llvm dev - Jan 2012 - [LLVMdev] Fwd: How to force the creation of arrays with zeroes?

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

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

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