CodeGen: Use MachineInstr& in TargetLowering, NFC

This is a mechanical change to make TargetLowering API take MachineInstr&
(instead of MachineInstr*), since the argument is expected to be a valid
MachineInstr.  In one case, changed a parameter from MachineInstr* to
MachineBasicBlock::iterator, since it was used as an insertion point.

As a side effect, this removes a bunch of MachineInstr* to
MachineBasicBlock::iterator implicit conversions, a necessary step
toward fixing PR26753.

llvm-svn: 274287
diff --git a/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp b/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp
index 3262aff..6aeca59 100644
--- a/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp
@@ -2812,18 +2812,17 @@
   return DAG.getNode(HexagonISD::AT_PCREL, SDLoc(Table), VT, T);
 }
 
-MachineBasicBlock *
-HexagonTargetLowering::EmitInstrWithCustomInserter(MachineInstr *MI,
-                                                   MachineBasicBlock *BB)
-      const {
-  switch (MI->getOpcode()) {
-    case Hexagon::ALLOCA: {
-      MachineFunction *MF = BB->getParent();
-      auto *FuncInfo = MF->getInfo<HexagonMachineFunctionInfo>();
-      FuncInfo->addAllocaAdjustInst(MI);
-      return BB;
-    }
-    default: llvm_unreachable("Unexpected instr type to insert");
+MachineBasicBlock *HexagonTargetLowering::EmitInstrWithCustomInserter(
+    MachineInstr &MI, MachineBasicBlock *BB) const {
+  switch (MI.getOpcode()) {
+  case Hexagon::ALLOCA: {
+    MachineFunction *MF = BB->getParent();
+    auto *FuncInfo = MF->getInfo<HexagonMachineFunctionInfo>();
+    FuncInfo->addAllocaAdjustInst(&MI);
+    return BB;
+  }
+  default:
+    llvm_unreachable("Unexpected instr type to insert");
   } // switch
 }