mesa/src/gallium/drivers/llvmpipe

LLVMPIPE -- a fork of softpipe that employs LLVM for code generation.


Status
======

Done so far is:

 - the whole fragment pipeline is code generated in a single function
 
   - input interpolation
   
   - depth testing
 
   - texture sampling (not all state/formats are supported) 
   
   - fragment shader TGSI translation
     - same level of support as the TGSI SSE2 exec machine, with the exception
       we don't fallback to TGSI interpretation when an unsupported opcode is
       found, but just ignore it
     - done in SoA layout
     - input interpolation also code generated
 
   - alpha testing
 
   - blend (including logic ops)
     - both in SoA and AoS layouts, but only the former used for now
 
 - code is generic
   - intermediates can be vectors of floats, ubytes, fixed point, etc, and of
     any width and length
   - not all operations are implemented for these types yet though

Most mesa/progs/demos/* work. 

To do (probably by this order):

 - code generate stipple and stencil testing

 - translate the remaining bits of texture sampling state

 - translate TGSI control flow instructions, and all other remaining opcodes
 
 - integrate with the draw module for VS code generation

 - code generate the triangle setup and rasterization


Requirements
============

 - Linux
 
 - A x86 or amd64 processor.  64bit mode is preferred.
 
   Support for sse2 is strongly encouraged.  Support for ssse3, and sse4.1 will
   yield the most efficient code.  The less features the CPU has the more
   likely is that you ran into underperforming, buggy, or incomplete code.  
   
   See /proc/cpuinfo to know what your CPU supports.
 
 - LLVM 2.5 or greater. LLVM 2.6 is preferred.
 
   On Debian based distributions do:
 
     aptitude install llvm-dev

   There is a typo in one of the llvm 2.5 headers, that may cause compilation
   errors. To fix it apply the change:

     --- /usr/include/llvm-c/Core.h.orig	2009-08-10 15:38:54.000000000 +0100
     +++ /usr/include/llvm-c/Core.h	2009-08-10 15:38:25.000000000 +0100
     @@ -831,7 +831,7 @@
        template<typename T>
        inline T **unwrap(LLVMValueRef *Vals, unsigned Length) {
          #if DEBUG
     -    for (LLVMValueRef *I = Vals, E = Vals + Length; I != E; ++I)
     +    for (LLVMValueRef *I = Vals, *E = Vals + Length; I != E; ++I)
            cast<T>(*I);
          #endif
          return reinterpret_cast<T**>(Vals);
 
 - scons (optional)

 - udis86, http://udis86.sourceforge.net/ (optional):
 
     git clone git://udis86.git.sourceforge.net/gitroot/udis86/udis86
     cd udis86
     ./autogen.sh
     ./configure --with-pic
     make
     sudo make install
 

Building
========

To build everything invoke scons as:

  scons debug=yes statetrackers=mesa drivers=llvmpipe winsys=xlib dri=false -k

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.


Using
=====

Building will create a drop-in alternative for libGL.so. To use it set the
environment variables:

  export LD_LIBRARY_PATH=$PWD/build/linux-x86_64-debug/lib:$LD_LIBRARY_PATH

or

  export LD_LIBRARY_PATH=$PWD/build/linux-x86-debug/lib:$LD_LIBRARY_PATH

For performance evaluation pass debug=no to scons, and use the corresponding
lib directory without the "-debug" suffix.


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.  

- All lp_bld_*.[ch] are isolated from the rest of the driver, and could/may be 
  put in a stand-alone Gallium state -> LLVM IR translation module.

- 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 
  http://npcontemplation.blogspot.com/2008/06/secret-of-llvm-c-bindings.html
  for a stand-alone example.