On Fri, 17 May 2019, Jeff Law wrote: > So my question is are these showing up in practice? The gimple based > tests seem to be skipping the optimizers that would have eliminated this > stuff. > > In each of the testcases I would have expected jump threading to have > eliminated the problematical path through the CFG.
If there's anything slightly complicated, like say a loop, between the (lack of) definition and the use, optimizations won't be able to simplify the flow and the false positive/negative can be seen. In fact Vlad's first patch submission used a trivial loop in a C testcase alongside a minimized gimple testcase to showcase how this happens: https://gcc.gnu.org/ml/gcc-patches/2019-04/msg00040.html Alexander
