RFR: 8214512: Jtreg test compiler/c2/Test8062950.java fails on ARM32

[Nick Gasson (Arm Technology China)]

Hi Dean,

Sorry for the delay. This is submitted on behalf of ARM Ltd.

Thanks,
Nick


From: dean.long at oracle.com <dean.long at oracle.com>
Sent: 13 December 2018 12:01
To: Nick Gasson (Arm Technology China) <Nick.Gasson at arm.com>; hotspot-dev at openjdk.java.net; Boris Ulasevich <boris.ulasevich at bell-sw.com>
Cc: hotspot-compiler-dev at openjdk.java.net compiler <hotspot-compiler-dev at openjdk.java.net>; nd <nd at arm.com>; aarch32-port-dev at openjdk.java.net
Subject: Re: RFR: 8214512: Jtreg test compiler/c2/Test8062950.java fails on ARM32

Nick, can you please confirm that you are covered under the
•  ARM Ltd. - OpenJDK, MySQL

OCA agreement?  I'm guessing Arm Technology China is under ARM Ltd., judging
by your email domain, but please confirm.

dl

On 12/11/18 5:30 PM, dean.long at oracle.com<mailto:dean.long at oracle.com> wrote:
I can help you commit it, but first I think another review would be good.

dl

On 12/11/18 5:15 PM, Nick Gasson (Arm Technology China) wrote:

Hi Nick.  This change looks good to me.
Thanks Dean. Could you help me to commit this patch if it doesn't need other reviews?

Nick



-----Original Message-----
From: dean.long at oracle.com<mailto:dean.long at oracle.com> <dean.long at oracle.com><mailto:dean.long at oracle.com>
Sent: 12 December 2018 06:05
To: Nick Gasson (Arm Technology China) <Nick.Gasson at arm.com><mailto:Nick.Gasson at arm.com>; hotspot-
dev at openjdk.java.net<mailto:dev at openjdk.java.net>; Boris Ulasevich <boris.ulasevich at bell-sw.com><mailto:boris.ulasevich at bell-sw.com>
Cc: nd <nd at arm.com><mailto:nd at arm.com>; hotspot-compiler-dev at openjdk.java.net<mailto:hotspot-compiler-dev at openjdk.java.net> compiler
<hotspot-compiler-dev at openjdk.java.net><mailto:hotspot-compiler-dev at openjdk.java.net>; aarch32-port-
dev at openjdk.java.net<mailto:dev at openjdk.java.net>
Subject: Re: RFR: 8214512: Jtreg test compiler/c2/Test8062950.java fails on
ARM32

Hi Nick.  This change looks good to me.

dl

On 12/2/18 10:06 PM, Nick Gasson wrote:

Hi,

Could someone please help me review this fix for a test failure on ARM32:

Bug: https://bugs.openjdk.java.net/browse/JDK-8214512
Webrev: http://cr.openjdk.java.net/~njian/8214512/webrev.0/

This fixes two assertion failures related to biased locking when C2's
bias inlining feature is disabled (-XX:-OptoBiasInlining):

MacroAssembler::atomic_cas_bool takes three register arguments plus a
temporary register for use in the CAS loop. If the caller passes
`noreg' as this temporary register (which happens in the
!OptoBiasInlining call path from MacroAssembler::fast_lock) then
MacroAssembler::atomic_cas_bool will default to using LR as a
temporary. But it's possible with C2 that LR is one of the other three
arguments which then triggers an assert_different_registers assertion
failure. Fix this by supplying an additional scratch register to
MacroAssembler::fast_lock if !OptoBiasInlining.

In the !OptoBiasInlining case MacroAssembler::fast_lock calls
MacroAssembler::biased_locking_enter to handle the case where the mark
word contains the biased lock pattern which fast_lock wouldn't
otherwise see if OptoBiasInlining was true. However in the case that
we fail to acquire the biased lock this falls through to label
`failed' and runs the normal fast_lock code that implicitly assumes
the mark word does not have the bias pattern. This means we can end up
with a BasicLock where _displaced_header contains the biased lock
pattern which is an illegal state and subsequently triggers an
assertion failure in ObjectSynchronizer::fast_exit.

The right thing to do here is branch to `done' whenever the bias lock
pattern is present and let the runtime handle the failure case.  Also
edited the comment describing MacroAssembler::biased_locking_enter to
more accurately describe what it does (the comment about `slow_case'
being optional is wrong).

Jtreg test compiler/c2/Test8062950.java now passes on ARM32 with this
patch.

Thanks,
Nick