[SelectDagISEL] refactor HandlePHINodesInSuccessorBlocks NFC.

While working on this code to support outputs from callbr along indirect
branches, I kept making these changes again and again. Precommit these.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D137445

Author: nickdesaulniers

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -10811,14 +10811,12 @@ void SelectionDAGISel::LowerArguments(const Function &F) {
 void
 SelectionDAGBuilder::HandlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
-  const Instruction *TI = LLVMBB->getTerminator();
 
   SmallPtrSet<MachineBasicBlock *, 4> SuccsHandled;
 
   // Check PHI nodes in successors that expect a value to be available from this
   // block.
-  for (unsigned succ = 0, e = TI->getNumSuccessors(); succ != e; ++succ) {
-    const BasicBlock *SuccBB = TI->getSuccessor(succ);
+  for (const BasicBlock *SuccBB : successors(LLVMBB->getTerminator())) {
     if (!isa<PHINode>(SuccBB->begin())) continue;
     MachineBasicBlock *SuccMBB = FuncInfo.MBBMap[SuccBB];
 
@@ -10844,7 +10842,7 @@ SelectionDAGBuilder::HandlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
       unsigned Reg;
       const Value *PHIOp = PN.getIncomingValueForBlock(LLVMBB);
 
-      if (const Constant *C = dyn_cast<Constant>(PHIOp)) {
+      if (const auto *C = dyn_cast<Constant>(PHIOp)) {
         unsigned &RegOut = ConstantsOut[C];
         if (RegOut == 0) {
           RegOut = FuncInfo.CreateRegs(C);
@@ -10875,10 +10873,9 @@ SelectionDAGBuilder::HandlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
       // the input for this MBB.
       SmallVector<EVT, 4> ValueVTs;
       ComputeValueVTs(TLI, DAG.getDataLayout(), PN.getType(), ValueVTs);
-      for (unsigned vti = 0, vte = ValueVTs.size(); vti != vte; ++vti) {
-        EVT VT = ValueVTs[vti];
-        unsigned NumRegisters = TLI.getNumRegisters(*DAG.getContext(), VT);
-        for (unsigned i = 0, e = NumRegisters; i != e; ++i)
+      for (EVT VT : ValueVTs) {
+        const unsigned NumRegisters = TLI.getNumRegisters(*DAG.getContext(), VT);
+        for (unsigned i = 0; i != NumRegisters; ++i)
           FuncInfo.PHINodesToUpdate.push_back(
               std::make_pair(&*MBBI++, Reg + i));
         Reg += NumRegisters;