On current x86 and x86_64 processors denormal numbers are handled as a special
case and very slowly. This can have a detrimental impact on the performance of
numerical programs. A common fix for this problem, at the cost of some
numerical stability, is to set the processor flag to flush denormals to zero.
This can be achieved in C with the following on SSE machines:
_MM_SET_FLUSH_ZERO_MODE (_MM_FLUSH_ZERO_ON);
However it is not desirable to include C in a fortran program or library. Other
compiler tackle this by adding flags (ifort, NAG f95) or environment variables
(g95) which set this flush mode during program initialization. It would be good
if gfortran offered a similar facility (I have not been able to locate any
reference to one at the moment).
--
Summary: Flush denormals to Zero Flag
Product: gcc
Version: 4.3.1
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: fortran
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: J dot Hogg at rl dot ac dot uk
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36821
