Implement basic support for deferred slow path code with calls that save and restore live registers.

runtime/vm/locations.h

Index: runtime/vm/locations.h
diff --git a/runtime/vm/locations.h b/runtime/vm/locations.h
index 6e4393ca6a797b7fe8e340687aa270a6547c086c..cad43ea58b04f3b02298bd6f42ca9a3b95c5d945 100644
--- a/runtime/vm/locations.h
+++ b/runtime/vm/locations.h
@@ -208,12 +208,34 @@ class Location : public ValueObject {
 };
 
 
+class RegisterSet : public ValueObject {
+ public:
+  RegisterSet() : registers_(0) {
+    ASSERT(kNumberOfCpuRegisters < (kWordSize * kBitsPerByte));
+  }
+
+  void Add(Register reg) {
+    registers_ |= (1 << reg);
+  }
+
+  bool Contains(Register reg) {
+    return (registers_ & (1 << reg)) != 0;
+  }
+
+ private:
+  intptr_t registers_;
+
+  DISALLOW_COPY_AND_ASSIGN(RegisterSet);
+};
+
+
 // Specification of locations for inputs and output.
 class LocationSummary : public ZoneAllocated {
  public:
   enum ContainsCall {
     kNoCall,
     kCall,
+    kCallOnSlowPath
   };
 
   LocationSummary(intptr_t input_count,
@@ -262,7 +284,6 @@ class LocationSummary : public ZoneAllocated {
     return &output_location_;
   }
 
-
   void set_out(Location loc) {
     ASSERT(!is_call() || loc.IsRegister());
     output_location_ = loc;
@@ -271,14 +292,22 @@ class LocationSummary : public ZoneAllocated {
   BitmapBuilder* stack_bitmap() const { return stack_bitmap_; }
 
   bool is_call() const {
-    return is_call_;
+    return contains_call_ == kCall;
+  }
+
+  bool contains_call() const {

[srdjan, 2012/08/15 00:12:03]

I find is_call vs contains_call too similar/confusing

maybe is_always_call vs is_slow_path_call ?

Also, I would expect an accessor named contains_call() to return the field
contains_call_

[Vyacheslav Egorov (Google), 2012/08/15 13:08:07]

I rename contains_call() into can_call(), is_call into always_calls()

+    return contains_call_ != kNoCall;
   }
 
   void PrintTo(BufferFormatter* f) const;
 
   static LocationSummary* Make(intptr_t input_count,
                                Location out,
-                               LocationSummary::ContainsCall contains_call);
+                               ContainsCall contains_call);
+
+  RegisterSet* live_registers() {
+    return &live_registers_;
+  }
 
  private:
   // TODO(vegorov): replace with ZoneArray.
@@ -286,7 +315,9 @@ class LocationSummary : public ZoneAllocated {
   GrowableArray<Location> temp_locations_;
   Location output_location_;
   BitmapBuilder* stack_bitmap_;
-  const bool is_call_;
+
+  const ContainsCall contains_call_;
+  RegisterSet live_registers_;
 };