https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102188
Bug ID: 102188
Summary: Over widening detection doesn't work when no range
information
Product: gcc
Version: 12.0
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 example:
#include <stdint.h>
int f( int16_t a[16] )
{
int res = 0;
for ( int i = 0; i < 16; i++ )
res |= (a[i]);
return res;
}
gets vectorized with the ORs happening as int32, but since | can't overflow or
underflow the ORs could have been done as int16. This saves 2 ORs and 4
widenings.
I would have expected overwidening detection to handle this, however that fails
because VRP has no range information for `a` but in this case it's safe to do
based on the type alone.
