[PATCH] Allow loop vectorization with llvm.lifetime calls

Jessome, Marc marc.jessome at intel.com
Tue Aug 6 07:50:11 PDT 2013


I've expanded the test, and taught the cost model about lifetime intrinsics. The call itself is scalarized, rather than reconstructed and output.

Marc

From: Nadav Rotem [mailto:nrotem at apple.com] 
Sent: Friday, August 02, 2013 2:54 PM
To: Jessome, Marc
Cc: llvm-commits at cs.uiuc.edu; Arnold Schwaighofer
Subject: Re: [PATCH] Allow loop vectorization with llvm.lifetime calls

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?

-------------- next part --------------
A non-text attachment was scrubbed...
Name: vectorize_lifetime.4.patch
Type: application/octet-stream
Size: 5977 bytes
Desc: vectorize_lifetime.4.patch
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130806/9372c6db/attachment.obj>


More information about the llvm-commits mailing list