Fix getting frame backrefs from a traceback in uncached-only interpreter

Author: timfel

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/traceback/TracebackBuiltins.java

@@ -189,18 +189,38 @@ static void doMaterialize(Node inliningTarget, PTraceback tb,
              * must be the same.
              */
             PException pException = lazyTraceback.getException();
+            PFrame outermostVisibleFrame = null;
+            PFrame calleeFrame = null;
             List<TruffleStackTraceElement> stackTrace = TruffleStackTrace.getStackTrace(pException);
             if (stackTrace != null) {
                 for (int truffleIndex = pException.getTracebackStartIndex(), pyIndex = 0; truffleIndex < stackTrace.size() && pyIndex < pException.getTracebackFrameCount(); truffleIndex++) {
                     TruffleStackTraceElement element = stackTrace.get(truffleIndex);
                     if (LazyTraceback.elementWantedForTraceback(element)) {
                         PFrame pFrame = materializeFrame(element, materializeFrameNode, pException, stackTrace);
+                        // When the traceback frames are already popped off the stack, f_back can
+                        // only work through the escaped Reference chain. In cached mode we have
+                        // the assumptions on the root nodes that set the caller info, but in
+                        // uncached we explicitly avoid invalidating the assumptions. So it can
+                        // happen that we are walking here during an uncached execution and we'll
+                        // need the caller frame later. We connect links between the freshly
+                        // materialized traceback frames explicitly in that case.
+                        //
+                        // (tfel): I would like to assert this, but I'm not sure how I can.
+                        if (calleeFrame != null && calleeFrame.getRef().getCallerInfo() == null) {
+                            calleeFrame.getRef().setCallerInfo(pFrame.getRef());
+                        }
                         next = PFactory.createTraceback(language, pFrame, pFrame.getLine(), next);
                         next.setLocation(pFrame.getBci(), pFrame.getBytecodeNode());
+                        outermostVisibleFrame = pFrame;
+                        calleeFrame = pFrame;
                         pyIndex++;
                     }
                 }
             }
+            // see comment in the loop, same idea.
+            if (outermostVisibleFrame != null && lazyTraceback.getFrameInfo() != null && outermostVisibleFrame.getRef().getCallerInfo() == null) {
+                outermostVisibleFrame.getRef().setCallerInfo(lazyTraceback.getFrameInfo());
+            }
             if (lazyTraceback.catchingFrameWantedForTraceback()) {
                 tb.setLocation(pException.getCatchBci(), pException.getBytecodeNode());
                 tb.setLineno(pException.getCatchLine());