[PATCH] Improve alloca alignment

[Rainer Orth]

Jeff Law <law@redhat.com> writes:

> On 08/22/2017 08:15 AM, Wilco Dijkstra wrote:
>> Jeff Law wrote:
>> On 07/26/2017 05:29 PM, Wilco Dijkstra wrote:
>> 
>>>> But then the check size_align % MAX_SUPPORTED_STACK_ALIGNMENT != 0
>>>> seems wrong too given that round_push uses a different alignment to
>>>> align to.
>>> I had started to dig into the history of this code, but just didn't have
>>> the time to do so fully before needing to leave for the day.  To some
>>> degree I was hoping you knew the rationale behind the test against
>>> MAX_SUPPORTED_STACK_ALIGNMENT and I wouldn't have to do a ton of digging :-)
>> 
>> I looked further into this - it appears this works correctly since it is
>> only bypassed if
>> size_align is already maximally aligned. round_push aligns to the
>> preferred alignment,
>> which may be lower or equal to MAX_SUPPORTED_STACK_ALIGNMENT (which is
>> at least STACK_BOUNDARY).
>> 
>> Here is the updated version:
>> 
>> ChangeLog:
>> 2017-08-22  Wilco Dijkstra  <wdijkstr@arm.com>
>> 
>> 	* explow.c (get_dynamic_stack_size): Improve dynamic alignment.
> OK.  I wonder if this will make it easier to write stack-clash tests of
> the dynamic space for boundary conditions :-)  I was always annoyed that
> I had to fiddle around with magic adjustments to the sizes of objects to
> tickle boundary cases.

This patch brought back PR libgomp/78468, which had caused its
predecessor to be backed out of gcc-7.

	Rainer

-- 
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Rainer Orth, Center for Biotechnology, Bielefeld University