RFR: 8342941: IGV: Add new graph dumps for post loop, empty loop removal, and one iteration removal [v3]

[Daniel Lundén]

On Mon, 7 Jul 2025 23:04:51 GMT, Saranya Natarajan <snatarajan at openjdk.org> wrote:

>> This changeset adds BEFORE/AFTER graph dumps for creating a post loop (`insert_post_loop()`), removing an empty loop (`do_remove_empty_loop()`), and removing a one iteration loop (`do_one_iteration_loop()`).
>> 
>> Changes:
>> - Added `BEFORE_POST_LOOP` and `AFTER_POST_LOOP` for dumping graphs before and after `insert_post_loop()`.
>> - Added `BEFORE_REMOVE_EMPTY_LOOP` and `AFTER_REMOVE_EMPTY_LOOP` for dumping graphs before and after `do_remove_empty_loop()`.
>> - Added `BEFORE_ONE_ITERATION_LOOP` and `AFTER_ONE_ITERATION_LOOP` for dumping graphs before and after `do_one_iteration_loop()`.
>> 
>> Below are sample screenshots (IGV print level 4 ) mainly showing the new phase .
>> 1. `BEFORE_POST_LOOP` and `AFTER_POST_LOOP` 
>> ![image](https://github.com/user-attachments/assets/1661cede-5d70-4e0d-abec-3d091c7675c8)
>> 2. `BEFORE_POST_LOOP` and `AFTER_POST_LOOP` with SuperWordLoopUnrollAnalysis enabled
>> ![image](https://github.com/user-attachments/assets/6a22e6f0-4e6c-4e9d-8b6b-2bf75fac783d)
>> 3.` BEFORE_REMOVE_EMPTY_LOOP `and `AFTER_REMOVE_EMPTY_LOOP`
>> ![image](https://github.com/user-attachments/assets/3281f00b-575e-4604-83dd-831037d8dd47)
>> 4. `BEFORE_ONE_ITERATION_LOOP` and `AFTER_ONE_ITERATION_LOOP`
>> ![image](https://github.com/user-attachments/assets/efddbc9a-64f7-403d-acfe-330d75a00911)
>> 
>> Question to reviewers:
>> Are the new compiler phases OK, or should we change anything?
>> 
>> Testing:
>> GitHub Actions
>> tier1 to tier5 on windows-x64, linux-x64, linux-aarch64, macosx-x64, and macosx-aarch64.
>> Tested that thousands of graphs are correctly opened and visualized with IGV using the same test used in ([JDK-8317349](https://bugs.openjdk.org/browse/JDK-8317349))
>
> Saranya Natarajan has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:
> 
>  - fix 2 of review
>  - Merge master
>  - Addressing review comments
>  - Initial Fix

Looks good! Just one (very) minor comment.

src/hotspot/share/opto/phasetype.hpp line 83:

> 81:   flags(AFTER_REMOVE_EMPTY_LOOP,        "After Remove Empty Loop") \
> 82:   flags(BEFORE_ONE_ITERATION_LOOP,      "Before Replacing One Iteration Loop") \
> 83:   flags(AFTER_ONE_ITERATION_LOOP,       "After Replacing One Iteration Loop") \

Very much a nit, but I think this should be "One-Iteration Loop". Or, is it in fact one _iteration loop_ (as it reads now)? Looking at the code, I think it is the former. @chhagedorn can maybe clarify?

This is not specific to your changeset, but also appears in existing source code comments. Maybe a good opportunity to clean this up everywhere?

Also, maybe "Replacing" should be "Replace"? Seems to better fit the style used for other phase names.

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

Marked as reviewed by dlunden (Committer).

PR Review: https://git.openjdk.org/jdk/pull/25756#pullrequestreview-3006984528
PR Review Comment: https://git.openjdk.org/jdk/pull/25756#discussion_r2198498500