Instrumentation with snippets

[Chris Atkin-Granville]

Hey guys,

I'm trying to instrument memory operations using snippets, but something is going wrong. At the moment I'm focussing on StoreIndexedNode and LoadIndexedNode - array access operations. To be clear I don't want to replace the behaviour associated with these nodes - just augment existing functionality to basically log each operation (but I haven't got to actually writing the instrumentation yet).

What I have at the moment is a new phase that I've added at PhasePosition.HIGH_LEVEL:

public class ArrayAccessInstrumentationPhase extends Phase {
	
	private ArrayAccessSnippets.Templates snippets;
	
	public ArrayAccessInstrumentationPhase(CodeCacheProvider runtime, Replacements replacements, TargetDescription target) {
		snippets = new ArrayAccessSnippets.Templates(runtime, replacements, target);
	}

	@Override
	protected void run(StructuredGraph graph) {
		for (Node node: graph.getNodes()) {
			if (node instanceof StoreIndexedNode)
				snippets.lower((StoreIndexedNode) node);
			
			if (node instanceof LoadIndexedNode)
				snippets.lower((LoadIndexedNode) node);
		}
	}

}

And the snippets:

public class ArrayAccessSnippets implements Snippets {
	
	@Snippet
	public static StoreIndexedNode arrayIndexStore(StoreIndexedNode n) {
		// TODO: add instrumentation here
		return n;
	}
	
	@Snippet
	public static LoadIndexedNode arrayIndexLoad(LoadIndexedNode n) {
		// TODO: add instrumentation here
		return n;
	}
	
	public static class Templates extends AbstractTemplates {
				
		private final SnippetInfo load = snippet(ArrayAccessSnippets.class, "arrayIndexLoad");
		private final SnippetInfo store = snippet(ArrayAccessSnippets.class, "arrayIndexStore");
		
		public Templates(CodeCacheProvider runtime, Replacements replacements, TargetDescription target) {
			super(runtime, replacements, target);
		}
		
		public void lower(final StoreIndexedNode node) {
			Arguments args = new Arguments(store) {{
				add("n", node);
			}};
			
			template(args).instantiate(runtime, node, DEFAULT_REPLACER, args);
		}
		
		public void lower(final LoadIndexedNode node) {
			Arguments args = new Arguments(load) {{
				add("n", node);
			}};
			
			template(args).instantiate(runtime, node, DEFAULT_REPLACER, args);
		}	
	}
}

However this causes Java to run out of heap space (java.lang.OutOfMemoryError) - I think because the JVM gets into an "infinite replacement" spiral?

At any rate, I see in HotSpotRuntime:lower() there's behaviour associated with StoreIndexedNode (line 582) and LoadIndexedNode (line 574) so I tried to move that over into my snippet - but that didn't work because I couldn't see any way to get access to a LoweringToolImpl from within my snippets.

Anybody have any thoughts of how I can achieve this access instrumentation?

Thanks, Chris

(P.S. Not sure what went wrong with my last email!)