Index: llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -85,11 +85,13 @@
 ScheduleRegionSizeBudget("slp-schedule-budget", cl::init(100000), cl::Hidden,
     cl::desc("Limit the size of the SLP scheduling region per block"));
 
+static cl::opt<int> MinVectorRegSizeOption(
+    "slp-min-reg-size", cl::init(128), cl::Hidden,
+    cl::desc("Attempt to vectorize for this register size in bits"));
+
 namespace {
 
 // FIXME: Set this via cl::opt to allow overriding.
-static const unsigned MinVecRegSize = 128;
-
 static const unsigned RecursionMaxDepth = 12;
 
 // Limit the number of alias checks. The limit is chosen so that
@@ -3418,6 +3420,8 @@
     else
       MaxVecRegSize = TTI->getRegisterBitWidth(true);
 
+    MinVecRegSize = MinVectorRegSizeOption;
+
     // Don't vectorize when the attribute NoImplicitFloat is used.
     if (F.hasFnAttribute(Attribute::NoImplicitFloat))
       return false;
@@ -3531,6 +3535,7 @@
   unsigned NumGEPs;
 
   unsigned MaxVecRegSize; // This is set by TTI or overridden by cl::opt.
+  unsigned MinVecRegSize; // Set by cl::opt (default: 128).
 };
 
 /// \brief Check that the Values in the slice in VL array are still existent in
@@ -3924,9 +3929,14 @@
   /// The width of one full horizontal reduction operation.
   unsigned ReduxWidth;
 
-  HorizontalReduction()
-    : ReductionRoot(nullptr), ReductionPHI(nullptr), ReductionOpcode(0),
-    ReducedValueOpcode(0), IsPairwiseReduction(false), ReduxWidth(0) {}
+  /// Minimal width of available vector registers. It's used to determine
+  /// ReduxWidth.
+  unsigned MinVecRegSize;
+
+  HorizontalReduction(unsigned MinVecRegSize)
+      : ReductionRoot(nullptr), ReductionPHI(nullptr), ReductionOpcode(0),
+        ReducedValueOpcode(0), IsPairwiseReduction(false), ReduxWidth(0),
+        MinVecRegSize(MinVecRegSize) {}
 
   /// \brief Try to find a reduction tree.
   bool matchAssociativeReduction(PHINode *Phi, BinaryOperator *B) {
@@ -4254,11 +4264,12 @@
 /// \returns true if a horizontal reduction was matched and reduced.
 /// \returns false if a horizontal reduction was not matched.
 static bool canMatchHorizontalReduction(PHINode *P, BinaryOperator *BI,
-                                        BoUpSLP &R, TargetTransformInfo *TTI) {
+                                        BoUpSLP &R, TargetTransformInfo *TTI,
+                                        unsigned MinRegSize) {
   if (!ShouldVectorizeHor)
     return false;
 
-  HorizontalReduction HorRdx;
+  HorizontalReduction HorRdx(MinRegSize);
   if (!HorRdx.matchAssociativeReduction(P, BI))
     return false;
 
@@ -4346,7 +4357,7 @@
         continue;
 
       // Try to match and vectorize a horizontal reduction.
-      if (canMatchHorizontalReduction(P, BI, R, TTI)) {
+      if (canMatchHorizontalReduction(P, BI, R, TTI, MinVecRegSize)) {
         Changed = true;
         it = BB->begin();
         e = BB->end();
@@ -4373,7 +4384,8 @@
       if (StoreInst *SI = dyn_cast<StoreInst>(it))
         if (BinaryOperator *BinOp =
                 dyn_cast<BinaryOperator>(SI->getValueOperand())) {
-          if (canMatchHorizontalReduction(nullptr, BinOp, R, TTI) ||
+          if (canMatchHorizontalReduction(nullptr, BinOp, R, TTI,
+                                          MinVecRegSize) ||
               tryToVectorize(BinOp, R)) {
             Changed = true;
             it = BB->begin();