llvm dev - Sep 2015 - RFC: faster simplifyInstructionsInBlock/SimplifyInstructions pass

> 
> Instead of adding the operands to a list, erase the instruction and add
them to the worklist wouldn’t be probably faster something like:
> 
> if (Instruction *Used = dyn_cast<Instruction>(*OI))
>   if (Used->hasOneUse())
>     WorkList.insert(Used);
> 
> If it has one use is going to be the instruction we are going to remove
anyway, right?
I don’t think this is strictly true, but someone correct me if I’m wrong: if you
have

%y = add i32 %x, %x

%x will have two uses, but it will have zero if %y is deleted. This was the
corner case I was worried about.

—escha
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> On 13 Sep 2015, at 11:11, escha <escha at apple.com> wrote:
> 
>> 
>> Instead of adding the operands to a list, erase the instruction and add
them to the worklist wouldn’t be probably faster something like:
>> 
>> if (Instruction *Used = dyn_cast<Instruction>(*OI))
>>   if (Used->hasOneUse())
>>     WorkList.insert(Used);
>> 
>> If it has one use is going to be the instruction we are going to remove
anyway, right?
> 
> I don’t think this is strictly true, but someone correct me if I’m wrong:
if you have
> 
> %y = add i32 %x, %x
> 
> %x will have two uses, but it will have zero if %y is deleted. This was the
corner case I was worried about.
Yeah, I think you are right , I didn’t think about this case!

Marcello
> 
> —escha
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> On Sep 13, 2015, at 11:32 AM, Marcello Maggioni <mmaggioni at
apple.com> wrote:
> 
>> 
>> On 13 Sep 2015, at 11:11, escha <escha at apple.com <mailto:escha
at apple.com>> wrote:
>> 
>>> 
>>> Instead of adding the operands to a list, erase the instruction and
add them to the worklist wouldn’t be probably faster something like:
>>> 
>>> if (Instruction *Used = dyn_cast<Instruction>(*OI))
>>>   if (Used->hasOneUse())
>>>     WorkList.insert(Used);
>>> 
>>> If it has one use is going to be the instruction we are going to
remove anyway, right?
>> 
>> I don’t think this is strictly true, but someone correct me if I’m
wrong: if you have
>> 
>> %y = add i32 %x, %x
>> 
>> %x will have two uses, but it will have zero if %y is deleted. This was
the corner case I was worried about.
> 
> Yeah, I think you are right , I didn’t think about this case!
> 
> Marcello
> 
>> 
>> —escha
On this note, I have a feeling that both IR and the DAG could use a hasOneUser()
function…

—escha
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