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[JSC] Create a save point only if actually checking for "use strict"
https://bugs.webkit.org/show_bug.cgi?id=317599 rdar://180322283 Reviewed by Yusuke Suzuki. In the existing code, Parser::parseSourceElements unconditionally creates a save point. A save point is only necessary if shouldCheckForUseStrict is true, and in the majority of cases (parsing statement blocks), that flag is false and the save point is unused. Creating a save point involves copying almost 100 bytes of parser and lexer state, so let's only do that when necessary. Covered by existing tests. Canonical link: https://commits.webkit.org/315637@main
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Lines changed: 7 additions & 5 deletions

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‎Source/JavaScriptCore/parser/Parser.cpp‎

Lines changed: 7 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -408,9 +408,11 @@ template <class TreeBuilder> TreeSourceElements Parser<LexerType>::parseSourceEl
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TreeSourceElements sourceElements = context.createSourceElements();
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const Identifier* directive = nullptr;
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unsigned directiveLiteralLength = 0;
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auto savePoint = createSavePoint(context);
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std::optional<SavePoint> savePoint;
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bool shouldCheckForUseStrict = mode == CheckForStrictMode;
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if (shouldCheckForUseStrict)
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savePoint.emplace(createSavePoint(context));
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while (TreeStatement statement = parseStatementListItem(context, directive, &directiveLiteralLength)) {
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if (shouldCheckForUseStrict) {
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if (directive) {
@@ -429,7 +431,7 @@ template <class TreeBuilder> TreeSourceElements Parser<LexerType>::parseSourceEl
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semanticFailIfFalse(isValidStrictMode(), "Invalid parameters or function name in strict mode");
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}
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// Since strict mode is changed, restoring lexer state by calling next() may cause errors.
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restoreSavePoint(context, savePoint);
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restoreSavePoint(context, *savePoint);
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propagateError();
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continue;
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}
@@ -4495,7 +4497,7 @@ template <class TreeBuilder> TreeExpression Parser<LexerType>::parseConditionalE
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JSTokenLocation location(tokenLocation());
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TreeExpression cond = parseBinaryExpression(context);
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failIfFalse(cond, "Cannot parse expression");
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if (!match(QUESTION))
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if (!match(QUESTION)) [[likely]]
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return cond;
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m_parserState.nonTrivialExpressionCount++;
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m_parserState.nonLHSCount++;
@@ -4562,7 +4564,7 @@ template <class TreeBuilder> TreeExpression Parser<LexerType>::parseBinaryExpres
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context.appendBinaryExpressionInfo(operandStackDepth, current, exprStart, lastTokenEndPosition(), lastTokenEndPosition(), initialAssignments != m_parserState.assignmentCount);
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int precedence = isBinaryOperator(m_token.m_type);
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if (!precedence)
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if (!precedence) [[likely]]
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break;
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// 12.6 https://tc39.github.io/ecma262/#sec-exp-operator

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