[Mlir-commits] [mlir] [mlir][bufferization] handle exit aliases in buffer-loop-hoisting (PR #226951)

[Matthias Springer]

================
@@ -66,6 +69,49 @@ static bool isSequentialLoop(Operation *op) {
   return !op->hasTrait<OpTrait::HasParallelRegion>() && isLoop(op);
 }
 
+/// Returns true if an allocation can be reused across iterations when its
+/// aliases have a common dominator outside the while loop.
+/// `aliases` must contain the complete forward alias set of the allocation.
+static bool
+canHoistFromWhile(scf::WhileOp loop,
+                  const BufferViewFlowAnalysis::ValueSetT &aliases) {
+  // Further hoisting across an enclosing loop with unmodeled parallel
+  // execution could share the allocation across iterations.
+  if (!isa<FunctionOpInterface>(loop->getParentOp()))
+    return false;
+
+  // Check all aliases, including loop results: memory effects alone do not rule
+  // out capture or uses that depend on allocation identity or lifetime.
+  for (Value alias : aliases) {
+    if (!isa<BaseMemRefType>(alias.getType()))
+      return false;
+    for (OpOperand &use : alias.getUses()) {
+      Operation *user = use.getOwner();
+      if (user->getParentOp() != loop && user->getBlock() != loop->getBlock())
+        return false;
+      if (auto load = dyn_cast<memref::LoadOp>(user)) {
+        if (load.getInvariant())
+          return false;
----------------
matthias-springer wrote:

Why does an `invariant` load disqualify hoisting? Can you add a comment?

https://github.com/llvm/llvm-project/pull/226951