https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79722
Bug ID: 79722
Summary: Missed opportunity for fused multiply/add with avx2
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: tkoenig at gcc dot gnu.org
Target Milestone: ---
Created attachment 40835
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40835&action=edit
Output of gcc -Ofast -mavx2 -S -o bar-gcc.s bar.c
The test case is the same as PR 79709:
typedef double v4do __attribute__((vector_size (32)));
typedef long int v4i __attribute__((vector_size (32)));
#define VSET(vect,val) do { vect[0]=val; vect[1]=val; vect[2]=val; vect[3]=val;
} while (0)
void foo(v4do cx, v4do cy, v4i *r)
{
v4do x, y, xn, yn;
v4i add, res;
v4do two, four;
long int done;
VSET(res, 0L);
VSET(two, 2.0);
VSET(four, 4.0);
x = cx;
y = cy;
done = 0;
while (1)
{
xn = x*x - y*y + cx;
yn = two*x*y + cy;
add = xn+xn + yn*yn < four;
res += add;
if (add[0] == 0 || add[1] == 0 || add[2] || add[3])
break;
x = xn;
y = yn;
}
*r = res;
}
With gcc, the inner loop is tranlsated into
.L13:
vpextrq $1, %xmm2, %rax
testq %rax, %rax
je .L2
vextracti128 $0x1, %ymm2, %xmm2
vmovq %xmm2, %rax
testq %rax, %rax
jne .L2
vpextrq $1, %xmm2, %rax
vmovapd %ymm4, %ymm3
testq %rax, %rax
jne .L2
.L3:
vmulpd %ymm3, %ymm3, %ymm4
vmulpd %ymm9, %ymm3, %ymm3
vaddpd %ymm0, %ymm4, %ymm4
vmulpd %ymm7, %ymm3, %ymm3
vsubpd %ymm10, %ymm4, %ymm4
vaddpd %ymm1, %ymm3, %ymm9
vaddpd %ymm4, %ymm4, %ymm2
vmulpd %ymm9, %ymm9, %ymm10
vaddpd %ymm10, %ymm2, %ymm2
vcmpltpd %ymm6, %ymm2, %ymm2
vmovq %xmm2, %rax
vpaddq %ymm2, %ymm8, %ymm8
testq %rax, %rax
jne .L13
icc -O3 -march=core-avx2 -S results in
..B1.6: # Preds ..B1.5
# Execution count [6.94e-01]
vmovdqa %ymm11, %ymm5 #27.7
# LOE rbx rdi r12 r13 r14 r15 ymm0 ymm1 ymm2
ymm3 ymm4 ymm5 ymm6 ymm7
..B1.2: # Preds ..B1.6 ..B1.1
# Execution count [1.69e+00]
vmovaps %ymm4, %ymm11 #21.24
vfmsub213pd %ymm6, %ymm4, %ymm11 #21.24
vfmsub231pd %ymm5, %ymm5, %ymm11 #21.24
vmulpd %ymm3, %ymm5, %ymm5 #22.16
vaddpd %ymm11, %ymm11, %ymm8 #23.16
vfmadd213pd %ymm7, %ymm5, %ymm4 #22.22
vfmadd231pd %ymm4, %ymm4, %ymm8 #23.24
vcmpltpd %ymm2, %ymm8, %ymm9 #23.29
vandpd %ymm9, %ymm1, %ymm10 #23.29
vmovups %ymm10, -64(%rsp) #23.7
vpaddq %ymm10, %ymm0, %ymm0 #24.7
cmpq $0, -64(%rsp) #25.21
je ..B1.7 # Prob 20% #25.21
# LOE rbx rdi r12 r13 r14 r15 ymm0 ymm1 ymm2
ymm3 ymm4 ymm6 ymm7 ymm11
..B1.3: # Preds ..B1.2
# Execution count [1.36e+00]
cmpq $0, -56(%rsp) #25.36
je ..B1.7 # Prob 20% #25.36
# LOE rbx rdi r12 r13 r14 r15 ymm0 ymm1 ymm2
ymm3 ymm4 ymm6 ymm7 ymm11
..B1.4: # Preds ..B1.3
# Execution count [1.08e+00]
cmpq $0, -48(%rsp) #25.45
jne ..B1.7 # Prob 20% #25.45
# LOE rbx rdi r12 r13 r14 r15 ymm0 ymm1 ymm2
ymm3 ymm4 ymm6 ymm7 ymm11
..B1.5: # Preds ..B1.4
# Execution count [8.67e-01]
cmpq $0, -40(%rsp) #25.55
je ..B1.6 # Prob 80% #25.55
# LOE rbx rdi r12 r13 r14 r15 ymm0 ymm1 ymm2
ymm3 ymm4 ymm6 ymm7 ymm11
where icc uses eight double precision floating point operations
vs. gcc's ten.
