document the new arguments

Author: BeMg

llvm/include/llvm/CodeGen/TargetInstrInfo.h

@@ -1018,6 +1018,11 @@ class TargetInstrInfo : public MCInstrInfo {
   /// The source and destination registers may overlap, which may require a
   /// careful implementation when multiple copy instructions are required for
   /// large registers. See for example the ARM target.
+  ///
+  /// If RenamableDest is true, the copy instruction's destination operand is
+  /// marked renamable.
+  /// If RenamableSrc is true, the copy instruction's source operand is
+  /// marked renamable.
   virtual void copyPhysReg(MachineBasicBlock &MBB,
                            MachineBasicBlock::iterator MI, const DebugLoc &DL,
                            MCRegister DestReg, MCRegister SrcReg, bool KillSrc,