RFR: 8342941: IGV: Add various new graph dumps during loop opts [v4]

[Daniel Lundén]

On Mon, 14 Jul 2025 18:28:57 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 incrementally with one additional commit since the last revision:
> 
>   addressing review comment

test/hotspot/jtreg/compiler/lib/ir_framework/CompilePhase.java line 94:

> 92:     AFTER_REMOVE_EMPTY_LOOP(        "After Remove Empty Loop"),
> 93:     BEFORE_ONE_ITERATION_LOOP(      "Before Replacing One Iteration Loop"),
> 94:     AFTER_ONE_ITERATION_LOOP(       "After Replacing One Iteration Loop"),

Suggestion:

    BEFORE_ONE_ITERATION_LOOP(      "Before Replacing One-Iteration Loop"),
    AFTER_ONE_ITERATION_LOOP(       "After Replacing One-Iteration Loop"),


I see there are also a few more occurrences that I think needs updating (`grep` for "one iteration loop")

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PR Review Comment: https://git.openjdk.org/jdk/pull/25756#discussion_r2206928409