RFR: 8294356: IGV: scheduled graphs contain duplicated elements

[Christian Hagedorn]

On Mon, 26 Sep 2022 13:55:56 GMT, Roberto Castañeda Lozano <rcastanedalo at openjdk.org> wrote:

> This changeset removes duplicated nodes and edges from graph dumps that include a control-flow graph:
> ![cfg-before-after](https://user-images.githubusercontent.com/8792647/192294554-73ca3927-dab3-4d8f-9503-0904a4da7434.png)
> This is achieved by ensuring that HotSpot only visits each node once when dumping IGV graphs.
> 
> #### Testing
> - Tested that tens of thousands of graphs do not contain duplicated nodes or edges by instrumenting IGV and running `java -Xcomp -XX:PrintIdealGraphLevel=4`.
> - Tested manually that unscheduled graphs are not affected by this changeset.
> - Tested that running compiler tests with `-XX:PrintIdealGraphLevel=3` does not trigger any failure.

Looks good!

src/hotspot/share/opto/idealGraphPrinter.cpp line 748:

> 746: 
> 747:   while (nodeStack.length() > 0) {
> 748: 

While at it, this empty line could be removed.

src/hotspot/share/opto/idealGraphPrinter.cpp line 763:

> 761: 
> 762:     for (uint i = 0; i < n->len(); i++) {
> 763:       if (n->in(i)) {

While at it, it might be good to replace this check with an explicit `!= nullptr` instead.

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Marked as reviewed by chagedorn (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10423