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6e6cd7d9创建于 2021年3月20日历史提交

LLVMpipe

Introduction

The Gallium llvmpipe driver is a software rasterizer that uses LLVM to do runtime code generation. Shaders, point/line/triangle rasterization and vertex processing are implemented with LLVM IR which is translated to x86, x86-64, or ppc64le machine code. Also, the driver is multithreaded to take advantage of multiple CPU cores (up to 8 at this time). It's the fastest software rasterizer for Mesa.

Requirements

  • For x86 or amd64 processors, 64-bit mode is recommended. Support for SSE2 is strongly encouraged. Support for SSE3 and SSE4.1 will yield the most efficient code. The fewer features the CPU has the more likely it is that you will run into underperforming, buggy, or incomplete code.

    For ppc64le processors, use of the Altivec feature (the Vector Facility) is recommended if supported; use of the VSX feature (the Vector-Scalar Facility) is recommended if supported AND Mesa is built with LLVM version 4.0 or later.

    See /proc/cpuinfo to know what your CPU supports.

  • Unless otherwise stated, LLVM version 3.4 is recommended; 3.3 or later is required.

    For Linux, on a recent Debian based distribution do:

    .. code-block:: console

    aptitude install llvm-dev

    If you want development snapshot builds of LLVM for Debian and derived distributions like Ubuntu, you can use the APT repository at apt.llvm.org, which are maintained by Debian's LLVM maintainer.

    For a RPM-based distribution do:

    .. code-block:: console

    yum install llvm-devel

    For Windows you will need to build LLVM from source with MSVC or MINGW (either natively or through cross compilers) and CMake, and set the LLVM environment variable to the directory you installed it to. LLVM will be statically linked, so when building on MSVC it needs to be built with a matching CRT as Mesa, and you'll need to pass -DLLVM_USE_CRT_xxx=yyy as described below.

    +-----------------+----------------------------------------------------------------+ | LLVM build-type | Mesa build-type | | +--------------------------------+-------------------------------+ | | debug,checked | release,profile | +=================+================================+===============================+ | Debug | -DLLVM_USE_CRT_DEBUG=MTd | -DLLVM_USE_CRT_DEBUG=MT | +-----------------+--------------------------------+-------------------------------+ | Release | -DLLVM_USE_CRT_RELEASE=MTd | -DLLVM_USE_CRT_RELEASE=MT | +-----------------+--------------------------------+-------------------------------+

    You can build only the x86 target by passing -DLLVM_TARGETS_TO_BUILD=X86 to cmake.

Building

To build everything on Linux invoke meson as:

.. code-block:: console

mkdir build cd build meson -D glx=gallium-xlib -D gallium-drivers=swrast ninja

Using

Linux


On Linux, building will create a drop-in alternative for ``libGL.so``
into

::

   build/foo/gallium/targets/libgl-xlib/libGL.so

or

::

   lib/gallium/libGL.so

To use it set the ``LD_LIBRARY_PATH`` environment variable accordingly.

Windows

On Windows, building will create build/windows-x86-debug/gallium/targets/libgl-gdi/opengl32.dll which is a drop-in alternative for system's opengl32.dll. To use it put it in the same directory as your application. It can also be used by replacing the native ICD driver, but it's quite an advanced usage, so if you need to ask, don't even try it.

There is however an easy way to replace the OpenGL software renderer that comes with Microsoft Windows 7 (or later) with llvmpipe (that is, on systems without any OpenGL drivers):

Profiling

Linux perf integration


On Linux, it is possible to have symbol resolution of JIT code with
[Linux perf](https://perf.wiki.kernel.org/):

::

   perf record -g /my/application
   perf report

When run inside Linux perf, llvmpipe will create a
``/tmp/perf-XXXXX.map`` file with symbol address table. It also dumps
assembly code to ``/tmp/perf-XXXXX.map.asm``, which can be used by the
``bin/perf-annotate-jit.py`` script to produce disassembly of the
generated code annotated with the samples.

You can obtain a call graph via
[Gprof2Dot](https://github.com/jrfonseca/gprof2dot#linux-perf).

Unit testing
------------

Building will also create several unit tests in
``build/linux-???-debug/gallium/drivers/llvmpipe``:

-  ``lp_test_blend``: blending
-  ``lp_test_conv``: SIMD vector conversion
-  ``lp_test_format``: pixel unpacking/packing

Some of these tests can output results and benchmarks to a tab-separated
file for later analysis, e.g.:

::

   build/linux-x86_64-debug/gallium/drivers/llvmpipe/lp_test_blend -o blend.tsv

Development Notes
-----------------

-  When looking at this code for the first time, start in lp_state_fs.c,
   and then skim through the ``lp_bld_*`` functions called there, and
   the comments at the top of the ``lp_bld_*.c`` functions.
-  The driver-independent parts of the LLVM / Gallium code are found in
   ``src/gallium/auxiliary/gallivm/``. The filenames and function
   prefixes need to be renamed from ``lp_bld_`` to something else
   though.
-  We use LLVM-C bindings for now. They are not documented, but follow
   the C++ interfaces very closely, and appear to be complete enough for
   code generation. See `this stand-alone
   example <https://npcontemplation.blogspot.com/2008/06/secret-of-llvm-c-bindings.html>`__.
   See the ``llvm-c/Core.h`` file for reference.

.. _recommended_reading:

Recommended Reading
-------------------

-  Rasterization

   -  `Triangle Scan Conversion using 2D Homogeneous
      Coordinates <https://www.cs.unc.edu/~olano/papers/2dh-tri/>`__
   -  `Rasterization on
      Larrabee <http://www.drdobbs.com/parallel/rasterization-on-larrabee/217200602>`__
      (`DevMaster
      copy <http://devmaster.net/posts/2887/rasterization-on-larrabee>`__)
   -  `Rasterization using half-space
      functions <http://devmaster.net/posts/6133/rasterization-using-half-space-functions>`__
   -  `Advanced
      Rasterization <http://devmaster.net/posts/6145/advanced-rasterization>`__
   -  `Optimizing Software Occlusion
      Culling <https://fgiesen.wordpress.com/2013/02/17/optimizing-sw-occlusion-culling-index/>`__

-  Texture sampling

   -  `Perspective Texture
      Mapping <http://chrishecker.com/Miscellaneous_Technical_Articles#Perspective_Texture_Mapping>`__
   -  `Texturing As In
      Unreal <https://www.flipcode.com/archives/Texturing_As_In_Unreal.shtml>`__
   -  `Run-Time MIP-Map
      Filtering <http://www.gamasutra.com/view/feature/3301/runtime_mipmap_filtering.php>`__
   -  `Will "brilinear" filtering
      persist? <http://alt.3dcenter.org/artikel/2003/10-26_a_english.php>`__
   -  `Trilinear
      filtering <http://ixbtlabs.com/articles2/gffx/nv40-rx800-3.html>`__
   -  `Texture
      Swizzling <http://devmaster.net/posts/12785/texture-swizzling>`__

-  SIMD

   -  `Whole-Function
      Vectorization <http://www.cdl.uni-saarland.de/projects/wfv/#header4>`__

-  Optimization

   -  `Optimizing Pixomatic For Modern x86
      Processors <http://www.drdobbs.com/optimizing-pixomatic-for-modern-x86-proc/184405807>`__
   -  `Intel 64 and IA-32 Architectures Optimization Reference
      Manual <http://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-optimization-manual.html>`__
   -  `Software optimization
      resources <http://www.agner.org/optimize/>`__
   -  `Intel Intrinsics
      Guide <https://software.intel.com/en-us/articles/intel-intrinsics-guide>`__

-  LLVM

   -  `LLVM Language Reference
      Manual <http://llvm.org/docs/LangRef.html>`__
   -  `The secret of LLVM C
      bindings <https://npcontemplation.blogspot.co.uk/2008/06/secret-of-llvm-c-bindings.html>`__

-  General

   -  `A trip through the Graphics
      Pipeline <https://fgiesen.wordpress.com/2011/07/09/a-trip-through-the-graphics-pipeline-2011-index/>`__
   -  `WARP Architecture and
      Performance <https://msdn.microsoft.com/en-us/library/gg615082.aspx#architecture>`__