https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126021
Bug ID: 126021
Summary: 1 >> a is sometimes better than a == 0 on specific
types and targets
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: kaelfandrew at gmail dot com
Target Milestone: ---
```
#define type int
type src (type a) {
if (a >= (sizeof (type) * __CHAR_BIT__))
__builtin_unreachable ();
return a == 0;
}
type tgt (type a) {
return 1 >> a;
}
```
https://godbolt.org/z/zajE6Mrdr
Since r15-6929, tgt is optimize to src.
Compile this with -O3 -march=znver5, using llvm-mca and type = int, tgt uses
one less instruction than src.
