[Mlir-commits] [mlir] [MLIR][Mem2Reg] Fix multi slot handling & move retry handling (PR #91464)

[Tobias Gysi]

================
@@ -636,20 +639,47 @@ LogicalResult mlir::tryToPromoteMemorySlots(
   // lazily and cached to avoid expensive recomputation.
   BlockIndexCache blockIndexCache;
 
-  for (PromotableAllocationOpInterface allocator : allocators) {
-    for (MemorySlot slot : allocator.getPromotableSlots()) {
-      if (slot.ptr.use_empty())
-        continue;
-
-      MemorySlotPromotionAnalyzer analyzer(slot, dominance, dataLayout);
-      std::optional<MemorySlotPromotionInfo> info = analyzer.computeInfo();
-      if (info) {
-        MemorySlotPromoter(slot, allocator, builder, dominance, dataLayout,
-                           std::move(*info), statistics, blockIndexCache)
-            .promoteSlot();
-        promotedAny = true;
+  SmallVector<PromotableAllocationOpInterface> workList(allocators.begin(),
+                                                        allocators.end());
+
+  SmallVector<PromotableAllocationOpInterface> newWorkList;
+  newWorkList.reserve(workList.size());
+  while (true) {
+    bool changesInThisRound = false;
+    for (PromotableAllocationOpInterface allocator : workList) {
+      for (MemorySlot slot : allocator.getPromotableSlots()) {
+        if (slot.ptr.use_empty())
+          continue;
+
+        MemorySlotPromotionAnalyzer analyzer(slot, dominance, dataLayout);
+        std::optional<MemorySlotPromotionInfo> info = analyzer.computeInfo();
+        if (info) {
+          std::optional<PromotableAllocationOpInterface> newAllocator =
+              MemorySlotPromoter(slot, allocator, builder, dominance,
+                                 dataLayout, std::move(*info), statistics,
+                                 blockIndexCache)
+                  .promoteSlot();
+          changesInThisRound = true;
+          // Add newly created allocators to the worklist for further
+          // processing.
+          if (newAllocator)
+            newWorkList.push_back(*newAllocator);
+
+          // Breaking is required, as a modification to an allocator might have
----------------
gysit wrote:

```suggestion
          // A break is required, since promoting a slot may invalidate the remaining slots of an allocator.
```
nit: I would use promotion instead of modification here

https://github.com/llvm/llvm-project/pull/91464