A small Truffle test program which demonstrates that Truffle will never include exception handlers in compiled code in some cases

README.md

The result of this "optimization" is that everytime the RootNode 1 case runs in compiled for it will deoptimize immediatly and then mements later compile again since nothing was changed.

ExceptionOnOnlyPath.java

package org.singingwizard.exception;

import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
import com.oracle.truffle.api.RootCallTarget;
import com.oracle.truffle.api.Truffle;
import com.oracle.truffle.api.frame.VirtualFrame;
import com.oracle.truffle.api.nodes.RootNode;

public class ExceptionOnOnlyPath {
	/** A simple exception which doesn't capture a stack.
	 */
	final static class TestException extends RuntimeException {
		@Override
		public synchronized Throwable fillInStackTrace() {
			return this;
		}
	}

	///// A root node with an exception on the normal path, but throwsControlFlowException = false
	// This case is optimized to an immediate deopt everytime it compiles, so it will repeatedly recompile.
	// This case is shown in RootNode1_*.png.
	
	@TruffleBoundary(allowInlining = true, throwsControlFlowException = false)
	private static Object doAThing1() {
		throw new TestException();
	}

	private static RootNode createRootNode1() {
		return new RootNode(null) {
			@Override
			public Object execute(VirtualFrame frame) {
				try {
					return doAThing1();
				} catch (RuntimeException e) {
					return "Success";
				}
			}
		};
	}

	///// A root node with an exception on the normal path, but throwsControlFlowException = true
	// This case is optimized to as `return "Success"` since the exception handling is inlined instead of ignored.
	// This case is shown in RootNode2_*.png.

	@TruffleBoundary(allowInlining = true, throwsControlFlowException = true)
	private static Object doAThing2() {
		throw new TestException();
	}

	private static RootNode createRootNode2() {
		return new RootNode(null) {
			@Override
			public Object execute(VirtualFrame frame) {
				try {
					return doAThing2();
				} catch (RuntimeException e) {
					return "Success";
				}
			}
		};
	}

	///// A trivial test harness
	
	private void runTest(RootNode n) {
		RootCallTarget intTgt = Truffle.getRuntime().createCallTarget(n);
		for (int i = 0; i < 10; i++) {
			intTgt.call();			
		}
	}

	public static void main(String[] args) {
		ExceptionOnOnlyPath test = new ExceptionOnOnlyPath();
		System.out.println("throwsControlFlowException = false");
		test.runTest(createRootNode1());
		System.out.println("throwsControlFlowException = true");
		test.runTest(createRootNode2());
	}
}

RootNode1_AfterPartialEvaluation.png

RootNode1_BeforeLowering.png

RootNode2_AfterPartialEvaluation.png

RootNode2_BeforeLowering.png