[llvm] r300200 - Re-apply "[GVNHoist] Move GVNHoist to function simplification part of pipeline."

[Chandler Carruth via llvm-commits]

Finally got a good test case for this:

http://llvm.org/PR32821

I'm going to flip the flag to "off" as suggested by Geoff, I completely
agree with that rather than moving it around.

On Mon, Apr 24, 2017 at 11:02 AM Aditya K <hiraditya at msn.com> wrote:

>
> >If any one decides to revert this, I'd like to request that you attempt
> >to do so by just turning off GVNHoist by default instead of reverting
> >r300200 if possible.  I believe the current location in the pass
> >pipeline is the desired one, and reverting r300200 will just move it
> >back to being done before inlining, which is likely just hiding bugs.
> >
> >FWIW, before re-enabling this most recently I did correctness testing on
> >X86 and AArch64 of the test-suite, SPEC and several other benchmarks, as
> >well as bootstrapping clang, all without issue.
>
> I have also tested the recent GVNHoist and it bootstraps, passes SPEC2006.
> Maybe it is related to the bug https://bugs.llvm.org/show_bug.cgi?id=30806
> If there is a test case to reproduce the bug I'll be glad to fix it.
>
>
> Thanks,
> -Aditya
>
> >
> >On 4/23/2017 12:45 PM, Philip Reames wrote:
> >> If this does turn out to be the problematic commit, I'll ask that we
> >> do not re-enable GVNHoist without some llvm-dev discussion of what
> >> we've done to test it. I've literally lost track of the number of
> >> times this has been enabled and disabled by now.  There's clearly a
> >> problem here; it's time we discuss it and what needs done to address
> >> it going forward.
> >>
> >> Philip
> >>
> >> On 04/21/2017 08:24 PM, Chandler Carruth via llvm-commits wrote:
> >>> FYI and just as a heads up, we're seeing buggy hoisting leading to
> >>> null pointers being accessed, and this commit is in the range and
> >>> seems very likely to be responsible. We're working on getting this
> >>> isolated enough to be sure, but wanted to mention it in case anyone
> >>> else is similarly looking at issues after this commit.
>
>
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