ecmascript/ic

Inline cache system for optimizing property access by caching lookup results and avoiding repeated prototype chain traversals. Primary Language: C++

Design

Implements inline cache with three kinds of states for fast property access:

  Property access: obj.prop
        │
        ▼
   IC lookup (ic_runtime.cpp)
        │
        ├──▶ Mono IC (monomorphic)
        │     ├── Single shape cached
        │     ├── Direct inline check and access
        │     └── Fastest path
        │
        ├──▶ Poly IC (polymorphic)
        │     ├── 2-4 shapes cached
        │     ├── Shape-based dispatch
        │     └── Fast path
        │
        └──▶ Mega IC (megamorphic)
              ├── Many shapes (threshold exceeded)
              ├── Hash table lookup
              └── Slowest IC path
        │
        ▼
   Prototype chain traversal (if IC miss)
        │
        ├──▶ Found property?
        │     ├── Yes → Update IC with result
        │     └── No → Return undefined
        │
        ▼
   Return value

IC polymorphic states:

• Mono IC — Single shape cached, fastest path with direct inline check
• Poly IC — 2-4 shapes cached, shape-based dispatch
• Mega IC — Many shapes cached, hash table lookup for megamorphic sites

IC operation types:

• LoadIC — Property getter caching
• StoreIC — Property setter caching
• ElementIC — Array element access caching
• GlobalIC — Global variable access caching

IC state transitions:

• Mono → Poly: When a second shape is encountered
• Poly → Mega: When shape count exceeds threshold (typically 4)
• IC miss triggers prototype chain traversal and IC update

Key abstractions:

• ICRuntime — IC lookup and update logic
• ICHandler — Compact bit-encoded handler describing property access patterns (LoadHandler/StoreHandler for inline fast path, TransitionHandler/PrototypeHandler/TransWithProtoHandler/StoreAOTHandler as TaggedObjects for complex cases)
• ProfileTypeInfo — Type feedback and profiling data structure storing IC handlers, hotness counters, and compilation thresholds (used by interpreter, JIT, and AOT)
• ProfileTypeInfoCell — Wrapper containing ProfileTypeInfo and MachineCode, shared across functions via FunctionTemplate
• MegaICCache — Per-VM IC cache storage
• PropertyBox — Property value storage

Reference Source

• arkcompiler/ets_runtime/ecmascript/ic/ic_runtime.h (1-100行) - IC runtime interface
• arkcompiler/ets_runtime/ecmascript/ic/ic_handler.h - IC handler definitions

Key Files

File	Role
ic_runtime.h/.cpp	IC lookup and update logic
ic_handler.h/.cpp	IC handler class definitions and bit encoding implementation
ic_runtime_stub.h/.cpp	IC runtime stub functions
profile_type_info.h/.cpp`	Type feedback collection
mega_ic_cache.h/.cpp	IC cache storage
properties_cache.h	Property cache utilities
property_box.h/.cpp	Property value storage
proto_change_details.h/.cpp	Prototype change tracking

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

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

python ark.py x64.debug unittest   # includes IC tests

Full OHOS tree:

./build.sh --product-name <product-name> --build-target ecmascript/ic/tests:host_unittest

Boundaries

• ICRuntime is a transient stack object created per property access operation.
• IC state transitions (Mono → Poly → Mega) are irreversible; Mega IC cannot downgrade.
• Prototype chain changes must invalidate relevant ICs via ProtoChangeDetails.
• ICHandler values must fit within JSTaggedValue size for inline fast path; complex cases use TaggedObject.
• IC slots are indexed by bytecode slot ID; ensure frontend and runtime slot numbering consistency.