Integrated: 8325372: Shenandoah: SIGSEGV crash in unnecessary_acquire due to LoadStore split through phi

[Roland Westrelin]

On Tue, 20 Feb 2024 09:46:31 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> After shenandoah barrier expansion, a shenandoah specific pass looks
> for heap stable checks that are back to back:
> 
> 
> if (heap_stable) {
>   // fast path 1
> } else {
>   // slow path 1
> }
> if (heap_stable) {
>   // fast path 2
> } else {
>   // slow path 2
> }
> 
> 
> and fuse them:
> 
> 
> if (heap_stable) {
>   // fast path 1
>   // fast path 2
> } else {
>   // slow path 1
>   // slow path 2
> }
> 
> 
> In the case of the failure, a `GetAndSetP` (or `GetAndSetN`) node is
> between the 2 heap_stable checks. The fusion of the 2 tests is
> implemented by taking advantage of the split if c2 optimization. But
> split if doesn't support having a `GetAndSet` node at the region where
> split if happens (that can only happen with shenandoah late barrier
> expansion). That causes the `GetAndSet` node to lose its `SCMemProj`
> which can then result in the `GetAndSet` being entirely removed.
> 
> The fix I propose is to not perform the heap_stable fusion in this
> particular case.

This pull request has now been integrated.

Changeset: 5d414da5
Author:    Roland Westrelin <roland at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/5d414da50459b7a1e6f0f537ff3b318854b2c427
Stats:     100 lines in 4 files changed: 99 ins; 0 del; 1 mod

8325372: Shenandoah: SIGSEGV crash in unnecessary_acquire due to LoadStore split through phi

Reviewed-by: shade, rkennke, thartmann

-------------

PR: https://git.openjdk.org/jdk/pull/17926