Introduce new Unroll And Jam loop transform for SCF/Affine loops (llvm#94142)

Unroll And Jam was supported in affine dialect long time ago using pass.
This commit exposes the pattern using transform and in addition adds
partial support for SCF loops.

Author: AviadCo

mlir/include/mlir/Dialect/SCF/TransformOps/SCFTransformOps.td

@@ -269,7 +269,41 @@ def LoopUnrollOp : Op<Transform_Dialect, "loop.unroll",
     This operation ignores non-`scf.for`, non-`affine.for` ops and drops them
     in the return. If all the operations referred to by the `target` operand
     unroll properly, the transform succeeds. Otherwise the transform produces a
-    silencebale failure.
+    silenceable failure.
+
+    Does not return handles as the operation may result in the loop being
+    removed after a full unrolling.
+  }];
+
+  let arguments = (ins TransformHandleTypeInterface:$target,
+                       ConfinedAttr<I64Attr, [IntPositive]>:$factor);
+
+  let assemblyFormat = "$target attr-dict `:` type($target)";
+
+  let extraClassDeclaration = [{
+    ::mlir::DiagnosedSilenceableFailure applyToOne(
+        ::mlir::transform::TransformRewriter &rewriter,
+        ::mlir::Operation *target,
+        ::mlir::transform::ApplyToEachResultList &results,
+        ::mlir::transform::TransformState &state);
+  }];
+}
+
+def LoopUnrollAndJamOp : Op<Transform_Dialect, "loop.unroll_and_jam",
+    [FunctionalStyleTransformOpTrait, MemoryEffectsOpInterface,
+     TransformOpInterface, TransformEachOpTrait]> {
+  let summary = "Unrolls and jam the given loop with the given unroll factor";
+  let description = [{
+    Unrolls & jams each loop associated with the given handle to have up to the given
+    number of loop body copies per iteration. If the unroll factor is larger
+    than the loop trip count, the latter is used as the unroll factor instead.
+
+    #### Return modes
+
+    This operation ignores non-`scf.for`, non-`affine.for` ops and drops them
+    in the return. If all the operations referred to by the `target` operand
+    unroll properly, the transform succeeds. Otherwise the transform produces a
+    silenceable failure.
 
     Does not return handles as the operation may result in the loop being
     removed after a full unrolling.

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

@@ -120,6 +120,14 @@ LogicalResult loopUnrollByFactor(
     scf::ForOp forOp, uint64_t unrollFactor,
     function_ref<void(unsigned, Operation *, OpBuilder)> annotateFn = nullptr);
 
+/// Unrolls and jams this `scf.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. In case of unroll factor of 1, the function
+/// bails out without doing anything (returns success). Currently, only constant
+/// trip count that are divided by the unroll factor is supported. Currently,
+/// for operations with results are not supported.
+LogicalResult loopUnrollJamByFactor(scf::ForOp forOp, uint64_t unrollFactor);
+
 /// Transform a loop with a strictly positive step
 ///   for %i = %lb to %ub step %s
 /// into a 0-based loop with step 1

mlir/include/mlir/Interfaces/LoopLikeInterface.h

@@ -48,6 +48,39 @@ class HasParallelRegion : public TraitBase<ConcreteType, HasParallelRegion> {
 };
 
 } // namespace OpTrait
+
+// Gathers all maximal sub-blocks of operations that do not themselves
+// include a `OpTy` (an operation could have a descendant `OpTy` though
+// in its tree). Ignores the block terminators.
+template <typename OpTy>
+struct JamBlockGatherer {
+  // Store iterators to the first and last op of each sub-block found.
+  SmallVector<std::pair<Block::iterator, Block::iterator>> subBlocks;
+
+  // This is a linear time walk.
+  void walk(Operation *op) {
+    for (Region &region : op->getRegions())
+      for (Block &block : region)
+        walk(block);
+  }
+
+  void walk(Block &block) {
+    assert(!block.empty() && block.back().hasTrait<OpTrait::IsTerminator>() &&
+           "expected block to have a terminator");
+    for (Block::iterator it = block.begin(), e = std::prev(block.end());
+         it != e;) {
+      Block::iterator subBlockStart = it;
+      while (it != e && !isa<OpTy>(&*it))
+        ++it;
+      if (it != subBlockStart)
+        subBlocks.emplace_back(subBlockStart, std::prev(it));
+      // Process all for ops that appear next.
+      while (it != e && isa<OpTy>(&*it))
+        walk(&*it++);
+    }
+  }
+};
+
 } // namespace mlir
 
 //===----------------------------------------------------------------------===//

mlir/lib/Dialect/Affine/Utils/LoopUtils.cpp

@@ -37,16 +37,6 @@ using namespace affine;
 using namespace presburger;
 using llvm::SmallMapVector;
 
-namespace {
-// This structure is to pass and return sets of loop parameters without
-// confusing the order.
-struct LoopParams {
-  Value lowerBound;
-  Value upperBound;
-  Value step;
-};
-} // namespace
-
 /// Computes the cleanup loop lower bound of the loop being unrolled with
 /// the specified unroll factor; this bound will also be upper bound of the main
 /// part of the unrolled loop. Computes the bound as an AffineMap with its
@@ -1101,34 +1091,6 @@ static bool areInnerBoundsInvariant(AffineForOp forOp) {
   return !walkResult.wasInterrupted();
 }
 
-// Gathers all maximal sub-blocks of operations that do not themselves
-// include a for op (a operation could have a descendant for op though
-// in its tree).  Ignore the block terminators.
-struct JamBlockGatherer {
-  // Store iterators to the first and last op of each sub-block found.
-  std::vector<std::pair<Block::iterator, Block::iterator>> subBlocks;
-
-  // This is a linear time walk.
-  void walk(Operation *op) {
-    for (auto &region : op->getRegions())
-      for (auto &block : region)
-        walk(block);
-  }
-
-  void walk(Block &block) {
-    for (auto it = block.begin(), e = std::prev(block.end()); it != e;) {
-      auto subBlockStart = it;
-      while (it != e && !isa<AffineForOp>(&*it))
-        ++it;
-      if (it != subBlockStart)
-        subBlocks.emplace_back(subBlockStart, std::prev(it));
-      // Process all for ops that appear next.
-      while (it != e && isa<AffineForOp>(&*it))
-        walk(&*it++);
-    }
-  }
-};
-
 /// Unrolls and jams this loop by the specified factor.
 LogicalResult mlir::affine::loopUnrollJamByFactor(AffineForOp forOp,
                                                   uint64_t unrollJamFactor) {
@@ -1158,7 +1120,7 @@ LogicalResult mlir::affine::loopUnrollJamByFactor(AffineForOp forOp,
     return failure();
 
   // Gather all sub-blocks to jam upon the loop being unrolled.
-  JamBlockGatherer jbg;
+  JamBlockGatherer<AffineForOp> jbg;
   jbg.walk(forOp);
   auto &subBlocks = jbg.subBlocks;
 

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

@@ -348,12 +348,36 @@ transform::LoopUnrollOp::applyToOne(transform::TransformRewriter &rewriter,
     result = loopUnrollByFactor(scfFor, getFactor());
   else if (AffineForOp affineFor = dyn_cast<AffineForOp>(op))
     result = loopUnrollByFactor(affineFor, getFactor());
+  else
+    return emitSilenceableError()
+           << "failed to unroll, incorrect type of payload";
+
+  if (failed(result))
+    return emitSilenceableError() << "failed to unroll";
+
+  return DiagnosedSilenceableFailure::success();
+}
+
+//===----------------------------------------------------------------------===//
+// LoopUnrollAndJamOp
+//===----------------------------------------------------------------------===//
+
+DiagnosedSilenceableFailure transform::LoopUnrollAndJamOp::applyToOne(
+    transform::TransformRewriter &rewriter, Operation *op,
+    transform::ApplyToEachResultList &results,
+    transform::TransformState &state) {
+  LogicalResult result(failure());
+  if (scf::ForOp scfFor = dyn_cast<scf::ForOp>(op))
+    result = loopUnrollJamByFactor(scfFor, getFactor());
+  else if (AffineForOp affineFor = dyn_cast<AffineForOp>(op))
+    result = loopUnrollJamByFactor(affineFor, getFactor());
+  else
+    return emitSilenceableError()
+           << "failed to unroll and jam, incorrect type of payload";
+
+  if (failed(result))
+    return emitSilenceableError() << "failed to unroll and jam";
 
-  if (failed(result)) {
-    DiagnosedSilenceableFailure diag = emitSilenceableError()
-                                       << "failed to unroll";
-    return diag;
-  }
   return DiagnosedSilenceableFailure::success();
 }