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sqrt via SSE2 registers


Is there any way of telling gcc that I care so little about precision that
I'm prepared to have it compute the square roots of objects in SSE2
registers by using SQRTSD rather than by storing the register to memory,
loading it onto the FP stack and calling fsqrt?

I've tried (on the principle of sticking in anything that might have an
effect)

-O3 -march=pentium4 -msse2 -mfpmath=sse{,387} -ffast-math \
-mno-fancy-math-387

but nonetheless always get the worst-of-both-worlds behavior described
above.

Am I just being too optimistic about mainline gcc's current level of support
for the P4? There is a sqrtdf2_1 instruction in i386.md which looks as if it
should behave correctly.

Tom


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