https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95230
Bug ID: 95230
Summary: Failure to optimize bit-scatter pattern to and 1
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: gabravier at gmail dot com
Target Milestone: ---
uint32_t scatter(uint32_t val)
{
uint32_t res = 0;
uint32_t off = 0;
for (uint32_t I = 0; I < 32; ++I)
if (1 & (1 << I))
res |= (val & (1 << off++)) << I;
return res;
}
This can be optimized to `return val & 1;`. LLVM does this transformation, but
GCC does not. There is a more generic optimization that looks like it can be
done using something else than `1` as the left operand of the `&` in the `if`.
