cppgc: Refactor object allocation to improve binary size

Refactor SpacePolicy on a non-templated class to avoid the situation
of having MakeGarbageCollectedTraitBase<T>::SpacePolicy<U> refer to
different T and U which make it hard for the compiler to alias
anything.

Bug: chromium:1056170
Change-Id: I78eb0362d43403ad2712bcb65746eeb9f6ad44fa
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2769338Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73494}

include/cppgc/allocation.h

@@ -43,6 +43,28 @@ class V8_EXPORT MakeGarbageCollectedTraitInternal {
                                       std::memory_order_release);
   }
 
+  template <typename U, typename CustomSpace>
+  struct SpacePolicy {
+    static void* Allocate(AllocationHandle& handle, size_t size) {
+      // Custom space.
+      static_assert(std::is_base_of<CustomSpaceBase, CustomSpace>::value,
+                    "Custom space must inherit from CustomSpaceBase.");
+      return MakeGarbageCollectedTraitInternal::Allocate(
+          handle, size, internal::GCInfoTrait<U>::Index(),
+          CustomSpace::kSpaceIndex);
+    }
+  };
+
+  template <typename U>
+  struct SpacePolicy<U, void> {
+    static void* Allocate(AllocationHandle& handle, size_t size) {
+      // Default space.
+      return MakeGarbageCollectedTraitInternal::Allocate(
+          handle, size, internal::GCInfoTrait<U>::Index());
+    }
+  };
+
+ private:
   static void* Allocate(cppgc::AllocationHandle& handle, size_t size,
                         GCInfoIndex index);
   static void* Allocate(cppgc::AllocationHandle& handle, size_t size,
@@ -71,27 +93,6 @@ class MakeGarbageCollectedTraitBase
                         internal::api_constants::kLargeObjectSizeThreshold,
                 "GarbageCollectedMixin may not be a large object");
 
-  template <typename U, typename CustomSpace>
-  struct SpacePolicy {
-    static void* Allocate(AllocationHandle& handle, size_t size) {
-      // Custom space.
-      static_assert(std::is_base_of<CustomSpaceBase, CustomSpace>::value,
-                    "Custom space must inherit from CustomSpaceBase.");
-      return internal::MakeGarbageCollectedTraitInternal::Allocate(
-          handle, size, internal::GCInfoTrait<U>::Index(),
-          CustomSpace::kSpaceIndex);
-    }
-  };
-
-  template <typename U>
-  struct SpacePolicy<U, void> {
-    static void* Allocate(AllocationHandle& handle, size_t size) {
-      // Default space.
-      return internal::MakeGarbageCollectedTraitInternal::Allocate(
-          handle, size, internal::GCInfoTrait<U>::Index());
-    }
-  };
-
  protected:
   /**
    * Allocates memory for an object of type T.
@@ -101,7 +102,7 @@ class MakeGarbageCollectedTraitBase
    * \param size The size that should be reserved for the object.
    * \returns the memory to construct an object of type T on.
    */
-  static void* Allocate(AllocationHandle& handle, size_t size) {
+  V8_INLINE static void* Allocate(AllocationHandle& handle, size_t size) {
     return SpacePolicy<
         typename internal::GCInfoFolding<
             T, typename T::ParentMostGarbageCollectedType>::ResultType,
@@ -114,7 +115,7 @@ class MakeGarbageCollectedTraitBase
    *
    * \param payload The base pointer the object is allocated at.
    */
-  static void MarkObjectAsFullyConstructed(const void* payload) {
+  V8_INLINE static void MarkObjectAsFullyConstructed(const void* payload) {
     internal::MakeGarbageCollectedTraitInternal::MarkObjectAsFullyConstructed(
         payload);
   }