[PATCH] D18069: Throttling LICM to reduce compile time of Value Propagation and Reg Splitting

[Xinliang David Li via llvm-commits]

On Fri, Mar 11, 2016 at 5:20 PM, Philip Reames <listmail at philipreames.com>
wrote:

> David,
>
> I very deeply believe that limiting hoisting in the IR to reduce register
> pressure is fundamentally the wrong approach.  The backend is responsible
> for sinking if desired to reduce register pressure. We do not model
> register pressure in the IR.  At all.  Period.


Agree -- with a small cost of doing optimization and undo it later.
Correcting aggressive LICM is probably straightforward to do. There are
also cases where this is not the case -- this is slightly off topic.

thanks,

David


>
>
> Philip
>
>
> On 03/11/2016 05:08 PM, David Li wrote:
>
>> davidxl added a comment.
>>
>> I have not read the patch in details, but it seems the main purpose of
>> the patch to throttle LICM to reduce register pressure and the compile time
>> benefit due to reduced LVI queries is just a good side effect of the patch?
>> Do we have any performance data (runtime) showing the usefulness of the
>> throttling?  (Whether this is the right approach to solve the spill problem
>> is also subject to discussions).
>>
>>
>> Repository:
>>    rL LLVM
>>
>> http://reviews.llvm.org/D18069
>>
>>
>>
>>
>
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