Index: llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -3714,11 +3714,11 @@
       return false;
 
     // Post order traverse the reduction tree starting at B. We only handle true
-    // trees containing only binary operators.
-    SmallVector<std::pair<BinaryOperator *, unsigned>, 32> Stack;
+    // trees containing only binary operators or selects.
+    SmallVector<std::pair<Instruction *, unsigned>, 32> Stack;
     Stack.push_back(std::make_pair(B, 0));
     while (!Stack.empty()) {
-      BinaryOperator *TreeN = Stack.back().first;
+      Instruction *TreeN = Stack.back().first;
       unsigned EdgeToVist = Stack.back().second++;
       bool IsReducedValue = TreeN->getOpcode() != ReductionOpcode;
 
@@ -3754,9 +3754,10 @@
 
       // Visit left or right.
       Value *NextV = TreeN->getOperand(EdgeToVist);
-      BinaryOperator *Next = dyn_cast<BinaryOperator>(NextV);
-      if (Next)
-        Stack.push_back(std::make_pair(Next, 0));
+      // We currently only allow BinaryOperator's and SelectInst's as reduction
+      // values in our tree.
+      if (isa<BinaryOperator>(NextV) || isa<SelectInst>(NextV))
+        Stack.push_back(std::make_pair(cast<Instruction>(NextV), 0));
       else if (NextV != Phi)
         return false;
     }
Index: llvm/trunk/test/Transforms/SLPVectorizer/AArch64/horizontal.ll
===================================================================
--- llvm/trunk/test/Transforms/SLPVectorizer/AArch64/horizontal.ll
+++ llvm/trunk/test/Transforms/SLPVectorizer/AArch64/horizontal.ll
@@ -0,0 +1,73 @@
+; RUN: opt -slp-vectorizer -slp-threshold=-6 -slp-vectorize-hor -S <  %s | FileCheck %s
+
+; FIXME: The threshold is changed to keep this test case a bit smaller.
+; The AArch64 cost model should not give such high costs to select statements.
+
+target datalayout = "e-m:e-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64--linux"
+
+; CHECK-LABEL: test_select
+; CHECK: load <4 x i32>
+; CHECK: load <4 x i32>
+; CHECK: select <4 x i1>
+define i32 @test_select(i32* noalias nocapture readonly %blk1, i32* noalias nocapture readonly %blk2, i32 %lx, i32 %h) {
+entry:
+  %cmp.22 = icmp sgt i32 %h, 0
+  br i1 %cmp.22, label %for.body.lr.ph, label %for.end
+
+for.body.lr.ph:                                   ; preds = %entry
+  %idx.ext = sext i32 %lx to i64
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %for.body.lr.ph
+  %s.026 = phi i32 [ 0, %for.body.lr.ph ], [ %add27, %for.body ]
+  %j.025 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.body ]
+  %p2.024 = phi i32* [ %blk2, %for.body.lr.ph ], [ %add.ptr29, %for.body ]
+  %p1.023 = phi i32* [ %blk1, %for.body.lr.ph ], [ %add.ptr, %for.body ]
+  %0 = load i32, i32* %p1.023, align 4
+  %1 = load i32, i32* %p2.024, align 4
+  %sub = sub nsw i32 %0, %1
+  %cmp2 = icmp slt i32 %sub, 0
+  %sub3 = sub nsw i32 0, %sub
+  %sub3.sub = select i1 %cmp2, i32 %sub3, i32 %sub
+  %add = add nsw i32 %sub3.sub, %s.026
+  %arrayidx4 = getelementptr inbounds i32, i32* %p1.023, i64 1
+  %2 = load i32, i32* %arrayidx4, align 4
+  %arrayidx5 = getelementptr inbounds i32, i32* %p2.024, i64 1
+  %3 = load i32, i32* %arrayidx5, align 4
+  %sub6 = sub nsw i32 %2, %3
+  %cmp7 = icmp slt i32 %sub6, 0
+  %sub9 = sub nsw i32 0, %sub6
+  %v.1 = select i1 %cmp7, i32 %sub9, i32 %sub6
+  %add11 = add nsw i32 %add, %v.1
+  %arrayidx12 = getelementptr inbounds i32, i32* %p1.023, i64 2
+  %4 = load i32, i32* %arrayidx12, align 4
+  %arrayidx13 = getelementptr inbounds i32, i32* %p2.024, i64 2
+  %5 = load i32, i32* %arrayidx13, align 4
+  %sub14 = sub nsw i32 %4, %5
+  %cmp15 = icmp slt i32 %sub14, 0
+  %sub17 = sub nsw i32 0, %sub14
+  %sub17.sub14 = select i1 %cmp15, i32 %sub17, i32 %sub14
+  %add19 = add nsw i32 %add11, %sub17.sub14
+  %arrayidx20 = getelementptr inbounds i32, i32* %p1.023, i64 3
+  %6 = load i32, i32* %arrayidx20, align 4
+  %arrayidx21 = getelementptr inbounds i32, i32* %p2.024, i64 3
+  %7 = load i32, i32* %arrayidx21, align 4
+  %sub22 = sub nsw i32 %6, %7
+  %cmp23 = icmp slt i32 %sub22, 0
+  %sub25 = sub nsw i32 0, %sub22
+  %v.3 = select i1 %cmp23, i32 %sub25, i32 %sub22
+  %add27 = add nsw i32 %add19, %v.3
+  %add.ptr = getelementptr inbounds i32, i32* %p1.023, i64 %idx.ext
+  %add.ptr29 = getelementptr inbounds i32, i32* %p2.024, i64 %idx.ext
+  %inc = add nuw nsw i32 %j.025, 1
+  %exitcond = icmp eq i32 %inc, %h
+  br i1 %exitcond, label %for.end.loopexit, label %for.body
+
+for.end.loopexit:                                 ; preds = %for.body
+  br label %for.end
+
+for.end:                                          ; preds = %for.end.loopexit, %entry
+  %s.0.lcssa = phi i32 [ 0, %entry ], [ %add27, %for.end.loopexit ]
+  ret i32 %s.0.lcssa
+}