------- Comment #15 from changpeng dot fang at amd dot com 2010-07-01 00:34
-------
Unrolling of the peeled loop is partially the reason for test_fpu.f90
compilation
time and code size increase. Vectorization peeled a few iteration of the the
loop, the prefetching and unrolling passes does not recognize that a loop is a
peeled version and still unroll the loop.
MODULE kinds
INTEGER, PARAMETER :: RK8 = SELECTED_REAL_KIND(15, 300)
END MODULE kinds
! --------------------------------------------------------------------
PROGRAM TEST_FPU ! A number-crunching benchmark using matrix inversion.
USE kinds ! Implemented by: David Frank dave_fr...@hotmail.com
IMPLICIT NONE ! Gauss routine by: Tim Prince n...@aol.com
! Crout routine by: James Van Buskirk tor...@ix.netcom.com
! Lapack routine by: Jos Bergervoet berge...@iaehv.nl
REAL(RK8) :: pool(101, 101,1000), a(101, 101)
INTEGER :: i
DO i = 1,1000
a = pool(:,:,i) ! get next matrix to invert
END DO
END PROGRAM TEST_FPU
In this example, prefetching will unroll tree version of the innermost loop.
If we turn off the vectorizer, it unrolls the only loop.
In addition, -fprefetch-loop-arrays and -funroll-loops (turned on at the same
time) will unroll the same loop. This is over-unrolling and -funroll-loops
should recognize that the loop has already been unrolled by prefetching.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44576
