Reapply "Initial implementation of on-stack replacement (OSR)."

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"
@@ skipping 1400 matching lines @@
     __ pushq(ic_reg);       // Argument.
     __ pushq(func_reg);     // Argument.
     __ CallRuntime(kTraceICCallRuntimeEntry);
     __ popq(RAX);          // Discard argument;
     __ popq(RAX);          // Discard argument;
     __ popq(ic_reg);       // Restore.
     __ popq(argdesc_reg);  // Restore.
     __ popq(func_reg);     // Restore.
     __ LeaveFrame();
   }
-  Label is_hot;
-  if (FlowGraphCompiler::CanOptimize()) {
-    ASSERT(FLAG_optimization_counter_threshold > 1);
-    __ cmpq(FieldAddress(func_reg, Function::usage_counter_offset()),
-        Immediate(FLAG_optimization_counter_threshold));
-    __ j(GREATER_EQUAL, &is_hot, Assembler::kNearJump);
-    // As long as VM has no OSR do not optimize in the middle of the function
-    // but only at exit so that we have collected all type feedback before
-    // optimizing.
-  }
   __ incq(FieldAddress(func_reg, Function::usage_counter_offset()));
-  __ Bind(&is_hot);
 }
 
 
 // Loads function into 'temp_reg', preserves 'ic_reg'.
 void StubCode::GenerateUsageCounterIncrement(Assembler* assembler,
                                              Register temp_reg) {
   Register ic_reg = RBX;
   Register func_reg = temp_reg;
   ASSERT(ic_reg != func_reg);
   __ movq(func_reg, FieldAddress(ic_reg, ICData::function_offset()));
-  Label is_hot;
-  if (FlowGraphCompiler::CanOptimize()) {
-    ASSERT(FLAG_optimization_counter_threshold > 1);
-    // The usage_counter is always less than FLAG_optimization_counter_threshold
-    // except when the function gets optimized.
-    __ cmpq(FieldAddress(func_reg, Function::usage_counter_offset()),
-        Immediate(FLAG_optimization_counter_threshold));
-    __ j(EQUAL, &is_hot, Assembler::kNearJump);
-    // As long as VM has no OSR do not optimize in the middle of the function
-    // but only at exit so that we have collected all type feedback before
-    // optimizing.
-  }
   __ incq(FieldAddress(func_reg, Function::usage_counter_offset()));
-  __ Bind(&is_hot);
 }
 
+
 // Generate inline cache check for 'num_args'.
 //  RBX: Inline cache data object.
 //  R10: Arguments descriptor array.
 //  TOS(0): return address
 // Control flow:
 // - If receiver is null -> jump to IC miss.
 // - If receiver is Smi -> load Smi class.
 // - If receiver is not-Smi -> load receiver's class.
 // - Check if 'num_args' (including receiver) match any IC data group.
 // - Match found -> jump to target.
@@ skipping 632 matching lines @@
   __ cmpq(left, right);
   __ Bind(&done);
   __ popq(right);
   __ popq(left);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64