https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110088
Bug ID: 110088
Summary: [avr] Improve operation with const on l-reg after move
from d-reg
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: gjl at gcc dot gnu.org
Target Milestone: ---
The register allocator might generate code that moves a value from a d-reg to
an l-reg, and then performs operation like PLUS, IOR, AND with a constant. So
we have a sequence like:
lreg = dreg
lreg = lreg <op> const
This is expensive because lreg cannot handle const and needs a QI scratch to
load bytes of const. Instead, if dreg dies after the first insn, better code
is:
dreg = dreg <op> const
lreg = dreg
An RTL peephole can catch this.
