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Re: [PATCH, alpha]: Wrap {un,}aligned_store sequence with memory blockages.


On 07/07/2014 09:35 AM, Uros Bizjak wrote:
> On Mon, Jul 7, 2014 at 5:01 PM, Richard Henderson <rth@redhat.com> wrote:
> 
>> Early alpha can't store sub-4-byte quantities.  Altivec can't store anything
>> but 16 byte quantities.  In order to perform smaller stores, we have to do a
>> read-modify-write sequence on a larger aligned chunk of memory.  Two such RMW
>> sequences must conflict, lest we interleave and thus bork the operation.
>>
>> I don't recall how much we ever did for this, exactly, but it's certainly
>> possible to know that some memory operations cannot conflict with these RMW
>> sequence.  E.g. through size + alignment of the other memory operation.  E.g.
>> on Alpha, a byte RMW store can't conflict with a normal DImode memory access.
>>
>>> Btw, if the mem is MEM_READONLY_P how can it be part of
>>> a {un}aligned_store sequence?
>>
>> Er... that's an excellent question.  Uros?
> 
> This flag is copied from the original memory operand by
> alpha_set_memflags to all memory operands in the expanded sequence.

Misses the point.  Store on a MEM_READONLY_P?

I suppose I should take a closer look today...


r~


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