http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57037
Bug #: 57037
Summary: GCC does not generate non-temporal stores on i386 with
SSE2+
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: anl...@gmx.de
Hello,
it appears that gcc does not generate non-temporal stores
available on i386 at least with SSE2. This is an important
optimization for some memory-bandwidth limited codes.
Example: for the stream triad kernel,
subroutine stream_kernel_triad (a, b, c, n, s)
integer , intent(in) :: n
double precision :: a(*), b(*), c(*)
double precision, intent(in) :: s
integer :: j
do j = 1,n
a(j) = b(j) + s*c(j)
end do
end subroutine stream_kernel_triad
the Intel compiler generates vectorized code with a
throughput that is 25% higher on my Core2 than when
disabling the generation of non-temporal stores
(i.e. compiling with "-opt-streaming-stores never").
gfortran (using -Ofast -fprefetch-loop-arrays) exactly
reproduces the performance of the Intel compiler without
temporal stores. It appears that this is an important
optimization.
Harald
