https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89430
Bug ID: 89430
Summary: A missing ifcvt optimization to generate csel
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jiangning.liu at amperecomputing dot com
Target Milestone: ---
For a small case,
unsigned *a;
void test(unsigned k, unsigned b) {
if (b < a[k]) {
a[k] = b;
}
}
"gcc -O3 -S" generates,
adrp x2, a
uxtw x0, w0
ldr x2, [x2, #:lo12:a]
ldr w3, [x2, x0, lsl 2]
cmp w3, w1
bls .L1
str w1, [x2, x0, lsl 2]
Actually we should use csel instruction instead of conditional branch, so
expect to have the followings generated,
adrp x2, a
uxtw x0, w0
ldr x2, [x2, #:lo12:a]
ldr w3, [x2, x0, lsl 2]
cmp w3, w1
csel w1, w1, w3, hi
str w1, [x2, x0, lsl 2]
RTL optimization ifcvt misses this opportunity.
