RFR (S): JDK-8213479: Missing x86_64.ad patterns for 8-bit logical operators with destination in memory

[B. Blaser]

Hi Vladimir,

On Wed, 7 Nov 2018 at 19:59, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
>
> Hi Bernard,
>
> I am concern about next statement in Intel's Manual for these byte instructions:
>
> "*In 64-bit mode, r/m8 can not be encoded to access the following byte registers if a REX prefix is
> used: AH, BH, CH, DH."

yes, that's right but I guess we use AL, BL, CL and DL?

> Also I have question about applications which benefit from it. Which applications has such pattern?
> I did not find it in discussion you pointed.

for example:

http://hg.openjdk.java.net/jdk/jdk/file/f6583d7cff56/src/java.base/share/classes/java/lang/invoke/LambdaFormBuffer.java#l42
http://hg.openjdk.java.net/jdk/jdk/file/f6583d7cff56/src/java.base/share/classes/java/lang/invoke/LambdaFormBuffer.java#l234
http://hg.openjdk.java.net/jdk/jdk/file/f6583d7cff56/src/java.base/share/classes/java/lang/invoke/LambdaFormBuffer.java#l293

would benefit from these instructions.

Please, let me know if you have any other comment.

Thanks,
Bernard

> Thanks,
> Vladimir
>
> On 11/7/18 10:10 AM, B. Blaser wrote:
> > Hi,
> >
> > Please review the following small fix for [1] briefly discussed in thread [2]:
> >
> > http://cr.openjdk.java.net/~bsrbnd/jdk8213479/webrev.00/
> >
> > It adds missing patterns to x86_64.ad for 8-bit logical operators with
> > destination in memory.
> > For example, the following method would use 4 instructions and 2
> > registers instead of currently 10 instructions and 5 registers, see
> > [1]:
> >
> >      private static byte and = 0b0011, or = 0b0011, xor = 0b0011;
> >      private static byte mask = 0b0101;
> >
> >      public static void test() {
> >          and &= mask;
> >
> >          or |= mask;
> >
> >          xor ^= mask;
> >      }
> >
> > Tier1 is OK (hotspot+jdk+langtools).
> >
> > Any feedback is welcome,
> > Bernard
> >
> > [1] https://bugs.openjdk.java.net/browse/JDK-8213479
> > [2] http://mail.openjdk.java.net/pipermail/jdk-dev/2018-November/002181.html
> >