X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=docs%2FCompilerDriver.html;h=761d6ee6810db1da1eaff7e5a4d9988e045278b5;hb=f9be95f867745b6754b2402b9b72f9eaeabd637f;hp=253f4719a63269ba4730cbaaddd204d90159c3de;hpb=04367bfc20c021c4105abf0c33b86d55f782d1e8;p=oota-llvm.git diff --git a/docs/CompilerDriver.html b/docs/CompilerDriver.html index 253f4719a63..761d6ee6810 100644 --- a/docs/CompilerDriver.html +++ b/docs/CompilerDriver.html @@ -1,823 +1,735 @@ - - + + +
- -NOTE: This document is a work in progress!
-Contents
+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 as its configuration language, you +need to be familiar with it to customize LLVMC.
This document describes the requirements, design, and configuration of the - LLVM compiler driver, llvmc. The compiler driver knows about LLVM's - tool set and can be configured to know about a variety of compilers for - source languages. It uses this knowledge to execute the tools necessary - to accomplish general compilation, optimization, and linking tasks. The main - purpose of llvmc is to provide a simple and consistent interface to - all compilation tasks. This reduces the burden on the end user who can just - learn to use llvmc instead of the entire LLVM tool set and all the - source language compilers compatible with LLVM.
+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++ vs. 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 clang compiler with the -clang option.
The llvmc tool is a configurable compiler - driver. As such, it isn't a compiler, optimizer, - or a linker itself but it drives (invokes) other software that perform those - tasks. If you are familiar with the GNU Compiler Collection's gcc - tool, llvmc is very similar.
-The following introductory sections will help you understand why this tool - is necessary and what it does.
+LLVMC has some built-in options that can't be overridden in the +configuration libraries:
+llvmc was invented to make compilation of user programs with - LLVM-based tools easier. To accomplish this, llvmc strives to:
-Additionally, llvmc makes it easier to write a compiler for use - with LLVM, because it:
-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 ++
To build your plugin as a dynamic library, just cd to its source +directory and run make. The resulting file will be called +plugin_llvmc_$(LLVMC_PLUGIN).$(DLL_EXTENSION) (in our case, +plugin_llvmc_MyPlugin.so). This library can be then loaded in with the +-load option. Example:
++$ cd $LLVMC_DIR/plugins/Simple +$ make +$ llvmc -load $LLVM_DIR/Release/lib/plugin_llvmc_Simple.so +
At a high level, llvmc operation is very simple. The basic action - taken by llvmc is to simply invoke some tool or set of tools to fill - the user's request for compilation. Every execution of llvmctakes the - following sequence of steps:
-llvmc's operation must be simple, regular and predictable. - Developers need to be able to rely on it to take a consistent approach to - compilation. For example, the invocation:
-
- llvmc -O2 x.c y.c z.c -o xyz
- must produce exactly the same results as:
-- llvmc -O2 x.c -o x.o - llvmc -O2 y.c -o y.o - llvmc -O2 z.c -o z.o - llvmc -O2 x.o y.o z.o -o xyz-
To accomplish this, llvmc uses a very simple goal oriented - procedure to do its work. The overall goal is to produce a functioning - executable. To accomplish this, llvmc always attempts to execute a - series of compilation phases in the same sequence. - However, the user's options to llvmc can cause the sequence of phases - to start in the middle or finish early.
+By default, the llvmc executable consists of a driver core plus several +statically linked plugins (Base and Clang at the moment). You can +produce a standalone LLVMC-based driver executable by linking the core with your +own plugins. The recommended way to do this is by starting with the provided +Skeleton example ($LLVMC_DIR/example/Skeleton):
++$ cd $LLVMC_DIR/example/ +$ cp -r Skeleton mydriver +$ cd mydriver +$ vim Makefile +[...] +$ make ++
If you're compiling LLVM with different source and object directories, then you +must perform the following additional steps before running make:
++# LLVMC_SRC_DIR = $LLVM_SRC_DIR/tools/llvmc/ +# LLVMC_OBJ_DIR = $LLVM_OBJ_DIR/tools/llvmc/ +$ cp $LLVMC_SRC_DIR/example/mydriver/Makefile \ + $LLVMC_OBJ_DIR/example/mydriver/ +$ cd $LLVMC_OBJ_DIR/example/mydriver +$ make ++
Another way to do the same thing is by using the following command:
++$ cd $LLVMC_DIR +$ make LLVMC_BUILTIN_PLUGINS=MyPlugin LLVMC_BASED_DRIVER_NAME=mydriver ++
This works with both srcdir == objdir and srcdir != objdir, but assumes that the +plugin source directory was placed under $LLVMC_DIR/plugins.
+Sometimes, you will want a 'bare-bones' version of LLVMC that has no +built-in plugins. It can be compiled with the following command:
++$ cd $LLVMC_DIR +$ make LLVMC_BUILTIN_PLUGINS="" +
llvmc breaks every compilation task into the following five - distinct phases:
-The following table shows the inputs, outputs, and command line options - applicable to each phase.
-Phase | -Inputs | -Outputs | -Options | -
---|---|---|---|
Preprocessing | -
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Translation | -
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Optimization | -
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Linking | -
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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.
An action, with regard to llvmc is a basic operation that it takes - in order to fulfill the user's request. Each phase of compilation will invoke - zero or more actions in order to accomplish that phase.
-Actions come in two forms:
-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 without arguments, for example +-O2 or -time. At most one occurrence is allowed.
+- parameter_option - option that takes one argument, for example +-std=c99. It is also allowed to use spaces instead of the equality +sign: -std c99. At most one occurrence is allowed.
+- parameter_list_option - same as the above, but more than one option +occurence is allowed.
+- prefix_option - same as the parameter_option, but the option name and +argument do not have to be separated. Example: -ofile. This can be also +specified as -o file; however, -o=file will be parsed incorrectly +(=file will be interpreted as option value). At most one occurrence is +allowed.
+- 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 must be specified exactly once (or, in case of +the list options without the multi_val property, at least +once). Incompatible with zero_or_one and one_or_more.
+- one_or_more - the option must be specified at least one time. Useful +only for list options in conjunction with multi_val; for ordinary lists +it is synonymous with required. Incompatible with required and +zero_or_one.
+- zero_or_one - the option can be specified zero or one times. Useful +only for list options in conjunction with multi_val. Incompatible with +required and one_or_more.
+- hidden - the description of this option will not appear in +the --help output (but will appear in the --help-hidden +output).
+- really_hidden - the option will not be mentioned in any help +output.
+- multi_val n - this option takes n arguments (can be useful in some +special cases). Usage example: (parameter_list_option "foo", (multi_val +3)); the command-line syntax is '-foo a b c'. Only list options can have +this attribute; you can, however, use the one_or_more, zero_or_one +and required properties.
+- init - this option has a default value, either a string (if it is a +parameter), or a boolean (if it is a switch; boolean constants are called +true and false). List options can't have this attribute. Usage +examples: (switch_option "foo", (init true)); (prefix_option "bar", +(init "baz")).
+- 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 must be marked as +extern. This is what the extern option property is +for. Example:
++... +(switch_option "E", (extern)) +... ++
If an external option has additional attributes besides 'extern', they are +ignored. See also the section on plugin priorities.
This section of the document describes the configuration files used by - llvmc. Configuration information is relatively static for a - given release of LLVM and a compiler tool. However, the details may - change from release to release of either. Users are encouraged to simply use - the various options of the llvmc command and ignore the configuration - of the tool. These configuration files are for compiler writers and LLVM - developers. Those wishing to simply use llvmc don't need to understand - this section but it may be instructive on how the tool works.
llvmc is highly configurable both on the command line and in -configuration files. The options it understands are generic, consistent and -simple by design. Furthermore, the llvmc options apply to the -compilation of any LLVM enabled programming language. To be enabled as a -supported source language compiler, a compiler writer must provide a -configuration file that tells llvmc how to invoke the compiler -and what its capabilities are. The purpose of the configuration files then -is to allow compiler writers to specify to llvmc how the compiler -should be invoked. Users may but are not advised to alter the compiler's -llvmc configuration.
- -Because llvmc just invokes other programs, it must deal with the -available command line options for those programs regardless of whether they -were written for LLVM or not. Furthermore, not all compiler tools will -have the same capabilities. Some compiler tools will simply generate LLVM assembly -code, others will be able to generate fully optimized bitcode. In general, -llvmc doesn't make any assumptions about the capabilities or command -line options of a sub-tool. It simply uses the details found in the -configuration files and leaves it to the compiler writer to specify the -configuration correctly.
- -This approach means that new compiler tools can be up and working very -quickly. As a first cut, a tool can simply compile its source to raw -(unoptimized) bitcode or LLVM assembly and llvmc can be configured -to pick up the slack (translate LLVM assembly to bitcode, optimize the -bitcode, generate native assembly, link, etc.). In fact, the compiler tools -need not use any LLVM libraries, and it could be written in any language -(instead of C++). The configuration data will allow the full range of -optimization, assembly, and linking capabilities that LLVM provides to be added -to these kinds of tools. Enabling the rapid development of front-ends is one -of the primary goals of llvmc.
- -As a compiler tool matures, it may utilize the LLVM libraries and tools -to more efficiently produce optimized bitcode directly in a single compilation -and optimization program. In these cases, multiple tools would not be needed -and the configuration data for the compiler would change.
- -Configuring llvmc to the needs and capabilities of a source language -compiler is relatively straight-forward. A compiler writer must provide a -definition of what to do for each of the five compilation phases for each of -the optimization levels. The specification consists simply of prototypical -command lines into which llvmc can substitute command line -arguments and file names. Note that any given phase can be completely blank if -the source language's compiler combines multiple phases into a single program. -For example, quite often pre-processing, translation, and optimization are -combined into a single program. The specification for such a compiler would have -blank entries for pre-processing and translation but a full command line for -optimization.
+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.
+Each configuration file provides the details for a single source language - that is to be compiled. This configuration information tells llvmc - how to invoke the language's pre-processor, translator, optimizer, assembler - and linker. Note that a given source language needn't provide all these tools - as many of them exist in llvm currently.
+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"))
+- error - exit with error. +Example: (error "Mixing -c and -S is not allowed!").
+- warning - print a warning. +Example: (warning "Specifying both -O1 and -O2 is meaningless!").
+- 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,").
+
llvmc always looks for files of a specific name. It uses the
- first file with the name its looking for by searching directories in the
- following order:
-
The first file found in this search will be used. Other files with the - same name will be ignored even if they exist in one of the subsequent search - locations.
In the directories searched, each configuration file is given a specific - name to foster faster lookup (so llvmc doesn't have to do directory searches). - The name of a given language specific configuration file is simply the same - as the suffix used to identify files containing source in that language. - For example, a configuration file for C++ source might be named - cpp, C, or cxx. For languages that support multiple - file suffixes, multiple (probably identical) files (or symbolic links) will - need to be provided.
+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.
Which configuration files are read depends on the command line options and - the suffixes of the file names provided on llvmc's command line. Note - that the -x LANGUAGE option alters the language that llvmc - uses for the subsequent files on the command line. Only the configuration - files actually needed to complete llvmc's task are read. Other - language specific files will be ignored.
+It is sometimes useful to run error-checking code before processing the +compilation graph. For example, if optimization options "-O1" and "-O2" are +implemented as switches, we might want to output a warning if the user invokes +the driver with both of these options enabled.
+The OptionPreprocessor feature is reserved specially for these +occasions. Example (adapted from the built-in Base plugin):
++def Preprocess : OptionPreprocessor< +(case (and (switch_on "O3"), (any_switch_on ["O0", "O1", "O2"])), + [(unset_option ["O0", "O1", "O2"]), + (warning "Multiple -O options specified, defaulted to -O3.")], + (and (switch_on "O2"), (any_switch_on ["O0", "O1"])), + (unset_option ["O0", "O1"]), + (and (switch_on "O1"), (switch_on "O0")), + (unset_option "O0")) +>; ++
Here, OptionPreprocessor is used to unset all spurious optimization options +(so that they are not forwarded to the compiler).
+OptionPreprocessor is basically a single big case expression, which is +evaluated only once right after the plugin is loaded. The only allowed actions +in OptionPreprocessor are error, warning and a special action +unset_option, which, as the name suggests, unsets a given option. For +convenience, unset_option also works on lists.
The syntax of the configuration files is very simple and somewhat - compatible with Java's property files. Here are the syntax rules:
-Normally, LLVMC executes programs from the system PATH. Sometimes, +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 PluginMain.cpp or drop a .cpp file into the +your plugin directory. Hooks should live in the hooks namespace +and have the signature std::string hooks::MyHookName ([const char* +Arg0 [ const char* Arg2 [, ...]]]). They can be used from the +cmd_line tool property:
++(cmd_line "$CALL(MyHook)/path/to/file -o $CALL(AnotherHook)") ++
To pass arguments to hooks, use the following syntax:
++(cmd_line "$CALL(MyHook, 'Arg1', 'Arg2', 'Arg # 3')/path/to/file -o1 -o2") ++
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")) +
The table below provides definitions of the allowed configuration items - that may appear in a configuration file. Every item has a default value and - does not need to appear in the configuration file. Missing items will have the - default value. Each identifier may appear as all lower case, first letter - capitalized or all upper case.
-Name | -Value Type | -Description | -Default | -
---|---|---|---|
LLVMC ITEMS | |||
version | -string | -Provides the version string for the contents of this - configuration file. What is accepted as a legal configuration file - will change over time and this item tells llvmc which version - should be expected. | -b | -
LANG ITEMS | |||
lang.name | -string | -Provides the common name for a language definition. - For example "C++", "Pascal", "FORTRAN", etc. | -blank | -
lang.opt1 | -string | -Specifies the parameters to give the optimizer when - -O1 is specified on the llvmc command line. | --simplifycfg -instcombine -mem2reg | -
lang.opt2 | -string | -Specifies the parameters to give the optimizer when - -O2 is specified on the llvmc command line. | -TBD | -
lang.opt3 | -string | -Specifies the parameters to give the optimizer when - -O3 is specified on the llvmc command line. | -TBD | -
lang.opt4 | -string | -Specifies the parameters to give the optimizer when - -O4 is specified on the llvmc command line. | -TBD | -
lang.opt5 | -string | -Specifies the parameters to give the optimizer when - -O5 is specified on the llvmc command line. | -TBD | -
PREPROCESSOR ITEMS | |||
preprocessor.command | -command | -This provides the command prototype that will be used - to run the preprocessor. This is generally only used with the - -E option. | -<blank> | -
preprocessor.required | -boolean | -This item specifies whether the pre-processing phase - is required by the language. If the value is true, then the - preprocessor.command value must not be blank. With this option, - llvmc will always run the preprocessor as it assumes that the - translation and optimization phases don't know how to pre-process their - input. | -false | -
TRANSLATOR ITEMS | |||
translator.command | -command | -This provides the command prototype that will be used - to run the translator. Valid substitutions are %in% for the - input file and %out% for the output file. | -<blank> | -
translator.output | -bitcode or assembly | -This item specifies the kind of output the language's - translator generates. | -bitcode | -
translator.preprocesses | -boolean | -Indicates that the translator also preprocesses. If - this is true, then llvmc will skip the pre-processing phase - whenever the final phase is not pre-processing. | -false | -
OPTIMIZER ITEMS | |||
optimizer.command | -command | -This provides the command prototype that will be used - to run the optimizer. Valid substitutions are %in% for the - input file and %out% for the output file. | -<blank> | -
optimizer.output | -bitcode or assembly | -This item specifies the kind of output the language's - optimizer generates. Valid values are "assembly" and "bitcode" | -bitcode | -
optimizer.preprocesses | -boolean | -Indicates that the optimizer also preprocesses. If - this is true, then llvmc will skip the pre-processing phase - whenever the final phase is optimization or later. | -false | -
optimizer.translates | -boolean | -Indicates that the optimizer also translates. If - this is true, then llvmc will skip the translation phase - whenever the final phase is optimization or later. | -false | -
ASSEMBLER ITEMS | |||
assembler.command | -command | -This provides the command prototype that will be used - to run the assembler. Valid substitutions are %in% for the - input file and %out% for the output file. | -<blank> | -
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.
On any configuration item that ends in command, you must - specify substitution tokens. Substitution tokens begin and end with a percent - sign (%) and are replaced by the corresponding text. Any substitution - token may be given on any command line but some are more useful than - others. In particular each command should have both an %in% - and an %out% substitution. The table below provides definitions of - each of the allowed substitution tokens.
-Substitution Token | -Replacement Description | -
---|---|
%args% | -Replaced with all the tool-specific arguments given - to llvmc via the -T set of options. This just allows - you to place these arguments in the correct place on the command line. - If the %args% option does not appear on your command line, - then you are explicitly disallowing the -T option for your - tool. - | -
%force% | -Replaced with the -f option if it was - specified on the llvmc command line. This is intended to tell - the compiler tool to force the overwrite of output files. - | -
%in% | -Replaced with the full path of the input file. You - needn't worry about the cascading of file names. llvmc will - create temporary files and ensure that the output of one phase is the - input to the next phase. | -
%opt% | -Replaced with the optimization options for the - tool. If the tool understands the -O options then that will - be passed. Otherwise, the lang.optN series of configuration - items will specify which arguments are to be given. | -
%out% | -Replaced with the full path of the output file. - Note that this is not necessarily the output file specified with the - -o option on llvmc's command line. It might be a - temporary file that will be passed to a subsequent phase's input. - | -
%stats% | -If your command accepts the -stats option, - use this substitution token. If the user requested -stats - from the llvmc command line then this token will be replaced - with -stats, otherwise it will be ignored. - | -
%target% | -Replaced with the name of the target "machine" for - which code should be generated. The value used here is taken from the - llvmc option -march. - | -
%time% | -If your command accepts the -time-passes - option, use this substitution token. If the user requested - -time-passes from the llvmc command line then this - token will be replaced with -time-passes, otherwise it will - be ignored. - | -
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 and +Ghostview are installed. There is also a --write-graph option that +creates a Graphviz source file (compilation-graph.dot) in the +current directory.
+Another useful llvmc option is --check-graph. 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 --check-graph, llvmc doesn't +perform any compilation tasks and returns the number of encountered +errors as its status code.
For now, the executable name (the value passed to the driver in argv[0]) is +accessible only in the C++ code (i.e. hooks). Use the following code:
++namespace llvmc { +extern const char* ProgramName; +} + +std::string MyHook() { +//... +if (strcmp(ProgramName, "mydriver") == 0) { + //... + +} ++
In general, you're encouraged not to make the behaviour dependent on the +executable file name, and use command-line switches instead. See for example how +the Base plugin behaves when it needs to choose the correct linker options +(think g++ vs. gcc).
+Since an example is always instructive, here's how the Stacker language - configuration file looks.
--# Stacker Configuration File For llvmc - -########################################################## -# Language definitions -########################################################## - lang.name=Stacker - lang.opt1=-simplifycfg -instcombine -mem2reg - lang.opt2=-simplifycfg -instcombine -mem2reg -load-vn \ - -gcse -dse -scalarrepl -sccp - lang.opt3=-simplifycfg -instcombine -mem2reg -load-vn \ - -gcse -dse -scalarrepl -sccp -branch-combine -adce \ - -globaldce -inline -licm - lang.opt4=-simplifycfg -instcombine -mem2reg -load-vn \ - -gcse -dse -scalarrepl -sccp -ipconstprop \ - -branch-combine -adce -globaldce -inline -licm - lang.opt5=-simplifycfg -instcombine -mem2reg --load-vn \ - -gcse -dse scalarrepl -sccp -ipconstprop \ - -branch-combine -adce -globaldce -inline -licm \ - -block-placement - -########################################################## -# Pre-processor definitions -########################################################## - - # Stacker doesn't have a preprocessor but the following - # allows the -E option to be supported - preprocessor.command=cp %in% %out% - preprocessor.required=false - -########################################################## -# Translator definitions -########################################################## - - # To compile stacker source, we just run the stacker - # compiler with a default stack size of 2048 entries. - translator.command=stkrc -s 2048 %in% -o %out% %time% \ - %stats% %force% %args% - - # stkrc doesn't preprocess but we set this to true so - # that we don't run the cp command by default. - translator.preprocesses=true - - # The translator is required to run. - translator.required=true - - # stkrc doesn't handle the -On options - translator.output=bitcode - -########################################################## -# Optimizer definitions -########################################################## - - # For optimization, we use the LLVM "opt" program - optimizer.command=opt %in% -o %out% %opt% %time% %stats% \ - %force% %args% - - optimizer.required = true - - # opt doesn't translate - optimizer.translates = no - - # opt doesn't preprocess - optimizer.preprocesses=no - - # opt produces bitcode - optimizer.output = bc - -########################################################## -# Assembler definitions -########################################################## - assembler.command=llc %in% -o %out% %target% %time% %stats% --
This document uses precise terms in reference to the various artifacts and - concepts related to compilation. The terms used throughout this document are - defined below.
-