Make return statements single steppable

runtime/vm/intermediate_language_mips.cc

Index: runtime/vm/intermediate_language_mips.cc
===================================================================
--- runtime/vm/intermediate_language_mips.cc	(revision 31428)
+++ runtime/vm/intermediate_language_mips.cc	(working copy)
@@ -101,13 +101,7 @@
     __ Bind(&stack_ok);
   }
 #endif
-  // This sequence is patched by a debugger breakpoint. There is no need for
-  // extra NOP instructions here because the sequence patched in for a
-  // breakpoint is shorter than the sequence here.
   __ LeaveDartFrameAndReturn();
-  compiler->AddCurrentDescriptor(PcDescriptors::kReturn,
-                                 Isolate::kNoDeoptId,
-                                 token_pos());
 }
 
 
@@ -786,6 +780,34 @@
 }
 
 
+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;
+  }
+}
+
+
 LocationSummary* StringFromCharCodeInstr::MakeLocationSummary(bool opt) const {
   const intptr_t kNumInputs = 1;
   // TODO(fschneider): Allow immediate operands for the char code.