https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119966
--- Comment #13 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Dimitar Dimitrov <dimi...@gcc.gnu.org>: https://gcc.gnu.org/g:2dcc6dbd8a00caf7cfa8cac17b3fd1c33d658016 commit r16-1565-g2dcc6dbd8a00caf7cfa8cac17b3fd1c33d658016 Author: Dimitar Dimitrov <dimi...@dinux.eu> Date: Mon Jun 2 08:10:16 2025 +0300 emit-rtl: Use simplify_subreg_regno to validate hardware subregs [PR119966] PR119966 showed that combine could generate unfoldable hardware subregs for pru-unknown-elf. To fix, strengthen the checks performed by validate_subreg. The simplify_subreg_regno performs more validity checks than the simple info.representable_p. Most importantly, the targetm.hard_regno_mode_ok hook is called to ensure the hardware register is valid in subreg's outer mode. This fixes the rootcause for PR119966. The checks for stack-related registers are bypassed because the i386 backend generates them, in this seemingly valid peephole optimization: ;; Attempt to always use XOR for zeroing registers (including FP modes). (define_peephole2 [(set (match_operand 0 "general_reg_operand") (match_operand 1 "const0_operand"))] "GET_MODE_SIZE (GET_MODE (operands[0])) <= UNITS_PER_WORD && (! TARGET_USE_MOV0 || optimize_insn_for_size_p ()) && peep2_regno_dead_p (0, FLAGS_REG)" [(parallel [(set (match_dup 0) (const_int 0)) (clobber (reg:CC FLAGS_REG))])] "operands[0] = gen_lowpart (word_mode, operands[0]);") Testing done: * No regressions were detected for C and C++ on x86_64-pc-linux-gnu. * "contrib/compare-all-tests i386" showed no difference in code generation. * No regressions for pru-unknown-elf. * Reverted r16-809-gf725d6765373f7 to expose the now latent PR119966. Then ensured pru-unknown-elf build is ok. Only two cases regressed where rnreg pass transforms a valid hardware subreg into invalid one. But I think that is not related to combine's PR119966: gcc.c-torture/execute/20040709-1.c gcc.c-torture/execute/20040709-2.c PR target/119966 gcc/ChangeLog: * emit-rtl.cc (validate_subreg): Call simplify_subreg_regno instead of checking info.representable_p.. * rtl.h (simplify_subreg_regno): Add new argument allow_stack_regs. * rtlanal.cc (simplify_subreg_regno): Do not reject stack-related registers if allow_stack_regs is true. Co-authored-by: Richard Sandiford <richard.sandif...@arm.com> Co-authored-by: Andrew Pinski <quic_apin...@quicinc.com> Signed-off-by: Dimitar Dimitrov <dimi...@dinux.eu>
