RFR: 8313672: C2: PhaseCCP does not correctly track analysis dependencies involving shift, convert, and mask [v2]

[Daniel Lundén]

On Tue, 31 Oct 2023 09:50:01 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> `MulNode::AndIL_shift_and_mask_is_always_zero` only covers the case where there is one conversion. So, currently, such a case is impossible in the analysis.
>
> Just because a son only has one father does not mean that a father only has one son ;)
> 
> `MulNode::AndIL_shift_and_mask_is_always_zero` looks up through its inputs and only walks by one `ConvI2L` at most, on the way to the `Shift` node. But going down from a `shift`, there could be multiple `ConvI2L` nodes, and you do not know which ones would lead to the `add-shift` pattern (there could be multiple), and which ones lead to other structures.
> 
> What do you think?

Ah, good point. So, essentially, the `if (conv)` in my fix will only check from the ConvI2L last visited by the first call to `ConstraintCastNode::visit_uncasted_uses` (which may not be the one leading to AndL).

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PR Review Comment: https://git.openjdk.org/jdk/pull/16429#discussion_r1377340192