Re: [RFC: Patch, PR 60158] gcc/varasm.c : Pass actual alignment value to output_constant_pool_2

[Jeff Law <law@redhat.com>]

On 05/15/2015 04:37 AM, Dharmakan Rohit Arul Raj wrote:
>
>> -----Original Message-----
>> From: Jeff Law [mailto:law@redhat.com]
>> Sent: Friday, May 15, 2015 10:30 AM
>>> Just to summarize: By default in GCC v4.7.x, all the constants are put
>>> into '.rodata.str1.4' section. In GCC v4.8.x from r192719 onwards, one
>>> of the move instruction of the string constant ".LC0" is getting
>>> spilled. The reload pass, for any constants that aren't allowed and
>>> can't be reloaded in to registers tries to change them into memory
>>> references. Then while emitting that string constant to asm code
>>> (A:varasm.c: output_constant_pool_1), it explicitly passes the
>>> alignment as 1 which prevents the generation of fix-up table entries
>>> in  'B: rs6000.c:rs6000_assemble_integer' because the data is
>>> considered unaligned now.
>>>
>>> The bug seems to have gone latent with an unrelated trunk commit
>>> r204695 [* tree-ssa-loop-ivopts.c (force_expr_to_var_cost): Refactor
>>> the code. Handle type conversion.]. This commit chooses different
>>> spill candidates hence all the string constants are being put in to
>>> '.rodata.str1.4´section.
>>>
>>> The check I had in the test case is that if there is a
>>> '.data.rel.ro.local', then there should be '.fixup' section generated.
>>>
>>> Please let me know if you need any other details.
>> Thanks.  Even though I wasn't able to trigger the bug with the testcase from
>> 65018, I went ahead and committed this patch to the trunk.  It can't hurt and
>> it's the right thing to do.
>>
>> Thanks for your patience,
>>
>
> Jeff, Thanks for checking-in the changes.
> Can we apply the patch to GCC v4.8 and GCC v4.9 branch as well?
That's up to the branch maintainers.  I'd think it's safe, but it's 
ultimately their call.

jeff