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getting-graphs.md

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Getting Graphs

GraalVM Compiler as a Java compiler

-Dgraal.Dump=:1 is a simple option to enable Graal graph dumping.

The value of Dump is a dump filter. The format of dump filters is documented, but in simple cases :1 will be enough and will give you everything.

You may want to combine with -XX:CompileOnly=Foo::foo (you can omit the class part) to restrict compilation to a single method to give smaller dumps, and to some extent make graphs simpler by avoiding what you want to look at being inlined, or other things being inlined into it.

Graal tends to be quite aggressive about loop peeling, which can produce massive graphs with the logic repeated. I often use these flags to simplify the graph without significantly effecting too much how the logic in it is compiled.

  -Dgraal.PartialUnroll=false \
  -Dgraal.LoopPeeling=false \
  -Dgraal.LoopUnswitch=false \
  -Dgraal.OptScheduleOutOfLoops=false

Also on Graal EE:

  -Dgraal.VectorizeLoops=false

GraalVM's Native Image compiler

When using native-image you will want to use the -H: format.

% native-image -H:Dump=:1 -H:MethodFilter=fib Fib

TruffleRuby and other Truffle languages

Use the same options as for GraalVM for Java, except they're prefixed with --vm., for example --vm.Dgraal.Dump=Truffle:1.

  --vm.Dgraal.PartialUnroll=false \
  --vm.Dgraal.LoopPeeling=false \
  --vm.Dgraal.LoopUnswitch=false \
  --vm.Dgraal.OptScheduleOutOfLoops=false

On Graal EE:

  --vm.Dgraal.VectorizeLoops=false

Use with --engine.CompileOnly=foo.

A good filter to use for Truffle languages is --vm.Dgraal.Dump=Truffle:1, which will only give you Truffle compilations if you don't care about the whole Graal compilation pipeline.

You may want to disable on-stack-replacement and inlining with --engine.Inlining=false and --engine.OSR=false in order to make graphs easier to understand.

For source information, you want to run with --engine.NodeSourcePositions. This only works on JVM or on Native when built with -H:+IncludeNodeSourcePositions, which isn't set by default.

You may need to use --experimental-options.

Getting basic blocks

To get the graph when scheduled, so that you can see basic blocks, use -Dgraal.PrintGraphWithSchedule=true. Truffle graphs beyond the initial stages have scheduling information by default.