RFR: 8302738: IGV: refine 'Simplify graph' filter
Roberto Castañeda Lozano
rcastanedalo at openjdk.org
Thu Mar 9 18:41:32 UTC 2023
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):
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 affect layout quality negatively:
Note that the exact input indices can still be retrieved via the incoming edge's tooltips:
The control-flow graph view is also adapted to this representation:
#### 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:
### 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).
-------------
Commit messages:
- Document filter helpers
- Combine Bool nodes into SubTypeCheck comparisons as well
- Generalize null-pointer slot text filter
- Fix figure selection
- Split simplify graph filter into two, ensure they are applied in right order
- Make slots searchable and selectable
- Make dots bolder
- Remove broken attempt to add split nodes as output slots
- Restore default settings
- Undo pretty-printing of CatchProj nodes from HotSpot side
- ... and 34 more: https://git.openjdk.org/jdk/compare/56512cfe...b379e87c
Changes: https://git.openjdk.org/jdk/pull/12955/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12955&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8302738
Stats: 935 lines in 39 files changed: 574 ins; 213 del; 148 mod
Patch: https://git.openjdk.org/jdk/pull/12955.diff
Fetch: git fetch https://git.openjdk.org/jdk pull/12955/head:pull/12955
PR: https://git.openjdk.org/jdk/pull/12955
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