On Wed, Aug 8, 2012 at 1:31 PM, <ganesh.gopalasubraman...@amd.com> wrote:
> Bdver2 cpu supports both fma and fma4 instructions. > Previous to patch, option "-mno-xop" removes "-mfma4". > Similarly, option "-mno-fma4" removes "-mxop". It looks to me that there is some misunderstanding. AFAICS: -mxop implies -mfma4, but reverse is not true. Please see #define OPTION_MASK_ISA_FMA4_SET \ (OPTION_MASK_ISA_FMA4 | OPTION_MASK_ISA_SSE4A_SET \ | OPTION_MASK_ISA_AVX_SET) #define OPTION_MASK_ISA_XOP_SET \ (OPTION_MASK_ISA_XOP | OPTION_MASK_ISA_FMA4_SET) So, -mxop sets -mfma4, etc ..., but -mfma4 does NOT enable -mxop. OTOH, #define OPTION_MASK_ISA_FMA4_UNSET \ (OPTION_MASK_ISA_FMA4 | OPTION_MASK_ISA_XOP_UNSET) #define OPTION_MASK_ISA_XOP_UNSET OPTION_MASK_ISA_XOP -mno-fma4 implies -mno-xop, but again reverse is not true. Thus, -mno-xop does NOT imply -mno-fma4. > So, the patch conditionally disables "-mfma" or "-mfma4". > Enabling "-mxop" is done by also checking "-mfma". Please note that conditional handling of ISA flags belongs to ix86_option_override_internal. However, if someone set -mfma4 together with -mfma on the command line, we should NOT disable selected ISA behind user's back, in the same way as we don't disable anything with "-march=i386 -msse4". With -march=bdver2, we already marked that only fma is supported, and if user selected "-march=bdver2 -mfma4" on the command line, we shouldn't disable anything. Uros.
