[Mlir-commits] [mlir] [mlir] Fix crash in ForwardDominanceIterator when encountering graph regions (PR #185043)

[Matthias Springer]

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@@ -40,25 +40,26 @@ struct ReverseIterator {
 /// enumerated according to their successor relationship. Unreachable blocks are
 /// not enumerated. Blocks may not be erased during the traversal.
 ///
-/// Note: If `NoGraphRegions` is set to "true", this iterator asserts that each
-/// visited region has SSA dominance. In either case, the ops in such regions
-/// are visited in forward order, but for regions without SSA dominance this
-/// does not guarantee that defining ops are visited before their users.
+/// Note: If `NoGraphRegions` is set to "true", graph regions (regions without
+/// SSA dominance) are skipped during the traversal. If set to "false" (the
+/// default), graph regions are visited but without dominance guarantees (i.e.,
+/// defining ops are not guaranteed to be visited before their users).
 template <bool NoGraphRegions = false>
 struct ForwardDominanceIterator {
   static Block &makeIterable(Block &range) {
     return ForwardIterator::makeIterable(range);
   }
 
   static auto makeIterable(Region &region) {
-    if (NoGraphRegions) {
-      // Only regions with SSA dominance are allowed.
-      assert(mayHaveSSADominance(region) && "graph regions are not allowed");
+    Block *null = nullptr;
+    if (NoGraphRegions && !mayHaveSSADominance(region)) {
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matthias-springer wrote:

I would expand the documentation of `ForwardDominanceIterator` to say that ops in regions of unregistered ops are iterated over as if they were SSACFG regions.


https://github.com/llvm/llvm-project/pull/185043