[InstCombine] Use replaceOperand() in some select transforms

To make sure the old operand is DCEd.

NFC apart from worklist order.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -2696,8 +2696,8 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
       // paths for the values (this helps GetUnderlyingObjects() for example).
       if (TrueSI->getFalseValue() == FalseVal && TrueSI->hasOneUse()) {
         Value *And = Builder.CreateAnd(CondVal, TrueSI->getCondition());
-        SI.setOperand(0, And);
-        SI.setOperand(1, TrueSI->getTrueValue());
+        replaceOperand(SI, 0, And);
+        replaceOperand(SI, 1, TrueSI->getTrueValue());
         return &SI;
       }
     }
@@ -2713,8 +2713,8 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
       // select(C0, a, select(C1, a, b)) -> select(C0|C1, a, b)
       if (FalseSI->getTrueValue() == TrueVal && FalseSI->hasOneUse()) {
         Value *Or = Builder.CreateOr(CondVal, FalseSI->getCondition());
-        SI.setOperand(0, Or);
-        SI.setOperand(2, FalseSI->getFalseValue());
+        replaceOperand(SI, 0, Or);
+        replaceOperand(SI, 2, FalseSI->getFalseValue());
         return &SI;
       }
     }
@@ -2741,14 +2741,14 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
       canMergeSelectThroughBinop(TrueBO)) {
     if (auto *TrueBOSI = dyn_cast<SelectInst>(TrueBO->getOperand(0))) {
       if (TrueBOSI->getCondition() == CondVal) {
-        TrueBO->setOperand(0, TrueBOSI->getTrueValue());
+        replaceOperand(*TrueBO, 0, TrueBOSI->getTrueValue());
         Worklist.push(TrueBO);
         return &SI;
       }
     }
     if (auto *TrueBOSI = dyn_cast<SelectInst>(TrueBO->getOperand(1))) {
       if (TrueBOSI->getCondition() == CondVal) {
-        TrueBO->setOperand(1, TrueBOSI->getTrueValue());
+        replaceOperand(*TrueBO, 1, TrueBOSI->getTrueValue());
         Worklist.push(TrueBO);
         return &SI;
       }
@@ -2761,14 +2761,14 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
       canMergeSelectThroughBinop(FalseBO)) {
     if (auto *FalseBOSI = dyn_cast<SelectInst>(FalseBO->getOperand(0))) {
       if (FalseBOSI->getCondition() == CondVal) {
-        FalseBO->setOperand(0, FalseBOSI->getFalseValue());
+        replaceOperand(*FalseBO, 0, FalseBOSI->getFalseValue());
         Worklist.push(FalseBO);
         return &SI;
       }
     }
     if (auto *FalseBOSI = dyn_cast<SelectInst>(FalseBO->getOperand(1))) {
       if (FalseBOSI->getCondition() == CondVal) {
-        FalseBO->setOperand(1, FalseBOSI->getFalseValue());
+        replaceOperand(*FalseBO, 1, FalseBOSI->getFalseValue());
         Worklist.push(FalseBO);
         return &SI;
       }