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);

[Yang, 2016/12/16 14:02:21]

Is this a spec change? So this function can be called as a constructor?

[jungshik at Google, 2016/12/16 18:12:36]

I asked about this previously because having that check leads to a few
additional entries in the profiling result (accounting for 6(?)% of the total
ticks).  Dan said that that check could be gone. 

StringTo{Lower,Upper}CaseJS() in src/js/string.js does not have that check.
Because To{Lower,Upper}CaseI18N replace StringTo{Lower,Upper}CaseJS when
--icu_case_mapping flag is on, I thought I could drop the check. 

// ECMA-262, 15.5.4.16
function StringToLowerCaseJS() {
  CHECK_OBJECT_COERCIBLE(this, "String.prototype.toLowerCase");

  return %StringToLowerCase(TO_STRING(this));
}

[Dan Ehrenberg, 2016/12/17 00:42:19]

The %FunctionRemovePrototype call should be enough to prevent calls to this as a
constructor. I'd like to remove all of them in a follow-on patch. It makes sense
to do it earlier here because it will let us flip this flag on without the
performance regression.

[jungshik at Google, 2016/12/19 06:38:56]

Thank you for confirming, Dan. 

I dropped the check in all the case-conversion related functions in i18n.js in
this CL. i18n.js still has about 10 of them in other (localeCompare,
Number.toLocaleString, Date.toLocaleString, etc) functions. I'll see if I can
drop them in a separate CL. 

-  }
   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);
 }