diff --git a/mlir/lib/Analysis/SliceAnalysis.cpp b/mlir/lib/Analysis/SliceAnalysis.cpp
--- a/mlir/lib/Analysis/SliceAnalysis.cpp
+++ b/mlir/lib/Analysis/SliceAnalysis.cpp
@@ -102,9 +102,10 @@
       // blocks of parentOp, which are not technically backward unless they flow
       // into us. For now, just bail.
       if (parentOp && backwardSlice->count(parentOp) == 0) {
-        assert(parentOp->getNumRegions() == 1 &&
-               parentOp->getRegion(0).getBlocks().size() == 1);
-        getBackwardSliceImpl(parentOp, backwardSlice, filter);
+        if (parentOp->getNumRegions() == 1 &&
+            parentOp->getRegion(0).getBlocks().size() == 1) {
+          getBackwardSliceImpl(parentOp, backwardSlice, filter);
+        }
       }
     } else {
       llvm_unreachable("No definingOp and not a block argument.");