Enable small object optimization (SOO) for RepeatedField in order to …

…reduce data indirections.

The arena and the heap representation are both aligned to 8 bytes so we can use the lowest 3 bits of the heap pointer to encode whether the RepeatedField is in SOO mode or not, and if it is in SOO mode, to record the size. Therefore, we can have SOO sizes from 0 to 3 and one bit for whether we're in SOO mode. Note that we also tried using 3 bits for SOO size with a sentinel value for not-SOO-mode, but that was slower.

PiperOrigin-RevId: 659578775

src/google/protobuf/compiler/cpp/unittest.inc

@@ -27,8 +27,9 @@
 #include <memory>
 #include <vector>
 
-#include "google/protobuf/compiler/cpp/unittest.h"
+#include "absl/base/attributes.h"
 #include "absl/strings/cord.h"
+#include "google/protobuf/compiler/cpp/unittest.h"
 #include "absl/strings/string_view.h"
 #ifndef _MSC_VER
 // We exclude this large proto because it's too large for
@@ -482,25 +483,11 @@ TEST(GENERATED_MESSAGE_TEST_NAME, ADLSwap) {
   UNITTEST::TestAllTypes message1, message2;
   TestUtil::SetAllFields(&message1);
 
-  // Note the address of one of the repeated fields, to verify it was swapped
-  // rather than copied.
-  const int32_t* addr = &message1.repeated_int32().Get(0);
-#ifdef PROTOBUF_FORCE_COPY_IN_SWAP
-  const int32_t value = *addr;
-#endif
-
   using std::swap;
   swap(message1, message2);
 
   TestUtil::ExpectAllFieldsSet(message2);
   TestUtil::ExpectClear(message1);
-
-#ifdef PROTOBUF_FORCE_COPY_IN_SWAP
-  EXPECT_NE(addr, &message2.repeated_int32().Get(0));
-  EXPECT_EQ(value, message2.repeated_int32().Get(0));
-#else
-  EXPECT_EQ(addr, &message2.repeated_int32().Get(0));
-#endif
 }
 
 TEST(GENERATED_MESSAGE_TEST_NAME, CopyConstructor) {

src/google/protobuf/extension_set_unittest.cc

@@ -11,6 +11,7 @@
 
 #include "google/protobuf/extension_set.h"
 
+#include <algorithm>
 #include <cstdint>
 #include <string>
 
@@ -841,10 +842,12 @@ TEST(ExtensionSetTest, SpaceUsedExcludingSelf) {
     const size_t old_capacity =                                                \
         message->GetRepeatedExtension(unittest::repeated_##type##_extension)   \
             .Capacity();                                                       \
-    EXPECT_GE(                                                                 \
-        old_capacity,                                                          \
-        (RepeatedFieldLowerClampLimit<cpptype, std::max(sizeof(cpptype),       \
-                                                        sizeof(void*))>()));   \
+    if (sizeof(cpptype) > 1) {                                                 \
+      EXPECT_GE(                                                               \
+          old_capacity,                                                        \
+          (RepeatedFieldLowerClampLimit<cpptype, std::max(sizeof(cpptype),     \
+                                                          sizeof(void*))>())); \
+    }                                                                          \
     for (int i = 0; i < 16; ++i) {                                             \
       message->AddExtension(unittest::repeated_##type##_extension, value);     \
     }                                                                          \