RFR: 8332268: C2: Add missing optimizations for UDivI/L and UModI/L and unify the shared logic with the signed nodes

[Emanuel Peter]

On Wed, 13 Nov 2024 09:45:37 GMT, theoweidmannoracle <duke at openjdk.org> wrote:

> This PR introduces
> - several new optimizations to unsigned division and modulo
>    - x % 1, x % x, x % 2^k
>    - x / 1, x / x, x / 2^k 
>    - does not implement the Granlund and Montgomery algorithm, which has been implemented for signed modulo division in the past. It is unclear if a lot is to be gained by implementing this.
> - tests to test existing optimizations for signed division and modulo 
>    - does not test the Granlund and Montgomery algorithm directly

Nice improvements, some comments/ questions below about testing.

src/hotspot/share/opto/divnode.cpp line 518:

> 516: 
> 517:   if (is_power_of_2(l)) {
> 518:     return make_urshift<TypeClass>(div->in(1), phase->intcon(log2i_graceful(l)));

Are we testing optimizations like these with random constants somewhere, and comparing it to the interpreter results?

test/hotspot/jtreg/compiler/c2/irTests/ModINodeIdealizationTests.java line 2:

> 1: /*
> 2:  * Copyright (c) 2022, 2024, Oracle and/or its affiliates. All rights reserved.

Suggestion:

 * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.

Check the others too. I don't think a new file requires old dates ;)

test/hotspot/jtreg/compiler/c2/irTests/ModLNodeIdealizationTests.java line 2:

> 1: /*
> 2:  * Copyright (c) 2022, 2024, Oracle and/or its affiliates. All rights reserved.

Suggestion:

 * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.

-------------

Changes requested by epeter (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/22061#pullrequestreview-2457735736
PR Review Comment: https://git.openjdk.org/jdk/pull/22061#discussion_r1856180636
PR Review Comment: https://git.openjdk.org/jdk/pull/22061#discussion_r1856174160
PR Review Comment: https://git.openjdk.org/jdk/pull/22061#discussion_r1856174977