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

[Chris Lattner]

Hi Stephan,

I've been thinking about this a bit and have some more specific ideas, I'll write up a design and maybe implement it over the next few days.

-Chris

On Jan 21, 2012, at 11:50 PM, Stepan Dyatkovskiy <STPWORLD at narod.ru> wrote:

> 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
>>>  _______________________________________________
>>>  LLVM Developers mailing list
>>>  LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>  http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>> 
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev