[mlir][scf] Expose isPerfectlyNestedForLoops

Author: Shay Kleiman

mlir/include/mlir/Dialect/SCF/Transforms/TileUsingInterface.h

@@ -364,6 +364,14 @@ FailureOr<scf::SCFTilingResult>
 tileReductionUsingScf(RewriterBase &b, PartialReductionOpInterface op,
                       ArrayRef<OpFoldResult> tileSizes);
 
+/// Check if the provided loops are perfectly nested for-loops. Perfect nesting
+/// means:
+/// 1. All loops are scf.for operations
+/// 2. Each outer loop's region iter args match the inner loop's init args
+/// 3. Each outer loop's yields match the inner loop's results
+/// 4. Each region iter arg and result has exactly one use
+bool isPerfectlyNestedForLoops(MutableArrayRef<LoopLikeOpInterface> loops);
+
 } // namespace scf
 } // namespace mlir
 

mlir/lib/Dialect/SCF/Transforms/TileUsingInterface.cpp

@@ -1927,8 +1927,8 @@ static FailureOr<OpOperand *> getConsumerFromLoopUses(RewriterBase &rewriter,
 ///    yield %1
 /// ```
 /// Here loops should be [%0, %1].
-static bool
-isPerfectlyNestedForLoops(MutableArrayRef<LoopLikeOpInterface> loops) {
+bool mlir::scf::isPerfectlyNestedForLoops(
+    MutableArrayRef<LoopLikeOpInterface> loops) {
   assert(!loops.empty() && "unexpected empty loop nest");
   if (loops.size() == 1) {
     return isa_and_nonnull<scf::ForOp>(loops.front().getOperation());
@@ -1991,7 +1991,7 @@ getUntiledConsumerFromSlice(RewriterBase &rewriter,
   }
 
   // 2. Check that the loop is perfectly nested.
-  if (!isPerfectlyNestedForLoops(loops)) {
+  if (!mlir::scf::isPerfectlyNestedForLoops(loops)) {
     return rewriter.notifyMatchFailure(
         candidateSliceOp, "expected passed loops to be perfectly nested.");
   }