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93 lines
2.7 KiB
ReStructuredText
======================
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Tutorial - Using LLVMC
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======================
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LLVMC is a generic compiler driver, which plays the same role for LLVM
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as the ``gcc`` program does for GCC - the difference being that LLVMC
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is designed to be more adaptable and easier to customize. This
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tutorial describes the basic usage and configuration of LLVMC.
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.. contents::
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Compiling with LLVMC
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====================
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In general, LLVMC tries to be command-line compatible with ``gcc`` as
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much as possible, so most of the familiar options work::
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$ llvmc2 -O3 -Wall hello.cpp
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$ ./a.out
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hello
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For further help on command-line LLVMC usage, refer to the ``llvmc
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--help`` output.
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Using LLVMC to generate toolchain drivers
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=========================================
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At the time of writing LLVMC does not support on-the-fly reloading of
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configuration, so it will be necessary to recompile its source
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code. LLVMC uses TableGen [1]_ as its configuration language, so
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you'll need to familiar with it.
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Start by compiling ``examples/Simple.td``, which is a simple wrapper
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for ``gcc``::
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$ cd $LLVM_DIR/tools/llvmc2
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$ make TOOLNAME=mygcc GRAPH=examples/Simple.td
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$ edit hello.c
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$ mygcc hello.c
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$ ./hello.out
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Hello
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Contents of the file ``Simple.td`` look like this::
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// Include common definitions
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include "Common.td"
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// Tool descriptions
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def gcc : Tool<
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[(in_language "c"),
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(out_language "executable"),
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(output_suffix "out"),
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(cmd_line "gcc $INFILE -o $OUTFILE"),
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(sink)
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]>;
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// Language map
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def LanguageMap : LanguageMap<[LangToSuffixes<"c", ["c"]>]>;
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// Compilation graph
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def CompilationGraph : CompilationGraph<[Edge<root, gcc>]>;
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As you can see, this file consists of three parts: tool descriptions,
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language map, and the compilation graph definition.
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At the heart of LLVMC is the idea of a transformation graph: vertices
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in this graph are tools, and edges signify that there is a
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transformation path between two tools (for example, assembly source
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produced by the compiler can be transformed into executable code by an
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assembler). A special node named ``root`` is used to mark the graph
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entry points.
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Tool descriptions are basically lists of properties: most properties
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in the example above should be self-explanatory; the ``sink`` property
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means that all options lacking an explicit description should be
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forwarded to this tool.
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``LanguageMap`` associates a language name with a list of suffixes and
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is used for deciding which toolchain corresponds to a given input
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file.
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To learn more about LLVMC customization, refer to the reference
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manual and sample configuration files in the ``examples`` directory.
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References
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==========
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.. [1] TableGen Fundamentals
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http://llvm.cs.uiuc.edu/docs/TableGenFundamentals.html
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