https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71336
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |jakub at gcc dot gnu.org,
| |uros at gcc dot gnu.org
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The problem is that this is done usually during the ce* passes in a target
mov<mode>cc expander, but unfortunately that expander doesn't know if the
comparison operand has just a single bit set (and which one). For that query
the most natural predicate would be nonzero_bits, but only the combiner pass
has infrastructure to track non-zero bits in between different instructions.
The ce* passes don't even compute a reaching defs df problem nor ud chains,
though perhaps the ce* pass just could walk a few insns backwards looking for
unconditional setter of the pseudo in the comparison (it would only work then
if the masking is done right before comparison though).
