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

[Steven Wu]

Hi Quentin

Here is a patch with testcase added according to Tim’s suggestion. Thanks for the review

Steven

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> 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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