cppgc: Require object for cppgc::subtle::Resize()

Resize() is not similar to realloc() in that it allocates a new object
when passed a nullptr object.

Avoid corner cases around Resize(nullptr, size) where size may be
problematic if non-null by just requiring a valid object. The caller
can perform the necesary nullptr check.

Bug: chromium:1056170
Change-Id: Ic05972ae67c2968fc3eb002a6302b44e56b41ab4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2752147Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73336}

include/cppgc/explicit-management.h

@@ -61,11 +61,10 @@ void FreeUnreferencedObject(T* object) {
  *   on, and false otherwise.
  */
 template <typename T>
-bool Resize(T* object, AdditionalBytes additional_bytes) {
+bool Resize(T& object, AdditionalBytes additional_bytes) {
   static_assert(IsGarbageCollectedTypeV<T>,
                 "Object must be of type GarbageCollected.");
-  if (!object) return true;
-  return internal::Resize(object, sizeof(T) + additional_bytes.value);
+  return internal::Resize(&object, sizeof(T) + additional_bytes.value);
 }
 
 }  // namespace subtle

test/unittests/heap/cppgc/explicit-management-unittest.cc

@@ -121,11 +121,11 @@ TEST_F(ExplicitManagementTest, GrowAtLAB) {
   auto& header = HeapObjectHeader::FromPayload(o);
   constexpr size_t size_of_o = sizeof(DynamicallySized);
   constexpr size_t kFirstDelta = 8;
-  EXPECT_TRUE(subtle::Resize(o, AdditionalBytes(kFirstDelta)));
+  EXPECT_TRUE(subtle::Resize(*o, AdditionalBytes(kFirstDelta)));
   EXPECT_EQ(RoundUp<kAllocationGranularity>(size_of_o + kFirstDelta),
             header.ObjectSize());
   constexpr size_t kSecondDelta = 9;
-  EXPECT_TRUE(subtle::Resize(o, AdditionalBytes(kSecondDelta)));
+  EXPECT_TRUE(subtle::Resize(*o, AdditionalBytes(kSecondDelta)));
   EXPECT_EQ(RoundUp<kAllocationGranularity>(size_of_o + kSecondDelta),
             header.ObjectSize());
   // Second round didn't actually grow object because alignment restrictions
@@ -133,7 +133,7 @@ TEST_F(ExplicitManagementTest, GrowAtLAB) {
   EXPECT_EQ(RoundUp<kAllocationGranularity>(size_of_o + kFirstDelta),
             RoundUp<kAllocationGranularity>(size_of_o + kSecondDelta));
   constexpr size_t kThirdDelta = 16;
-  EXPECT_TRUE(subtle::Resize(o, AdditionalBytes(kThirdDelta)));
+  EXPECT_TRUE(subtle::Resize(*o, AdditionalBytes(kThirdDelta)));
   EXPECT_EQ(RoundUp<kAllocationGranularity>(size_of_o + kThirdDelta),
             header.ObjectSize());
 }
@@ -144,10 +144,10 @@ TEST_F(ExplicitManagementTest, GrowShrinkAtLAB) {
   auto& header = HeapObjectHeader::FromPayload(o);
   constexpr size_t size_of_o = sizeof(DynamicallySized);
   constexpr size_t kDelta = 27;
-  EXPECT_TRUE(subtle::Resize(o, AdditionalBytes(kDelta)));
+  EXPECT_TRUE(subtle::Resize(*o, AdditionalBytes(kDelta)));
   EXPECT_EQ(RoundUp<kAllocationGranularity>(size_of_o + kDelta),
             header.ObjectSize());
-  EXPECT_TRUE(subtle::Resize(o, AdditionalBytes(0)));
+  EXPECT_TRUE(subtle::Resize(*o, AdditionalBytes(0)));
   EXPECT_EQ(RoundUp<kAllocationGranularity>(size_of_o), header.ObjectSize());
 }
 
@@ -160,7 +160,7 @@ TEST_F(ExplicitManagementTest, ShrinkFreeList) {
   ResetLinearAllocationBuffers();
   auto& header = HeapObjectHeader::FromPayload(o);
   constexpr size_t size_of_o = sizeof(DynamicallySized);
-  EXPECT_TRUE(subtle::Resize(o, AdditionalBytes(0)));
+  EXPECT_TRUE(subtle::Resize(*o, AdditionalBytes(0)));
   EXPECT_EQ(RoundUp<kAllocationGranularity>(size_of_o), header.ObjectSize());
   EXPECT_TRUE(space->free_list().ContainsForTesting(
       {header.PayloadEnd(), ObjectAllocator::kSmallestSpaceSize}));
@@ -175,7 +175,7 @@ TEST_F(ExplicitManagementTest, ShrinkFreeListBailoutAvoidFragmentation) {
   ResetLinearAllocationBuffers();
   auto& header = HeapObjectHeader::FromPayload(o);
   constexpr size_t size_of_o = sizeof(DynamicallySized);
-  EXPECT_TRUE(subtle::Resize(o, AdditionalBytes(0)));
+  EXPECT_TRUE(subtle::Resize(*o, AdditionalBytes(0)));
   EXPECT_EQ(RoundUp<kAllocationGranularity>(
                 size_of_o + ObjectAllocator::kSmallestSpaceSize - 1),
             header.ObjectSize());