https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113134
Bug ID: 113134
Summary: Middle end early break vectorization: Fail to
vectorize a simple early break code
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: juzhe.zhong at rivai dot ai
Target Milestone: ---
Hi, as reference shows:
https://compiler-explorer.com/z/zMzba7WT1
void add(int N, int *__restrict a, int *__restrict b, int *__restrict c) {
for (int i = 0; i < N; i++) {
c[i] = a[i] + b[i];
if (i > 1000) {
break;
}
}
}
GCC failed to vectorize it:
add:
cmp w0, 0
ble .L1
sbfiz x6, x0, 2, 32
mov x4, 0
.L3:
ldr w0, [x1, x4]
ldr w5, [x2, x4]
add w0, w0, w5
str w0, [x3, x4]
cmp x4, 4004
beq .L1
add x4, x4, 4
cmp x6, x4
bne .L3
.L1:
ret
But clang is able to vectorize it:
add: // @add
cmp w0, #1
b.lt .LBB0_8
mov w8, w0
mov w9, #1001 // =0x3e9
sub x8, x8, #1
cmp x8, #1001
csel x9, x8, x9, lo
add x10, x9, #1
cnth x9
cmp x10, x9
b.hs .LBB0_3
mov x9, xzr
b .LBB0_6
.LBB0_3:
ptrue p0.s
neg x9, x9
mov x11, xzr
and x9, x10, x9
addvl x12, x1, #1
addvl x13, x2, #1
addvl x14, x3, #1
.LBB0_4: // =>This Inner Loop Header: Depth=1
ld1w { z0.s }, p0/z, [x1, x11, lsl #2]
ld1w { z1.s }, p0/z, [x2, x11, lsl #2]
ld1w { z2.s }, p0/z, [x12, x11, lsl #2]
ld1w { z3.s }, p0/z, [x13, x11, lsl #2]
add z0.s, z1.s, z0.s
add z1.s, z3.s, z2.s
st1w { z0.s }, p0, [x3, x11, lsl #2]
st1w { z1.s }, p0, [x14, x11, lsl #2]
inch x11
cmp x9, x11
b.ne .LBB0_4
cmp x10, x9
b.eq .LBB0_8
.LBB0_6: // =>This Inner Loop Header: Depth=1
lsl x10, x9, #2
cmp x9, #1001
ldr w11, [x1, x10]
ldr w12, [x2, x10]
add w11, w12, w11
str w11, [x3, x10]
b.eq .LBB0_8
cmp x8, x9
add x9, x9, #1
b.ne .LBB0_6
.LBB0_8:
ret
