late-combine: Preserve INSN_CODE when modifying notes [PR116343]

When it removes a definition, late-combine tries to update all
uses in notes.  It does this using the same insn_propagation class
that it uses for patterns.

However, insn_propagation uses validate_change, which in turn
resets the INSN_CODE.  This is inefficient in the best case,
since it forces the pattern to be rerecognised even though
changing a note can't affect the INSN_CODE.  But in the PR
it's a correctness problem: resetting INSN_CODE means we lose
the NOOP_INSN_MOVE_CODE, which in turn means that rtl-ssa doesn't
queue it for deletion.

This patch adds a routine specifically for propagating into notes.
A belt-and-braces fix would be to rerecognise noop moves in
function_info::change_insns, but I can't think of a good reason
why that would be necessary, and it could paper over latent bugs.

gcc/
	PR testsuite/116343
	* recog.h (insn_propagation::apply_to_note): Declare.
	* recog.cc (insn_propagation::apply_to_note): New function.
	* late-combine.cc (insn_combination::substitute_note): Use
	apply_to_note instead of apply_to_rvalue.
	* rtl-ssa/changes.cc (rtl_ssa::changes_are_worthwhile): Improve
	dumping of costs for noop moves.

gcc/testsuite/
	PR testsuite/116343
	* gcc.dg/torture/pr116343.c: New test.

0 files changed, 0 insertions, 0 deletions