Fix regexp perf: Only increase array size if needed

src/jsregexp.cc

 // Copyright 2012 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/v8.h"
 
 #include "src/ast.h"
 #include "src/base/platform/platform.h"
 #include "src/compilation-cache.h"
 #include "src/compiler.h"
@@ skipping 600 matching lines @@
   }
   if (res == RE_EXCEPTION) {
     DCHECK(isolate->has_pending_exception());
     return MaybeHandle<Object>();
   }
   DCHECK(res == RE_FAILURE);
   return isolate->factory()->null_value();
 }
 
 
+static void EnsureSize(Handle<JSArray> array, uint32_t minimum_size) {
+  if (static_cast<uint32_t>(array->elements()->length()) < minimum_size) {
+    JSArray::SetLength(array, minimum_size);
+  }
+}
+
+
 Handle<JSArray> RegExpImpl::SetLastMatchInfo(Handle<JSArray> last_match_info,
                                              Handle<String> subject,
                                              int capture_count,
                                              int32_t* match) {
   DCHECK(last_match_info->HasFastObjectElements());
   int capture_register_count = (capture_count + 1) * 2;
-  JSArray::SetLength(last_match_info,
-                     capture_register_count + kLastMatchOverhead);
+  EnsureSize(last_match_info, capture_register_count + kLastMatchOverhead);
   DisallowHeapAllocation no_allocation;
   FixedArray* array = FixedArray::cast(last_match_info->elements());
   if (match != NULL) {
     for (int i = 0; i < capture_register_count; i += 2) {
       SetCapture(array, i, match[i]);
       SetCapture(array, i + 1, match[i + 1]);
     }
   }
   SetLastCaptureCount(array, capture_register_count);
   SetLastSubject(array, *subject);
@@ skipping 5710 matching lines @@
   bool too_much = pattern->length() > RegExpImpl::kRegExpTooLargeToOptimize;
   if (heap->total_regexp_code_generated() > RegExpImpl::kRegExpCompiledLimit &&
       heap->isolate()->memory_allocator()->SizeExecutable() >
           RegExpImpl::kRegExpExecutableMemoryLimit) {
     too_much = true;
   }
   return too_much;
 }
 }  // namespace internal
 }  // namespace v8