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

[Jeff Law <jeffreyalaw@gmail.com>]

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.


Jeff