6889740: G1: OpenDS fails with "unhandled exception in compiled code"

Summary: Incorrect code was being generated for the store operation in the null case of the aastore bytecode template. The bad code was generated by the store_heap_oop routine which takes a Register as its second argument. Passing NULL_WORD (0) as the second argument causes the value to be converted to Register(0), which is rax. Thus the generated store was "mov (dst), $rax" instead of "mov (dst), $0x0". Changed calls to store_heap_oop that pass NULL_WORD as the second argument to a new routine store_heap_oop_null.
Reviewed-by: kvn, twisti

src/cpu/x86/vm/assembler_x86.cpp

@@ -8214,6 +8214,15 @@ void MacroAssembler::store_heap_oop(Address dst, Register src) {
   }
 }
 
+// Used for storing NULLs.
+void MacroAssembler::store_heap_oop_null(Address dst) {
+  if (UseCompressedOops) {
+    movl(dst, (int32_t)NULL_WORD);
+  } else {
+    movslq(dst, (int32_t)NULL_WORD);
+  }
+}
+
 // Algorithm must match oop.inline.hpp encode_heap_oop.
 void MacroAssembler::encode_heap_oop(Register r) {
   assert (UseCompressedOops, "should be compressed");

src/cpu/x86/vm/assembler_x86.hpp

@@ -1682,6 +1682,17 @@ class MacroAssembler: public Assembler {
 
   void load_heap_oop(Register dst, Address src);
   void store_heap_oop(Address dst, Register src);
+
+  // This dummy is to prevent a call to store_heap_oop from
+  // converting a zero (like NULL) into a Register by giving
+  // the compiler two choices it can't resolve
+
+  void store_heap_oop(Address dst, void* dummy);
+
+  // Used for storing NULL. All other oop constants should be
+  // stored using routines that take a jobject.
+  void store_heap_oop_null(Address dst);
+
   void encode_heap_oop(Register r);
   void decode_heap_oop(Register r);
   void encode_heap_oop_not_null(Register r);

src/cpu/x86/vm/templateTable_x86_64.cpp

@@ -139,7 +139,7 @@ static void do_oop_store(InterpreterMacroAssembler* _masm,
         }
         __ g1_write_barrier_pre(rdx, r8, rbx, val != noreg);
         if (val == noreg) {
-          __ store_heap_oop(Address(rdx, 0), NULL_WORD);
+          __ store_heap_oop_null(Address(rdx, 0));
         } else {
           __ store_heap_oop(Address(rdx, 0), val);
           __ g1_write_barrier_post(rdx, val, r8, rbx);
@@ -152,7 +152,7 @@ static void do_oop_store(InterpreterMacroAssembler* _masm,
     case BarrierSet::CardTableExtension:
       {
         if (val == noreg) {
-          __ store_heap_oop(obj, NULL_WORD);
+          __ store_heap_oop_null(obj);
         } else {
           __ store_heap_oop(obj, val);
           // flatten object address if needed
@@ -168,7 +168,7 @@ static void do_oop_store(InterpreterMacroAssembler* _masm,
     case BarrierSet::ModRef:
     case BarrierSet::Other:
       if (val == noreg) {
-        __ store_heap_oop(obj, NULL_WORD);
+        __ store_heap_oop_null(obj);
       } else {
         __ store_heap_oop(obj, val);
       }