[LLVMdev] ATS workaround for Clang 3.5

[Greg Fitzgerald]

> Is there a bug filed with the affected C code

I just added:  http://llvm.org/bugs/show_bug.cgi?id=22360


> or better, a standalone reproducer?

I added code sent by Hongwei Xi to the bug report, but it is not
minimal or standalone.  :-/

A job for bugpoint?


> I don't know ATS, so it's hard to diagnose from an ATS diff.

The diff just aims to demonstrate that that the bug is likely in Clang
and not the ATS-generated C code.  He added a level of indirection to
prevent the optimizer for kicking in.

-Greg

On Tue, Jan 27, 2015 at 2:11 PM, Reid Kleckner <rnk at google.com> wrote:
> Is there a bug filed with the affected C code, or better, a standalone
> reproducer? I don't know ATS, so it's hard to diagnose from an ATS diff.
>
> On Tue, Jan 27, 2015 at 10:04 AM, Greg Fitzgerald <garious at gmail.com> wrote:
>>
>> The ATS community is having trouble with clang.  They had been using
>> an older version of clang and upgraded because newer versions give
>> higher quality warning messages.  Unfortunately, with 3.5, moving from
>> -O1 to -O2 triggers a crash on startup in the clang-generated
>> executable.  I had suggested building with -fsanitize=undefined and
>> -fsanitize=address to weed out any dependencies undefined behavior.
>> All their generated C code came out clean.  Here is the workaround
>> Hongwei Xi came up with:
>>
>>
>> https://github.com/githwxi/ATS-Postiats/commit/5e17db4badf58b404598e8b3ae4a666b8b0e889c
>>
>> Looks like a bug on the LLVM side.  He says it worked with clang 3.3,
>> but breaks on 3.4 and 3.5.  Would someone be interested in
>> investigating this further?  It's fallen down to an area I don't think
>> I can debug quickly and if we can squeeze a fix into 3.6, that'd be
>> great.  ATS is such an interesting language, I hope we can help.
>>
>> Thanks,
>> Greg
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