[jdk21u] RFR: 8317121: vector_masked_load instruction is moved too early after JDK-8286941

[Aleksey Shipilev]

On Tue, 3 Oct 2023 19:44:21 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> Clean backport for JDK-8317121.
> 
> [JDK-8286941](https://bugs.openjdk.org/browse/JDK-8286941) changed how masked vector operations are created and processed. It calls LoadNode::Ideal() which tries to find best place in code for it.
> Unfortunately some places do not expect to have vector access to modified memory.
> In LoadNode::find_previous_arraycopy() the call to ArrayCopyNode::modifies() assumes that it access only one element and did not take into account that a vector may access wider memory.
> The same issue exists with Unsafe mismatching (bigger size) access.
> 
> The fix is to take into account size of memory access.
> 
> New regression test is added which show the issue. Verified with original Repro.java test case.
> 
> Tested tier1-7. xcomp, stress.

Looks fine.

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Marked as reviewed by shade (Reviewer).

PR Review: https://git.openjdk.org/jdk21u/pull/226#pullrequestreview-1657144956