#594: Support use of SSE2 in the x86 native code genreator
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Reporter: simonmar | Owner: simonmar
Type: task | Status: closed
Priority: normal | Milestone: 6.14.1
Component: Compiler (NCG) | Version: 6.4.1
Resolution: fixed | Keywords:
Difficulty: Moderate (less than a day) | Os: Unknown/Multiple
Testcase: N/A | Architecture: Unknown/Multiple
Failure: Runtime performance bug |
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Changes (by simonmar):
* status: assigned => closed
* resolution: => fixed
Comment:
Done:
{{{
Thu Feb 4 10:48:49 GMT 2010 Simon Marlow <[email protected]>
* Implement SSE2 floating-point support in the x86 native code generator
(#594)
The new flag -msse2 enables code generation for SSE2 on x86. It
results in substantially faster floating-point performance; the main
reason for doing this was that our x87 code generation is appallingly
bad, and since we plan to drop -fvia-C soon, we need a way to generate
half-decent floating-point code.
The catch is that SSE2 is only available on CPUs that support it (P4+,
AMD K8+). We'll have to think hard about whether we should enable it
by default for the libraries we ship. In the meantime, at least
-msse2 should be an acceptable replacement for "-fvia-C
-optc-ffast-math -fexcess-precision".
SSE2 also has the advantage of performing all operations at the
correct precision, so floating-point results are consistent with other
platforms.
I also tweaked the x87 code generation a bit while I was here, now
it's slighlty less bad than before.
}}}
I measured the FF ray tracer benchmark, and `-msse2` seems on par with, or
possibly better than, `"-fvia-C -optc-O3 -fexcess-precision -ffast-math"`,
although the results are quite variable on the machine I tried it on. I
suspect we're suffering from randomly misaligned Doubles on the stack and
heap.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/594#comment:12>
GHC <http://www.haskell.org/ghc/>
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