V8 Torque

Torque is an Ahead-of-Time (AOT) generator that transforms .tq DSL into highly-optimized C++ CodeStubAssembler (CSA) code, which is then compiled into the mksnapshot binary.

Execution Pipeline

To debug failures, you must understand its multi-stage build:

1. Generation: The Torque compiler reads .tq files and generates C++ CodeStubAssembler files (.cc, .h, .inc) in out/<config>/gen/torque-generated/.
2. Compilation: mksnapshot (or the d8 build) compiles the generated C++ files.
3. Snapshotting: mksnapshot executes the generated C++ code (via TurboFan or Maglev) to emit highly-optimized raw machine code.
4. Linking: The machine code is serialized into a snapshot and linked into V8, meaning Torque builtins run with zero translation overhead at runtime.

Implementation Patterns

Common Torque syntax, keywords, and linkage definitions:

// 1. Type Casting & Checks
const array = Cast<JSArray>(object) otherwise GotoLabel;
if (Is<JSArray>(object)) { ... }

// 2. Control Flow
try {
  const smi = Cast<Smi>(input) otherwise IsNotSmi;
} label IsNotSmi deferred {
  return runtime::DoSomething(context, input);
}

// 3. Signatures & Keywords
// 'macro': Inlined functions for reusable logic.
transitioning macro Name(implicit context: Context)(arg: JSAny): JSAny

// 'builtin': Non-inlined functions, callable from other builtins or JavaScript.
transitioning builtin Name(implicit context: Context)(arg: JSAny): JSAny

// 'javascript': Marks a builtin as directly callable from JavaScript, with JS linkage.
transitioning javascript builtin Name(js-implicit context: NativeContext, receiver: JSAny)(arg: JSAny): JSAny

// 'transitioning': Indicates a function can cause an object's map to change (e.g. adding properties).
// 'extern': Used to call C++ defined CSA functions from Torque.
extern transitioning macro NameInCpp(Context, JSAny): JSAny;

Mandatory verification workflow

The task is incomplete until you successfully execute this sequence:

1. Build

Run the gm.py wrapper to trigger the Torque generator and C++ compilation.

tools/dev/gm.py quiet {arch}.{type}

(e.g., x64.optdebug or arm64.release). Use optdebug for logic/debugging, release for performance/benchmarking.

2. Verify with Tests

Run the relevant test suite (usually mjsunit for JavaScript-exposed builtins) to ensure correctness. Match the {arch}.{type} to your build.

tools/run-tests.py --progress dots --outdir=out/{arch}.{type} mjsunit/<test_name>

3. Debug (If Necessary)

If the build fails during "Generation", inspect the .tq syntax. If it fails during "Compilation", check the generated C++ in out/<config>/gen/torque-generated/.