[PATCH] Allow loop vectorization with llvm.lifetime calls

[Nadav Rotem]

The lifetime marker sequence below is legal and the stack-coloring code should not have a problem handling it.  

Thanks for working on this!

Nadav

On Aug 2, 2013, at 7:05 AM, Jessome, Marc <marc.jessome at intel.com> wrote:

> Hi Nadav,
> 
> I'd like to continue with this patch before it falls through the cracks; Would you be able to give any insight on this remaining question?
> 
>> The question then remains whether to subsequent calls to a lifetime intrinsic are legal. I don’t see anything in "http://llvm.org/docs/LangRef.html#llvm-lifetime-start-intrinsic” that leads me to believe it would not be.
>> 
>> +  %0 = bitcast [1024 x i32]* % arr to i8*
>> +  call void @llvm.lifetime.start(i64 4, i8* %0) #1
>> +  call void @llvm.lifetime.start(i64 4, i8* %0) #1
>> 
>> Maybe Nadav knows?
> 
> Thanks,
>  Marc
> ________________________________________
> From: Arnold Schwaighofer [aschwaighofer at apple.com]
> Sent: Wednesday, July 31, 2013 3:08 PM
> To: Jessome, Marc
> Cc: llvm-commits at cs.uiuc.edu; Nadav Rotem
> Subject: Re: [PATCH] Allow loop vectorization with llvm.lifetime calls
> 
> On Jul 31, 2013, at 1:34 PM, Jessome, Marc <marc.jessome at intel.com> wrote:
> 
>> Hi Arnold,
>> 
>> I've attached an updated patch, however I do have a quick question about one of your comments.
>> 
>> Your comment about the need to use getVectorValue() rather than getArgOperand() is spot on. I am wondering, however, if we want to do this only for the first element of the vector, or if it should be done for each element?
>> In the latter case, a simple scalarizeInstruction() would suffice, rather than manually extracting the arguments and rebuilding lifetime.* calls.
> 
> I was (probably mistakenly) assuming that we cannot have loop variant pointers as argument to lifetime intrinsic calls. For example:
> 
> +for.body:
> +  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
> +  %0 = getelementptr [1024 x i32]* %arr, 0, indvars.iv
> +  %1 = bitcast [1024 x i32]* %0 to i8*
> +  call void @llvm.lifetime.start(i64 4, i8* %1) #1
> 
> 
> If we can have a construct like the one above (which I don’t see why we shouldn’t) then yes you need to scalarize the elements of getVectorValue() individually like done by scalarizeInstruction.
> 
> The question then remains whether to subsequent calls to a lifetime intrinsic are legal. I don’t see anything in "http://llvm.org/docs/LangRef.html#llvm-lifetime-start-intrinsic” that leads me to believe it would not be.
> 
> +  %0 = bitcast [1024 x i32]* % arr to i8*
> +  call void @llvm.lifetime.start(i64 4, i8* %0) #1
> +  call void @llvm.lifetime.start(i64 4, i8* %0) #1
> 
> Maybe Nadav knows?

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