https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100874
Bug ID: 100874
Summary: [12 Regression] slight missed optimization with
min<a,CST>-CST on aarch64
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Target: aarch64-*-*
Take:
int f(int a) { return a < 4 ? a - 4 : 0; }
int f1(int a) { int x = a - 4; if (a < 4) return x; return 0; }
int f2(int a) { int t = a < 4 ? a : 4; return t - 4; }
In GCC 11, we produce:
f(int):
mov w1, 4
cmp w0, w1
csel w0, w0, w1, le
sub w0, w0, #4
ret
f1(int):
subs w0, w0, 4
csel w0, w0, wzr, lt
ret
f2(int):
mov w1, 4
cmp w0, w1
csel w0, w0, w1, le
sub w0, w0, #4
ret
On the trunk all three give the same code gen (due to PHI-OPT being improved)
but of what f and f2 used to give.
All three should produce what f1 had produed instead.
This is gcc.target/aarch64/subs_compare_2.c
