraph.td TOOLNAME=my_llvmc +$ cd $LLVMC_DIR/plugins +$ cp -r Simple MyPlugin +$ cd MyPlugin +$ ls +Makefile PluginMain.cpp Simple.td ++
As you can see, our basic plugin consists of only two files (not +counting the build script). Simple.td contains TableGen +description of the compilation graph; its format is documented in the +following sections. PluginMain.cpp is just a helper file used to +compile the auto-generated C++ code produced from TableGen source. It +can also contain hook definitions (see below).
+The first thing that you should do is to change the LLVMC_PLUGIN +variable in the Makefile to avoid conflicts (since this variable +is used to name the resulting library):
++LLVMC_PLUGIN=MyPlugin ++
It is also a good idea to rename Simple.td to something less +generic:
++$ mv Simple.td MyPlugin.td ++
Note that the plugin source directory must be placed under +$LLVMC_DIR/plugins to make use of the existing build +infrastructure. To build a version of the LLVMC executable called +mydriver with your plugin compiled in, use the following command:
++$ cd $LLVMC_DIR +$ make BUILTIN_PLUGINS=MyPlugin DRIVER_NAME=mydriver ++
To build your plugin as a dynamic library, just cd to its source +directory and run make. The resulting file will be called +LLVMC$(LLVMC_PLUGIN).$(DLL_EXTENSION) (in our case, +LLVMCMyPlugin.so). This library can be then loaded in with the +-load option. Example:
++$ cd $LLVMC_DIR/plugins/Simple +$ make +$ llvmc -load $LLVM_DIR/Release/lib/LLVMCSimple.so ++
Sometimes, you will want a 'bare-bones' version of LLVMC that has no +built-in plugins. It can be compiled with the following command:
++$ cd $LLVMC_DIR +$ make BUILTIN_PLUGINS="" ++
Each TableGen configuration file should include the common +definitions:
++include "llvm/CompilerDriver/Common.td"-
This will build an executable named my_llvmc. There are also -several sample configuration files in the llvmc2/examples -subdirectory that should help to get you started.
Internally, LLVMC stores information about possible source transformations in form of a graph. Nodes in this graph represent tools, and edges between two nodes represent a transformation path. A special "root" node is used to mark entry points for the transformations. LLVMC also assigns a weight to each edge (more on this later) to choose between several alternative edges.
-The definition of the compilation graph (see file Graph.td) is -just a list of edges:
+The definition of the compilation graph (see file +plugins/Base/Base.td for an example) is just a list of edges:
def CompilationGraph : CompilationGraph<[ - Edge<root, llvm_gcc_c>, - Edge<root, llvm_gcc_assembler>, + Edge<"root", "llvm_gcc_c">, + Edge<"root", "llvm_gcc_assembler">, ... - Edge<llvm_gcc_c, llc>, - Edge<llvm_gcc_cpp, llc>, + Edge<"llvm_gcc_c", "llc">, + Edge<"llvm_gcc_cpp", "llc">, ... - OptionalEdge<llvm_gcc_c, opt, [(switch_on "opt")]>, - OptionalEdge<llvm_gcc_cpp, opt, [(switch_on "opt")]>, + OptionalEdge<"llvm_gcc_c", "opt", (case (switch_on "opt"), + (inc_weight))>, + OptionalEdge<"llvm_gcc_cpp", "opt", (case (switch_on "opt"), + (inc_weight))>, ... - OptionalEdge<llvm_gcc_assembler, llvm_gcc_cpp_linker, + OptionalEdge<"llvm_gcc_assembler", "llvm_gcc_cpp_linker", (case (input_languages_contain "c++"), (inc_weight), (or (parameter_equals "linker", "g++"), (parameter_equals "linker", "c++")), (inc_weight))>, @@ -150,80 +213,50 @@ def CompilationGraph : CompilationGraph<[ ]>;
As you can see, the edges can be either default or optional, where -optional edges are differentiated by sporting a case expression -used to calculate the edge's weight.
+optional edges are differentiated by an additional case expression +used to calculate the weight of this edge. Notice also that we refer +to tools via their names (as strings). This makes it possible to add +edges to an existing compilation graph in plugins without having to +know about all tool definitions used in the graph.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 case expression. It is also possible to provide an integer parameter to inc_weight and dec_weight - in this case, the weight is increased (or decreased) by the provided value instead -of the default 2.
+of the default 2. It is also possible to change the default weight of +an optional edge by using the default clause of the case +construct.When passing an input file through the graph, LLVMC picks the edge with the maximum weight. To avoid ambiguity, there should be only one default edge between two nodes (with the exception of the root node, which gets a special treatment - there you are allowed to specify one default edge per language).
+When multiple plugins are loaded, their compilation graphs are merged +together. Since multiple edges that have the same end nodes are not +allowed (i.e. the graph is not a multigraph), an edge defined in +several plugins will be replaced by the definition from the plugin +that was loaded last. Plugin load order can be controlled by using the +plugin priority feature described above.
To get a visual representation of the compilation graph (useful for -debugging), run llvmc2 --view-graph. You will need dot and +debugging), run llvmc --view-graph. You will need dot and gsview installed for this to work properly.
As was said earlier, nodes in the compilation graph represent tools, -which are described separately. A tool definition looks like this -(taken from the Tools.td file):
+Command-line options that the plugin supports are defined by using an +OptionList:
-def llvm_gcc_cpp : Tool<[ - (in_language "c++"), - (out_language "llvm-assembler"), - (output_suffix "bc"), - (cmd_line "llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm"), - (sink) - ]>; +def Options : OptionList<[ +(switch_option "E", (help "Help string")), +(alias_option "quiet", "q") +... +]>;-
This defines a new tool called llvm_gcc_cpp, which is an alias for -llvm-g++. As you can see, a tool definition is just a list of -properties; most of them should be self-explanatory. The sink -property means that this tool should be passed all command-line -options that lack explicit descriptions.
-The complete list of the currently implemented tool properties follows:
-The next tool definition is slightly more complex:
--def llvm_gcc_linker : Tool<[ - (in_language "object-code"), - (out_language "executable"), - (output_suffix "out"), - (cmd_line "llvm-gcc $INFILE -o $OUTFILE"), - (join), - (prefix_list_option "L", (forward), - (help "add a directory to link path")), - (prefix_list_option "l", (forward), - (help "search a library when linking")), - (prefix_list_option "Wl", (unpack_values), - (help "pass options to linker")) - ]>; --
This tool has a "join" property, which means that it behaves like a -linker. This tool also defines several command-line options: -l, --L and -Wl which have their usual meaning. An option has two -attributes: a name and a (possibly empty) list of properties. All -currently implemented option types and properties are described below:
+As you can see, the option list is just a list of DAGs, where each DAG +is an option description consisting of the option name and some +properties. A plugin can define more than one option list (they are +all merged together in the end), which can be handy if one wants to +separate option groups syntactically.
Possible option types:
@@ -247,88 +280,59 @@ example: (alias_optionPossible option properties:
-
- append_cmd - append a string to the tool invocation command.
-- forward - forward this option unchanged.
-- output_suffix - modify the output suffix of this -tool. Example : (switch "E", (output_suffix "i").
-- stop_compilation - stop compilation after this phase.
-- unpack_values - used for for splitting and forwarding -comma-separated lists of options, e.g. -Wa,-foo=bar,-baz is -converted to -foo=bar -baz and appended to the tool invocation -command.
- help - help string associated with this option. Used for --help output.
- required - this option is obligatory.
+- hidden - this option should not appear in the --help +output (but should appear in the --help-hidden output).
+- really_hidden - the option should not appear in any help +output.
+- extern - this option is defined in some other plugin, see below.
It can be handy to have all information about options gathered in a -single place to provide an overview. This can be achieved by using a -so-called OptionList:
+Sometimes, when linking several plugins together, one plugin needs to +access options defined in some other plugin. Because of the way +options are implemented, such options should be marked as +extern. This is what the extern option property is +for. Example:
-def Options : OptionList<[ -(switch_option "E", (help "Help string")), -(alias_option "quiet", "q") ... -]>; +(switch_option "E", (extern)) +...-
OptionList is also a good place to specify option aliases.
-Tool-specific option properties like append_cmd have (obviously) -no meaning in the context of OptionList, so the only properties -allowed there are help and required.
-Option lists are used at the file scope. See file -examples/Clang.td for an example of OptionList usage.
+See also the section on plugin priorities.
Normally, LLVMC executes programs from the system PATH. Sometimes, -this is not sufficient: for example, we may want to specify tool names -in the configuration file. This can be achieved via the mechanism of -hooks - to compile LLVMC with your hooks, just drop a .cpp file into -tools/llvmc2 directory. Hooks should live in the hooks -namespace and have the signature std::string hooks::MyHookName -(void). They can be used from the cmd_line tool property:
--(cmd_line "$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)") --
It is also possible to use environment variables in the same manner:
--(cmd_line "$ENV(VAR1)/path/to/file -o $ENV(VAR2)") --
To change the command line string based on user-provided options use -the case expression (documented below):
--(cmd_line - (case - (switch_on "E"), - "llvm-g++ -E -x c $INFILE -o $OUTFILE", - (default), - "llvm-g++ -c -x c $INFILE -o $OUTFILE -emit-llvm")) -
The 'case' construct can be used to calculate weights of the optional -edges and to choose between several alternative command line strings -in the cmd_line tool property. It is designed after the -similarly-named construct in functional languages and takes the form -(case (test_1), statement_1, (test_2), statement_2, ... (test_N), -statement_N). The statements are evaluated only if the corresponding -tests evaluate to true.
+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 (case (test_1), statement_1, +(test_2), statement_2, ... (test_N), statement_N). The statements +are evaluated only if the corresponding tests evaluate to true.
Examples:
+// Edge weight calculation + // Increases edge weight by 5 if "-A" is provided on the // command-line, and by 5 more if "-B" is also provided. (case (switch_on "A"), (inc_weight 5), (switch_on "B"), (inc_weight 5)) -// Evaluates to "cmdline1" if option "-A" is provided on the -// command line, otherwise to "cmdline2" + +// Tool command line specification + +// Evaluates to "cmdline1" if the option "-A" is provided on the +// command line; to "cmdline2" if "-B" is provided; +// otherwise to "cmdline3". + (case (switch_on "A"), "cmdline1", (switch_on "B"), "cmdline2", @@ -349,25 +353,25 @@ readability. It is usually better to split tool descriptions and/or use TableGen inheritance instead.
One last thing that you will need to modify when adding support for a -new language to LLVMC is the language map, which defines mappings from -file extensions to language names. It is used to choose the proper -toolchain(s) for a given input file set. Language map definition is -located in the file Tools.td and looks like this:
+As was said earlier, nodes in the compilation graph represent tools, +which are described separately. A tool definition looks like this +(taken from the include/llvm/CompilerDriver/Tools.td file):
++def llvm_gcc_cpp : Tool<[ + (in_language "c++"), + (out_language "llvm-assembler"), + (output_suffix "bc"), + (cmd_line "llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm"), + (sink) + ]>; ++
This defines a new tool called llvm_gcc_cpp, which is an alias for +llvm-g++. As you can see, a tool definition is just a list of +properties; most of them should be self-explanatory. The sink +property means that this tool should be passed all command-line +options that aren't mentioned in the option list.
+The complete list of all currently implemented tool properties follows.
+A tool often needs to react to command-line options, and this is +precisely what the actions property is for. The next example +illustrates this feature:
++def llvm_gcc_linker : Tool<[ + (in_language "object-code"), + (out_language "executable"), + (output_suffix "out"), + (cmd_line "llvm-gcc $INFILE -o $OUTFILE"), + (join), + (actions (case (not_empty "L"), (forward "L"), + (not_empty "l"), (forward "l"), + (not_empty "dummy"), + [(append_cmd "-dummy1"), (append_cmd "-dummy2")]) + ]>; ++
The actions tool property is implemented on top of the omnipresent +case expression. It associates one or more different actions +with given conditions - in the example, the actions are forward, +which forwards a given option unchanged, and append_cmd, which +appends a given string to the tool execution command. Multiple actions +can be associated with a single condition by using a list of actions +(used in the example to append some dummy options). The same case +construct can also be used in the cmd_line property to modify the +tool command line.
+The "join" property used in the example means that this tool behaves +like a linker.
+The list of all possible actions follows.
+Possible actions:
++++
+- append_cmd - append a string to the tool invocation +command. +Example: (case (switch_on "pthread"), (append_cmd "-lpthread"))
+- forward - forward an option unchanged. +Example: (forward "Wall").
+- forward_as - Change the name of an option, but forward the +argument unchanged. +Example: (forward_as "O0" "--disable-optimization").
+- output_suffix - modify the output suffix of this +tool. +Example: (output_suffix "i").
+- stop_compilation - stop compilation after this tool processes +its input. Used without arguments.
+- unpack_values - used for for splitting and forwarding +comma-separated lists of options, e.g. -Wa,-foo=bar,-baz is +converted to -foo=bar -baz and appended to the tool invocation +command. +Example: (unpack_values "Wa,").
+
If you are adding support for a new language to LLVMC, you'll need to +modify the language map, which defines mappings from file extensions +to language names. It is used to choose the proper toolchain(s) for a +given input file set. Language map definition looks like this:
def LanguageMap : LanguageMap< [LangToSuffixes<"c++", ["cc", "cp", "cxx", "cpp", "CPP", "c++", "C"]>, @@ -395,26 +498,106 @@ def LanguageMap : LanguageMap< ... ]>;+
For example, without those definitions the following command wouldn't work:
++$ llvmc hello.cpp +llvmc: Unknown suffix: cpp ++
The language map entries should be added only for tools that are +linked with the root node. Since tools are not allowed to have +multiple output languages, for nodes "inside" the graph the input and +output languages should match. This is enforced at compile-time.
[1] | TableGen Fundamentals + |
[1] | TableGen Fundamentals http://llvm.cs.uiuc.edu/docs/TableGenFundamentals.html |
[2] | Graphviz +http://www.graphviz.org/ |
[3] | Ghostview +http://pages.cs.wisc.edu/~ghost/ |
Author: | +Mikhail Glushenkov <foldr@codedegers.com> |
---|
LLVMC is a generic compiler driver, designed to be customizable and +extensible. It plays the same role for LLVM as the gcc program +does for GCC - LLVMC's job is essentially to transform a set of input +files into a set of targets depending on configuration rules and user +options. What makes LLVMC different is that these transformation rules +are completely customizable - in fact, LLVMC knows nothing about the +specifics of transformation (even the command-line options are mostly +not hard-coded) and regards the transformation structure as an +abstract graph. The structure of this graph is completely determined +by plugins, which can be either statically or dynamically linked. This +makes it possible to easily adapt LLVMC for other purposes - for +example, as a build tool for game resources.
+Because LLVMC employs TableGen [1] as its configuration language, you +need to be familiar with it to customize LLVMC.
+LLVMC tries hard to be as compatible with gcc as possible, +although there are some small differences. Most of the time, however, +you shouldn't be able to notice them:
++$ # This works as expected: +$ llvmc -O3 -Wall hello.cpp +$ ./a.out +hello ++
One nice feature of LLVMC is that one doesn't have to distinguish +between different compilers for different languages (think g++ and +gcc) - 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 -x option, just like you would do it with gcc:
++$ # hello.c is really a C++ file +$ llvmc -x c++ hello.c +$ ./a.out +hello ++
On the other hand, when using LLVMC as a linker to combine several C++ +object files you should provide the --linker option since it's +impossible for LLVMC to choose the right linker in that case:
++$ llvmc -c hello.cpp +$ llvmc hello.o +[A lot of link-time errors skipped] +$ llvmc --linker=c++ hello.o +$ ./a.out +hello ++
By default, LLVMC uses llvm-gcc to compile the source code. It is +also possible to choose the work-in-progress clang compiler with +the -clang option.
+LLVMC has some built-in options that can't be overridden in the +configuration libraries:
+It's easiest to start working on your own LLVMC plugin by copying the +skeleton project which lives under $LLVMC_DIR/plugins/Simple:
++$ cd $LLVMC_DIR/plugins +$ cp -r Simple MyPlugin +$ cd MyPlugin +$ ls +Makefile PluginMain.cpp Simple.td ++
As you can see, our basic plugin consists of only two files (not +counting the build script). Simple.td contains TableGen +description of the compilation graph; its format is documented in the +following sections. PluginMain.cpp is just a helper file used to +compile the auto-generated C++ code produced from TableGen source. It +can also contain hook definitions (see below).
+The first thing that you should do is to change the LLVMC_PLUGIN +variable in the Makefile to avoid conflicts (since this variable +is used to name the resulting library):
++LLVMC_PLUGIN=MyPlugin ++
It is also a good idea to rename Simple.td to something less +generic:
++$ mv Simple.td MyPlugin.td ++
Note that the plugin source directory must be placed under +$LLVMC_DIR/plugins to make use of the existing build +infrastructure. To build a version of the LLVMC executable called +mydriver with your plugin compiled in, use the following command:
++$ cd $LLVMC_DIR +$ make BUILTIN_PLUGINS=MyPlugin DRIVER_NAME=mydriver ++
To build your plugin as a dynamic library, just cd to its source +directory and run make. The resulting file will be called +LLVMC$(LLVMC_PLUGIN).$(DLL_EXTENSION) (in our case, +LLVMCMyPlugin.so). This library can be then loaded in with the +-load option. Example:
++$ cd $LLVMC_DIR/plugins/Simple +$ make +$ llvmc -load $LLVM_DIR/Release/lib/LLVMCSimple.so ++
Sometimes, you will want a 'bare-bones' version of LLVMC that has no +built-in plugins. It can be compiled with the following command:
++$ cd $LLVMC_DIR +$ make BUILTIN_PLUGINS="" ++
Each TableGen configuration file should include the common +definitions:
++include "llvm/CompilerDriver/Common.td" ++
Internally, LLVMC stores information about possible source +transformations in form of a graph. Nodes in this graph represent +tools, and edges between two nodes represent a transformation path. A +special "root" node is used to mark entry points for the +transformations. LLVMC also assigns a weight to each edge (more on +this later) to choose between several alternative edges.
+The definition of the compilation graph (see file +plugins/Base/Base.td for an example) is just a list of edges:
++def CompilationGraph : CompilationGraph<[ + Edge<"root", "llvm_gcc_c">, + Edge<"root", "llvm_gcc_assembler">, + ... + + Edge<"llvm_gcc_c", "llc">, + Edge<"llvm_gcc_cpp", "llc">, + ... + + OptionalEdge<"llvm_gcc_c", "opt", (case (switch_on "opt"), + (inc_weight))>, + OptionalEdge<"llvm_gcc_cpp", "opt", (case (switch_on "opt"), + (inc_weight))>, + ... + + OptionalEdge<"llvm_gcc_assembler", "llvm_gcc_cpp_linker", + (case (input_languages_contain "c++"), (inc_weight), + (or (parameter_equals "linker", "g++"), + (parameter_equals "linker", "c++")), (inc_weight))>, + ... + + ]>; ++
As you can see, the edges can be either default or optional, where +optional edges are differentiated by an additional case expression +used to calculate the weight of this edge. Notice also that we refer +to tools via their names (as strings). This makes it possible to add +edges to an existing compilation graph in plugins without having to +know about all tool definitions used in the graph.
+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 case expression. It is also possible to provide an +integer parameter to inc_weight and dec_weight - 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 default clause of the case +construct.
+When passing an input file through the graph, LLVMC picks the edge +with the maximum weight. To avoid ambiguity, there should be only one +default edge between two nodes (with the exception of the root node, +which gets a special treatment - there you are allowed to specify one +default edge per language).
+When multiple plugins are loaded, their compilation graphs are merged +together. Since multiple edges that have the same end nodes are not +allowed (i.e. the graph is not a multigraph), an edge defined in +several plugins will be replaced by the definition from the plugin +that was loaded last. Plugin load order can be controlled by using the +plugin priority feature described above.
+To get a visual representation of the compilation graph (useful for +debugging), run llvmc --view-graph. You will need dot and +gsview installed for this to work properly.
+Command-line options that the plugin supports are defined by using an +OptionList:
++def Options : OptionList<[ +(switch_option "E", (help "Help string")), +(alias_option "quiet", "q") +... +]>; ++
As you can see, the option list is just a list of DAGs, where each DAG +is an option description consisting of the option name and some +properties. A plugin can define more than one option list (they are +all merged together in the end), which can be handy if one wants to +separate option groups syntactically.
+Possible option types:
++++
+- switch_option - a simple boolean switch, for example -time.
+- parameter_option - option that takes an argument, for example +-std=c99;
+- parameter_list_option - same as the above, but more than one +occurence of the option is allowed.
+- prefix_option - same as the parameter_option, but the option name +and parameter value are not separated.
+- prefix_list_option - same as the above, but more than one +occurence of the option is allowed; example: -lm -lpthread.
+- alias_option - a special option type for creating +aliases. Unlike other option types, aliases are not allowed to +have any properties besides the aliased option name. Usage +example: (alias_option "preprocess", "E")
+
Possible option properties:
++++
+- help - help string associated with this option. Used for +--help output.
+- required - this option is obligatory.
+- hidden - this option should not appear in the --help +output (but should appear in the --help-hidden output).
+- really_hidden - the option should not appear in any help +output.
+- extern - this option is defined in some other plugin, see below.
+
Sometimes, when linking several plugins together, one plugin needs to +access options defined in some other plugin. Because of the way +options are implemented, such options should be marked as +extern. This is what the extern option property is +for. Example:
++... +(switch_option "E", (extern)) +... ++
See also the section on plugin priorities.
+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 (case (test_1), statement_1, +(test_2), statement_2, ... (test_N), statement_N). The statements +are evaluated only if the corresponding tests evaluate to true.
+Examples:
++// Edge weight calculation + +// Increases edge weight by 5 if "-A" is provided on the +// command-line, and by 5 more if "-B" is also provided. +(case + (switch_on "A"), (inc_weight 5), + (switch_on "B"), (inc_weight 5)) + + +// Tool command line specification + +// Evaluates to "cmdline1" if the option "-A" is provided on the +// command line; to "cmdline2" if "-B" is provided; +// otherwise to "cmdline3". + +(case + (switch_on "A"), "cmdline1", + (switch_on "B"), "cmdline2", + (default), "cmdline3") ++
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 "B" switch is never checked when switch "A" is +enabled, and the whole expression always evaluates to "cmdline1" in +that case.
+Case expressions can also be nested, i.e. the following is legal:
++(case (switch_on "E"), (case (switch_on "o"), ..., (default), ...) + (default), ...) ++
You should, however, try to avoid doing that because it hurts +readability. It is usually better to split tool descriptions and/or +use TableGen inheritance instead.
+As was said earlier, nodes in the compilation graph represent tools, +which are described separately. A tool definition looks like this +(taken from the include/llvm/CompilerDriver/Tools.td file):
++def llvm_gcc_cpp : Tool<[ + (in_language "c++"), + (out_language "llvm-assembler"), + (output_suffix "bc"), + (cmd_line "llvm-g++ -c $INFILE -o $OUTFILE -emit-llvm"), + (sink) + ]>; ++
This defines a new tool called llvm_gcc_cpp, which is an alias for +llvm-g++. As you can see, a tool definition is just a list of +properties; most of them should be self-explanatory. The sink +property means that this tool should be passed all command-line +options that aren't mentioned in the option list.
+The complete list of all currently implemented tool properties follows.
+A tool often needs to react to command-line options, and this is +precisely what the actions property is for. The next example +illustrates this feature:
++def llvm_gcc_linker : Tool<[ + (in_language "object-code"), + (out_language "executable"), + (output_suffix "out"), + (cmd_line "llvm-gcc $INFILE -o $OUTFILE"), + (join), + (actions (case (not_empty "L"), (forward "L"), + (not_empty "l"), (forward "l"), + (not_empty "dummy"), + [(append_cmd "-dummy1"), (append_cmd "-dummy2")]) + ]>; ++
The actions tool property is implemented on top of the omnipresent +case expression. It associates one or more different actions +with given conditions - in the example, the actions are forward, +which forwards a given option unchanged, and append_cmd, which +appends a given string to the tool execution command. Multiple actions +can be associated with a single condition by using a list of actions +(used in the example to append some dummy options). The same case +construct can also be used in the cmd_line property to modify the +tool command line.
+The "join" property used in the example means that this tool behaves +like a linker.
+The list of all possible actions follows.
+Possible actions:
++++
+- append_cmd - append a string to the tool invocation +command. +Example: (case (switch_on "pthread"), (append_cmd "-lpthread"))
+- forward - forward an option unchanged. +Example: (forward "Wall").
+- forward_as - Change the name of an option, but forward the +argument unchanged. +Example: (forward_as "O0" "--disable-optimization").
+- output_suffix - modify the output suffix of this +tool. +Example: (output_suffix "i").
+- stop_compilation - stop compilation after this tool processes +its input. Used without arguments.
+- unpack_values - used for for splitting and forwarding +comma-separated lists of options, e.g. -Wa,-foo=bar,-baz is +converted to -foo=bar -baz and appended to the tool invocation +command. +Example: (unpack_values "Wa,").
+
If you are adding support for a new language to LLVMC, you'll need to +modify the language map, which defines mappings from file extensions +to language names. It is used to choose the proper toolchain(s) for a +given input file set. Language map definition looks like this:
++def LanguageMap : LanguageMap< + [LangToSuffixes<"c++", ["cc", "cp", "cxx", "cpp", "CPP", "c++", "C"]>, + LangToSuffixes<"c", ["c"]>, + ... + ]>; ++
For example, without those definitions the following command wouldn't work:
++$ llvmc hello.cpp +llvmc: Unknown suffix: cpp ++
The language map entries should be added only for tools that are +linked with the root node. Since tools are not allowed to have +multiple output languages, for nodes "inside" the graph the input and +output languages should match. This is enforced at compile-time.
+Normally, LLVMC executes programs from the system PATH. Sometimes, +this is not sufficient: for example, we may want to specify tool names +in the configuration file. This can be achieved via the mechanism of +hooks - to write your own hooks, just add their definitions to the +PluginMain.cpp or drop a .cpp file into the +$LLVMC_DIR/driver directory. Hooks should live in the hooks +namespace and have the signature std::string hooks::MyHookName +(void). They can be used from the cmd_line tool property:
++(cmd_line "$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)") ++
It is also possible to use environment variables in the same manner:
++(cmd_line "$ENV(VAR1)/path/to/file -o $ENV(VAR2)") ++
To change the command line string based on user-provided options use +the case expression (documented above):
++(cmd_line + (case + (switch_on "E"), + "llvm-g++ -E -x c $INFILE -o $OUTFILE", + (default), + "llvm-g++ -c -x c $INFILE -o $OUTFILE -emit-llvm")) ++
It is possible for LLVMC plugins to depend on each other. For example, +one can create edges between nodes defined in some other plugin. To +make this work, however, that plugin should be loaded first. To +achieve this, the concept of plugin priority was introduced. By +default, every plugin has priority zero; to specify the priority +explicitly, put the following line in your plugin's TableGen file:
++def Priority : PluginPriority<$PRIORITY_VALUE>; +# Where PRIORITY_VALUE is some integer > 0 ++
Plugins are loaded in order of their (increasing) priority, starting +with 0. Therefore, the plugin with the highest priority value will be +loaded last.
+When writing LLVMC plugins, it can be useful to get a visual view of +the resulting compilation graph. This can be achieved via the command +line option --view-graph. This command assumes that Graphviz [2] and +Ghostview [3] are installed. There is also a --dump-graph option that +creates a Graphviz source file(compilation-graph.dot) in the +current directory.
+[1] | TableGen Fundamentals +http://llvm.cs.uiuc.edu/docs/TableGenFundamentals.html |
[2] | Graphviz +http://www.graphviz.org/ |
[3] | Ghostview +http://pages.cs.wisc.edu/~ghost/ |