Add flag —enable-debugger (default true) in order to disable debugger single stepping code.

runtime/vm/stub_code_arm64.cc

 // Copyright (c) 2014, 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/globals.h"
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_compiler.h"
 #include "vm/heap.h"
 #include "vm/instructions.h"
 #include "vm/object_store.h"
 #include "vm/stack_frame.h"
 #include "vm/stub_code.h"
 #include "vm/tags.h"
 
 #define __ assembler->
 
 namespace dart {
 
 DEFINE_FLAG(bool, inline_alloc, true, "Inline allocation of objects.");
 DEFINE_FLAG(bool, use_slow_path, false,
     "Set to true for debugging & verifying the slow paths.");
 DECLARE_FLAG(bool, trace_optimized_ic_calls);
 
+DECLARE_FLAG(bool, enable_debugger);
+
 // Input parameters:
 //   LR : return address.
 //   SP : address of last argument in argument array.
 //   SP + 8*R4 - 8 : address of first argument in argument array.
 //   SP + 8*R4 : address of return value.
 //   R5 : address of the runtime function to call.
 //   R4 : number of arguments to the call.
 void StubCode::GenerateCallToRuntimeStub(Assembler* assembler) {
   const intptr_t isolate_offset = NativeArguments::isolate_offset();
   const intptr_t argc_tag_offset = NativeArguments::argc_tag_offset();
@@ skipping 1264 matching lines @@
                       kNoPP, kUnsignedWord);
     ASSERT(ICData::NumArgsTestedShift() == 0);  // No shift needed.
     __ andi(R6, R6, ICData::NumArgsTestedMask());
     __ CompareImmediate(R6, num_args, kNoPP);
     __ b(&ok, EQ);
     __ Stop("Incorrect stub for IC data");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
-  // Check single stepping.
-  Label not_stepping;
-  __ LoadFieldFromOffset(R6, CTX, Context::isolate_offset(), kNoPP);
-  __ LoadFromOffset(
-      R6, R6, Isolate::single_step_offset(), kNoPP, kUnsignedByte);
-  __ CompareRegisters(R6, ZR);
-  __ b(&not_stepping, EQ);
-  __ EnterStubFrame();
-  __ Push(R5);  // Preserve IC data.
-  __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
-  __ Pop(R5);
-  __ LeaveStubFrame();
-  __ Bind(&not_stepping);
+  if (FLAG_enable_debugger) {
+    // Check single stepping.
+    Label not_stepping;
+    __ LoadFieldFromOffset(R6, CTX, Context::isolate_offset(), kNoPP);
+    __ LoadFromOffset(
+        R6, R6, Isolate::single_step_offset(), kNoPP, kUnsignedByte);
+    __ CompareRegisters(R6, ZR);
+    __ b(&not_stepping, EQ);
+    __ EnterStubFrame();
+    __ Push(R5);  // Preserve IC data.
+    __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
+    __ Pop(R5);
+    __ LeaveStubFrame();
+    __ Bind(&not_stepping);
+  }
 
   // Load arguments descriptor into R4.
   __ LoadFieldFromOffset(R4, R5, ICData::arguments_descriptor_offset(), kNoPP);
   // Loop that checks if there is an IC data match.
   Label loop, update, test, found, get_class_id_as_smi;
   // R5: IC data object (preserved).
   __ LoadFieldFromOffset(R6, R5, ICData::ic_data_offset(), kNoPP);
   // R6: ic_data_array with check entries: classes and target functions.
   __ AddImmediate(R6, R6, Array::data_offset() - kHeapObjectTag, kNoPP);
   // R6: points directly to the first ic data array element.
@@ skipping 578 matching lines @@
   const Register right = R0;
   __ LoadFromOffset(left, SP, 1 * kWordSize, kNoPP);
   __ LoadFromOffset(right, SP, 0 * kWordSize, kNoPP);
   GenerateIdenticalWithNumberCheckStub(assembler, left, right, temp);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64