ecmascript/compiler/baseline

A fast, non-optimizing compiler that translates bytecode directly to machine code without going through the full Circuit IR and optimization pass pipeline, providing faster compilation at the cost of less-optimized output. Primary Language: C++

Design

The baseline compiler sits between the interpreter and the optimizing compiler in the execution tier hierarchy:

  ABC bytecode
       │
       ▼
  BaselineCompiler
    ├── Iterates bytecodes sequentially
    ├── Uses BaselineAssembler to emit code per-bytecode
    └── Calls into BaselineStubs for complex operations
       │
       ▼
  Machine code (installed directly, no .an file)

Key design decisions:

• No IR — Bytecodes are lowered directly to machine instructions via BaselineAssembler, skipping Circuit IR entirely.
• Stub-based — Complex operations (e.g., type checks, property access) call into BaselineStubs rather than being inlined, keeping the compiler simple.
• Architecture-dependent — Uses the assembler/ module's MacroAssembler for instruction emission.

Key abstractions:

• BaselineCompiler — Main compilation driver; walks bytecodes and dispatches to assembler helpers.
• BaselineAssembler — Bytecode-to-machine-code emission helpers.
• BaselineStubBuilder / BaselineStubs — Runtime helper stubs specific to baseline-compiled code.
• BaselineCallSignature — Calling conventions for baseline stubs.

Key Files

File	Role
baseline_compiler.cpp/.h	Main compilation flow
baseline_assembler.cpp/.h	Code emission helpers
baseline_stub_builder.cpp/.h	Stub construction
baseline_stubs.cpp/.h	Runtime stub definitions
baseline_call_signature.cpp/.h	Calling convention definitions
baseline_compiler_builtins.h	Built-in operation definitions

How to Modify

Add baseline support for a new bytecode:

1. Add the emission case to BaselineCompiler (in baseline_compiler.cpp)
2. If it needs a stub, add it to BaselineStubs and register via BaselineCallSignature
3. Implement architecture-specific call in compiler/trampoline/{aarch64,x64}/baseline_call.cpp

Add a new baseline stub:

1. Define the stub signature in baseline_call_signature.cpp
2. Implement the stub in baseline_stubs.cpp or baseline_stub_builder.cpp
3. Add call-path in compiler/trampoline/{aarch64,x64}/baseline_call.cpp

Building

Standalone repo (from repo root ../../):

python ark.py x64.debug

Full OHOS tree:

./build.sh --product-name <product-name> --build-target ark_js_host_linux_tools_packages

Tests

Run all unit tests: python ark.py x64.debug unittest (from repo root ../../)

No dedicated baseline tests. Coverage through:

• Aggregate runtime tests: ark_js_unittest
• Related call-path code: compiler/trampoline/{aarch64,x64}/baseline_call.cpp

Add baseline-focused tests to ecmascript/compiler/tests/BUILD.gn.

Boundaries

• Keep baseline logic separate from AOT/JIT optimization passes — baseline does no optimization.
• ABI/signature changes must be synchronized with trampoline/ and call_signature* definitions.
• Compiled as part of libark_jsoptimizer_sources in ecmascript/compiler/BUILD.gn.