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[compiler] Prune all unused array destructure items during DCE #31619

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Nov 22, 2024
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,6 @@
*/

import {
ArrayPattern,
BlockId,
HIRFunction,
Identifier,
Expand Down Expand Up @@ -184,29 +183,28 @@ function rewriteInstruction(instr: Instruction, state: State): void {
switch (instr.value.lvalue.pattern.kind) {
case 'ArrayPattern': {
/*
* For arrays, we can only eliminate unused items from the end of the array,
* so we iterate from the end and break once we find a used item. Note that
* we already know at least one item is used, from the pruneableValue check.
* For arrays, we can prune items prior to the end by replacing
* them with a hole. Items at the end can simply be dropped.
*/
let nextItems: ArrayPattern['items'] | null = null;
const originalItems = instr.value.lvalue.pattern.items;
for (let i = originalItems.length - 1; i >= 0; i--) {
const item = originalItems[i];
let lastEntryIndex = 0;
const items = instr.value.lvalue.pattern.items;
for (let i = 0; i < items.length; i++) {
const item = items[i];
if (item.kind === 'Identifier') {
if (state.isIdOrNameUsed(item.identifier)) {
nextItems = originalItems.slice(0, i + 1);
break;
if (!state.isIdOrNameUsed(item.identifier)) {
items[i] = {kind: 'Hole'};
} else {
lastEntryIndex = i;
}
} else if (item.kind === 'Spread') {
if (state.isIdOrNameUsed(item.place.identifier)) {
nextItems = originalItems.slice(0, i + 1);
break;
if (!state.isIdOrNameUsed(item.place.identifier)) {
items[i] = {kind: 'Hole'};
} else {
lastEntryIndex = i;
}
}
}
if (nextItems !== null) {
instr.value.lvalue.pattern.items = nextItems;
}
items.length = lastEntryIndex + 1;
break;
}
case 'ObjectPattern': {
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ function component() {
import { c as _c } from "react/compiler-runtime";
function component() {
const $ = _c(1);
const [x, setX] = useState(0);
const [, setX] = useState(0);
let t0;
if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
const handler = (v) => setX(v);
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -35,8 +35,7 @@ function Component(props) {
}
let d;
if ($[2] !== props.c) {
const [c, ...t0] = props.c;
d = t0;
[, ...d] = props.c;
$[2] = props.c;
$[3] = d;
} else {
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,7 @@ function Component(props) {
import { c as _c } from "react/compiler-runtime";
function Component(props) {
const $ = _c(2);
const [value, setValue] = useState(null);
const [, setValue] = useState(null);
let t0;
if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
t0 = (e) => setValue((value_0) => value_0 + e.target.value);
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -39,7 +39,7 @@ import { useState } from "react";

function Component(props) {
const $ = _c(1);
const [_state, setState] = useState();
const [, setState] = useState();
let t0;
if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
const a = () => b();
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,7 @@ import { useCallback, useTransition } from "react";

function useFoo() {
const $ = _c(1);
const [t, start] = useTransition();
const [, start] = useTransition();
let t0;
if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
t0 = () => {
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -32,7 +32,7 @@ function Component(props) {
const $ = _c(5);
React.useContext(FooContext);
const ref = React.useRef();
const [x, setX] = React.useState(false);
const [, setX] = React.useState(false);
let t0;
if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
t0 = () => {
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -61,8 +61,8 @@ import { useState } from "react";

function Component(props) {
const $ = _c(5);
const [x, setX] = useState(false);
const [y, setY] = useState(false);
const [, setX] = useState(false);
const [, setY] = useState(false);
let setState;
if (props.cond) {
setState = setX;
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -52,8 +52,7 @@ function Component(props) {
const { buttons } = props;
let nonPrimaryButtons;
if ($[0] !== buttons) {
const [primaryButton, ...t0] = buttons;
nonPrimaryButtons = t0;
[, ...nonPrimaryButtons] = buttons;
$[0] = buttons;
$[1] = nonPrimaryButtons;
} else {
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ export const FIXTURE_ENTRYPOINT = {

```javascript
function foo(props) {
const [x, unused, y] = props.a;
const [x, , y] = props.a;
return x + y;
}

Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@ import { useActionState } from "react";

function Component() {
const $ = _c(1);
const [actionState, dispatchAction] = useActionState();
const [, dispatchAction] = useActionState();
let t0;
if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
const onSubmitAction = () => {
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,7 @@ import { useReducer } from "react";

function f() {
const $ = _c(1);
const [state, dispatch] = useReducer();
const [, dispatch] = useReducer();
let t0;
if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
const onClick = () => {
Expand Down
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