https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92283
--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
So unrolling the inner loop of
846 if(iperturb.ge.2) then
do m3=1,3
do m4=1,3
fn(m2,konl(m1))=fn(m2,konl(m1))+
& xsj*skl(m4,m3)*weight*
& (vkl(m2,m4)*shp(m3,m1)+
& vkl(m2,m3)*shp(m4,m1))/2.d0
enddo
enddo
endif
is enough to trigger the failure for example but I don't see anything wrong
happening here. -fdbgcnt=gimple_unroll:0:24 succeeds, 0:25 fails but
25:26 succeeds (only above loop unrolled). There's subtle association
differences but entirely within the scope of the fortran standard
(parenthesis honored, only the adds are associated).
Given other loops play into this as well here
the issue is probably inconsistencies leading to failing cancelling or
simply too much jitter....
Thus we're unlucky(?)
Building results.f with -fno-associative-math doesn't help but I'm not
sure how much the frontend likes to be messed with its choice of default
option values for those.
Not unrolled loop:
.L169:
# results.f:852: & vkl(m2,m3)*shp(m4,m1))/2.d0
vmovsd -40(%rdi,%r8,8), %xmm8 # MEM[base: _4159, index:
ivtmp.1147_4167, step: 8, offset: -40B], _1031
movq %r8, %rax # ivtmp.1147, tmp2656
salq $5, %rax #, tmp2656
vmovsd -32(%rcx,%rax), %xmm6 # MEM[base: _4156, index: _4155,
offset: -32B], _1036
xorl %eax, %eax # ivtmp.1141
.L167:
vmulsd %xmm0, %xmm5, %xmm0 # pretmp_5253, xsj.389_997, tmp2657
vmulsd %xmm4, %xmm0, %xmm1 # weight, tmp2657, _1023
vmulsd -32(%rdi,%rax), %xmm6, %xmm0 # MEM[base: _4159, index:
ivtmp.1141_4178, offset: -32B], _1036, tmp2658
vfmadd231sd (%rcx,%rax,4), %xmm8, %xmm0 # MEM[base: _4156,
index: ivtmp.1141_4178, step: 4, offset: 0B], _1031, _1041
# results.f:848: do m4=1,3
addq $8, %rax #, ivtmp.1141
# results.f:852: & vkl(m2,m3)*shp(m4,m1))/2.d0
vmulsd %xmm1, %xmm0, %xmm0 # _1023, _1041, tmp2659
vfmadd231sd %xmm7, %xmm0, %xmm3 # tmp3594, tmp2659,
fn__I_lsm.737
# results.f:848: do m4=1,3
cmpq $24, %rax #, ivtmp.1141
je .L166 #,
# results.f:852: & vkl(m2,m3)*shp(m4,m1))/2.d0
vmovsd -24(%r9,%rax), %xmm0 # MEM[base: _4168, index:
ivtmp.1141_4177, offset: -24B], pretmp_5253
jmp .L167 #
.p2align 4
.p2align 3
.L166:
# results.f:847: do m3=1,3
incq %r8 # ivtmp.1147
cmpq $4, %r8 #, ivtmp.1147
je .L168 #,
# results.f:852: & vkl(m2,m3)*shp(m4,m1))/2.d0
vmovsd (%r9), %xmm0 # MEM[base: _4154, offset: 0B], pretmp_5253
addq $24, %r9 #, ivtmp.1164
jmp .L169 #
unrolled one:
.L167:
vmovsd (%rdi), %xmm15 # MEM[base: _4141, offset: 0B], _1036
vmovsd (%r8), %xmm0 # MEM[base: _4142, offset: 0B], _1031
# results.f:847: do m3=1,3
addq $24, %rdx #, ivtmp.1140
addq $8, %r8 #, ivtmp.1132
addq $32, %rdi #, ivtmp.1136
# results.f:852: & vkl(m2,m3)*shp(m4,m1))/2.d0
vmulsd %xmm12, %xmm6, %xmm12 # pretmp_5248, xsj.389_997, tmp2676
vmulsd %xmm4, %xmm12, %xmm13 # weight, tmp2676, _4551
vmulsd %xmm10, %xmm15, %xmm12 # _4543, _1036, tmp2677
vfmadd231sd %xmm11, %xmm0, %xmm12 # _4547, _1031, _4541
vmulsd %xmm13, %xmm12, %xmm12 # _4551, _4541, tmp2678
vmulsd -16(%rdx), %xmm6, %xmm13 # MEM[base: _4140, offset: 8B],
xsj.389_997, tmp2680
vfmadd132sd %xmm7, %xmm1, %xmm12 # tmp3622, fn__I_lsm.737, _4537
vmulsd %xmm8, %xmm15, %xmm1 # _4515, _1036, tmp2681
vmulsd %xmm3, %xmm15, %xmm15 # _1039, _1036, tmp2685
vfmadd231sd %xmm9, %xmm0, %xmm1 # _4519, _1031, _4513
vfmadd132sd %xmm5, %xmm15, %xmm0 # _1027, tmp2685, _1041
vmulsd %xmm4, %xmm13, %xmm13 # weight, tmp2680, _4523
vmulsd %xmm13, %xmm1, %xmm1 # _4523, _4513, tmp2682
vfmadd132sd %xmm7, %xmm12, %xmm1 # tmp3622, _4537, _4509
vmulsd -8(%rdx), %xmm6, %xmm12 # MEM[base: _4140, offset: 16B],
xsj.389_997, tmp2684
vmulsd %xmm4, %xmm12, %xmm12 # weight, tmp2684, _1023
vmulsd %xmm12, %xmm0, %xmm0 # _1023, _1041, tmp2686
vfmadd231sd %xmm7, %xmm0, %xmm1 # tmp3622, tmp2686,
fn__I_lsm.737
# results.f:847: do m3=1,3
cmpq %rdx, %r12 # ivtmp.1140, _4136
je .L166 #,
# results.f:852: & vkl(m2,m3)*shp(m4,m1))/2.d0
vmovsd (%rdx), %xmm12 # MEM[base: _4138, offset: 0B], pretmp_5248
jmp .L167 #
but as said, not unrolling others while still unrolling this one doesn't
help.
Disabling FMA with -mno-fma helps.
-fdbgcnt=gimple_unroll:25:27 unrolling the preceeding loop at 839 as well
(there's CSE and thus more association opportunities then) doesn't trigger
the failure on its own either.
I'm going to test & commit the dbgcnt patch.
