From 0d22b8712e0cf80e18d3ed9c981f491475bced41 Mon Sep 17 00:00:00 2001
From: Christian Humer <christian.humer@oracle.com>
Date: Wed, 10 Dec 2025 21:29:21 +0100
Subject: [PATCH] Fix bytecode index lookup should not fail if never
 initialized.

---
 .../test/StoreBytecodeEliminationTest.java    | 57 +++++++++++++++++++
 .../generator/BytecodeRootNodeElement.java    |  4 ++
 2 files changed, 61 insertions(+)

diff --git a/truffle/src/com.oracle.truffle.api.bytecode.test/src/com/oracle/truffle/api/bytecode/test/StoreBytecodeEliminationTest.java b/truffle/src/com.oracle.truffle.api.bytecode.test/src/com/oracle/truffle/api/bytecode/test/StoreBytecodeEliminationTest.java
index c5ab252e60ea..1936bea7ff69 100644
--- a/truffle/src/com.oracle.truffle.api.bytecode.test/src/com/oracle/truffle/api/bytecode/test/StoreBytecodeEliminationTest.java
+++ b/truffle/src/com.oracle.truffle.api.bytecode.test/src/com/oracle/truffle/api/bytecode/test/StoreBytecodeEliminationTest.java
@@ -45,9 +45,13 @@
 import static org.junit.Assert.assertTrue;
 
 import java.lang.reflect.Field;
+import java.util.List;
 
 import org.junit.Test;
 
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.TruffleStackTrace;
+import com.oracle.truffle.api.TruffleStackTraceElement;
 import com.oracle.truffle.api.bytecode.BytecodeConfig;
 import com.oracle.truffle.api.bytecode.BytecodeParser;
 import com.oracle.truffle.api.bytecode.BytecodeRootNode;
@@ -63,6 +67,7 @@
 import com.oracle.truffle.api.bytecode.test.error_tests.ExpectWarning;
 import com.oracle.truffle.api.dsl.Bind;
 import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.exception.AbstractTruffleException;
 import com.oracle.truffle.api.frame.FrameDescriptor;
 import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.nodes.Node;
@@ -156,6 +161,28 @@ public void testExplicitUsesSingleton() {
         assertTrue(nodeArgument.getSpecializationInfo().get(0).isActive());
     }
 
+    /*
+     * This tests that if the frame update was optimized out, that capture stack does not fail, but
+     * instead returns -1 as bytecode index.
+     */
+    @Test
+    @SuppressWarnings("unchecked")
+    public void testClearBci() {
+        StoreBytecodeEliminationRootNode root = parseNode((StoreBytecodeEliminationRootNodeGen.Builder b) -> {
+            b.beginRoot();
+            b.emitClearBCI();
+            b.beginReturn();
+            b.emitCaptureStack();
+            b.endReturn();
+            b.endRoot();
+        });
+
+        root.getBytecodeNode().setUncachedThreshold(0);
+
+        List<TruffleStackTraceElement> t = (List<TruffleStackTraceElement>) root.getCallTarget().call();
+        assertEquals(-1, t.get(0).getBytecodeIndex());
+    }
+
     @GenerateBytecode(languageClass = BytecodeDSLTestLanguage.class, enableQuickening = true, enableUncachedInterpreter = true, storeBytecodeIndexInFrame = true, enableSpecializationIntrospection = true)
     abstract static class StoreBytecodeEliminationRootNode extends RootNode implements BytecodeRootNode {
 
@@ -269,6 +296,36 @@ public static int s1(VirtualFrame frame, int v, @Bind Node node) {
 
         }
 
+        @Operation(storeBytecodeIndex = false)
+        public static final class ClearBCI {
+
+            @Specialization
+            public static void doDefault(VirtualFrame f) {
+                f.clear(BCI_INDEX);
+            }
+
+        }
+
+        @Operation(storeBytecodeIndex = false)
+        @SuppressWarnings("unused")
+        public static final class CaptureStack {
+
+            @Specialization
+            @TruffleBoundary
+            public static Object doDefault(@Bind Node node) {
+                return TruffleStackTrace.getStackTrace(new TestException(node));
+            }
+
+        }
+
+    }
+
+    @SuppressWarnings("serial")
+    static class TestException extends AbstractTruffleException {
+        TestException(Node node) {
+            super(node);
+        }
+
     }
 
     @GenerateBytecode(languageClass = BytecodeDSLTestLanguage.class, enableQuickening = true, enableUncachedInterpreter = true, storeBytecodeIndexInFrame = true)
diff --git a/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/generator/BytecodeRootNodeElement.java b/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/generator/BytecodeRootNodeElement.java
index 81a2aec3cfd2..b21f879e76ca 100644
--- a/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/generator/BytecodeRootNodeElement.java
+++ b/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/generator/BytecodeRootNodeElement.java
@@ -875,6 +875,10 @@ private Element createFindBytecodeIndex() {
             b.startStaticCall(types.BytecodeNode, "get").string("node").end().instanceOf(abstractBytecodeNode.asType()).string(" : ").doubleQuote("invalid bytecode node passed");
             b.end();
              */
+            b.startIf().string("frame.getTag(BCI_INDEX) == ").staticReference(types.FrameSlotKind, "Illegal").string(".tag").end().startBlock();
+            b.lineComment("The bci index might be illegal if it was never set due to optimizations.");
+            b.statement("return -1");
+            b.end();
             b.startReturn();
             b.startCall("frame.getInt").string("BCI_INDEX").end();
             b.end();