RFR: 8302738: IGV: refine 'Simplify graph' filter [v4]

[Tobias Holenstein]

On Wed, 29 Mar 2023 07:38:13 GMT, Roberto Castañeda Lozano <rcastanedalo at openjdk.org> wrote:

>> The "Simplify graph" filter abstracts away details from the graph that are typically unnecessary for debugging or analyzing the represented program. This changeset decouples this filter into two:
>> 
>> - "Simplify graph", which hides elements that are typically (but not always) unnecessary, and
>> - "Condense graph", which makes the graph more compact without loss of information.
>> 
>> Together, these two filters reduce the average graph size by a factor of 1.6x (nodes) and 1.9x (edges):
>> 
>> ![without-with-filters](https://user-images.githubusercontent.com/8792647/224118397-e6bd45d1-0b90-4d94-88ae-0a83f9ef20da.png)
>> 
>> Besides decoupling the "Simplify graph" filter, the changeset extends its functionality by:
>> - combining Bool and conversion nodes into their predecessors,
>> - inlining all Parm nodes except control into their successors (this removes lots of long edges),
>> - removing "top" inputs from call-like nodes,
>> - inlining more source nodes (such as MachTemp and ThreadLocal) into their successors,
>> - pretty-printing the labels of many inlined and combined nodes such as Bool comparisons or Catch projections (via a new filter that edits node properties), and
>> - using a sparse representation of nodes with empty inputs (e.g. call-like nodes after applying "Simplify graph").
>> 
>> The sparse input representation shows dots between non-contiguous inputs, instead of horizontal space proportional to the number of empty inputs. This helps reducing node width, which is known to improve overall layout quality:
>> 
>> ![dense-vs-sparse](https://user-images.githubusercontent.com/8792647/224118703-04f663b7-7a73-4e49-87d9-2acd8b98522b.png)
>> 
>> Note that the exact input indices can still be retrieved via the incoming edge's tooltips:
>> 
>> ![tooltip-with-input-index](https://user-images.githubusercontent.com/8792647/224119319-7f40fba2-1e9f-436e-a11c-8c3d428d46a6.png)
>> 
>> The control-flow graph view is also adapted to this representation:
>> 
>> ![sparse-in-cfg](https://user-images.githubusercontent.com/8792647/224119399-884e2516-a9a1-43fd-b5f5-747c99472ace.png)
>> 
>> #### Additional improvements
>> 
>> Additionally, this changeset:
>> - ensures that the selected filter subset is applied in the order listed in the "Filter" window (this is necessary for combining effectively the "Simplify graph" and "Condense graph" filters, but is also generally desirable for simplicity and consistency),
>> - introduces a complementary filter "Show custom node info" (enabled by default) that extends the labels of call and exception-creation nodes with custom information,
>> - extends the search functionality so that combined and inlined nodes can also be searched on and selected, and
>> - defines and documents JavaScript helpers to simplify the new and existing available filters.
>> 
>> Here is an example of the effect of the new "Show custom node info" filter:
>> 
>> ![show-custom-node-info](https://user-images.githubusercontent.com/8792647/224119545-fd564224-7ccc-4829-988e-77f05d25b3bc.png)
>> 
>> ### Testing
>> 
>> #### Functionality
>> 
>> - Tested the functionality manually on a small selection of graphs.
>> 
>> - Tested automatically that viewing thousands of graphs in the three views with different filter subsets enabled does not trigger any assertion failure (by instrumenting IGV to view graphs as they are loaded and running `java -Xcomp -XX:-TieredCompilation -XX:PrintIdealGraphLevel=4`).
>> 
>> #### Performance
>> 
>> Measured the combined filter application and view creation time for the sea-of-nodes view on a selection of 100 medium-sized graphs (200-500 nodes). On average, applying the new "Show custom node info" filter introduces a minimal overhead of around 1%, which motivates enabling it by default. Applying the "simplify graph" and "condense graph" on top actually gives a speedup of about 12%, since the additional filter application time is amortized by laying out and drawing fewer nodes. However, these filters are not enabled by default, since they cause a (minor) loss of information which is not desirable in every use case.
>> 
>> The graph size reduction and performance results are [attached](https://github.com/openjdk/jdk/files/10934804/performance-evaluation.ods) (note that each time measurement in the sheet corresponds to the median of ten runs).
>
> Roberto Castañeda Lozano has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix comment typo

looks good to me now! thanks for the work @robcasloz

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Marked as reviewed by tholenstein (Committer).

PR Review: https://git.openjdk.org/jdk/pull/12955#pullrequestreview-1362561621