[mlir] Extend SCF loopUnrollByFactor to return the result loops

mlir/include/mlir/Dialect/SCF/Utils/Utils.h

@@ -111,11 +111,13 @@ LogicalResult coalescePerfectlyNestedSCFForLoops(scf::ForOp op);
 void collapseParallelLoops(RewriterBase &rewriter, scf::ParallelOp loops,
                            ArrayRef<std::vector<unsigned>> combinedDimensions);
 
-/// Unrolls this for operation by the specified unroll factor. Returns failure
-/// if the loop cannot be unrolled either due to restrictions or due to invalid
-/// unroll factors. Requires positive loop bounds and step. If specified,
-/// annotates the Ops in each unrolled iteration by applying `annotateFn`.
-LogicalResult loopUnrollByFactor(
+/// Unrolls this for operation by the specified unroll factor. Returns the
+/// unrolled main loop and the eplilog loop in sequence, if the loop is
+/// unrolled. Otherwise returns an empty vector if the loop cannot be unrolled
+/// either due to restrictions or due to invalid unroll factors. Requires
+/// positive loop bounds and step. If specified, annotates the Ops in each
+/// unrolled iteration by applying `annotateFn`.
+SmallVector<scf::ForOp> loopUnrollByFactor(
     scf::ForOp forOp, uint64_t unrollFactor,
     function_ref<void(unsigned, Operation *, OpBuilder)> annotateFn = nullptr);
 

mlir/lib/Dialect/SCF/TransformOps/SCFTransformOps.cpp

@@ -353,8 +353,10 @@ transform::LoopUnrollOp::applyToOne(transform::TransformRewriter &rewriter,
                                     transform::ApplyToEachResultList &results,
                                     transform::TransformState &state) {
   LogicalResult result(failure());
-  if (scf::ForOp scfFor = dyn_cast<scf::ForOp>(op))
-    result = loopUnrollByFactor(scfFor, getFactor());
+  if (scf::ForOp scfFor = dyn_cast<scf::ForOp>(op)) {
+    auto resultLoops = loopUnrollByFactor(scfFor, getFactor());
+    result = resultLoops.empty() ? failure() : success();
+  }
   else if (AffineForOp affineFor = dyn_cast<AffineForOp>(op))
     result = loopUnrollByFactor(affineFor, getFactor());
   else

mlir/lib/Dialect/SCF/Utils/Utils.cpp

@@ -372,15 +372,17 @@ static void generateUnrolledLoop(
   loopBodyBlock->getTerminator()->setOperands(lastYielded);
 }
 
-/// Unrolls 'forOp' by 'unrollFactor', returns success if the loop is unrolled.
-LogicalResult mlir::loopUnrollByFactor(
+/// Unrolls 'forOp' by 'unrollFactor', returns the unrolled main loop and the
+/// eplilog loop in sequence, if the loop is unrolled. Otherwise return an empty
+/// vector.
+SmallVector<scf::ForOp> mlir::loopUnrollByFactor(
     scf::ForOp forOp, uint64_t unrollFactor,
     function_ref<void(unsigned, Operation *, OpBuilder)> annotateFn) {
   assert(unrollFactor > 0 && "expected positive unroll factor");
 
   // Return if the loop body is empty.
   if (llvm::hasSingleElement(forOp.getBody()->getOperations()))
-    return success();
+    return {forOp};
 
   // Compute tripCount = ceilDiv((upperBound - lowerBound), step) and populate
   // 'upperBoundUnrolled' and 'stepUnrolled' for static and dynamic cases.
@@ -401,8 +403,8 @@ LogicalResult mlir::loopUnrollByFactor(
     if (unrollFactor == 1) {
       if (*constTripCount == 1 &&
           failed(forOp.promoteIfSingleIteration(rewriter)))
-        return failure();
-      return success();
+        return {};
+      return {forOp};
     }
 
     int64_t tripCountEvenMultiple =
@@ -450,6 +452,9 @@ LogicalResult mlir::loopUnrollByFactor(
         boundsBuilder.create<arith::MulIOp>(loc, step, unrollFactorCst);
   }
 
+  SmallVector<scf::ForOp, 2> resultLoops;
+  resultLoops.push_back(forOp);
+
   // Create epilogue clean up loop starting at 'upperBoundUnrolled'.
   if (generateEpilogueLoop) {
     OpBuilder epilogueBuilder(forOp->getContext());
@@ -468,6 +473,7 @@ LogicalResult mlir::loopUnrollByFactor(
     epilogueForOp->setOperands(epilogueForOp.getNumControlOperands(),
                                epilogueForOp.getInitArgs().size(), results);
     (void)epilogueForOp.promoteIfSingleIteration(rewriter);
+    resultLoops.push_back(epilogueForOp);
   }
 
   // Create unrolled loop.
@@ -490,7 +496,7 @@ LogicalResult mlir::loopUnrollByFactor(
       annotateFn, iterArgs, yieldedValues);
   // Promote the loop body up if this has turned into a single iteration loop.
   (void)forOp.promoteIfSingleIteration(rewriter);
-  return success();
+  return resultLoops;
 }
 
 /// Check if bounds of all inner loops are defined outside of `forOp`