getManualMemoizationReplacement() — react Function Reference

Source Code

compiler/packages/babel-plugin-react-compiler/src/Inference/DropManualMemoization.ts lines 226–288

function getManualMemoizationReplacement(
  fn: Place,
  loc: SourceLocation,
  kind: 'useMemo' | 'useCallback',
): LoadLocal | CallExpression {
  if (kind === 'useMemo') {
    /*
     * Replace the hook callee with the fn arg.
     *
     * before:
     *   $1 = LoadGlobal useMemo       // load the useMemo global
     *   $2 = FunctionExpression ...   // memo function
     *   $3 = ArrayExpression [ ... ]  // deps array
     *   $4 = Call $1 ($2, $3 )        // invoke useMemo w fn and deps
     *
     * after:
     *   $1 = LoadGlobal useMemo       // load the useMemo global (dead code)
     *   $2 = FunctionExpression ...   // memo function
     *   $3 = ArrayExpression [ ... ]  // deps array (dead code)
     *   $4 = Call $2 ()               // invoke the memo function itself
     *
     * Note that a later pass (InlineImmediatelyInvokedFunctionExpressions) will
     * inline the useMemo callback along with any other immediately invoked IIFEs.
     */
    return {
      kind: 'CallExpression',
      callee: fn,
      /*
       * Drop the args, including the deps array which DCE will remove
       * later.
       */
      args: [],
      loc,
    };
  } else {
    /*
     * Instead of a Call, just alias the callback directly.
     *
     * before:
     *   $1 = LoadGlobal useCallback
     *   $2 = FunctionExpression ...   // the callback being memoized
     *   $3 = ArrayExpression ...      // deps array
     *   $4 = Call $1 ( $2, $3 )       // invoke useCallback
     *
     * after:
     *   $1 = LoadGlobal useCallback   // dead code
     *   $2 = FunctionExpression ...   // the callback being memoized
     *   $3 = ArrayExpression ...      // deps array (dead code)
     *   $4 = LoadLocal $2             // reference the function
     */
    return {
      kind: 'LoadLocal',
      place: {
        kind: 'Identifier',
        identifier: fn.identifier,
        effect: Effect.Unknown,
        reactive: false,
        loc,
      },
      loc,
    };
  }
}