[MLIR] Update affine.for unroll utility for iter_args support

[bondhugula]

Summary

Update affine.for loop unroll utility for iteration arguments support.
Fix promoteIfSingleIteration as well.

Fixes https://bugs.llvm.org/show_bug.cgi?id=49084

[bondhugula]

Rebase on main tip. Minor doc comment and commit summary update.

[dcaballe]

Thanks for the fix, Uday! LGTM. Just a couple of minor comments.

mlir/lib/Transforms/Utils/LoopUtils.cpp

153

Even if we limit the utility only to SCF and Affine for ops, would it be possible to use LoopLikeInterface here instead of the the template?

1169

nit: avoid auto here?

[bondhugula]

Address review comment on auto.

[bondhugula]

mlir/lib/Transforms/Utils/LoopUtils.cpp

153

I explored that but we unfortunately can't since not all ops that implement the LoopLikeOpInterface have a getIterOperands, getRegionIterArgs, or results.

mlir/lib/Transforms/Utils/LoopUtils.cpp

static Value ceilDivPositive(OpBuilder &builder, Location loc, Value dividend,
   assert(dividend.getType().isIndex() && "expected index-typed value");
 
   Value cstOne = builder.create<ConstantIndexOp>(loc, 1);
   Value divisorMinusOne = builder.create<SubIOp>(loc, divisor, cstOne);
   Value sum = builder.create<AddIOp>(loc, dividend, divisorMinusOne);
   return builder.create<SignedDivIOp>(loc, sum, divisor);
 }
 
+/// Helper to replace uses of loop carried values (iter_args) and loop
+/// yield values while promoting single iteration affine.for and scf.for ops.
+template <typename AffineOrSCFForOp>
+static void replaceIterArgsAndYieldResults(AffineOrSCFForOp forOp) {
+  static_assert(
+      llvm::is_one_of<AffineOrSCFForOp, AffineForOp, scf::ForOp>::value,
+      "only for affine.for and scf.for ops");
+  // Replace uses of iter arguments with iter operands (initial values).
+  auto iterOperands = forOp.getIterOperands();
+  auto iterArgs = forOp.getRegionIterArgs();
+  for (auto e : llvm::zip(iterOperands, iterArgs))
+    std::get<1>(e).replaceAllUsesWith(std::get<0>(e));
+
+  // Replace uses of loop results with the values yielded by the loop.
+  auto outerResults = forOp.getResults();
+  auto innerResults = forOp.getBody()->getTerminator()->getOperands();
+  for (auto e : llvm::zip(outerResults, innerResults))
+    std::get<0>(e).replaceAllUsesWith(std::get<1>(e));
+}
+
 /// Promotes the loop body of a forOp to its containing block if the forOp
 /// was known to have a single iteration.
 // TODO: extend this for arbitrary affine bounds.
 LogicalResult mlir::promoteIfSingleIteration(AffineForOp forOp) {
   Optional<uint64_t> tripCount = getConstantTripCount(forOp);
   if (!tripCount || tripCount.getValue() != 1)
     return failure();
 
if (forOp.hasConstantLowerBound()) {
         iv.replaceAllUsesWith(lbOperands[0]);
       } else {
         auto affineApplyOp =
             builder.create<AffineApplyOp>(forOp.getLoc(), lbMap, lbOperands);
         iv.replaceAllUsesWith(affineApplyOp);
       }
     }
   }
+
+  replaceIterArgsAndYieldResults(forOp);
+
   // Move the loop body operations, except for its terminator, to the loop's
   // containing block.
   forOp.getBody()->back().erase();
   parentBlock->getOperations().splice(Block::iterator(forOp),
                                       forOp.getBody()->getOperations());
   forOp.erase();
   return success();
 }
if (!lbCstOp || !ubCstOp || !stepCstOp || lbCstOp.getValue() < 0 ||
     return failure();
   int64_t tripCount = mlir::ceilDiv(ubCstOp.getValue() - lbCstOp.getValue(),
                                     stepCstOp.getValue());
   if (tripCount != 1)
     return failure();
   auto iv = forOp.getInductionVar();
   iv.replaceAllUsesWith(lbCstOp);
 
-  // Replace uses of iterArgs with iterOperands.
-  auto iterOperands = forOp.getIterOperands();
-  auto iterArgs = forOp.getRegionIterArgs();
-  for (auto e : llvm::zip(iterOperands, iterArgs))
-    std::get<1>(e).replaceAllUsesWith(std::get<0>(e));
-
-  // Replace uses of loop results with the values yielded by the loop.
-  auto outerResults = forOp.getResults();
-  auto innerResults = forOp.getBody()->getTerminator()->getOperands();
-  for (auto e : llvm::zip(outerResults, innerResults))
-    std::get<0>(e).replaceAllUsesWith(std::get<1>(e));
+  replaceIterArgsAndYieldResults(forOp);
 
   // Move the loop body operations, except for its terminator, to the loop's
   // containing block.
   auto *parentBlock = forOp->getBlock();
   forOp.getBody()->getTerminator()->erase();
   parentBlock->getOperations().splice(Block::iterator(forOp),
                                       forOp.getBody()->getOperations());
   forOp.erase();
LogicalResult mlir::loopUnrollByFactor(AffineForOp forOp,
   if (mayBeConstantTripCount.hasValue() &&
       mayBeConstantTripCount.getValue() < unrollFactor)
     return failure();
 
   // Generate the cleanup loop if trip count isn't a multiple of unrollFactor.
   if (getLargestDivisorOfTripCount(forOp) % unrollFactor != 0) {
     OpBuilder builder(forOp->getBlock(), std::next(Block::iterator(forOp)));
     auto cleanupForOp = cast<AffineForOp>(builder.clone(*forOp));
+
+    // Update users of loop results.
+    auto results = forOp.getResults();
+    auto cleanupResults = cleanupForOp.getResults();
+    auto cleanupIterOperands = cleanupForOp.getIterOperands();
+
+    for (auto e : llvm::zip(results, cleanupResults, cleanupIterOperands)) {
+      std::get<0>(e).replaceAllUsesWith(std::get<1>(e));
+      cleanupForOp->replaceUsesOfWith(std::get<2>(e), std::get<0>(e));
+    }
+
     AffineMap cleanupMap;
     SmallVector<Value, 4> cleanupOperands;
     getCleanupLoopLowerBound(forOp, unrollFactor, cleanupMap, cleanupOperands);
     assert(cleanupMap &&
            "cleanup loop lower bound map for single result lower bound maps "
            "can always be determined");
     cleanupForOp.setLowerBound(cleanupOperands, cleanupMap);
     // Promote the loop body up if this has turned into a single iteration loop.
     (void)promoteIfSingleIteration(cleanupForOp);
 
     // Adjust upper bound of the original loop; this is the same as the lower
     // bound of the cleanup loop.
     forOp.setUpperBound(cleanupOperands, cleanupMap);
   }
 
+  auto iterArgs = ValueRange(forOp.getRegionIterArgs());
+  auto yieldedValues = forOp.getBody()->getTerminator()->getOperands();
+
   // Scale the step of loop being unrolled by unroll factor.
   int64_t step = forOp.getStep();
   forOp.setStep(step * unrollFactor);
-  generateUnrolledLoop(forOp.getBody(), forOp.getInductionVar(), unrollFactor,
-                       [&](unsigned i, Value iv, OpBuilder b) {
-                         // iv' = iv + i * step
-                         auto d0 = b.getAffineDimExpr(0);
-                         auto bumpMap = AffineMap::get(1, 0, d0 + i * step);
-                         return b.create<AffineApplyOp>(forOp.getLoc(), bumpMap,
-                                                        iv);
-                       },
-                       /*iterArgs=*/{}, /*yieldedValues=*/{});
+  generateUnrolledLoop(
+      forOp.getBody(), forOp.getInductionVar(), unrollFactor,
+        return b.create<AffineApplyOp>(forOp.getLoc(), bumpMap, iv);
+      /*iterArgs=*/iterArgs, /*yieldedValues=*/yieldedValues);
 
   // Promote the loop body up if this has turned into a single iteration loop.
   (void)promoteIfSingleIteration(forOp);
   return success();
 }
 
 /// Unrolls 'forOp' by 'unrollFactor', returns success if the loop is unrolled.
 LogicalResult mlir::loopUnrollByFactor(scf::ForOp forOp,

mlir/test/Dialect/Affine/unroll.mlir

func @unroll_by_one_should_promote_single_iteration_loop() {
   affine.for %i = 0 to 1 {
     %x = "foo"(%i) : (index) -> i32
   }
   return
 // UNROLL-BY-1-NEXT: %c0 = constant 0 : index
 // UNROLL-BY-1-NEXT: %0 = "foo"(%c0) : (index) -> i32
 // UNROLL-BY-1-NEXT: return
 }
+
+// Test unrolling with affine.for iter_args.
+
+// UNROLL-BY-4-LABEL: loop_unroll_with_iter_args_and_cleanup
+func @loop_unroll_with_iter_args_and_cleanup(%arg0 : f32, %arg1 : f32, %n : index) -> (f32,f32) {
+  %cf1 = constant 1.0 : f32
+  %cf2 = constant 2.0 : f32
+  %sum:2 = affine.for %iv = 0 to 10 iter_args(%i0 = %arg0, %i1 = %arg1) -> (f32, f32) {
+    %sum0 = addf %i0, %cf1 : f32
+    %sum1 = addf %i1, %cf2 : f32
+    affine.yield %sum0, %sum1 : f32, f32
+  }
+  return %sum#0, %sum#1 : f32, f32
+  // UNROLL-BY-4:      %[[SUM:.*]]:2 = affine.for {{.*}} = 0 to 8 step 4 iter_args
+  // UNROLL-BY-4-NEXT:   addf
+  // UNROLL-BY-4-NEXT:   addf
+  // UNROLL-BY-4-NEXT:   addf
+  // UNROLL-BY-4-NEXT:   addf
+  // UNROLL-BY-4-NEXT:   addf
+  // UNROLL-BY-4-NEXT:   addf
+  // UNROLL-BY-4-NEXT:   %[[Y1:.*]] = addf
+  // UNROLL-BY-4-NEXT:   %[[Y2:.*]] = addf
+  // UNROLL-BY-4-NEXT:   affine.yield %[[Y1]], %[[Y2]]
+  // UNROLL-BY-4-NEXT: }
+  // UNROLL-BY-4-NEXT: %[[SUM1:.*]]:2 = affine.for {{.*}} = 8 to 10 iter_args(%[[V1:.*]] = %[[SUM]]#0, %[[V2:.*]] = %[[SUM]]#1)
+  // UNROLL-BY-4:      }
+  // UNROLL-BY-4-NEXT: return %[[SUM1]]#0, %[[SUM1]]#1
+}
+
+// The epilogue being a single iteration loop gets promoted here.
+
+// UNROLL-BY-4-LABEL: unroll_with_iter_args_and_promotion
+func @unroll_with_iter_args_and_promotion(%arg0 : f32, %arg1 : f32) -> f32 {
+  %from = constant 0 : index
+  %to = constant 10 : index
+  %step = constant 1 : index
+  %sum = affine.for %iv = 0 to 9 iter_args(%sum_iter = %arg0) -> (f32) {
+    %next = addf %sum_iter, %arg1 : f32
+    affine.yield %next : f32
+  }
+  // UNROLL-BY-4:      %[[SUM:.*]] = affine.for %{{.*}} = 0 to 8 step 4 iter_args(%[[V0:.*]] =
+  // UNROLL-BY-4-NEXT:   %[[V1:.*]] = addf %[[V0]]
+  // UNROLL-BY-4-NEXT:   %[[V2:.*]] = addf %[[V1]]
+  // UNROLL-BY-4-NEXT:   %[[V3:.*]] = addf %[[V2]]
+  // UNROLL-BY-4-NEXT:   %[[V4:.*]] = addf %[[V3]]
+  // UNROLL-BY-4-NEXT:   affine.yield %[[V4]]
+  // UNROLL-BY-4-NEXT: }
+  // UNROLL-BY-4-NEXT: %[[RES:.*]] = addf %[[SUM]],
+  // UNROLL-BY-4-NEXT: return %[[RES]]
+  return %sum : f32
+}