https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96176
--- Comment #3 from CVS 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:410675cb63466d8de9ad590521f0766b012d2475 commit r11-2103-g410675cb63466d8de9ad590521f0766b012d2475 Author: Jakub Jelinek <ja...@redhat.com> Date: Wed Jul 15 11:26:22 2020 +0200 builtins: Avoid useless char/short -> int promotions before atomics [PR96176] As mentioned in the PR, we generate a useless movzbl insn before lock cmpxchg. The problem is that the builtin for the char/short cases has the arguments promoted to int and combine gives up, because the instructions have MEM_VOLATILE_P arguments and recog in that case doesn't recognize anything when volatile_ok is false, and nothing afterwards optimizes the (reg:SI a) = (zero_extend:SI (reg:QI a)) ... (subreg:QI (reg:SI a) 0) ... The following patch fixes it at expansion time, we already have a function that is meant to undo the promotion, so this just adds the very common case to that. 2020-07-15 Jakub Jelinek <ja...@redhat.com> PR target/96176 * builtins.c: Include gimple-ssa.h, tree-ssa-live.h and tree-outof-ssa.h. (expand_expr_force_mode): If exp is a SSA_NAME with different mode from MODE and get_gimple_for_ssa_name is a cast from MODE, use the cast's rhs. * gcc.target/i386/pr96176.c: New test.
