[SLP Vectorizer]Generate extract for in-tree uses if the use is scalar operand in vectorized instruction

[Arnold Schwaighofer]

The test case has trailing whitespaces.

Note, that the ExternalUse created during vectorizing the tree won’t participate in the cost estimate. I am not sure that fixing this would be worth the added complexity.

Otherwise, LGTM.

Thanks!


> On Aug 29, 2014, at 2:02 PM, Yi Jiang <yjiang at apple.com> wrote:
> 
> Hi, 
> 
> This patch is for radar 18144665 which is exposed by Machael Z's commit.  We will get an assertion if enabling the vectorization of GEP with multiple-uses on this case:
> 
> fn2() {
>   a[11] = a + 11;
>   a[12] = a + 56;
> }
> 
> The reason of this bug is that our current framework assumes that all in-tree scalars will eventually become vectors so all in-tree uses do not need extract. However, it is not the case for vector instructions that has scalar operands; the scalar operands will remain scalar and we still need the extract.  For example in this test case:
> 
>   %0 = load i64** @a, align 8, !tbaa !1
>   %add.ptr1 = getelementptr inbounds i64* %0, i64 56      // A
>   %add.ptr = getelementptr inbounds i64* %0, i64 11        // B
>   %1 = insertelement <2 x i64*> undef, i64* %0, i32 0
>   %2 = insertelement <2 x i64*> %1, i64* %0, i32 1
>   %3 = getelementptr <2 x i64*> %2, <2 x i64> <i64 11, i64 56>   // C: Vectorized Value
>   %4 = ptrtoint <2 x i64*> %3 to <2 x i64>
>   %arrayidx2 = getelementptr inbounds i64* %0, i64 12
>   %5 = bitcast i64* %add.ptr to <2 x i64>*    //  D
>   store <2 x i64> %4, <2 x i64>* %5, align 8, !tbaa !5
>   ret i32 undef
> 
> Now Our framework vectorizes A and B to C. add.ptr(A) is used by D as the pointer operand. Although it is in-tree uses, we still need to extract this value from C.
> 
> So here is my proposal in my patch to solve this:
> 1) When we build ExternalUses List, we need to find out if the in-tree use needs extract instead of ignoring all of them. It will help us to make the cost model right.
> 2) When we vectorize load and store, currently we will generate bitcast to transfer pointer operand. Now we need to add this bitcast to ExternalUses List and tell the SLP-vectorizer to extract the value. 
> 
> By applying this patch, we can re-enable the vectorization of GEP with multiple-uses. Any comment is appreciated. 
>  
> 
> <18144665.patch>
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