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Re: [PATCH] PR91195: fix -Wmaybe-uninitialized warning for conditional store optimization


On Tue, Jul 30, 2019 at 10:35 AM Jakub Jelinek <jakub@redhat.com> wrote:
>
> On Tue, Jul 30, 2019 at 10:21:15AM +0200, Richard Biener wrote:
> > Would you need to LTO stream & merge the bitmaps / maps somehow?
>
> Yes.  And if we do not throw unneeded warnings from the sets normally, LTO
> streaming might be a good time to do that, so that we merge in only warnings
> that will be tested during/post IPA.
>
> > (maybe "unmap" to sth else when streaming individual stmts)  Not sure if
> > a bitmap is really necessary, we could simply have a tree/gimple * -> vec<>
> > mapping with records about emitted (or queued) diagnostics, like
> > OPT_, message pairs or so.
>
> Right now we use it both for the case we've already emitted some diagnostics
> and don't want to emit it again later, or for the case where we insert
> something in the IL that a warning could be diagnosed on but we know we
> don't want that.  The latter is the case e.g. for when we add
> TREE_NO_WARNING on the last value in a statement expression so that we don't
> diagnose it as unused, or the case we are discussing here.
> If we need queued diagnostics, sure, we could add it in, but I don't see a
> need for that right now.  vecs compared to bitmap might be larger and harder
> to avoid duplicates.  I guess we'd need to do some analysis though, and e.g.
> if 99% of cases we need to disable just one warning and not multiple,
> perhaps optimize for that case.

I was thinking we may want to use the same facility to record warnings we
want to not emit if we later figure a stmt was in an unreachable region.  For
this we need to record the actual warning, not only the warning kind.

Richard.

>
>         Jakub


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