https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94740
--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Richard Sandiford <rsand...@gcc.gnu.org>: https://gcc.gnu.org/g:66ec22b0d3feb96049283abe5c6c9a05ecef8b86 commit r11-4-g66ec22b0d3feb96049283abe5c6c9a05ecef8b86 Author: Richard Sandiford <richard.sandif...@arm.com> Date: Thu Apr 30 20:00:52 2020 +0100 cse: Use simplify_replace_fn_rtx to process notes [PR94740] cse_process_notes did a very simple substitution, which in the wrong circumstances could create non-canonical RTL and invalid MEMs. Various sticking plasters have been applied to cse_process_notes_1 to handle cases like ZERO_EXTEND, SIGN_EXTEND and UNSIGNED_FLOAT, but I think this PR is a plaster too far. The code is trying hard to avoid creating unnecessary rtl, which of course is a good thing. If we continue to do that, then we can end up changing subexpressions while keeping the containing rtx. This in turn means that validate_change will be a no-op on the containing rtx, even if its contents have changed. So in these cases we have to apply validate_change to the individual subexpressions. On the other hand, if we always apply validate_change to the individual subexpressions, we'll end up calling validate_change on something before it has been simplified and canonicalised. And that's one of the situations we're trying to avoid. There might be a middle ground in which we queue the validate_changes as part of a group, and so can cancel the pending validate_changes for subexpressions if there's a change in the outer expression. But that seems even more ad-hoc than the current code. It would also be quite an invasive change. I think the best thing is just to hook into the existing simplify_replace_fn_rtx function, keeping the REG and MEM handling from cse_process_notes_1 essentially unchanged. It can generate more redundant rtl when a simplification takes place, but it has the advantage of being relative well-used code (both directly and via simplify_replace_rtx). 2020-04-30 Richard Sandiford <richard.sandif...@arm.com> gcc/ PR rtl-optimization/94740 * cse.c (cse_process_notes_1): Replace with... (cse_process_note_1): ...this new function, acting as a simplify_replace_fn_rtx callback to process_note. Handle only REGs and MEMs directly. Validate the MEM if cse_process_note changes its address. (cse_process_notes): Replace with... (cse_process_note): ...this new function. (cse_extended_basic_block): Update accordingly, iterating over the register notes and passing individual notes to cse_process_note.
