src/hotspot/cpu/aarch64/c1_MacroAssembler_aarch64.cpp

@@ -178,24 +178,29 @@
    }
  }
  
  void C1_MacroAssembler::initialize_header(Register obj, Register klass, Register len, Register t1, Register t2) {
    assert_different_registers(obj, klass, len);
-   // This assumes that all prototype bits fit in an int32_t
-   mov(t1, (int32_t)(intptr_t)markWord::prototype().value());
-   str(t1, Address(obj, oopDesc::mark_offset_in_bytes()));
- 
-   if (UseCompressedClassPointers) { // Take care not to kill klass
-     encode_klass_not_null(t1, klass);
-     strw(t1, Address(obj, oopDesc::klass_offset_in_bytes()));
+   if (UseCompactObjectHeaders) {
+     ldr(t1, Address(klass, Klass::prototype_header_offset()));
+     str(t1, Address(obj, oopDesc::mark_offset_in_bytes()));
    } else {
-     str(klass, Address(obj, oopDesc::klass_offset_in_bytes()));
+     // This assumes that all prototype bits fit in an int32_t
+     mov(t1, (int32_t)(intptr_t)markWord::prototype().value());
+     str(t1, Address(obj, oopDesc::mark_offset_in_bytes()));
+ 
+     if (UseCompressedClassPointers) { // Take care not to kill klass
+       encode_klass_not_null(t1, klass);
+       strw(t1, Address(obj, oopDesc::klass_offset_in_bytes()));
+     } else {
+       str(klass, Address(obj, oopDesc::klass_offset_in_bytes()));
+     }
    }
  
    if (len->is_valid()) {
      strw(len, Address(obj, arrayOopDesc::length_offset_in_bytes()));
-   } else if (UseCompressedClassPointers) {
+   } else if (UseCompressedClassPointers && !UseCompactObjectHeaders) {
      store_klass_gap(obj, zr);
    }
  }
  
  // preserves obj, destroys len_in_bytes

@@ -269,11 +274,11 @@
      far_call(RuntimeAddress(Runtime1::entry_for(Runtime1::dtrace_object_alloc_id)));
    }
  
    verify_oop(obj);
  }
- void C1_MacroAssembler::allocate_array(Register obj, Register len, Register t1, Register t2, int header_size, int f, Register klass, Label& slow_case) {
+ void C1_MacroAssembler::allocate_array(Register obj, Register len, Register t1, Register t2, int base_offset_in_bytes, int f, Register klass, Label& slow_case) {
    assert_different_registers(obj, len, t1, t2, klass);
  
    // determine alignment mask
    assert(!(BytesPerWord & 1), "must be a multiple of 2 for masking code to work");
  

@@ -282,20 +287,31 @@
    cmp(len, rscratch1);
    br(Assembler::HS, slow_case);
  
    const Register arr_size = t2; // okay to be the same
    // align object end
-   mov(arr_size, (int32_t)header_size * BytesPerWord + MinObjAlignmentInBytesMask);
+   mov(arr_size, (int32_t)base_offset_in_bytes + MinObjAlignmentInBytesMask);
    add(arr_size, arr_size, len, ext::uxtw, f);
    andr(arr_size, arr_size, ~MinObjAlignmentInBytesMask);
  
    try_allocate(obj, arr_size, 0, t1, t2, slow_case);
  
    initialize_header(obj, klass, len, t1, t2);
  
+   // Clear leading 4 bytes, if necessary.
+   // TODO: This could perhaps go into initialize_body() and also clear the leading 4 bytes
+   // for non-array objects, thereby replacing the klass-gap clearing code in initialize_header().
+   int base_offset = base_offset_in_bytes;
+   if (!is_aligned(base_offset, BytesPerWord)) {
+     assert(is_aligned(base_offset, BytesPerInt), "must be 4-byte aligned");
+     strw(zr, Address(obj, base_offset));
+     base_offset += BytesPerInt;
+   }
+   assert(is_aligned(base_offset, BytesPerWord), "must be word-aligned");
+ 
    // clear rest of allocated space
-   initialize_body(obj, arr_size, header_size * BytesPerWord, t1, t2);
+   initialize_body(obj, arr_size, base_offset, t1, t2);
    if (Compilation::current()->bailed_out()) {
      return;
    }
  
    membar(StoreStore);

@@ -311,11 +327,15 @@
  
  void C1_MacroAssembler::inline_cache_check(Register receiver, Register iCache) {
    verify_oop(receiver);
    // explicit null check not needed since load from [klass_offset] causes a trap
    // check against inline cache
-   assert(!MacroAssembler::needs_explicit_null_check(oopDesc::klass_offset_in_bytes()), "must add explicit null check");
+   if (UseCompactObjectHeaders) {
+     assert(!MacroAssembler::needs_explicit_null_check(oopDesc::mark_offset_in_bytes()), "must add explicit null check");
+   } else {
+     assert(!MacroAssembler::needs_explicit_null_check(oopDesc::klass_offset_in_bytes()), "must add explicit null check");
+   }
  
    cmp_klass(receiver, iCache, rscratch1);
  }