https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113921
--- Comment #12 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-13 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:4040d472825f203660371331c9e86cd75e30f8d2 commit r13-8328-g4040d472825f203660371331c9e86cd75e30f8d2 Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Feb 15 15:53:01 2024 +0100 expand: Fix handling of asm goto outputs vs. PHI argument adjustments [PR113921] The Linux kernel and the following testcase distilled from it is miscompiled, because tree-outof-ssa.cc (eliminate_phi) emits some fixups on some of the edges (but doesn't commit edge insertions). Later expand_asm_stmt emits further instructions on the same edge. Now the problem is that expand_asm_stmt uses insert_insn_on_edge to add its own fixups, but that function appends to the existing sequence on the edge if any. And the bug triggers when the fixup sequence emitted by eliminate_phi uses a pseudo which the fixup sequence emitted by expand_asm_stmt later on sets. So, we end up with (set (reg A) (asm_operands ...)) and on one of the edges queued sequence (set (reg C) (reg B)) // added by eliminate_phi (set (reg B) (reg A)) // added by expand_asm_stmt That is wrong, what we emit by expand_asm_stmt needs to be as close to the asm_operands as possible (they aren't known until expand_asm_stmt is called, the PHI fixup code assumes it is reg B which holds the right value) and the PHI adjustments need to be done after it. So, the following patch introduces a prepend_insn_to_edge function and uses it from expand_asm_stmt, so that we queue (set (reg B) (reg A)) // added by expand_asm_stmt (set (reg C) (reg B)) // added by eliminate_phi instead and so the value from the asm_operands output propagates correctly to the PHI result. 2024-02-15 Jakub Jelinek <ja...@redhat.com> PR middle-end/113921 * cfgrtl.h (prepend_insn_to_edge): New declaration. * cfgrtl.cc (insert_insn_on_edge): Clarify behavior in function comment. (prepend_insn_to_edge): New function. * cfgexpand.cc (expand_asm_stmt): Use prepend_insn_to_edge instead of insert_insn_on_edge. * gcc.target/i386/pr113921.c: New test. (cherry picked from commit 2b4efc5db2aedb59196987300e14951d08cd7106)
