[PATCH] [SLP] Vectorize all-constant entries.

[Nadav Rotem]

LGTM! 

> On Jun 18, 2015, at 5:27 PM, Michael Zolotukhin <mzolotukhin at apple.com> wrote:
> 
> Hi nadav, aschwaighofer,
> 
> Currently SLP gives up when a tree contains a set of constants, and that can be easily fixed.
> 
> http://reviews.llvm.org/D10558
> 
> Files:
>  lib/Transforms/Vectorize/SLPVectorizer.cpp
>  test/Transforms/SLPVectorizer/X86/tiny-tree.ll
> 
> Index: lib/Transforms/Vectorize/SLPVectorizer.cpp
> ===================================================================
> --- lib/Transforms/Vectorize/SLPVectorizer.cpp
> +++ lib/Transforms/Vectorize/SLPVectorizer.cpp
> @@ -1637,8 +1637,10 @@
>   if (VectorizableTree.size() != 2)
>     return false;
> 
> -  // Handle splat stores.
> -  if (!VectorizableTree[0].NeedToGather && isSplat(VectorizableTree[1].Scalars))
> +  // Handle splat and all-constants stores.
> +  if (!VectorizableTree[0].NeedToGather &&
> +      (allConstant(VectorizableTree[1].Scalars) ||
> +       isSplat(VectorizableTree[1].Scalars)))
>     return true;
> 
>   // Gathering cost would be too much for tiny trees.
> Index: test/Transforms/SLPVectorizer/X86/tiny-tree.ll
> ===================================================================
> --- test/Transforms/SLPVectorizer/X86/tiny-tree.ll
> +++ test/Transforms/SLPVectorizer/X86/tiny-tree.ll
> @@ -153,3 +153,19 @@
>   store float %1, float* %6, align 4
>   ret void
> }
> +
> +
> +; CHECK-LABEL: store_const
> +; CHECK: store <4 x i32>
> +define void @store_const(i32* %a) {
> +entry:
> +  %ptr0 = getelementptr inbounds i32, i32* %a, i64 0
> +  store i32 10, i32* %ptr0, align 4
> +  %ptr1 = getelementptr inbounds i32, i32* %a, i64 1
> +  store i32 30, i32* %ptr1, align 4
> +  %ptr2 = getelementptr inbounds i32, i32* %a, i64 2
> +  store i32 20, i32* %ptr2, align 4
> +  %ptr3 = getelementptr inbounds i32, i32* %a, i64 3
> +  store i32 40, i32* %ptr3, align 4
> +  ret void
> +}
> 
> EMAIL PREFERENCES
>  http://reviews.llvm.org/settings/panel/emailpreferences/
> <D10558.27980.patch>