RewriteInstructionKindsBasedOnReassignment.ts — react Source File

Source Code

/**
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

import {CompilerError} from '../CompilerError';
import {
  DeclarationId,
  GeneratedSource,
  HIRFunction,
  InstructionKind,
  LValue,
  LValuePattern,
  Place,
} from '../HIR/HIR';
import {printPlace} from '../HIR/PrintHIR';
import {eachPatternOperand} from '../HIR/visitors';

/**
 * This pass rewrites the InstructionKind of instructions which declare/assign variables,
 * converting the first declaration to a Const/Let depending on whether it is subsequently
 * reassigned, and ensuring that subsequent reassignments are marked as a Reassign. Note
 * that declarations which were const in the original program cannot become `let`, but the
 * inverse is not true: a `let` which was reassigned in the source may be converted to a
 * `const` if the reassignment is not used and was removed by dead code elimination.
 *
 * NOTE: this is a subset of the operations previously performed by the LeaveSSA pass.
 */
export function rewriteInstructionKindsBasedOnReassignment(
  fn: HIRFunction,
): void {
  const declarations = new Map<DeclarationId, LValue | LValuePattern>();
  for (const param of fn.params) {
    let place: Place = param.kind === 'Identifier' ? param : param.place;
    if (place.identifier.name !== null) {
      declarations.set(place.identifier.declarationId, {
        kind: InstructionKind.Let,
        place,
      });
    }
  }
  for (const place of fn.context) {
    if (place.identifier.name !== null) {
      declarations.set(place.identifier.declarationId, {
        kind: InstructionKind.Let,
        place,
      });
    }
  }
  for (const [, block] of fn.body.blocks) {
    for (const instr of block.instructions) {
      const {value} = instr;
      switch (value.kind) {
        case 'DeclareLocal': {
          const lvalue = value.lvalue;
          CompilerError.invariant(
            !declarations.has(lvalue.place.identifier.declarationId),
            {
// ... (109 more lines)