[Patch] [AArch64] Fix registerAllocator assigns same register for base and wback in pre/post-index load and store

[Quentin Colombet]

Thanks Steven!

I’ve committed the patch on your behalf, with a slightly modified test case.
This is Committed revision 215390.

-Quentin
> On Aug 11, 2014, at 2:08 PM, Steven Wu <stevenwu at apple.com> wrote:
> 
> Hi Quentin
> 
> Here is a patch with testcase added according to Tim’s suggestion. Thanks for the review
> 
> Steven
> 
> <postindex.patch>
> 
>> On Aug 8, 2014, at 5:20 PM, Quentin Colombet <qcolombet at apple.com> wrote:
>> 
>> Hi Steven,
>> 
>> Could you add a few test cases? (Ideally one per instruction you are patching.)
>> 
>> Thanks,
>> -Quentin
>> 
>> On Aug 8, 2014, at 5:15 PM, Steven Wu <stevenwu at apple.com> wrote:
>> 
>>> Hi
>>> 
>>> This patch fix a bug that sometimes register allocator may assign same register as base and writeback register in pre/post-index loads and stores for AArch64.
>>> According to ARMv8 manual, such result will have uncertain behaviors and clang as will reject them as well. Adding earlyclobber constraints to avoid them.
>>> Since this behavior will depend on the register allocator so I am not sure how to produce a test. I can provide a testcase if anyone want to reproduce the problem.
>>> 
>>> Patch attached. Please review and commit it for me.
>>> 
>>> Thanks
>>> 
>>> Steven
>>> <postindex.patch>
>>> 
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>> 
> 

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