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Bug 1879918 - Move NON_DEDUP_BIT to bit 15 to free up a bit r=jandem

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Differential Revision: https://phabricator.services.mozilla.com/D204836
This commit is contained in:
Steve Fink 2024-03-25 23:36:16 +00:00
parent a12e130f8d
commit 33c87443b9
3 changed files with 29 additions and 12 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

10
js/src/gc/Tenuring.cpp
View file

@ -920,6 +920,7 @@ JSString* js::gc::TenuringTracer::promoteString(JSString* src) {
// the atom. Don't do this for dependent strings because they're more
// complicated. See StringRelocationOverlay and DeduplicationStringHasher
// comments.
MOZ_ASSERT(!src->isAtom());
if (src->isLinear() && src->inStringToAtomCache() &&
src->isDeduplicatable() && !src->hasBase()) {
JSLinearString* linear = &src->asLinear();
@ -963,6 +964,7 @@ JSString* js::gc::TenuringTracer::promoteString(JSString* src) {
if (shouldTenure(zone, JS::TraceKind::String, src) &&
src->length() < MAX_DEDUPLICATABLE_STRING_LENGTH && src->isLinear() &&
src->isDeduplicatable() && stringDeDupSet.isSome()) {
src->clearBitsOnTenure();
auto p = stringDeDupSet->lookupForAdd(src);
if (p) {
// Deduplicate to the looked-up string!
@ -987,14 +989,15 @@ JSString* js::gc::TenuringTracer::promoteString(JSString* src) {
} else {
dst = allocString(src, zone, dstKind);
if (dst->isTenured()) {
dst->clearNonDeduplicatable();
src->clearBitsOnTenure();
dst->clearBitsOnTenure();
}
}
zone->stringStats.ref().noteTenured(src->allocSize());
auto* overlay = StringRelocationOverlay::forwardCell(src, dst);
MOZ_ASSERT_IF(dst->isTenured(), dst->isDeduplicatable());
MOZ_ASSERT_IF(dst->isTenured() && dst->isLinear(), dst->isDeduplicatable());
if (dst->hasBase() || dst->isRope()) {
// dst or one of its leaves might have a base that will be deduplicated.
@ -1114,7 +1117,8 @@ void js::gc::TenuringTracer::collectToStringFixedPoint() {
MOZ_ASSERT_IF(IsInsideNursery(str), !nursery().inCollectedRegion(str));
// To ensure the NON_DEDUP_BIT was reset properly.
MOZ_ASSERT_IF(str->isTenured(), str->isDeduplicatable());
MOZ_ASSERT(!str->isAtom());
MOZ_ASSERT_IF(str->isTenured() && str->isLinear(), str->isDeduplicatable());
// The nursery root base might not be forwarded before
// traceString(str). traceString(str) will forward the root

5
js/src/vm/StringType.cpp
View file

@ -411,9 +411,6 @@ void ForEachStringFlag(const JSString* str, uint32_t flags, KnownF known,
case JSString::INDEX_VALUE_BIT:
known("INDEX_VALUE_BIT");
break;
case JSString::NON_DEDUP_BIT:
known("NON_DEDUP_BIT");
break;
case JSString::IN_STRING_TO_ATOM_CACHE:
known("IN_STRING_TO_ATOM_CACHE");
break;
@ -421,7 +418,7 @@ void ForEachStringFlag(const JSString* str, uint32_t flags, KnownF known,
if (str->isRope()) {
known("FLATTEN_VISIT_RIGHT");
} else {
unknown(i);
known("NON_DEDUP_BIT");
}
break;
case JSString::FLATTEN_FINISH_NODE:

26
js/src/vm/StringType.h
View file

@ -407,8 +407,10 @@ class JSString : public js::gc::CellWithLengthAndFlags {
static const uint32_t INDEX_VALUE_BIT = js::Bit(11);
static const uint32_t INDEX_VALUE_SHIFT = 16;
// NON_DEDUP_BIT is used in string deduplication during tenuring.
static const uint32_t NON_DEDUP_BIT = js::Bit(12);
// NON_DEDUP_BIT is used in string deduplication during tenuring. This bit is
// shared with both FLATTEN_FINISH_NODE and ATOM_IS_PERMANENT_BIT, since it
// only applies to linear non-atoms.
static const uint32_t NON_DEDUP_BIT = js::Bit(15);
// If IN_STRING_TO_ATOM_CACHE is set, this string had an entry in the
// StringToAtomCache at some point. Note that GC can purge the cache without
@ -627,13 +629,27 @@ class JSString : public js::gc::CellWithLengthAndFlags {
}
MOZ_ALWAYS_INLINE
void setNonDeduplicatable() { setFlagBit(NON_DEDUP_BIT); }
void setNonDeduplicatable() {
MOZ_ASSERT(isLinear());
MOZ_ASSERT(!isAtom());
setFlagBit(NON_DEDUP_BIT);
}
// After copying a string from the nursery to the tenured heap, adjust bits
// that no longer apply.
MOZ_ALWAYS_INLINE
void clearNonDeduplicatable() { clearFlagBit(NON_DEDUP_BIT); }
void clearBitsOnTenure() {
MOZ_ASSERT(!isAtom());
clearFlagBit(NON_DEDUP_BIT | IN_STRING_TO_ATOM_CACHE);
}
// NON_DEDUP_BIT is only valid for linear non-atoms.
MOZ_ALWAYS_INLINE
bool isDeduplicatable() { return !(flags() & NON_DEDUP_BIT); }
bool isDeduplicatable() {
MOZ_ASSERT(isLinear());
MOZ_ASSERT(!isAtom());
return !(flags() & NON_DEDUP_BIT);
}
void setInStringToAtomCache() {
MOZ_ASSERT(!isAtom());