Re: [PATCH][RFC] tree-optimization/105646 - re-interpret always executed in uninit diag

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Sep 27, 2022 at 5:48 PM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
> On 8/22/22 00:16, Richard Biener via Gcc-patches wrote:
> > The following fixes PR105646, not diagnosing
> >
> > int f1();
> > int f3(){
> >      auto const & a = f1();
> >      bool v3{v3};
> >      return a;
> > }
> >
> > with optimization because the early uninit diagnostic pass only
> > diagnoses always executed cases.  The patch does this by
> > re-interpreting what always executed means and choosing to
> > ignore exceptional and abnormal control flow for this.  At the
> > same time it improves things as suggested in a comment - when
> > the value-numbering run done without optimizing figures there's
> > a fallthru path, consider blocks on it as always executed.
> >
> > Bootstrapped and tested on x86_64-unknown-linux-gnu.
> >
> > OK?
> >
> > Thanks,
> > Richard.
> >
> >       PR tree-optimization/105646
> >       * tree-ssa-uninit.cc (warn_uninitialized_vars): Pre-compute
> >       the set of fallthru reachable blocks from function entry
> >       and use that to determine wlims.always_executed.
> >
> >       * g++.dg/uninit-pr105646.C: New testcase.
>
> I'm torn on this.  On one hand, ignoring abnormal flow control in the
> early pass is almost certainly going to result in false positives but
> it's also going to result in fixing some false negatives.
>
> I'm willing to ACK and see what the real world fallout is in the spring
> when the distros run their builds.  Your call.

I have pushed this now after retesting.  Let's see if there's any bad
fallout - we can certainly reconsider.

Richard.

>
> Jeff
>
>