https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117360
--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:eb9f1baf2a50f2f1ebe23c5ad62b035d5bcfc14b commit r15-5814-geb9f1baf2a50f2f1ebe23c5ad62b035d5bcfc14b Author: Jakub Jelinek <ja...@redhat.com> Date: Sat Nov 30 01:51:24 2024 +0100 ext-dce: Fix SIGN_EXTEND handling and cleanups [PR117360] This is mostly a blind attempt to fix the PR + various cleanups. The PR is about a shift of a HOST_WIDE_INT by 127 invoking UB. Most of carry_backpropagate works on GET_MODE_INNER of the operand, mode is assigned enum machine_mode mode = GET_MODE_INNER (GET_MODE (x)); at the beginning and everything is done using that mode, so for vector modes (or complex even?) we work with the element modes rather than vector/complex modes. But the SIGN_EXTEND handling does that inconsistently, it looks at mode of the operand and uses GET_MODE_INNER in GET_MODE_MASK, but doesn't use it in the shift. The following patch appart from the cleanups fixes it by doing essentially: mode = GET_MODE (XEXP (x, 0)); if (mask & ~GET_MODE_MASK (GET_MODE_INNER (mode))) - mask |= 1ULL << (GET_MODE_BITSIZE (mode).to_constant () - 1); + mask |= 1ULL << (GET_MODE_BITSIZE (GET_MODE_INNER (mode)).to_constant () - 1); i.e. also shifting by GET_MODE_BITSIZE of the GET_MODE_INNER of the operand's mode. We don't need to check if it is at most 64 bits, at the start of the function we've already verified the result mode is at most 64 bits and SIGN_EXTEND by definition extends from a narrower mode. The rest of the patch are cleanups. For HOST_WIDE_INT we have the HOST_WIDE_INT_{UC,1U} macros, a HWI isn't necessarily unsigned long long, so using ULL suffixes for it is weird. More importantly, the function does scalar_int_mode smode; if (!is_a <scalar_int_mode> (mode, &smode) || GET_MODE_BITSIZE (smode) > HOST_BITS_PER_WIDE_INT) return mmask; early, so we don't need to use GET_MODE_BITSIZE (mode) which is a poly_int but can use GET_MODE_BITSIZE (smode) with the same value but in unsigned short, so we don't need to use known_lt or .to_constant () everywhere. Plus some formatting issues. What I've left around is if (!GET_MODE_BITSIZE (GET_MODE (x)).is_constant () || !GET_MODE_BITSIZE (GET_MODE (XEXP (x, 0))).is_constant ()) return -1; at the start of SIGN_EXTEND or ZERO_EXTEND, I'm afraid I don't know enough about aarch64/riscv VL vectors to know why this is done (though even that return -1; is weird, rest of the code does return mmask; if it wants to punt. 2024-11-30 Jakub Jelinek <ja...@redhat.com> PR rtl-optimization/117360 * ext-dce.cc (ext_dce_process_sets): Use HOST_WIDE_INT_UC macro instead of ULL suffixed constants. (carry_backpropagate): Likewise. Use HOST_WIDE_INT_1U instead of 1ULL. Use GET_MODE_BITSIZE (smode) instead of GET_MODE_BITSIZE (mode) and with that avoid having to use known_lt instead of < or use .to_constant (). Formatting fixes. (case SIGN_EXTEND): Set mode to GET_MODE_INNER (GET_MODE (XEXP (x, 0))) rather than GET_MODE (XEXP (x, 0)) and don't use GET_MODE_INNER (mode). (ext_dce_process_uses): Use HOST_WIDE_INT_UC macro instead of ULL suffixed constants.
