[Mlir-commits] [mlir] [MLIR] `remove-dead-values` and RegionBranchOp canononicalizations fixes around the `IsolatedFromAbove` ops (PR #224831)

[Matthias Springer]

================
@@ -744,8 +742,19 @@ struct MakeRegionBranchOpSuccessorInputsDead : public RewritePattern {
               /*maxReachableValues=*/1)) ||
           reachableValues.empty())
         continue;
-      assert(*reachableValues.begin() != value &&
+      Value replacement = *reachableValues.begin();
+      assert(replacement != value &&
              "successor inputs are supposed to be excluded");
+      // A value inside an isolated region cannot be replaced with a value from
+      // another region, even if the replacement dominates its uses. Op results
+      // are in the parent region and do not cross this isolation boundary.
+      // Successor inputs are direct region arguments or results of this op.
+      // Valid input IR already prevents captures across nested isolation
+      // boundaries, so only this op's boundary needs an additional check.
+      Region *valueRegion = value.getParentRegion();
----------------
matthias-springer wrote:

This looks correct, but can you also add a small IR snippet, similar to the `isDefinedBefore` check below?

https://github.com/llvm/llvm-project/pull/224831