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@7
(line 373)
; - java.nio.ByteBuffer::wrap@4
(line 396)
; -
bytebuffertests.ByteBufferTests3::getLong@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@1 (line 545)
; -
java.nio.HeapByteBuffer::getLong@18 (line 465)
; -
bytebuffertests.ByteBufferTests3::getLong@5 (line 23)
;; B3: # B6 B4 <- B2 Freq: 0.999999
0x00007f2948acbf94: mov %r10d,%ebp
0x00007f2948acbf97: sub %ecx,%ebp ;*isub
; -
java.nio.Buffer::checkIndex@10 (line 545)
; -
java.nio.HeapByteBuffer::getLong@18 (line 465)
; -
bytebuffertests.ByteBufferTests3::getLong@5 (line 23)
0x00007f2948acbf99: cmp $0x8,%ebp
0x00007f2948acbf9c: jl 0x00007f2948acbfd5 ;*if_icmple
; -
java.nio.Buffer::checkIndex@11 (line 545)
; -
java.nio.HeapByteBuffer::getLong@18 (line 465)
; -
bytebuffertests.ByteBufferTests3::getLong@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@1 (line
61)
; -
java.nio.HeapByteBuffer::getLong@41 (line 466)
; -
bytebuffertests.ByteBufferTests3::getLong@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.
