344 lines
11 KiB
HTML
344 lines
11 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html lang="en">
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<head>
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<meta http-equiv="content-type" content="text/html; charset=utf-8">
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<title>Gallium LLVMpipe Driver</title>
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<link rel="stylesheet" type="text/css" href="mesa.css">
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</head>
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<body>
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<div class="header">
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The Mesa 3D Graphics Library
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</div>
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<iframe src="contents.html"></iframe>
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<div class="content">
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<h1>Gallium LLVMpipe Driver</h1>
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<h2>Introduction</h2>
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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, x86-64, or ppc64le 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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<h2>Requirements</h2>
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<ul>
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<li>
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<p>
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For x86 or amd64 processors, 64-bit mode is recommended.
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Support for SSE2 is strongly encouraged. Support for SSE3 and SSE4.1 will
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yield the most efficient code. The fewer features the CPU has the more
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likely it is that you will run into underperforming, buggy, or incomplete code.
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</p>
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<p>
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For ppc64le processors, use of the Altivec feature (the Vector
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Facility) is recommended if supported; use of the VSX feature (the
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Vector-Scalar Facility) is recommended if supported AND Mesa is
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built with LLVM version 4.0 or later.
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</p>
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<p>
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See <code>/proc/cpuinfo</code> 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>Unless otherwise stated, LLVM version 3.4 is recommended; 3.3 or later is required.</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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<p>
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If you want development snapshot builds of LLVM for Debian and derived
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distributions like Ubuntu, you can use the APT repository at <a
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href="https://apt.llvm.org/" title="Debian Development packages for LLVM"
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>apt.llvm.org</a>, which are maintained by Debian's LLVM maintainer.
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</p>
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<p>
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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
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<code>LLVM</code> environment variable to the directory you installed
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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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<code>-DLLVM_USE_CRT_xxx=yyy</code> as described below.
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</p>
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<table border="1">
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<tr>
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<th rowspan="2">LLVM build-type</th>
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<th colspan="2" align="center">Mesa build-type</th>
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</tr>
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<tr>
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<th>debug,checked</th>
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<th>release,profile</th>
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</tr>
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<tr>
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<th>Debug</th>
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<td><code>-DLLVM_USE_CRT_DEBUG=MTd</code></td>
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<td><code>-DLLVM_USE_CRT_DEBUG=MT</code></td>
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</tr>
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<tr>
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<th>Release</th>
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<td><code>-DLLVM_USE_CRT_RELEASE=MTd</code></td>
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<td><code>-DLLVM_USE_CRT_RELEASE=MT</code></td>
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</tr>
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</table>
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<p>
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You can build only the x86 target by passing
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<code>-DLLVM_TARGETS_TO_BUILD=X86</code> 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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<h2>Building</h2>
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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 meson with:
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<pre>
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mkdir build
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cd build
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meson -D glx=gallium-xlib -D gallium-drivers=swrast
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ninja
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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 platform=windows build=debug libgl-gdi
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</pre>
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<h2>Using</h2>
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<h3>Linux</h3>
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<p>On Linux, building will create a drop-in alternative for
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<code>libGL.so</code> into</p>
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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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<p>To use it set the <code>LD_LIBRARY_PATH</code> environment variable
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accordingly.</p>
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<p>For performance evaluation pass <code>build=release</code> to scons,
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and use the corresponding lib directory without the <code>-debug</code>
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suffix.</p>
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<h3>Windows</h3>
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<p>
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On Windows, building will create
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<code>build/windows-x86-debug/gallium/targets/libgl-gdi/opengl32.dll</code>
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which is a drop-in alternative for system's <code>opengl32.dll</code>. To use
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it put it in the same directory as your 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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</p>
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<p>
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There is however an easy way to replace the OpenGL software renderer that comes
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with Microsoft Windows 7 (or later) with llvmpipe (that is, on systems without
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any OpenGL drivers):
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</p>
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<ul>
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<li><p>copy <code>build/windows-x86-debug/gallium/targets/libgl-gdi/opengl32.dll</code>
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to <code>C:\Windows\SysWOW64\mesadrv.dll</code>
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</p></li>
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<li><p>load this registry settings:</p>
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<pre>REGEDIT4
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; https://technet.microsoft.com/en-us/library/cc749368.aspx
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; https://www.msfn.org/board/topic/143241-portable-windows-7-build-from-winpe-30/page-5#entry942596
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[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\OpenGLDrivers\MSOGL]
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"DLL"="mesadrv.dll"
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"DriverVersion"=dword:00000001
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"Flags"=dword:00000001
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"Version"=dword:00000002
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</pre>
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</li>
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<li>Ditto for 64 bits drivers if you need them.</li>
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</ul>
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<h2>Profiling</h2>
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<p>
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To profile llvmpipe you should build as
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</p>
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<pre>
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scons build=profile <same-as-before>
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</pre>
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<p>
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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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</p>
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<h3>Linux perf integration</h3>
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<p>
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On Linux, it is possible to have symbol resolution of JIT code with <a href="https://perf.wiki.kernel.org/">Linux perf</a>:
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</p>
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<pre>
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perf record -g /my/application
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perf report
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</pre>
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<p>
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When run inside Linux perf, llvmpipe will create a
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<code>/tmp/perf-XXXXX.map</code> file with symbol address table. It also
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dumps assembly code to <code>/tmp/perf-XXXXX.map.asm</code>, which can be
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used by the <code>bin/perf-annotate-jit.py</code> script to produce
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disassembly of the generated code annotated with the samples.
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</p>
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<p>You can obtain a call graph via
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<a href="https://github.com/jrfonseca/gprof2dot#linux-perf">Gprof2Dot</a>.</p>
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<h2>Unit testing</h2>
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<p>
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Building will also create several unit tests in
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<code>build/linux-???-debug/gallium/drivers/llvmpipe</code>:
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</p>
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<ul>
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<li> <code>lp_test_blend</code>: blending
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<li> <code>lp_test_conv</code>: SIMD vector conversion
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<li> <code>lp_test_format</code>: pixel unpacking/packing
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</ul>
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<p>
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Some of these tests can output results and benchmarks to a tab-separated file
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for later 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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<h2>Development Notes</h2>
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<ul>
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<li>
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When looking at this code for the first time, start in lp_state_fs.c, and
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then skim through the <code>lp_bld_*</code> functions called there, and
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the comments at the top of the <code>lp_bld_*.c</code> 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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<code>src/gallium/auxiliary/gallivm/</code>. The filenames and function
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prefixes need to be renamed from <code>lp_bld_</code> to something else
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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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<a href="https://npcontemplation.blogspot.com/2008/06/secret-of-llvm-c-bindings.html">
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this stand-alone example</a>. See the <code>llvm-c/Core.h</code> file for
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reference.
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</li>
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</ul>
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<h2 id="recommended_reading">Recommended Reading</h2>
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<ul>
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<li>
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<p>Rasterization</p>
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<ul>
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<li><a href="https://www.cs.unc.edu/~olano/papers/2dh-tri/">Triangle Scan Conversion using 2D Homogeneous Coordinates</a></li>
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<li><a href="http://www.drdobbs.com/parallel/rasterization-on-larrabee/217200602">Rasterization on Larrabee</a> (<a href="http://devmaster.net/posts/2887/rasterization-on-larrabee">DevMaster copy</a>)</li>
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<li><a href="http://devmaster.net/posts/6133/rasterization-using-half-space-functions">Rasterization using half-space functions</a></li>
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<li><a href="http://devmaster.net/posts/6145/advanced-rasterization">Advanced Rasterization</a></li>
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<li><a href="https://fgiesen.wordpress.com/2013/02/17/optimizing-sw-occlusion-culling-index/">Optimizing Software Occlusion Culling</a></li>
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</ul>
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</li>
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<li>
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<p>Texture sampling</p>
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<ul>
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<li><a href="http://chrishecker.com/Miscellaneous_Technical_Articles#Perspective_Texture_Mapping">Perspective Texture Mapping</a></li>
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<li><a href="https://www.flipcode.com/archives/Texturing_As_In_Unreal.shtml">Texturing As In Unreal</a></li>
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<li><a href="http://www.gamasutra.com/view/feature/3301/runtime_mipmap_filtering.php">Run-Time MIP-Map Filtering</a></li>
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<li><a href="http://alt.3dcenter.org/artikel/2003/10-26_a_english.php">Will "brilinear" filtering persist?</a></li>
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<li><a href="http://ixbtlabs.com/articles2/gffx/nv40-rx800-3.html">Trilinear filtering</a></li>
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<li><a href="http://devmaster.net/posts/12785/texture-swizzling">Texture Swizzling</a></li>
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</ul>
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</li>
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<li>
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<p>SIMD</p>
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<ul>
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<li><a href="http://www.cdl.uni-saarland.de/projects/wfv/#header4">Whole-Function Vectorization</a></li>
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</ul>
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</li>
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<li>
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<p>Optimization</p>
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<ul>
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<li><a href="http://www.drdobbs.com/optimizing-pixomatic-for-modern-x86-proc/184405807">Optimizing Pixomatic For Modern x86 Processors</a></li>
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<li><a href="http://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-optimization-manual.html">Intel 64 and IA-32 Architectures Optimization Reference Manual</a></li>
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<li><a href="http://www.agner.org/optimize/">Software optimization resources</a></li>
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<li><a href="https://software.intel.com/en-us/articles/intel-intrinsics-guide">Intel Intrinsics Guide</a></li>
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</ul>
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</li>
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<li>
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<p>LLVM</p>
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<ul>
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<li><a href="http://llvm.org/docs/LangRef.html">LLVM Language Reference Manual</a></li>
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<li><a href="https://npcontemplation.blogspot.co.uk/2008/06/secret-of-llvm-c-bindings.html">The secret of LLVM C bindings</a></li>
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</ul>
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</li>
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<li>
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<p>General</p>
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<ul>
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<li><a href="https://fgiesen.wordpress.com/2011/07/09/a-trip-through-the-graphics-pipeline-2011-index/">A trip through the Graphics Pipeline</a></li>
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<li><a href="https://msdn.microsoft.com/en-us/library/gg615082.aspx#architecture">WARP Architecture and Performance</a></li>
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</ul>
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</li>
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</ul>
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</div>
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</body>
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</html>
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