RFR: 8256858: C2: Devirtualize PhaseIterGVN-specific methods

[Vladimir Kozlov]

On Mon, 23 Nov 2020 13:48:21 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> PhaseValues define the virtual method is_IterGVN, which is trivially returning 0(!) for all types except those derived from PhaseIterGVN. Similarly there's igvn_rehash_node_delayed which is virtual and a no-op in base types, but implemented to call rehash_node_delayed in PhaseIterGVN.
> 
> By devirtualizing we allow for more aggressive inlining and slightly better code generation in a few places. 
> 
> This increases sizeof(PhaseValues) from 2480 to 2488 on x64. Since we only go through a limited number of phases per compilation this seems acceptable.

Good.

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Marked as reviewed by kvn (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1385