RFR: C1 stores constants without read barriers

[Aleksey Shipilev]

I do not understand what you are saying. I have been running this patch for
hours on x86 now, and it works.

-Aleksey

P.S. Tether your phone to computer, and hop onto IRC?

On 06/29/2017 02:13 PM, Roman Kennke wrote:
> IIRC, it doesn't compile like this. If it's not a reg, it needs to emit a mov
> from const to reg.
> 
> Roman
> 
> Am 29. Juni 2017 14:04:12 MESZ schrieb Aleksey Shipilev <shade at redhat.com>:
> 
>     Well, the symmetry argument still stands: x86 and aarch64 versions should be
>     consistent. aarch64 makes unconditional RB for store values. I think it makes no
>     harm to emit RB there for extra safety.
> 
>     -Aleksey
> 
>     On 06/29/2017 01:59 PM, Roman Kennke wrote:
> 
>         I thought that too. But then realized we don't need barriers on
>         constants for
>         store values. Will explain on IRC as soon as my internet conn is back
>         alive...
> 
>         Am 29. Juni 2017 13:55:31 MESZ schrieb Aleksey Shipilev <shade at redhat.com>:
> 
>         I think this part of C1 is incorrect when barriers are required for
>         constants:
>         http://cr.openjdk.java.net/~shade/shenandoah/c1-store-const-rb/webrev.01
>         <http://cr.openjdk.java.net/%7Eshade/shenandoah/c1-store-const-rb/webrev.01>
>         <http://cr.openjdk.java.net/%7Eshade/shenandoah/c1-store-const-rb/webrev.01>/
> 
>         This might explain a few test failures we have: the from-space constant
>         is read
>         before concurrent evacuation has the chance to update it. Then it gets
>         stored to
>         another heap location, and everything blows up.
> 
>         While we could conditionalize this on ShBarriersForConst, this is C1
>         code, which
>         does not have to be super-optimal. Surprisingly, the new code is what
>         c1_LIRGenerator_aarch64 is already doing, so this patch seems good from the
>         symmetry standpoint too.
> 
>         Testing: hotspot_gc_shenandoah
> 
>         Thanks,
>         -Aleksey
> 
> 
> 
>         -- 
>         Diese Nachricht wurde von meinem Android-Gerät mit K-9 Mail gesendet.
> 
> 
> 
> 
> -- 
> Diese Nachricht wurde von meinem Android-Gerät mit K-9 Mail gesendet.