RFR: 8270533: AArch64: size_fits_all_mem_uses should return false if its output is a CAS

[Nick Gasson]

On Thu, 15 Jul 2021 09:31:49 GMT, Andrew Haley <aph at openjdk.org> wrote:

> `size_fits_all_mem_uses(AddPNode)` is used to determine if an add with shift expression can be used as an input to a MemNode. However, it is not correct when one of its outputs is a CAS. This causes a crash when a single AddPNode feeds a CAS and an ordinary MemNode.
> 
> This bug is probably latent in the current HotSpot because `pd_clone_address_expressions()` clones AddPNodes that are used as inputs to MemNodes, so `size_fits_all_mem_uses()` never sees a CAS as one of its outputs. The matcher for a CompareAndSwapX node doesn't call `size_fits_all_mem_uses()`, so this can only happen when the same expression feeds both an ordinary MemNode and a CompareAndSwapX.
> 
> This bug has been back-ported to JDK 8u, so it must be fixed there. Even though the bug is latent in current HotSpot, it should be fixed.

Marked as reviewed by ngasson (Committer).

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PR: https://git.openjdk.java.net/jdk/pull/4790