Chunk getSerializedSize() into 32 field chunks to make it more JIT friendly.

This follows the precedent that was previously done for buildPartial (including the exact number of fields per chunk).

PiperOrigin-RevId: 866458607

Author: protobuf-github-bot

src/google/protobuf/compiler/java/full/message.cc

@@ -11,6 +11,7 @@
 
 #include "google/protobuf/compiler/java/full/message.h"
 
+#include <algorithm>
 #include <memory>
 #include <string>
 #include <utility>
@@ -608,9 +609,33 @@ void ImmutableMessageGenerator::GenerateMessageSerializationMethods(
   }
 
   printer->Outdent();
+  printer->Print("}\n");
+
+  // Chunk up the getSerializedSize() into chunks to be JIT friendly.
+  constexpr int kNumFieldsPerChunk = 32;
+  int num_chunks = (descriptor_->field_count() + kNumFieldsPerChunk - 1) /
+                   kNumFieldsPerChunk;
+  for (int i = 0; i < num_chunks; ++i) {
+    printer->Print(
+        "private int computeSerializedSize_$chunk$() {\n"
+        "  int size = 0;\n",
+        "chunk", absl::StrCat(i));
+    printer->Indent();
+
+    int chunk_field_start = i * kNumFieldsPerChunk;
+    int chunk_field_end = std::min(chunk_field_start + kNumFieldsPerChunk,
+                                   descriptor_->field_count());
+
+    for (int j = chunk_field_start; j < chunk_field_end; ++j) {
+      field_generators_.get(sorted_fields[j])
+          .GenerateSerializedSizeCode(printer);
+    }
+    printer->Outdent();
+    printer->Print("  return size;\n");
+    printer->Print("}\n");
+  }
+
   printer->Print(
-      "}\n"
-      "\n"
       "@java.lang.Override\n"
       "public int getSerializedSize() {\n"
       "  int size = memoizedSize;\n"
@@ -620,8 +645,9 @@ void ImmutableMessageGenerator::GenerateMessageSerializationMethods(
 
   printer->Print("size = 0;\n");
 
-  for (int i = 0; i < descriptor_->field_count(); i++) {
-    field_generators_.get(sorted_fields[i]).GenerateSerializedSizeCode(printer);
+  for (int i = 0; i < num_chunks; ++i) {
+    printer->Print("size += computeSerializedSize_$chunk$();\n", "chunk",
+                   absl::StrCat(i));
   }
 
   if (descriptor_->extension_range_count() > 0) {