[Bug tree-optimization/103509] New: ((-1u >> t) & b) != 0 is not optimized to b != 0
pinskia at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Tue Nov 30 23:35:00 GMT 2021
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103509
Bug ID: 103509
Summary: ((-1u >> t) & b) != 0 is not optimized to b != 0
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Take:
bool f1(bool a, int t)
{
unsigned tt = -1;
tt >>= t;
return (a&tt) != 0;
}
bool f2(bool a, int t)
{
unsigned tt = -1;
tt >>= t;
return (tt) != 0;
}
As shown by the above, we know that (-1u>>t)!=0 is always true Therefore we
should be able to optimize f1 to just a!=0
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