if (VM.VerifyAssertions) VM.assert(x >= 0 && x < (FIXED_SIZE_MASK >>> FIXED_SIZE_SHIFT));
if (VM.VerifyAssertions) VM._assert(x >= 0 && x < (FIXED_SIZE_MASK >>> FIXED_SIZE_SHIFT));
  final void setFrameFixedSize(int x) {    if (VM.VerifyAssertions) VM.assert(x >= 0 && x < (FIXED_SIZE_MASK >>> FIXED_SIZE_SHIFT));    _bits = (_bits & ~FIXED_SIZE_MASK) | (((long)x) << FIXED_SIZE_SHIFT);  }