[LLVMdev] Fwd: How to force the creation of arrays with zeroes?

[Stepan Dyatkovskiy]

Hi Chris. The main question is how to implement ConstantAggregateXXXXX::getOperand? Should it be empty collection, or it must return the item aggregated? 

-Stepan.

22.01.2012, 04:43, "Chris Lattner" <clattner at apple.com>:
> Yep check out PR1324.  Doing something like this would be a great improvement.
>
> -Chris
>
> On Jan 21, 2012, at 9:42 AM, Duncan Sands <baldrick at free.fr> wrote:
>
>>  Hi Anton, in a solution without CAZ, isNullValue can just return true when it
>>  sees the special "this ConstantArray is all zero" flag.  So all the places that
>>  now look for CAZ can just use isNullValue instead and there need be no
>>  performance loss.  That said, CAZ is more "in your force" so less likely to be
>>  forgotten about.  Another interesting possibility is to handle more than just
>>  all zero values: if a constant array has many repeated elements, maybe the
>>  array could be stored in a compressed form.  An all zeros array would just be a
>>  special case of this.
>>
>>  Ciao, Duncan.
>>
>>  On 21/01/12 18:13, Anton Korobeynikov wrote:
>>>  Sorry, forgot to reply-all
>>>
>>>  ---------- Forwarded message ----------
>>>  From: Anton Korobeynikov<anton at korobeynikov.info>
>>>  Date: Sat, Jan 21, 2012 at 20:59
>>>  Subject: Re: [LLVMdev] How to force the creation of arrays with zeroes?
>>>  To: Stepan Dyatkovskiy<STPWORLD at narod.ru>
>>>>  Though, there is also cases when we really need to transform it to 10,000 zeroes (just look at CBackend.cpp, when we print constant arrays, string #1027). There is also cases when we need to get either operand[i] or zero (SCCP.cpp, str #413). Both for CBackend and for SCCP we can reduce code size keeping performance on the same level.
>>>  In these 2 particular cases the changes of the code size can
>>>  definitely be neglected. Even more, in SCCP the use of CAZ is a
>>>  performance win, since we do not have to check at all operands are
>>>  zero, we already (!) know this.
>>>
>>>  --
>>>  With best regards, Anton Korobeynikov
>>>  Faculty of Mathematics and Mechanics, Saint Petersburg State University
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