[PATCH] Fix loop-header copying do-while loop detection (PR85116)

[Jeff Law]

On 04/28/2018 12:46 AM, Richard Biener wrote:
> On Fri, 27 Apr 2018, Richard Biener wrote:
> 
>> On Fri, 27 Apr 2018, David Edelsohn wrote:
>>
>>> Hi, Richi
>>>
>>> This patches causes a boostrap failure on AIX.  Everything miscompares.
>>> The code itself is the same, but the DWARF debug information contains many
>>> differences.
>>
>> Does AIX use bootstrap-debug by default?  I don't see how the patch
>> can cause this kind of issue directly but of course it will change
>> CH decisions which may expose latent bugs somewhere.
>>
>> Can you provide more details please, like actual differences?
>> I would have expected the dwarf2out.c change to be a more likely
>> candidate for such symtoms but I trust that you did properly
>> bisect to my patch?
> 
> OK, so the x86-64 -O3 bootstrap failure is not caused by this patch,
> reverting it doesn't fix the issue.
> 
> The difference w/ the patch reverted is in debug info, all (indirect)
> strings reside at different offsets.  If I strip the objects they
> compare identical.
> 
> I'm trying reversal of that dwarf2out patch now.
> 
FWIW, the PA port has been failing a standard -O2 bootstrap for a few days.

r259643 is good, r259672 is bad.

I haven't looked into it any deeper yet.

jeff