1 files changed, 28 insertions, 15 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index fbff5dd4a8cd5..0a842b4e10475 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -23,8 +23,11 @@ using namespace PatternMatch;
 // Given pattern:
 //   (x shiftopcode Q) shiftopcode K
 // we should rewrite it as
-//   x shiftopcode (Q+K)  iff (Q+K) u< bitwidth(x)
-// This is valid for any shift, but they must be identical.
+//   x shiftopcode (Q+K)  iff (Q+K) u< bitwidth(x) and
+//
+// This is valid for any shift, but they must be identical, and we must be
+// careful in case we have (zext(Q)+zext(K)) and look past extensions,
+// (Q+K) must not overflow or else (Q+K) u< bitwidth(x) is bogus.
 //
 // AnalyzeForSignBitExtraction indicates that we will only analyze whether this
 // pattern has any 2 right-shifts that sum to 1 less than original bit width.
@@ -58,6 +61,23 @@ Value *InstCombiner::reassociateShiftAmtsOfTwoSameDirectionShifts(
   if (ShAmt0->getType() != ShAmt1->getType())
     return nullptr;
 
+  // As input, we have the following pattern:
+  //   Sh0 (Sh1 X, Q), K
+  // We want to rewrite that as:
+  //   Sh x, (Q+K)  iff (Q+K) u< bitwidth(x)
+  // While we know that originally (Q+K) would not overflow
+  // (because  2 * (N-1) u<= iN -1), we have looked past extensions of
+  // shift amounts. so it may now overflow in smaller bitwidth.
+  // To ensure that does not happen, we need to ensure that the total maximal
+  // shift amount is still representable in that smaller bit width.
+  unsigned MaximalPossibleTotalShiftAmount =
+      (Sh0->getType()->getScalarSizeInBits() - 1) +
+      (Sh1->getType()->getScalarSizeInBits() - 1);
+  APInt MaximalRepresentableShiftAmount =
+      APInt::getAllOnesValue(ShAmt0->getType()->getScalarSizeInBits());
+  if (MaximalRepresentableShiftAmount.ult(MaximalPossibleTotalShiftAmount))
+    return nullptr;
+
   // We are only looking for signbit extraction if we have two right shifts.
   bool HadTwoRightShifts = match(Sh0, m_Shr(m_Value(), m_Value())) &&
                            match(Sh1, m_Shr(m_Value(), m_Value()));
@@ -388,8 +408,7 @@ Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
     // demand the sign bit (and many others) here??
     Value *Rem = Builder.CreateAnd(A, ConstantInt::get(I.getType(), *B - 1),
                                    Op1->getName());
-    I.setOperand(1, Rem);
-    return &I;
+    return replaceOperand(I, 1, Rem);
   }
 
   if (Instruction *Logic = foldShiftOfShiftedLogic(I, Builder))
@@ -593,19 +612,13 @@ static Value *getShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
   // We can always evaluate constants shifted.
   if (Constant *C = dyn_cast<Constant>(V)) {
     if (isLeftShift)
-      V = IC.Builder.CreateShl(C, NumBits);
+      return IC.Builder.CreateShl(C, NumBits);
     else
-      V = IC.Builder.CreateLShr(C, NumBits);
-    // If we got a constantexpr back, try to simplify it with TD info.
-    if (auto *C = dyn_cast<Constant>(V))
-      if (auto *FoldedC =
-              ConstantFoldConstant(C, DL, &IC.getTargetLibraryInfo()))
-        V = FoldedC;
-    return V;
+      return IC.Builder.CreateLShr(C, NumBits);
   }
 
   Instruction *I = cast<Instruction>(V);
-  IC.Worklist.Add(I);
+  IC.Worklist.push(I);
 
   switch (I->getOpcode()) {
   default: llvm_unreachable("Inconsistency with CanEvaluateShifted");
@@ -761,7 +774,7 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
           APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val);
           Constant *Mask = ConstantInt::get(I.getContext(), Bits);
           if (VectorType *VT = dyn_cast<VectorType>(X->getType()))
-            Mask = ConstantVector::getSplat(VT->getNumElements(), Mask);
+            Mask = ConstantVector::getSplat(VT->getElementCount(), Mask);
           return BinaryOperator::CreateAnd(X, Mask);
         }
 
@@ -796,7 +809,7 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
           APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val);
           Constant *Mask = ConstantInt::get(I.getContext(), Bits);
           if (VectorType *VT = dyn_cast<VectorType>(X->getType()))
-            Mask = ConstantVector::getSplat(VT->getNumElements(), Mask);
+            Mask = ConstantVector::getSplat(VT->getElementCount(), Mask);
           return BinaryOperator::CreateAnd(X, Mask);
         }