An In-Depth Understanding of Flutter Compilation Principles and Optimizations


Introduction to Flutter

Flutter Project Structure

Flutter Mode

  • Debug Mode: It corresponds to JIT mode of Dart, which is also called check mode or slow mode. This mode supports devices and simulators (iOS/Android) and permits assertion, including all debugging information, service extension, observatory, and other debugging aids. It is optimized for rapid development and operation, but not for execution speed, packet size, and deployment. In Debug mode, the compilation uses JIT technology to support the popular sub-second hot reload.
  • Release Mode: It corresponds to AOT mode of Dart, with the aim of deployment to end users. This mode only supports physical devices, not simulators. All assertions and debugging tools are restricted, and debugging information is removed as much as possible. It is optimized for quick start, quick execution, and packet size. All debugging aids and service extensions are prohibited.
  • Profile Mode: It is similar to Release mode while providing more support for service extensions. It also supports tracking and minimizing the dependencies required to use the tracking information. For example, the Observatory can connect to processes. Profile mode does not support simulators because judgments on simulators do not represent true performance.

Compilation and Operation of Flutter Code (iOS)

Compilation in Release Mode

Operation in Release Mode

Compilation in Debug Mode

Compilation and Operation of Flutter Code (Android)

Compilation in Release Mode

Operation in Release Mode

Compilation in Debug Mode

Customization and Optimization Related to Flutter Construction


if [[ ! -f "SNAPSHOT_PATH" ]] || [[ ! -s "STAMP_PATH" ]] || [[ "(cat "STAMP_PATH")" != "revision" ]] || [[ "FLUTTER_TOOLS_DIR/pubspec.yaml" -nt "$FLUTTER_TOOLS_DIR/pubspec.lock" ]]; then
rm -f "$FLUTTER_ROOT/version"
touch "$FLUTTER_ROOT/bin/cache/.dartignore"
echo Building flutter tool...
if [[ "$TRAVIS" == "true" ]] || [[ "$BOT" == "true" ]] || [[ "$CONTINUOUS_INTEGRATION" == "true" ]] || [[ "$CHROME_HEADLESS" == "1" ]] || [[ "$APPVEYOR" == "true" ]] || [[ "$CI" == "true" ]]; then
export PUB_ENVIRONMENT="$PUB_ENVIRONMENT:flutter_install"

if [[ -d "$FLUTTER_ROOT/.pub-cache" ]]; then
export PUB_CACHE="${PUB_CACHE:-"$FLUTTER_ROOT/.pub-cache"}"

while : ; do
"$PUB" upgrade --verbosity=error --no-packages-dir && break
echo Error: Unable to 'pub upgrade' flutter tool. Retrying in five seconds...
sleep 5
"$DART" --snapshot="$SNAPSHOT_PATH" --packages="$FLUTTER_TOOLS_DIR/.packages" "$SCRIPT_PATH"
echo "$revision" > "$STAMP_PATH"


./flutter/tools/gn --runtime-mode=debug --ios --ios-cpu=arm
ninja -C out/ios_debug_arm

Debugging flutter_tools

  1. Understand the command line parameters of flutter_tools
  1. Open packages/flutter_tools in a Dart project. Modify flutter_tools.dart based on the obtained parameters and set the command line dart app to start debugging.

Engine Customization and Debugging

./flutter/tools/gn --runtime-mode=debug --ios --ios-cpu=arm
ninja -C out/ios_debug_arm
./flutter/tools/gn --runtime-mode=release --ios --ios-cpu=arm
ninja -C out/ios_release_arm
./flutter/tools/gn --runtime-mode=profile --ios --ios-cpu=arm
ninja -C out/ios_profile_arm
./flutter/tools/gn --runtime-mode=debug --ios --ios-cpu=arm64
ninja -C out/ios_debug
./flutter/tools/gn --runtime-mode=release --ios --ios-cpu=arm64
ninja -C out/ios_release
./flutter/tools/gn --runtime-mode=profile --ios --ios-cpu=arm64
ninja -C out/ios_profile
./flutter/tools/gn --runtime-mode=debug --unoptimized --ios --ios-cpu=arm64
ninja -C out/ios_debug_unopt
./flutter/tools/gn --runtime-mode=debug --android --android-cpu=arm
ninja -C out/android_debug
./flutter/tools/gn --runtime-mode=release --android --android-cpu=arm
ninja -C out/android_release
./flutter/tools/gn --runtime-mode=profile --android --android-cpu=arm
ninja -C out/android_profile


  1. Flutter’s Modes
  2. iOS Builds Supporting ARMv7
  3. Contributing to the Flutter Engine
  4. Flutter System Architecture
  5. Symbolicating Production Crash Stacks

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