https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103860
--- Comment #14 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:5d96fb401e1c03b6b6a6ec2c5276dfdc479bb3e4 commit r9-10115-g5d96fb401e1c03b6b6a6ec2c5276dfdc479bb3e4 Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Dec 30 14:23:18 2021 +0100 shrink-wrapping: Fix up prologue block discovery [PR103860] The following testcase is miscompiled, because a prologue which contains subq $8, %rsp instruction is emitted at the start of a basic block which contains conditional jump that depends on flags register set in an earlier basic block, the prologue instruction then clobbers those flags. Normally this case is checked by can_get_prologue predicate, but this is done only at the start of the loop. If we update pro later in the loop (because some bb shouldn't be duplicated) and then don't push anything further into vec and the vec is already empty (this can happen when the new pro is already in bb_with bitmask and either has no successors (that is the case in the testcase where that bb ends with a trap) or all the successors are already in bb_with, then the loop doesn't iterate further and can_get_prologue will not be checked. The following simple patch makes sure we call can_get_prologue even after the last former iteration when vec is already empty and only break from the loop afterwards (and only if the updating of pro done because of !can_get_prologue didn't push anything into vec again). 2021-12-30 Jakub Jelinek <ja...@redhat.com> PR rtl-optimization/103860 * shrink-wrap.c (try_shrink_wrapping): Make sure can_get_prologue is called on pro even if nothing further is pushed into vec. * gcc.dg/pr103860.c: New test. (cherry picked from commit 1820137ba624d7eb2004a10f9632498b6bc1696a)
