Reland of [compiler] Make feedback vector cope with flag changes.

src/compiler.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/compiler.h"
 
 #include <algorithm>
 
 #include "src/ast/ast-numbering.h"
 #include "src/ast/prettyprinter.h"
@@ skipping 726 matching lines @@
     PROFILE(info->isolate(),
             CodeCreateEvent(log_tag, *abstract_code, *shared, info, script_name,
                             line_num, column_num));
   }
 }
 
 void EnsureFeedbackVector(CompilationInfo* info) {
   if (!info->has_shared_info()) return;
 
   // If no type feedback vector exists, we create one now. At this point the
-  // AstNumbering pass has already run. Note that we should reuse any existing
-  // feedback vector rather than creating a new one.
-  if (info->shared_info()->feedback_vector()->is_empty()) {
+  // AstNumbering pass has already run. Note the snapshot can contain outdated
+  // vectors for a different configuration, hence we also recreate a new vector
+  // when the function is not compiled (i.e. no code was serialized).
+  if (info->shared_info()->feedback_vector()->is_empty() ||
+      !info->shared_info()->is_compiled()) {
     Handle<TypeFeedbackMetadata> feedback_metadata = TypeFeedbackMetadata::New(
         info->isolate(), info->literal()->feedback_vector_spec());
     Handle<TypeFeedbackVector> feedback_vector =
         TypeFeedbackVector::New(info->isolate(), feedback_metadata);
     info->shared_info()->set_feedback_vector(*feedback_vector);
   }
 
   // It's very important that recompiles do not alter the structure of the type
   // feedback vector. Verify that the structure fits the function literal.
   CHECK(!info->shared_info()->feedback_vector()->metadata()->SpecDiffersFrom(
@@ skipping 1138 matching lines @@
     MaybeHandle<Code> code;
     if (cached.code != nullptr) code = handle(cached.code);
     Handle<Context> native_context(function->context()->native_context());
     SharedFunctionInfo::AddToOptimizedCodeMap(shared, native_context, code,
                                               literals, BailoutId::None());
   }
 }
 
 }  // namespace internal
 }  // namespace v8