Inline one level of recursive call of WriteToFlat for the common case of cons string list.

src/objects.cc

 // Copyright 2012 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 6844 matching lines @@
             from = 0;
           } else {
             from -= boundary;
           }
           to -= boundary;
           source = cons_string->second();
         } else {
           // Left hand side is longer.  Recurse over right.
           if (to > boundary) {
             String* second = cons_string->second();
-            WriteToFlat(second,
-                        sink + boundary - from,
-                        0,
+            // When repeatedly appending to a string, we get a cons string that
+            // is unbalanced to the left, a list, essentially.  We inline the
+            // common case of sequential ascii right child.
+            if (to - boundary == 1) {
+              sink[boundary - from] = static_cast<sinkchar>(second->Get(0));

[piscisaureus, 2012/05/08 00:00:09]

MSVC refuses to inline the Get(0) call. My benchmarks show that the difference
is significant though. Any chance we could get a __forceinline or
__attribute__((always_inline)) decorator on the Get method?

+            } else if (second->IsSeqAsciiString()) {
+              CopyChars(sink + boundary - from,

[piscisaureus, 2012/05/08 00:00:09]

Ditto.

+                        SeqAsciiString::cast(second)->GetChars(),
                         to - boundary);
+            } else {
+              WriteToFlat(second,
+                          sink + boundary - from,
+                          0,
+                          to - boundary);
+            }
             to = boundary;
           }
           source = first;
         }
         break;
       }
       case kAsciiStringTag | kSlicedStringTag:
       case kTwoByteStringTag | kSlicedStringTag: {
         SlicedString* slice = SlicedString::cast(source);
         unsigned offset = slice->offset();
@@ skipping 6279 matching lines @@
   if (break_point_objects()->IsUndefined()) return 0;
   // Single break point.
   if (!break_point_objects()->IsFixedArray()) return 1;
   // Multiple break points.
   return FixedArray::cast(break_point_objects())->length();
 }
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 
 } }  // namespace v8::internal