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Optimize substring handling in js::SubstringKernel by caching leftChild length

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wuggy 2026-04-22 03:35:52 -07:00
commit 2c30d61740
1 changed files with 8 additions and 7 deletions
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15
js/src/jsstr.cpp
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@ -564,14 +564,15 @@ js::SubstringKernel(JSContext* cx, HandleString str, int32_t beginInt, int32_t l
*/ */
if (str->isRope()) { if (str->isRope()) {
JSRope* rope = &str->asRope(); JSRope* rope = &str->asRope();
size_t leftLength = rope->leftChild()->length();
/* Substring is totally in leftChild of rope. */ /* Substring is totally in leftChild of rope. */
if (begin + len <= rope->leftChild()->length()) if (begin + len <= leftLength)
return NewDependentString(cx, rope->leftChild(), begin, len); return NewDependentString(cx, rope->leftChild(), begin, len);
/* Substring is totally in rightChild of rope. */ /* Substring is totally in rightChild of rope. */
if (begin >= rope->leftChild()->length()) { if (begin >= leftLength) {
begin -= rope->leftChild()->length(); begin -= leftLength;
return NewDependentString(cx, rope->rightChild(), begin, len); return NewDependentString(cx, rope->rightChild(), begin, len);
} }
@ -579,11 +580,11 @@ js::SubstringKernel(JSContext* cx, HandleString str, int32_t beginInt, int32_t l
* Requested substring is partly in the left and partly in right child. * Requested substring is partly in the left and partly in right child.
* Create a rope of substrings for both childs. * Create a rope of substrings for both childs.
*/ */
MOZ_ASSERT(begin < rope->leftChild()->length() && MOZ_ASSERT(begin < leftLength &&
begin + len > rope->leftChild()->length()); begin + len > leftLength);
size_t lhsLength = rope->leftChild()->length() - begin; size_t lhsLength = leftLength - begin;
size_t rhsLength = begin + len - rope->leftChild()->length(); size_t rhsLength = begin + len - leftLength;
Rooted<JSRope*> ropeRoot(cx, rope); Rooted<JSRope*> ropeRoot(cx, rope);
RootedString lhs(cx, NewDependentString(cx, ropeRoot->leftChild(), begin, lhsLength)); RootedString lhs(cx, NewDependentString(cx, ropeRoot->leftChild(), begin, lhsLength));