https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127336
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
--- a/gcc/optabs.cc 2026-09-08 12:52:03.000000000 +0200
+++ b/gcc/optabs.cc 2026-09-11 17:53:40.257036917 +0200
@@ -8153,6 +8153,12 @@ expand_atomic_fetch_op_no_fallback (rtx
try that operation. */
if (after || unused_result || optab.reverse_code != UNKNOWN)
{
+ rtx_insn *start = get_last_insn ();
+ /* Force val into a register if it could change value when the
+ atomic insn updates mem. */
+ if (!unused_result && reg_overlap_mentioned_p (mem, val))
+ val = force_reg (mode, val);
+
/* Try the __atomic version, then the older __sync version. */
result = maybe_emit_op (&optab, target, mem, val, true, model, !after);
if (!result)
@@ -8179,6 +8185,8 @@ expand_atomic_fetch_op_no_fallback (rtx
true, OPTAB_LIB_WIDEN);
return result;
}
+ else
+ delete_insns_since (start);
}
/* No direct opcode can be generated. */
fixes this, but need to look also whether the expansion as compare and exchange
loop doesn't have similar bug.
