From df80cf91404e8e3b0f0a4eb271467448d126199e Mon Sep 17 00:00:00 2001
From: Vyacheslav Egorov <vegorov@google.com>
Date: Thu, 21 Mar 2024 11:10:10 +0000
Subject: [PATCH] [core] Improve JSON decoding performance

Avoid polymorphic character access by turning _ChunkedJsonParser
into a mixin instead of the base class.

TEST=ci

Change-Id: Id2080724e07d16e96734a80629c8bd8906dc590b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/358445
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Slava Egorov <vegorov@google.com>
---
 sdk/lib/_internal/vm/lib/convert_patch.dart | 47 +++++++++++++++------
 1 file changed, 33 insertions(+), 14 deletions(-)

diff --git a/sdk/lib/_internal/vm/lib/convert_patch.dart b/sdk/lib/_internal/vm/lib/convert_patch.dart
index 9a9ee1ed6bd..a5e0186b41f 100644
--- a/sdk/lib/_internal/vm/lib/convert_patch.dart
+++ b/sdk/lib/_internal/vm/lib/convert_patch.dart
@@ -59,9 +59,7 @@ class _JsonUtf8Decoder extends Converter<List<int>, Object?> {
 
   Object? convert(List<int> input) {
     var parser = _JsonUtf8DecoderSink._createParser(_reviver, _allowMalformed);
-    parser.chunk = input;
-    parser.chunkEnd = input.length;
-    parser.parse(0);
+    parser.parseChunk(input, 0, input.length);
     parser.close();
     return parser.result;
   }
@@ -249,6 +247,11 @@ class _NumberBuffer {
   double parseDouble() => double.parse(getString());
 }
 
+abstract class _JsonParserWithListener {
+  final _JsonListener listener;
+  _JsonParserWithListener(this.listener);
+}
+
 /**
  * Chunked JSON parser.
  *
@@ -256,8 +259,13 @@ class _NumberBuffer {
  * and stores input state between chunks.
  *
  * Implementations include [String] and UTF-8 parsers.
+ *
+ * Note: this is a mixin instead of the base class to allow compilers
+ * to specialize applications otherwise accessing chunk characters becomes
+ * polymorphic.
+ *
  */
-abstract class _ChunkedJsonParser<T> {
+mixin _ChunkedJsonParser<T> on _JsonParserWithListener {
   // A simple non-recursive state-based parser for JSON.
   //
   // Literal values accepted in states ARRAY_EMPTY, ARRAY_COMMA, OBJECT_COLON
@@ -388,8 +396,6 @@ abstract class _ChunkedJsonParser<T> {
   // Mask used to mask off two lower bits.
   static const int TWO_BIT_MASK = 3;
 
-  final _JsonListener listener;
-
   // The current parsing state.
   int state = STATE_INITIAL;
   List<int> states = <int>[];
@@ -440,8 +446,6 @@ abstract class _ChunkedJsonParser<T> {
    */
   dynamic buffer = null;
 
-  _ChunkedJsonParser(this.listener);
-
   /**
    * Push the current parse [state] on a stack.
    *
@@ -1380,7 +1384,8 @@ abstract class _ChunkedJsonParser<T> {
 /**
  * Chunked JSON parser that parses [String] chunks.
  */
-class _JsonStringParser extends _ChunkedJsonParser<String> {
+class _JsonStringParser extends _JsonParserWithListener
+    with _ChunkedJsonParser<String> {
   String chunk = '';
   int chunkEnd = 0;
 
@@ -1477,11 +1482,12 @@ class _JsonStringDecoderSink extends StringConversionSinkBase {
 /**
  * Chunked JSON parser that parses UTF-8 chunks.
  */
-class _JsonUtf8Parser extends _ChunkedJsonParser<List<int>> {
+class _JsonUtf8Parser extends _JsonParserWithListener
+    with _ChunkedJsonParser<Uint8List> {
   static final Uint8List emptyChunk = Uint8List(0);
 
   final _Utf8Decoder decoder;
-  List<int> chunk = emptyChunk;
+  Uint8List chunk = emptyChunk;
   int chunkEnd = 0;
 
   _JsonUtf8Parser(_JsonListener listener, bool allowMalformed)
@@ -1492,6 +1498,21 @@ class _JsonUtf8Parser extends _ChunkedJsonParser<List<int>> {
         _ChunkedJsonParser.PARTIAL_KEYWORD | _ChunkedJsonParser.KWD_BOM;
   }
 
+  void parseChunk(List<int> value, int start, int end) {
+    if (value is Uint8List) {
+      chunk = value;
+    } else {
+      final bytes = Uint8List(end - start);
+      bytes.setRange(0, bytes.length, value, start);
+      end = bytes.length;
+      start = 0;
+      chunk = bytes;
+    }
+    chunkEnd = end;
+    parse(start);
+  }
+
+  @pragma('vm:prefer-inline')
   int getChar(int position) => chunk[position];
 
   String getString(int start, int end, int bits) {
@@ -1569,9 +1590,7 @@ class _JsonUtf8DecoderSink extends ByteConversionSink {
   }
 
   void _addChunk(List<int> chunk, int start, int end) {
-    _parser.chunk = chunk;
-    _parser.chunkEnd = end;
-    _parser.parse(start);
+    _parser.parseChunk(chunk, start, end);
   }
 
   void close() {