docs/llvmpipe.html

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   9 <H1>Introduction</H1>
  10
  11 <p>
  12 The Gallium llvmpipe driver is a software rasterizer that uses LLVM to
  13 do runtime code generation.
  14 Shaders, point/line/triangle rasterization and vertex processing are
  15 implemented with LLVM IR which is translated to x86 or x86-64 machine
  16 code.
  17 Also, the driver is multithreaded to take advantage of multiple CPU cores
  18 (up to 8 at this time).
  19 It's the fastest software rasterizer for Mesa.
  20 </p>
  21
  22
  23 <h1>Requirements</h1>
  24
  25 <ul>
  26 <li>
  27          <p>An x86 or amd64 processor; 64-bit mode recommended.</p
  28    <p>
  29    Support for SSE2 is strongly encouraged.  Support for SSSE3 and SSE4.1 will
  30    yield the most efficient code.  The fewer features the CPU has the more
  31    likely is that you run into underperforming, buggy, or incomplete code.
  32    </p>
  33    <p>
  34    See /proc/cpuinfo to know what your CPU supports.
  35    </p>
  36 </li>
  37 <li>
  38          <p>LLVM: version 2.9 recommended; 2.6 or later required.</p>
  39    <b>NOTE</b>: LLVM 2.8 and earlier will not work on systems that support the
  40    Intel AVX extensions (e.g. Sandybridge).  LLVM's code generator will
  41    fail when trying to emit AVX instructions.  This was fixed in LLVM 2.9.
  42    </p>
  43    <p>
  44    For Linux, on a recent Debian based distribution do:
  45    </p>
  46 <pre>
  47      aptitude install llvm-dev
  48 </pre>
  49    For a RPM-based distribution do:
  50    </p>
  51 <pre>
  52      yum install llvm-devel
  53 </pre>
  54
  55    <p>
  56          For Windows you will need to build LLVM from source with MSVC or MINGW
  57          (either natively or through cross compilers) and CMake, and set the LLVM
  58          environment variable to the directory you installed it to.
  59
  60    LLVM will be statically linked, so when building on MSVC it needs to be
  61    built with a matching CRT as Mesa, and you'll need to pass
  62    -DLLVM_USE_CRT_RELEASE=MTd for debug and checked builds,
  63    -DLLVM_USE_CRT_RELEASE=MTd for profile and release builds.
  64
  65    You can build only the x86 target by passing -DLLVM_TARGETS_TO_BUILD=X86
  66    to cmake.
  67    </p>
  68 </li>
  69
  70 <li>
  71    <p>scons (optional)</p>
  72 </li>
  73 </ul>
  74
  75
  76
  77
  78 <h1>Building</h1>
  79
  80 To build everything on Linux invoke scons as:
  81
  82 <pre>
  83   scons build=debug libgl-xlib
  84 </pre>
  85
  86 Alternatively, you can build it with GNU make, if you prefer, by invoking it as
  87
  88 <pre>
  89   make linux-llvm
  90 </pre>
  91
  92 but the rest of these instructions assume that scons is used.
  93
  94 For Windows the procedure is similar except the target:
  95
  96 <pre>
  97   scons build=debug libgl-gdi
  98 </pre>
  99
 100
 101 <h1>Using</h1>
 102
 103 On Linux, building will create a drop-in alternative for libGL.so into
 104
 105 <pre>
 106   build/foo/gallium/targets/libgl-xlib/libGL.so
 107 </pre>
 108 or
 109 <pre>
 110   lib/gallium/libGL.so
 111 </pre>
 112
 113 To use it set the LD_LIBRARY_PATH environment variable accordingly.
 114
 115 For performance evaluation pass debug=no to scons, and use the corresponding
 116 lib directory without the "-debug" suffix.
 117
 118 On Windows, building will create a drop-in alternative for opengl32.dll. To use
 119 it put it in the same directory as the application. It can also be used by
 120 replacing the native ICD driver, but it's quite an advanced usage, so if you
 121 need to ask, don't even try it.
 122
 123
 124 <h1>Profiling</h1>
 125
 126 To profile llvmpipe you should pass the options
 127
 128 <pre>
 129   scons build=profile <same-as-before>
 130 </pre>
 131
 132 This will ensure that frame pointers are used both in C and JIT functions, and
 133 that no tail call optimizations are done by gcc.
 134
 135 To better profile JIT code you'll need to build LLVM with oprofile integration.
 136
 137 <pre>
 138   ./configure \
 139       --prefix=$install_dir \
 140       --enable-optimized \
 141       --disable-profiling \
 142       --enable-targets=host-only \
 143       --with-oprofile
 144
 145   make -C "$build_dir"
 146   make -C "$build_dir" install
 147
 148   find "$install_dir/lib" -iname '*.a' -print0 | xargs -0 strip --strip-debug
 149 </pre>
 150
 151 The you should define
 152
 153 <pre>
 154   export LLVM=/path/to/llvm-2.6-profile
 155 </pre>
 156
 157 and rebuild.
 158
 159
 160 <h1>Unit testing</h1>
 161
 162 <p>
 163 Building will also create several unit tests in
 164 build/linux-???-debug/gallium/drivers/llvmpipe:
 165 </p>
 166
 167 </ul>
 168 <li> lp_test_blend: blending
 169 <li> lp_test_conv: SIMD vector conversion
 170 <li> lp_test_format: pixel unpacking/packing
 171 </ul>
 172
 173 <p>
 174 Some of this tests can output results and benchmarks to a tab-separated-file
 175 for posterior analysis, e.g.:
 176 </p>
 177 <pre>
 178   build/linux-x86_64-debug/gallium/drivers/llvmpipe/lp_test_blend -o blend.tsv
 179 </pre>
 180
 181
 182 <h1>Development Notes</h1>
 183
 184 <ul>
 185 <li>
 186   When looking to this code by the first time start in lp_state_fs.c, and
 187   then skim through the lp_bld_* functions called in there, and the comments
 188   at the top of the lp_bld_*.c functions.
 189 </li>
 190 <li>
 191   The driver-independent parts of the LLVM / Gallium code are found in
 192   src/gallium/auxiliary/gallivm/.  The filenames and function prefixes
 193   need to be renamed from "lp_bld_" to something else though.
 194 </li>
 195 <li>
 196   We use LLVM-C bindings for now. They are not documented, but follow the C++
 197   interfaces very closely, and appear to be complete enough for code
 198   generation. See
 199   http://npcontemplation.blogspot.com/2008/06/secret-of-llvm-c-bindings.html
 200   for a stand-alone example.  See the llvm-c/Core.h file for reference.
 201 </li>
 202 </ul>