RFR(S): 8231612: 100% cpu on arm32 in Service Thread

[Erik Joelsson]

Looks good!

/Erik

On 2019-11-18 05:10, Aleksei Voitylov wrote:
> Hi,
>
> please review this build-only workaround for a GCC bug [1]. The problem
> surfaced on ARM32 when new code [2] got inlined with old code. In GCC at
> RTL level there is no good distinction between pointer and int, which
> makes it hard for the aliasing code to correctly recognize base
> addresses for objects, which leads to incorrect aliasing. As a
> consequence one of the loads in this code was completely eliminated on
> ARM32 by DSE. All GCC versions I could reach are affected.
>
> Thanks to the GCC community, the fix will appear in GCC 10 but before it
> becomes mainstream we need a workaround. The workaround is to disable
> -ftree-pre optimization on ARM32 which triggers the bug. The problem
> does not surface on x86 in this code.
>
> issue: https://bugs.openjdk.java.net/browse/JDK-8231612
> webrev: http://cr.openjdk.java.net/~avoitylov/webrev.8231612.02/
>
> Testing on ARM32: the problem described in 8231612 (100% CPU utilization
> in Service Thread) no longer appears, the load is not eliminated as
> observed by disassembly.
> Testing on x86_64: linux-x86_64-server-release builds OK after this change.
>
> Thanks,
>
> -Aleksei
>
> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92462
> [2] https://bugs.openjdk.java.net/browse/JDK-8226366
>
>