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

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(int, optimization_counter_threshold);
+DECLARE_FLAG(bool, support_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();
@@ skipping 1346 matching lines @@
                       kNoPP, kUnsignedWord);
     ASSERT(ICData::NumArgsTestedShift() == 0);  // No shift needed.
     __ andi(R6, R6, Immediate(ICData::NumArgsTestedMask()));
     __ CompareImmediate(R6, num_args, kNoPP);
     __ b(&ok, EQ);
     __ Stop("Incorrect stub for IC data");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
-  __ Comment("Check single stepping");
   Label stepping, done_stepping;
-  __ LoadIsolate(R6, kNoPP);
-  __ LoadFromOffset(
-      R6, R6, Isolate::single_step_offset(), kNoPP, kUnsignedByte);
-  __ CompareRegisters(R6, ZR);
-  __ b(&stepping, NE);
-  __ Bind(&done_stepping);
+  if (FLAG_support_debugger) {
+    __ Comment("Check single stepping");
+    __ LoadIsolate(R6, kNoPP);
+    __ LoadFromOffset(
+        R6, R6, Isolate::single_step_offset(), kNoPP, kUnsignedByte);
+    __ CompareRegisters(R6, ZR);
+    __ b(&stepping, NE);
+    __ Bind(&done_stepping);
+  }
 
   __ Comment("Range feedback collection");
   Label not_smi_or_overflow;
   if (range_collection_mode == kCollectRanges) {
     ASSERT((num_args == 1) || (num_args == 2));
     if (num_args == 2) {
       __ ldr(R0, Address(SP, 1 * kWordSize));
       __ UpdateRangeFeedback(R0, 0, R5, R1, R4, &not_smi_or_overflow);
     }
 
@@ skipping 143 matching lines @@
     Label done;
     __ ldr(R5, Address(FP, kFirstLocalSlotFromFp * kWordSize));
     __ UpdateRangeFeedback(R0, 2, R5, R1, R4, &done);
     __ Bind(&done);
     __ LeaveStubFrame();
     __ ret();
   } else {
     __ br(R2);
   }
 
-  __ Bind(&stepping);
-  __ EnterStubFrame();
-  __ Push(R5);  // Preserve IC data.
-  __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
-  __ Pop(R5);
-  __ LeaveStubFrame();
-  __ b(&done_stepping);
+  if (FLAG_support_debugger) {
+    __ Bind(&stepping);
+    __ EnterStubFrame();
+    __ Push(R5);  // Preserve IC data.
+    __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
+    __ Pop(R5);
+    __ LeaveStubFrame();
+    __ b(&done_stepping);
+  }
 }
 
 
 // Use inline cache data array to invoke the target or continue in inline
 // cache miss handler. Stub for 1-argument check (receiver class).
 //  LR: return address.
 //  R5: inline cache data object.
 // Inline cache data object structure:
 // 0: function-name
 // 1: N, number of arguments checked.
@@ skipping 107 matching lines @@
     __ andi(R6, R6, Immediate(ICData::NumArgsTestedMask()));
     __ CompareImmediate(R6, 0, kNoPP);
     __ b(&ok, EQ);
     __ Stop("Incorrect IC data for unoptimized static call");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
   // Check single stepping.
   Label stepping, done_stepping;
-  __ LoadIsolate(R6, kNoPP);
-  __ LoadFromOffset(
-      R6, R6, Isolate::single_step_offset(), kNoPP, kUnsignedByte);
-  __ CompareImmediate(R6, 0, kNoPP);
-  __ b(&stepping, NE);
-  __ Bind(&done_stepping);
+    if (FLAG_support_debugger) {
+    __ LoadIsolate(R6, kNoPP);
+    __ LoadFromOffset(
+        R6, R6, Isolate::single_step_offset(), kNoPP, kUnsignedByte);
+    __ CompareImmediate(R6, 0, kNoPP);
+    __ b(&stepping, NE);
+    __ Bind(&done_stepping);
+  }
 
   // R5: IC data object (preserved).
   __ LoadFieldFromOffset(R6, R5, ICData::ic_data_offset(), kNoPP);
   // R6: ic_data_array with entries: target functions and count.
   __ AddImmediate(R6, R6, Array::data_offset() - kHeapObjectTag, kNoPP);
   // R6: points directly to the first ic data array element.
   const intptr_t target_offset = ICData::TargetIndexFor(0) * kWordSize;
   const intptr_t count_offset = ICData::CountIndexFor(0) * kWordSize;
 
   if (FLAG_optimization_counter_threshold >= 0) {
@@ skipping 11 matching lines @@
   // Get function and call it, if possible.
   __ LoadFromOffset(R0, R6, target_offset, kNoPP);
   __ LoadFieldFromOffset(R2, R0, Function::instructions_offset(), kNoPP);
 
   // R0: function.
   // R2: target instructons.
   __ AddImmediate(
       R2, R2, Instructions::HeaderSize() - kHeapObjectTag, kNoPP);
   __ br(R2);
 
-  __ Bind(&stepping);
-  __ EnterStubFrame();
-  __ Push(R5);  // Preserve IC data.
-  __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
-  __ Pop(R5);
-  __ LeaveStubFrame();
-  __ b(&done_stepping);
+  if (FLAG_support_debugger) {
+    __ Bind(&stepping);
+    __ EnterStubFrame();
+    __ Push(R5);  // Preserve IC data.
+    __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
+    __ Pop(R5);
+    __ LeaveStubFrame();
+    __ b(&done_stepping);
+  }
 }
 
 
 void StubCode::GenerateOneArgUnoptimizedStaticCallStub(Assembler* assembler) {
   GenerateUsageCounterIncrement(assembler, R6);
   GenerateNArgsCheckInlineCacheStub(
       assembler, 1, kStaticCallMissHandlerOneArgRuntimeEntry, Token::kILLEGAL,
       kIgnoreRanges);
 }
 
@@ skipping 318 matching lines @@
 
 // Called only from unoptimized code. All relevant registers have been saved.
 // LR: return address.
 // SP + 4: left operand.
 // SP + 0: right operand.
 // Return Zero condition flag set if equal.
 void StubCode::GenerateUnoptimizedIdenticalWithNumberCheckStub(
     Assembler* assembler) {
   // Check single stepping.
   Label stepping, done_stepping;
-  __ LoadIsolate(R1, kNoPP);
-  __ LoadFromOffset(
-      R1, R1, Isolate::single_step_offset(), kNoPP, kUnsignedByte);
-  __ CompareImmediate(R1, 0, kNoPP);
-  __ b(&stepping, NE);
-  __ Bind(&done_stepping);
+  if (FLAG_support_debugger) {
+    __ LoadIsolate(R1, kNoPP);
+    __ LoadFromOffset(
+        R1, R1, Isolate::single_step_offset(), kNoPP, kUnsignedByte);
+    __ CompareImmediate(R1, 0, kNoPP);
+    __ b(&stepping, NE);
+    __ Bind(&done_stepping);
+  }
 
   const Register left = R1;
   const Register right = R0;
   __ LoadFromOffset(left, SP, 1 * kWordSize, kNoPP);
   __ LoadFromOffset(right, SP, 0 * kWordSize, kNoPP);
   GenerateIdenticalWithNumberCheckStub(assembler, left, right);
   __ ret();
 
-  __ Bind(&stepping);
-  __ EnterStubFrame();
-  __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
-  __ LeaveStubFrame();
-  __ b(&done_stepping);
+  if (FLAG_support_debugger) {
+    __ Bind(&stepping);
+    __ EnterStubFrame();
+    __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
+    __ LeaveStubFrame();
+    __ b(&done_stepping);
+  }
 }
 
 
 // Called from optimized code only.
 // LR: return address.
 // SP + 4: left operand.
 // SP + 0: right operand.
 // Return Zero condition flag set if equal.
 void StubCode::GenerateOptimizedIdenticalWithNumberCheckStub(
     Assembler* assembler) {
@@ skipping 56 matching lines @@
 // Result:
 //  R1: entry point.
 void StubCode::GenerateMegamorphicLookupStub(Assembler* assembler) {
   EmitMegamorphicLookup(assembler, R0, R1, R1);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64