On Wed, 2026-06-24 at 23:11 +0800, YunQiang Su wrote: > Xi Ruoyao <[email protected]> 于2026年6月23日周二 22:10写道： > > > > In GCC, if the RTL template of define_insn has multiple elements, it's > > treated as a parallel expression. And, "in parallel" means that first > > all the values used in the invidiviual side-effects are computed, and > > second all the actual side-effects are performed. So when the value of > > operand 1 (the output reg) is used, it's not set yet. > > > > When optimization is enabled, the uninitialized value is replaced with 0 > > and then for e.g. if atomic_hiqi_op is plus, (plus (0) (val)) is folded > > to simply (val). Now the RTL template happens to be matched by > > sync_old_nand_12 (of which the RTL is written in a really inconsistent > > way), causing "0 + 1 = -1". > > > > Is there any test case for it?
As the PR indicates, the bug already causes the test case stdatomic-op- 1.c to fail (actually, alongside some dozens of other tests). So we can consider the test case already existing. -- Xi Ruoyao <[email protected]>
