Revert r358268 "[DebugInfo] DW_OP_deref_size in PrologEpilogInserter."

It causes clang to crash while building Chromium. See https://crbug.com/952230
for reproducer.

> The PrologEpilogInserter need to insert a DW_OP_deref_size before
> prepending a memory location expression to an already implicit
> expression to avoid having the existing expression act on the memory
> address instead of the value behind it.
>
> The reason for using DW_OP_deref_size and not plain DW_OP_deref is that
> big-endian targets need to read the right size as simply truncating a
> larger read would yield the wrong result (LSB bytes are not at the lower
> address).
>
> Differential Revision: https://reviews.llvm.org/D59687

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358281 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/DebugInfoMetadata.cpp

@@ -833,7 +833,6 @@ unsigned DIExpression::ExprOperand::getSize() const {
   case dwarf::DW_OP_LLVM_fragment:
     return 3;
   case dwarf::DW_OP_constu:
-  case dwarf::DW_OP_deref_size:
   case dwarf::DW_OP_plus_uconst:
     return 2;
   default:
@@ -890,7 +889,6 @@ bool DIExpression::isValid() const {
     case dwarf::DW_OP_shr:
     case dwarf::DW_OP_shra:
     case dwarf::DW_OP_deref:
-    case dwarf::DW_OP_deref_size:
     case dwarf::DW_OP_xderef:
     case dwarf::DW_OP_lit0:
     case dwarf::DW_OP_not:
@@ -901,19 +899,6 @@ bool DIExpression::isValid() const {
   return true;
 }
 
-bool DIExpression::isImplicit() const {
-  unsigned N = getNumElements();
-  if (isValid() && N > 0) {
-    switch (getElement(N-1)) {
-      case dwarf::DW_OP_stack_value: return true;
-      case dwarf::DW_OP_LLVM_fragment:
-        return N > 1 && getElement(N-2) == dwarf::DW_OP_stack_value;
-      default: break;
-    }
-  }
-  return false;
-}
-
 Optional<DIExpression::FragmentInfo>
 DIExpression::getFragmentInfo(expr_op_iterator Start, expr_op_iterator End) {
   for (auto I = Start; I != End; ++I)