SSE and x86 FP ABI (again)

[Drew Hess <dhess at ilm dot com>]

Has there been any resolution on the issue of whether -msse and -msse2
break the x86 FP ABI?  I didn't think there was a consensus after the last
thread on this topic.

Some of us don't require the extra precision of x87 extended double, and
would prefer the speedup (on Pentium 4, at least)  and predictable
behavior of the SSE modes.  But we still need IEEE-compliant FP, so
throwing them into the -ffast-math option along with the other
non-compliant optimizations seems severe.

I suspect that those who run math-intensive codes on multiple platforms
would agree, since x86 with -msse and -msse2 behaves a lot more like other
architectures than x87 FP does.  Yes, we can use -ffloat-store, but it
sometimes comes with considerable performance loss.  The SSE modes give us
the best of both worlds.

I'm not arguing that SSE should be the default FP mode on x86, I'm just
hoping to maintain the status quo.

Thanks to Jan and the others for their work.


-dwh-