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<HTML>
<TITLE>llvmpipe</TITLE>
<link rel="stylesheet" type="text/css" href="mesa.css"></head>
<BODY>
<H1>Introduction</H1>
<p>
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.
</p>
<h1>Requirements</h1>
<ul>
<li>
<p>An x86 or amd64 processor; 64-bit mode recommended.</p
<p>
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.
</p>
<p>
See /proc/cpuinfo to know what your CPU supports.
</p>
</li>
<li>
<p>LLVM: version 2.9 recommended; 2.6 or later required.</p>
<b>NOTE</b>: 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.
</p>
<p>
For Linux, on a recent Debian based distribution do:
</p>
<pre>
aptitude install llvm-dev
</pre>
For a RPM-based distribution do:
</p>
<pre>
yum install llvm-devel
</pre>
<p>
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_RELEASE=MTd for debug and checked builds,
-DLLVM_USE_CRT_RELEASE=MTd for profile and release builds.
You can build only the x86 target by passing -DLLVM_TARGETS_TO_BUILD=X86
to cmake.
</p>
</li>
<li>
<p>scons (optional)</p>
</li>
</ul>
<h1>Building</h1>
To build everything on Linux invoke scons as:
<pre>
scons build=debug libgl-xlib
</pre>
Alternatively, you can build it with GNU make, if you prefer, by invoking it as
<pre>
make linux-llvm
</pre>
but the rest of these instructions assume that scons is used.
For Windows the procedure is similar except the target:
<pre>
scons build=debug libgl-gdi
</pre>
<h1>Using</h1>
On Linux, building will create a drop-in alternative for libGL.so into
<pre>
build/foo/gallium/targets/libgl-xlib/libGL.so
</pre>
or
<pre>
lib/gallium/libGL.so
</pre>
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.
<h1>Profiling</h1>
To profile llvmpipe you should pass the options
<pre>
scons build=profile <same-as-before>
</pre>
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.
<pre>
./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
</pre>
The you should define
<pre>
export LLVM=/path/to/llvm-2.6-profile
</pre>
and rebuild.
<h1>Unit testing</h1>
<p>
Building will also create several unit tests in
build/linux-???-debug/gallium/drivers/llvmpipe:
</p>
</ul>
<li> lp_test_blend: blending
<li> lp_test_conv: SIMD vector conversion
<li> lp_test_format: pixel unpacking/packing
</ul>
<p>
Some of this tests can output results and benchmarks to a tab-separated-file
for posterior analysis, e.g.:
</p>
<pre>
build/linux-x86_64-debug/gallium/drivers/llvmpipe/lp_test_blend -o blend.tsv
</pre>
<h1>Development Notes</h1>
<ul>
<li>
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.
</li>
<li>
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.
</li>
<li>
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.
</li>
</ul>
|
