https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116783
--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-14 branch has been updated by Alex Coplan <acop...@gcc.gnu.org>: https://gcc.gnu.org/g:434483ac32a08d1f3608c26fe2da302f0e09d6a2 commit r14-10853-g434483ac32a08d1f3608c26fe2da302f0e09d6a2 Author: Alex Coplan <alex.cop...@arm.com> Date: Wed Oct 30 13:46:12 2024 +0000 aarch64: Assume alias conflict if common address reg changes [PR116783] As the PR shows, pair fusion was tricking memory_modified_in_insn_p into returning false when a common base register (in this case, x1) was modified between the mem and the store insn. This lead to wrong code as the accesses really did alias. To avoid this sort of problem, this patch avoids invoking RTL alias analysis altogether (and assume an alias conflict) if the two insns to be compared share a common address register R, and the insns see different definitions of R (i.e. it was modified in between). This is a backport (but not a straight cherry pick) of r15-4518-gc0e54ce1999ccf2241f74c5188b11b92e5aedc1f. gcc/ChangeLog: PR rtl-optimization/116783 * config/aarch64/aarch64-ldp-fusion.cc (def_walker::cand_addr_uses): New. (def_walker::def_walker): Add parameter for candidate address uses. (def_walker::alias_conflict_p): Declare. (def_walker::addr_reg_conflict_p): New. (def_walker::conflict_p): New. (store_walker::store_walker): Add parameter for candidate address uses and pass to base ctor. (store_walker::conflict_p): Rename to ... (store_walker::alias_conflict_p): ... this. (load_walker::load_walker): Add parameter for candidate address uses and pass to base ctor. (load_walker::conflict_p): Rename to ... (load_walker::alias_conflict_p): ... this. (ldp_bb_info::try_fuse_pair): Collect address register uses for candidate insns and pass down to alias walkers. gcc/testsuite/ChangeLog: PR rtl-optimization/116783 * g++.dg/torture/pr116783.C: New test.
