On 02/24/2015 02:48 PM, Andrew Haley wrote:
>private static final boolean IS_UNALIGNED = theUnsafe.unalignedAccess();
>
>public void putIntUnaligned(Object o, long offset, int x) { if (IS_UNALIGNED ||
(offset & 3) == 0) { putInt(o, offset, x); } else if (byteOrder == BIG_ENDIAN) {
putIntB(o, offset, x); } else { putIntL(o, offset, x); } }
Yes. It certainly could be done like this but I think C1 doesn't do
the optimization to remove the IS_UNALIGNED test, so we'd still want
the C1 builtins. Perhaps we could do without the C2 builtins but they
cost very little, they save C2 a fair amount of work, and they remove
the vagaries of inlining. I take your point about the interpreter,
though.
What about if you make unalignedAccess() and getByteOrder() static
methods in Unsafe (they are safe aren't they?) and then do the following:
public abstract class Unsafe {
...
private static final Unsafe theUnsafe =
unalignedAccess()
? (getByteOrder() ? new UnsafeUB() : new UnsafeUL())
: (getByteOrder() ? new UnsafeAB() : new UnsafeAL());
...
public abstract int getIntUnaligned(Object o, long offset);
...
private static final class UnsafeUB extends Unsafe { ... }
private static final class UnsafeUL extends Unsafe { ... }
private static final class UnsafeAB extends Unsafe { ... }
private static final class UnsafeAL extends Unsafe { ... }
There will be only one runtime Unsafe sub-type ever observed in a
particular VM.
Peter
