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LLVMPIPE -- a fork of softpipe that employs LLVM for code generation.
Requirements
============
- 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. Version 2.8 recommended. 2.6 or later required.
NOTE: LLVM 2.8 and earlier will not work on systems that support the
Intel AVX extensions (e.g. Sandybridge). LLVM's code generator will
fail when trying to emit AVX instructions. This was fixed in LLVM 2.9.
For Linux, on a recent Debian based distribution do:
aptitude install llvm-dev
For Windows download pre-built MSVC 9.0 or MinGW binaries from
http://people.freedesktop.org/~jrfonseca/llvm/ and set the LLVM environment
variable to the extracted path.
For MSVC there are two set of binaries: llvm-x.x-msvc32mt.7z and
llvm-x.x-msvc32mtd.7z .
You have to set the LLVM=/path/to/llvm-x.x-msvc32mtd env var when passing
debug=yes to scons, and LLVM=/path/to/llvm-x.x-msvc32mt when building with
debug=no. This is necessary as LLVM builds as static library so the chosen
MS CRT must match.
- 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 is everything the except except the winsys:
scons build=debug libgl-gdi
Using
=====
On Linux, building will create a drop-in alternative for libGL.so into
build/foo/gallium/targets/libgl-xlib/libGL.so
To use it set the LD_LIBRARY_PATH environment variable accordingly.
For performance evaluation pass debug=no to scons, and use the corresponding
lib directory without the "-debug" suffix.
On Windows, building will create a drop-in alternative for opengl32.dll. To use
it put it in the same directory as the 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.
Profiling
=========
To profile llvmpipe you should pass the options
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.
To better profile JIT code you'll need to build LLVM with oprofile integration.
./configure \
--prefix=$install_dir \
--enable-optimized \
--disable-profiling \
--enable-targets=host-only \
--with-oprofile
make -C "$build_dir"
make -C "$build_dir" install
find "$install_dir/lib" -iname '*.a' -print0 | xargs -0 strip --strip-debug
The you should define
export LLVM=/path/to/llvm-2.6-profile
and rebuild.
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
http://npcontemplation.blogspot.com/2008/06/secret-of-llvm-c-bindings.html
for a stand-alone example. See the llvm-c/Core.h file for reference.
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