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Re: New GCC releases comparison and comparison of GCC4.4 and LLVM2.5 on SPEC2000
On Wed, 13 May 2009, Richard Guenther wrote:
> -mpc64 sets the x87 floating point control register to not use the 80bit
> extended precision. This causes some x87 floating point operations
> to operate faster and there are no issues with the extra roundings you
> get when storing an 80bit precision register to a 64bit memory location.
Note that this is purely a link-time option; it does not cause
TARGET_96_ROUND_53_LONG_DOUBLE to be set so the compiler will not know
internally how long double behaves in the processor. Note also that you
still have the extended exponent range and associated issues with storing
to memory with that (including extra roundings for subnormals).
--
Joseph S. Myers
joseph@codesourcery.com