Integrated: 8256046: Shenandoah: Mix-in NULL_PTR in non-strong ShLRBNode's type

[Roman Kennke]

On Mon, 9 Nov 2020 11:10:27 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> Testing found this problem (very rare/hard to reproduce):
> 
> # Internal Error (d:/a/jdk/jdk/jdk/src/hotspot/cpu/x86/macroAssembler_x86.cpp:880), pid=6160, tid=5828
> # fatal error: DEBUG MESSAGE: unexpected null in intrinsic
> 
> I believe this may be caused by non-strong LRB reporting a non-NULL type by passing-through its input's type, even though it may actually return NULL on non-NULL inputs. If this serves as input to an intrinsic, it may lead to elimination of surrounding null-check, and thus end up passing a NULL to the intrinsic even thought it should not. 
> 
> Testing:
>  - [x] hotspot_gc_shenandoah
>  - [ ] tier1+Shenandoah
>  - [ ] tier2+Shenandoah

This pull request has now been integrated.

Changeset: 97d6e4ae
Author:    Roman Kennke <rkennke at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/97d6e4ae
Stats:     11 lines in 1 file changed: 8 ins; 0 del; 3 mod

8256046: Shenandoah: Mix-in NULL_PTR in non-strong ShLRBNode's type

Reviewed-by: roland, shade

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PR: https://git.openjdk.java.net/jdk/pull/1120