https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120550
--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jeff Law <l...@gcc.gnu.org>: https://gcc.gnu.org/g:34e1e5e33ec3eb475c0c8278800b6fc246a86763 commit r16-1613-g34e1e5e33ec3eb475c0c8278800b6fc246a86763 Author: Jeff Law <j...@ventanamicro.com> Date: Sun Jun 22 12:06:08 2025 -0600 [committed][PR rtl-optimization/120550] Drop REG_EQUAL note after ext-dce transformation This bug was found by Edwin's fuzzing efforts on RISC-V, though it likely affects other targets. In simplest terms when ext-dce converts an extension into a (possibly simplified) subreg copy it may make an attached REG_EQUAL note invalid. In the case Edwin found the note was an extension, but I don't think that would necessarily always be the case. The note could have other forms which potentially need invalidation. So the safest thing to do is just remove any attached REG_EQUAL or REG_EQUIV note. Note adjusting Edwin's testcase in the obvious way to avoid having to interpret printf output for pass/fail status makes the bug go latent. That's why no testcase is included with this patch. Bootstrapped and regression tested on x86_64. Obviously also verified it fixes the testcase Edwin filed. This is a good candidate for cherry-picking to the gcc-15 release branch after simmering on the trunk a bit. PR rtl-optimization/120550 gcc/ * ext-dce.cc (ext_dce_try_optimize_insn): Drop REG_EQUAL/REG_EQUIV notes on modified insns.
