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

runtime/vm/stub_code_x64.cc

 // Copyright (c) 2013, 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_X64)
 
 #include "vm/assembler.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/resolver.h"
 #include "vm/scavenger.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:
 //   RSP : points to return address.
 //   RSP + 8 : address of last argument in argument array.
 //   RSP + 8*R10 : address of first argument in argument array.
 //   RSP + 8*R10 + 8 : address of return value.
 //   RBX : address of the runtime function to call.
 //   R10 : number of arguments to the call.
 // Must preserve callee saved registers R12 and R13.
 void StubCode::GenerateCallToRuntimeStub(Assembler* assembler) {
@@ skipping 1297 matching lines @@
     __ movl(RCX, FieldAddress(RBX, ICData::state_bits_offset()));
     ASSERT(ICData::NumArgsTestedShift() == 0);  // No shift needed.
     __ andq(RCX, Immediate(ICData::NumArgsTestedMask()));
     __ cmpq(RCX, Immediate(num_args));
     __ j(EQUAL, &ok, Assembler::kNearJump);
     __ Stop("Incorrect stub for IC data");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
-  __ Comment("Check single stepping");
   Label stepping, done_stepping;
-  __ LoadIsolate(RAX);
-  __ cmpb(Address(RAX, Isolate::single_step_offset()), Immediate(0));
-  __ j(NOT_EQUAL, &stepping);
-  __ Bind(&done_stepping);
+  if (FLAG_support_debugger) {
+    __ Comment("Check single stepping");
+    __ LoadIsolate(RAX);
+    __ cmpb(Address(RAX, Isolate::single_step_offset()), Immediate(0));
+    __ j(NOT_EQUAL, &stepping);
+    __ 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) {
       __ movq(RAX, Address(RSP, + 2 * kWordSize));
       __ UpdateRangeFeedback(RAX, 0, RBX, RCX, &not_smi_or_overflow);
     }
 
@@ skipping 133 matching lines @@
     __ movq(RDX, RAX);
     __ movq(RBX, Address(RBP, kFirstLocalSlotFromFp * kWordSize));
     __ UpdateRangeFeedback(RDX, 2, RBX, RCX, &done);
     __ Bind(&done);
     __ LeaveStubFrame();
     __ ret();
   } else {
     __ jmp(RCX);
   }
 
-  __ Bind(&stepping);
-  __ EnterStubFrame();
-  __ pushq(RBX);
-  __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
-  __ popq(RBX);
-  __ LeaveStubFrame();
-  __ jmp(&done_stepping);
+  if (FLAG_support_debugger) {
+    __ Bind(&stepping);
+    __ EnterStubFrame();
+    __ pushq(RBX);
+    __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
+    __ popq(RBX);
+    __ LeaveStubFrame();
+    __ jmp(&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).
 //  RBX: Inline cache data object.
 //  TOS(0): Return address.
 // Inline cache data object structure:
 // 0: function-name
 // 1: N, number of arguments checked.
@@ skipping 129 matching lines @@
     __ andq(RCX, Immediate(ICData::NumArgsTestedMask()));
     __ cmpq(RCX, Immediate(0));
     __ j(EQUAL, &ok, Assembler::kNearJump);
     __ Stop("Incorrect IC data for unoptimized static call");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
   // Check single stepping.
   Label stepping, done_stepping;
-  __ LoadIsolate(RAX);
-  __ movzxb(RAX, Address(RAX, Isolate::single_step_offset()));
-  __ cmpq(RAX, Immediate(0));
+  if (FLAG_support_debugger) {
+    __ LoadIsolate(RAX);
+    __ movzxb(RAX, Address(RAX, Isolate::single_step_offset()));
+    __ cmpq(RAX, Immediate(0));
 #if defined(DEBUG)
       static const bool kJumpLength = Assembler::kFarJump;
 #else
       static const bool kJumpLength = Assembler::kNearJump;
 #endif  // DEBUG
-  __ j(NOT_EQUAL, &stepping, kJumpLength);
-  __ Bind(&done_stepping);
+    __ j(NOT_EQUAL, &stepping, kJumpLength);
+    __ Bind(&done_stepping);
+  }
 
   // RBX: IC data object (preserved).
   __ movq(R12, FieldAddress(RBX, ICData::ic_data_offset()));
   // R12: ic_data_array with entries: target functions and count.
   __ leaq(R12, FieldAddress(R12, Array::data_offset()));
   // R12: 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) {
     // Increment count for this call.
     __ movq(R8, Address(R12, count_offset));
     __ addq(R8, Immediate(Smi::RawValue(1)));
     __ movq(R9, Immediate(Smi::RawValue(Smi::kMaxValue)));
     __ cmovnoq(R9, R8);
     __ StoreIntoSmiField(Address(R12, count_offset), R9);
   }
 
   // Load arguments descriptor into R10.
   __ movq(R10, FieldAddress(RBX, ICData::arguments_descriptor_offset()));
 
   // Get function and call it, if possible.
   __ movq(RAX, Address(R12, target_offset));
   __ movq(RCX, FieldAddress(RAX, Function::instructions_offset()));
   // RCX: Target instructions.
   __ addq(RCX, Immediate(Instructions::HeaderSize() - kHeapObjectTag));
   __ jmp(RCX);
 
-  __ Bind(&stepping);
-  __ EnterStubFrame();
-  __ pushq(RBX);  // Preserve IC data object.
-  __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
-  __ popq(RBX);
-  __ LeaveStubFrame();
-  __ jmp(&done_stepping, Assembler::kNearJump);
+  if (FLAG_support_debugger) {
+    __ Bind(&stepping);
+    __ EnterStubFrame();
+    __ pushq(RBX);  // Preserve IC data object.
+    __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
+    __ popq(RBX);
+    __ LeaveStubFrame();
+    __ jmp(&done_stepping, Assembler::kNearJump);
+  }
 }
 
 
 void StubCode::GenerateOneArgUnoptimizedStaticCallStub(Assembler* assembler) {
   GenerateUsageCounterIncrement(assembler, RCX);
   GenerateNArgsCheckInlineCacheStub(
       assembler,
       1,
       kStaticCallMissHandlerOneArgRuntimeEntry,
       Token::kILLEGAL,
@@ skipping 350 matching lines @@
 
 // Called only from unoptimized code. All relevant registers have been saved.
 // TOS + 0: return address
 // TOS + 1: right argument.
 // TOS + 2: left argument.
 // Returns ZF set.
 void StubCode::GenerateUnoptimizedIdenticalWithNumberCheckStub(
     Assembler* assembler) {
   // Check single stepping.
   Label stepping, done_stepping;
-  __ LoadIsolate(RAX);
-  __ movzxb(RAX, Address(RAX, Isolate::single_step_offset()));
-  __ cmpq(RAX, Immediate(0));
-  __ j(NOT_EQUAL, &stepping);
-  __ Bind(&done_stepping);
+  if (FLAG_support_debugger) {
+    __ LoadIsolate(RAX);
+    __ movzxb(RAX, Address(RAX, Isolate::single_step_offset()));
+    __ cmpq(RAX, Immediate(0));
+    __ j(NOT_EQUAL, &stepping);
+    __ Bind(&done_stepping);
+  }
 
   const Register left = RAX;
   const Register right = RDX;
 
   __ movq(left, Address(RSP, 2 * kWordSize));
   __ movq(right, Address(RSP, 1 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right);
   __ ret();
 
-  __ Bind(&stepping);
-  __ EnterStubFrame();
-  __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
-  __ LeaveStubFrame();
-  __ jmp(&done_stepping);
+  if (FLAG_support_debugger) {
+    __ Bind(&stepping);
+    __ EnterStubFrame();
+    __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
+    __ LeaveStubFrame();
+    __ jmp(&done_stepping);
+  }
 }
 
 
 // Called from optimized code only.
 // TOS + 0: return address
 // TOS + 1: right argument.
 // TOS + 2: left argument.
 // Returns ZF set.
 void StubCode::GenerateOptimizedIdenticalWithNumberCheckStub(
     Assembler* assembler) {
@@ skipping 55 matching lines @@
 // Result:
 //  RCX: entry point.
 void StubCode::GenerateMegamorphicLookupStub(Assembler* assembler) {
   EmitMegamorphicLookup(assembler, RDI, RBX, RCX);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64