The problem is that expansion can use const0_rtx as an indicator that we are
not interested in the value. This is an invalid as a target of a move, so, we
must always have a valid target. This dummies up a target, just like in the
NULL_RTX case.
Ok?
diff --git a/gcc/optabs.c b/gcc/optabs.c
index 353727f..a091deb 100644
--- a/gcc/optabs.c
+++ b/gcc/optabs.c
@@ -7174,6 +7174,8 @@ expand_atomic_test_and_set (rtx target, rtx mem, enum
memmodel model)
{
trueval = const1_rtx;
subtarget = target ? target : gen_reg_rtx (mode);
+ if (subtarget == const0_rtx)
+ subtarget = gen_reg_rtx (mode);
}
else
{
