src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp

@@ -5058,12 +5058,12 @@
  // Input:
  // src - the oop we want to load the klass from.
  // dst - output narrow klass.
  void MacroAssembler::load_narrow_klass_compact(Register dst, Register src) {
    assert(UseCompactObjectHeaders, "expects UseCompactObjectHeaders");
-   ldr(dst, Address(src, oopDesc::mark_offset_in_bytes()));
-   lsr(dst, dst, markWord::klass_shift);
+   ldrw(dst, Address(src, oopDesc::mark_offset_in_bytes()));
+   lsrw(dst, dst, markWord::klass_shift);
  }
  
  void MacroAssembler::load_klass(Register dst, Register src) {
    if (UseCompactObjectHeaders) {
      load_narrow_klass_compact(dst, src);

@@ -5900,25 +5900,32 @@
                                        Register tmp4, Register tmp5, Register result,
                                        Register cnt1, int elem_size) {
    Label DONE, SAME;
    Register tmp1 = rscratch1;
    Register tmp2 = rscratch2;
+   Register cnt2 = tmp2;  // cnt2 only used in array length compare
    int elem_per_word = wordSize/elem_size;
    int log_elem_size = exact_log2(elem_size);
    int klass_offset  = arrayOopDesc::klass_offset_in_bytes();
    int length_offset = arrayOopDesc::length_offset_in_bytes();
    int base_offset
      = arrayOopDesc::base_offset_in_bytes(elem_size == 2 ? T_CHAR : T_BYTE);
    // When the length offset is not aligned to 8 bytes,
    // then we align it down. This is valid because the new
    // offset will always be the klass which is the same
    // for type arrays.
-   int start_offset = align_down(length_offset, BytesPerWord);
+   // With 4-byte headers, we need to start at the base-offset, and check
+   // the length field explicitly.
+   int start_offset = UseCompactObjectHeaders ? base_offset : align_down(length_offset, BytesPerWord);
    int extra_length = base_offset - start_offset;
-   assert(start_offset == length_offset || start_offset == klass_offset,
-          "start offset must be 8-byte-aligned or be the klass offset");
-   assert(base_offset != start_offset, "must include the length field");
+   if (UseCompactObjectHeaders) {
+     assert(base_offset == start_offset, "must start at base-offset");
+   } else {
+     assert(start_offset == length_offset || start_offset == klass_offset,
+            "start offset must be 8-byte-aligned or be the klass offset");
+     assert(base_offset != start_offset, "must include the length field");
+   }
    extra_length = extra_length / elem_size; // We count in elements, not bytes.
    int stubBytesThreshold = 3 * 64 + (UseSIMDForArrayEquals ? 0 : 16);
  
    assert(elem_size == 1 || elem_size == 2, "must be char or byte");
    assert_different_registers(a1, a2, result, cnt1, rscratch1, rscratch2);