[PATCH] ARM: disable GCC SRA optimization

[Ard Biesheuvel]

On 2 September 2015 at 23:17, Nathan Lynch <Nathan_Lynch at mentor.com> wrote:
> On 09/02/2015 11:45 AM, Ard Biesheuvel wrote:
>> On 2 September 2015 at 18:28, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
>>> This is a known but as yet unresolved issue.
>>> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65932). In this particular
>>> case, it is causing the second while loop to be executed erroneously a
>>> single time, causing the additional space characters to be printed.
>>>
>>> So disable the optimization by passing -fno-ipa-sra.
>>>
>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>>> ---
>>>
>>> Needs to go to stable perhaps?
>>> The emitted asm is at the end of this patch.
>>>
>>
>> Another report of the same issue:
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66271
>
> Comments in both bugs indicate that this happens only when building with
> -Os and not -O2.  Have you (or anyone else) been able to get bad code
> with -O2?
>

For me, it occurred with -O2, I did not test -Os in fact. I did
confirm that the problem goes away with -O1

> I don't think the answer should affect the patch itself, but it might be
> kind to note in the commit message whether -Os definitely makes the
> difference here, if this information is known.
>