Move alignment-gap-clearing into allocate_array() (aarch64)

src/hotspot/cpu/aarch64/c1_MacroAssembler_aarch64.cpp

@@ -193,10 +193,6 @@ void C1_MacroAssembler::initialize_header(Register obj, Register klass, Register
 
   if (len->is_valid()) {
     strw(len, Address(obj, arrayOopDesc::length_offset_in_bytes()));
-    if (!is_aligned(arrayOopDesc::header_size_in_bytes(), BytesPerWord)) {
-      assert(is_aligned(arrayOopDesc::header_size_in_bytes(), BytesPerInt), "must be 4-byte aligned");
-      strw(zr, Address(obj, arrayOopDesc::header_size_in_bytes()));
-    }
   } else if (UseCompressedClassPointers) {
     store_klass_gap(obj, zr);
   }
@@ -296,11 +292,19 @@ void C1_MacroAssembler::allocate_array(Register obj, Register len, Register t1,
 
   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
-  // We align-up the header size to word-size, because we clear the
-  // possible alignment gap in initialize_header().
-  int hdr_size = align_up(base_offset_in_bytes, BytesPerWord);
-  initialize_body(obj, arr_size, hdr_size, t1, t2);
+  initialize_body(obj, arr_size, base_offset, t1, t2);
   if (Compilation::current()->bailed_out()) {
     return;
   }