[InstUtils] Look through move as copy/cast inst.

Add move_value to the list of instructions through which
getSingleValueCopyOrCast looks.

Author: nate-chandler

include/swift/SIL/InstructionUtils.h

@@ -88,8 +88,8 @@ SILValue stripBorrow(SILValue V);
 //===----------------------------------------------------------------------===//
 
 /// Return a non-null SingleValueInstruction if the given instruction merely
-/// copies the value of its first operand, possibly changing its type or
-/// ownership state, but otherwise having no effect.
+/// copies or moves the value of its first operand, possibly changing its type
+/// or ownership state, but otherwise having no effect.
 ///
 /// The returned instruction may have additional "incidental" operands;
 /// mark_dependence for example.

lib/SIL/Utils/InstructionUtils.cpp

@@ -256,6 +256,7 @@ SingleValueInstruction *swift::getSingleValueCopyOrCast(SILInstruction *I) {
   case SILInstructionKind::BeginBorrowInst:
   case SILInstructionKind::BeginAccessInst:
   case SILInstructionKind::MarkDependenceInst:
+  case SILInstructionKind::MoveValueInst:
     return cast<SingleValueInstruction>(I);
   }
 }