https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123386
--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <[email protected]>: https://gcc.gnu.org/g:c158d510ee96158a4f90255148222fb1ce356832 commit r16-7447-gc158d510ee96158a4f90255148222fb1ce356832 Author: Jakub Jelinek <[email protected]> Date: Wed Feb 11 11:31:26 2026 +0100 cfgrtl: Fix up force_nonfallthru_and_redirect asm goto handling [PR123386] force_nonfallthru_and_redirect has some extra code to handle asm gotos if we are forcing or redirecting the EDGE_FALLTHRU in case. This was done for PR51767, PR53589, PR54127. It is done for the cases where some asm goto label points to the bb after the fallthru edge (i.e. there is edge sharing between the fallthru and the label, partly or fully degenerate asm goto) and/or if the label points to the TARGET bb (before/after). In such case it changes the label from e->dest's label to target's label and similarly to the case of 2+ successor e->src a new bb is created as new fallthru from e->src and in the asm goto case an additional edge is added, so there is | asm goto -----+ maybe other edges | fallthru \ v v jumpblock -> target and the jumpblock -> target edge isn't EDGE_FALLTHRU. This was done that way to fix various ICEs with the degenerate asm gotos, see above for list. I believe it will still ICE if we decide to force_nonfallthru_and_redirect E bb5->bb6 to l2, because in that case there are already two+ edges, one pointing from bb5->l2 and we create another edge bb5->l2: bb5: asm goto ("" : : : : (l2)); bb6: ... l2: but maybe nothing tries that in that case. Anyway, the reason why the following two (PR116600 and PR123386) testcases are miscompiled is that we try to (during shrink-wrapping) emit some insns on the bb3->bb7 edge, and see bb7 predecessor edge is EDGE_FALLTHRU in: bb3: __asm__ goto ("" : : : : d); if (c) bar (a); bb6: __asm__ goto ("" : : : : d); d: // == bb7 in rtl_split_edge: /* We are going to place the new block in front of edge destination. Avoid existence of fallthru predecessors. */ if ((edge_in->flags & EDGE_FALLTHRU) == 0) { edge e = find_fallthru_edge (edge_in->dest->preds); if (e) force_nonfallthru (e); } Now, the asm goto in bb6 is degenerate, so shrink-wrapping isn't aware that there would be multiple edges from it, there is just single one. But we still while splitting the bb3->bb7 edge in order to emit there pending insns on that edge turn the single successor asm goto bb into one with two successors (initially with two different ways to reach the same destination). But unfortunately such change confuses the shrink-wrapping logic which isn't aware of such a change and so the separate shrink wrapping insns end up just on one of the paths instead of being on both, and we then ICE in dwarf2 pass because there is an disagreement on the CFI state (of course it is a wrong-code too). Note, force_nonfallthru calls force_nonfallthru_and_redirect with target set to e->dest. The following patch reworks this. Instead of creating that | asm goto -----+ maybe other edges | fallthru \ v v jumpblock -> target for initially degenerate asm goto we now create | asm goto maybe other edges | fallthru v jumpblock -> target i.e. the asm goto keeps being degenerate, all we've changed is adding a new bb on the fallthru edge and making the edge from that new bb non-fallthru. Furthermore, for the case where there would be before an asm goto -> target edge before for the e->dest != target case, those edges are untouched. For the immediate effect after the operation, the asm goto keeps the existing behavior, if it falls through, it will reach target by hopping through jumpblock, if it jumps to that label, previously it jumped directly to target, now it jumps to jumpblock and from there to target. But shrink-wrapping etc. then put the right fixups everywhere where it belongs. 2026-02-11 Jakub Jelinek <[email protected]> PR rtl-optimization/116600 PR middle-end/123386 * cfgrtl.cc (force_nonfallthru_and_redirect): Don't do any asm goto adjustments early, only note in asm_goto_edge if any labels point originally to e->dest head. After jumpblock creation don't add an extra edge for asm_goto_edge, instead adjust those labels pointing to former e->dest head to point to jumpblock instead. * gcc.c-torture/compile/pr116600.c: New test. * gcc.c-torture/compile/pr123386.c: New test.
