Compiler Configuration on JVM

The options for configuring the Graal compiler on the JVM are in 3 categories.

General Options

These are general options for setting/getting configuration details.

-XX:-UseJVMCICompiler: This disables use of the Graal compiler as the top tier JIT. This is useful when wanting to compare performance of the Graal compiler against the native JIT compilers.
-Dgraal.CompilerConfiguration=<name>: Selects the Graal compiler configuration to use. If omitted, the compiler configuration with the highest auto-selection priority is used. To see the set of available configurations, supply the value help to this option.

The current configurations and their semantics are:
- enterprise: To produce highly optimized code with a possible trade-off to compilation time. [GraalVM Enterprise]
- community: To produce reasonably optimized code with a faster compilation time.
- economy: To compile as fast as possible with less optimal throughput of the generated code.
-Dgraal.ShowConfiguration=none: Prints information about the Graal compiler configuration selected. This option only produces output when the compiler is initialized. By default, the Graal compiler is initialized on the first top-tier compilation. For this reason, the way to use this option is as follows: java -XX:+EagerJVMCI -Dgraal.ShowConfiguration=info -version.

The accepted values for this option are:
- none: To show no information.
- info: To print one line of output showing the name of the compiler configuration in use and the location it is loaded from.
- verbose: To print detailed compiler configuration information.
-Dgraal.MitigateSpeculativeExecutionAttacks=None: Selects a strategy to mitigate speculative execution attacks (e.g., SPECTRE).

Accepted values are:
- None: No mitigations are used in JIT compiled code.
- AllTargets: All branches are protected against speculative attacks. This has a large performance impact.
- GuardTargets: Only branches that preserve Java memory safety are protected. This has reduced performance impact.
- NonDeoptGuardTargets: Same as GuardTargets except that branches which deoptimize are not protected since they can not be executed repeatedly.

Performance Tuning Options

-Dgraal.UsePriorityInlining=true: This can be used to disable use of the advanced inlining algorithm that favours throughput over compilation speed. [GraalVM Enterprise]
-Dgraal.Vectorization=true: This can be used to disable the auto vectorization optimization. [GraalVM Enterprise]
-Dgraal.OptDuplication=true: This can be used to disable the path duplication optimization. [GraalVM Enterprise]
-Dgraal.TuneInlinerExploration=0: This can be used to try tune for better peak performance or faster warmup. It automatically adjusts values governing the effort spent during inlining. The value of the option is a float clamped between -1 and 1 inclusive. Anything below 0 reduces inlining effort and anything above 0 increases inlining effort. In general, peak performance is improved with more inlining effort while less inlining effort improves warmup (albeit to a lower peak). Note that this option is only a heuristic and the optimal value can differ from application to application. [GraalVM Enterprise]

-Dgraal.TraceInlining=false: Enables tracing of inlining decisions. This can be used for advanced tuning where it may be possible to change the source code of the program. The output format is shown below:

compilation of 'Signature of the compilation root method':
at 'Sig of the root method' ['Bytecode index']: <'Phase'> 'Child method signature': 'Decision made about this callsite'
  at 'Signature of the child method' ['Bytecode index']:
     |--<'Phase 1'> 'Grandchild method signature': 'First decision made about this callsite'
     \--<'Phase 2'> 'Grandchild method signature': 'Second decision made about this callsite'
  at 'Signature of the child method' ['Bytecode index']: <'Phase'> 'Another grandchild method signature': 'The only decision made about this callsite.'

For example:

compilation of java.lang.Character.toUpperCaseEx(int):
at java.lang.Character.toUpperCaseEx(Character.java:7138) [bci: 22]:
   ├──<GraphBuilderPhase> java.lang.CharacterData.of(int): no, bytecode parser did not replace invoke
   └──<PriorityInliningPhase> java.lang.CharacterData.of(int): yes, worth inlining according to the cost-benefit analysis.
at java.lang.Character.toUpperCaseEx(Character.java:7138) [bci: 26]:
   ├──<GraphBuilderPhase> java.lang.CharacterDataLatin1.toUpperCaseEx(int): no, bytecode parser did not replace invoke
   └──<PriorityInliningPhase> java.lang.CharacterDataLatin1.toUpperCaseEx(int): yes, worth inlining according to the cost-benefit analysis.
  at java.lang.CharacterDataLatin1.toUpperCaseEx(CharacterDataLatin1.java:223) [bci: 4]:
     ├──<GraphBuilderPhase> java.lang.CharacterDataLatin1.getProperties(int): no, bytecode parser did not replace invoke
     └──<PriorityInliningPhase> java.lang.CharacterDataLatin1.getProperties(int): yes, worth inlining according to the cost-benefit analysis.

Diagnostic Options

-Dgraal.CompilationFailureAction=Silent: Specifies the action to take when compilation fails by throwing an exception.

The accepted values are:
- Silent: Print nothing to the console.
- Print: Print a stack trace to the console.
- Diagnose: Retry the compilation with extra diagnostics enabled. On VM exit, the collected diagnostics are saved to a zip file that can be submitted along with a bug report. A message is printed to the console describing where the diagnostics file is saved:
```
Graal diagnostic output saved in /Users/graal/graal_dumps/1549459528316/graal_diagnostics_22774.zip
```
- ExitVM: Same as Diagnose except that the VM process exits after retrying.
For all values except for ExitVM, the VM continues executing.
-Dgraal.CompilationBailoutAsFailure=false: The compiler may not complete compilation of a method due to some property or code shape in the method (e.g., exotic uses of the jsr and ret bytecodes). In this case the compilation bails out. If you want to be informed of such bailouts, this option makes GraalVM treat bailouts as failures and thus be subject to the action specified by the -Dgraal.CompilationFailureAction option.

-Dgraal.PrintCompilation=false: Prints an informational line to the console for each completed compilation. For example:

HotSpotCompilation-11  Ljava/lang/Object;                            wait          ()V       |  591ms    12B    92B  4371kB
HotSpotCompilation-175 Ljava/lang/String;                            lastIndexOf   (II)I     |  590ms   126B   309B  4076kB
HotSpotCompilation-184 Ljava/util/concurrent/ConcurrentHashMap;      setTabAt      ([Ljava/util/concurrent/ConcurrentHashMap$Node;ILjava/util/concurrent/ConcurrentHashMap$Node;)V  |  591ms    38B    67B  3411kB
HotSpotCompilation-136 Lsun/nio/cs/UTF_8$Encoder;                    encode        ([CII[B)I |  591ms   740B   418B  4921

Setting Compiler Options with Language Launchers

The Graal compiler properties above are usable with some other GraalVM launchers such as node, js and lli. The prefix for specifying the properties is slightly different. For example:

java -XX:+EagerJVMCI -Dgraal.ShowConfiguration=info -version

Becomes:

js --jvm --vm.Dgraal.ShowConfiguration=info -version

Note the -D prefix is replaced by --vm.D.