[mlir][scf] Implement getSingle... of LoopLikeOpinterface for scf::ParallelOp (#68511)

This adds implementations for `getSingleIterationVar`,
`getSingleLowerBound`, `getSingleUpperBound`, `getSingleStep` of
`LoopLikeOpInterface` to `scf::ParallelOp`. Until now, the
implementations for these methods defaulted to returning `std::nullopt`,
even in the special case where the parallel Op only has one dimension.

Related: #67883

Author: ubfx

mlir/include/mlir/Dialect/SCF/IR/SCFOps.td

@@ -791,7 +791,8 @@ def IfOp : SCF_Op<"if", [DeclareOpInterfaceMethods<RegionBranchOpInterface, [
 def ParallelOp : SCF_Op<"parallel",
     [AutomaticAllocationScope,
      AttrSizedOperandSegments,
-     DeclareOpInterfaceMethods<LoopLikeOpInterface>,
+     DeclareOpInterfaceMethods<LoopLikeOpInterface, ["getSingleInductionVar",
+          "getSingleLowerBound", "getSingleUpperBound", "getSingleStep"]>,
      RecursiveMemoryEffects,
      DeclareOpInterfaceMethods<RegionBranchOpInterface>,
      SingleBlockImplicitTerminator<"scf::YieldOp">]> {

mlir/lib/Dialect/SCF/IR/SCF.cpp

@@ -2936,6 +2936,30 @@ void ParallelOp::print(OpAsmPrinter &p) {
 
 SmallVector<Region *> ParallelOp::getLoopRegions() { return {&getRegion()}; }
 
+std::optional<Value> ParallelOp::getSingleInductionVar() {
+  if (getNumLoops() != 1)
+    return std::nullopt;
+  return getBody()->getArgument(0);
+}
+
+std::optional<OpFoldResult> ParallelOp::getSingleLowerBound() {
+  if (getNumLoops() != 1)
+    return std::nullopt;
+  return getLowerBound()[0];
+}
+
+std::optional<OpFoldResult> ParallelOp::getSingleUpperBound() {
+  if (getNumLoops() != 1)
+    return std::nullopt;
+  return getUpperBound()[0];
+}
+
+std::optional<OpFoldResult> ParallelOp::getSingleStep() {
+  if (getNumLoops() != 1)
+    return std::nullopt;
+  return getStep()[0];
+}
+
 ParallelOp mlir::scf::getParallelForInductionVarOwner(Value val) {
   auto ivArg = llvm::dyn_cast<BlockArgument>(val);
   if (!ivArg)

mlir/unittests/Dialect/CMakeLists.txt

@@ -9,6 +9,7 @@ target_link_libraries(MLIRDialectTests
 add_subdirectory(Index)
 add_subdirectory(LLVMIR)
 add_subdirectory(MemRef)
+add_subdirectory(SCF)
 add_subdirectory(SparseTensor)
 add_subdirectory(SPIRV)
 add_subdirectory(Transform)

mlir/unittests/Dialect/SCF/CMakeLists.txt

@@ -0,0 +1,8 @@
+add_mlir_unittest(MLIRSCFTests
+  LoopLikeSCFOpsTest.cpp
+)
+target_link_libraries(MLIRSCFTests
+  PRIVATE
+  MLIRIR
+  MLIRSCFDialect
+)

mlir/unittests/Dialect/SCF/LoopLikeSCFOpsTest.cpp

@@ -0,0 +1,89 @@
+//===- LoopLikeSCFOpsTest.cpp - SCF LoopLikeOpInterface Tests -------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Dialect/Arith/IR/Arith.h"
+#include "mlir/Dialect/SCF/IR/SCF.h"
+#include "mlir/IR/Diagnostics.h"
+#include "mlir/IR/MLIRContext.h"
+#include "gtest/gtest.h"
+
+using namespace mlir;
+using namespace mlir::scf;
+
+//===----------------------------------------------------------------------===//
+// Test Fixture
+//===----------------------------------------------------------------------===//
+
+class SCFLoopLikeTest : public ::testing::Test {
+protected:
+  SCFLoopLikeTest() : b(&context), loc(UnknownLoc::get(&context)) {
+    context.loadDialect<arith::ArithDialect, scf::SCFDialect>();
+  }
+
+  void checkUnidimensional(LoopLikeOpInterface loopLikeOp) {
+    std::optional<OpFoldResult> maybeLb = loopLikeOp.getSingleLowerBound();
+    EXPECT_TRUE(maybeLb.has_value());
+    std::optional<OpFoldResult> maybeUb = loopLikeOp.getSingleUpperBound();
+    EXPECT_TRUE(maybeUb.has_value());
+    std::optional<OpFoldResult> maybeStep = loopLikeOp.getSingleStep();
+    EXPECT_TRUE(maybeStep.has_value());
+    std::optional<OpFoldResult> maybeIndVar =
+        loopLikeOp.getSingleInductionVar();
+    EXPECT_TRUE(maybeIndVar.has_value());
+  }
+
+  void checkMultidimensional(LoopLikeOpInterface loopLikeOp) {
+    std::optional<OpFoldResult> maybeLb = loopLikeOp.getSingleLowerBound();
+    EXPECT_FALSE(maybeLb.has_value());
+    std::optional<OpFoldResult> maybeUb = loopLikeOp.getSingleUpperBound();
+    EXPECT_FALSE(maybeUb.has_value());
+    std::optional<OpFoldResult> maybeStep = loopLikeOp.getSingleStep();
+    EXPECT_FALSE(maybeStep.has_value());
+    std::optional<OpFoldResult> maybeIndVar =
+        loopLikeOp.getSingleInductionVar();
+    EXPECT_FALSE(maybeIndVar.has_value());
+  }
+
+  MLIRContext context;
+  OpBuilder b;
+  Location loc;
+};
+
+TEST_F(SCFLoopLikeTest, queryUnidimensionalLooplikes) {
+  Value lb = b.create<arith::ConstantIndexOp>(loc, 0);
+  Value ub = b.create<arith::ConstantIndexOp>(loc, 10);
+  Value step = b.create<arith::ConstantIndexOp>(loc, 2);
+
+  auto forOp = b.create<scf::ForOp>(loc, lb, ub, step);
+  checkUnidimensional(forOp);
+
+  auto forallOp = b.create<scf::ForallOp>(
+      loc, ArrayRef<OpFoldResult>(lb), ArrayRef<OpFoldResult>(ub),
+      ArrayRef<OpFoldResult>(step), ValueRange(), std::nullopt);
+  checkUnidimensional(forallOp);
+
+  auto parallelOp = b.create<scf::ParallelOp>(
+      loc, ValueRange(lb), ValueRange(ub), ValueRange(step), ValueRange());
+  checkUnidimensional(parallelOp);
+}
+
+TEST_F(SCFLoopLikeTest, queryMultidimensionalLooplikes) {
+  Value lb = b.create<arith::ConstantIndexOp>(loc, 0);
+  Value ub = b.create<arith::ConstantIndexOp>(loc, 10);
+  Value step = b.create<arith::ConstantIndexOp>(loc, 2);
+
+  auto forallOp = b.create<scf::ForallOp>(
+      loc, ArrayRef<OpFoldResult>({lb, lb}), ArrayRef<OpFoldResult>({ub, ub}),
+      ArrayRef<OpFoldResult>({step, step}), ValueRange(), std::nullopt);
+  checkMultidimensional(forallOp);
+
+  auto parallelOp =
+      b.create<scf::ParallelOp>(loc, ValueRange({lb, lb}), ValueRange({ub, ub}),
+                                ValueRange({step, step}), ValueRange());
+  checkMultidimensional(parallelOp);
+}