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Put ThinStrings behind a flag (off by default)

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Review-Url: https://codereview.chromium.org/2663713002
Cr-Commit-Position: refs/heads/master@{#42804}
This commit is contained in:
jkummerow 2017-01-30 22:41:14 -08:00 committed by Commit bot
parent ebe9aa253c
commit daad4319c9
4 changed files with 68 additions and 41 deletions
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1
src/flag-definitions.h
View File

@ -885,6 +885,7 @@ DEFINE_INT(random_seed, 0,
"(0, the default, means to use system random).")
// objects.cc
DEFINE_BOOL(thin_strings, false, "Enable ThinString support")
DEFINE_BOOL(trace_weak_arrays, false, "Trace WeakFixedArray usage")
DEFINE_BOOL(trace_prototype_users, false,
"Trace updates to prototype user tracking")

102
src/objects.cc
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@ -16292,13 +16292,16 @@ class InternalizedStringKey : public HashTableKey {
DCHECK(string_->IsInternalizedString());
return string_;
}
// External strings get special treatment, to avoid copying their contents.
if (string_->IsExternalOneByteString()) {
return isolate->factory()
->InternalizeExternalString<ExternalOneByteString>(string_);
} else if (string_->IsExternalTwoByteString()) {
return isolate->factory()
->InternalizeExternalString<ExternalTwoByteString>(string_);
if (FLAG_thin_strings) {
// External strings get special treatment, to avoid copying their
// contents.
if (string_->IsExternalOneByteString()) {
return isolate->factory()
->InternalizeExternalString<ExternalOneByteString>(string_);
} else if (string_->IsExternalTwoByteString()) {
return isolate->factory()
->InternalizeExternalString<ExternalTwoByteString>(string_);
}
}
// Otherwise allocate a new internalized string.
return isolate->factory()->NewInternalizedStringImpl(
@ -17329,40 +17332,61 @@ Handle<String> StringTable::LookupString(Isolate* isolate,
InternalizedStringKey key(string);
Handle<String> result = LookupKey(isolate, &key);
if (string->IsExternalString()) {
if (result->IsExternalOneByteString()) {
MigrateExternalStringResource<ExternalOneByteString>(isolate, string,
result);
} else if (result->IsExternalTwoByteString()) {
MigrateExternalStringResource<ExternalTwoByteString>(isolate, string,
result);
} else {
// If the external string is duped into an existing non-external
// internalized string, free its resource (it's about to be rewritten
// into a ThinString below).
isolate->heap()->FinalizeExternalString(*string);
if (FLAG_thin_strings) {
if (string->IsExternalString()) {
if (result->IsExternalOneByteString()) {
MigrateExternalStringResource<ExternalOneByteString>(isolate, string,
result);
} else if (result->IsExternalTwoByteString()) {
MigrateExternalStringResource<ExternalTwoByteString>(isolate, string,
result);
} else {
// If the external string is duped into an existing non-external
// internalized string, free its resource (it's about to be rewritten
// into a ThinString below).
isolate->heap()->FinalizeExternalString(*string);
}
}
}
// The LookupKey() call above tries to internalize the string in-place.
// In cases where that wasn't possible (e.g. new-space strings), turn them
// into ThinStrings referring to their internalized versions now.
if (!string->IsInternalizedString()) {
DisallowHeapAllocation no_gc;
bool one_byte = result->IsOneByteRepresentation();
Handle<Map> map = one_byte ? isolate->factory()->thin_one_byte_string_map()
: isolate->factory()->thin_string_map();
int old_size = string->Size();
DCHECK(old_size >= ThinString::kSize);
string->synchronized_set_map(*map);
Handle<ThinString> thin = Handle<ThinString>::cast(string);
thin->set_actual(*result);
Address thin_end = thin->address() + ThinString::kSize;
int size_delta = old_size - ThinString::kSize;
if (size_delta != 0) {
Heap* heap = isolate->heap();
heap->CreateFillerObjectAt(thin_end, size_delta, ClearRecordedSlots::kNo);
heap->AdjustLiveBytes(*thin, -size_delta);
// The LookupKey() call above tries to internalize the string in-place.
// In cases where that wasn't possible (e.g. new-space strings), turn them
// into ThinStrings referring to their internalized versions now.
if (!string->IsInternalizedString()) {
DisallowHeapAllocation no_gc;
bool one_byte = result->IsOneByteRepresentation();
Handle<Map> map = one_byte
? isolate->factory()->thin_one_byte_string_map()
: isolate->factory()->thin_string_map();
int old_size = string->Size();
DCHECK(old_size >= ThinString::kSize);
string->synchronized_set_map(*map);
Handle<ThinString> thin = Handle<ThinString>::cast(string);
thin->set_actual(*result);
Address thin_end = thin->address() + ThinString::kSize;
int size_delta = old_size - ThinString::kSize;
if (size_delta != 0) {
Heap* heap = isolate->heap();
heap->CreateFillerObjectAt(thin_end, size_delta,
ClearRecordedSlots::kNo);
heap->AdjustLiveBytes(*thin, -size_delta);
}
}
} else { // !FLAG_thin_strings
if (string->IsConsString()) {
Handle<ConsString> cons = Handle<ConsString>::cast(string);
cons->set_first(*result);
cons->set_second(isolate->heap()->empty_string());
} else if (string->IsSlicedString()) {
STATIC_ASSERT(ConsString::kSize == SlicedString::kSize);
DisallowHeapAllocation no_gc;
bool one_byte = result->IsOneByteRepresentation();
Handle<Map> map = one_byte
? isolate->factory()->cons_one_byte_string_map()
: isolate->factory()->cons_string_map();
string->set_map(*map);
Handle<ConsString> cons = Handle<ConsString>::cast(string);
cons->set_first(*result);
cons->set_second(isolate->heap()->empty_string());
}
}
return result;

4
test/cctest/test-code-stub-assembler.cc
View File

@ -313,14 +313,14 @@ TEST(TryToName) {
ft.CheckTrue(key, expect_bailout);
}
{
if (FLAG_thin_strings) {
// TryToName(<thin string>) => internalized version.
Handle<String> s = isolate->factory()->NewStringFromAsciiChecked("foo");
Handle<String> internalized = isolate->factory()->InternalizeString(s);
ft.CheckTrue(s, expect_unique, internalized);
}
{
if (FLAG_thin_strings) {
// TryToName(<thin two-byte string>) => internalized version.
uc16 array1[] = {2001, 2002, 2003};
Vector<const uc16> str1(array1);

2
test/cctest/test-strings.cc
View File

@ -1196,6 +1196,8 @@ class OneByteVectorResource : public v8::String::ExternalOneByteStringResource {
};
TEST(InternalizeExternal) {
FLAG_thin_strings = true;
CcTest::InitializeVM();
i::Isolate* isolate = CcTest::i_isolate();
Factory* factory = isolate->factory();
// This won't leak; the external string mechanism will call Dispose() on it.