[serializer] do not copy code if snapshot is not required to be deterministic.

src/snapshot/serializer.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/snapshot/serializer.h"
 
 #include "src/macro-assembler.h"
 #include "src/snapshot/natives.h"
 
 namespace v8 {
@@ skipping 689 matching lines @@
           ExtraNatives::GetSourceCache(serializer_->isolate()->heap()),
           kExtraNativesStringResource)) {
     return;
   }
   // One of the strings in the natives cache should match the resource.  We
   // don't expect any other kinds of external strings here.
   UNREACHABLE();
 }
 
 Address Serializer::ObjectSerializer::PrepareCode() {
-  // To make snapshots reproducible, we make a copy of the code object
-  // and wipe all pointers in the copy, which we then serialize.
-  Code* original = Code::cast(object_);
-  Code* code = serializer_->CopyCode(original);
+  Code* code = Code::cast(object_);
+  if (FLAG_predictable) {
+    // To make snapshots reproducible, we make a copy of the code object
+    // and wipe all pointers in the copy, which we then serialize.
+    code = serializer_->CopyCode(code);
+    int mode_mask = RelocInfo::kCodeTargetMask |
+                    RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT) |
+                    RelocInfo::ModeMask(RelocInfo::EXTERNAL_REFERENCE) |
+                    RelocInfo::ModeMask(RelocInfo::RUNTIME_ENTRY) |
+                    RelocInfo::ModeMask(RelocInfo::INTERNAL_REFERENCE) |
+                    RelocInfo::ModeMask(RelocInfo::INTERNAL_REFERENCE_ENCODED);
+    for (RelocIterator it(code, mode_mask); !it.done(); it.next()) {
+      RelocInfo* rinfo = it.rinfo();
+      rinfo->WipeOut();
+    }
+    // We need to wipe out the header fields *after* wiping out the
+    // relocations, because some of these fields are needed for the latter.
+    code->WipeOutHeader();
+  }
   // Code age headers are not serializable.
   code->MakeYoung(serializer_->isolate());
-  int mode_mask = RelocInfo::kCodeTargetMask |
-                  RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT) |
-                  RelocInfo::ModeMask(RelocInfo::EXTERNAL_REFERENCE) |
-                  RelocInfo::ModeMask(RelocInfo::RUNTIME_ENTRY) |
-                  RelocInfo::ModeMask(RelocInfo::INTERNAL_REFERENCE) |
-                  RelocInfo::ModeMask(RelocInfo::INTERNAL_REFERENCE_ENCODED);
-  for (RelocIterator it(code, mode_mask); !it.done(); it.next()) {
-    RelocInfo* rinfo = it.rinfo();
-    rinfo->WipeOut();
-  }
-  // We need to wipe out the header fields *after* wiping out the
-  // relocations, because some of these fields are needed for the latter.
-  code->WipeOutHeader();
   return code->address();
 }
 
 int Serializer::ObjectSerializer::OutputRawData(
     Address up_to, Serializer::ObjectSerializer::ReturnSkip return_skip) {
   Address object_start = object_->address();
   int base = bytes_processed_so_far_;
   int up_to_offset = static_cast<int>(up_to - object_start);
   int to_skip = up_to_offset - bytes_processed_so_far_;
   int bytes_to_output = to_skip;
@@ skipping 30 matching lines @@
   if (to_skip != 0 && return_skip == kIgnoringReturn) {
     sink_->Put(kSkip, "Skip");
     sink_->PutInt(to_skip, "SkipDistance");
     to_skip = 0;
   }
   return to_skip;
 }
 
 }  // namespace internal
 }  // namespace v8