[Mlir-commits] [mlir] ee1bf18 - [mlir][SCF] Further simplify affine maps during `for-loop-canonicalization`
Matthias Springer
llvmlistbot at llvm.org
Wed Nov 24 19:49:11 PST 2021
Author: Matthias Springer
Date: 2021-11-25T12:44:19+09:00
New Revision: ee1bf186723abb933b2c337e589c5958167f3cbe
URL: https://github.com/llvm/llvm-project/commit/ee1bf186723abb933b2c337e589c5958167f3cbe
DIFF: https://github.com/llvm/llvm-project/commit/ee1bf186723abb933b2c337e589c5958167f3cbe.diff
LOG: [mlir][SCF] Further simplify affine maps during `for-loop-canonicalization`
* Implement `FlatAffineConstraints::getConstantBound(EQ)`.
* Inject a simpler constraint for loops that have at most 1 iteration.
* Taking into account constant EQ bounds of FlatAffineConstraint dims/symbols during canonicalization of the resulting affine map in `canonicalizeMinMaxOp`.
Differential Revision: https://reviews.llvm.org/D114138
Added:
Modified:
mlir/include/mlir/Analysis/AffineStructures.h
mlir/lib/Analysis/AffineStructures.cpp
mlir/lib/Dialect/SCF/Transforms/LoopSpecialization.cpp
mlir/test/Dialect/SCF/for-loop-canonicalization.mlir
Removed:
################################################################################
diff --git a/mlir/include/mlir/Analysis/AffineStructures.h b/mlir/include/mlir/Analysis/AffineStructures.h
index 53b3d043606e4..fa58e3e3412fa 100644
--- a/mlir/include/mlir/Analysis/AffineStructures.h
+++ b/mlir/include/mlir/Analysis/AffineStructures.h
@@ -385,7 +385,6 @@ class FlatAffineConstraints {
/// Returns the constant bound for the pos^th identifier if there is one;
/// None otherwise.
- // TODO: Support EQ bounds.
Optional<int64_t> getConstantBound(BoundType type, unsigned pos) const;
/// Gets the lower and upper bound of the `offset` + `pos`th identifier
diff --git a/mlir/lib/Analysis/AffineStructures.cpp b/mlir/lib/Analysis/AffineStructures.cpp
index c0465a2532b46..21dd469b812f9 100644
--- a/mlir/lib/Analysis/AffineStructures.cpp
+++ b/mlir/lib/Analysis/AffineStructures.cpp
@@ -2836,11 +2836,22 @@ FlatAffineConstraints::computeConstantLowerOrUpperBound(unsigned pos) {
Optional<int64_t> FlatAffineConstraints::getConstantBound(BoundType type,
unsigned pos) const {
- assert(type != BoundType::EQ && "EQ not implemented");
FlatAffineConstraints tmpCst(*this);
if (type == BoundType::LB)
- return tmpCst.computeConstantLowerOrUpperBound</*isLower=*/true>(pos);
- return tmpCst.computeConstantLowerOrUpperBound</*isLower=*/false>(pos);
+ return FlatAffineConstraints(*this)
+ .computeConstantLowerOrUpperBound</*isLower=*/true>(pos);
+ if (type == BoundType::UB)
+ return FlatAffineConstraints(*this)
+ .computeConstantLowerOrUpperBound</*isLower=*/false>(pos);
+
+ assert(type == BoundType::EQ && "expected EQ");
+ Optional<int64_t> lb =
+ FlatAffineConstraints(*this)
+ .computeConstantLowerOrUpperBound</*isLower=*/true>(pos);
+ Optional<int64_t> ub =
+ FlatAffineConstraints(*this)
+ .computeConstantLowerOrUpperBound</*isLower=*/false>(pos);
+ return (lb && ub && *lb == *ub) ? Optional<int64_t>(*ub) : None;
}
// A simple (naive and conservative) check for hyper-rectangularity.
diff --git a/mlir/lib/Dialect/SCF/Transforms/LoopSpecialization.cpp b/mlir/lib/Dialect/SCF/Transforms/LoopSpecialization.cpp
index c54f634dcac04..a71d9fe045f43 100644
--- a/mlir/lib/Dialect/SCF/Transforms/LoopSpecialization.cpp
+++ b/mlir/lib/Dialect/SCF/Transforms/LoopSpecialization.cpp
@@ -305,6 +305,16 @@ canonicalizeMinMaxOp(RewriterBase &rewriter, Operation *op, AffineMap map,
AffineMap newMap = alignedBoundMap;
SmallVector<Value> newOperands;
unpackOptionalValues(constraints.getMaybeDimAndSymbolValues(), newOperands);
+ // If dims/symbols have known constant values, use those in order to simplify
+ // the affine map further.
+ for (int64_t i = 0; i < constraints.getNumDimAndSymbolIds(); ++i) {
+ // Skip unused operands and operands that are already constants.
+ if (!newOperands[i] || getConstantIntValue(newOperands[i]))
+ continue;
+ if (auto bound = constraints.getConstantBound(FlatAffineConstraints::EQ, i))
+ newOperands[i] =
+ rewriter.create<arith::ConstantIndexOp>(op->getLoc(), *bound);
+ }
mlir::canonicalizeMapAndOperands(&newMap, &newOperands);
rewriter.setInsertionPoint(op);
rewriter.replaceOpWithNewOp<AffineApplyOp>(op, newMap, newOperands);
@@ -457,19 +467,30 @@ mlir::scf::canonicalizeMinMaxOpInLoop(RewriterBase &rewriter, Operation *op,
if (ubInt)
constraints.addBound(FlatAffineConstraints::EQ, dimUb, *ubInt);
- // iv >= lb (equiv.: iv - lb >= 0)
+ // Lower bound: iv >= lb (equiv.: iv - lb >= 0)
SmallVector<int64_t> ineqLb(constraints.getNumCols(), 0);
ineqLb[dimIv] = 1;
ineqLb[dimLb] = -1;
constraints.addInequality(ineqLb);
- // iv < lb + step * ((ub - lb - 1) floorDiv step) + 1
- AffineExpr exprLb = lbInt ? rewriter.getAffineConstantExpr(*lbInt)
- : rewriter.getAffineDimExpr(dimLb);
- AffineExpr exprUb = ubInt ? rewriter.getAffineConstantExpr(*ubInt)
- : rewriter.getAffineDimExpr(dimUb);
- AffineExpr ivUb =
- exprLb + 1 + (*stepInt * ((exprUb - exprLb - 1).floorDiv(*stepInt)));
+ // Upper bound
+ AffineExpr ivUb;
+ if (lbInt && ubInt && (*lbInt + *stepInt >= *ubInt)) {
+ // The loop has at most one iteration.
+ // iv < lb + 1
+ // TODO: Try to derive this constraint by simplifying the expression in
+ // the else-branch.
+ ivUb = rewriter.getAffineDimExpr(dimLb) + 1;
+ } else {
+ // The loop may have more than one iteration.
+ // iv < lb + step * ((ub - lb - 1) floorDiv step) + 1
+ AffineExpr exprLb = lbInt ? rewriter.getAffineConstantExpr(*lbInt)
+ : rewriter.getAffineDimExpr(dimLb);
+ AffineExpr exprUb = ubInt ? rewriter.getAffineConstantExpr(*ubInt)
+ : rewriter.getAffineDimExpr(dimUb);
+ ivUb =
+ exprLb + 1 + (*stepInt * ((exprUb - exprLb - 1).floorDiv(*stepInt)));
+ }
auto map = AffineMap::get(
/*dimCount=*/constraints.getNumDimIds(),
/*symbolCount=*/constraints.getNumSymbolIds(), /*result=*/ivUb);
diff --git a/mlir/test/Dialect/SCF/for-loop-canonicalization.mlir b/mlir/test/Dialect/SCF/for-loop-canonicalization.mlir
index a07e5688ead36..add420b3b508f 100644
--- a/mlir/test/Dialect/SCF/for-loop-canonicalization.mlir
+++ b/mlir/test/Dialect/SCF/for-loop-canonicalization.mlir
@@ -348,3 +348,22 @@ func @tensor_dim_of_loop_result_no_canonicalize(%t : tensor<?x?xf32>,
%dim = tensor.dim %1, %c0 : tensor<?x?xf32>
return %dim : index
}
+
+// -----
+
+// CHECK-LABEL: func @one_trip_scf_for_canonicalize_min
+// CHECK: %[[C4:.*]] = arith.constant 4 : i64
+// CHECK: scf.for
+// CHECK: memref.store %[[C4]], %{{.*}}[] : memref<i64>
+func @one_trip_scf_for_canonicalize_min(%A : memref<i64>) {
+ %c0 = arith.constant 0 : index
+ %c2 = arith.constant 2 : index
+ %c4 = arith.constant 4 : index
+
+ scf.for %i = %c0 to %c4 step %c4 {
+ %1 = affine.min affine_map<(d0, d1)[] -> (4, d1 - d0)> (%i, %c4)
+ %2 = arith.index_cast %1: index to i64
+ memref.store %2, %A[]: memref<i64>
+ }
+ return
+}
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