The Mesa 3D Graphics Library

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 or x86-64 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

   
An x86 or amd64 processor; 64-bit mode recommended.

   Support for SSE2 is strongly encouraged.  Support for SSSE3 and SSE4.1 will

   yield the most efficient code.  The fewer features the CPU has the more

   likely is that you run into underperforming, buggy, or incomplete code.

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

   
LLVM: version 3.4 recommended; 3.3 or later required.

   For Linux, on a recent Debian based distribution do:

     aptitude install llvm-dev

   For a RPM-based distribution do:

     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.

   
scons (optional)

Building

To build everything on Linux invoke scons as:

  scons build=debug libgl-xlib

Alternatively, you can build it with GNU make, if you prefer, by invoking it as

  make linux-llvm

but the rest of these instructions assume that scons is used.

For Windows the procedure is similar except the target:

  scons platform=windows build=debug libgl-gdi

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.

For performance evaluation pass build=release to scons, and use the corresponding

lib directory without the "-debug" suffix.

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):

  
copy build/windows-x86-debug/gallium/targets/libgl-gdi/opengl32.dll to C:\Windows\SysWOW64\mesadrv.dll

  
load this registry settings:

  
REGEDIT4

; http://technet.microsoft.com/en-us/library/cc749368.aspx

; http://www.msfn.org/board/topic/143241-portable-windows-7-build-from-winpe-30/page-5#entry942596

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\OpenGLDrivers\MSOGL]

"DLL"="mesadrv.dll"

"DriverVersion"=dword:00000001

"Flags"=dword:00000001

"Version"=dword:00000002

  
Ditto for 64 bits drivers if you need them.

Profiling

To profile llvmpipe you should build as

  scons build=profile <same-as-before>

This will ensure that frame pointers are used both in C and JIT functions, and

that no tail call optimizations are done by gcc.

Linux perf integration

On Linux, it is possible to have symbol resolution of JIT code with Linux perf:

	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 script to produce disassembly of

the generated code annotated with the samples.

You can obtain a call graph via

Gprof2Dot.

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 this tests can output results and benchmarks to a tab-separated-file

for posterior analysis, e.g.:

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

Development Notes

  When looking to this code by the first time start in lp_state_fs.c, and

  then skim through the lp_bld_* functions called in 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.  See the llvm-c/Core.h file for reference.

Recommended Reading

    
Rasterization

      
Triangle Scan Conversion using 2D Homogeneous Coordinates

      
Rasterization on Larrabee (DevMaster copy)

      
Rasterization using half-space functions

      
Advanced Rasterization

      
Optimizing Software Occlusion Culling

    
Texture sampling

      
Perspective Texture Mapping

      
Texturing As In Unreal

      
Run-Time MIP-Map Filtering

      
Will "brilinear" filtering persist?

      
Trilinear filtering

      
Texture Swizzling

    
SIMD

      
Whole-Function Vectorization

    
Optimization

      
Optimizing Pixomatic For Modern x86 Processors

      
Intel 64 and IA-32 Architectures Optimization Reference Manual

      
Software optimization resources

      
Intel Intrinsics Guide

    
LLVM

      
LLVM Language Reference Manual

      
The secret of LLVM C bindings

    
General

      
A trip through the Graphics Pipeline

      
WARP Architecture and Performance