[aarch64-port-dev ] RFR: 8243339: AArch64: Obsolete UseBarriersForVolatile option

[Xiaohong Gong]

Hi Andrew,

> On 5/21/20 11:24 AM, Xiaohong Gong wrote:
 > > I'v created a new patch to add the condition when inserting
 > "DMBs"
 > > before volatile load for C1/Interpreter.
 > > The updated webrev:
 > > http://cr.openjdk.java.net/~xgong/rfr/8243339/webrev.01/
 > >
 > > It adds a new function "is_c1_or_interpreter_only()" , which can
 > > decide whether C2/JVMCI is used. Besides, since AOT also uses
 > Graal
 > > compiler as the codegen, it always return false if AOT mode is
 > enabled.
 > 
 > Looks good to me, thanks.
 > 
 > As far as I remember, Graal does optimize volatile accesses to use
 > ldar/stlr, or at least it will do so in the future, so if we're
 > using AOT or JVMCI the safe thing to do is add the DMBs.

Yes, exactly! It has a patch in Graal github to do this optimization (https://github.com/oracle/graal/pull/1772).

Thanks,
Xiaohong

-----Original Message-----
From: Andrew Haley <aph at redhat.com> 
Sent: Thursday, May 21, 2020 10:06 PM
To: Xiaohong Gong <Xiaohong.Gong at arm.com>; Andrew Dinn <adinn at redhat.com>; Derek White <derekw at marvell.com>; aarch64-port-dev at openjdk.java.net; hotspot-compiler-dev at openjdk.java.net
Cc: nd <nd at arm.com>
Subject: Re: [aarch64-port-dev ] RFR: 8243339: AArch64: Obsolete UseBarriersForVolatile option

On 5/21/20 11:24 AM, Xiaohong Gong wrote:
> I'v created a new patch to add the condition when inserting "DMBs" 
> before volatile load for C1/Interpreter.
> The updated webrev: 
> http://cr.openjdk.java.net/~xgong/rfr/8243339/webrev.01/
>
> It adds a new function "is_c1_or_interpreter_only()" , which can 
> decide whether C2/JVMCI is used. Besides, since AOT also uses Graal 
> compiler as the codegen, it always return false if AOT mode is enabled.

Looks good to me, thanks.

As far as I remember, Graal does optimize volatile accesses to use ldar/stlr, or at least it will do so in the future, so if we're using AOT or JVMCI the safe thing to do is add the DMBs.

--
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com> https://keybase.io/andrewhaley
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