Add flag --support_debugger, controls emitting single stepping checks. Disable in --noopt, 6% gain.

runtime/vm/flow_graph_builder.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/flow_graph_builder.h"
 
 #include "lib/invocation_mirror.h"
 #include "vm/ast_printer.h"
 #include "vm/bit_vector.h"
 #include "vm/class_finalizer.h"
@@ skipping 17 matching lines @@
 #include "vm/symbols.h"
 #include "vm/token.h"
 #include "vm/zone.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool, eliminate_type_checks, true,
             "Eliminate type checks when allowed by static type analysis.");
 DEFINE_FLAG(bool, print_ast, false, "Print abstract syntax tree.");
 DEFINE_FLAG(bool, print_scopes, false, "Print scopes of local variables.");
+DEFINE_FLAG(bool, support_debugger, true, "Emit code needed for debugging");

[hausner, 2015/05/05 15:59:15]

Would be nice to use the --debug command line option for this, but unfortunately
that lives in the embedder. Maybe you can at least programmatically set this
flag when --debug is used? Otherwise we force users to remember and type several
flags when they want to debug a program.

[srdjan, 2015/05/06 21:02:54]

This flag should not be used by user, the flag will be set only when running
with --noopt, for precompilation, when no debugging is supported. Right now we
can also use it internally for measuring overheade by debugging code.

 DEFINE_FLAG(bool, trace_type_check_elimination, false,
             "Trace type check elimination at compile time.");
 
 DECLARE_FLAG(bool, enable_asserts);
 DECLARE_FLAG(bool, enable_type_checks);
 DECLARE_FLAG(int, optimization_counter_threshold);
 DECLARE_FLAG(bool, warn_on_javascript_compatibility);
 DECLARE_FLAG(bool, use_field_guards);
 
 // Quick access to the locally defined zone() method.
@@ skipping 987 matching lines @@
     }
     return_value = Bind(BuildLoadLocal(*temp));
   }
 
   // Call to stub that checks whether the debugger is in single
   // step mode. This call must happen before the contexts are
   // unchained so that captured variables can be inspected.
   // No debugger check is done in native functions or for return
   // statements for which there is no associated source position.
   const Function& function = owner()->function();
-  if ((node->token_pos() != Scanner::kNoSourcePos) && !function.is_native()) {
+  if (FLAG_support_debugger &&
+      (node->token_pos() != Scanner::kNoSourcePos) && !function.is_native()) {
     AddInstruction(new(Z) DebugStepCheckInstr(node->token_pos(),
                                               RawPcDescriptors::kRuntimeCall));
   }
 
   if (Isolate::Current()->TypeChecksEnabled()) {
     const bool is_implicit_dynamic_getter =
         (!function.is_static() &&
         ((function.kind() == RawFunction::kImplicitGetter) ||
          (function.kind() == RawFunction::kImplicitStaticFinalGetter)));
     // Implicit getters do not need a type check at return, unless they compute
@@ skipping 2375 matching lines @@
 }
 
 
 // <Expression> ::= StoreLocal { local: LocalVariable
 //                               value: <Expression> }
 void EffectGraphVisitor::VisitStoreLocalNode(StoreLocalNode* node) {
   // If the right hand side is an expression that does not contain
   // a safe point for the debugger to stop, add an explicit stub
   // call. Exception: don't do this when assigning to or from internal
   // variables, or for generated code that has no source position.
-  if ((node->value()->IsLiteralNode() ||
-      (node->value()->IsLoadLocalNode() &&
-          !node->value()->AsLoadLocalNode()->local().IsInternal()) ||
-      node->value()->IsClosureNode()) &&
-      !node->local().IsInternal() &&
-      (node->token_pos() != Scanner::kNoSourcePos)) {
-    AddInstruction(new(Z) DebugStepCheckInstr(
-        node->token_pos(), RawPcDescriptors::kRuntimeCall));
+  if (FLAG_support_debugger) {
+    if ((node->value()->IsLiteralNode() ||
+        (node->value()->IsLoadLocalNode() &&
+            !node->value()->AsLoadLocalNode()->local().IsInternal()) ||
+        node->value()->IsClosureNode()) &&
+        !node->local().IsInternal() &&
+        (node->token_pos() != Scanner::kNoSourcePos)) {
+      AddInstruction(new(Z) DebugStepCheckInstr(
+          node->token_pos(), RawPcDescriptors::kRuntimeCall));
+    }
   }
 
   ValueGraphVisitor for_value(owner());
   node->value()->Visit(&for_value);
   Append(for_value);
   Value* store_value = for_value.value();
   if (Isolate::Current()->TypeChecksEnabled()) {
     store_value = BuildAssignableValue(node->value()->token_pos(),
                                        store_value,
                                        node->local().type(),
@@ skipping 783 matching lines @@
   ASSERT(!func.IsNull());
   return new(Z) StaticCallInstr(token_pos,
                                 func,
                                 Object::null_array(),  // No names.
                                 arguments,
                                 owner()->ic_data_array());
 }
 
 
 void EffectGraphVisitor::BuildThrowNode(ThrowNode* node) {
-  if (node->exception()->IsLiteralNode() ||
-      node->exception()->IsLoadLocalNode() ||
-      node->exception()->IsClosureNode()) {
-    AddInstruction(new(Z) DebugStepCheckInstr(
-        node->token_pos(), RawPcDescriptors::kRuntimeCall));
+  if (FLAG_support_debugger) {
+    if (node->exception()->IsLiteralNode() ||
+        node->exception()->IsLoadLocalNode() ||
+        node->exception()->IsClosureNode()) {
+      AddInstruction(new(Z) DebugStepCheckInstr(
+          node->token_pos(), RawPcDescriptors::kRuntimeCall));
+    }
   }
   ValueGraphVisitor for_exception(owner());
   node->exception()->Visit(&for_exception);
   Append(for_exception);
   PushArgument(for_exception.value());
   Instruction* instr = NULL;
   if (node->stacktrace() == NULL) {
     instr = new(Z) ThrowInstr(node->token_pos());
   } else {
     ValueGraphVisitor for_stack_trace(owner());
@@ skipping 110 matching lines @@
   Report::MessageF(Report::kBailout,
                    Script::Handle(function.script()),
                    function.token_pos(),
                    "FlowGraphBuilder Bailout: %s %s",
                    String::Handle(function.name()).ToCString(),
                    reason);
   UNREACHABLE();
 }
 
 }  // namespace dart