[llvm-dev] Non-Temporal hints from Loop Vectorizer

[hameeza ahmed via llvm-dev]

Actually i am working on vector accelerator which will perform those
instructions which are non temporal.

for instance if i have this loop

for(i=0;i<2048;i++)
a[i]=b[i]+c[i];

currently it emits following IR;


  %0 = getelementptr inbounds [2048 x i32], [2048 x i32]* @b, i64 0, i64
%index
  %1 = bitcast i32* %0 to <16 x i32>*
  %wide.load = load <16 x i32>, <16 x i32>* %1, align 16, !tbaa !1
  %8 = getelementptr inbounds [2048 x i32], [2048 x i32]* @c, i64 0, i64
%index
  %9 = bitcast i32* %8 to <16 x i32>*
  %wide.load14 = load <16 x i32>, <16 x i32>* %9, align 16, !tbaa !1
  %16 = add nsw <16 x i32> %wide.load14, %wide.load
  %20 = getelementptr inbounds [2048 x i32], [2048 x i32]* @a, i64 0, i64
%index
  %21 = bitcast i32* %20 to <16 x i32>*
  store <16 x i32> %16, <16 x i32>* %21, align 16, !tbaa !1


However, i want it to emit following IR

  %0 = getelementptr inbounds [2048 x i32], [2048 x i32]* @b, i64 0, i64
%index
  %1 = bitcast i32* %0 to <16 x i32>*
  %wide.load = load <16 x i32>, <16 x i32>* %1, align 16, !tbaa !1,
!nontemporal !1
  %8 = getelementptr inbounds [2048 x i32], [2048 x i32]* @c, i64 0, i64
%index
  %9 = bitcast i32* %8 to <16 x i32>*
  %wide.load14 = load <16 x i32>, <16 x i32>* %9, align 16, !tbaa
!1, !nontemporal !1
  %16 = add nsw <16 x i32> %wide.load14, %wide.load, !nontemporal !1
  %20 = getelementptr inbounds [2048 x i32], [2048 x i32]* @a, i64 0, i64
%index
  %21 = bitcast i32* %20 to <16 x i32>*
  store <16 x i32> %16, <16 x i32>* %21, align 16, !tbaa !1, !nontemporal !1

so that i can offload load, add, store to accelerator hardware. is it
possible here? do i need a separate pass to detect whether the loop has non
temporal data or polly will help here? what do you say?






On Sat, Jan 20, 2018 at 11:02 PM, Simon Pilgrim <llvm-dev at redking.me.uk>
wrote:

> On 20/01/2018 17:44, hameeza ahmed via llvm-dev wrote:
>
>> Hello,
>>
>> My work deals with non-temporal loads and stores i found non-temporal
>> meta data in llvm documentation but its not shown in IR.
>>
>> How to get non-temporal meta data?
>>
> llvm\test\CodeGen\X86\nontemporal-loads.ll shows how to create nt vector
> loads in IR - is that what you're after?
>
> Simon.
>
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