RFR: 8279219: [REDO] C2 crash when allocating array of size too large

[Aleksey Shipilev]

On Tue, 4 Jan 2022 08:51:30 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> The new fix is largely similar to the previous one. 3 bugs were filed
> because of the previous change but there are only really 2 issues:
> 
> - attaching the valid length condition at expansion time to the new
>   array runtime call causes issues. With Shenandoah, passes of loop
>   opts are executed after macro expansion but precedence edges are
>   ignored when assigning controls to nodes which causes loop opts to
>   incorrectly attempt to eliminate the node pointed to by the
>   precedence edge. A similar issue occurs when the runtime call ends
>   up in a subgraph that dies after macro expansion because the
>   precedence edge is not cleared by dead code elimination which causes
>   the runtime call to still be reachable. In the new patch, this is
>   fixed by appending an extra input to the runtime call instead of
>   using a precedence edge.
> 
> - In the previous patch, a top valid length input is used when there's
>   no valid length input that needs to be recorded. That can cause an
>   assert failure during CCP. If valid length initially has type top,
>   the CatchNode out of the AllocateArray then have type (control,
>   control). If next, the valid length input becomes constant 0, the
>   CatchNode has type (top, control). An assert catches that the type
>   of the CatchNode doesn't widen. This fixed by using 1 by default as
>   valid length input and tweaking CatchNode::Value.
> 
> The new patch includes test cases for both issues.

FWIW, this patch passes these configs (which are not tested by GHA, but were failing in the previous patch iteration):
 - [x] Linux x86_64 fastdebug `tier1` with `-XX:+UseShenandoahGC`
 - [x] Linux x86_64 fastdebug `tier2` with `-XX:+UseShenandoahGC`
 - [x]  Linux x86_32 fastdebug `tier1` with `-XX:+UseShenandoahGC`
 - [x]  Linux x86_32 fastdebug `tier2` with `-XX:+UseShenandoahGC` (some unrelated failures)

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PR: https://git.openjdk.java.net/jdk/pull/6952