Fix the value_type of defusechain_iterator to match its operator*()

defusechain_iterator has an operator*() and operator->() that return
references to a MachineOperand, but its "reference" and "pointer"
typedefs are set as if the iterator returns a MachineInstr reference.
This causes compilation errors when defusechain_iterator is used in
generic code that uses the "reference" and "pointer" typedefs.
This patch fixes this by updating the typedefs to use MachineOperand
instead of MachineInstr.

Reviewed By: mkitzan

Differential Revision: https://reviews.llvm.org/D97522

Author: nlguillemot

llvm/include/llvm/CodeGen/MachineRegisterInfo.h

@@ -968,10 +968,10 @@ class MachineRegisterInfo {
   /// returns defs.  If neither are true then you are silly and it always
   /// returns end().  If SkipDebug is true it skips uses marked Debug
   /// when incrementing.
-  template<bool ReturnUses, bool ReturnDefs, bool SkipDebug,
-           bool ByOperand, bool ByInstr, bool ByBundle>
-  class defusechain_iterator
-    : public std::iterator<std::forward_iterator_tag, MachineInstr, ptrdiff_t> {
+  template <bool ReturnUses, bool ReturnDefs, bool SkipDebug, bool ByOperand,
+            bool ByInstr, bool ByBundle>
+  class defusechain_iterator : public std::iterator<std::forward_iterator_tag,
+                                                    MachineOperand, ptrdiff_t> {
     friend class MachineRegisterInfo;
 
     MachineOperand *Op = nullptr;
@@ -1008,10 +1008,10 @@ class MachineRegisterInfo {
     }
 
   public:
-    using reference = std::iterator<std::forward_iterator_tag,
-                                    MachineInstr, ptrdiff_t>::reference;
-    using pointer = std::iterator<std::forward_iterator_tag,
-                                  MachineInstr, ptrdiff_t>::pointer;
+    using reference = std::iterator<std::forward_iterator_tag, MachineOperand,
+                                    ptrdiff_t>::reference;
+    using pointer = std::iterator<std::forward_iterator_tag, MachineOperand,
+                                  ptrdiff_t>::pointer;
 
     defusechain_iterator() = default;