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Re: New GCC releases comparison and comparison of GCC4.4 and LLVM2.5 on SPEC2000
On Mon, 25 May 2009, Chris Lattner wrote:
> On May 13, 2009, at 5:26 AM, Duncan Sands wrote:
>
> > Hi Richard,
> >
> > > -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.
>
> However, this does break long double, right?
I already said in <http://gcc.gnu.org/ml/gcc/2009-05/msg00341.html> that
it is a purely link-time option that does not cause
TARGET_96_ROUND_53_LONG_DOUBLE to be set; fixing that would make long
double behave correctly, although not necessarily calls to libgcc,
libstdc++, libm or other library functions that did not expect to be
called in the different mode, unless extra multilibs built to expect that
mode are added (and the source code to libraries such as libm adjusted to
handle this).
--
Joseph S. Myers
joseph@codesourcery.com