Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1380,8 +1380,9 @@
   // (add (and A, B) (or A, B)) --> (add A, B)
   if (match(&I, m_c_BinOp(m_Or(m_Value(A), m_Value(B)),
                           m_c_And(m_Deferred(A), m_Deferred(B))))) {
-    I.setOperand(0, A);
-    I.setOperand(1, B);
+    // Replacing operands in-place to preserve nuw/nsw flags.
+    replaceOperand(I, 0, A);
+    replaceOperand(I, 1, B);
     return &I;
   }
 
Index: llvm/lib/Transforms/InstCombine/InstCombineAtomicRMW.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAtomicRMW.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAtomicRMW.cpp
@@ -138,13 +138,11 @@
   if (RMWI.getType()->isIntegerTy() &&
       RMWI.getOperation() != AtomicRMWInst::Or) {
     RMWI.setOperation(AtomicRMWInst::Or);
-    RMWI.setOperand(1, ConstantInt::get(RMWI.getType(), 0));
-    return &RMWI;
+    return replaceOperand(RMWI, 1, ConstantInt::get(RMWI.getType(), 0));
   } else if (RMWI.getType()->isFloatingPointTy() &&
              RMWI.getOperation() != AtomicRMWInst::FAdd) {
     RMWI.setOperation(AtomicRMWInst::FAdd);
-    RMWI.setOperand(1, ConstantFP::getNegativeZero(RMWI.getType()));
-    return &RMWI;
+    return replaceOperand(RMWI, 1, ConstantFP::getNegativeZero(RMWI.getType()));
   }
 
   // Check if the required ordering is compatible with an atomic load.
Index: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -6023,14 +6023,11 @@
   // If we're just checking for a NaN (ORD/UNO) and have a non-NaN operand,
   // then canonicalize the operand to 0.0.
   if (Pred == CmpInst::FCMP_ORD || Pred == CmpInst::FCMP_UNO) {
-    if (!match(Op0, m_PosZeroFP()) && isKnownNeverNaN(Op0, &TLI)) {
-      I.setOperand(0, ConstantFP::getNullValue(OpType));
-      return &I;
-    }
-    if (!match(Op1, m_PosZeroFP()) && isKnownNeverNaN(Op1, &TLI)) {
-      I.setOperand(1, ConstantFP::getNullValue(OpType));
-      return &I;
-    }
+    if (!match(Op0, m_PosZeroFP()) && isKnownNeverNaN(Op0, &TLI))
+      return replaceOperand(I, 0, ConstantFP::getNullValue(OpType));
+
+    if (!match(Op1, m_PosZeroFP()) && isKnownNeverNaN(Op1, &TLI))
+      return replaceOperand(I, 1, ConstantFP::getNullValue(OpType));
   }
 
   // fcmp pred (fneg X), (fneg Y) -> fcmp swap(pred) X, Y
@@ -6055,10 +6052,8 @@
 
   // The sign of 0.0 is ignored by fcmp, so canonicalize to +0.0:
   // fcmp Pred X, -0.0 --> fcmp Pred X, 0.0
-  if (match(Op1, m_AnyZeroFP()) && !match(Op1, m_PosZeroFP())) {
-    I.setOperand(1, ConstantFP::getNullValue(OpType));
-    return &I;
-  }
+  if (match(Op1, m_AnyZeroFP()) && !match(Op1, m_PosZeroFP()))
+    return replaceOperand(I, 1, ConstantFP::getNullValue(OpType));
 
   // Handle fcmp with instruction LHS and constant RHS.
   Instruction *LHSI;
Index: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -56,7 +56,8 @@
 /// Replace a select operand based on an equality comparison with the identity
 /// constant of a binop.
 static Instruction *foldSelectBinOpIdentity(SelectInst &Sel,
-                                            const TargetLibraryInfo &TLI) {
+                                            const TargetLibraryInfo &TLI,
+                                            InstCombiner &IC) {
   // The select condition must be an equality compare with a constant operand.
   Value *X;
   Constant *C;
@@ -107,8 +108,7 @@
   // S = { select (cmp eq X, C), BO, ? } or { select (cmp ne X, C), ?, BO }
   // =>
   // S = { select (cmp eq X, C),  Y, ? } or { select (cmp ne X, C), ?,  Y }
-  Sel.setOperand(IsEq ? 1 : 2, Y);
-  return &Sel;
+  return IC.replaceOperand(Sel, IsEq ? 1 : 2, Y);
 }
 
 /// This folds:
@@ -997,7 +997,7 @@
 /// constant operand of the select.
 static Instruction *
 canonicalizeMinMaxWithConstant(SelectInst &Sel, ICmpInst &Cmp,
-                               InstCombiner::BuilderTy &Builder) {
+                               InstCombiner &IC) {
   if (!Cmp.hasOneUse() || !isa<Constant>(Cmp.getOperand(1)))
     return nullptr;
 
@@ -1014,7 +1014,7 @@
     return nullptr;
 
   // Create the canonical compare and plug it into the select.
-  Sel.setCondition(Builder.CreateICmp(CanonicalPred, LHS, RHS));
+  IC.replaceOperand(Sel, 0, IC.Builder.CreateICmp(CanonicalPred, LHS, RHS));
 
   // If the select operands did not change, we're done.
   if (Sel.getTrueValue() == LHS && Sel.getFalseValue() == RHS)
@@ -1322,7 +1322,7 @@
 // and swap the hands of select.
 static Instruction *
 tryToReuseConstantFromSelectInComparison(SelectInst &Sel, ICmpInst &Cmp,
-                                         InstCombiner::BuilderTy &Builder) {
+                                         InstCombiner &IC) {
   ICmpInst::Predicate Pred;
   Value *X;
   Constant *C0;
@@ -1374,13 +1374,13 @@
     return nullptr;
 
   // It matched! Lets insert the new comparison just before select.
-  InstCombiner::BuilderTy::InsertPointGuard Guard(Builder);
-  Builder.SetInsertPoint(&Sel);
+  InstCombiner::BuilderTy::InsertPointGuard Guard(IC.Builder);
+  IC.Builder.SetInsertPoint(&Sel);
 
   Pred = ICmpInst::getSwappedPredicate(Pred); // Yes, swapped.
-  Value *NewCmp = Builder.CreateICmp(Pred, X, FlippedStrictness->second,
-                                     Cmp.getName() + ".inv");
-  Sel.setCondition(NewCmp);
+  Value *NewCmp = IC.Builder.CreateICmp(Pred, X, FlippedStrictness->second,
+                                        Cmp.getName() + ".inv");
+  IC.replaceOperand(Sel, 0, NewCmp);
   Sel.swapValues();
   Sel.swapProfMetadata();
 
@@ -1393,7 +1393,7 @@
   if (Value *V = foldSelectValueEquivalence(SI, *ICI, SQ))
     return replaceInstUsesWith(SI, V);
 
-  if (Instruction *NewSel = canonicalizeMinMaxWithConstant(SI, *ICI, Builder))
+  if (Instruction *NewSel = canonicalizeMinMaxWithConstant(SI, *ICI, *this))
     return NewSel;
 
   if (Instruction *NewAbs = canonicalizeAbsNabs(SI, *ICI, Builder))
@@ -1403,7 +1403,7 @@
     return NewAbs;
 
   if (Instruction *NewSel =
-          tryToReuseConstantFromSelectInComparison(SI, *ICI, Builder))
+          tryToReuseConstantFromSelectInComparison(SI, *ICI, *this))
     return NewSel;
 
   bool Changed = adjustMinMax(SI, *ICI);
@@ -1966,7 +1966,7 @@
 /// other operations in IR and having all operands of a select be vector types
 /// is likely better for vector codegen.
 static Instruction *canonicalizeScalarSelectOfVecs(
-    SelectInst &Sel, InstCombiner::BuilderTy &Builder) {
+    SelectInst &Sel, InstCombiner &IC) {
   Type *Ty = Sel.getType();
   if (!Ty->isVectorTy())
     return nullptr;
@@ -1980,9 +1980,7 @@
   // Splatting the extracted condition reduces code (we could directly create a
   // splat shuffle of the source vector to eliminate the intermediate step).
   unsigned NumElts = Ty->getVectorNumElements();
-  Value *SplatCond = Builder.CreateVectorSplat(NumElts, Cond);
-  Sel.setCondition(SplatCond);
-  return &Sel;
+  return IC.replaceOperand(Sel, 0, IC.Builder.CreateVectorSplat(NumElts, Cond));
 }
 
 /// Reuse bitcasted operands between a compare and select:
@@ -2388,7 +2386,7 @@
   if (Instruction *I = canonicalizeSelectToShuffle(SI))
     return I;
 
-  if (Instruction *I = canonicalizeScalarSelectOfVecs(SI, Builder))
+  if (Instruction *I = canonicalizeScalarSelectOfVecs(SI, *this))
     return I;
 
   // Canonicalize a one-use integer compare with a non-canonical predicate by
@@ -2691,8 +2689,7 @@
       if (TrueSI->getCondition() == CondVal) {
         if (SI.getTrueValue() == TrueSI->getTrueValue())
           return nullptr;
-        SI.setOperand(1, TrueSI->getTrueValue());
-        return &SI;
+        return replaceOperand(SI, 1, TrueSI->getTrueValue());
       }
       // select(C0, select(C1, a, b), b) -> select(C0&C1, a, b)
       // We choose this as normal form to enable folding on the And and shortening
@@ -2711,8 +2708,7 @@
       if (FalseSI->getCondition() == CondVal) {
         if (SI.getFalseValue() == FalseSI->getFalseValue())
           return nullptr;
-        SI.setOperand(2, FalseSI->getFalseValue());
-        return &SI;
+        return replaceOperand(SI, 2, FalseSI->getFalseValue());
       }
       // select(C0, a, select(C1, a, b)) -> select(C0|C1, a, b)
       if (FalseSI->getTrueValue() == TrueVal && FalseSI->hasOneUse()) {
@@ -2781,7 +2777,7 @@
 
   Value *NotCond;
   if (match(CondVal, m_Not(m_Value(NotCond)))) {
-    SI.setOperand(0, NotCond);
+    replaceOperand(SI, 0, NotCond);
     SI.swapValues();
     SI.swapProfMetadata();
     return &SI;
@@ -2819,7 +2815,7 @@
   if (Instruction *Select = foldSelectCmpXchg(SI))
     return Select;
 
-  if (Instruction *Select = foldSelectBinOpIdentity(SI, TLI))
+  if (Instruction *Select = foldSelectBinOpIdentity(SI, TLI, *this))
     return Select;
 
   if (Instruction *Rot = foldSelectRotate(SI))
Index: llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -388,8 +388,7 @@
     // 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))
Index: llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -1739,7 +1739,8 @@
 
 /// 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) {
+static Instruction *foldShuffleWithInsert(ShuffleVectorInst &Shuf,
+                                          InstCombiner &IC) {
   Value *V0 = Shuf.getOperand(0), *V1 = Shuf.getOperand(1);
   SmallVector<int, 16> Mask = Shuf.getShuffleMask();
 
@@ -1759,20 +1760,16 @@
   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 (none_of(Mask, [IdxC](int MaskElt) { return MaskElt == (int)IdxC; }))
+      return IC.replaceOperand(Shuf, 0, X);
   }
   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;
-    }
+    if (none_of(Mask, [IdxC](int MaskElt) { return MaskElt == (int)IdxC; }))
+      return IC.replaceOperand(Shuf, 1, X);
   }
 
   // shuffle (insert ?, Scalar, IndexC), V1, Mask --> insert V1, Scalar, IndexC'
@@ -1949,7 +1946,7 @@
 
   // These transforms have the potential to lose undef knowledge, so they are
   // intentionally placed after SimplifyDemandedVectorElts().
-  if (Instruction *I = foldShuffleWithInsert(SVI))
+  if (Instruction *I = foldShuffleWithInsert(SVI, *this))
     return I;
   if (Instruction *I = foldIdentityPaddedShuffles(SVI))
     return I;