Make return statements single steppable

runtime/vm/intermediate_language_x64.cc

Index: runtime/vm/intermediate_language_x64.cc
===================================================================
--- runtime/vm/intermediate_language_x64.cc	(revision 31428)
+++ runtime/vm/intermediate_language_x64.cc	(working copy)
@@ -96,11 +96,8 @@
     __ Bind(&done);
   }
 #endif
-
-  __ ReturnPatchable();
-  compiler->AddCurrentDescriptor(PcDescriptors::kReturn,
-                                 Isolate::kNoDeoptId,
-                                 token_pos());
+  __ LeaveDartFrame();
+  __ ret();
 }
 
 
@@ -640,6 +637,34 @@
 }
 
 
+LocationSummary* DebugStepCheckInstr::MakeLocationSummary(bool opt) const {
+  const intptr_t kNumInputs = 0;
+  const intptr_t kNumTemps = 0;
+  LocationSummary* locs =
+      new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kCall);
+  return locs;
+}
+
+
+void DebugStepCheckInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  if (!compiler->is_optimizing()) {
+    const ExternalLabel label("debug_step_check",
+                              StubCode::DebugStepCheckEntryPoint());
+    compiler->GenerateCall(token_pos(),
+                           &label,
+                           PcDescriptors::kReturn,
+                           locs());
+  }
+}
+
+
+Instruction* DebugStepCheckInstr::Canonicalize(FlowGraph* flow_graph) {
+  if (compiler->is_optimizing()) {
+    return NULL;
+  }
+}
+
+
 static bool CanBeImmediateIndex(Value* index, intptr_t cid) {
   if (!index->definition()->IsConstant()) return false;
   const Object& constant = index->definition()->AsConstant()->value();