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.
-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 was invented to make compilation of user programs with - LLVM-based tools easier. To accomplish this, llvmc strives to:
--
-
- Be the single point of access to most of the LLVM tool set. -
- Hide the complexities of the LLVM tools through a single interface. -
- Provide a consistent interface for compiling all languages. -
Additionally, llvmc makes it easier to write a compiler for use - with LLVM, because it:
--
-
- Makes integration of existing non-LLVM tools simple. -
- Extends the capabilities of minimal compiler tools by optimizing their - output. -
- Reduces the number of interfaces a compiler writer must know about - before a working compiler can be completed (essentially only the VMCore - interfaces need to be understood). -
- Supports source language translator invocation via both dynamically - loadable shared objects and invocation of an executable. -
Note: This document is a work-in-progress. Additions and clarifications + are welcome.
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:
--
-
- Collect Command Line Options -
- The command line options provide the marching orders to llvmc - on what actions it should perform. This is the request the user is making - of llvmc and it is interpreted first. See the llvmc - manual page for details on the - options. -
- Read Configuration Files -
- Based on the options and the suffixes of the filenames presented, a set - of configuration files are read to configure the actions llvmc will - take. Configuration files are provided by either LLVM or the - compiler tools that llvmc invokes. These files determine what - actions llvmc will take in response to the user's request. See - the section on configuration for more details. - -
- Determine Phases To Execute -
- Based on the command line options and configuration files, - llvmc determines the compilation phases that - must be executed by the user's request. This is the primary work of - llvmc. -
- Determine Actions To Execute -
- Each phase to be executed can result in the - invocation of one or more actions. An action is - either a whole program or a function in a dynamically linked shared library. - In this step, llvmc determines the sequence of actions that must be - executed. Actions will always be executed in a deterministic order. -
- Execute Actions -
- The actions necessary to support the user's - original request are executed sequentially and deterministically. All - actions result in either the invocation of a whole program to perform the - action or the loading of a dynamically linkable shared library and invocation - of a standard interface function within that library. -
- Termination -
- If any action fails (returns a non-zero result code), llvmc - also fails and returns the result code from the failing action. If - everything succeeds, llvmc will return a zero result code. -
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.
+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. 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 +need to be familiar with it to customize LLVMC.
+-
+
- Compiling with LLVMC +
- Predefined options +
- Customizing LLVMC: the compilation graph +
- Writing a tool description +
- Option list - specifying all options in a single place +
- Using hooks and environment variables in the cmd_line property +
- Conditional evaluation: the case expression +
- Language map +
- References +
llvmc breaks every compilation task into the following five - distinct phases:
-- Preprocessing
- Not all languages support preprocessing; - but for those that do, this phase can be invoked. This phase is for - languages that provide combining, filtering, or otherwise altering with the - source language input before the translator parses it. Although C and C++ - are the most common users of this phase, other languages may provide their - own preprocessor (whether its the C pre-processor or not). -
- Translation
- The translation phase converts the source - language input into something that LLVM can interpret and use for - downstream phases. The translation is essentially from "non-LLVM form" to - "LLVM form". -
- Optimization
- Once an LLVM Module has been obtained from - the translation phase, the program enters the optimization phase. This phase - attempts to optimize all of the input provided on the command line according - to the options provided. -
- Linking
- The inputs are combined to form a complete - program. -
The following table shows the inputs, outputs, and command line options - applicabe to each phase.
-| Phase | -Inputs | -Outputs | -Options | -
|---|---|---|---|
| Preprocessing | -
|
-
|
-
|
-
| Translation | -
|
-
|
-
|
-
| Optimization | -
|
-
|
-
|
-
| Linking | -
|
-
|
-
|
-
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:
--
-
- Invokable Executables -
- Functions in a shared library -
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 +$ ./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:
++$ llvmc2 -x c hello.cpp +$ # hello.cpp is really a C file +$ ./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:
++$ llvmc2 -c hello.cpp +$ llvmc2 hello.o +[A lot of link-time errors skipped] +$ llvmc2 --linker=c++ hello.o +$ ./a.out +hello +
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 has some built-in options that can't be overridden in the +configuration files:
+-
+
- -o FILE - Output file name. +
- -x LANGUAGE - Specify the language of the following input files +until the next -x option. +
- -v - Enable verbose mode, i.e. print out all executed commands. +
- --view-graph - Show a graphical representation of the compilation +graph. Requires that you have dot and gv commands +installed. Hidden option, useful for debugging. +
- --write-graph - Write a compilation-graph.dot file in the +current directory with the compilation graph description in the +Graphviz format. Hidden option, useful for debugging. +
- --save-temps - Write temporary files to the current directory +and do not delete them on exit. Hidden option, useful for debugging. +
- --help, --help-hidden, --version - These options have +their standard meaning. +
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 byte code. 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) bytecode or LLVM assembly and llvmc can be configured -to pick up the slack (translate LLVM assembly to bytecode, optimize the -bytecode, 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 bytecode 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.
-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.
+ +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 $LLVM_DIR/tools/llvmc2). The +default configuration files are Common.td (contains common +definitions, don't forget to include it in your configuration +files), Tools.td (tool descriptions) and Graph.td (compilation +graph definition).
+To compile LLVMC with your own configuration file (say,``MyGraph.td``), +run make like this:
++$ cd $LLVM_DIR/tools/llvmc2 +$ make GRAPH=MyGraph.td TOOLNAME=my_llvmc ++
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:
++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, [(switch_on "opt")]>, + OptionalEdge<llvm_gcc_cpp, opt, [(switch_on "opt")]>, + ... + + 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 sporting a case expression +used to calculate the edge's weight.
+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.
+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).
+To get a visual representation of the compilation graph (useful for +debugging), run llvmc2 --view-graph. You will need dot and +gsview installed for this to work properly.
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:
-
-
-
- Any directory specified by the -config-dir option will be - checked first. -
- If the environment variable LLVM_CONFIG_DIR is set, and it contains - the name of a valid directory, that directory will be searched next. -
- If the user's home directory (typically /home/user contains - a sub-directory named .llvm and that directory contains a - sub-directory named etc then that directory will be tried - next. -
- If the LLVM installation directory (typically /usr/local/llvm - contains a sub-directory named etc then that directory will be - tried last. -
- A standard "system" directory will be searched next. This is typically - /etc/llvm on UNIX™ and C:\WINNT on Microsoft - Windows™. -
- If the configuration file sought still can't be found, llvmc - will print an error message and exit. -
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.
+ +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):
++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 lack explicit descriptions.
+The complete list of the currently implemented tool properties follows:
+-
+
- Possible tool properties:
-
+
- in_language - input language name. +
- out_language - output language name. +
- output_suffix - output file suffix. +
- cmd_line - the actual command used to run the tool. You can +use $INFILE and $OUTFILE variables, output redirection +with >, hook invocations ($CALL), environment variables +(via $ENV) and the case construct (more on this below). +
- join - this tool is a "join node" in the graph, i.e. it gets a +list of input files and joins them together. Used for linkers. +
- sink - all command-line options that are not handled by other +tools are passed to this tool. +
+
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:
+-
+
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:
++
+-
+
- 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. +
+
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.
+ +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:
++def Options : OptionList<[ +(switch_option "E", (help "Help string")), +(alias_option "quiet", "q") +... +]>; ++
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.
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.
+ +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 syntax of the configuration files is very simple and somewhat - compatible with Java's property files. Here are the syntax rules:
--
-
- The file encoding is ASCII. -
- The file is line oriented. There should be one configuration definition - per line. Lines are terminated by the newline (0x0A) and/or carriage return - characters (0x0D) -
- A backslash (\) before a newline causes the newline to be - ignored. This is useful for line continuation of long definitions. A - backslash anywhere else is recognized as a backslash. -
- A configuration item consists of a name, an = and a value. -
- A name consists of a sequence of identifiers separated by period. -
- An identifier consists of specific keywords made up of only lower case - and upper case letters (e.g. lang.name). -
- Values come in four flavors: booleans, integers, commands and - strings. -
- Valid "false" boolean values are false False FALSE no No NO - off Off and OFF. -
- Valid "true" boolean values are true True TRUE yes Yes YES - on On and ON. -
- Integers are simply sequences of digits. -
- Commands start with a program name and are followed by a sequence of - words that are passed to that program as command line arguments. Program - arguments that begin and end with the % sign will have their value - substituted. Program names beginning with / are considered to be - absolute. Otherwise the PATH will be applied to find the program to - execute. -
- Strings are composed of multiple sequences of characters from the - character class [-A-Za-z0-9_:%+/\\|,] separated by white - space. -
- White space on a line is folded. Multiple blanks or tabs will be - reduced to a single blank. -
- White space before the configuration item's name is ignored. -
- White space on either side of the = is ignored. -
- White space in a string value is used to separate the individual - components of the string value but otherwise ignored. -
- Comments are introduced by the # character. Everything after a - # and before the end of line is ignored. -
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.
+Examples:
++// 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" +(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.
+-
+
- Possible tests are:
-
+
- switch_on - Returns true if a given command-line option is +provided by the user. Example: (switch_on "opt"). Note that +you have to define all possible command-line options separately in +the tool descriptions. See the next doc_text for the discussion of +different kinds of command-line options. +
- parameter_equals - Returns true if a command-line parameter equals +a given value. Example: (parameter_equals "W", "all"). +
- element_in_list - Returns true if a command-line parameter list +includes a given value. Example: (parameter_in_list "l", "pthread"). +
- input_languages_contain - Returns true if a given language +belongs to the current input language set. Example: +`(input_languages_contain "c++"). +
- in_language - Evaluates to true if the language of the input +file equals to the argument. Valid only when using case +expression in a cmd_line tool property. Example: +`(in_language "c++"). +
- not_empty - Returns true if a given option (which should be +either a parameter or a parameter list) is set by the +user. Example: `(not_empty "o"). +
- default - Always evaluates to true. Should always be the last +test in the case expression. +
- and - A standard logical combinator that returns true iff all +of its arguments return true. Used like this: (and (test1), +(test2), ... (testN)). Nesting of and and or is allowed, +but not encouraged. +
- or - Another logical combinator that returns true only if any +one of its arguments returns true. Example: (or (test1), +(test2), ... (testN)). +
+
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 | -bytecode or assembly | -This item specifies the kind of output the language's - translator generates. | -bytecode | -|
| 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 | -bytecode or assembly | -This item specifies the kind of output the language's - optimizer generates. Valid values are "assembly" and "bytecode" | - | bytecode | -
| 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> | -|
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:
++def LanguageMap : LanguageMap< + [LangToSuffixes<"c++", ["cc", "cp", "cxx", "cpp", "CPP", "c++", "C"]>, + LangToSuffixes<"c", ["c"]>, + ... + ]>; +
On any configruation 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% substittution. 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. - | -
| [1] | TableGen Fundamentals +http://llvm.cs.uiuc.edu/docs/TableGenFundamentals.html |
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=bytecode - -########################################################## -# 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 bytecode - 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.
--
-
- assembly -
- A compilation phase in which LLVM bytecode or - LLVM assembly code is assembled to a native code format (either target - specific aseembly language or the platform's native object file format). - - -
- compiler -
- Refers to any program that can be invoked by llvmc to accomplish - the work of one or more compilation phases. - -
- driver -
- Refers to llvmc itself. - -
- linking -
- A compilation phase in which LLVM bytecode files - and (optionally) native system libraries are combined to form a complete - executable program. - -
- optimization -
- A compilation phase in which LLVM bytecode is - optimized. - -
- phase -
- Refers to any one of the five compilation phases that that - llvmc supports. The five phases are: - preprocessing, - translation, - optimization, - assembly, - linking. - -
- source language -
- Any common programming language (e.g. C, C++, Java, Stacker, ML, - FORTRAN). These languages are distinguished from any of the lower level - languages (such as LLVM or native assembly), by the fact that a - translation phase - is required before LLVM can be applied. - -
- tool -
- Refers to any program in the LLVM tool set. - -
- translation -
- A compilation phase in which - source language code is translated into - either LLVM assembly language or LLVM bytecode. -
-
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