Use ICU case conversion/transliterator for case conversion behind a flag

src/runtime/runtime-strings.cc

Index: src/runtime/runtime-strings.cc
diff --git a/src/runtime/runtime-strings.cc b/src/runtime/runtime-strings.cc
index e3b589643b474ce291a0d668f669316d8e40f2cb..33f89f42245579276edb762579d65f94470c2697 100644
--- a/src/runtime/runtime-strings.cc
+++ b/src/runtime/runtime-strings.cc
@@ -12,6 +12,11 @@
 #include "src/string-builder.h"
 #include "src/string-search.h"
 
+#ifdef V8_I18N_SUPPORT
+#include "unicode/uchar.h"
+#include "unicode/unistr.h"
+#endif
+
 namespace v8 {
 namespace internal {
 
@@ -1079,19 +1084,231 @@ MUST_USE_RESULT static Object* ConvertCase(
 }
 
 
+#ifdef V8_I18N_SUPPORT
+namespace {
+
+MUST_USE_RESULT static Handle<String> ConvertCaseICU(Handle<String> s,
+                                                     Isolate* isolate,
+                                                     bool is_to_upper) {
+  int32_t length = s->length();
+
+  // If we already have a UTF-16 string, use that, otherwise build it
+  base::SmartArrayPointer<uc16> sap;
+  const UChar* src;
+  if (StringShape(*s).IsSequentialTwoByte()) {
+    src =
+        reinterpret_cast<const UChar*>(SeqTwoByteString::cast(*s)->GetChars());
+  } else {
+    sap = s->ToWideCString(ROBUST_STRING_TRAVERSAL);
+    src = reinterpret_cast<const UChar*>(sap.get());
+  }
+
+  // This UnicodeString ctor has copy-on-write semantics. It starts as a
+  // read-only alias but the buffer is copied when it's written to.
+  icu::UnicodeString converted(0, src, length);
+  if (is_to_upper)
+    converted.toUpper();
+  else
+    converted.toLower();
+
+#if 0
+  Handle<String> result;
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+      isolate, result,
+      isolate->factory()->NewStringFromTwoByte(Vector<const uint16_t>(
+          reinterpret_cast<const uint16_t*>(converted.getBuffer()),
+          converted.length())));
+#endif
+  return isolate->factory()->NewStringFromTwoByte(Vector<const uint16_t>(
+      reinterpret_cast<const uint16_t*>(converted.getBuffer()),
+      converted.length())).ToHandleChecked();
+}
+
+
+inline bool IsASCIIUpper(uint16_t ch) { return ch >= 'A' && ch <= 'Z'; }
+
+
+inline uint16_t ToASCIILower(uint16_t ch) {
+  return ch | ((ch >= 'A' && ch <= 'Z') << 5);
+}
+
+
+inline uint16_t ToASCIIUpper(uint16_t ch) {
+  return ch & ~((ch >= 'a' && ch <= 'z') << 5);
+}
+
+
+MUST_USE_RESULT Handle<String> StringToLowerCase(Handle<String> s,
+                                                 Isolate* isolate) {
+  // Note: This is a hot function in the Dromaeo benchmark, specifically the
+  // no-op code path up through the first 'return' statement.
+
+  int length = s->length();
+  // First scan the string for uppercase and non-ASCII characters:
+  if (s->HasOnlyOneByteChars()) {
+    unsigned first_index_to_lower = length;
+    for (int index = 0; index < length; ++index) {
+      // Blink specializes this path for one-byte strings, so it
+      // does not need to do a generic get, but can do the equivalent
+      // of SeqOneByteStringGet.
+      uint16_t ch = s->Get(index);
+      if (V8_UNLIKELY(IsASCIIUpper(ch) || ch & ~0x7F)) {
+        first_index_to_lower = index;
+        break;
+      }
+    }
+
+    // Nothing to do if the string is all ASCII with no uppercase.
+    if (first_index_to_lower == length) return s;
+
+    // We depend here on the invariant that the length of a Latin1
+    // string is invariant under ToLowerCase, and the result always
+    // fits in the Latin1 range (untrue for ToUpperCase, and might
+    // be untrue in some locales, but this is the root locale)
+    Handle<SeqOneByteString> result =
+        isolate->factory()->NewRawOneByteString(length).ToHandleChecked();
+    // In Blink, this is a simple memcpy, but in V8, the path applies in
+    // more cases. The optimization here is conditional on whether the
+    // source is actually a simple 8-bit string (always true in Blink).
+    // The broader condition lets us eliminate a bunch of duplicate code
+    // which Blink had in a separate section below.
+    if (StringShape(*s).IsSequentialOneByte()) {
+      // In this path, we can use the one-byte-specific Get, and
+      // memcpy until the first_index_to_lower.
+      SeqOneByteString* source = SeqOneByteString::cast(*s);
+      memcpy(result->GetChars(), source->GetChars(), first_index_to_lower);
+      for (int index = first_index_to_lower; index < length; ++index) {
+        uint16_t ch = source->SeqOneByteStringGet(index);
+        result->SeqOneByteStringSet(index,
+                                    V8_UNLIKELY(ch & ~0x7F)
+                                        ? static_cast<uint16_t>(u_tolower(ch))
+                                        : ToASCIILower(ch));
+      }
+    } else {
+      // In this path, we start from the beginning of the string,
+      // since there is nothing to memcpy from, and we have to
+      // use the generic Get. Another  option here would be to create
+      // a two-byte string as output, and do a memcpy from that,
+      // as Blink does, but there's also the ConsString case.
+      for (int index = 0; index < length; ++index) {
+        uint16_t ch = s->Get(index);
+        result->SeqOneByteStringSet(index,
+                                    V8_UNLIKELY(ch & ~0x7F)
+                                        ? static_cast<uint16_t>(u_tolower(ch))
+                                        : ToASCIILower(ch));
+      }
+    }
+
+    return Handle<String>(*result);
+  }
+
+  // Blink had an additional case here for ASCII 2-byte strings, but
+  // that is subsumed by the above code (assuming there isn't a false
+  // negative for HasOnlyOneByteChars).
+
+  // Do a slower implementation for cases that include non-ASCII characters.
+  return ConvertCaseICU(s, isolate, u_strToLower);
+}
+
+
+const uint16_t sharp_s = L'\u00DF';
+
+MUST_USE_RESULT Handle<String> StringToUpperCase(Handle<String> s,
+                                                 Isolate* isolate) {
+  // This function could be optimized for no-op cases the way lower() is,
+  // but in empirical testing, few actual calls to upper() are no-ops, so
+  // it wouldn't be worth the extra time for pre-scanning.
+
+  int32_t length = s->length();
+
+  if (s->HasOnlyOneByteChars()) {
+    Handle<SeqOneByteString> result =
+        isolate->factory()->NewRawOneByteString(length).ToHandleChecked();
+
+    // Do a faster loop for the case where all the characters are ASCII.
+    uint16_t ored = 0;
+    for (int index = 0; index < length; ++index) {
+      uint16_t ch = s->Get(index);
+      ored |= ch;
+      result->SeqOneByteStringSet(index, ToASCIIUpper(ch));
+    }
+    if (!(ored & ~0x7F)) return Handle<String>(*result);
+
+    // Do a slower implementation for cases that include non-ASCII Latin-1
+    // characters.
+    int sharp_s_count = 0;
+
+    // There are two special cases.
+    //  1. latin-1 characters when converted to upper case are 16 bit
+    //  characters.
+    //  2. Lower case sharp-S converts to "SS" (two characters)
+    for (int32_t index = 0; index < length; ++index) {
+      uint16_t ch = s->Get(index);
+      if (V8_UNLIKELY(ch == sharp_s)) ++sharp_s_count;
+      uint16_t upper = static_cast<uint16_t>(u_toupper(static_cast<UChar>(ch)));
+      if (V8_UNLIKELY(upper > 0xff)) {
+        // Since this upper-cased character does not fit in an 8-bit string, we
+        // need to take the 16-bit path.
+        goto upconvert;
+      }
+      result->SeqOneByteStringSet(index, upper);
+    }
+
+    if (sharp_s_count == 0) return Handle<String>(*result);
+
+    // We have sharp_s_count sharp-s characters, but none of the other special
+    // characters.
+    result = isolate->factory()
+                 ->NewRawOneByteString(length + sharp_s_count)
+                 .ToHandleChecked();
+    for (int32_t index = 0, dest_index = 0; index < length; ++index) {
+      uint16_t ch = s->Get(index);
+      if (ch == sharp_s) {
+        result->SeqOneByteStringSet(dest_index++, 'S');
+        result->SeqOneByteStringSet(dest_index++, 'S');
+      } else {
+        uint16_t upper =
+            static_cast<uint16_t>(u_toupper(static_cast<UChar>(ch)));
+        result->SeqOneByteStringSet(dest_index++, upper);
+      }
+    }
+
+    return Handle<String>(*result);
+  }
+
+upconvert:
+  return ConvertCaseICU(s, isolate, u_strToUpper);
+}
+
+}  // namespace
+#endif
+
+
 RUNTIME_FUNCTION(Runtime_StringToLowerCase) {
   HandleScope scope(isolate);
-  DCHECK(args.length() == 1);
+  DCHECK_EQ(args.length(), 1);
   CONVERT_ARG_HANDLE_CHECKED(String, s, 0);
-  return ConvertCase(s, isolate, isolate->runtime_state()->to_lower_mapping());
+#ifdef V8_I18N_SUPPORT
+  if (FLAG_icu_case_mapping)
+    return *StringToLowerCase(s, isolate);
+  else
+#endif
+    return ConvertCase(s, isolate,
+                       isolate->runtime_state()->to_lower_mapping());
 }
 
 
 RUNTIME_FUNCTION(Runtime_StringToUpperCase) {
   HandleScope scope(isolate);
-  DCHECK(args.length() == 1);
+  DCHECK_EQ(args.length(), 1);
   CONVERT_ARG_HANDLE_CHECKED(String, s, 0);
-  return ConvertCase(s, isolate, isolate->runtime_state()->to_upper_mapping());
+#ifdef V8_I18N_SUPPORT
+  if (FLAG_icu_case_mapping)
+    return *StringToUpperCase(s, isolate);
+  else
+#endif
+    return ConvertCase(s, isolate,
+                       isolate->runtime_state()->to_upper_mapping());
 }