Special case handling of one char split on an ASCII string.

src/runtime.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5736 matching lines @@
 
 template <typename SubjectChar, typename PatternChar>
 void FindStringIndices(Isolate* isolate,
                        Vector<const SubjectChar> subject,
                        Vector<const PatternChar> pattern,
                        ZoneList<int>* indices,
                        unsigned int limit) {
   ASSERT(limit > 0);
   // Collect indices of pattern in subject, and the end-of-string index.
   // Stop after finding at most limit values.
-  StringSearch<PatternChar, SubjectChar> search(isolate, pattern);
   int pattern_length = pattern.length();
   int index = 0;
-  while (limit > 0) {
-    index = search.Search(subject, index);
-    if (index < 0) return;
-    indices->Add(index);
-    index += pattern_length;
-    limit--;
+  if (sizeof(SubjectChar) == kCharSize &&
+      sizeof(PatternChar) == kCharSize &&
+      pattern_length == 1) {
+    // ASCII subject with one char ASCII pattern allows direct use of memchr.
+    char pattern_first_char = pattern[0];
+    const char* subject_start = reinterpret_cast<const char*>(subject.start());
+    const char* subject_end = subject_start + subject.length();
+    const char* pos = subject_start;
+    while (limit > 0) {
+      pos = reinterpret_cast<const char*>(
+          memchr(pos, pattern_first_char, subject_end - pos));
+      if (pos == NULL) return;
+      indices->Add(pos - subject_start);
+      pos++;
+      limit--;
+    }
+  } else {
+    StringSearch<PatternChar, SubjectChar> search(isolate, pattern);
+    while (limit > 0) {
+      index = search.Search(subject, index);
+      if (index < 0) return;
+      indices->Add(index);
+      index += pattern_length;
+      limit--;
+    }
   }
 }
 
-
 RUNTIME_FUNCTION(MaybeObject*, Runtime_StringSplit) {
   ASSERT(args.length() == 3);
   HandleScope handle_scope(isolate);
   CONVERT_ARG_CHECKED(String, subject, 0);
   CONVERT_ARG_CHECKED(String, pattern, 1);
   CONVERT_NUMBER_CHECKED(uint32_t, limit, Uint32, args[2]);
 
   int subject_length = subject->length();
   int pattern_length = pattern->length();
   RUNTIME_ASSERT(pattern_length > 0);
@@ skipping 6777 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(false);
   }
 }
 
 
 } }  // namespace v8::internal