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

[Michael Zolotukhin]

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
+}

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