Optimize case conversion with icu_case_mapping

src/js/i18n.js

Index: src/js/i18n.js
diff --git a/src/js/i18n.js b/src/js/i18n.js
index b051b090bcee57af0da4a558eb4c79fa824ba426..678f5ce490bb6cb8bd739a3c2cfaab6ebca0bd05 100644
--- a/src/js/i18n.js
+++ b/src/js/i18n.js
@@ -2121,27 +2121,16 @@ OverrideFunction(GlobalString.prototype, 'normalize', function() {
 );
 
 function ToLowerCaseI18N() {
-  if (!IS_UNDEFINED(new.target)) {
-    throw %make_type_error(kOrdinaryFunctionCalledAsConstructor);
-  }

[jungshik at Google, 2016/12/02 06:52:38]

WIth this check in place, the JS portion of profiles has 5 ~ 6 extra functions
(compared with non-i18n version) accounting for about 7% of the total run time. 

The corresponding function is strings.js does not have this check. Is it ok NOT
to check for this?  

[Dan Ehrenberg, 2016/12/02 23:35:08]

I don't understand why that check is in there. I can't find it in the current or
any historical version of ECMA 402. I wonder if removing it would cause any
test262 tests to fail, though--I can only imagine that this was included due to
an older draft spec or possibly-incorrect test262 tests. Seems like a good idea
to remove it.

   CHECK_OBJECT_COERCIBLE(this, "String.prototype.toLowerCase");
-  var s = TO_STRING(this);
-  return %StringToLowerCaseI18N(s);
+  return %StringToLowerCaseI18N(TO_STRING(this));
 }
 
 function ToUpperCaseI18N() {
-  if (!IS_UNDEFINED(new.target)) {
-    throw %make_type_error(kOrdinaryFunctionCalledAsConstructor);
-  }
   CHECK_OBJECT_COERCIBLE(this, "String.prototype.toUpperCase");
-  var s = TO_STRING(this);
-  return %StringToUpperCaseI18N(s);
+  return %StringToUpperCaseI18N(TO_STRING(this));
 }
 
 function ToLocaleLowerCaseI18N(locales) {
-  if (!IS_UNDEFINED(new.target)) {
-    throw %make_type_error(kOrdinaryFunctionCalledAsConstructor);
-  }
   CHECK_OBJECT_COERCIBLE(this, "String.prototype.toLocaleLowerCase");
   return LocaleConvertCase(TO_STRING(this), locales, false);
 }
@@ -2149,9 +2138,6 @@ function ToLocaleLowerCaseI18N(locales) {
 %FunctionSetLength(ToLocaleLowerCaseI18N, 0);
 
 function ToLocaleUpperCaseI18N(locales) {
-  if (!IS_UNDEFINED(new.target)) {
-    throw %make_type_error(kOrdinaryFunctionCalledAsConstructor);
-  }
   CHECK_OBJECT_COERCIBLE(this, "String.prototype.toLocaleUpperCase");
   return LocaleConvertCase(TO_STRING(this), locales, true);
 }