| 1 | /** |
| 2 | * Copyright (c) Meta Platforms, Inc. and affiliates. |
| 3 | * |
| 4 | * This source code is licensed under the MIT license found in the |
| 5 | * LICENSE file in the root directory of this source tree. |
| 6 | */ |
| 7 | |
| 8 | import {CompilerError} from '..'; |
| 9 | import {BlockId, GotoVariant, HIRFunction} from './HIR'; |
| 10 | |
| 11 | export function pruneUnusedLabelsHIR(fn: HIRFunction): void { |
| 12 | const merged: Array<{ |
| 13 | label: BlockId; |
| 14 | next: BlockId; |
| 15 | fallthrough: BlockId; |
| 16 | }> = []; |
| 17 | const rewrites: Map<BlockId, BlockId> = new Map(); |
| 18 | for (const [blockId, block] of fn.body.blocks) { |
| 19 | const terminal = block.terminal; |
| 20 | if (terminal.kind === 'label') { |
| 21 | const {block: nextId, fallthrough: fallthroughId} = terminal; |
| 22 | const next = fn.body.blocks.get(nextId)!; |
| 23 | const fallthrough = fn.body.blocks.get(fallthroughId)!; |
| 24 | if ( |
| 25 | next.terminal.kind === 'goto' && |
| 26 | next.terminal.variant === GotoVariant.Break && |
| 27 | next.terminal.block === fallthroughId |
| 28 | ) { |
| 29 | if (next.kind === 'block' && fallthrough.kind === 'block') { |
| 30 | // Only merge normal block types |
| 31 | merged.push({ |
| 32 | label: blockId, |
| 33 | next: nextId, |
| 34 | fallthrough: fallthroughId, |
| 35 | }); |
| 36 | } |
| 37 | } |
| 38 | } |
| 39 | } |
| 40 | |
| 41 | for (const { |
| 42 | label: originalLabelId, |
| 43 | next: nextId, |
| 44 | fallthrough: fallthroughId, |
| 45 | } of merged) { |
| 46 | const labelId = rewrites.get(originalLabelId) ?? originalLabelId; |
| 47 | const label = fn.body.blocks.get(labelId)!; |
| 48 | const next = fn.body.blocks.get(nextId)!; |
| 49 | const fallthrough = fn.body.blocks.get(fallthroughId)!; |
| 50 | |
| 51 | // Merge block and fallthrough |
| 52 | CompilerError.invariant( |
| 53 | next.phis.size === 0 && fallthrough.phis.size === 0, |
| 54 | { |
| 55 | reason: 'Unexpected phis when merging label blocks', |
| 56 | loc: label.terminal.loc, |
| 57 | }, |
| 58 | ); |
| 59 | |
| 60 | CompilerError.invariant( |
| 61 | next.preds.size === 1 && |
| 62 | fallthrough.preds.size === 1 && |
| 63 | next.preds.has(originalLabelId) && |
| 64 | fallthrough.preds.has(nextId), |
| 65 | { |
| 66 | reason: 'Unexpected block predecessors when merging label blocks', |
| 67 | loc: label.terminal.loc, |
| 68 | }, |
| 69 | ); |
| 70 | |
| 71 | label.instructions.push(...next.instructions, ...fallthrough.instructions); |
| 72 | label.terminal = fallthrough.terminal; |
| 73 | fn.body.blocks.delete(nextId); |
| 74 | fn.body.blocks.delete(fallthroughId); |
| 75 | rewrites.set(fallthroughId, labelId); |
| 76 | } |
| 77 | |
| 78 | for (const [_, block] of fn.body.blocks) { |
| 79 | for (const pred of block.preds) { |
| 80 | const rewritten = rewrites.get(pred); |
| 81 | if (rewritten != null) { |
| 82 | block.preds.delete(pred); |
| 83 | block.preds.add(rewritten); |
| 84 | } |
| 85 | } |
| 86 | } |
| 87 | } |