[interpreter] Allow mixed stacks if bytecode is preserved.

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 <memory>
 
 #include "src/asmjs/asm-js.h"
@@ skipping 929 matching lines @@
 
   // TODO(4280): For now we do not switch generators or async functions to
   // baseline code because there might be suspended activations stored in
   // generator objects on the heap. We could eventually go directly to
   // TurboFan in this case.
   if (function->shared()->is_resumable()) {
     return MaybeHandle<Code>();
   }
 
   // TODO(4280): For now we disable switching to baseline code in the presence
-  // of interpreter activations of the given function. The reasons are:
-  //  1) The debugger assumes each function is either full-code or bytecode.
-  //  2) The underlying bytecode is cleared below, breaking stack unwinding.
-  InterpreterActivationsFinder activations_finder(function->shared());
-  if (HasInterpreterActivations(isolate, &activations_finder)) {
-    if (FLAG_trace_opt) {
-      OFStream os(stdout);
-      os << "[unable to switch " << Brief(*function) << " due to activations]"
-         << std::endl;
-    }
-
-    if (activations_finder.MarkActivationsForBaselineOnReturn(isolate)) {
+  // of interpreter activations of the given function. The reasons is that the
+  // underlying bytecode is cleared below.

[rmcilroy, 2016/08/22 15:33:03]

nit - could you update the comment to mention we only do this if
FLAG_ignition_preserve_bytecode isn't set

[Michael Starzinger, 2016/08/22 15:44:22]

Done.

+  if (!FLAG_ignition_preserve_bytecode) {
+    InterpreterActivationsFinder activations_finder(function->shared());
+    if (HasInterpreterActivations(isolate, &activations_finder)) {
       if (FLAG_trace_opt) {
         OFStream os(stdout);
-        os << "[marking " << Brief(function->shared())
-           << " for baseline recompilation on return]" << std::endl;
+        os << "[unable to switch " << Brief(*function) << " due to activations]"
+           << std::endl;
       }
+
+      if (activations_finder.MarkActivationsForBaselineOnReturn(isolate)) {
+        if (FLAG_trace_opt) {
+          OFStream os(stdout);
+          os << "[marking " << Brief(function->shared())
+             << " for baseline recompilation on return]" << std::endl;
+        }
+      }
+
+      return MaybeHandle<Code>();
     }
-
-    return MaybeHandle<Code>();
   }
 
   if (FLAG_trace_opt) {
     OFStream os(stdout);
     os << "[switching method " << Brief(*function) << " to baseline code]"
        << std::endl;
   }
 
   // Parse and update CompilationInfo with the results.
   if (!Parser::ParseStatic(info.parse_info())) return MaybeHandle<Code>();
@@ skipping 427 matching lines @@
     CompilationInfo unoptimized(info->parse_info(), info->closure());
     unoptimized.EnableDeoptimizationSupport();
 
     // TODO(4280): For now we do not switch generators or async functions to
     // baseline code because there might be suspended activations stored in
     // generator objects on the heap. We could eventually go directly to
     // TurboFan in this case.
     if (shared->is_resumable()) return false;
 
     // TODO(4280): For now we disable switching to baseline code in the presence
-    // of interpreter activations of the given function. The reasons are:
-    //  1) The debugger assumes each function is either full-code or bytecode.
-    //  2) The underlying bytecode is cleared below, breaking stack unwinding.
-    // The expensive check for activations only needs to be done when the given
-    // function has bytecode, otherwise we can be sure there are no activations.
-    if (shared->HasBytecodeArray()) {
+    // of interpreter activations of the given function. The reasons is that the
+    // underlying bytecode is cleared below. The expensive check for activations
+    // only needs to be done when the given function has bytecode, otherwise we
+    // can be sure there are no activations.

[rmcilroy, 2016/08/22 15:33:03]

And here

[Michael Starzinger, 2016/08/22 15:44:22]

Done.

+    if (!FLAG_ignition_preserve_bytecode && shared->HasBytecodeArray()) {
       InterpreterActivationsFinder activations_finder(*shared);
       if (HasInterpreterActivations(info->isolate(), &activations_finder)) {
         return false;
       }
     }
 
     // If the current code has reloc info for serialization, also include
     // reloc info for serialization for the new code, so that deopt support
     // can be added without losing IC state.
     if (shared->code()->kind() == Code::FUNCTION &&
         shared->code()->has_reloc_info_for_serialization()) {
       unoptimized.PrepareForSerializing();
     }
     EnsureFeedbackMetadata(&unoptimized);
     if (!FullCodeGenerator::MakeCode(&unoptimized)) return false;
 
     // TODO(4280): For now we play it safe and remove the bytecode array when we
     // switch to baseline code. We might consider keeping around the bytecode so
     // that it can be used as the "source of truth" eventually.

[rmcilroy, 2016/08/22 15:33:03]

nit - could you update the comment

[Michael Starzinger, 2016/08/22 15:44:23]

Done.

-    if (shared->HasBytecodeArray()) {
-      if (!FLAG_ignition_preserve_bytecode) shared->ClearBytecodeArray();
+    if (!FLAG_ignition_preserve_bytecode && shared->HasBytecodeArray()) {
+      shared->ClearBytecodeArray();
     }
 
     // The scope info might not have been set if a lazily compiled
     // function is inlined before being called for the first time.
     if (shared->scope_info() == ScopeInfo::Empty(info->isolate())) {
       InstallSharedScopeInfo(info, shared);
     }
 
     // Install compilation result on the shared function info
     shared->EnableDeoptimizationSupport(*unoptimized.code());
@@ skipping 512 matching lines @@
     DCHECK(shared->is_compiled());
     function->set_literals(cached.literals);
   } else if (shared->is_compiled()) {
     // TODO(mvstanton): pass pretenure flag to EnsureLiterals.
     JSFunction::EnsureLiterals(function);
   }
 }
 
 }  // namespace internal
 }  // namespace v8