203 lines
5.0 KiB
HTML
203 lines
5.0 KiB
HTML
<HTML>
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<TITLE>llvmpipe</TITLE>
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<link rel="stylesheet" type="text/css" href="mesa.css"></head>
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<BODY>
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<H1>Introduction</H1>
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<p>
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The Gallium llvmpipe driver is a software rasterizer that uses LLVM to
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do runtime code generation.
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Shaders, point/line/triangle rasterization and vertex processing are
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implemented with LLVM IR which is translated to x86 or x86-64 machine
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code.
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Also, the driver is multithreaded to take advantage of multiple CPU cores
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(up to 8 at this time).
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It's the fastest software rasterizer for Mesa.
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</p>
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<h1>Requirements</h1>
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<ul>
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<li>
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<p>An x86 or amd64 processor; 64-bit mode recommended.</p
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<p>
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Support for SSE2 is strongly encouraged. Support for SSSE3, and SSE4.1 will
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yield the most efficient code. The less features the CPU has the more
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likely is that you ran into underperforming, buggy, or incomplete code.
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</p>
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<p>
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See /proc/cpuinfo to know what your CPU supports.
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</p>
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</li>
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<li>
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<p>LLVM: version 2.9 recommended; 2.6 or later required.</p>
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<b>NOTE</b>: LLVM 2.8 and earlier will not work on systems that support the
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Intel AVX extensions (e.g. Sandybridge). LLVM's code generator will
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fail when trying to emit AVX instructions. This was fixed in LLVM 2.9.
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</p>
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<p>
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For Linux, on a recent Debian based distribution do:
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</p>
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<pre>
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aptitude install llvm-dev
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</pre>
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For a RPM-based distribution do:
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</p>
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<pre>
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yum install llvm-devel
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</pre>
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<p>
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For Windows you will need to build LLVM from source with MSVC or MINGW
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(either natively or through cross compilers) and CMake, and set the LLVM
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environment variable to the directory you installed it to.
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LLVM will be statically linked, so when building on MSVC it needs to be
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built with a matching CRT as Mesa, and you'll need to pass
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-DLLVM_USE_CRT_RELEASE=MTd for debug and checked builds,
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-DLLVM_USE_CRT_RELEASE=MTd for profile and release builds.
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You can build only the x86 target by passing -DLLVM_TARGETS_TO_BUILD=X86
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to cmake.
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</p>
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</li>
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<li>
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<p>scons (optional)</p>
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</li>
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</ul>
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<h1>Building</h1>
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To build everything on Linux invoke scons as:
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<pre>
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scons build=debug libgl-xlib
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</pre>
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Alternatively, you can build it with GNU make, if you prefer, by invoking it as
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<pre>
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make linux-llvm
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</pre>
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but the rest of these instructions assume that scons is used.
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For Windows the procedure is similar except the target:
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<pre>
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scons build=debug libgl-gdi
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</pre>
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<h1>Using</h1>
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On Linux, building will create a drop-in alternative for libGL.so into
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<pre>
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build/foo/gallium/targets/libgl-xlib/libGL.so
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</pre>
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or
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<pre>
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lib/gallium/libGL.so
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</pre>
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To use it set the LD_LIBRARY_PATH environment variable accordingly.
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For performance evaluation pass debug=no to scons, and use the corresponding
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lib directory without the "-debug" suffix.
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On Windows, building will create a drop-in alternative for opengl32.dll. To use
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it put it in the same directory as the application. It can also be used by
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replacing the native ICD driver, but it's quite an advanced usage, so if you
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need to ask, don't even try it.
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<h1>Profiling</h1>
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To profile llvmpipe you should pass the options
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<pre>
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scons build=profile <same-as-before>
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</pre>
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This will ensure that frame pointers are used both in C and JIT functions, and
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that no tail call optimizations are done by gcc.
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To better profile JIT code you'll need to build LLVM with oprofile integration.
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<pre>
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./configure \
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--prefix=$install_dir \
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--enable-optimized \
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--disable-profiling \
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--enable-targets=host-only \
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--with-oprofile
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make -C "$build_dir"
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make -C "$build_dir" install
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find "$install_dir/lib" -iname '*.a' -print0 | xargs -0 strip --strip-debug
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</pre>
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The you should define
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<pre>
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export LLVM=/path/to/llvm-2.6-profile
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</pre>
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and rebuild.
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<h1>Unit testing</h1>
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<p>
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Building will also create several unit tests in
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build/linux-???-debug/gallium/drivers/llvmpipe:
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</p>
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</ul>
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<li> lp_test_blend: blending
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<li> lp_test_conv: SIMD vector conversion
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<li> lp_test_format: pixel unpacking/packing
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</ul>
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<p>
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Some of this tests can output results and benchmarks to a tab-separated-file
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for posterior analysis, e.g.:
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</p>
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<pre>
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build/linux-x86_64-debug/gallium/drivers/llvmpipe/lp_test_blend -o blend.tsv
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</pre>
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<h1>Development Notes</h1>
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<ul>
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<li>
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When looking to this code by the first time start in lp_state_fs.c, and
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then skim through the lp_bld_* functions called in there, and the comments
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at the top of the lp_bld_*.c functions.
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</li>
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<li>
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The driver-independent parts of the LLVM / Gallium code are found in
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src/gallium/auxiliary/gallivm/. The filenames and function prefixes
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need to be renamed from "lp_bld_" to something else though.
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</li>
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<li>
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We use LLVM-C bindings for now. They are not documented, but follow the C++
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interfaces very closely, and appear to be complete enough for code
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generation. See
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http://npcontemplation.blogspot.com/2008/06/secret-of-llvm-c-bindings.html
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for a stand-alone example. See the llvm-c/Core.h file for reference.
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</li>
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</ul>
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