https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111157

--- Comment #7 from Martin Jambor <jamborm at gcc dot gnu.org> ---
(In reply to Jan Hubicka from comment #4)
> So here ipa-modref declares the field dead, while ipa-prop determines its
> value even if it is unused and makes it used later?

This is what I wanted to ask about.  Looking at the dumps, ipa-modref
knows it is "killed."  Is that enough or does it need to be also not
read to be know to be useless?

> 
> I think dead argument is probably better than optimizing out one store, so I
> think ipa-prop, however question is how to detect this reliably.
> 
> ipa-modref has update_signature which updates summaries after ipa-sra work,
> so it is also place to erase the info about parameter being dead from the
> summary.

This is what I have been looking at last week and where I'd like to
plug such mechanism in so that it is not even streamed from WPA.

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