Vendor import of llvm trunk r126079:

http://llvm.org/svn/llvm-project/llvm/trunk@126079

1 files changed, 139 insertions, 133 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index a58124d..5caa12d 100644
--- a/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -18,7 +18,7 @@ using namespace llvm;
 /// CheapToScalarize - Return true if the value is cheaper to scalarize than it
 /// is to leave as a vector operation.
 static bool CheapToScalarize(Value *V, bool isConstant) {
-  if (isa<ConstantAggregateZero>(V)) 
+  if (isa<ConstantAggregateZero>(V))
     return true;
   if (ConstantVector *C = dyn_cast<ConstantVector>(V)) {
     if (isConstant) return true;
@@ -31,7 +31,7 @@ static bool CheapToScalarize(Value *V, bool isConstant) {
   }
   Instruction *I = dyn_cast<Instruction>(V);
   if (!I) return false;
-  
+
   // Insert element gets simplified to the inserted element or is deleted if
   // this is constant idx extract element and its a constant idx insertelt.
   if (I->getOpcode() == Instruction::InsertElement && isConstant &&
@@ -49,26 +49,24 @@ static bool CheapToScalarize(Value *V, bool isConstant) {
         (CheapToScalarize(CI->getOperand(0), isConstant) ||
          CheapToScalarize(CI->getOperand(1), isConstant)))
       return true;
-  
+
   return false;
 }
 
-/// Read and decode a shufflevector mask.
-///
-/// It turns undef elements into values that are larger than the number of
-/// elements in the input.
-static std::vector<unsigned> getShuffleMask(const ShuffleVectorInst *SVI) {
+/// getShuffleMask - Read and decode a shufflevector mask.
+/// Turn undef elements into negative values.
+static std::vector<int> getShuffleMask(const ShuffleVectorInst *SVI) {
   unsigned NElts = SVI->getType()->getNumElements();
   if (isa<ConstantAggregateZero>(SVI->getOperand(2)))
-    return std::vector<unsigned>(NElts, 0);
+    return std::vector<int>(NElts, 0);
   if (isa<UndefValue>(SVI->getOperand(2)))
-    return std::vector<unsigned>(NElts, 2*NElts);
-  
-  std::vector<unsigned> Result;
+    return std::vector<int>(NElts, -1);
+
+  std::vector<int> Result;
   const ConstantVector *CP = cast<ConstantVector>(SVI->getOperand(2));
   for (User::const_op_iterator i = CP->op_begin(), e = CP->op_end(); i!=e; ++i)
     if (isa<UndefValue>(*i))
-      Result.push_back(NElts*2);  // undef -> 8
+      Result.push_back(-1);  // undef
     else
       Result.push_back(cast<ConstantInt>(*i)->getZExtValue());
   return Result;
@@ -83,42 +81,41 @@ static Value *FindScalarElement(Value *V, unsigned EltNo) {
   unsigned Width = PTy->getNumElements();
   if (EltNo >= Width)  // Out of range access.
     return UndefValue::get(PTy->getElementType());
-  
+
   if (isa<UndefValue>(V))
     return UndefValue::get(PTy->getElementType());
   if (isa<ConstantAggregateZero>(V))
     return Constant::getNullValue(PTy->getElementType());
   if (ConstantVector *CP = dyn_cast<ConstantVector>(V))
     return CP->getOperand(EltNo);
-  
+
   if (InsertElementInst *III = dyn_cast<InsertElementInst>(V)) {
     // If this is an insert to a variable element, we don't know what it is.
-    if (!isa<ConstantInt>(III->getOperand(2))) 
+    if (!isa<ConstantInt>(III->getOperand(2)))
       return 0;
     unsigned IIElt = cast<ConstantInt>(III->getOperand(2))->getZExtValue();
-    
+
     // If this is an insert to the element we are looking for, return the
     // inserted value.
-    if (EltNo == IIElt) 
+    if (EltNo == IIElt)
       return III->getOperand(1);
-    
+
     // Otherwise, the insertelement doesn't modify the value, recurse on its
     // vector input.
     return FindScalarElement(III->getOperand(0), EltNo);
   }
-  
+
   if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(V)) {
     unsigned LHSWidth =
-    cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements();
-    unsigned InEl = getShuffleMask(SVI)[EltNo];
-    if (InEl < LHSWidth)
-      return FindScalarElement(SVI->getOperand(0), InEl);
-    else if (InEl < LHSWidth*2)
-      return FindScalarElement(SVI->getOperand(1), InEl - LHSWidth);
-    else
+      cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements();
+    int InEl = getShuffleMask(SVI)[EltNo];
+    if (InEl < 0)
       return UndefValue::get(PTy->getElementType());
+    if (InEl < (int)LHSWidth)
+      return FindScalarElement(SVI->getOperand(0), InEl);
+    return FindScalarElement(SVI->getOperand(1), InEl - LHSWidth);
   }
-  
+
   // Otherwise, we don't know.
   return 0;
 }
@@ -127,11 +124,11 @@ Instruction *InstCombiner::visitExtractElementInst(ExtractElementInst &EI) {
   // If vector val is undef, replace extract with scalar undef.
   if (isa<UndefValue>(EI.getOperand(0)))
     return ReplaceInstUsesWith(EI, UndefValue::get(EI.getType()));
-  
+
   // If vector val is constant 0, replace extract with scalar 0.
   if (isa<ConstantAggregateZero>(EI.getOperand(0)))
     return ReplaceInstUsesWith(EI, Constant::getNullValue(EI.getType()));
-  
+
   if (ConstantVector *C = dyn_cast<ConstantVector>(EI.getOperand(0))) {
     // If vector val is constant with all elements the same, replace EI with
     // that element. When the elements are not identical, we cannot replace yet
@@ -139,53 +136,53 @@ Instruction *InstCombiner::visitExtractElementInst(ExtractElementInst &EI) {
     Constant *op0 = C->getOperand(0);
     for (unsigned i = 1; i != C->getNumOperands(); ++i)
       if (C->getOperand(i) != op0) {
-        op0 = 0; 
+        op0 = 0;
         break;
       }
     if (op0)
       return ReplaceInstUsesWith(EI, op0);
   }
-  
+
   // If extracting a specified index from the vector, see if we can recursively
   // find a previously computed scalar that was inserted into the vector.
   if (ConstantInt *IdxC = dyn_cast<ConstantInt>(EI.getOperand(1))) {
     unsigned IndexVal = IdxC->getZExtValue();
     unsigned VectorWidth = EI.getVectorOperandType()->getNumElements();
-    
+
     // If this is extracting an invalid index, turn this into undef, to avoid
     // crashing the code below.
     if (IndexVal >= VectorWidth)
       return ReplaceInstUsesWith(EI, UndefValue::get(EI.getType()));
-    
+
     // This instruction only demands the single element from the input vector.
     // If the input vector has a single use, simplify it based on this use
     // property.
     if (EI.getOperand(0)->hasOneUse() && VectorWidth != 1) {
       APInt UndefElts(VectorWidth, 0);
       APInt DemandedMask(VectorWidth, 0);
-      DemandedMask.set(IndexVal);
+      DemandedMask.setBit(IndexVal);
       if (Value *V = SimplifyDemandedVectorElts(EI.getOperand(0),
                                                 DemandedMask, UndefElts)) {
         EI.setOperand(0, V);
         return &EI;
       }
     }
-    
+
     if (Value *Elt = FindScalarElement(EI.getOperand(0), IndexVal))
       return ReplaceInstUsesWith(EI, Elt);
-    
+
     // If the this extractelement is directly using a bitcast from a vector of
     // the same number of elements, see if we can find the source element from
     // it.  In this case, we will end up needing to bitcast the scalars.
     if (BitCastInst *BCI = dyn_cast<BitCastInst>(EI.getOperand(0))) {
-      if (const VectorType *VT = 
+      if (const VectorType *VT =
           dyn_cast<VectorType>(BCI->getOperand(0)->getType()))
         if (VT->getNumElements() == VectorWidth)
           if (Value *Elt = FindScalarElement(BCI->getOperand(0), IndexVal))
             return new BitCastInst(Elt, EI.getType());
     }
   }
-  
+
   if (Instruction *I = dyn_cast<Instruction>(EI.getOperand(0))) {
     // Push extractelement into predecessor operation if legal and
     // profitable to do so
@@ -193,11 +190,11 @@ Instruction *InstCombiner::visitExtractElementInst(ExtractElementInst &EI) {
       if (I->hasOneUse() &&
           CheapToScalarize(BO, isa<ConstantInt>(EI.getOperand(1)))) {
         Value *newEI0 =
-        Builder->CreateExtractElement(BO->getOperand(0), EI.getOperand(1),
-                                      EI.getName()+".lhs");
+          Builder->CreateExtractElement(BO->getOperand(0), EI.getOperand(1),
+                                        EI.getName()+".lhs");
         Value *newEI1 =
-        Builder->CreateExtractElement(BO->getOperand(1), EI.getOperand(1),
-                                      EI.getName()+".rhs");
+          Builder->CreateExtractElement(BO->getOperand(1), EI.getOperand(1),
+                                        EI.getName()+".rhs");
         return BinaryOperator::Create(BO->getOpcode(), newEI0, newEI1);
       }
     } else if (InsertElementInst *IE = dyn_cast<InsertElementInst>(I)) {
@@ -215,21 +212,22 @@ Instruction *InstCombiner::visitExtractElementInst(ExtractElementInst &EI) {
       // If this is extracting an element from a shufflevector, figure out where
       // it came from and extract from the appropriate input element instead.
       if (ConstantInt *Elt = dyn_cast<ConstantInt>(EI.getOperand(1))) {
-        unsigned SrcIdx = getShuffleMask(SVI)[Elt->getZExtValue()];
+        int SrcIdx = getShuffleMask(SVI)[Elt->getZExtValue()];
         Value *Src;
         unsigned LHSWidth =
-        cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements();
-        
-        if (SrcIdx < LHSWidth)
+          cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements();
+
+        if (SrcIdx < 0)
+          return ReplaceInstUsesWith(EI, UndefValue::get(EI.getType()));
+        if (SrcIdx < (int)LHSWidth)
           Src = SVI->getOperand(0);
-        else if (SrcIdx < LHSWidth*2) {
+        else {
           SrcIdx -= LHSWidth;
           Src = SVI->getOperand(1);
-        } else {
-          return ReplaceInstUsesWith(EI, UndefValue::get(EI.getType()));
         }
+        const Type *Int32Ty = Type::getInt32Ty(EI.getContext());
         return ExtractElementInst::Create(Src,
-                                          ConstantInt::get(Type::getInt32Ty(EI.getContext()),
+                                          ConstantInt::get(Int32Ty,
                                                            SrcIdx, false));
       }
     }
@@ -239,42 +237,42 @@ Instruction *InstCombiner::visitExtractElementInst(ExtractElementInst &EI) {
 }
 
 /// CollectSingleShuffleElements - If V is a shuffle of values that ONLY returns
-/// elements from either LHS or RHS, return the shuffle mask and true. 
+/// elements from either LHS or RHS, return the shuffle mask and true.
 /// Otherwise, return false.
 static bool CollectSingleShuffleElements(Value *V, Value *LHS, Value *RHS,
                                          std::vector<Constant*> &Mask) {
   assert(V->getType() == LHS->getType() && V->getType() == RHS->getType() &&
          "Invalid CollectSingleShuffleElements");
   unsigned NumElts = cast<VectorType>(V->getType())->getNumElements();
-  
+
   if (isa<UndefValue>(V)) {
     Mask.assign(NumElts, UndefValue::get(Type::getInt32Ty(V->getContext())));
     return true;
   }
-  
+
   if (V == LHS) {
     for (unsigned i = 0; i != NumElts; ++i)
       Mask.push_back(ConstantInt::get(Type::getInt32Ty(V->getContext()), i));
     return true;
   }
-  
+
   if (V == RHS) {
     for (unsigned i = 0; i != NumElts; ++i)
       Mask.push_back(ConstantInt::get(Type::getInt32Ty(V->getContext()),
                                       i+NumElts));
     return true;
   }
-  
+
   if (InsertElementInst *IEI = dyn_cast<InsertElementInst>(V)) {
     // If this is an insert of an extract from some other vector, include it.
     Value *VecOp    = IEI->getOperand(0);
     Value *ScalarOp = IEI->getOperand(1);
     Value *IdxOp    = IEI->getOperand(2);
-    
+
     if (!isa<ConstantInt>(IdxOp))
       return false;
     unsigned InsertedIdx = cast<ConstantInt>(IdxOp)->getZExtValue();
-    
+
     if (isa<UndefValue>(ScalarOp)) {  // inserting undef into vector.
       // Okay, we can handle this if the vector we are insertinting into is
       // transitively ok.
@@ -282,13 +280,13 @@ static bool CollectSingleShuffleElements(Value *V, Value *LHS, Value *RHS,
         // If so, update the mask to reflect the inserted undef.
         Mask[InsertedIdx] = UndefValue::get(Type::getInt32Ty(V->getContext()));
         return true;
-      }      
+      }
     } else if (ExtractElementInst *EI = dyn_cast<ExtractElementInst>(ScalarOp)){
       if (isa<ConstantInt>(EI->getOperand(1)) &&
           EI->getOperand(0)->getType() == V->getType()) {
         unsigned ExtractedIdx =
         cast<ConstantInt>(EI->getOperand(1))->getZExtValue();
-        
+
         // This must be extracting from either LHS or RHS.
         if (EI->getOperand(0) == LHS || EI->getOperand(0) == RHS) {
           // Okay, we can handle this if the vector we are insertinting into is
@@ -296,15 +294,14 @@ static bool CollectSingleShuffleElements(Value *V, Value *LHS, Value *RHS,
           if (CollectSingleShuffleElements(VecOp, LHS, RHS, Mask)) {
             // If so, update the mask to reflect the inserted value.
             if (EI->getOperand(0) == LHS) {
-              Mask[InsertedIdx % NumElts] = 
+              Mask[InsertedIdx % NumElts] =
               ConstantInt::get(Type::getInt32Ty(V->getContext()),
                                ExtractedIdx);
             } else {
               assert(EI->getOperand(0) == RHS);
-              Mask[InsertedIdx % NumElts] = 
+              Mask[InsertedIdx % NumElts] =
               ConstantInt::get(Type::getInt32Ty(V->getContext()),
                                ExtractedIdx+NumElts);
-              
             }
             return true;
           }
@@ -313,7 +310,7 @@ static bool CollectSingleShuffleElements(Value *V, Value *LHS, Value *RHS,
     }
   }
   // TODO: Handle shufflevector here!
-  
+
   return false;
 }
 
@@ -322,11 +319,11 @@ static bool CollectSingleShuffleElements(Value *V, Value *LHS, Value *RHS,
 /// that computes V and the LHS value of the shuffle.
 static Value *CollectShuffleElements(Value *V, std::vector<Constant*> &Mask,
                                      Value *&RHS) {
-  assert(V->getType()->isVectorTy() && 
+  assert(V->getType()->isVectorTy() &&
          (RHS == 0 || V->getType() == RHS->getType()) &&
          "Invalid shuffle!");
   unsigned NumElts = cast<VectorType>(V->getType())->getNumElements();
-  
+
   if (isa<UndefValue>(V)) {
     Mask.assign(NumElts, UndefValue::get(Type::getInt32Ty(V->getContext())));
     return V;
@@ -338,25 +335,25 @@ static Value *CollectShuffleElements(Value *V, std::vector<Constant*> &Mask,
     Value *VecOp    = IEI->getOperand(0);
     Value *ScalarOp = IEI->getOperand(1);
     Value *IdxOp    = IEI->getOperand(2);
-    
+
     if (ExtractElementInst *EI = dyn_cast<ExtractElementInst>(ScalarOp)) {
       if (isa<ConstantInt>(EI->getOperand(1)) && isa<ConstantInt>(IdxOp) &&
           EI->getOperand(0)->getType() == V->getType()) {
         unsigned ExtractedIdx =
-        cast<ConstantInt>(EI->getOperand(1))->getZExtValue();
+          cast<ConstantInt>(EI->getOperand(1))->getZExtValue();
         unsigned InsertedIdx = cast<ConstantInt>(IdxOp)->getZExtValue();
-        
+
         // Either the extracted from or inserted into vector must be RHSVec,
         // otherwise we'd end up with a shuffle of three inputs.
         if (EI->getOperand(0) == RHS || RHS == 0) {
           RHS = EI->getOperand(0);
           Value *V = CollectShuffleElements(VecOp, Mask, RHS);
-          Mask[InsertedIdx % NumElts] = 
-          ConstantInt::get(Type::getInt32Ty(V->getContext()),
-                           NumElts+ExtractedIdx);
+          Mask[InsertedIdx % NumElts] =
+            ConstantInt::get(Type::getInt32Ty(V->getContext()),
+                             NumElts+ExtractedIdx);
           return V;
         }
-        
+
         if (VecOp == RHS) {
           Value *V = CollectShuffleElements(EI->getOperand(0), Mask, RHS);
           // Everything but the extracted element is replaced with the RHS.
@@ -367,7 +364,7 @@ static Value *CollectShuffleElements(Value *V, std::vector<Constant*> &Mask,
           }
           return V;
         }
-        
+
         // If this insertelement is a chain that comes from exactly these two
         // vectors, return the vector and the effective shuffle.
         if (CollectSingleShuffleElements(IEI, EI->getOperand(0), RHS, Mask))
@@ -376,7 +373,7 @@ static Value *CollectShuffleElements(Value *V, std::vector<Constant*> &Mask,
     }
   }
   // TODO: Handle shufflevector here!
-  
+
   // Otherwise, can't do anything fancy.  Return an identity vector.
   for (unsigned i = 0; i != NumElts; ++i)
     Mask.push_back(ConstantInt::get(Type::getInt32Ty(V->getContext()), i));
@@ -387,32 +384,32 @@ Instruction *InstCombiner::visitInsertElementInst(InsertElementInst &IE) {
   Value *VecOp    = IE.getOperand(0);
   Value *ScalarOp = IE.getOperand(1);
   Value *IdxOp    = IE.getOperand(2);
-  
+
   // Inserting an undef or into an undefined place, remove this.
   if (isa<UndefValue>(ScalarOp) || isa<UndefValue>(IdxOp))
     ReplaceInstUsesWith(IE, VecOp);
-  
-  // If the inserted element was extracted from some other vector, and if the 
+
+  // If the inserted element was extracted from some other vector, and if the
   // indexes are constant, try to turn this into a shufflevector operation.
   if (ExtractElementInst *EI = dyn_cast<ExtractElementInst>(ScalarOp)) {
     if (isa<ConstantInt>(EI->getOperand(1)) && isa<ConstantInt>(IdxOp) &&
         EI->getOperand(0)->getType() == IE.getType()) {
       unsigned NumVectorElts = IE.getType()->getNumElements();
       unsigned ExtractedIdx =
-      cast<ConstantInt>(EI->getOperand(1))->getZExtValue();
+        cast<ConstantInt>(EI->getOperand(1))->getZExtValue();
       unsigned InsertedIdx = cast<ConstantInt>(IdxOp)->getZExtValue();
-      
+
       if (ExtractedIdx >= NumVectorElts) // Out of range extract.
         return ReplaceInstUsesWith(IE, VecOp);
-      
+
       if (InsertedIdx >= NumVectorElts)  // Out of range insert.
         return ReplaceInstUsesWith(IE, UndefValue::get(IE.getType()));
-      
+
       // If we are extracting a value from a vector, then inserting it right
       // back into the same place, just use the input vector.
       if (EI->getOperand(0) == VecOp && ExtractedIdx == InsertedIdx)
-        return ReplaceInstUsesWith(IE, VecOp);      
-      
+        return ReplaceInstUsesWith(IE, VecOp);
+
       // If this insertelement isn't used by some other insertelement, turn it
       // (and any insertelements it points to), into one big shuffle.
       if (!IE.hasOneUse() || !isa<InsertElementInst>(IE.use_back())) {
@@ -421,18 +418,20 @@ Instruction *InstCombiner::visitInsertElementInst(InsertElementInst &IE) {
         Value *LHS = CollectShuffleElements(&IE, Mask, RHS);
         if (RHS == 0) RHS = UndefValue::get(LHS->getType());
         // We now have a shuffle of LHS, RHS, Mask.
-        return new ShuffleVectorInst(LHS, RHS,
-                                     ConstantVector::get(Mask));
+        return new ShuffleVectorInst(LHS, RHS, ConstantVector::get(Mask));
       }
     }
   }
-  
+
   unsigned VWidth = cast<VectorType>(VecOp->getType())->getNumElements();
   APInt UndefElts(VWidth, 0);
   APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
-  if (SimplifyDemandedVectorElts(&IE, AllOnesEltMask, UndefElts))
+  if (Value *V = SimplifyDemandedVectorElts(&IE, AllOnesEltMask, UndefElts)) {
+    if (V != &IE)
+      return ReplaceInstUsesWith(IE, V);
     return &IE;
-  
+  }
+
   return 0;
 }
 
@@ -440,27 +439,29 @@ Instruction *InstCombiner::visitInsertElementInst(InsertElementInst &IE) {
 Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
   Value *LHS = SVI.getOperand(0);
   Value *RHS = SVI.getOperand(1);
-  std::vector<unsigned> Mask = getShuffleMask(&SVI);
-  
+  std::vector<int> Mask = getShuffleMask(&SVI);
+
   bool MadeChange = false;
-  
+
   // Undefined shuffle mask -> undefined value.
   if (isa<UndefValue>(SVI.getOperand(2)))
     return ReplaceInstUsesWith(SVI, UndefValue::get(SVI.getType()));
-  
+
   unsigned VWidth = cast<VectorType>(SVI.getType())->getNumElements();
-  
+
   if (VWidth != cast<VectorType>(LHS->getType())->getNumElements())
     return 0;
-  
+
   APInt UndefElts(VWidth, 0);
   APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
-  if (SimplifyDemandedVectorElts(&SVI, AllOnesEltMask, UndefElts)) {
+  if (Value *V = SimplifyDemandedVectorElts(&SVI, AllOnesEltMask, UndefElts)) {
+    if (V != &SVI)
+      return ReplaceInstUsesWith(SVI, V);
     LHS = SVI.getOperand(0);
     RHS = SVI.getOperand(1);
     MadeChange = true;
   }
-  
+
   // Canonicalize shuffle(x    ,x,mask) -> shuffle(x, undef,mask')
   // Canonicalize shuffle(undef,x,mask) -> shuffle(x, undef,mask').
   if (LHS == RHS || isa<UndefValue>(LHS)) {
@@ -468,16 +469,16 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
       // shuffle(undef,undef,mask) -> undef.
       return ReplaceInstUsesWith(SVI, LHS);
     }
-    
+
     // Remap any references to RHS to use LHS.
     std::vector<Constant*> Elts;
     for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
-      if (Mask[i] >= 2*e)
+      if (Mask[i] < 0)
         Elts.push_back(UndefValue::get(Type::getInt32Ty(SVI.getContext())));
       else {
-        if ((Mask[i] >= e && isa<UndefValue>(RHS)) ||
-            (Mask[i] <  e && isa<UndefValue>(LHS))) {
-          Mask[i] = 2*e;     // Turn into undef.
+        if ((Mask[i] >= (int)e && isa<UndefValue>(RHS)) ||
+            (Mask[i] <  (int)e && isa<UndefValue>(LHS))) {
+          Mask[i] = -1;     // Turn into undef.
           Elts.push_back(UndefValue::get(Type::getInt32Ty(SVI.getContext())));
         } else {
           Mask[i] = Mask[i] % e;  // Force to LHS.
@@ -493,59 +494,65 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
     RHS = SVI.getOperand(1);
     MadeChange = true;
   }
-  
+
   // Analyze the shuffle, are the LHS or RHS and identity shuffles?
   bool isLHSID = true, isRHSID = true;
-  
+
   for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
-    if (Mask[i] >= e*2) continue;  // Ignore undef values.
+    if (Mask[i] < 0) continue;  // Ignore undef values.
     // Is this an identity shuffle of the LHS value?
-    isLHSID &= (Mask[i] == i);
-    
+    isLHSID &= (Mask[i] == (int)i);
+
     // Is this an identity shuffle of the RHS value?
     isRHSID &= (Mask[i]-e == i);
   }
-  
+
   // Eliminate identity shuffles.
   if (isLHSID) return ReplaceInstUsesWith(SVI, LHS);
   if (isRHSID) return ReplaceInstUsesWith(SVI, RHS);
-  
+
   // If the LHS is a shufflevector itself, see if we can combine it with this
   // one without producing an unusual shuffle.  Here we are really conservative:
   // we are absolutely afraid of producing a shuffle mask not in the input
   // program, because the code gen may not be smart enough to turn a merged
   // shuffle into two specific shuffles: it may produce worse code.  As such,
-  // we only merge two shuffles if the result is one of the two input shuffle
-  // masks.  In this case, merging the shuffles just removes one instruction,
-  // which we know is safe.  This is good for things like turning:
-  // (splat(splat)) -> splat.
+  // we only merge two shuffles if the result is either a splat or one of the
+  // two input shuffle masks.  In this case, merging the shuffles just removes
+  // one instruction, which we know is safe.  This is good for things like
+  // turning: (splat(splat)) -> splat.
   if (ShuffleVectorInst *LHSSVI = dyn_cast<ShuffleVectorInst>(LHS)) {
     if (isa<UndefValue>(RHS)) {
-      std::vector<unsigned> LHSMask = getShuffleMask(LHSSVI);
-      
+      std::vector<int> LHSMask = getShuffleMask(LHSSVI);
+
       if (LHSMask.size() == Mask.size()) {
-        std::vector<unsigned> NewMask;
-        for (unsigned i = 0, e = Mask.size(); i != e; ++i)
-          if (Mask[i] >= e)
-            NewMask.push_back(2*e);
+        std::vector<int> NewMask;
+        bool isSplat = true;
+        int SplatElt = -1; // undef
+        for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
+          int MaskElt;
+          if (Mask[i] < 0 || Mask[i] >= (int)e)
+            MaskElt = -1; // undef
           else
-            NewMask.push_back(LHSMask[Mask[i]]);
-        
+            MaskElt = LHSMask[Mask[i]];
+          // Check if this could still be a splat.
+          if (MaskElt >= 0) {
+            if (SplatElt >=0 && SplatElt != MaskElt)
+              isSplat = false;
+            SplatElt = MaskElt;
+          }
+          NewMask.push_back(MaskElt);
+        }
+
         // If the result mask is equal to the src shuffle or this
         // shuffle mask, do the replacement.
-        if (NewMask == LHSMask || NewMask == Mask) {
-          unsigned LHSInNElts =
-          cast<VectorType>(LHSSVI->getOperand(0)->getType())->
-          getNumElements();
+        if (isSplat || NewMask == LHSMask || NewMask == Mask) {
           std::vector<Constant*> Elts;
+          const Type *Int32Ty = Type::getInt32Ty(SVI.getContext());
           for (unsigned i = 0, e = NewMask.size(); i != e; ++i) {
-            if (NewMask[i] >= LHSInNElts*2) {
-              Elts.push_back(UndefValue::get(
-                                             Type::getInt32Ty(SVI.getContext())));
+            if (NewMask[i] < 0) {
+              Elts.push_back(UndefValue::get(Int32Ty));
             } else {
-              Elts.push_back(ConstantInt::get(
-                                              Type::getInt32Ty(SVI.getContext()),
-                                              NewMask[i]));
+              Elts.push_back(ConstantInt::get(Int32Ty, NewMask[i]));
             }
           }
           return new ShuffleVectorInst(LHSSVI->getOperand(0),
@@ -555,7 +562,6 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
       }
     }
   }
-  
+
   return MadeChange ? &SVI : 0;
 }
-