Make String::IsOneByteRepresentationUnderneath static

and non-recursive in order to let Clang inline it.
Bonus: Drop IsTwoByteRepresentationUnderneath, which was dead code
except for one test, and is semantically redundant.

Bug: chromium:910573
Change-Id: I86f1c312e93ab875b4b42101ac65ddc94b1c9518
Reviewed-on: https://chromium-review.googlesource.com/c/1369086Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58171}

src/builtins/builtins-string.cc

@@ -461,7 +461,7 @@ V8_WARN_UNUSED_RESULT static Object* ConvertCase(
   // character is also ASCII.  This is currently the case, but it
   // might break in the future if we implement more context and locale
   // dependent upper/lower conversions.
-  if (s->IsOneByteRepresentationUnderneath()) {
+  if (String::IsOneByteRepresentationUnderneath(*s)) {
     // Same length as input.
     Handle<SeqOneByteString> result =
         isolate->factory()->NewRawOneByteString(length).ToHandleChecked();

src/conversions.cc

@@ -209,7 +209,7 @@ class StringToIntHelper {
 
   bool IsOneByte() const {
     return raw_one_byte_subject_ != nullptr ||
-           subject_->IsOneByteRepresentationUnderneath();
+           String::IsOneByteRepresentationUnderneath(*subject_);
   }
 
   Vector<const uint8_t> GetOneByteVector() {

src/json-stringifier.cc

@@ -901,14 +901,14 @@ void JsonStringifier::SerializeDeferredKey(bool deferred_comma,
 void JsonStringifier::SerializeString(Handle<String> object) {
   object = String::Flatten(isolate_, object);
   if (builder_.CurrentEncoding() == String::ONE_BYTE_ENCODING) {
-    if (object->IsOneByteRepresentationUnderneath()) {
+    if (String::IsOneByteRepresentationUnderneath(*object)) {
       SerializeString_<uint8_t, uint8_t>(object);
     } else {
       builder_.ChangeEncoding();
       SerializeString(object);
     }
   } else {
-    if (object->IsOneByteRepresentationUnderneath()) {
+    if (String::IsOneByteRepresentationUnderneath(*object)) {
       SerializeString_<uint8_t, uc16>(object);
     } else {
       SerializeString_<uc16, uc16>(object);

src/objects.cc

@@ -16725,7 +16725,7 @@ MaybeHandle<String> EscapeRegExpSource(Isolate* isolate,
                                        Handle<String> source) {
   DCHECK(source->IsFlat());
   if (source->length() == 0) return isolate->factory()->query_colon_string();
-  bool one_byte = source->IsOneByteRepresentationUnderneath();
+  bool one_byte = String::IsOneByteRepresentationUnderneath(*source);
   int escapes = one_byte ? CountRequiredEscapes<uint8_t>(source)
                          : CountRequiredEscapes<uc16>(source);
   if (escapes == 0) return source;

src/objects/string-inl.h

@@ -162,33 +162,20 @@ bool String::IsTwoByteRepresentation() const {
   return (type & kStringEncodingMask) == kTwoByteStringTag;
 }
 
-bool String::IsOneByteRepresentationUnderneath() {
-  uint32_t type = map()->instance_type();
-  STATIC_ASSERT(kIsIndirectStringTag != 0);
-  STATIC_ASSERT((kIsIndirectStringMask & kStringEncodingMask) == 0);
-  DCHECK(IsFlat());
-  switch (type & (kIsIndirectStringMask | kStringEncodingMask)) {
-    case kOneByteStringTag:
-      return true;
-    case kTwoByteStringTag:
-      return false;
-    default:  // Cons, sliced, thin, strings need to go deeper.
-      return GetUnderlying()->IsOneByteRepresentationUnderneath();
-  }
-}
-
-bool String::IsTwoByteRepresentationUnderneath() {
-  uint32_t type = map()->instance_type();
-  STATIC_ASSERT(kIsIndirectStringTag != 0);
-  STATIC_ASSERT((kIsIndirectStringMask & kStringEncodingMask) == 0);
-  DCHECK(IsFlat());
-  switch (type & (kIsIndirectStringMask | kStringEncodingMask)) {
-    case kOneByteStringTag:
-      return false;
-    case kTwoByteStringTag:
-      return true;
-    default:  // Cons, sliced, thin, strings need to go deeper.
-      return GetUnderlying()->IsTwoByteRepresentationUnderneath();
+bool String::IsOneByteRepresentationUnderneath(String string) {
+  while (true) {
+    uint32_t type = string.map()->instance_type();
+    STATIC_ASSERT(kIsIndirectStringTag != 0);
+    STATIC_ASSERT((kIsIndirectStringMask & kStringEncodingMask) == 0);
+    DCHECK(string.IsFlat());
+    switch (type & (kIsIndirectStringMask | kStringEncodingMask)) {
+      case kOneByteStringTag:
+        return true;
+      case kTwoByteStringTag:
+        return false;
+      default:  // Cons, sliced, thin, strings need to go deeper.
+        string = string.GetUnderlying();
+    }
   }
 }
 

src/objects/string.h

@@ -164,9 +164,9 @@ class String : public Name {
 
   // Cons and slices have an encoding flag that may not represent the actual
   // encoding of the underlying string.  This is taken into account here.
-  // Requires: this->IsFlat()
-  inline bool IsOneByteRepresentationUnderneath();
-  inline bool IsTwoByteRepresentationUnderneath();
+  // This function is static because that helps it get inlined.
+  // Requires: string.IsFlat()
+  static inline bool IsOneByteRepresentationUnderneath(String string);
 
   // NOTE: this should be considered only a hint.  False negatives are
   // possible.

src/regexp/jsregexp.cc

@@ -410,7 +410,7 @@ int RegExpImpl::IrregexpPrepare(Isolate* isolate, Handle<JSRegExp> regexp,
   DCHECK(subject->IsFlat());
 
   // Check representation of the underlying storage.
-  bool is_one_byte = subject->IsOneByteRepresentationUnderneath();
+  bool is_one_byte = String::IsOneByteRepresentationUnderneath(*subject);
   if (!EnsureCompiledIrregexp(isolate, regexp, subject, is_one_byte)) return -1;
 
 #ifdef V8_INTERPRETED_REGEXP
@@ -436,7 +436,7 @@ int RegExpImpl::IrregexpExecRaw(Isolate* isolate, Handle<JSRegExp> regexp,
   DCHECK_LE(index, subject->length());
   DCHECK(subject->IsFlat());
 
-  bool is_one_byte = subject->IsOneByteRepresentationUnderneath();
+  bool is_one_byte = String::IsOneByteRepresentationUnderneath(*subject);
 
 #ifndef V8_INTERPRETED_REGEXP
   DCHECK(output_size >= (IrregexpNumberOfCaptures(*irregexp) + 1) * 2);
@@ -472,7 +472,7 @@ int RegExpImpl::IrregexpExecRaw(Isolate* isolate, Handle<JSRegExp> regexp,
     // being internal and external, and even between being Latin1 and UC16,
     // but the characters are always the same).
     IrregexpPrepare(isolate, regexp, subject);
-    is_one_byte = subject->IsOneByteRepresentationUnderneath();
+    is_one_byte = String::IsOneByteRepresentationUnderneath(*subject);
   } while (true);
   UNREACHABLE();
 #else  // V8_INTERPRETED_REGEXP

src/regexp/regexp-macro-assembler.cc

@@ -161,7 +161,7 @@ int NativeRegExpMacroAssembler::CheckStackGuardState(
   HandleScope handles(isolate);
   Handle<Code> code_handle(re_code, isolate);
   Handle<String> subject_handle(String::cast(ObjectPtr(*subject)), isolate);
-  bool is_one_byte = subject_handle->IsOneByteRepresentationUnderneath();
+  bool is_one_byte = String::IsOneByteRepresentationUnderneath(*subject_handle);
 
   StackLimitCheck check(isolate);
   bool js_has_overflowed = check.JsHasOverflowed();
@@ -192,7 +192,8 @@ int NativeRegExpMacroAssembler::CheckStackGuardState(
   // If we continue, we need to update the subject string addresses.
   if (return_value == 0) {
     // String encoding might have changed.
-    if (subject_handle->IsOneByteRepresentationUnderneath() != is_one_byte) {
+    if (String::IsOneByteRepresentationUnderneath(*subject_handle) !=
+        is_one_byte) {
       // If we changed between an LATIN1 and an UC16 string, the specialized
       // code cannot be used, and we need to restart regexp matching from
       // scratch (including, potentially, compiling a new version of the code).

src/uri.cc

@@ -493,7 +493,7 @@ static MaybeHandle<String> EscapePrivate(Isolate* isolate,
 MaybeHandle<String> Uri::Escape(Isolate* isolate, Handle<String> string) {
   Handle<String> result;
   string = String::Flatten(isolate, string);
-  return string->IsOneByteRepresentationUnderneath()
+  return String::IsOneByteRepresentationUnderneath(*string)
              ? EscapePrivate<uint8_t>(isolate, string)
              : EscapePrivate<uc16>(isolate, string);
 }
@@ -501,7 +501,7 @@ MaybeHandle<String> Uri::Escape(Isolate* isolate, Handle<String> string) {
 MaybeHandle<String> Uri::Unescape(Isolate* isolate, Handle<String> string) {
   Handle<String> result;
   string = String::Flatten(isolate, string);
-  return string->IsOneByteRepresentationUnderneath()
+  return String::IsOneByteRepresentationUnderneath(*string)
              ? UnescapePrivate<uint8_t>(isolate, string)
              : UnescapePrivate<uc16>(isolate, string);
 }

test/cctest/test-strings.cc

@@ -1832,9 +1832,8 @@ TEST(Regress876759) {
   CHECK(grandparent->IsOneByteRepresentation());
   CHECK(parent->IsTwoByteRepresentation());
   CHECK(sliced->IsTwoByteRepresentation());
-  // The *Underneath versions return the correct representation.
-  CHECK(sliced->IsOneByteRepresentationUnderneath());
-  CHECK(!sliced->IsTwoByteRepresentationUnderneath());
+  // The *Underneath version returns the correct representation.
+  CHECK(String::IsOneByteRepresentationUnderneath(*sliced));
 }
 
 }  // namespace test_strings