RFR: 8313672: C2: PhaseCCP does not correctly track analysis dependencies involving shift, convert, and mask [v5]

[Emanuel Peter]

On Tue, 31 Oct 2023 15:01:55 GMT, Daniel Lundén <duke at openjdk.org> wrote:

>> This changeset fixes an issue where the `PhaseCCP` analysis stopped before fixpoint due to `Value`-updates for `AndL` nodes involving shift, convert, and mask (`MulNode::AndIL_shift_and_mask_is_always_zero`). Such updates did not previously repopulate the `PhaseCCP` worklist correctly.
>> 
>> Changes:
>> - Fix the issue by adding the missing pattern to `PhaseCCP::push_and`.
>> - Update the `assert` error message that reported the issue to better describe the problem. The `PhaseCCP` analysis is optimistic, and the previous error message seemed to indicate the opposite ("Missed optimization opportunity"). If the assert triggers, it could be that the analysis result leads to unsound transformations later on.
>> 
>> Result after `PhaseCCP` analysis (without fix, note `long:0` for node 116):
>> ![before](https://github.com/openjdk/jdk/assets/4222397/3f2343da-8573-464d-9352-a147d0faeab8)
>> 
>> Result after `PhaseCCP` analysis (with fix, note `long` for node 116):
>> ![after](https://github.com/openjdk/jdk/assets/4222397/6bf44964-cff8-49db-9825-4a4667f4e769)
>> 
>> ### Testing (on all Oracle-supported platforms)
>> - `tier1`
>> - HotSpot parts of `tier2` and `tier3`
>
> Daniel Lundén has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add second test case with reduced set of flags

A few more comments :)

test/hotspot/jtreg/compiler/ccp/TestShiftConvertAndNotification.java line 62:

> 60:   }
> 61:   public static void main(String[] strArr) {
> 62:       for (int i = 0; i < 1000; i++)

Suggestion:

      for (int i = 0; i < 20_000; i++)

This would ensure that `test` is compiled even without `-Xcomp`, which may be helpful for the "vanilla" (your run with fewer flags)

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

Changes requested by epeter (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16429#pullrequestreview-1706746382
PR Review Comment: https://git.openjdk.org/jdk/pull/16429#discussion_r1377859213