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[fix #574] deopt when binding is present in diff scope #597

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merged 4 commits into from
Aug 7, 2017
Merged

[fix #574] deopt when binding is present in diff scope #597

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f727407
[fix #574] deopt when binding is present in diff scope
vigneshshanmugam Jun 21, 2017
f1819f5
fix binding check
vigneshshanmugam Jun 22, 2017
57fe8ff
small changes
vigneshshanmugam Aug 7, 2017
483a69a
Fix detection of different scope
boopathi Aug 7, 2017
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10 changes: 10 additions & 0 deletions packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2462,4 +2462,14 @@ describe("dce-plugin", () => {
}
`
);

thePlugin(
"should deopt when binding is on different scope - issue #574",
`
function foo(v) {
if (v) var w = 10;
if (w) console.log("hello", v);
}
`
);
});
47 changes: 39 additions & 8 deletions packages/babel-plugin-minify-dead-code-elimination/src/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -187,9 +187,13 @@ module.exports = ({ types: t, traverse }) => {
) {
continue;
} else if (binding.path.isVariableDeclarator()) {
const declaration = binding.path.parentPath;
const maybeBlockParent = declaration.parentPath;
if (
binding.path.parentPath.parentPath &&
binding.path.parentPath.parentPath.isForXStatement()
maybeBlockParent &&
maybeBlockParent.isForXStatement({
left: declaration.node
})
) {
// Can't remove if in a for-in/for-of/for-await statement `for (var x in wat)`.
continue;
Expand Down Expand Up @@ -293,14 +297,10 @@ module.exports = ({ types: t, traverse }) => {
let replacementPath = binding.path;
let isReferencedBefore = false;

if (binding.referencePaths.length > 1) {
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unnecessary check.

throw new Error("Expected only one reference");
}
const refPath = binding.referencePaths[0];

if (t.isVariableDeclarator(replacement)) {
const _prevSiblings = prevSiblings(replacementPath);

// traverse ancestors of a reference checking if it's before declaration
forEachAncestor(refPath, ancestor => {
if (_prevSiblings.indexOf(ancestor) > -1) {
Expand All @@ -309,7 +309,7 @@ module.exports = ({ types: t, traverse }) => {
});

// deopt if reference is in different scope than binding
// since we don't know if it's sync or async execition
// since we don't know if it's sync or async execution
// (i.e. whether value has been assigned to a reference or not)
if (isReferencedBefore && refPath.scope !== binding.scope) {
continue;
Expand Down Expand Up @@ -774,8 +774,39 @@ module.exports = ({ types: t, traverse }) => {
const evalResult = test.evaluate();
const isPure = test.isPure();

const replacements = [];
const binding = path.scope.getBinding(test.node.name);

// Ref - https://github.com/babel/babili/issues/574
// deopt if var is declared in other scope
// if (a) { var b = blahl;} if (b) { //something }
if (
binding &&
binding.path.parentPath.isVariableDeclaration({ kind: "var" })
) {
let ifStatementParent = null;

const fnParent =
binding.path.getFunctionParent() ||
binding.path.getProgramParent();

forEachAncestor(binding.path.parentPath, parent => {
if (fnParent === parent) return;
if (parent.isIfStatement()) {
ifStatementParent = parent;
}
});

if (
ifStatementParent &&
binding.referencePaths.some(
ref => !ref.isDescendant(ifStatementParent)
)
) {
return;
}
}

const replacements = [];
if (evalResult.confident && !isPure && test.isSequenceExpression()) {
replacements.push(
t.expressionStatement(extractSequenceImpure(test))
Expand Down