[WinEH] Rename CatchReturnInst::getParentPad, NFC

[JosephTremoulet]

Summary

Rename to getCatchSwitchParentPad, to make it more clear which ancestor
the "parent" in question is. Add a comment pointing out the key feature
that the returned pad indicates which funclet contains the successor
block.

[majnemer]

LGTM

include/llvm/IR/Instructions.h

public:
 
   BasicBlock *getSuccessor() const { return cast<BasicBlock>(Op<1>()); }
   void setSuccessor(BasicBlock *NewSucc) {
     assert(NewSucc);
     Op<1>() = NewSucc;
   }
   unsigned getNumSuccessors() const { return 1; }
 
-  Value *getParentPad() const {
+  /// Get the parentPad of this catchret's catchpad's catchswitch.
+  /// The successor block is implicitly a member of this funclet.
+  Value *getCatchSwitchParentPad() const {
     return getCatchPad()->getCatchSwitch()->getParentPad();
   }
 
   // Methods for support type inquiry through isa, cast, and dyn_cast:
   static inline bool classof(const Instruction *I) {
     return (I->getOpcode() == Instruction::CatchRet);
   }
   static inline bool classof(const Value *V) {

lib/Analysis/EHPersonalities.cpp

while (!Worklist.empty()) {
     DEBUG_WITH_TYPE("winehprepare-coloring",
                     dbgs() << "  Assigned color \'" << Color->getName()
                            << "\' to block \'" << Visiting->getName()
                            << "\'.\n");
 
     BasicBlock *SuccColor = Color;
     TerminatorInst *Terminator = Visiting->getTerminator();
     if (auto *CatchRet = dyn_cast<CatchReturnInst>(Terminator)) {
-      Value *ParentPad = CatchRet->getParentPad();
+      Value *ParentPad = CatchRet->getCatchSwitchParentPad();
       if (isa<ConstantTokenNone>(ParentPad))
         SuccColor = EntryBlock;
       else
         SuccColor = cast<Instruction>(ParentPad)->getParent();
     }
 
     for (BasicBlock *Succ : successors(Visiting))
       Worklist.push_back({Succ, SuccColor});
   }
   return BlockColors;
 }

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

if (TargetMBB != NextBlock(FuncInfo.MBB) ||
                               getControlRoot(), DAG.getBasicBlock(TargetMBB)));
     return;
   }
 
   // Figure out the funclet membership for the catchret's successor.
   // This will be used by the FuncletLayout pass to determine how to order the
   // BB's.
   // A 'catchret' returns to the outer scope's color.
-  Value *ParentPad = I.getParentPad();
+  Value *ParentPad = I.getCatchSwitchParentPad();
   const BasicBlock *SuccessorColor;
   if (isa<ConstantTokenNone>(ParentPad))
     SuccessorColor = &FuncInfo.Fn->getEntryBlock();
   else
     SuccessorColor = cast<Instruction>(ParentPad)->getParent();
   assert(SuccessorColor && "No parent funclet for catchret!");
   MachineBasicBlock *SuccessorColorMBB = FuncInfo.MBBMap[SuccessorColor];
   assert(SuccessorColorMBB && "No MBB for SuccessorColor!");

lib/CodeGen/WinEHPrepare.cpp

for (auto &Funclets : FuncletBlocks) {
     SmallVector<CatchReturnInst *, 2> FixupCatchrets;
     for (auto &BBMapping : Orig2Clone) {
       BasicBlock *OldBlock = BBMapping.first;
       BasicBlock *NewBlock = BBMapping.second;
 
       FixupCatchrets.clear();
       for (BasicBlock *Pred : predecessors(OldBlock))
         if (auto *CatchRet = dyn_cast<CatchReturnInst>(Pred->getTerminator()))
-          if (CatchRet->getParentPad() == FuncletToken)
+          if (CatchRet->getCatchSwitchParentPad() == FuncletToken)
             FixupCatchrets.push_back(CatchRet);
 
       for (CatchReturnInst *CatchRet : FixupCatchrets)
         CatchRet->setSuccessor(NewBlock);
     }
 
     auto UpdatePHIOnClonedBlock = [&](PHINode *PN, bool IsForOldBlock) {
       unsigned NumPreds = PN->getNumIncomingValues();
       for (unsigned PredIdx = 0, PredEnd = NumPreds; PredIdx != PredEnd;
            ++PredIdx) {
         BasicBlock *IncomingBlock = PN->getIncomingBlock(PredIdx);
         bool EdgeTargetsFunclet;
         if (auto *CRI =
                 dyn_cast<CatchReturnInst>(IncomingBlock->getTerminator())) {
-          EdgeTargetsFunclet = (CRI->getParentPad() == FuncletToken);
+          EdgeTargetsFunclet = (CRI->getCatchSwitchParentPad() == FuncletToken);
         } else {
           ColorVector &IncomingColors = BlockColors[IncomingBlock];
           assert(!IncomingColors.empty() && "Block not colored!");
           assert((IncomingColors.size() == 1 ||
                   llvm::all_of(IncomingColors,
                                [&](BasicBlock *Color) {
                                  return Color != FuncletPadBB;
                                })) &&