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Re: fancy x87 ops, SSE and -mfpmath=sse,387 performance


On 8/6/06, Paolo Bonzini <paolo.bonzini@lu.unisi.ch> wrote:
> Is there a way to enable such exotic codegen for 32bit environments?

With libgcc-math you didn't have exotic instructions, but you had
trascendental operations compiled with -mfpmath=sse and with a special
ABI.  -mfpmath=sse won about 8% over -mfpmath=387 for tramp3d, which
does have trascendental operations.

Let's see what happens for 4.3.
I'm not sure i groked the fuss about libgcc-math.
What i know is that -mfpmath=sse in recent gcc does wonders, just like
SSE implementations of such library calls as i can experience them in
a sane environment like linux x86-64. But it's truely horrible in
cygwin and off the mark by an order of magnitude.

My complaint is that atm the only stopgap on such platform is to
ressort to -mfpmath=sse,387 which is not without drawbacks.

I understand -march=k8 -mfpmath=sse -mfancy-math-387 is out of
question, but could clarify what i should expect from 4.3?


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