Skip to content

Ensure all unused elements are removed during applyDCEGraphRemovals. NFC #21840

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Apr 30, 2024
Merged

Ensure all unused elements are removed during applyDCEGraphRemovals. NFC #21840

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
36 changes: 14 additions & 22 deletions test/optimizer/applyDCEGraphRemovals-output.js
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -5,38 +5,30 @@ var wasmImports = {
save2: 2
};

var expD1 = Module["expD1"] = wasmExports["expD1"];
var _expD1 = Module["_expD1"] = wasmExports["expD1"];

var expD2 = Module["expD2"] = wasmExports["expD2"];
var _expD2 = Module["_expD2"] = wasmExports["expD2"];

var expD3 = Module["expD3"] = wasmExports["expD3"];
var _expD3 = Module["_expD3"] = wasmExports["expD3"];

var expD4;
var _expD5 = wasmExports["expD5"];

var expD5 = wasmExports["expD5"];
var _expI1 = Module["_expI1"] = () => (expI1 = Module["_expI1"] = wasmExports["expI1"])();

var expD6;
var _expI2 = Module["_expI2"] = () => (expI2 = Module["_expI2"] = wasmExports["expI2"])();

var expI1 = Module["expI1"] = () => (expI1 = Module["expI1"] = wasmExports["expI1"])();
var _expI3 = Module["_expI3"] = () => (expI3 = Module["_expI3"] = wasmExports["expI3"])();

var expI2 = Module["expI2"] = () => (expI2 = Module["expI2"] = wasmExports["expI2"])();
var _expI5 = () => (_expI5 = wasmExports["expI5"])();

var expI3 = Module["expI3"] = () => (expI3 = Module["expI3"] = wasmExports["expI3"])();
_expD1;

var expI4;
Module["_expD2"];

var expI5 = () => (expI5 = wasmExports["expI5"])();
wasmExports["_expD3"];

var expI6;
_expI1;

expD1;
Module["_expI2"];

Module["expD2"];

wasmExports["expD3"];

expI1;

Module["expI2"];

wasmExports["expI3"];
wasmExports["_expI3"];
46 changes: 26 additions & 20 deletions test/optimizer/applyDCEGraphRemovals.js
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,32 +1,38 @@
var name;
var wasmImports = { save1: 1, number: 33, name: name, func: function() {}, save2: 2 };
var wasmImports = {
save1: 1,
number: 33,
name: name,
func: function() {},
save2: 2
};

// exports gotten directly
var expD1 = Module['expD1'] = wasmExports['expD1'];
var expD2 = Module['expD2'] = wasmExports['expD2'];
var expD3 = Module['expD3'] = wasmExports['expD3'];
var expD4 = Module['expD4'] = wasmExports['expD4'];
var _expD1 = Module['_expD1'] = wasmExports['expD1'];
var _expD2 = Module['_expD2'] = wasmExports['expD2'];
var _expD3 = Module['_expD3'] = wasmExports['expD3'];
var _expD4 = Module['_expD4'] = wasmExports['expD4'];
// Like above, but not exported on the Module
var expD5 = wasmExports['expD5'];
var expD6 = wasmExports['expD6'];
var _expD5 = wasmExports['expD5'];
var _expD6 = wasmExports['expD6'];

// exports gotten indirectly (async compilation
var expI1 = Module['expI1'] = () => (expI1 = Module['expI1'] = wasmExports['expI1'])();
var expI2 = Module['expI2'] = () => (expI2 = Module['expI2'] = wasmExports['expI2'])();
var expI3 = Module['expI3'] = () => (expI3 = Module['expI3'] = wasmExports['expI3'])();
var expI4 = Module['expI4'] = () => (expI4 = Module['expI4'] = wasmExports['expI4'])();
var _expI1 = Module['_expI1'] = () => (expI1 = Module['_expI1'] = wasmExports['expI1'])();
var _expI2 = Module['_expI2'] = () => (expI2 = Module['_expI2'] = wasmExports['expI2'])();
var _expI3 = Module['_expI3'] = () => (expI3 = Module['_expI3'] = wasmExports['expI3'])();
var _expI4 = Module['_expI4'] = () => (expI4 = Module['_expI4'] = wasmExports['expI4'])();

// Like above, but not exported on the Module
var expI5 = () => (expI5 = wasmExports['expI5'])();
var expI6 = () => (expI6 = wasmExports['expI6'])();
var _expI5 = () => (_expI5 = wasmExports['expI5'])();
var _expI6 = () => (_expI6 = wasmExports['expI6'])();

// add uses for some of them, leave *4 as non-roots
expD1;
Module['expD2'];
wasmExports['expD3'];
_expD1;
Module['_expD2'];
wasmExports['_expD3'];

expI1;
Module['expI2'];
wasmExports['expI3'];
_expI1;
Module['_expI2'];
wasmExports['_expI3'];

// EXTRA_INFO: { "unused": ["emcc$import$number", "emcc$import$name", "emcc$import$func", "emcc$export$expD4", "emcc$export$expD6", "emcc$export$expI4", "emcc$export$expI6"] }
// EXTRA_INFO: { "unusedImports": ["number", "name", "func"], "unusedExports": ["expD4", "expD6", "expI4", "expI6"] }
12 changes: 6 additions & 6 deletions test/optimizer/minimal-runtime-applyDCEGraphRemovals-output.js
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -7,15 +7,15 @@ var wasmImports = {

WebAssembly.instantiate(Module["wasm"], imports).then(output => {
wasmExports = output.instance.exports;
expD1 = wasmExports["expD1"];
expD2 = wasmExports["expD2"];
expD3 = wasmExports["expD3"];
_expD1 = wasmExports["expD1"];
_expD2 = wasmExports["expD2"];
_expD3 = wasmExports["expD3"];
initRuntime(wasmExports);
ready();
});

expD1;
_expD1;

Module["expD2"];
Module["_expD2"];

wasmExports["expD3"];
wasmExports["_expD3"];
24 changes: 15 additions & 9 deletions test/optimizer/minimal-runtime-applyDCEGraphRemovals.js
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,20 +1,26 @@
var name;
var wasmImports = { save1: 1, number: 33, name: name, func: function() {}, save2: 2 };
var wasmImports = {
save1: 1,
number: 33,
name: name,
func: function() {},
save2: 2
};

// exports gotten directly in the minimal runtime style
WebAssembly.instantiate(Module["wasm"], imports).then((output) => {
wasmExports = output.instance.exports;
expD1 = wasmExports['expD1'];
expD2 = wasmExports['expD2'];
expD3 = wasmExports['expD3'];
expD4 = wasmExports['expD4'];
_expD1 = wasmExports['expD1'];
_expD2 = wasmExports['expD2'];
_expD3 = wasmExports['expD3'];
_expD4 = wasmExports['expD4'];
initRuntime(wasmExports);
ready();
});

// add uses for some of them, leave *4 as non-roots
expD1;
Module['expD2'];
wasmExports['expD3'];
_expD1;
Module['_expD2'];
wasmExports['_expD3'];

// EXTRA_INFO: { "unused": ["emcc$import$number", "emcc$import$name", "emcc$import$func", "emcc$export$expD4", "emcc$export$expI4"] }
// EXTRA_INFO: { "unusedImports": ["number", "name", "func"], "unusedExports": ["expD4"] }
125 changes: 73 additions & 52 deletions tools/acorn-optimizer.mjs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -89,14 +89,6 @@ function emptyOut(node) {
node.type = 'EmptyStatement';
}

// This converts the node into something that terser will ignore in a var
// declaration, that is, it is a way to get rid of initial values.
function convertToNothingInVarInit(node) {
node.type = 'Literal';
node.value = undefined;
node.raw = 'undefined';
}

function convertToNullStatement(node) {
node.type = 'ExpressionStatement';
node.expression = {
Expand Down Expand Up @@ -591,18 +583,25 @@ function isDynamicDynCall(node) {

//
// Matches the wasm export wrappers generated by emcc (see make_export_wrappers
// in emscripten.py). For example:
// in emscripten.py). For example, the right hand side of these assignments:
//
// var _foo = (a0, a1) => (_foo = wasmExports['foo'])(a0, a1):
//
// or
//
// var _foo = (a0, a1) => (_foo = Module['_foo'] = wasmExports['foo'])(a0, a1):
//
function isExportWrapperFunction(f) {
if (f.body.type != 'CallExpression') return null;
let callee = f.body.callee;
if (callee.type == 'ParenthesizedExpression') {
callee = callee.expression;
}
if (callee.type != 'AssignmentExpression' || callee.right.type != 'MemberExpression') return null;
if (callee.type != 'AssignmentExpression') return null;
var rhs = callee.right;
if (rhs.type == 'AssignmentExpression') {
rhs = rhs.right;
}
if (rhs.type != 'MemberExpression' || !isExportUse(rhs)) return null;
return getExportOrModuleUseName(rhs);
}
Expand Down Expand Up @@ -740,7 +739,9 @@ function emitDCEGraph(ast) {
emptyOut(node);
} else if (value && value.type === 'ArrowFunctionExpression') {
// this is
// var x = () => (x = wasmExports['x'])(..)
// () => (x = wasmExports['x'])(..)
// or
// () => (x = Module['_x'] = wasmExports['x'])(..)
let asmName = isExportWrapperFunction(value);
if (asmName) {
saveAsmExport(name, asmName);
Expand Down Expand Up @@ -978,67 +979,84 @@ function emitDCEGraph(ast) {
// way (and we leave further DCE on the JS and wasm sides to their respective
// optimizers, closure compiler and binaryen).
function applyDCEGraphRemovals(ast) {
const unused = new Set(extraInfo.unused);
const unusedExports = new Set(extraInfo.unusedExports);
const unusedImports = new Set(extraInfo.unusedImports);
const foundUnusedImports = new Set();
const foundUnusedExports = new Set();
trace('unusedExports:', unusedExports);
trace('unusedImports:', unusedImports);

fullWalk(ast, (node) => {
if (isWasmImportsAssign(node)) {
const assignedObject = getWasmImportsValue(node);
assignedObject.properties = assignedObject.properties.filter((item) => {
const name = item.key.name;
const value = item.value;
const full = 'emcc$import$' + name;
return !(unused.has(full) && !hasSideEffects(value));
});
} else if (node.type === 'AssignmentExpression') {
// when we assign to a thing we don't need, we can just remove the assign
// var x = Module['x'] = wasmExports['x'];
const target = node.left;
if (isExportUse(target) || isModuleUse(target)) {
const name = getExportOrModuleUseName(target);
const full = 'emcc$export$' + name;
const value = node.right;
if (unused.has(full) && (isExportUse(value) || !hasSideEffects(value))) {
// This will be in a var init, and we just remove that value.
convertToNothingInVarInit(node);
if (unusedImports.has(name)) {
foundUnusedImports.add(name);
return hasSideEffects(value);
}
}
return true;
});
} else if (node.type === 'VariableDeclaration') {
// Handle the case we declare a variable but don't assign to the module:
// var x = wasmExports['x'];
// and
// var x = () => (x = wasmExports['x']).apply(...);
// Handle the various ways in which we extract wasmExports:
// 1. var _x = wasmExports['x'];
// or
// 2. var _x = Module['_x'] = wasmExports['x'];
//
// Or for delayed instantiation:
// 3. var _x = () => (_x = wasmExports['x'])(...);
// or
// 4. var _x = Module['_x] = () => (_x = Module['_x'] = wasmExports['x'])(...);
const init = node.declarations[0].init;
if (init) {
if (isExportUse(init)) {
const name = getExportOrModuleUseName(init);
const full = 'emcc$export$' + name;
if (unused.has(full)) {
convertToNothingInVarInit(init);
}
} else if (init.type == 'ArrowFunctionExpression') {
const name = isExportWrapperFunction(init);
const full = 'emcc$export$' + name;
if (unused.has(full)) {
convertToNothingInVarInit(init);
}
if (!init) {
return;
}

// Look through the optional `Module['_x']`
let realInit = init;
if (init.type == 'AssignmentExpression' && isModuleUse(init.left)) {
realInit = init.right;
}

if (isExportUse(realInit)) {
const export_name = getExportOrModuleUseName(realInit);
if (unusedExports.has(export_name)) {
// Case (1) and (2)
trace('found unused export:', export_name);
emptyOut(node);
foundUnusedExports.add(export_name);
}
} else if (realInit.type == 'ArrowFunctionExpression') {
const export_name = isExportWrapperFunction(realInit);
if (unusedExports.has(export_name)) {
// Case (3) and (4)
trace('found unused export:', export_name);
emptyOut(node);
foundUnusedExports.add(export_name);
}
}
} else if (node.type === 'ExpressionStatement') {
const expr = node.expression;
// In the MINIMAL_RUNTIME code pattern we have just
// x = wasmExports['x']
// _x = wasmExports['x']
// and never in a var.
if (expr.operator === '=' && expr.left.type === 'Identifier' && isExportUse(expr.right)) {
const name = expr.left.name;
if (name === getExportOrModuleUseName(expr.right)) {
const full = 'emcc$export$' + name;
if (unused.has(full)) {
emptyOut(node);
}
const export_name = getExportOrModuleUseName(expr.right);
if (unusedExports.has(export_name)) {
emptyOut(node);
foundUnusedExports.add(export_name);
}
}
}
});

for (const i of unusedImports) {
assert(foundUnusedImports.has(i), 'unused import not found: ' + i);
}
for (const e of unusedExports) {
assert(foundUnusedExports.has(e), 'unused export not found: ' + e);
}
}

// Need a parser to pass to acorn.Node constructor.
Expand Down Expand Up @@ -2050,7 +2068,10 @@ const registry = {
minifyGlobals: minifyGlobals,
};

passes.forEach((pass) => registry[pass](ast));
passes.forEach((pass) => {
trace(`running AST pass: ${pass}`);
registry[pass](ast);
});

if (!noPrint) {
const terserAst = terser.AST_Node.from_mozilla_ast(ast);
Expand Down
Loading