https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95254
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Richard Sandiford <rsand...@gcc.gnu.org>: https://gcc.gnu.org/g:9a182ef9ee011935d827ab5c6c9a7cd8e22257d8 commit r11-966-g9a182ef9ee011935d827ab5c6c9a7cd8e22257d8 Author: Fei Yang <felix.y...@huawei.com> Date: Fri Jun 5 10:34:59 2020 +0100 expand: Simplify removing subregs when expanding a copy [PR95254] In rtl expand, if we have a copy that matches one of the following patterns: (set (subreg:M1 (reg:M2 ...)) (subreg:M1 (reg:M2 ...))) (set (subreg:M1 (reg:M2 ...)) (mem:M1 ADDR)) (set (mem:M1 ADDR) (subreg:M1 (reg:M2 ...))) (set (subreg:M1 (reg:M2 ...)) (constant C)) where mode M1 is equal in size to M2, try to detect whether the mode change involves an implicit round trip through memory. If so, see if we can avoid that by removing the subregs and doing the move in mode M2 instead. 2020-06-05 Felix Yang <felix.y...@huawei.com> gcc/ PR target/95254 * expr.c (emit_move_insn): Check src and dest of the copy to see if one or both of them are subregs, try to remove the subregs when innermode and outermode are equal in size and the mode change involves an implicit round trip through memory. gcc/testsuite/ PR target/95254 * gcc.target/aarch64/pr95254.c: New test. * gcc.target/i386/pr67609.c: Check "movq\t%xmm0" instead of "movdqa".