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From: "irar at il dot ibm.com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/51499] vectorizer missing simple case Date: Mon, 12 Dec 2011 11:13:00 -0000 [thread overview] Message-ID: <bug-51499-4-maxQeUMh64@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-51499-4@http.gcc.gnu.org/bugzilla/> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51499 --- Comment #8 from Ira Rosen <irar at il dot ibm.com> 2011-12-12 11:03:59 UTC --- (In reply to comment #6) > While investigating pr51597, I have found that vectorized loops in programs as > simple as > > subroutine spmmult(x,b,ad) > implicit none > integer, parameter :: nxyz=1008315 > real(8),dimension(nxyz):: x,b,ad > b = ad*x > end subroutine spmmult !========================================= > > has always an additional non-vectorized loop, This loop has a prologue loop for alignment purposes. > L5: > movsd -8(%rdi,%rax,8), %xmm0 > mulsd -8(%rdx,%rax,8), %xmm0 > movsd %xmm0, -8(%rsi,%rax,8) > addq $1, %rax > cmpq %rcx, %rax > jne L5 > > even when the above loops are unrolled. How can the loop L5 be unrolled if it > is only there for a "scalar epilogue"? It can't be unrolled, since the alignment is unknown, so we don't know the number of iterations of the prologue loop, and, therefore, we don't know the number of iterations of the epilogue.
next prev parent reply other threads:[~2011-12-12 11:04 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-12-10 18:39 [Bug tree-optimization/51499] New: " fb.programming at gmail dot com 2011-12-11 8:29 ` [Bug tree-optimization/51499] " irar at il dot ibm.com 2011-12-11 8:48 ` fb.programming at gmail dot com 2011-12-11 9:05 ` irar at il dot ibm.com 2011-12-11 12:13 ` fb.programming at gmail dot com 2011-12-11 13:39 ` irar at il dot ibm.com 2011-12-11 14:55 ` dominiq at lps dot ens.fr 2011-12-11 16:58 ` fb.programming at gmail dot com 2011-12-12 11:13 ` irar at il dot ibm.com [this message] 2011-12-12 11:23 ` irar at il dot ibm.com 2011-12-12 11:27 ` rguenth at gcc dot gnu.org 2011-12-12 12:21 ` irar at il dot ibm.com 2011-12-12 13:10 ` dominiq at lps dot ens.fr 2011-12-12 14:31 ` fb.programming at gmail dot com 2011-12-13 16:33 ` irar at il dot ibm.com 2021-08-07 5:19 ` [Bug tree-optimization/51499] -Ofast does not vectorize while -O3 does pinskia at gcc dot gnu.org
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