Add partitionAllocActualSize() for predicting actual size of allocation

Source/wtf/PartitionAllocTest.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 575 matching lines @@
 
     TestShutdown();
 }
 
 // Test that we can fetch the real allocated size after an allocation.
 TEST(WTF_PartitionAlloc, GenericAllocGetSize)
 {
     TestSetup();
 
     void* ptr;
-    size_t requestedSize, actualSize;
+    size_t requestedSize, actualSize, predictedSize;
 
     EXPECT_TRUE(partitionAllocSupportsGetSize());
 
     // Allocate something small.
     requestedSize = 511 - kExtraAllocSize;
+    predictedSize = partitionAllocActualSize(genericAllocator.root(), requestedSize);
     ptr = partitionAllocGeneric(genericAllocator.root(), requestedSize);
     EXPECT_TRUE(ptr);
     actualSize = partitionAllocGetSize(ptr);
+    EXPECT_EQ(predictedSize, actualSize);
     EXPECT_LT(requestedSize, actualSize);
     partitionFreeGeneric(genericAllocator.root(), ptr);
 
     // Allocate a size that should be a perfect match for a bucket, because it
     // is an exact power of 2.
     requestedSize = (256 * 1024) - kExtraAllocSize;
+    predictedSize = partitionAllocActualSize(genericAllocator.root(), requestedSize);
     ptr = partitionAllocGeneric(genericAllocator.root(), requestedSize);
     EXPECT_TRUE(ptr);
     actualSize = partitionAllocGetSize(ptr);
+    EXPECT_EQ(predictedSize, actualSize);
     EXPECT_EQ(requestedSize, actualSize);
     partitionFreeGeneric(genericAllocator.root(), ptr);
 
     // Allocate a size that is a system page smaller than a bucket. GetSize()
     // should return a larger size than we asked for now.
     requestedSize = (256 * 1024) - WTF::kSystemPageSize - kExtraAllocSize;
+    predictedSize = partitionAllocActualSize(genericAllocator.root(), requestedSize);
     ptr = partitionAllocGeneric(genericAllocator.root(), requestedSize);
     EXPECT_TRUE(ptr);
     actualSize = partitionAllocGetSize(ptr);
+    EXPECT_EQ(predictedSize, actualSize);
     EXPECT_EQ(requestedSize + WTF::kSystemPageSize, actualSize);
     // Check that we can write at the end of the reported size too.
     char* charPtr = reinterpret_cast<char*>(ptr);
     *(charPtr + (actualSize - 1)) = 'A';
     partitionFreeGeneric(genericAllocator.root(), ptr);
 
     // Allocate something very large, and uneven.
     requestedSize = 512 * 1024 * 1024 - 1;
+    predictedSize = partitionAllocActualSize(genericAllocator.root(), requestedSize);
     ptr = partitionAllocGeneric(genericAllocator.root(), requestedSize);
     EXPECT_TRUE(ptr);
     actualSize = partitionAllocGetSize(ptr);
+    EXPECT_EQ(predictedSize, actualSize);
     EXPECT_LT(requestedSize, actualSize);
     partitionFreeGeneric(genericAllocator.root(), ptr);
 
+    // Too large allocation.
+    requestedSize = INT_MAX;
+    predictedSize = partitionAllocActualSize(genericAllocator.root(), requestedSize);
+    EXPECT_EQ(requestedSize, predictedSize);
+
     TestShutdown();
 }
 
 // Test the realloc() contract.
 TEST(WTF_PartitionAlloc, Realloc)
 {
     TestSetup();
 
     // realloc(0, size) should be equivalent to malloc().
     void* ptr = partitionReallocGeneric(genericAllocator.root(), 0, kTestAllocSize);
@@ skipping 464 matching lines @@
     EXPECT_EQ(32u, WTF::countLeadingZerosSizet(0));
     EXPECT_EQ(31u, WTF::countLeadingZerosSizet(1));
     EXPECT_EQ(1u, WTF::countLeadingZerosSizet(1 << 30));
     EXPECT_EQ(0u, WTF::countLeadingZerosSizet(1 << 31));
 #endif
 }
 
 } // namespace
 
 #endif // !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)