Temporarily revert upstream llvm trunk r240144 (by Michael Zolotukhin):

  [SLP] Vectorize for all-constant entries.

This should fix libc++'s iostream initialization SIGBUSing whenever the
global cout symbol is not aligned to 16 bytes.

Introduced here: http://svnweb.freebsd.org/changeset/base/289072

Index: lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -1642,10 +1642,8 @@ bool BoUpSLP::isFullyVectorizableTinyTree() {
   if (VectorizableTree.size() != 2)
     return false;
 
-  // Handle splat and all-constants stores.
-  if (!VectorizableTree[0].NeedToGather &&
-      (allConstant(VectorizableTree[1].Scalars) ||
-       isSplat(VectorizableTree[1].Scalars)))
+  // Handle splat stores.
+  if (!VectorizableTree[0].NeedToGather && 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
@@ -153,19 +153,3 @@ define void @store_splat(float*, float) {
   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
-}