[regexp] implement /ui to mirror the implementation for /i.

src/regexp/regexp-parser.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/regexp/regexp-parser.h"
 
 #include "src/char-predicates-inl.h"
 #include "src/factory.h"
 #include "src/isolate.h"
 #include "src/objects-inl.h"
@@ skipping 1276 matching lines @@
     if (to >= kNonBmpStart) return true;
     // Check for lone surrogates.
     if (from <= kTrailSurrogateEnd && to >= kLeadSurrogateStart) return true;
   }
   return false;
 }
 
 
 bool RegExpBuilder::NeedsDesugaringForIgnoreCase(uc32 c) {
 #ifdef V8_I18N_SUPPORT
-  if (unicode() && ignore_case()) {
+  if (unicode() && ignore_case() && c >= kNonBmpStart) {
+    // BMP characters are handled in the case-insensitive TextEmitPass.
+    // Surrogate code units do not have case equivalents.
+    // Non-BMP characters need to be desugared into two uc16 parts.
     USet* set = uset_open(c, c);
     uset_closeOver(set, USET_CASE_INSENSITIVE);
     uset_removeAllStrings(set);
     bool result = uset_size(set) > 1;
     uset_close(set);
     return result;
   }
   // In the case where ICU is not included, we act as if the unicode flag is
   // not set, and do not desugar.
 #endif  // V8_I18N_SUPPORT
@@ skipping 54 matching lines @@
     return false;
   }
   terms_.Add(new (zone()) RegExpQuantifier(min, max, quantifier_type, atom),
              zone());
   LAST(ADD_TERM);
   return true;
 }
 
 }  // namespace internal
 }  // namespace v8