https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118562
--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Richard Sandiford <rsand...@gcc.gnu.org>: https://gcc.gnu.org/g:3dbcf794f0fe89443288143405718d72e7963805 commit r15-7162-g3dbcf794f0fe89443288143405718d72e7963805 Author: Richard Sandiford <richard.sandif...@arm.com> Date: Thu Jan 23 13:57:02 2025 +0000 rtl-ssa: Avoid dangling phi uses [PR118562] rtl-ssa uses degenerate phis to maintain an RPO list of accesses in which every use is of the RPO-previous definition. Thus, if it finds that a phi is always equal to a particular value V, it sometimes needs to keep the phi and make V the single input, rather than replace all uses of the phi with V. The code to do that rerouted the phi's first input to the single value V. But as this PR shows, it failed to unlink the uses of the other inputs. The specific problem in the PR was that we had: x = PHI<x(a), V(b)> The code replaced the first input with V and removed the second input from the phi, but it didn't unlink the use of V associated with that second input. gcc/ PR rtl-optimization/118562 * rtl-ssa/blocks.cc (function_info::replace_phi): When converting to a degenerate phi, make sure to remove all uses of the previous inputs. gcc/testsuite/ PR rtl-optimization/118562 * gcc.dg/torture/pr118562.c: New test.
