Fix missing cases of empty_string canonicalization

src/objects.cc

 // Copyright 2015 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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 11690 matching lines @@
     // Isolate the array index form the full hash field.
     *index = ArrayIndexValueBits::decode(field);
     return true;
   } else {
     return ComputeArrayIndex(index);
   }
 }
 
 
 Handle<String> SeqString::Truncate(Handle<SeqString> string, int new_length) {
+  Heap* heap = string->GetHeap();
+  if (new_length == 0) return heap->isolate()->factory()->empty_string();
+
   int new_size, old_size;
   int old_length = string->length();
   if (old_length <= new_length) return string;
 
   if (string->IsSeqOneByteString()) {
     old_size = SeqOneByteString::SizeFor(old_length);
     new_size = SeqOneByteString::SizeFor(new_length);
   } else {
     DCHECK(string->IsSeqTwoByteString());
     old_size = SeqTwoByteString::SizeFor(old_length);
     new_size = SeqTwoByteString::SizeFor(new_length);
   }
 
   int delta = old_size - new_size;
 
   Address start_of_string = string->address();
   DCHECK_OBJECT_ALIGNED(start_of_string);
   DCHECK_OBJECT_ALIGNED(start_of_string + new_size);
 
-  Heap* heap = string->GetHeap();
   // Sizes are pointer size aligned, so that we can use filler objects
   // that are a multiple of pointer size.
   heap->CreateFillerObjectAt(start_of_string + new_size, delta,
                              ClearRecordedSlots::kNo);
   heap->AdjustLiveBytes(*string, -delta);
 
   // We are storing the new length using release store after creating a filler
   // for the left-over space to avoid races with the sweeper thread.
   string->synchronized_set_length(new_length);
 
-  if (new_length == 0) return heap->isolate()->factory()->empty_string();
   return string;
 }
 
 
 uint32_t StringHasher::MakeArrayIndexHash(uint32_t value, int length) {
   // For array indexes mix the length into the hash as an array index could
   // be zero.
   DCHECK(length > 0);
   DCHECK(length <= String::kMaxArrayIndexSize);
   DCHECK(TenToThe(String::kMaxCachedArrayIndexLength) <
@@ skipping 8456 matching lines @@
       // depend on this.
       return DICTIONARY_ELEMENTS;
     }
     DCHECK_LE(kind, LAST_ELEMENTS_KIND);
     return kind;
   }
 }
 
 }  // namespace internal
 }  // namespace v8