ARM port of r42723.

runtime/vm/assembler_arm.h

Index: runtime/vm/assembler_arm.h
===================================================================
--- runtime/vm/assembler_arm.h	(revision 42713)
+++ runtime/vm/assembler_arm.h	(working copy)
@@ -642,10 +642,12 @@
                                DRegister dtmp0, DRegister dtmp1,
                                Label* overflow);
 
-  // Load and Store. May clobber IP.
+  // Load and Store.
+  // These three do not clobber IP.
   void LoadPatchableImmediate(Register rd, int32_t value, Condition cond = AL);
   void LoadDecodableImmediate(Register rd, int32_t value, Condition cond = AL);
   void LoadImmediate(Register rd, int32_t value, Condition cond = AL);
+  // These two may clobber IP.
   void LoadSImmediate(SRegister sd, float value, Condition cond = AL);
   void LoadDImmediate(DRegister dd, double value,
                       Register scratch, Condition cond = AL);
@@ -662,6 +664,14 @@
   void PushObject(const Object& object);
   void CompareObject(Register rn, const Object& object);
 
+  // When storing into a heap object field, knowledge of the previous content
+  // is expressed through these constants.
+  enum FieldContent {
+    kEmptyOrSmiOrNull,  // Empty = garbage/zapped in release/debug mode.
+    kHeapObjectOrSmi,
+    kOnlySmi,
+  };
+
   void StoreIntoObject(Register object,  // Object we are storing into.
                        const Address& dest,  // Where we are storing into.
                        Register value,  // Value we are storing.
@@ -673,16 +683,27 @@
 
   void StoreIntoObjectNoBarrier(Register object,
                                 const Address& dest,
-                                Register value);
-  void StoreIntoObjectNoBarrierOffset(Register object,
-                                      int32_t offset,
-                                      Register value);
+                                Register value,
+                                FieldContent old_content = kHeapObjectOrSmi);
+  void InitializeFieldNoBarrier(Register object,
+                                const Address& dest,
+                                Register value) {
+    StoreIntoObjectNoBarrier(object, dest, value, kEmptyOrSmiOrNull);
+  }
+  void StoreIntoObjectNoBarrierOffset(
+      Register object,
+      int32_t offset,
+      Register value,
+      FieldContent old_content = kHeapObjectOrSmi);
   void StoreIntoObjectNoBarrier(Register object,
                                 const Address& dest,
-                                const Object& value);
-  void StoreIntoObjectNoBarrierOffset(Register object,
-                                      int32_t offset,
-                                      const Object& value);
+                                const Object& value,
+                                FieldContent old_content = kHeapObjectOrSmi);
+  void StoreIntoObjectNoBarrierOffset(
+      Register object,
+      int32_t offset,
+      const Object& value,
+      FieldContent old_content = kHeapObjectOrSmi);
 
   // Store value_even, value_odd, value_even, ... into the words in the address
   // range [begin, end), assumed to be uninitialized fields in object (tagged).
@@ -1096,7 +1117,9 @@
                               Condition cond = AL);
   // Writes new_value to address and its shadow location, if enabled, after
   // verifying that its old value matches its shadow.
-  void VerifiedWrite(const Address& address, Register new_value);
+  void VerifiedWrite(const Address& address,
+                     Register new_value,
+                     FieldContent old_content);
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Assembler);