https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112664
Bug ID: 112664
Summary: missed-optimization: extra comparison when reordering
statements
Product: gcc
Version: 13.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: goon.pri.low at gmail dot com
Target Milestone: ---
These two functions which you would expect to be essentially equivalent, has
the first one with an extra comparison.
int unopt(int v) {
if (v < 6) {
return 15;
}
if (v > 6) {
return 3;
}
return 9;
}
unopt:
mov eax, 15
cmp edi, 5
jle .L1
cmp edi, 6
mov eax, 3
mov edx, 9
cmove eax, edx
.L1:
ret
The second one it reuses the old comparison.
int opt(int v) {
if (v > 6) {
return 3;
}
if (v < 6) {
return 15;
}
return 9;
}
opt:
mov eax, 3
cmp edi, 6
jg .L6
mov eax, 15
mov edx, 9
cmove eax, edx
.L6:
ret
