https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110206
--- Comment #17 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Uros Bizjak <u...@gcc.gnu.org>: https://gcc.gnu.org/g:1815e313a8fb519a77c94a908eb6dafc4ce51ffe commit r14-2525-g1815e313a8fb519a77c94a908eb6dafc4ce51ffe Author: Uros Bizjak <ubiz...@gmail.com> Date: Fri Jul 14 11:46:22 2023 +0200 cprop: Do not set REG_EQUAL note when simplifying paradoxical subreg [PR110206] cprop1 pass does not consider paradoxical subreg and for (insn 22) claims that it equals 8 elements of HImodeby setting REG_EQUAL note: (insn 21 19 22 4 (set (reg:V4QI 98) (mem/u/c:V4QI (symbol_ref/u:DI ("*.LC1") [flags 0x2]) [0 S4 A32])) "pr110206.c":12:42 1530 {*movv4qi_internal} (expr_list:REG_EQUAL (const_vector:V4QI [ (const_int -52 [0xffffffffffffffcc]) repeated x4 ]) (nil))) (insn 22 21 23 4 (set (reg:V8HI 100) (zero_extend:V8HI (vec_select:V8QI (subreg:V16QI (reg:V4QI 98) 0) (parallel [ (const_int 0 [0]) (const_int 1 [0x1]) (const_int 2 [0x2]) (const_int 3 [0x3]) (const_int 4 [0x4]) (const_int 5 [0x5]) (const_int 6 [0x6]) (const_int 7 [0x7]) ])))) "pr110206.c":12:42 7471 {sse4_1_zero_extendv8qiv8hi2} (expr_list:REG_EQUAL (const_vector:V8HI [ (const_int 204 [0xcc]) repeated x8 ]) (expr_list:REG_DEAD (reg:V4QI 98) (nil)))) We rely on the "undefined" vals to have a specific value (from the earlier REG_EQUAL note) but actual code generation doesn't ensure this (it doesn't need to). That said, the issue isn't the constant folding per-se but that we do not actually constant fold but register an equality that doesn't hold. PR target/110206 gcc/ChangeLog: * fwprop.cc (contains_paradoxical_subreg_p): Move to ... * rtlanal.cc (contains_paradoxical_subreg_p): ... here. * rtlanal.h (contains_paradoxical_subreg_p): Add prototype. * cprop.cc (try_replace_reg): Do not set REG_EQUAL note when the original source contains a paradoxical subreg. gcc/testsuite/ChangeLog: * gcc.target/i386/pr110206.c: New test.
