Revert "[InstCombine] Return instruction from replaceUse()"

This reverts commit 27c4e23310.

I think I made a mistake with the use in RemoveConditionFromAssume(),
because the instruction being changed is not the current one, but
the next assume. Revert the change for now.

llvm/include/llvm/Transforms/InstCombine/InstCombiner.h

@@ -446,10 +446,9 @@ public:
   }
 
   /// Replace use and add the previously used value to the worklist.
-  Instruction *replaceUse(Use &U, Value *NewValue) {
+  void replaceUse(Use &U, Value *NewValue) {
     Worklist.addValue(U);
     U = NewValue;
-    return cast<Instruction>(U.getUser());
   }
 
   /// Combiner aware instruction erasure.

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -2436,8 +2436,8 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
       assert(isa<AssumeInst>(Assume));
       if (isAssumeWithEmptyBundle(*cast<AssumeInst>(II)))
         return eraseInstFromFunction(CI);
-      return replaceUse(II->getOperandUse(0),
-                        ConstantInt::getTrue(II->getContext()));
+      replaceUse(II->getOperandUse(0), ConstantInt::getTrue(II->getContext()));
+      return nullptr;
     };
     // Remove an assume if it is followed by an identical assume.
     // TODO: Do we need this? Unless there are conflicting assumptions, the
@@ -2964,8 +2964,10 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     }
     // Can remove shuffle iff just shuffled elements, no repeats, undefs, or
     // other changes.
-    if (UsedIndices.all())
-      return replaceUse(II->getOperandUse(ArgIdx), V);
+    if (UsedIndices.all()) {
+      replaceUse(II->getOperandUse(ArgIdx), V);
+      return nullptr;
+    }
     break;
   }
   case Intrinsic::is_fpclass: {

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -1251,7 +1251,7 @@ static bool replaceInInstruction(Value *V, Value *Old, Value *New,
   bool Changed = false;
   for (Use &U : I->operands()) {
     if (U == Old) {
-      IC.addToWorklist(IC.replaceUse(U, New));
+      IC.replaceUse(U, New);
       Changed = true;
     } else {
       Changed |= replaceInInstruction(U, Old, New, IC, Depth + 1);