[Mlir-commits] [mlir] [mlir][mem2reg] Promote memory slots through transparent view operations (PR #196924)

[Tobias Gysi]

================
@@ -8,5 +8,114 @@
 
 #include "mlir/Interfaces/MemorySlotInterfaces.h"
 
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+
 #include "mlir/Interfaces/MemorySlotOpInterfaces.cpp.inc"
 #include "mlir/Interfaces/MemorySlotTypeInterfaces.cpp.inc"
+
+using namespace mlir;
+
+namespace {
+/// One step in a view chain, leaf-first. `inputElemType` is the elemType
+/// of the slot one step closer to root; `outputElemType` is the elemType
+/// this step exposes.
+struct ViewStep {
+  PromotableOpInterface view;
+  Type inputElemType;
+  Type outputElemType;
+};
+} // namespace
+
+/// Walks back from `value` to `rootSlot.ptr` along
+/// `getPromotableSlotView` chains. On success, populates `chainOut` with
+/// the view ops leaf-to-root and writes the type at which `value` aliases
+/// the underlying slot to `*outViewElemType`.
+static bool walkPromotableSlotViewChain(Value value, const MemorySlot &rootSlot,
+                                        SmallVectorImpl<ViewStep> &chainOut,
+                                        Type *outViewElemType) {
+  if (value == rootSlot.ptr) {
+    if (outViewElemType)
+      *outViewElemType = rootSlot.elemType;
+    return true;
+  }
+
+  Value current = value;
+  Type aliasElemType{};
+  llvm::SmallPtrSet<Value, 4> seen;
+  while (current != rootSlot.ptr) {
+    if (!seen.insert(current).second)
+      return false;
+    auto promotable =
+        dyn_cast_or_null<PromotableOpInterface>(current.getDefiningOp());
+    if (!promotable)
+      return false;
+    std::optional<PromotableSlotView> info = promotable.getPromotableSlotView();
+    if (!info || info->view.ptr != current)
+      return false;
+    if (!aliasElemType)
+      aliasElemType = info->view.elemType;
+    chainOut.push_back(ViewStep{promotable, /*inputElemType=*/Type{},
+                                /*outputElemType=*/info->view.elemType});
+    current = info->slotPointerOperand;
+  }
----------------
gysit wrote:

PS if we would like to store the subviews somewhere then `MemorySlot` could be the right place. 


https://github.com/llvm/llvm-project/pull/196924