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< title > Tutorial - Using LLVMC< / title >
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< h1 class = "title" > Tutorial - Using LLVMC< / h1 >
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< div class = "contents topic" id = "contents" >
< p class = "topic-title first" > Contents< / p >
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< ul class = "simple" >
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< li > < a class = "reference internal" href = "#introduction" id = "id1" > Introduction< / a > < / li >
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< li > < a class = "reference internal" href = "#using-the-llvmc-program" id = "id2" > Using the < tt class = "docutils literal" > llvmc< / tt > program< / a > < / li >
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< li > < a class = "reference internal" href = "#using-llvmc-to-generate-toolchain-drivers" id = "id3" > Using LLVMC to generate toolchain drivers< / a > < / li >
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< / ul >
< / div >
< div class = "doc_author" >
< p > Written by < a href = "mailto:foldr@codedgers.com" > Mikhail Glushenkov< / a > < / p >
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< / div > < div class = "section" id = "introduction" >
< h1 > < a class = "toc-backref" href = "#id1" > Introduction< / a > < / h1 >
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< p > LLVMC is a generic compiler driver, which plays the same role for LLVM as the
< tt class = "docutils literal" > gcc< / tt > program does for GCC - the difference being that LLVMC is designed to be
more adaptable and easier to customize. Most of LLVMC functionality is
implemented via high-level TableGen code, from which a corresponding C++ source
file is automatically generated. This tutorial describes the basic usage and
configuration of LLVMC.< / p >
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< / div >
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< div class = "section" id = "using-the-llvmc-program" >
< h1 > < a class = "toc-backref" href = "#id2" > Using the < tt class = "docutils literal" > llvmc< / tt > program< / a > < / h1 >
< p > In general, < tt class = "docutils literal" > llvmc< / tt > tries to be command-line compatible with < tt class = "docutils literal" > gcc< / tt > as much
as possible, so most of the familiar options work:< / p >
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< pre class = "literal-block" >
$ llvmc -O3 -Wall hello.cpp
$ ./a.out
hello
< / pre >
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< p > This will invoke < tt class = "docutils literal" > < span class = "pre" > llvm-g++< / span > < / tt > under the hood (you can see which commands are
executed by using the < tt class = "docutils literal" > < span class = "pre" > -v< / span > < / tt > option). For further help on command-line LLVMC
usage, refer to the < tt class = "docutils literal" > llvmc < span class = "pre" > --help< / span > < / tt > output.< / p >
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< / div >
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< div class = "section" id = "using-llvmc-to-generate-toolchain-drivers" >
< h1 > < a class = "toc-backref" href = "#id3" > Using LLVMC to generate toolchain drivers< / a > < / h1 >
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< p > LLVMC-based drivers are written mostly using < a class = "reference external" href = "http://llvm.org/docs/TableGenFundamentals.html" > TableGen< / a > , so you need to be
familiar with it to get anything done.< / p >
< p > Start by compiling < tt class = "docutils literal" > example/Simple< / tt > , which is a primitive wrapper for
< tt class = "docutils literal" > gcc< / tt > :< / p >
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< pre class = "literal-block" >
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$ cd $LLVM_OBJ_DIR/tools/examples/Simple
$ make
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$ cat > hello.c
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#include < stdio.h>
int main() { printf(" Hello\n" ); }
$ $LLVM_BIN_DIR/Simple -v hello.c
gcc hello.c -o hello.out
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$ ./hello.out
Hello
< / pre >
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< p > We have thus produced a simple driver called, appropriately, < tt class = "docutils literal" > Simple< / tt > , from
the input TableGen file < tt class = "docutils literal" > Simple.td< / tt > . The < tt class = "docutils literal" > llvmc< / tt > program itself is generated
using a similar process (see < tt class = "docutils literal" > llvmc/src< / tt > ). Contents of the file < tt class = "docutils literal" > Simple.td< / tt >
look like this:< / p >
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< pre class = "literal-block" >
// Include common definitions
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include " llvm/CompilerDriver/Common.td"
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// Tool descriptions
def gcc : Tool<
[(in_language " c" ),
(out_language " executable" ),
(output_suffix " out" ),
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(command " gcc" ),
(sink),
// -o is what is used by default, out_file_option here is included for
// instructive purposes.
(out_file_option " -o" )
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]> ;
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// Language map
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def LanguageMap : LanguageMap< [(lang_to_suffixes " c" , " c" )]> ;
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// Compilation graph
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def CompilationGraph : CompilationGraph< [(edge " root" , " gcc" )]> ;
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< / pre >
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< p > As you can see, this file consists of three parts: tool descriptions, language
map, and the compilation graph definition.< / p >
< p > At the heart of LLVMC is the idea of a compilation graph: vertices in this graph
are tools, and edges represent a transformation path between two tools (for
example, assembly source produced by the compiler can be transformed into
executable code by an assembler). The compilation graph is basically a list of
edges; a special node named < tt class = "docutils literal" > root< / tt > is used to mark graph entry points.< / p >
< p > Tool descriptions are represented as property lists: most properties in the
example above should be self-explanatory; the < tt class = "docutils literal" > sink< / tt > property means that all
options lacking an explicit description should be forwarded to this tool.< / p >
< p > The < tt class = "docutils literal" > LanguageMap< / tt > associates a language name with a list of suffixes and is
used for deciding which toolchain corresponds to a given input file.< / p >
< p > To learn more about writing your own drivers with LLVMC, refer to the reference
manual and examples in the < tt class = "docutils literal" > examples< / tt > directory. Of a particular interest is
the < tt class = "docutils literal" > Skeleton< / tt > example, which can serve as a template for your LLVMC-based
drivers.< / p >
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< hr / >
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< address >
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< a href = "mailto:foldr@codedgers.com" > Mikhail Glushenkov< / a > < br / >
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< a href = "http://llvm.org" > LLVM Compiler Infrastructure< / a > < br / >
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