[clang] [clang] LazyOffsetPtr: Use native pointer width (PR #111995)

[Chuanqi Xu via cfe-commits]

================
@@ -326,25 +326,25 @@ struct LazyOffsetPtr {
   ///
   /// If the low bit is clear, a pointer to the AST node. If the low
   /// bit is set, the upper 63 bits are the offset.
-  mutable uint64_t Ptr = 0;
+  mutable uintptr_t Ptr = 0;
 
 public:
   LazyOffsetPtr() = default;
-  explicit LazyOffsetPtr(T *Ptr) : Ptr(reinterpret_cast<uint64_t>(Ptr)) {}
+  explicit LazyOffsetPtr(T *Ptr) : Ptr(reinterpret_cast<uintptr_t>(Ptr)) {}
 
-  explicit LazyOffsetPtr(uint64_t Offset) : Ptr((Offset << 1) | 0x01) {
-    assert((Offset << 1 >> 1) == Offset && "Offsets must require < 63 bits");
+  explicit LazyOffsetPtr(uintptr_t Offset) : Ptr((Offset << 1) | 0x01) {
+    assert((Offset << 1 >> 1) == Offset && "Offsets must fit in addressable bits");
     if (Offset == 0)
       Ptr = 0;
   }
 
   LazyOffsetPtr &operator=(T *Ptr) {
-    this->Ptr = reinterpret_cast<uint64_t>(Ptr);
+    this->Ptr = reinterpret_cast<uintptr_t>(Ptr);
     return *this;
   }
 
-  LazyOffsetPtr &operator=(uint64_t Offset) {
-    assert((Offset << 1 >> 1) == Offset && "Offsets must require < 63 bits");
+  LazyOffsetPtr &operator=(uintptr_t Offset) {
----------------
ChuanqiXu9 wrote:

Some update: the higher 32 bits are required here: https://github.com/llvm/llvm-project/blob/d54953ef472bfd8d4b503aae7682aa76c49f8cc0/clang/include/clang/AST/ExternalASTSource.h#L580-L582

where the `GlobalDeclID`'s higher 32 bits are meaningful. And we may get the `Ptr` converted to `GlobalDeclID` here:

`https://github.com/llvm/llvm-project/blob/d54953ef472bfd8d4b503aae7682aa76c49f8cc0/clang/include/clang/AST/ExternalASTSource.h#L378`

so we need to preserve at least 64 bits in this structure.

https://github.com/llvm/llvm-project/pull/111995