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

[Matteo Di Iorio]

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@@ -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
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splicer3 wrote:

`scf.for` goes through the same `isLegalPlacement` check, which already rejects loops with the `HasParallelRegion` trait. That stops hoisting across scf.parallel, but there is no additional protection for parallel loops without that trait, as in #226090.

I added the function-parent check to keep the new while fallback from exposing the same problem, but I think I can just use the existing stopping condition and allow a non-loop parent or one with HasParallelRegion. That will let the allocation move before the `while` and also keep it inside the parent.

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