RFR: 8265132 : C2 compilation fails with assert "missing precedence edge" [v4]

[Dean Long]

On Fri, 18 Jun 2021 01:17:46 GMT, Jamsheed Mohammed C M <jcm at openjdk.org> wrote:

>> You seem to have replaced LCA == store_null_block with the equivalent of store_null_block->dominates(get_block_for_node(load)).  Please explain.
>
> LCA was schedule late location for the load after gcm schedule late and that is null block for the store.I tried improving the fix
> saying if null block for the store dominates load block then ignore the case.

Can you think of a case where store_null_check != NULL, and the following are not true?
>    LCA == store_null_block
>    get_block_for_node(null_block_region)->dominates(get_block_for_node(load))

It sounds like you expect LCA == store_null_block to always be true.  Do you have an example where the dominates check would not be true?  If both are are preconditions that are always true, then how about making them asserts?

>    assert(null_block_region != NULL, "null check without null region");
>    assert(LCA == store_null_block, "wrong LCA");
>    assert(get_block_for_node(null_block_region)->dominates(get_block_for_node(load)), "does not dominate");
>    return true;

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PR: https://git.openjdk.java.net/jdk/pull/4200