RFR: 8324790: ifnode::fold_compares_helper cleanup

[Joshua Cao]

On Wed, 7 Feb 2024 09:18:03 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> I have not yet looked at your code. But I'm not sure your assumptions are all correct:
> 
> > we assert that if_proj is an IfTrue or IfFalse, so it is safe to assume if_proj->_in is an IfNode
> 
> Generally, during IGVN, ctrl inputs could always be TOP, if we are in a dead-code place. Are you sure there is always an IfNode above the projections? Maybe that is true in this specific call chain?
> 
> > the 1'th input of a CmpNode is a BoolNode
> 
> Do you mean the 1st input of BoolNode is a CmpNode? I think we may also fold CmpNodes to constants, or TOP. Is that somehow excluded in your cases?
> 
> The problem with testing of this: getting TOP inputs is kinda rare. But you can make it more likely with `StressIGVN`.

I removed all my changes in `filtered_int_type()`. There are some other callers which may have some unexpected constants or TOPs.

My main motivation anyway was in `fold_compares_helper()`, and I think that cleanup is still valid.

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PR Comment: https://git.openjdk.org/jdk/pull/17601#issuecomment-1949502747