RFR: 8306456: Don't leak _worklist's memory in PhaseLive::compute

[Dean Long]

On Wed, 19 Apr 2023 14:21:13 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

> `PhaseLive::compute` used to do this: `_worklist = new (_arena) Block_List();`. This allocates the `Block_List` to the `_arena`, but the backing array is allocated on the resource area: `Block_List() : Block_Array(Thread::current()->resource_area()), _cnt(0) {}`. This causes at most 5 worklists and at least 4 worklists to be created and not freed until the compilation is finished. This patch allocates the worklist within `PhaseLive::compute`:s local resource mark.

Changes requested by dlong (Reviewer).

src/hotspot/share/opto/live.cpp line 92:

> 90:   Block_List wl;
> 91:   _worklist = &wl;
> 92: 

Now `_worklist` is a dangling pointer to released stack memory at the end of this method.  How do we make sure it isn't used?

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PR Review: https://git.openjdk.org/jdk/pull/13535#pullrequestreview-1393009006
PR Review Comment: https://git.openjdk.org/jdk/pull/13535#discussion_r1171940037