MergeConsecutiveBlocks.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 {
  BlockId,
  Effect,
  GeneratedSource,
  HIRFunction,
  Instruction,
  Place,
} from './HIR';
import {markPredecessors} from './HIRBuilder';
import {terminalFallthrough, terminalHasFallthrough} from './visitors';

/*
 * Merges sequences of blocks that will always execute consecutively —
 * ie where the predecessor always transfers control to the successor
 * (ie ends in a goto) and where the predecessor is the only predecessor
 * for that successor (ie, there is no other way to reach the successor).
 *
 * Note that this pass leaves value/loop blocks alone because they cannot
 * be merged without breaking the structure of the high-level terminals
 * that reference them.
 */
export function mergeConsecutiveBlocks(fn: HIRFunction): void {
  const merged = new MergedBlocks();
  const fallthroughBlocks = new Set<BlockId>();
  for (const [, block] of fn.body.blocks) {
    const fallthrough = terminalFallthrough(block.terminal);
    if (fallthrough !== null) {
      fallthroughBlocks.add(fallthrough);
    }

    for (const instr of block.instructions) {
      if (
        instr.value.kind === 'FunctionExpression' ||
        instr.value.kind === 'ObjectMethod'
      ) {
        mergeConsecutiveBlocks(instr.value.loweredFunc.func);
      }
    }

    if (
      // Can only merge blocks with a single predecessor
      block.preds.size !== 1 ||
      // Value blocks cannot merge
      block.kind !== 'block' ||
      // Merging across fallthroughs could move the predecessor out of its block scope
      fallthroughBlocks.has(block.id)
    ) {
      continue;
    }
    const originalPredecessorId = Array.from(block.preds)[0]!;
    const predecessorId = merged.get(originalPredecessorId);
    const predecessor = fn.body.blocks.get(predecessorId);
// ... (87 more lines)