[ptr-compr] Use only Tagged_t part when comparing Object values

... as it uniquely idenifies object inside an Isolate.
This also allows comparisons between full tagged values ([Maybe]Object)
and potentially compressed tagged values ([Strong]TaggedValue).

As a side effect with this change we should generate a bit less code.

Bug: v8:7703
Change-Id: I822df24e03653fa73314e0a6f81f0fa7b5c61eba
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1643433Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61998}

src/objects/heap-object.h

@@ -22,7 +22,9 @@ class Heap;
 // objects.
 class HeapObject : public Object {
  public:
-  bool is_null() const { return ptr() == kNullAddress; }
+  bool is_null() const {
+    return static_cast<Tagged_t>(ptr()) == static_cast<Tagged_t>(kNullAddress);
+  }
 
   // [map]: Contains a map which contains the object's reflective
   // information.

src/objects/tagged-impl.h

@@ -40,16 +40,24 @@ class TaggedImpl {
   // Make clang on Linux catch what MSVC complains about on Windows:
   operator bool() const = delete;
 
-  constexpr bool operator==(TaggedImpl other) const {
-    return ptr_ == other.ptr_;
+  template <typename U>
+  constexpr bool operator==(TaggedImpl<kRefType, U> other) const {
+    static_assert(
+        std::is_same<U, Address>::value || std::is_same<U, Tagged_t>::value,
+        "U must be either Address or Tagged_t");
+    return static_cast<Tagged_t>(ptr_) == static_cast<Tagged_t>(other.ptr());
   }
-  constexpr bool operator!=(TaggedImpl other) const {
-    return ptr_ != other.ptr_;
+  template <typename U>
+  constexpr bool operator!=(TaggedImpl<kRefType, U> other) const {
+    static_assert(
+        std::is_same<U, Address>::value || std::is_same<U, Tagged_t>::value,
+        "U must be either Address or Tagged_t");
+    return static_cast<Tagged_t>(ptr_) != static_cast<Tagged_t>(other.ptr());
   }
 
   // For using in std::set and std::map.
   constexpr bool operator<(TaggedImpl other) const {
-    return ptr_ < other.ptr();
+    return static_cast<Tagged_t>(ptr_) < static_cast<Tagged_t>(other.ptr());
   }
 
   constexpr StorageType ptr() const { return ptr_; }