RFR: 8073093: AARCH64: C2 generates poor code for ByteBuffer accesses

[Vitaly Davidovich]

Indeed, that's quite nice and not what I saw in java 7 so good to see that
this case is EA'd out.  Does anyone know if there was EA work done in java
9 or is this simply inlining policy change that makes EA work (as John
alluded to)?

sent from my phone
On Feb 18, 2015 6:13 AM, "Andrew Haley" <aph at redhat.com> wrote:

> On 02/18/2015 09:15 AM, Andrew Haley wrote:
> > On 18/02/15 09:14, Florian Weimer wrote:
> >> Wow, looks nice.  What OpenJDK build did you use?  I want to see if this
> >> happens on x86_64, too.
> >
> > I'm working on JDK9.  You don't have this code yet.  I'll do an x86
> > build.
>
>   0x00007f2948acbf8c: mov    0xc(%rdx),%r10d    ;*synchronization entry
>                                                 ; -
> java.nio.HeapByteBuffer::<init>@-1 (line 84)
>                                                 ; -
> java.nio.ByteBuffer::wrap at 7 (line 373)
>                                                 ; -
> java.nio.ByteBuffer::wrap at 4 (line 396)
>                                                 ; -
> bytebuffertests.ByteBufferTests3::getLong at 1 (line 23)
>                                                 ; implicit exception:
> dispatches to 0x00007f2948acbff5
>   ;; B2: #      B5 B3 <- B1  Freq: 0.999999
>
>   ;; MEMBAR-release ! (empty encoding)
>
>   0x00007f2948acbf90: test   %ecx,%ecx
>   0x00007f2948acbf92: jl     0x00007f2948acbfb5  ;*iflt
>                                                 ; -
> java.nio.Buffer::checkIndex at 1 (line 545)
>                                                 ; -
> java.nio.HeapByteBuffer::getLong at 18 (line 465)
>                                                 ; -
> bytebuffertests.ByteBufferTests3::getLong at 5 (line 23)
>
>   ;; B3: #      B6 B4 <- B2  Freq: 0.999999
>
>   0x00007f2948acbf94: mov    %r10d,%ebp
>   0x00007f2948acbf97: sub    %ecx,%ebp          ;*isub
>                                                 ; -
> java.nio.Buffer::checkIndex at 10 (line 545)
>                                                 ; -
> java.nio.HeapByteBuffer::getLong at 18 (line 465)
>                                                 ; -
> bytebuffertests.ByteBufferTests3::getLong at 5 (line 23)
>
>   0x00007f2948acbf99: cmp    $0x8,%ebp
>   0x00007f2948acbf9c: jl     0x00007f2948acbfd5  ;*if_icmple
>                                                 ; -
> java.nio.Buffer::checkIndex at 11 (line 545)
>                                                 ; -
> java.nio.HeapByteBuffer::getLong at 18 (line 465)
>                                                 ; -
> bytebuffertests.ByteBufferTests3::getLong at 5 (line 23)
>
>   ;; B4: #      N95 <- B3  Freq: 0.999998
>
>   0x00007f2948acbf9e: movslq %ecx,%r10
>   0x00007f2948acbfa1: mov    0x10(%rdx,%r10,1),%rax
>   0x00007f2948acbfa6: bswap  %rax               ;*invokestatic reverseBytes
>                                                 ; - java.nio.Bits::swap at 1
> (line 61)
>                                                 ; -
> java.nio.HeapByteBuffer::getLong at 41 (line 466)
>                                                 ; -
> bytebuffertests.ByteBufferTests3::getLong at 5 (line 23)
>
> So, just the same except that there is no explicit fence instruction
> to remove.  It's a shame for AArch64 because that fence really kills
> performance but it's bad for x86 too.  Even on machines that don't
> emit fence instructions the fence still acts as a compiler barrier.
>
> Andrew.
>