RFR: 8304049: C2 can not merge trivial Ifs due to CastII

Thu Mar 16 12:00:20 UTC 2023

On Thu, 16 Mar 2023 11:41:44 GMT, Yi Yang <yyang at openjdk.org> wrote:

> But this can not solve the above trivial case, because CastII#58 generated in [PhiNode::Ideal](https://github.com/y1yang0/jdk/commit/6961dea52a6aae94d1fb4573de64525f4934352e#diff-8ffaebb53d272c5385ca4d9df21e8bda21133d11ad64d4c4a5ab4c3a3301ce17R1697) carries unnecessarily strong dependency anyway, I wonder if it's possible to make strong dependency only when we have precise pattern described in https://bugs.openjdk.org/browse/JDK-8139771

Nothing says the pattern of that test case is the only that can cause a problem. It still seems simpler to me to do this in `PhaseIdealLoop::identical_backtoback_ifs()` and I don't understand why you're against it.

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PR: https://git.openjdk.org/jdk/pull/13039