| 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 { |
| 9 | HIRFunction, |
| 10 | InstructionId, |
| 11 | Place, |
| 12 | ReactiveScope, |
| 13 | makeInstructionId, |
| 14 | } from '.'; |
| 15 | import {getPlaceScope} from '../HIR/HIR'; |
| 16 | import {isMutable} from '../ReactiveScopes/InferReactiveScopeVariables'; |
| 17 | import DisjointSet from '../Utils/DisjointSet'; |
| 18 | import {getOrInsertDefault} from '../Utils/utils'; |
| 19 | import { |
| 20 | eachInstructionLValue, |
| 21 | eachInstructionOperand, |
| 22 | eachTerminalOperand, |
| 23 | } from './visitors'; |
| 24 | |
| 25 | /** |
| 26 | * While previous passes ensure that reactive scopes span valid sets of program |
| 27 | * blocks, pairs of reactive scopes may still be inconsistent with respect to |
| 28 | * each other. |
| 29 | * |
| 30 | * (a) Reactive scopes ranges must form valid blocks in the resulting javascript |
| 31 | * program. Any two scopes must either be entirely disjoint or one scope must be |
| 32 | * nested within the other. |
| 33 | * ```js |
| 34 | * // Scopes 1:3 and 3:5 are valid because they contain no common instructions |
| 35 | * [1] ⌝ |
| 36 | * [2] ⌟ |
| 37 | * [3] ⌝ |
| 38 | * [4] ⌟ |
| 39 | * // Scopes 1:3 and 1:5 are valid because the former is nested within the other |
| 40 | * [1] ⌝ ⌝ |
| 41 | * [2] ⌟ | |
| 42 | * [3] | |
| 43 | * [4] ⌟ |
| 44 | * // Scopes 1:4 and 2:5 are invalid because we cannot produce if-else memo |
| 45 | * // blocks representing these scopes in the output program. |
| 46 | * [1] ⌝ |
| 47 | * [2] | ⌝ |
| 48 | * [3] ⌟ | |
| 49 | * [4] ⌟ |
| 50 | * ``` |
| 51 | * |
| 52 | * (b) A scope's own instructions may only mutate that scope. |
| 53 | * For each reactive scope, we currently produce exactly one if-block which |
| 54 | * spans the instruction range of the scope. In this simple example, instr [2] |
| 55 | * does not mutate any values but is included within scope @0. |
| 56 | * ```js |
| 57 | * // IR instructions |
| 58 | * [1] (writes to scope @0's values) |
| 59 | * [2] (does not mutate anything) |
| 60 | * [3] (writes to scope @0's values) |
| 61 | * |
| 62 | * // javascript output |
| 63 | * if (( scope @0's dependencies changed )) { |
| 64 | * [1] |
| 65 | * [2] |
| 66 | * [3] |
| 67 | * } |
| 68 | * ``` |
| 69 | * Nested scopes may be modeled as a tree in which child scopes are contained |
| 70 | * within parent scopes. This corresponds to nested if-else memo blocks in the |
| 71 | * output program). An instruction may only mutate its own "active" scope. |
| 72 | * ```js |
| 73 | * // Active scopes for a simple program |
| 74 | * scope @0 { |
| 75 | * [0] (active scope=@0) |
| 76 | * scope @1 { |
| 77 | * [1] (active scope=@1) |
| 78 | * [2] (active scope=@1) |
| 79 | * } |
| 80 | * [3] (active scope=@0) |
| 81 | * } |
| 82 | * [4] (no active scope) |
| 83 | * |
| 84 | * // In this example, scopes @0 and @1 must be merged because instr [2]'s |
| 85 | * // active scope is scope@1 but it mutates scope@0. |
| 86 | * scope @0, produces x { |
| 87 | * [0] x = [] |
| 88 | * scope @1, produces y { |
| 89 | * [1] y = [] |
| 90 | * [2] x.push(2) |
| 91 | * [3] y.push(3) |
| 92 | * } |
| 93 | * [3] x.push(1) |
| 94 | * } |
| 95 | * ``` |
| 96 | * |
| 97 | * As mentioned, these constraints arise entirely from the current design of |
| 98 | * compiler output. |
| 99 | * - instruction ordering is preserved (otherwise, disjoint ranges for scopes |
| 100 | * may be produced by reordering their mutating instructions) |
| 101 | * - exactly one if-else block per scope, which does not allow the composition |
| 102 | * of a reactive scope from disconnected instruction ranges. |
| 103 | */ |
| 104 | |
| 105 | export function mergeOverlappingReactiveScopesHIR(fn: HIRFunction): void { |
| 106 | /** |
| 107 | * Collect all scopes eagerly because some scopes begin before the first |
| 108 | * instruction that references them (due to alignReactiveScopesToBlocks) |
| 109 | */ |
| 110 | const scopesInfo = collectScopeInfo(fn); |
| 111 | |
| 112 | /** |
| 113 | * Iterate through scopes and instructions to find which should be merged |
| 114 | */ |
| 115 | const joinedScopes = getOverlappingReactiveScopes(fn, scopesInfo); |
| 116 | |
| 117 | /** |
| 118 | * Merge scopes and rewrite all references |
| 119 | */ |
| 120 | joinedScopes.forEach((scope, groupScope) => { |
| 121 | if (scope !== groupScope) { |
| 122 | groupScope.range.start = makeInstructionId( |
| 123 | Math.min(groupScope.range.start, scope.range.start), |
| 124 | ); |
| 125 | groupScope.range.end = makeInstructionId( |
| 126 | Math.max(groupScope.range.end, scope.range.end), |
| 127 | ); |
| 128 | } |
| 129 | }); |
| 130 | for (const [place, originalScope] of scopesInfo.placeScopes) { |
| 131 | const nextScope = joinedScopes.find(originalScope); |
| 132 | if (nextScope !== null && nextScope !== originalScope) { |
| 133 | place.identifier.scope = nextScope; |
| 134 | } |
| 135 | } |
| 136 | } |
| 137 | |
| 138 | type ScopeInfo = { |
| 139 | scopeStarts: Array<{id: InstructionId; scopes: Set<ReactiveScope>}>; |
| 140 | scopeEnds: Array<{id: InstructionId; scopes: Set<ReactiveScope>}>; |
| 141 | placeScopes: Map<Place, ReactiveScope>; |
| 142 | }; |
| 143 | |
| 144 | type TraversalState = { |
| 145 | joined: DisjointSet<ReactiveScope>; |
| 146 | activeScopes: Array<ReactiveScope>; |
| 147 | }; |
| 148 | |
| 149 | function collectScopeInfo(fn: HIRFunction): ScopeInfo { |
| 150 | const scopeStarts: Map<InstructionId, Set<ReactiveScope>> = new Map(); |
| 151 | const scopeEnds: Map<InstructionId, Set<ReactiveScope>> = new Map(); |
| 152 | const placeScopes: Map<Place, ReactiveScope> = new Map(); |
| 153 | |
| 154 | function collectPlaceScope(place: Place): void { |
| 155 | const scope = place.identifier.scope; |
| 156 | if (scope != null) { |
| 157 | placeScopes.set(place, scope); |
| 158 | /** |
| 159 | * Record both mutating and non-mutating scopes to merge scopes with |
| 160 | * still-mutating values with inner scopes that alias those values |
| 161 | * (see `nonmutating-capture-in-unsplittable-memo-block`) |
| 162 | * |
| 163 | * Note that this isn't perfect, as it also leads to merging of mutating |
| 164 | * scopes with JSX single-instruction scopes (see `mutation-within-jsx`) |
| 165 | */ |
| 166 | if (scope.range.start !== scope.range.end) { |
| 167 | getOrInsertDefault(scopeStarts, scope.range.start, new Set()).add( |
| 168 | scope, |
| 169 | ); |
| 170 | getOrInsertDefault(scopeEnds, scope.range.end, new Set()).add(scope); |
| 171 | } |
| 172 | } |
| 173 | } |
| 174 | |
| 175 | for (const [, block] of fn.body.blocks) { |
| 176 | for (const instr of block.instructions) { |
| 177 | for (const operand of eachInstructionLValue(instr)) { |
| 178 | collectPlaceScope(operand); |
| 179 | } |
| 180 | for (const operand of eachInstructionOperand(instr)) { |
| 181 | collectPlaceScope(operand); |
| 182 | } |
| 183 | } |
| 184 | for (const operand of eachTerminalOperand(block.terminal)) { |
| 185 | collectPlaceScope(operand); |
| 186 | } |
| 187 | } |
| 188 | |
| 189 | return { |
| 190 | scopeStarts: [...scopeStarts.entries()] |
| 191 | .map(([id, scopes]) => ({id, scopes})) |
| 192 | .sort((a, b) => b.id - a.id), |
| 193 | scopeEnds: [...scopeEnds.entries()] |
| 194 | .map(([id, scopes]) => ({id, scopes})) |
| 195 | .sort((a, b) => b.id - a.id), |
| 196 | placeScopes, |
| 197 | }; |
| 198 | } |
| 199 | |
| 200 | function visitInstructionId( |
| 201 | id: InstructionId, |
| 202 | {scopeEnds, scopeStarts}: ScopeInfo, |
| 203 | {activeScopes, joined}: TraversalState, |
| 204 | ): void { |
| 205 | /** |
| 206 | * Handle all scopes that end at this instruction. |
| 207 | */ |
| 208 | const scopeEndTop = scopeEnds.at(-1); |
| 209 | if (scopeEndTop != null && scopeEndTop.id <= id) { |
| 210 | scopeEnds.pop(); |
| 211 | |
| 212 | /** |
| 213 | * Match scopes that end at this instruction with our stack of active |
| 214 | * scopes (from traversal state). We need to sort these in descending |
| 215 | * order of start IDs because the scopes stack is ordered as such |
| 216 | */ |
| 217 | const scopesSortedStartDescending = [...scopeEndTop.scopes].sort( |
| 218 | (a, b) => b.range.start - a.range.start, |
| 219 | ); |
| 220 | for (const scope of scopesSortedStartDescending) { |
| 221 | const idx = activeScopes.indexOf(scope); |
| 222 | if (idx !== -1) { |
| 223 | /** |
| 224 | * Detect and merge all overlapping scopes. `activeScopes` is ordered |
| 225 | * by scope start, so every active scope between a completed scope s |
| 226 | * and the top of the stack (1) started later than s and (2) completes after s. |
| 227 | */ |
| 228 | if (idx !== activeScopes.length - 1) { |
| 229 | joined.union([scope, ...activeScopes.slice(idx + 1)]); |
| 230 | } |
| 231 | activeScopes.splice(idx, 1); |
| 232 | } |
| 233 | } |
| 234 | } |
| 235 | |
| 236 | /** |
| 237 | * Handle all scopes that begin at this instruction by adding them |
| 238 | * to the scopes stack |
| 239 | */ |
| 240 | const scopeStartTop = scopeStarts.at(-1); |
| 241 | if (scopeStartTop != null && scopeStartTop.id <= id) { |
| 242 | scopeStarts.pop(); |
| 243 | |
| 244 | const scopesSortedEndDescending = [...scopeStartTop.scopes].sort( |
| 245 | (a, b) => b.range.end - a.range.end, |
| 246 | ); |
| 247 | activeScopes.push(...scopesSortedEndDescending); |
| 248 | /** |
| 249 | * Merge all identical scopes (ones with the same start and end), |
| 250 | * as they end up with the same reactive block |
| 251 | */ |
| 252 | for (let i = 1; i < scopesSortedEndDescending.length; i++) { |
| 253 | const prev = scopesSortedEndDescending[i - 1]; |
| 254 | const curr = scopesSortedEndDescending[i]; |
| 255 | if (prev.range.end === curr.range.end) { |
| 256 | joined.union([prev, curr]); |
| 257 | } |
| 258 | } |
| 259 | } |
| 260 | } |
| 261 | |
| 262 | function visitPlace( |
| 263 | id: InstructionId, |
| 264 | place: Place, |
| 265 | {activeScopes, joined}: TraversalState, |
| 266 | ): void { |
| 267 | /** |
| 268 | * If an instruction mutates an outer scope, flatten all scopes from the top |
| 269 | * of the stack to the mutated outer scope. |
| 270 | */ |
| 271 | const placeScope = getPlaceScope(id, place); |
| 272 | if (placeScope != null && isMutable({id}, place)) { |
| 273 | const placeScopeIdx = activeScopes.indexOf(placeScope); |
| 274 | if (placeScopeIdx !== -1 && placeScopeIdx !== activeScopes.length - 1) { |
| 275 | joined.union([placeScope, ...activeScopes.slice(placeScopeIdx + 1)]); |
| 276 | } |
| 277 | } |
| 278 | } |
| 279 | |
| 280 | function getOverlappingReactiveScopes( |
| 281 | fn: HIRFunction, |
| 282 | context: ScopeInfo, |
| 283 | ): DisjointSet<ReactiveScope> { |
| 284 | const state: TraversalState = { |
| 285 | joined: new DisjointSet<ReactiveScope>(), |
| 286 | activeScopes: [], |
| 287 | }; |
| 288 | |
| 289 | for (const [, block] of fn.body.blocks) { |
| 290 | for (const instr of block.instructions) { |
| 291 | visitInstructionId(instr.id, context, state); |
| 292 | for (const place of eachInstructionOperand(instr)) { |
| 293 | if ( |
| 294 | (instr.value.kind === 'FunctionExpression' || |
| 295 | instr.value.kind === 'ObjectMethod') && |
| 296 | place.identifier.type.kind === 'Primitive' |
| 297 | ) { |
| 298 | continue; |
| 299 | } |
| 300 | visitPlace(instr.id, place, state); |
| 301 | } |
| 302 | for (const place of eachInstructionLValue(instr)) { |
| 303 | visitPlace(instr.id, place, state); |
| 304 | } |
| 305 | } |
| 306 | visitInstructionId(block.terminal.id, context, state); |
| 307 | for (const place of eachTerminalOperand(block.terminal)) { |
| 308 | visitPlace(block.terminal.id, place, state); |
| 309 | } |
| 310 | } |
| 311 | |
| 312 | return state.joined; |
| 313 | } |