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diff --git a/lib/AST/Interp/Pointer.h b/lib/AST/Interp/Pointer.h
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+//===--- Pointer.h - Types for the constexpr VM -----------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Defines the classes responsible for pointer tracking.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_INTERP_POINTER_H
+#define LLVM_CLANG_AST_INTERP_POINTER_H
+
+#include "Block.h"
+#include "Descriptor.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/DeclCXX.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/ComparisonCategories.h"
+#include "llvm/ADT/PointerUnion.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace clang {
+namespace interp {
+class Block;
+class DeadBlock;
+class Context;
+class InterpState;
+class Pointer;
+class Function;
+enum PrimType : unsigned;
+
+/// A pointer to a memory block, live or dead.
+///
+/// This object can be allocated into interpreter stack frames. If pointing to
+/// a live block, it is a link in the chain of pointers pointing to the block.
+class Pointer {
+private:
+  static constexpr unsigned PastEndMark = (unsigned)-1;
+  static constexpr unsigned RootPtrMark = (unsigned)-1;
+
+public:
+  Pointer() {}
+  Pointer(Block *B);
+  Pointer(const Pointer &P);
+  Pointer(Pointer &&P);
+  ~Pointer();
+
+  void operator=(const Pointer &P);
+  void operator=(Pointer &&P);
+
+  /// Converts the pointer to an APValue.
+  APValue toAPValue() const;
+
+  /// Offsets a pointer inside an array.
+  Pointer atIndex(unsigned Idx) const {
+    if (Base == RootPtrMark)
+      return Pointer(Pointee, RootPtrMark, getDeclDesc()->getSize());
+    unsigned Off = Idx * elemSize();
+    if (getFieldDesc()->ElemDesc)
+      Off += sizeof(InlineDescriptor);
+    else
+      Off += sizeof(InitMap *);
+    return Pointer(Pointee, Base, Base + Off);
+  }
+
+  /// Creates a pointer to a field.
+  Pointer atField(unsigned Off) const {
+    unsigned Field = Offset + Off;
+    return Pointer(Pointee, Field, Field);
+  }
+
+  /// Restricts the scope of an array element pointer.
+  Pointer narrow() const {
+    // Null pointers cannot be narrowed.
+    if (isZero() || isUnknownSizeArray())
+      return *this;
+
+    // Pointer to an array of base types - enter block.
+    if (Base == RootPtrMark)
+      return Pointer(Pointee, 0, Offset == 0 ? Offset : PastEndMark);
+
+    // Pointer is one past end - magic offset marks that.
+    if (isOnePastEnd())
+      return Pointer(Pointee, Base, PastEndMark);
+
+    // Primitive arrays are a bit special since they do not have inline
+    // descriptors. If Offset != Base, then the pointer already points to
+    // an element and there is nothing to do. Otherwise, the pointer is
+    // adjusted to the first element of the array.
+    if (inPrimitiveArray()) {
+      if (Offset != Base)
+        return *this;
+      return Pointer(Pointee, Base, Offset + sizeof(InitMap *));
+    }
+
+    // Pointer is to a field or array element - enter it.
+    if (Offset != Base)
+      return Pointer(Pointee, Offset, Offset);
+
+    // Enter the first element of an array.
+    if (!getFieldDesc()->isArray())
+      return *this;
+
+    const unsigned NewBase = Base + sizeof(InlineDescriptor);
+    return Pointer(Pointee, NewBase, NewBase);
+  }
+
+  /// Expands a pointer to the containing array, undoing narrowing.
+  Pointer expand() const {
+    if (isElementPastEnd()) {
+      // Revert to an outer one-past-end pointer.
+      unsigned Adjust;
+      if (inPrimitiveArray())
+        Adjust = sizeof(InitMap *);
+      else
+        Adjust = sizeof(InlineDescriptor);
+      return Pointer(Pointee, Base, Base + getSize() + Adjust);
+    }
+
+    // Do not step out of array elements.
+    if (Base != Offset)
+      return *this;
+
+    // If at base, point to an array of base types.
+    if (Base == 0)
+      return Pointer(Pointee, RootPtrMark, 0);
+
+    // Step into the containing array, if inside one.
+    unsigned Next = Base - getInlineDesc()->Offset;
+    Descriptor *Desc = Next == 0 ? getDeclDesc() : getDescriptor(Next)->Desc;
+    if (!Desc->IsArray)
+      return *this;
+    return Pointer(Pointee, Next, Offset);
+  }
+
+  /// Checks if the pointer is null.
+  bool isZero() const { return Pointee == nullptr; }
+  /// Checks if the pointer is live.
+  bool isLive() const { return Pointee && !Pointee->IsDead; }
+  /// Checks if the item is a field in an object.
+  bool isField() const { return Base != 0 && Base != RootPtrMark; }
+
+  /// Accessor for information about the declaration site.
+  Descriptor *getDeclDesc() const { return Pointee->Desc; }
+  SourceLocation getDeclLoc() const { return getDeclDesc()->getLocation(); }
+
+  /// Returns a pointer to the object of which this pointer is a field.
+  Pointer getBase() const {
+    if (Base == RootPtrMark) {
+      assert(Offset == PastEndMark && "cannot get base of a block");
+      return Pointer(Pointee, Base, 0);
+    }
+    assert(Offset == Base && "not an inner field");
+    unsigned NewBase = Base - getInlineDesc()->Offset;
+    return Pointer(Pointee, NewBase, NewBase);
+  }
+  /// Returns the parent array.
+  Pointer getArray() const {
+    if (Base == RootPtrMark) {
+      assert(Offset != 0 && Offset != PastEndMark && "not an array element");
+      return Pointer(Pointee, Base, 0);
+    }
+    assert(Offset != Base && "not an array element");
+    return Pointer(Pointee, Base, Base);
+  }
+
+  /// Accessors for information about the innermost field.
+  Descriptor *getFieldDesc() const {
+    if (Base == 0 || Base == RootPtrMark)
+      return getDeclDesc();
+    return getInlineDesc()->Desc;
+  }
+
+  /// Returns the type of the innermost field.
+  QualType getType() const { return getFieldDesc()->getType(); }
+
+  /// Returns the element size of the innermost field.
+  size_t elemSize() const {
+    if (Base == RootPtrMark)
+      return getDeclDesc()->getSize();
+    return getFieldDesc()->getElemSize();
+  }
+  /// Returns the total size of the innermost field.
+  size_t getSize() const { return getFieldDesc()->getSize(); }
+
+  /// Returns the offset into an array.
+  unsigned getOffset() const {
+    assert(Offset != PastEndMark && "invalid offset");
+    if (Base == RootPtrMark)
+      return Offset;
+
+    unsigned Adjust = 0;
+    if (Offset != Base) {
+      if (getFieldDesc()->ElemDesc)
+        Adjust = sizeof(InlineDescriptor);
+      else
+        Adjust = sizeof(InitMap *);
+    }
+    return Offset - Base - Adjust;
+  }
+
+  /// Checks if the innermost field is an array.
+  bool inArray() const { return getFieldDesc()->IsArray; }
+  /// Checks if the structure is a primitive array.
+  bool inPrimitiveArray() const { return getFieldDesc()->isPrimitiveArray(); }
+  /// Checks if the structure is an array of unknown size.
+  bool isUnknownSizeArray() const {
+    return getFieldDesc()->isUnknownSizeArray();
+  }
+  /// Checks if the pointer points to an array.
+  bool isArrayElement() const { return Base != Offset; }
+  /// Pointer points directly to a block.
+  bool isRoot() const {
+    return (Base == 0 || Base == RootPtrMark) && Offset == 0;
+  }
+
+  /// Returns the record descriptor of a class.
+  Record *getRecord() const { return getFieldDesc()->ElemRecord; }
+  /// Returns the field information.
+  const FieldDecl *getField() const { return getFieldDesc()->asFieldDecl(); }
+
+  /// Checks if the object is a union.
+  bool isUnion() const;
+
+  /// Checks if the storage is extern.
+  bool isExtern() const { return Pointee->isExtern(); }
+  /// Checks if the storage is static.
+  bool isStatic() const { return Pointee->isStatic(); }
+  /// Checks if the storage is temporary.
+  bool isTemporary() const { return Pointee->isTemporary(); }
+  /// Checks if the storage is a static temporary.
+  bool isStaticTemporary() const { return isStatic() && isTemporary(); }
+
+  /// Checks if the field is mutable.
+  bool isMutable() const { return Base != 0 && getInlineDesc()->IsMutable; }
+  /// Checks if an object was initialized.
+  bool isInitialized() const;
+  /// Checks if the object is active.
+  bool isActive() const { return Base == 0 || getInlineDesc()->IsActive; }
+  /// Checks if a structure is a base class.
+  bool isBaseClass() const { return isField() && getInlineDesc()->IsBase; }
+
+  /// Checks if an object or a subfield is mutable.
+  bool isConst() const {
+    return Base == 0 ? getDeclDesc()->IsConst : getInlineDesc()->IsConst;
+  }
+
+  /// Returns the declaration ID.
+  llvm::Optional<unsigned> getDeclID() const { return Pointee->getDeclID(); }
+
+  /// Returns the byte offset from the start.
+  unsigned getByteOffset() const {
+    return Offset;
+  }
+
+  /// Returns the number of elements.
+  unsigned getNumElems() const { return getSize() / elemSize(); }
+
+  /// Returns the index into an array.
+  int64_t getIndex() const {
+    if (isElementPastEnd())
+      return 1;
+    if (auto ElemSize = elemSize())
+      return getOffset() / ElemSize;
+    return 0;
+  }
+
+  /// Checks if the index is one past end.
+  bool isOnePastEnd() const {
+    return isElementPastEnd() || getSize() == getOffset();
+  }
+
+  /// Checks if the pointer is an out-of-bounds element pointer.
+  bool isElementPastEnd() const { return Offset == PastEndMark; }
+
+  /// Dereferences the pointer, if it's live.
+  template <typename T> T &deref() const {
+    assert(isLive() && "Invalid pointer");
+    return *reinterpret_cast<T *>(Pointee->data() + Offset);
+  }
+
+  /// Dereferences a primitive element.
+  template <typename T> T &elem(unsigned I) const {
+    return reinterpret_cast<T *>(Pointee->data())[I];
+  }
+
+  /// Initializes a field.
+  void initialize() const;
+  /// Activats a field.
+  void activate() const;
+  /// Deactivates an entire strurcutre.
+  void deactivate() const;
+
+  /// Checks if two pointers are comparable.
+  static bool hasSameBase(const Pointer &A, const Pointer &B);
+  /// Checks if two pointers can be subtracted.
+  static bool hasSameArray(const Pointer &A, const Pointer &B);
+
+  /// Prints the pointer.
+  void print(llvm::raw_ostream &OS) const {
+    OS << "{" << Base << ", " << Offset << ", ";
+    if (Pointee)
+      OS << Pointee->getSize();
+    else
+      OS << "nullptr";
+    OS << "}";
+  }
+
+private:
+  friend class Block;
+  friend class DeadBlock;
+
+  Pointer(Block *Pointee, unsigned Base, unsigned Offset);
+
+  /// Returns the embedded descriptor preceding a field.
+  InlineDescriptor *getInlineDesc() const { return getDescriptor(Base); }
+
+  /// Returns a descriptor at a given offset.
+  InlineDescriptor *getDescriptor(unsigned Offset) const {
+    assert(Offset != 0 && "Not a nested pointer");
+    return reinterpret_cast<InlineDescriptor *>(Pointee->data() + Offset) - 1;
+  }
+
+  /// Returns a reference to the pointer which stores the initialization map.
+  InitMap *&getInitMap() const {
+    return *reinterpret_cast<InitMap **>(Pointee->data() + Base);
+  }
+
+  /// The block the pointer is pointing to.
+  Block *Pointee = nullptr;
+  /// Start of the current subfield.
+  unsigned Base = 0;
+  /// Offset into the block.
+  unsigned Offset = 0;
+
+  /// Previous link in the pointer chain.
+  Pointer *Prev = nullptr;
+  /// Next link in the pointer chain.
+  Pointer *Next = nullptr;
+};
+
+inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const Pointer &P) {
+  P.print(OS);
+  return OS;
+}
+
+} // namespace interp
+} // namespace clang
+
+#endif