[interpreter] Add ability to preserve bytecode.

This adds the --ignition-preserve-bytecode flag which will preserve any
existing bytecode, even if a tier-up to baseline code is performed. This
is preparatory work in order to allow mixed stacks where bytecode and
baseline code can be active at the same time.

It also adds a {HasBaselineCode} predicate symmetric to the existing
{HasBytecodeArray} predicate. Both predicates are independent and any
combination of answers is valid.

Further adaptation of the rest of the runtime will be done step-wise in
follow-up changes.

R=yangguo@chromium.org
BUG=v8:5265

Review-Url: https://codereview.chromium.org/2224923003
Cr-Commit-Position: refs/heads/master@{#38540}

src/compiler.cc

@@ -992,7 +992,7 @@ MaybeHandle<Code> GetBaselineCode(Handle<JSFunction> function) {
   // 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.
-  shared->ClearBytecodeArray();
+  if (!FLAG_ignition_preserve_bytecode) shared->ClearBytecodeArray();
 
   // Update the shared function info with the scope info.
   InstallSharedScopeInfo(&info, shared);
@@ -1432,7 +1432,7 @@ bool Compiler::EnsureDeoptimizationSupport(CompilationInfo* info) {
     // 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.
-    shared->ClearBytecodeArray();
+    if (!FLAG_ignition_preserve_bytecode) shared->ClearBytecodeArray();
 
     // The scope info might not have been set if a lazily compiled
     // function is inlined before being called for the first time.

src/debug/liveedit.cc

@@ -986,9 +986,9 @@ void LiveEdit::ReplaceFunctionCode(
     // Clear old bytecode. This will trigger self-healing if we do not install
     // new bytecode.
     shared_info->ClearBytecodeArray();
-    if (old_code->is_interpreter_trampoline_builtin()) {
+    if (!shared_info->HasBaselineCode()) {
       // Every function from this SFI is interpreted.
-      if (new_code->is_interpreter_trampoline_builtin()) {
+      if (!new_shared_info->HasBaselineCode()) {
         // We have newly compiled bytecode. Simply replace the old one.
         shared_info->set_bytecode_array(new_shared_info->bytecode_array());
       } else {

src/flag-definitions.h

@@ -308,6 +308,8 @@ DEFINE_BOOL(ignition_peephole, true, "use ignition peephole optimizer")
 DEFINE_BOOL(ignition_reo, true, "use ignition register equivalence optimizer")
 DEFINE_BOOL(ignition_filter_expression_positions, true,
             "filter expression positions before the bytecode pipeline")
+DEFINE_BOOL(ignition_preserve_bytecode, false,
+            "preserve generated bytecode even when switching tiers")
 DEFINE_BOOL(print_bytecode, false,
             "print bytecode generated by ignition interpreter")
 DEFINE_BOOL(trace_ignition, false,

src/objects-inl.h

@@ -6103,6 +6103,9 @@ void SharedFunctionInfo::ReplaceCode(Code* value) {
   if (is_compiled()) set_never_compiled(false);
 }
 
+bool SharedFunctionInfo::HasBaselineCode() const {
+  return code()->kind() == Code::FUNCTION;
+}
 
 ScopeInfo* SharedFunctionInfo::scope_info() const {
   return reinterpret_cast<ScopeInfo*>(READ_FIELD(this, kScopeInfoOffset));
@@ -6119,8 +6122,7 @@ void SharedFunctionInfo::set_scope_info(ScopeInfo* value,
                             mode);
 }
 
-
-bool SharedFunctionInfo::is_compiled() {
+bool SharedFunctionInfo::is_compiled() const {
   Builtins* builtins = GetIsolate()->builtins();
   DCHECK(code() != builtins->builtin(Builtins::kCompileOptimizedConcurrent));
   DCHECK(code() != builtins->builtin(Builtins::kCompileOptimized));
@@ -6149,7 +6151,7 @@ DebugInfo* SharedFunctionInfo::GetDebugInfo() {
 
 bool SharedFunctionInfo::HasDebugCode() {
   return HasBytecodeArray() ||
-         (code()->kind() == Code::FUNCTION && code()->has_debug_break_slots());
+         (HasBaselineCode() && code()->has_debug_break_slots());
 }
 
 

src/objects.h

@@ -6894,6 +6894,7 @@ class SharedFunctionInfo: public HeapObject {
   inline AbstractCode* abstract_code();
 
   inline void ReplaceCode(Code* code);
+  inline bool HasBaselineCode() const;
 
   // [optimized_code_map]: Map from native context to optimized code
   // and a shared literals array.
@@ -6980,7 +6981,7 @@ class SharedFunctionInfo: public HeapObject {
   void SetConstructStub(Code* code);
 
   // Returns if this function has been compiled to native code yet.
-  inline bool is_compiled();
+  inline bool is_compiled() const;
 
   // [length]: The function length - usually the number of declared parameters.
   // Use up to 2^30 parameters.

src/runtime/runtime-test.cc

@@ -171,7 +171,7 @@ RUNTIME_FUNCTION(Runtime_OptimizeOsr) {
 
   // Make the profiler arm all back edges in unoptimized code.
   if (function->shared()->HasBytecodeArray() ||
-      function->shared()->code()->kind() == Code::FUNCTION) {
+      function->shared()->HasBaselineCode()) {
     isolate->runtime_profiler()->AttemptOnStackReplacement(
         *function, AbstractCode::kMaxLoopNestingMarker);
   }