https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116488
--- 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:36e91df7716d34aa5694533837551593ec28f22b commit r15-4532-g36e91df7716d34aa5694533837551593ec28f22b Author: Jeff Law <j...@ventanamicro.com> Date: Mon Oct 21 13:37:21 2024 -0600 [committed][PR rtl-optimization/116488] Fix SIGN_EXTEND source handling in ext-dce A while back I noticed that the code to call carry_backpropagate was being called after the optimization step. Which seemed wrong, but at the time I didn't have a testcase showing it as a problem. Now I have 4 :-) The way things used to work, the extension would be stripped away before calling carry_backpropagte, meaning carry_backpropagate would never see a SIGN_EXTENSION. Thus the code trying to account for the sign extended bit was never reached. Getting that bit marked live is what's needed to fix these testcases. Fallout is minor with just an adjustment needed to sensibly deal with vector modes in a place where we didn't have them before. I'm still somewhat concerned about this code. Specifically whether or not we can get in here with arbitrarily complex RTL, and if so do we need to recurse down and look at those sub-expressions. So while this patch fixes the most pressing issue, I wouldn't be terribly surprised if we're back inside this code at some point. Bootstrapped and regression tested on x86_64, ppc64le, riscv64, s390x, mips64, loongarch, aarch64, m68k, alpha, hppa, sh4, sh4eb, perhaps something else that I've forgotten... Also tested on all the crosses in my tester. PR rtl-optimization/116488 PR rtl-optimization/116579 PR rtl-optimization/116915 PR rtl-optimization/117226 gcc/ * ext-dce.cc (carry_backpropagate): Properly handle SIGN_EXTEND, add ZERO_EXTEND handling as well. (ext_dce_process_uses): Call carry_backpropagate before the optimization step. gcc/testsuite/ * gcc.dg/torture/pr116488.c: New test. * gcc.dg/torture/pr116579.c: New test. * gcc.dg/torture/pr116915.c: New test. * gcc.dg/torture/pr117226.c: New test.
