applyConstantPropagation() — react Function Reference

Source Code

compiler/packages/babel-plugin-react-compiler/src/Optimization/ConstantPropagation.ts lines 107–166

function applyConstantPropagation(
  fn: HIRFunction,
  constants: Constants,
): boolean {
  let hasChanges = false;
  for (const [, block] of fn.body.blocks) {
    /*
     * Initialize phi values if all operands have the same known constant value.
     * Note that this analysis uses a single-pass only, so it will never fill in
     * phi values for blocks that have a back-edge.
     */
    for (const phi of block.phis) {
      let value = evaluatePhi(phi, constants);
      if (value !== null) {
        constants.set(phi.place.identifier.id, value);
      }
    }

    for (let i = 0; i < block.instructions.length; i++) {
      if (block.kind === 'sequence' && i === block.instructions.length - 1) {
        /*
         * evaluating the last value of a value block can break order of evaluation,
         * skip these instructions
         */
        continue;
      }
      const instr = block.instructions[i]!;
      const value = evaluateInstruction(constants, instr);
      if (value !== null) {
        constants.set(instr.lvalue.identifier.id, value);
      }
    }

    const terminal = block.terminal;
    switch (terminal.kind) {
      case 'if': {
        const testValue = read(constants, terminal.test);
        if (testValue !== null && testValue.kind === 'Primitive') {
          hasChanges = true;
          const targetBlockId = testValue.value
            ? terminal.consequent
            : terminal.alternate;
          block.terminal = {
            kind: 'goto',
            variant: GotoVariant.Break,
            block: targetBlockId,
            id: terminal.id,
            loc: terminal.loc,
          };
        }
        break;
      }
      default: {
        // no-op
      }
    }
  }

  return hasChanges;
}