[LLVMdev] Vectorizing alloca instructions

[Nadav Rotem]

On Oct 24, 2013, at 3:00 PM, Chandler Carruth <chandlerc at google.com> wrote:

> Just a note, I don't think you should or need to vectorize the actual alloca stuff. If you can simply transform the dynamically indexed load:
> 
> Then running SROA and InstCombine will mop up the rest. So its mostly about getting the SLPVectorizer to handle the dynamic GEP. As soon as it does that, everything else will fall away.
> 

I don’t think that Tom wants the SLP-vectorizer to handle dynamic GEPS.  What he wants is for the SLP-vectorizer to convert the first part of the code:


>> define void @vector(i32 addrspace(1)* %out, i32 %index) {
>> entry:
>>   %0 = alloca [4 x i32]
>>   %x = getelementptr [4 x i32]* %0, i32 0, i32 0
>>   %y = getelementptr [4 x i32]* %0, i32 0, i32 1
>>   %z = getelementptr [4 x i32]* %0, i32 0, i32 2
>>   %w = getelementptr [4 x i32]* %0, i32 0, i32 3
>>   store i32 0, i32* %x
>>   store i32 1, i32* %y
>>   store i32 2, i32* %z
>>   store i32 3, i32* %w
> 

Into this:   Store <i32 0, i32 1, i32 2, i32 3> ....     

> 
>>   %1 = bitcast [4 x i32]* %0 to <4 x i32>*
>>   %2 = load <4 x i32>* %1
>>   %3 = extractelement <4 x i32> %2, i32 %index
>>   store i32 %3, i32 addrspace(1)* %out
>>   ret void
>> }
> 


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