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

runtime/vm/flow_graph_compiler_x64.cc

Index: runtime/vm/flow_graph_compiler_x64.cc
diff --git a/runtime/vm/flow_graph_compiler_x64.cc b/runtime/vm/flow_graph_compiler_x64.cc
index d15ecea46eb52fbec7fa68fba0eaacdcaa669088..df39bc48ff4427ee6ba483e6484d541ec30fc432 100644
--- a/runtime/vm/flow_graph_compiler_x64.cc
+++ b/runtime/vm/flow_graph_compiler_x64.cc
@@ -23,6 +23,7 @@ namespace dart {
 
 DEFINE_FLAG(bool, trap_on_deoptimization, false, "Trap on deoptimization.");
 DECLARE_FLAG(int, optimization_counter_threshold);
+DECLARE_FLAG(int, reoptimization_counter_threshold);
 DECLARE_FLAG(bool, print_ast);
 DECLARE_FLAG(bool, print_scopes);
 DECLARE_FLAG(bool, enable_type_checks);
@@ -1071,34 +1072,43 @@ void FlowGraphCompiler::GenerateInlinedSetter(intptr_t offset) {
 
 void FlowGraphCompiler::EmitFrameEntry() {
   const Function& function = parsed_function().function();
-  if (CanOptimizeFunction() && function.is_optimizable()) {
-    const bool can_optimize = !is_optimizing() || may_reoptimize();
+  if (CanOptimizeFunction() &&
+      function.is_optimizable() &&
+      (!is_optimizing() || may_reoptimize())) {
     const Register function_reg = RDI;
-    if (can_optimize) {
-      __ LoadObject(function_reg, function);
-    }
+    __ LoadObject(function_reg, function);
     // Patch point is after the eventually inlined function object.
     AddCurrentDescriptor(PcDescriptors::kEntryPatch,
                          Isolate::kNoDeoptId,
                          0);  // No token position.
-    if (can_optimize) {
-      // Reoptimization of optimized function is triggered by counting in
+    if (is_optimizing()) {
+      // Reoptimization of an optimized function is triggered by counting in
       // IC stubs, but not at the entry of the function.
-      if (!is_optimizing()) {
-        __ incq(FieldAddress(function_reg, Function::usage_counter_offset()));
-      }
       __ cmpq(FieldAddress(function_reg, Function::usage_counter_offset()),
-          Immediate(FLAG_optimization_counter_threshold));
-      ASSERT(function_reg == RDI);
-      __ j(GREATER_EQUAL, &StubCode::OptimizeFunctionLabel());
+              Immediate(FLAG_reoptimization_counter_threshold));
+    } else {
+      __ incq(FieldAddress(function_reg, Function::usage_counter_offset()));
+      __ cmpq(FieldAddress(function_reg, Function::usage_counter_offset()),
+              Immediate(FLAG_optimization_counter_threshold));
     }
-  } else {
+    ASSERT(function_reg == RDI);
+    __ j(GREATER_EQUAL, &StubCode::OptimizeFunctionLabel());
+  } else if (!flow_graph().IsCompiledForOsr()) {
     AddCurrentDescriptor(PcDescriptors::kEntryPatch,
-                     Isolate::kNoDeoptId,
-                     0);  // No token position.
+                         Isolate::kNoDeoptId,
+                         0);  // No token position.
   }
   __ Comment("Enter frame");
-  __ EnterDartFrame(StackSize() * kWordSize);
+  if (flow_graph().IsCompiledForOsr()) {
+    intptr_t extra_slots = StackSize()
+        - flow_graph().num_stack_locals()
+        - flow_graph().num_copied_params();
+    ASSERT(extra_slots >= 0);
+    __ EnterOsrFrame(extra_slots * kWordSize);
+  } else {
+    ASSERT(StackSize() >= 0);
+    __ EnterDartFrame(StackSize() * kWordSize);
+  }
 }
 
 
@@ -1131,9 +1141,10 @@ void FlowGraphCompiler::CompileGraph() {
   if (num_copied_params == 0) {
 #ifdef DEBUG
     ASSERT(!parsed_function().function().HasOptionalParameters());
-    const bool check_arguments = true;
+    const bool check_arguments = !flow_graph().IsCompiledForOsr();
 #else
-    const bool check_arguments = function.IsClosureFunction();
+    const bool check_arguments =
+        function.IsClosureFunction() && !flow_graph().IsCompiledForOsr();
 #endif
     if (check_arguments) {
       __ Comment("Check argument count");
@@ -1191,7 +1202,7 @@ void FlowGraphCompiler::CompileGraph() {
     // The arguments descriptor is never saved in the absence of optional
     // parameters, since any argument definition test would always yield true.
     ASSERT(saved_args_desc_var == NULL);
-  } else {
+  } else if (!flow_graph().IsCompiledForOsr()) {
     if (saved_args_desc_var != NULL) {
       __ Comment("Save arguments descriptor");
       const Register kArgumentsDescriptorReg = R10;