1 files changed, 45 insertions, 50 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 9c890748e5ab..f604c9dc32ca 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -1390,20 +1390,6 @@ static Value *evaluateInDifferentElementOrder(Value *V, ArrayRef<int> Mask) {
   llvm_unreachable("failed to reorder elements of vector instruction!");
 }
 
-static void recognizeIdentityMask(const SmallVectorImpl<int> &Mask,
-                                  bool &isLHSID, bool &isRHSID) {
-  isLHSID = isRHSID = true;
-
-  for (unsigned i = 0, e = Mask.size(); i != e; ++i) {
-    if (Mask[i] < 0) continue;  // Ignore undef values.
-    // Is this an identity shuffle of the LHS value?
-    isLHSID &= (Mask[i] == (int)i);
-
-    // Is this an identity shuffle of the RHS value?
-    isRHSID &= (Mask[i]-e == i);
-  }
-}
-
 // Returns true if the shuffle is extracting a contiguous range of values from
 // LHS, for example:
 //                 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
@@ -1560,9 +1546,11 @@ static Instruction *foldSelectShuffle(ShuffleVectorInst &Shuf,
   if (!Shuf.isSelect())
     return nullptr;
 
-  // Canonicalize to choose from operand 0 first.
+  // Canonicalize to choose from operand 0 first unless operand 1 is undefined.
+  // Commuting undef to operand 0 conflicts with another canonicalization.
   unsigned NumElts = Shuf.getType()->getVectorNumElements();
-  if (Shuf.getMaskValue(0) >= (int)NumElts) {
+  if (!isa<UndefValue>(Shuf.getOperand(1)) &&
+      Shuf.getMaskValue(0) >= (int)NumElts) {
     // TODO: Can we assert that both operands of a shuffle-select are not undef
     // (otherwise, it would have been folded by instsimplify?
     Shuf.commute();
@@ -1753,7 +1741,8 @@ static Instruction *foldIdentityExtractShuffle(ShuffleVectorInst &Shuf) {
   return new ShuffleVectorInst(X, Y, ConstantVector::get(NewMask));
 }
 
-/// Try to replace a shuffle with an insertelement.
+/// Try to replace a shuffle with an insertelement or try to replace a shuffle
+/// operand with the operand of an insertelement.
 static Instruction *foldShuffleWithInsert(ShuffleVectorInst &Shuf) {
   Value *V0 = Shuf.getOperand(0), *V1 = Shuf.getOperand(1);
   SmallVector<int, 16> Mask = Shuf.getShuffleMask();
@@ -1765,6 +1754,31 @@ static Instruction *foldShuffleWithInsert(ShuffleVectorInst &Shuf) {
   if (NumElts != (int)(V0->getType()->getVectorNumElements()))
     return nullptr;
 
+  // This is a specialization of a fold in SimplifyDemandedVectorElts. We may
+  // not be able to handle it there if the insertelement has >1 use.
+  // If the shuffle has an insertelement operand but does not choose the
+  // inserted scalar element from that value, then we can replace that shuffle
+  // operand with the source vector of the insertelement.
+  Value *X;
+  uint64_t IdxC;
+  if (match(V0, m_InsertElement(m_Value(X), m_Value(), m_ConstantInt(IdxC)))) {
+    // shuf (inselt X, ?, IdxC), ?, Mask --> shuf X, ?, Mask
+    if (none_of(Mask, [IdxC](int MaskElt) { return MaskElt == (int)IdxC; })) {
+      Shuf.setOperand(0, X);
+      return &Shuf;
+    }
+  }
+  if (match(V1, m_InsertElement(m_Value(X), m_Value(), m_ConstantInt(IdxC)))) {
+    // Offset the index constant by the vector width because we are checking for
+    // accesses to the 2nd vector input of the shuffle.
+    IdxC += NumElts;
+    // shuf ?, (inselt X, ?, IdxC), Mask --> shuf ?, X, Mask
+    if (none_of(Mask, [IdxC](int MaskElt) { return MaskElt == (int)IdxC; })) {
+      Shuf.setOperand(1, X);
+      return &Shuf;
+    }
+  }
+
   // shuffle (insert ?, Scalar, IndexC), V1, Mask --> insert V1, Scalar, IndexC'
   auto isShufflingScalarIntoOp1 = [&](Value *&Scalar, ConstantInt *&IndexC) {
     // We need an insertelement with a constant index.
@@ -1891,29 +1905,21 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
           LHS, RHS, SVI.getMask(), SVI.getType(), SQ.getWithInstruction(&SVI)))
     return replaceInstUsesWith(SVI, V);
 
-  // Canonicalize shuffle(x    ,x,mask) -> shuffle(x, undef,mask')
-  // Canonicalize shuffle(undef,x,mask) -> shuffle(x, undef,mask').
+  // shuffle x, x, mask --> shuffle x, undef, mask'
   unsigned VWidth = SVI.getType()->getVectorNumElements();
   unsigned LHSWidth = LHS->getType()->getVectorNumElements();
   SmallVector<int, 16> Mask = SVI.getShuffleMask();
   Type *Int32Ty = Type::getInt32Ty(SVI.getContext());
-  if (LHS == RHS || isa<UndefValue>(LHS)) {
+  if (LHS == RHS) {
+    assert(!isa<UndefValue>(RHS) && "Shuffle with 2 undef ops not simplified?");
     // Remap any references to RHS to use LHS.
     SmallVector<Constant*, 16> Elts;
-    for (unsigned i = 0, e = LHSWidth; i != VWidth; ++i) {
-      if (Mask[i] < 0) {
-        Elts.push_back(UndefValue::get(Int32Ty));
-        continue;
-      }
-
-      if ((Mask[i] >= (int)e && isa<UndefValue>(RHS)) ||
-          (Mask[i] <  (int)e && isa<UndefValue>(LHS))) {
-        Mask[i] = -1;     // Turn into undef.
+    for (unsigned i = 0; i != VWidth; ++i) {
+      // Propagate undef elements or force mask to LHS.
+      if (Mask[i] < 0)
         Elts.push_back(UndefValue::get(Int32Ty));
-      } else {
-        Mask[i] = Mask[i] % e;  // Force to LHS.
-        Elts.push_back(ConstantInt::get(Int32Ty, Mask[i]));
-      }
+      else
+        Elts.push_back(ConstantInt::get(Int32Ty, Mask[i] % LHSWidth));
     }
     SVI.setOperand(0, SVI.getOperand(1));
     SVI.setOperand(1, UndefValue::get(RHS->getType()));
@@ -1921,6 +1927,12 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
     return &SVI;
   }
 
+  // shuffle undef, x, mask --> shuffle x, undef, mask'
+  if (isa<UndefValue>(LHS)) {
+    SVI.commute();
+    return &SVI;
+  }
+
   if (Instruction *I = canonicalizeInsertSplat(SVI, Builder))
     return I;
 
@@ -1948,16 +1960,6 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
   if (Instruction *I = foldIdentityPaddedShuffles(SVI))
     return I;
 
-  if (VWidth == LHSWidth) {
-    // Analyze the shuffle, are the LHS or RHS and identity shuffles?
-    bool isLHSID, isRHSID;
-    recognizeIdentityMask(Mask, isLHSID, isRHSID);
-
-    // Eliminate identity shuffles.
-    if (isLHSID) return replaceInstUsesWith(SVI, LHS);
-    if (isRHSID) return replaceInstUsesWith(SVI, RHS);
-  }
-
   if (isa<UndefValue>(RHS) && canEvaluateShuffled(LHS, Mask)) {
     Value *V = evaluateInDifferentElementOrder(LHS, Mask);
     return replaceInstUsesWith(SVI, V);
@@ -2235,12 +2237,5 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
     return new ShuffleVectorInst(newLHS, newRHS, ConstantVector::get(Elts));
   }
 
-  // If the result mask is an identity, replace uses of this instruction with
-  // corresponding argument.
-  bool isLHSID, isRHSID;
-  recognizeIdentityMask(newMask, isLHSID, isRHSID);
-  if (isLHSID && VWidth == LHSOp0Width) return replaceInstUsesWith(SVI, newLHS);
-  if (isRHSID && VWidth == RHSOp0Width) return replaceInstUsesWith(SVI, newRHS);
-
   return MadeChange ? &SVI : nullptr;
 }