https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70102
Bug ID: 70102
Summary: Tree re-association prevents SLP vectorization at
-Ofast.
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: vekumar at gcc dot gnu.org
Target Milestone: ---
The following test case failed to vectorize in gcc -Ofast.
(---snip---)
subroutine test (x,y,z)
integer x,y,z
real*8 a(5,x,y,z),b(5,x,y,z)
real*8 c
c = 0.0d0
do k=1,z
do j=1,y
do i=1,x
do l=1,5
c = c + a(l,i,j,k)*b(l,i,j,k)
enddo
enddo
enddo
enddo
write(30,*)'c ==',c
return
end
(---snip---)
Vectorizer dump
(---snip---)
test.f:9:0: note: original stmt _95 = _92 + _112;
test.f:9:0: note: Build SLP for _152 = _150 * _151;
test.f:9:0: note: Build SLP failed: different operation in stmt _152 = _150 *
_151;
test.f:9:0: note: original stmt _95 = _92 + _112;
test.f:9:0: note: Build SLP for _55 = _53 * _54;
test.f:9:0: note: Build SLP failed: different operation in stmt _55 = _53 *
_54;
test.f:9:0: note: original stmt _95 = _92 + _112;
test.f:1:0: note: vectorized 0 loops in function
(---snip---)
Re-association pass changes one of the tree expression and it prevents from SLP
block vectorization.
Before
(---snip---)
# VUSE <.MEM_7>
_90 = *A.18_37[_89];
# VUSE <.MEM_7>
_91 = *A.20_40[_89];
_92 = _90 * _91;
# VUSE <.MEM_7>
c.21_93 = cD.3439;
c.22_94 = _92 + c.21_93;
_109 = _87 + 2;
# VUSE <.MEM_7>
_110 = *A.18_37[_109];
# VUSE <.MEM_7>
_111 = *A.20_40[_109];
_112 = _110 * _111;
c.22_114 = c.22_94 + _112;
_129 = _87 + 3;
(---snip---)
After tree-reassoc
(---snip---)
# VUSE <.MEM_7>
_90 = *A.18_37[_89];
# VUSE <.MEM_7>
_91 = *A.20_40[_89];
_92 = _91 * _90;
# VUSE <.MEM_7>
c.21_93 = cD.3439;
_109 = _87 + 2;
# VUSE <.MEM_7>
_110 = *A.18_37[_109];
# VUSE <.MEM_7>
_111 = *A.20_40[_109];
_112 = _111 * _110;
_31 = _112 + _92; <== new statement
_129 = _87 + 3;
(---snip---)
