RFR: 8295166: IGV: dump graph at more locations [v7]

[Roberto Castañeda Lozano]

On Thu, 7 Dec 2023 15:52:51 GMT, Daniel Lundén <duke at openjdk.org> wrote:

>> This changeset
>> 1. adds a number of new graph dumps for IdealGraphVisualizer (IGV):
>>    - Before conditional constant propagation
>>    - After register allocation
>>    - After block ordering
>>    - After peephole optimization
>>    - After post-allocation expansion
>>    - Before and after
>>      - loop predication
>>      - loop peeling
>>      - pre/main/post loops
>>      - loop unrolling
>>      - range check elimination
>>      - loop unswitching
>>      - partial peeling
>>      - split if
>>      - superword
>> 2. adds support for enumeration of repeated IGV graph dumps.
>> 3. adjusts IGV print levels to encompass the new graph dumps. The old levels 4 and 5 are now levels 5 and 6. The new level 4 is for loop optimization dumps.
>> 
>> Example phase list screenshots in IGV (first at level 6, second at level 4)
>> ![Screenshot from 2023-12-04 13-55-38](https://github.com/openjdk/jdk/assets/4222397/6759dc5a-9c9a-42b9-8d9e-2d0b53e76ab4) ![Screenshot from 2023-12-04 13-56-29](https://github.com/openjdk/jdk/assets/4222397/44d6a239-587b-4f7c-8ce1-f7613cb2fa35)
>> 
>> 
>> Some notes:
>> - While discussing the above changes, a separate question was brought up by @chhagedorn:
>>   > On a separate note, I'm wondering how useful it is to always dump all JFR events when calling print_method(). Should this be revisited again in general?
>> - The new IGV graph dump enumeration enables a number of cleanups. There is now another RFE for IGV cleanup: [JDK-8319599](https://bugs.openjdk.org/browse/JDK-8319599).
>> 
>> ### Testing
>> #### Platforms: windows-x64, linux-x64, linux-aarch64, macosx-x64, macosx-aarch64
>> - tier1, tier2, tier3, tier4, tier5.
>> - Check that optimized builds (`--with-debug-level optimized`) still work.
>> 
>> #### Platforms: linux-x64
>> - Tested that thousands of graphs are correctly opened and visualized with IGV.
>
> Daniel Lundén has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update copyright

Thanks for addressing all the comments and thanks for this nice contribution! The additional dumps, in combination with the CFG view in IGV, make C2 loop optimizations much more approachable.

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Marked as reviewed by rcastanedalo (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16120#pullrequestreview-1770861075