Re: [PATCH] fix powerpc64le bootstrap failure caused by r243661 (PR 78817)

[Jeff Law <law at redhat dot com>]

On 12/19/2016 01:09 PM, Martin Sebor wrote:
> > > By moving the warning earlier, we'll still warn for the most cases, but
> > > won't warn in the more convoluted cases.  We can perhaps work on it
> > > further
> > > in GCC 8.  If we keep it as is, I think most users will just
> > > -Wno-nonnull
> > > as soon as they run into some warning that will be hard to figure out
> > > what
> > > is going on.  At that point they will not get warnings even for the
> > > obvious
> > > cases that we used to warn.  Look at how the Linux kernel folks
> > > disable most
> > > of warnings even for smaller reasons.
> > But again, the user case is no different than other warnings that are
> > sensitive to optimizations.
> >
> > My sense is that we should revert and table until gcc-8 where we can
> > evaluate the space more thoroughly.
>
> I think that would be unfortunate.  We have a number of alternatives
> that seem much preferable.
Definitely unfortunate, but I don't think we have agreement on the key 
issue, namely where the warning belongs.


> I have a trivial patch that avoids the sanitizer warnings by disabling
> the late -Wnonnull warning when -fsanitize=undefined is specified.
> A simple fix for the GCC warnings discovered by profiledbootstrap-O3
> and verified on powerpc64 and x86_63 was posted for review last week.
The former seems like a hack.  I can't recall which patch the latter was 
(was it the one that just ripped out the "can't happen code"?

> Jakub's patch avoids those warnings and obviates any GCC changes (IIUC).
Yes, but they suffer from missing warnings that are exposed by 
transformations later in the pipeline.

> There is also the option of introducing -Wnonnull=2 that warns late
> and not including it in -Wall or -Wextra.  All three of this have
> been tested.
Understood, but I'm not keep to start adding more levels of warning and 
code to support them until we have reached some kind of agreement.  And 
it's my sense that we need more time to hammer out that kind of agreement.


Jeff