The code which eliminates MemBars for scalarized objects was added in jdk8:
http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/6f3fd5150b67
An other store barrier change was also pushed into jdk8:
http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/fcf521c3fbc6
I don't remember we did anything special with membars in jdk9.
Regards,
Vladimir
On 2/18/15 6:27 AM, Vitaly Davidovich wrote:
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" <a...@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@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.
