docs/llvmpipe.html

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  10 <h1>Introduction</h1>
  11
  12 <p>
  13 The Gallium llvmpipe driver is a software rasterizer that uses LLVM to
  14 do runtime code generation.
  15 Shaders, point/line/triangle rasterization and vertex processing are
  16 implemented with LLVM IR which is translated to x86 or x86-64 machine
  17 code.
  18 Also, the driver is multithreaded to take advantage of multiple CPU cores
  19 (up to 8 at this time).
  20 It's the fastest software rasterizer for Mesa.
  21 </p>
  22
  23
  24 <h1>Requirements</h1>
  25
  26 <ul>
  27 <li>
  28          <p>An x86 or amd64 processor; 64-bit mode recommended.</p
  29    <p>
  30    Support for SSE2 is strongly encouraged.  Support for SSSE3 and SSE4.1 will
  31    yield the most efficient code.  The fewer features the CPU has the more
  32    likely is that you run into underperforming, buggy, or incomplete code.
  33    </p>
  34    <p>
  35    See /proc/cpuinfo to know what your CPU supports.
  36    </p>
  37 </li>
  38 <li>
  39          <p>LLVM: version 2.9 recommended; 2.6 or later required.</p>
  40    <b>NOTE</b>: LLVM 2.8 and earlier will not work on systems that support the
  41    Intel AVX extensions (e.g. Sandybridge).  LLVM's code generator will
  42    fail when trying to emit AVX instructions.  This was fixed in LLVM 2.9.
  43    </p>
  44    <p>
  45    For Linux, on a recent Debian based distribution do:
  46    </p>
  47 <pre>
  48      aptitude install llvm-dev
  49 </pre>
  50    For a RPM-based distribution do:
  51    </p>
  52 <pre>
  53      yum install llvm-devel
  54 </pre>
  55
  56    <p>
  57          For Windows you will need to build LLVM from source with MSVC or MINGW
  58          (either natively or through cross compilers) and CMake, and set the LLVM
  59          environment variable to the directory you installed it to.
  60
  61    LLVM will be statically linked, so when building on MSVC it needs to be
  62    built with a matching CRT as Mesa, and you'll need to pass
  63    -DLLVM_USE_CRT_RELEASE=MTd for debug and checked builds,
  64    -DLLVM_USE_CRT_RELEASE=MTd for profile and release builds.
  65
  66    You can build only the x86 target by passing -DLLVM_TARGETS_TO_BUILD=X86
  67    to cmake.
  68    </p>
  69 </li>
  70
  71 <li>
  72    <p>scons (optional)</p>
  73 </li>
  74 </ul>
  75
  76
  77
  78
  79 <h1>Building</h1>
  80
  81 To build everything on Linux invoke scons as:
  82
  83 <pre>
  84   scons build=debug libgl-xlib
  85 </pre>
  86
  87 Alternatively, you can build it with GNU make, if you prefer, by invoking it as
  88
  89 <pre>
  90   make linux-llvm
  91 </pre>
  92
  93 but the rest of these instructions assume that scons is used.
  94
  95 For Windows the procedure is similar except the target:
  96
  97 <pre>
  98   scons build=debug libgl-gdi
  99 </pre>
 100
 101
 102 <h1>Using</h1>
 103
 104 On Linux, building will create a drop-in alternative for libGL.so into
 105
 106 <pre>
 107   build/foo/gallium/targets/libgl-xlib/libGL.so
 108 </pre>
 109 or
 110 <pre>
 111   lib/gallium/libGL.so
 112 </pre>
 113
 114 To use it set the LD_LIBRARY_PATH environment variable accordingly.
 115
 116 For performance evaluation pass debug=no to scons, and use the corresponding
 117 lib directory without the "-debug" suffix.
 118
 119 On Windows, building will create a drop-in alternative for opengl32.dll. To use
 120 it put it in the same directory as the application. It can also be used by
 121 replacing the native ICD driver, but it's quite an advanced usage, so if you
 122 need to ask, don't even try it.
 123
 124
 125 <h1>Profiling</h1>
 126
 127 To profile llvmpipe you should pass the options
 128
 129 <pre>
 130   scons build=profile <same-as-before>
 131 </pre>
 132
 133 This will ensure that frame pointers are used both in C and JIT functions, and
 134 that no tail call optimizations are done by gcc.
 135
 136 To better profile JIT code you'll need to build LLVM with oprofile integration.
 137
 138 <pre>
 139   ./configure \
 140       --prefix=$install_dir \
 141       --enable-optimized \
 142       --disable-profiling \
 143       --enable-targets=host-only \
 144       --with-oprofile
 145
 146   make -C "$build_dir"
 147   make -C "$build_dir" install
 148
 149   find "$install_dir/lib" -iname '*.a' -print0 | xargs -0 strip --strip-debug
 150 </pre>
 151
 152 The you should define
 153
 154 <pre>
 155   export LLVM=/path/to/llvm-2.6-profile
 156 </pre>
 157
 158 and rebuild.
 159
 160
 161 <h1>Unit testing</h1>
 162
 163 <p>
 164 Building will also create several unit tests in
 165 build/linux-???-debug/gallium/drivers/llvmpipe:
 166 </p>
 167
 168 </ul>
 169 <li> lp_test_blend: blending
 170 <li> lp_test_conv: SIMD vector conversion
 171 <li> lp_test_format: pixel unpacking/packing
 172 </ul>
 173
 174 <p>
 175 Some of this tests can output results and benchmarks to a tab-separated-file
 176 for posterior analysis, e.g.:
 177 </p>
 178 <pre>
 179   build/linux-x86_64-debug/gallium/drivers/llvmpipe/lp_test_blend -o blend.tsv
 180 </pre>
 181
 182
 183 <h1>Development Notes</h1>
 184
 185 <ul>
 186 <li>
 187   When looking to this code by the first time start in lp_state_fs.c, and
 188   then skim through the lp_bld_* functions called in there, and the comments
 189   at the top of the lp_bld_*.c functions.
 190 </li>
 191 <li>
 192   The driver-independent parts of the LLVM / Gallium code are found in
 193   src/gallium/auxiliary/gallivm/.  The filenames and function prefixes
 194   need to be renamed from "lp_bld_" to something else though.
 195 </li>
 196 <li>
 197   We use LLVM-C bindings for now. They are not documented, but follow the C++
 198   interfaces very closely, and appear to be complete enough for code
 199   generation. See
 200   http://npcontemplation.blogspot.com/2008/06/secret-of-llvm-c-bindings.html
 201   for a stand-alone example.  See the llvm-c/Core.h file for reference.
 202 </li>
 203 </ul>
 204
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