https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123133
Bug ID: 123133
Summary: GCC misses opportunity to use ranges to elide
extensions
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: tnfchris at gcc dot gnu.org
Target Milestone: ---
The following testcase
#include <stdint.h>
int64_t bar(int32_t in) {
return (7 - (in % 8));
}
at -O3 produces
bar(int):
negs w1, w0
mov w2, 7
and w0, w0, w2
and w1, w1, w2
csneg w1, w0, w1, mi
sub w0, w2, w1
sxtw x0, w0
ret
but the result of the subtract is guaranteed to be positive so the sign
extension isn't needed.
Clang produces the optimal
bar(int):
negs w9, w0
and w10, w0, #0x7
mov w8, #7
and w9, w9, #0x7
csneg w9, w10, w9, mi
sub w0, w8, w9
ret
