https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99830
--- Comment #18 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-9 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:6bb1dccf0defbcf245b0804211e20be8624c1f40 commit r9-9445-g6bb1dccf0defbcf245b0804211e20be8624c1f40 Author: Jakub Jelinek <ja...@redhat.com> Date: Tue Apr 13 01:00:48 2021 +0200 combine: Don't fold away side-effects in simplify_and_const_int_1 [PR99830] Here is an alternate patch for the PR99830 bug. As discussed on IRC and in the PR, the reason why a (clobber:TI (const_int 0)) has been propagated into the debug insns is that it got optimized away during simplification from the i3 instruction pattern. And that happened because simplify_and_const_int_1 (SImode, varop, 255) with varop of (ashift:SI (subreg:SI (and:TI (clobber:TI (const_int 0 [0])) (const_int 255 [0xff])) 0) (const_int 16 [0x10])) was called and through nonzero_bits determined that (whatever << 16) & 255 is const0_rtx. It is, but if there are side-effects in varop and such clobbers are considered as such, we shouldn't optimize those away. 2021-04-13 Jakub Jelinek <ja...@redhat.com> PR debug/99830 * combine.c (simplify_and_const_int_1): Don't optimize varop away if it has side-effects. * gcc.dg/pr99830.c: New test. (cherry picked from commit 4ac7483ede91fef7cfd548ff6e30e46eeb9d95ae)
