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Re: [PATCH] Builtins handling in IVOPT


On Thu, Nov 21, 2013 at 10:36 PM, Wei Mi <wmi@google.com> wrote:
> On Thu, Nov 21, 2013 at 1:01 PM, Richard Biener
> <richard.guenther@gmail.com> wrote:
>> Wei Mi <wmi@google.com> wrote:
>>>On Thu, Nov 21, 2013 at 11:36 AM, Richard Biener
>>><richard.guenther@gmail.com> wrote:
>>>> Wei Mi <wmi@google.com> wrote:
>>>>>> So what you are doing is basically not only rewriting memory
>>>>>references
>>>>>> to possibly use TARGET_MEM_REF but also address uses to use
>>>>>> &TARGET_MEM_REF.  I think this is a good thing in general
>>>>>> (given instructions like x86 lea) and I would not bother
>>>>>distinguishing
>>>>>> the different kind of uses.
>>>>>>
>>>>>> Richard.
>>>>>>
>>>>>
>>>>>You mean to change normal expr to &TMR(expr) form in order to utilize
>>>>>x86 lea type instructions as much as possible. It is interesting. I
>>>>>can experiment that idea later. I am not sure if it could simply
>>>work.
>>>>>My concern is x86 lea still has some limitation (such as three
>>>>>operands lea will have longer latency and can only be issued to
>>>>>port1), if we change some expr to &TMR(expr), will it inhitbit cse
>>>>>opportunity if codegen find out it is not good to use lea?
>>>>
>>>> That needs to be determined.  Over all it might be because ivopts
>>>runs so early.  At rtl level there should not be big differences apart
>>>from better initial address computations.
>>>>
>>>> Did I misunderstand what your patch does?
>>>>
>>>> Richard.
>>>>
>>>
>>>My patch wants to address the issue that iv uses using as memory
>>>reference actuals for load/store/prefetch builtins are treated as
>>>non-linear iv uses instead of address iv uses, and the result of
>>>determine_use_iv_cost is wrong. After we change those uses to address
>>>uses, less ivs may be used, TMR will be generated for those iv uses
>>>and efficent addressing mode could be utilized.
>>
>> But are not all pointer typed uses address uses?!
>>
>> Richard.
>>
>
> If a pointer typed use is plainly value passed to a func call, it is
> not an address use, right? But as you said, x86 lea may help here.

But that's what you are matching ... (well, for builtins you know
will expand that to a memory reference).

What I dislike in the patch is the special-casing of some builtins
via a target hook.  I'd rather say treat all internal functions and
all target builtins that way.  Or simply all addresses.

Thanks,
Richard.

> Thanks,
> Wei.


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