FindLastUsageVisitor Class — react Architecture

Source Code

compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/MergeReactiveScopesThatInvalidateTogether.ts lines 101–119

class FindLastUsageVisitor extends ReactiveFunctionVisitor<void> {
  /*
   * TODO LeaveSSA: use IdentifierId for more precise tracking
   * Using DeclarationId is necessary for compatible output but produces suboptimal results
   * in cases where a scope defines a variable, but that version is never read and always
   * overwritten later.
   * see reassignment-separate-scopes.js for example
   */
  lastUsage: Map<DeclarationId, InstructionId> = new Map();

  override visitPlace(id: InstructionId, place: Place, _state: void): void {
    const previousUsage = this.lastUsage.get(place.identifier.declarationId);
    const lastUsage =
      previousUsage !== undefined
        ? makeInstructionId(Math.max(previousUsage, id))
        : id;
    this.lastUsage.set(place.identifier.declarationId, lastUsage);
  }
}