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Cache the results of simple identifiers before creating substrings.

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This commit is contained in:
Daniel Rosenwasser
2021-04-22 06:06:20 +00:00
committed by GitHub
parent ba68dc89b2
commit f63733b91b
1 changed files with 29 additions and 2 deletions
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31
src/compiler/scanner.ts
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@@ -11,6 +11,14 @@ namespace ts {
return token === SyntaxKind.GreaterThanToken || tokenIsIdentifierOrKeyword(token);
}
function djb2HashFromSubstring(str: string, start: number, end: number): number {
let acc = 5381;
for (let i = start; i < end; i++) {
acc = ((acc << 5) + acc) + str.charCodeAt(i);
}
return acc;
}
export interface Scanner {
getStartPos(): number;
getToken(): SyntaxKind;
@@ -921,7 +929,6 @@ namespace ts {
// Current position (end position of text of current token)
let pos: number;
// end of text
let end: number;
@@ -931,6 +938,9 @@ namespace ts {
// Start position of text of current token
let tokenPos: number;
// A cache for simple identifiers.
let identifierTextCache!: MultiMap<number, string>;
let token: SyntaxKind;
let tokenValue!: string;
let tokenFlags: TokenFlags;
@@ -2082,10 +2092,26 @@ namespace ts {
if (isIdentifierStart(ch, languageVersion)) {
pos += charSize(ch);
while (pos < end && isIdentifierPart(ch = codePointAt(text, pos), languageVersion)) pos += charSize(ch);
tokenValue = text.substring(tokenPos, pos);
if (ch === CharacterCodes.backslash) {
tokenValue = text.substring(tokenPos, pos);
tokenValue += scanIdentifierParts();
}
else {
// We've hit the abrupt end of an Identifier's text.
// This is the "common" case where we're just able to slice into the existing text;
// however, slicing over and over might just create a lot of garbage. We'll check our cache
// to try to avoid multiple allocations.
const hash = djb2HashFromSubstring(text, tokenPos, pos);
const cachedTokenTexts = identifierTextCache.get(hash);
const cachedTokenText = cachedTokenTexts?.find(tokenText => text.startsWith(tokenText, tokenPos));
if (cachedTokenText !== undefined) {
tokenValue = cachedTokenText;
}
else {
tokenValue = text.substring(tokenPos, pos);
identifierTextCache.add(hash, tokenValue);
}
}
return getIdentifierToken();
}
}
@@ -2525,6 +2551,7 @@ namespace ts {
text = newText || "";
end = length === undefined ? text.length : start! + length;
setTextPos(start || 0);
identifierTextCache = createMultiMap<number, string>();
}
function setOnError(errorCallback: ErrorCallback | undefined) {