On Tue, Jan 12, 2016 at 01:32:05PM +0100, Uros Bizjak wrote: > Using this patch, SSE math won't be emitted for a simple testcase > using " -O2 -msse -m32 -std=c99 -mfpmath=sse" compile flags: > > float test (float a, float b) > { > return a + b; > } > > since we start with: > > test (float a, float b) > { > long double _2; > long double _4; > long double _5; > float _6; > > <bb 2>: > _2 = (long double) a_1(D); > _4 = (long double) b_3(D); > _5 = _2 + _4; > _6 = (float) _5; > return _6; > } > > This is counter-intuitive, so I'd say we leave things as they are. The > situation where only floats are evaluated as floats and doubles are > evaluated as long doubles is not covered in the FLT_EVAL_METHOD spec.
Well, for the -fexcess-precision=standard case (== -std=c99) FLT_EVAL_METHOD 2 doesn't hurt, that forces in the FE long double computation. While if it is 0 with -msse -mfpmath=sse, it means that the FE leaves computations as is and they are computed in float precision for floats and in long double precision for doubles. For -fexcess-precision=fast it is different, because the FE doesn't do anything, so in the end it is mixed in that case. So, for -msse -mfpmath=sse, I think either we need FLT_EVAL_METHOD 2 or -1 or 2 for -fexcess-precision=standard and -1 for -fexcess-precision=fast. Jakub