Fix: check location tier of ContinuationRootNodeImpl in prepareForCompilation

Author: DSouzaM

truffle/src/com.oracle.truffle.api.bytecode.test/src/com/oracle/truffle/api/bytecode/test/RootNodeOverridesTest.java

@@ -126,7 +126,17 @@ public void testPrepareForCompilationContinuation() {
         cont = (ContinuationResult) root.getCallTarget().call();
         assertEquals(BytecodeTier.CACHED, root.getBytecodeNode().getTier());
 
-        // When the interpreter is cached, the parent impl should be delegated to.
+        // The continuation root does not transition to cached until its next execution.
+        // Until then, it should not be ready for compilation.
+        assertEquals(BytecodeTier.UNCACHED, cont.getBytecodeLocation().getBytecodeNode().getTier());
+        root.readyForCompilation = false;
+        assertEquals(false, invokePrepareForCompilation(cont.getContinuationRootNode()));
+        root.readyForCompilation = true;
+        assertEquals(false, invokePrepareForCompilation(cont.getContinuationRootNode()));
+
+        // After the continuation root transitions to cached, delegate to the root node.
+        cont.continueWith(123L);
+        assertEquals(BytecodeTier.CACHED, cont.getBytecodeLocation().getBytecodeNode().getTier());
         root.readyForCompilation = false;
         assertEquals(false, invokePrepareForCompilation(cont.getContinuationRootNode()));
         root.readyForCompilation = true;

truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/generator/BytecodeRootNodeElement.java

@@ -17937,7 +17937,12 @@ private CodeExecutableElement createPrepareForCompilation() {
 
             CodeExecutableElement ex = overrideImplementRootNodeMethod(model, "prepareForCompilation", new String[]{"rootCompilation", "compilationTier", "lastTier"});
             CodeTreeBuilder b = ex.createBuilder();
-            b.startReturn().startCall("root.prepareForCompilation").string("rootCompilation").string("compilationTier").string("lastTier").end(2);
+            b.startReturn();
+            b.startCall("root.prepareForCompilation").string("rootCompilation").string("compilationTier").string("lastTier").end();
+            b.string(" && ");
+            // Even if the root is ready, the continuation location may not have updated yet.
+            b.string("location.getBytecodeNode().getTier() != ").staticReference(types.BytecodeTier, "UNCACHED");
+            b.end();
             return ex;
         }