NullPointerException in HotSpotRuntime:lower when using Snippets

[ATKIN-GRANVILLE Chris]

Hi there,

I'm trying add arbitrary behaviour to array accesses - the end goal being to create traces of all memory operations within a program. What I've done so far was suggested to me in a previous thread on this list, but in short, I've got phases that add my own custom nodes to each LoadIndexedNode/StoreIndexedNode. These are then lowered to the desired behaviour via snippets:

public class InstrumentationSnippets implements Snippets {
	@Snippet
	public static void store(final ArrayStoreBehaviourNode<?> node) {
		Instrument.arrayStores.add(node.getInfo());
	}
	
	@Snippet
	public static void load(final ArrayLoadBehaviourNode<?> node) {
		Instrument.arrayLoads.add(node.getInfo());
	}
	
	public static class Templates extends AbstractTemplates {
		private final SnippetInfo store = snippet(InstrumentationSnippets.class, "store");
		private final SnippetInfo load = snippet(InstrumentationSnippets.class, "load");

		public Templates(MetaAccessProvider runtime, Replacements replacements, TargetDescription target) {
			super(runtime, replacements, target);
		}
		
		public void lower(final ArrayStoreBehaviourNode<?> node) {
			Arguments args = new Arguments(store);
			args.add("node", node);
			
			template(args).instantiate(runtime, node, DEFAULT_REPLACER, args);
		}
		
		public void lower(final ArrayLoadBehaviourNode<?> node) {
			Arguments args = new Arguments(load);
			args.add("node", node);
			
			template(args).instantiate(runtime, node, DEFAULT_REPLACER, args);
		}
	}
}

However, doing this causes NullPointerExceptions to be thrown in HotSpotRuntime:lower:

java.lang.NullPointerException
	at com.oracle.graal.hotspot.meta.HotSpotRuntime.lower(HotSpotRuntime.java:527)
	at com.oracle.graal.hotspot.amd64.AMD64HotSpotRuntime.lower(AMD64HotSpotRuntime.java:218)
	at com.oracle.graal.nodes.InvokeNode.lower(InvokeNode.java:97)
	at com.oracle.graal.phases.common.LoweringPhase$Round.process(LoweringPhase.java:232)
	at com.oracle.graal.phases.common.LoweringPhase$Round.processBlock(LoweringPhase.java:182)
	at com.oracle.graal.phases.common.LoweringPhase$Round.run(LoweringPhase.java:173)
	at com.oracle.graal.phases.Phase.run(Phase.java:51)
	at com.oracle.graal.phases.BasePhase$1.run(BasePhase.java:62)
	at com.oracle.graal.debug.internal.DebugScope.executeScope(DebugScope.java:179)
	at com.oracle.graal.debug.internal.DebugScope.scope(DebugScope.java:167)
	at com.oracle.graal.debug.Debug.scope(Debug.java:118)
	at com.oracle.graal.debug.Debug.scope(Debug.java:113)
	at com.oracle.graal.phases.BasePhase.apply(BasePhase.java:59)
	at com.oracle.graal.phases.BasePhase.apply(BasePhase.java:55)
	at com.oracle.graal.phases.PhaseSuite.run(PhaseSuite.java:59)
	at com.oracle.graal.phases.common.IncrementalCanonicalizerPhase.run(IncrementalCanonicalizerPhase.java:45)
	at com.oracle.graal.phases.common.IncrementalCanonicalizerPhase.run(IncrementalCanonicalizerPhase.java:1)
	at com.oracle.graal.phases.BasePhase$1.run(BasePhase.java:62)
	at com.oracle.graal.debug.internal.DebugScope.executeScope(DebugScope.java:179)
	at com.oracle.graal.debug.internal.DebugScope.scope(DebugScope.java:167)
	at com.oracle.graal.debug.Debug.scope(Debug.java:118)
	at com.oracle.graal.debug.Debug.scope(Debug.java:113)
	at com.oracle.graal.phases.BasePhase.apply(BasePhase.java:59)
	at com.oracle.graal.phases.BasePhase.apply(BasePhase.java:55)
	at com.oracle.graal.phases.common.LoweringPhase.run(LoweringPhase.java:145)
	at com.oracle.graal.phases.common.LoweringPhase.run(LoweringPhase.java:1)
	at com.oracle.graal.phases.BasePhase$1.run(BasePhase.java:62)
	at com.oracle.graal.debug.internal.DebugScope.executeScope(DebugScope.java:179)
	at com.oracle.graal.debug.internal.DebugScope.scope(DebugScope.java:167)
	at com.oracle.graal.debug.Debug.scope(Debug.java:118)
	at com.oracle.graal.debug.Debug.scope(Debug.java:113)
	at com.oracle.graal.phases.BasePhase.apply(BasePhase.java:59)
	at com.oracle.graal.phases.BasePhase.apply(BasePhase.java:55)
	at com.oracle.graal.compiler.GraalCompiler.emitHIR(GraalCompiler.java:143)
	at com.oracle.graal.compiler.GraalCompiler$1$1.call(GraalCompiler.java:66)
	at com.oracle.graal.compiler.GraalCompiler$1$1.call(GraalCompiler.java:1)
	at com.oracle.graal.debug.internal.DebugScope.call(DebugScope.java:301)
	at com.oracle.graal.debug.internal.DebugScope.executeScope(DebugScope.java:182)
	at com.oracle.graal.debug.internal.DebugScope.scope(DebugScope.java:167)
	at com.oracle.graal.debug.Debug.scope(Debug.java:138)
	at com.oracle.graal.debug.Debug.scope(Debug.java:109)
	at com.oracle.graal.compiler.GraalCompiler$1.run(GraalCompiler.java:63)
	at com.oracle.graal.debug.internal.DebugScope.executeScope(DebugScope.java:179)
	at com.oracle.graal.debug.internal.DebugScope.scope(DebugScope.java:167)
	at com.oracle.graal.debug.Debug.scope(Debug.java:118)
	at com.oracle.graal.compiler.GraalCompiler.compileMethod(GraalCompiler.java:59)
	at uk.ac.ed.inf.icsa.locomotion.Locomotion.compile(Locomotion.java:79)
	at uk.ac.ed.inf.icsa.locomotion.Application.run(Application.java:34)
	at uk.ac.ed.inf.icsa.locomotion.Application.main(Application.java:58)

Following the stack trace leads to this line being the problem:

!callTarget.isStatic() && receiver.kind() == Kind.Object && !receiver.objectStamp().nonNull()

Specifically, receiver == null causes the exception.

Does anyone have any ideas of how I can get around this problem? Ideally without modifying HotSpotRuntime, but if that's whats required then so be it.

chris

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