RFR: 8347645: C2: XOR bounded value handling blocks constant folding [v4]

[Quan Anh Mai]

On Wed, 22 Jan 2025 20:23:02 GMT, Johannes Graham <duke at openjdk.org> wrote:

>> C2 does not eliminate XOR nodes with constant arguments. This has a noticeable effect on `Long.expand` with a constant mask, on architectures that don't have instructions equivalent  to `PDEP` to be used in an intrinsic.
>> 
>> This patch demonstrates a potential fix to the problem, but there might well be better ways to do it.
>
> Johannes Graham has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix test names

src/hotspot/share/opto/addnode.cpp line 1003:

> 1001:         (r0->_hi > 0)  &&
> 1002:         (r1->_lo >= 0) &&
> 1003:         (r1->_hi > 0)) {

This can be simplified to:

    if (r0->_lo >= 0 && r1->_lo >= 0)

There is no need to check `_hi` here.

src/hotspot/share/opto/addnode.cpp line 1010:

> 1008:     }
> 1009: 
> 1010:     // Complementing a boolean?

This is subsumed by the more-general check above and can be removed.

test/hotspot/jtreg/compiler/c2/gvn/TestXorInt.java line 1:

> 1: /*

We have `compiler/c2/irTests/XorINodeIdealizationTest.java`, is adding a separate test file necessary?

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PR Review Comment: https://git.openjdk.org/jdk/pull/23089#discussion_r1926574177
PR Review Comment: https://git.openjdk.org/jdk/pull/23089#discussion_r1926574774
PR Review Comment: https://git.openjdk.org/jdk/pull/23089#discussion_r1926577039