[Mlir-commits] [mlir] 7709b23 - [mlir][scf] NFC: create dedicated files for affine utils
Lei Zhang
llvmlistbot at llvm.org
Tue Dec 7 08:01:16 PST 2021
Author: Lei Zhang
Date: 2021-12-07T10:55:32-05:00
New Revision: 7709b23bef490fd4c5f095853f9a486fb0f984ff
URL: https://github.com/llvm/llvm-project/commit/7709b23bef490fd4c5f095853f9a486fb0f984ff
DIFF: https://github.com/llvm/llvm-project/commit/7709b23bef490fd4c5f095853f9a486fb0f984ff.diff
LOG: [mlir][scf] NFC: create dedicated files for affine utils
These functions are generic utility functions that operates on
affine ops within SCF regions. Moving them to their own files
for a better code structure, instead of mixing with loop
specialization logic.
Reviewed By: nicolasvasilache
Differential Revision: https://reviews.llvm.org/D115245
Added:
mlir/include/mlir/Dialect/SCF/AffineCanonicalizationUtils.h
mlir/lib/Dialect/SCF/Transforms/AffineCanonicalizationUtils.cpp
Modified:
mlir/include/mlir/Dialect/SCF/Transforms.h
mlir/lib/Dialect/Linalg/Transforms/Loops.cpp
mlir/lib/Dialect/SCF/Transforms/CMakeLists.txt
mlir/lib/Dialect/SCF/Transforms/LoopCanonicalization.cpp
mlir/lib/Dialect/SCF/Transforms/LoopSpecialization.cpp
Removed:
################################################################################
diff --git a/mlir/include/mlir/Dialect/SCF/AffineCanonicalizationUtils.h b/mlir/include/mlir/Dialect/SCF/AffineCanonicalizationUtils.h
new file mode 100644
index 0000000000000..6288d19520fbc
--- /dev/null
+++ b/mlir/include/mlir/Dialect/SCF/AffineCanonicalizationUtils.h
@@ -0,0 +1,74 @@
+//===- AffineCanonicalizationUtils.h ----------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This header file defines utility functions to canonicalize affine ops
+// within SCF op regions.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef MLIR_DIALECT_SCF_AFFINECANONICALIZATIONUTILS_H_
+#define MLIR_DIALECT_SCF_AFFINECANONICALIZATIONUTILS_H_
+
+#include "mlir/Support/LLVM.h"
+
+namespace mlir {
+class AffineMap;
+struct LogicalResult;
+class Operation;
+class RewriterBase;
+class Value;
+class ValueRange;
+
+namespace scf {
+class IfOp;
+
+/// Match "for loop"-like operations: If the first parameter is an iteration
+/// variable, return lower/upper bounds via the second/third parameter and the
+/// step size via the last parameter. The function should return `success` in
+/// that case. If the first parameter is not an iteration variable, return
+/// `failure`.
+using LoopMatcherFn =
+ function_ref<LogicalResult(Value, Value &, Value &, Value &)>;
+
+/// Try to canonicalize an min/max operations in the context of for `loops` with
+/// a known range.
+///
+/// `map` is the body of the min/max operation and `operands` are the SSA values
+/// that the dimensions and symbols are bound to; dimensions are listed first.
+/// If `isMin`, the operation is a min operation; otherwise, a max operation.
+/// `loopMatcher` is used to retrieve loop bounds and the step size for a given
+/// iteration variable.
+///
+/// Note: `loopMatcher` allows this function to be used with any "for loop"-like
+/// operation (scf.for, scf.parallel and even ops defined in other dialects).
+LogicalResult canonicalizeMinMaxOpInLoop(RewriterBase &rewriter, Operation *op,
+ AffineMap map, ValueRange operands,
+ bool isMin, LoopMatcherFn loopMatcher);
+
+/// Try to simplify a min/max operation `op` after loop peeling. This function
+/// can simplify min/max operations such as (ub is the previous upper bound of
+/// the unpeeled loop):
+/// ```
+/// #map = affine_map<(d0)[s0, s1] -> (s0, -d0 + s1)>
+/// %r = affine.min #affine.min #map(%iv)[%step, %ub]
+/// ```
+/// and rewrites them into (in the case the peeled loop):
+/// ```
+/// %r = %step
+/// ```
+/// min/max operations inside the partial iteration are rewritten in a similar
+/// way.
+LogicalResult rewritePeeledMinMaxOp(RewriterBase &rewriter, Operation *op,
+ AffineMap map, ValueRange operands,
+ bool isMin, Value iv, Value ub, Value step,
+ bool insideLoop);
+
+} // namespace scf
+} // namespace mlir
+
+#endif // MLIR_DIALECT_SCF_AFFINECANONICALIZATIONUTILS_H_
diff --git a/mlir/include/mlir/Dialect/SCF/Transforms.h b/mlir/include/mlir/Dialect/SCF/Transforms.h
index b8aebcb9a1900..9efbf83a2a112 100644
--- a/mlir/include/mlir/Dialect/SCF/Transforms.h
+++ b/mlir/include/mlir/Dialect/SCF/Transforms.h
@@ -13,6 +13,7 @@
#ifndef MLIR_DIALECT_SCF_TRANSFORMS_H_
#define MLIR_DIALECT_SCF_TRANSFORMS_H_
+#include "mlir/Dialect/SCF/AffineCanonicalizationUtils.h"
#include "mlir/Support/LLVM.h"
#include "llvm/ADT/ArrayRef.h"
@@ -38,29 +39,6 @@ class ForOp;
class ParallelOp;
class ForOp;
-/// Match "for loop"-like operations: If the first parameter is an iteration
-/// variable, return lower/upper bounds via the second/third parameter and the
-/// step size via the last parameter. The function should return `success` in
-/// that case. If the first parameter is not an iteration variable, return
-/// `failure`.
-using LoopMatcherFn =
- function_ref<LogicalResult(Value, Value &, Value &, Value &)>;
-
-/// Try to canonicalize an min/max operations in the context of for `loops` with
-/// a known range.
-///
-/// `map` is the body of the min/max operation and `operands` are the SSA values
-/// that the dimensions and symbols are bound to; dimensions are listed first.
-/// If `isMin`, the operation is a min operation; otherwise, a max operation.
-/// `loopMatcher` is used to retrieve loop bounds and the step size for a given
-/// iteration variable.
-///
-/// Note: `loopMatcher` allows this function to be used with any "for loop"-like
-/// operation (scf.for, scf.parallel and even ops defined in other dialects).
-LogicalResult canonicalizeMinMaxOpInLoop(RewriterBase &rewriter, Operation *op,
- AffineMap map, ValueRange operands,
- bool isMin, LoopMatcherFn loopMatcher);
-
/// Fuses all adjacent scf.parallel operations with identical bounds and step
/// into one scf.parallel operations. Uses a naive aliasing and dependency
/// analysis.
@@ -111,24 +89,6 @@ void naivelyFuseParallelOps(Region ®ion);
LogicalResult peelAndCanonicalizeForLoop(RewriterBase &rewriter, ForOp forOp,
scf::ForOp &partialIteration);
-/// Try to simplify a min/max operation `op` after loop peeling. This function
-/// can simplify min/max operations such as (ub is the previous upper bound of
-/// the unpeeled loop):
-/// ```
-/// #map = affine_map<(d0)[s0, s1] -> (s0, -d0 + s1)>
-/// %r = affine.min #affine.min #map(%iv)[%step, %ub]
-/// ```
-/// and rewrites them into (in the case the peeled loop):
-/// ```
-/// %r = %step
-/// ```
-/// min/max operations inside the partial iteration are rewritten in a similar
-/// way.
-LogicalResult rewritePeeledMinMaxOp(RewriterBase &rewriter, Operation *op,
- AffineMap map, ValueRange operands,
- bool isMin, Value iv, Value ub, Value step,
- bool insideLoop);
-
/// Tile a parallel loop of the form
/// scf.parallel (%i0, %i1) = (%arg0, %arg1) to (%arg2, %arg3)
/// step (%arg4, %arg5)
diff --git a/mlir/lib/Dialect/Linalg/Transforms/Loops.cpp b/mlir/lib/Dialect/Linalg/Transforms/Loops.cpp
index 7a706141e4407..5958bf8be27f6 100644
--- a/mlir/lib/Dialect/Linalg/Transforms/Loops.cpp
+++ b/mlir/lib/Dialect/Linalg/Transforms/Loops.cpp
@@ -13,6 +13,7 @@
#include "mlir/Dialect/Linalg/Passes.h"
#include "mlir/Dialect/Linalg/Transforms/Transforms.h"
#include "mlir/Dialect/Linalg/Utils/Utils.h"
+#include "mlir/Dialect/SCF/AffineCanonicalizationUtils.h"
#include "mlir/Dialect/SCF/Transforms.h"
#include "mlir/Dialect/StandardOps/Utils/Utils.h"
#include "mlir/IR/AffineExpr.h"
diff --git a/mlir/lib/Dialect/SCF/Transforms/AffineCanonicalizationUtils.cpp b/mlir/lib/Dialect/SCF/Transforms/AffineCanonicalizationUtils.cpp
new file mode 100644
index 0000000000000..59dc76635f130
--- /dev/null
+++ b/mlir/lib/Dialect/SCF/Transforms/AffineCanonicalizationUtils.cpp
@@ -0,0 +1,325 @@
+//===- AffineCanonicalizationUtils.cpp - Affine Canonicalization in SCF ---===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Utility functions to canonicalize affine ops within SCF op regions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Dialect/SCF/AffineCanonicalizationUtils.h"
+#include "mlir/Analysis/AffineStructures.h"
+#include "mlir/Dialect/Affine/IR/AffineOps.h"
+#include "mlir/Dialect/SCF/SCF.h"
+#include "mlir/Dialect/Utils/StaticValueUtils.h"
+#include "mlir/IR/AffineMap.h"
+#include "mlir/IR/Matchers.h"
+#include "mlir/IR/PatternMatch.h"
+#include "llvm/Support/Debug.h"
+
+#define DEBUG_TYPE "mlir-scf-affine-utils"
+
+using namespace mlir;
+
+static void unpackOptionalValues(ArrayRef<Optional<Value>> source,
+ SmallVector<Value> &target) {
+ target = llvm::to_vector<4>(llvm::map_range(source, [](Optional<Value> val) {
+ return val.hasValue() ? *val : Value();
+ }));
+}
+
+/// Bound an identifier `pos` in a given FlatAffineValueConstraints with
+/// constraints drawn from an affine map. Before adding the constraint, the
+/// dimensions/symbols of the affine map are aligned with `constraints`.
+/// `operands` are the SSA Value operands used with the affine map.
+/// Note: This function adds a new symbol column to the `constraints` for each
+/// dimension/symbol that exists in the affine map but not in `constraints`.
+static LogicalResult alignAndAddBound(FlatAffineValueConstraints &constraints,
+ FlatAffineConstraints::BoundType type,
+ unsigned pos, AffineMap map,
+ ValueRange operands) {
+ SmallVector<Value> dims, syms, newSyms;
+ unpackOptionalValues(constraints.getMaybeDimValues(), dims);
+ unpackOptionalValues(constraints.getMaybeSymbolValues(), syms);
+
+ AffineMap alignedMap =
+ alignAffineMapWithValues(map, operands, dims, syms, &newSyms);
+ for (unsigned i = syms.size(); i < newSyms.size(); ++i)
+ constraints.appendSymbolId(newSyms[i]);
+ return constraints.addBound(type, pos, alignedMap);
+}
+
+/// Add `val` to each result of `map`.
+static AffineMap addConstToResults(AffineMap map, int64_t val) {
+ SmallVector<AffineExpr> newResults;
+ for (AffineExpr r : map.getResults())
+ newResults.push_back(r + val);
+ return AffineMap::get(map.getNumDims(), map.getNumSymbols(), newResults,
+ map.getContext());
+}
+
+/// This function tries to canonicalize min/max operations by proving that their
+/// value is bounded by the same lower and upper bound. In that case, the
+/// operation can be folded away.
+///
+/// Bounds are computed by FlatAffineValueConstraints. Invariants required for
+/// finding/proving bounds should be supplied via `constraints`.
+///
+/// 1. Add dimensions for `op` and `opBound` (lower or upper bound of `op`).
+/// 2. Compute an upper bound of `op` (in case of `isMin`) or a lower bound (in
+/// case of `!isMin`) and bind it to `opBound`. SSA values that are used in
+/// `op` but are not part of `constraints`, are added as extra symbols.
+/// 3. For each result of `op`: Add result as a dimension `r_i`. Prove that:
+/// * If `isMin`: r_i >= opBound
+/// * If `isMax`: r_i <= opBound
+/// If this is the case, ub(op) == lb(op).
+/// 4. Replace `op` with `opBound`.
+///
+/// In summary, the following constraints are added throughout this function.
+/// Note: `invar` are dimensions added by the caller to express the invariants.
+/// (Showing only the case where `isMin`.)
+///
+/// invar | op | opBound | r_i | extra syms... | const | eq/ineq
+/// ------+-------+---------+-----+---------------+-------+-------------------
+/// (various eq./ineq. constraining `invar`, added by the caller)
+/// ... | 0 | 0 | 0 | 0 | ... | ...
+/// ------+-------+---------+-----+---------------+-------+-------------------
+/// (various ineq. constraining `op` in terms of `op` operands (`invar` and
+/// extra `op` operands "extra syms" that are not in `invar`)).
+/// ... | -1 | 0 | 0 | ... | ... | >= 0
+/// ------+-------+---------+-----+---------------+-------+-------------------
+/// (set `opBound` to `op` upper bound in terms of `invar` and "extra syms")
+/// ... | 0 | -1 | 0 | ... | ... | = 0
+/// ------+-------+---------+-----+---------------+-------+-------------------
+/// (for each `op` map result r_i: set r_i to corresponding map result,
+/// prove that r_i >= minOpUb via contradiction)
+/// ... | 0 | 0 | -1 | ... | ... | = 0
+/// 0 | 0 | 1 | -1 | 0 | -1 | >= 0
+///
+static LogicalResult
+canonicalizeMinMaxOp(RewriterBase &rewriter, Operation *op, AffineMap map,
+ ValueRange operands, bool isMin,
+ FlatAffineValueConstraints constraints) {
+ RewriterBase::InsertionGuard guard(rewriter);
+ unsigned numResults = map.getNumResults();
+
+ // Add a few extra dimensions.
+ unsigned dimOp = constraints.appendDimId(); // `op`
+ unsigned dimOpBound = constraints.appendDimId(); // `op` lower/upper bound
+ unsigned resultDimStart = constraints.appendDimId(/*num=*/numResults);
+
+ // Add an inequality for each result expr_i of map:
+ // isMin: op <= expr_i, !isMin: op >= expr_i
+ auto boundType =
+ isMin ? FlatAffineConstraints::UB : FlatAffineConstraints::LB;
+ // Upper bounds are exclusive, so add 1. (`affine.min` ops are inclusive.)
+ AffineMap mapLbUb = isMin ? addConstToResults(map, 1) : map;
+ if (failed(
+ alignAndAddBound(constraints, boundType, dimOp, mapLbUb, operands)))
+ return failure();
+
+ // Try to compute a lower/upper bound for op, expressed in terms of the other
+ // `dims` and extra symbols.
+ SmallVector<AffineMap> opLb(1), opUb(1);
+ constraints.getSliceBounds(dimOp, 1, rewriter.getContext(), &opLb, &opUb);
+ AffineMap sliceBound = isMin ? opUb[0] : opLb[0];
+ // TODO: `getSliceBounds` may return multiple bounds at the moment. This is
+ // a TODO of `getSliceBounds` and not handled here.
+ if (!sliceBound || sliceBound.getNumResults() != 1)
+ return failure(); // No or multiple bounds found.
+ // Recover the inclusive UB in the case of an `affine.min`.
+ AffineMap boundMap = isMin ? addConstToResults(sliceBound, -1) : sliceBound;
+
+ // Add an equality: Set dimOpBound to computed bound.
+ // Add back dimension for op. (Was removed by `getSliceBounds`.)
+ AffineMap alignedBoundMap = boundMap.shiftDims(/*shift=*/1, /*offset=*/dimOp);
+ if (failed(constraints.addBound(FlatAffineConstraints::EQ, dimOpBound,
+ alignedBoundMap)))
+ return failure();
+
+ // If the constraint system is empty, there is an inconsistency. (E.g., this
+ // can happen if loop lb > ub.)
+ if (constraints.isEmpty())
+ return failure();
+
+ // In the case of `isMin` (`!isMin` is inversed):
+ // Prove that each result of `map` has a lower bound that is equal to (or
+ // greater than) the upper bound of `op` (`dimOpBound`). In that case, `op`
+ // can be replaced with the bound. I.e., prove that for each result
+ // expr_i (represented by dimension r_i):
+ //
+ // r_i >= opBound
+ //
+ // To prove this inequality, add its negation to the constraint set and prove
+ // that the constraint set is empty.
+ for (unsigned i = resultDimStart; i < resultDimStart + numResults; ++i) {
+ FlatAffineValueConstraints newConstr(constraints);
+
+ // Add an equality: r_i = expr_i
+ // Note: These equalities could have been added earlier and used to express
+ // minOp <= expr_i. However, then we run the risk that `getSliceBounds`
+ // computes minOpUb in terms of r_i dims, which is not desired.
+ if (failed(alignAndAddBound(newConstr, FlatAffineConstraints::EQ, i,
+ map.getSubMap({i - resultDimStart}), operands)))
+ return failure();
+
+ // If `isMin`: Add inequality: r_i < opBound
+ // equiv.: opBound - r_i - 1 >= 0
+ // If `!isMin`: Add inequality: r_i > opBound
+ // equiv.: -opBound + r_i - 1 >= 0
+ SmallVector<int64_t> ineq(newConstr.getNumCols(), 0);
+ ineq[dimOpBound] = isMin ? 1 : -1;
+ ineq[i] = isMin ? -1 : 1;
+ ineq[newConstr.getNumCols() - 1] = -1;
+ newConstr.addInequality(ineq);
+ if (!newConstr.isEmpty())
+ return failure();
+ }
+
+ // Lower and upper bound of `op` are equal. Replace `minOp` with its bound.
+ AffineMap newMap = alignedBoundMap;
+ SmallVector<Value> newOperands;
+ unpackOptionalValues(constraints.getMaybeDimAndSymbolValues(), newOperands);
+ mlir::canonicalizeMapAndOperands(&newMap, &newOperands);
+ rewriter.setInsertionPoint(op);
+ rewriter.replaceOpWithNewOp<AffineApplyOp>(op, newMap, newOperands);
+ return success();
+}
+
+static LogicalResult
+addLoopRangeConstraints(FlatAffineValueConstraints &constraints, Value iv,
+ Value lb, Value ub, Value step,
+ RewriterBase &rewriter) {
+ // FlatAffineConstraints does not support semi-affine expressions.
+ // Therefore, only constant step values are supported.
+ auto stepInt = getConstantIntValue(step);
+ if (!stepInt)
+ return failure();
+
+ unsigned dimIv = constraints.appendDimId(iv);
+ unsigned dimLb = constraints.appendDimId(lb);
+ unsigned dimUb = constraints.appendDimId(ub);
+
+ // If loop lower/upper bounds are constant: Add EQ constraint.
+ Optional<int64_t> lbInt = getConstantIntValue(lb);
+ Optional<int64_t> ubInt = getConstantIntValue(ub);
+ if (lbInt)
+ constraints.addBound(FlatAffineConstraints::EQ, dimLb, *lbInt);
+ if (ubInt)
+ constraints.addBound(FlatAffineConstraints::EQ, dimUb, *ubInt);
+
+ // 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)));
+ auto map = AffineMap::get(
+ /*dimCount=*/constraints.getNumDimIds(),
+ /*symbolCount=*/constraints.getNumSymbolIds(), /*result=*/ivUb);
+
+ return constraints.addBound(FlatAffineConstraints::UB, dimIv, map);
+}
+
+/// Canonicalize min/max operations in the context of for loops with a known
+/// range. Call `canonicalizeMinMaxOp` and add the following constraints to
+/// the constraint system (along with the missing dimensions):
+///
+/// * iv >= lb
+/// * iv < lb + step * ((ub - lb - 1) floorDiv step) + 1
+///
+/// Note: Due to limitations of FlatAffineConstraints, only constant step sizes
+/// are currently supported.
+LogicalResult scf::canonicalizeMinMaxOpInLoop(RewriterBase &rewriter,
+ Operation *op, AffineMap map,
+ ValueRange operands, bool isMin,
+ LoopMatcherFn loopMatcher) {
+ FlatAffineValueConstraints constraints;
+ DenseSet<Value> allIvs;
+
+ // Find all iteration variables among `minOp`'s operands add constrain them.
+ for (Value operand : operands) {
+ // Skip duplicate ivs.
+ if (llvm::find(allIvs, operand) != allIvs.end())
+ continue;
+
+ // If `operand` is an iteration variable: Find corresponding loop
+ // bounds and step.
+ Value iv = operand;
+ Value lb, ub, step;
+ if (failed(loopMatcher(operand, lb, ub, step)))
+ continue;
+ allIvs.insert(iv);
+
+ if (failed(
+ addLoopRangeConstraints(constraints, iv, lb, ub, step, rewriter)))
+ return failure();
+ }
+
+ return canonicalizeMinMaxOp(rewriter, op, map, operands, isMin, constraints);
+}
+
+/// Try to simplify a min/max operation `op` after loop peeling. This function
+/// can simplify min/max operations such as (ub is the previous upper bound of
+/// the unpeeled loop):
+/// ```
+/// #map = affine_map<(d0)[s0, s1] -> (s0, -d0 + s1)>
+/// %r = affine.min #affine.min #map(%iv)[%step, %ub]
+/// ```
+/// and rewrites them into (in the case the peeled loop):
+/// ```
+/// %r = %step
+/// ```
+/// min/max operations inside the partial iteration are rewritten in a similar
+/// way.
+///
+/// This function builds up a set of constraints, capable of proving that:
+/// * Inside the peeled loop: min(step, ub - iv) == step
+/// * Inside the partial iteration: min(step, ub - iv) == ub - iv
+///
+/// Returns `success` if the given operation was replaced by a new operation;
+/// `failure` otherwise.
+///
+/// Note: `ub` is the previous upper bound of the loop (before peeling).
+/// `insideLoop` must be true for min/max ops inside the loop and false for
+/// affine.min ops inside the partial iteration. For an explanation of the other
+/// parameters, see comment of `canonicalizeMinMaxOpInLoop`.
+LogicalResult scf::rewritePeeledMinMaxOp(RewriterBase &rewriter, Operation *op,
+ AffineMap map, ValueRange operands,
+ bool isMin, Value iv, Value ub,
+ Value step, bool insideLoop) {
+ FlatAffineValueConstraints constraints;
+ constraints.appendDimId({iv, ub, step});
+ if (auto constUb = getConstantIntValue(ub))
+ constraints.addBound(FlatAffineConstraints::EQ, 1, *constUb);
+ if (auto constStep = getConstantIntValue(step))
+ constraints.addBound(FlatAffineConstraints::EQ, 2, *constStep);
+
+ // Add loop peeling invariant. This is the main piece of knowledge that
+ // enables AffineMinOp simplification.
+ if (insideLoop) {
+ // ub - iv >= step (equiv.: -iv + ub - step + 0 >= 0)
+ // Intuitively: Inside the peeled loop, every iteration is a "full"
+ // iteration, i.e., step divides the iteration space `ub - lb` evenly.
+ constraints.addInequality({-1, 1, -1, 0});
+ } else {
+ // ub - iv < step (equiv.: iv + -ub + step - 1 >= 0)
+ // Intuitively: `iv` is the split bound here, i.e., the iteration variable
+ // value of the very last iteration (in the unpeeled loop). At that point,
+ // there are less than `step` elements remaining. (Otherwise, the peeled
+ // loop would run for at least one more iteration.)
+ constraints.addInequality({1, -1, 1, -1});
+ }
+
+ return canonicalizeMinMaxOp(rewriter, op, map, operands, isMin, constraints);
+}
diff --git a/mlir/lib/Dialect/SCF/Transforms/CMakeLists.txt b/mlir/lib/Dialect/SCF/Transforms/CMakeLists.txt
index 8f26aa9c15362..f517079990015 100644
--- a/mlir/lib/Dialect/SCF/Transforms/CMakeLists.txt
+++ b/mlir/lib/Dialect/SCF/Transforms/CMakeLists.txt
@@ -1,4 +1,5 @@
add_mlir_dialect_library(MLIRSCFTransforms
+ AffineCanonicalizationUtils.cpp
Bufferize.cpp
ForToWhile.cpp
LoopCanonicalization.cpp
diff --git a/mlir/lib/Dialect/SCF/Transforms/LoopCanonicalization.cpp b/mlir/lib/Dialect/SCF/Transforms/LoopCanonicalization.cpp
index a65ffc2d1b2c9..7c903b9c0843d 100644
--- a/mlir/lib/Dialect/SCF/Transforms/LoopCanonicalization.cpp
+++ b/mlir/lib/Dialect/SCF/Transforms/LoopCanonicalization.cpp
@@ -14,6 +14,7 @@
#include "PassDetail.h"
#include "mlir/Dialect/Affine/IR/AffineOps.h"
#include "mlir/Dialect/MemRef/IR/MemRef.h"
+#include "mlir/Dialect/SCF/AffineCanonicalizationUtils.h"
#include "mlir/Dialect/SCF/Passes.h"
#include "mlir/Dialect/SCF/SCF.h"
#include "mlir/Dialect/SCF/Transforms.h"
diff --git a/mlir/lib/Dialect/SCF/Transforms/LoopSpecialization.cpp b/mlir/lib/Dialect/SCF/Transforms/LoopSpecialization.cpp
index c54f634dcac04..6461ea9d5e6ce 100644
--- a/mlir/lib/Dialect/SCF/Transforms/LoopSpecialization.cpp
+++ b/mlir/lib/Dialect/SCF/Transforms/LoopSpecialization.cpp
@@ -15,6 +15,7 @@
#include "mlir/Analysis/AffineStructures.h"
#include "mlir/Dialect/Affine/IR/AffineOps.h"
#include "mlir/Dialect/Arithmetic/IR/Arithmetic.h"
+#include "mlir/Dialect/SCF/AffineCanonicalizationUtils.h"
#include "mlir/Dialect/SCF/Passes.h"
#include "mlir/Dialect/SCF/SCF.h"
#include "mlir/Dialect/SCF/Transforms.h"
@@ -146,227 +147,6 @@ static LogicalResult peelForLoop(RewriterBase &b, ForOp forOp,
return success();
}
-static void unpackOptionalValues(ArrayRef<Optional<Value>> source,
- SmallVector<Value> &target) {
- target = llvm::to_vector<4>(llvm::map_range(source, [](Optional<Value> val) {
- return val.hasValue() ? *val : Value();
- }));
-}
-
-/// Bound an identifier `pos` in a given FlatAffineValueConstraints with
-/// constraints drawn from an affine map. Before adding the constraint, the
-/// dimensions/symbols of the affine map are aligned with `constraints`.
-/// `operands` are the SSA Value operands used with the affine map.
-/// Note: This function adds a new symbol column to the `constraints` for each
-/// dimension/symbol that exists in the affine map but not in `constraints`.
-static LogicalResult alignAndAddBound(FlatAffineValueConstraints &constraints,
- FlatAffineConstraints::BoundType type,
- unsigned pos, AffineMap map,
- ValueRange operands) {
- SmallVector<Value> dims, syms, newSyms;
- unpackOptionalValues(constraints.getMaybeDimValues(), dims);
- unpackOptionalValues(constraints.getMaybeSymbolValues(), syms);
-
- AffineMap alignedMap =
- alignAffineMapWithValues(map, operands, dims, syms, &newSyms);
- for (unsigned i = syms.size(); i < newSyms.size(); ++i)
- constraints.appendSymbolId(newSyms[i]);
- return constraints.addBound(type, pos, alignedMap);
-}
-
-/// Add `val` to each result of `map`.
-static AffineMap addConstToResults(AffineMap map, int64_t val) {
- SmallVector<AffineExpr> newResults;
- for (AffineExpr r : map.getResults())
- newResults.push_back(r + val);
- return AffineMap::get(map.getNumDims(), map.getNumSymbols(), newResults,
- map.getContext());
-}
-
-/// This function tries to canonicalize min/max operations by proving that their
-/// value is bounded by the same lower and upper bound. In that case, the
-/// operation can be folded away.
-///
-/// Bounds are computed by FlatAffineValueConstraints. Invariants required for
-/// finding/proving bounds should be supplied via `constraints`.
-///
-/// 1. Add dimensions for `op` and `opBound` (lower or upper bound of `op`).
-/// 2. Compute an upper bound of `op` (in case of `isMin`) or a lower bound (in
-/// case of `!isMin`) and bind it to `opBound`. SSA values that are used in
-/// `op` but are not part of `constraints`, are added as extra symbols.
-/// 3. For each result of `op`: Add result as a dimension `r_i`. Prove that:
-/// * If `isMin`: r_i >= opBound
-/// * If `isMax`: r_i <= opBound
-/// If this is the case, ub(op) == lb(op).
-/// 4. Replace `op` with `opBound`.
-///
-/// In summary, the following constraints are added throughout this function.
-/// Note: `invar` are dimensions added by the caller to express the invariants.
-/// (Showing only the case where `isMin`.)
-///
-/// invar | op | opBound | r_i | extra syms... | const | eq/ineq
-/// ------+-------+---------+-----+---------------+-------+-------------------
-/// (various eq./ineq. constraining `invar`, added by the caller)
-/// ... | 0 | 0 | 0 | 0 | ... | ...
-/// ------+-------+---------+-----+---------------+-------+-------------------
-/// (various ineq. constraining `op` in terms of `op` operands (`invar` and
-/// extra `op` operands "extra syms" that are not in `invar`)).
-/// ... | -1 | 0 | 0 | ... | ... | >= 0
-/// ------+-------+---------+-----+---------------+-------+-------------------
-/// (set `opBound` to `op` upper bound in terms of `invar` and "extra syms")
-/// ... | 0 | -1 | 0 | ... | ... | = 0
-/// ------+-------+---------+-----+---------------+-------+-------------------
-/// (for each `op` map result r_i: set r_i to corresponding map result,
-/// prove that r_i >= minOpUb via contradiction)
-/// ... | 0 | 0 | -1 | ... | ... | = 0
-/// 0 | 0 | 1 | -1 | 0 | -1 | >= 0
-///
-static LogicalResult
-canonicalizeMinMaxOp(RewriterBase &rewriter, Operation *op, AffineMap map,
- ValueRange operands, bool isMin,
- FlatAffineValueConstraints constraints) {
- RewriterBase::InsertionGuard guard(rewriter);
- unsigned numResults = map.getNumResults();
-
- // Add a few extra dimensions.
- unsigned dimOp = constraints.appendDimId(); // `op`
- unsigned dimOpBound = constraints.appendDimId(); // `op` lower/upper bound
- unsigned resultDimStart = constraints.appendDimId(/*num=*/numResults);
-
- // Add an inequality for each result expr_i of map:
- // isMin: op <= expr_i, !isMin: op >= expr_i
- auto boundType =
- isMin ? FlatAffineConstraints::UB : FlatAffineConstraints::LB;
- // Upper bounds are exclusive, so add 1. (`affine.min` ops are inclusive.)
- AffineMap mapLbUb = isMin ? addConstToResults(map, 1) : map;
- if (failed(
- alignAndAddBound(constraints, boundType, dimOp, mapLbUb, operands)))
- return failure();
-
- // Try to compute a lower/upper bound for op, expressed in terms of the other
- // `dims` and extra symbols.
- SmallVector<AffineMap> opLb(1), opUb(1);
- constraints.getSliceBounds(dimOp, 1, rewriter.getContext(), &opLb, &opUb);
- AffineMap sliceBound = isMin ? opUb[0] : opLb[0];
- // TODO: `getSliceBounds` may return multiple bounds at the moment. This is
- // a TODO of `getSliceBounds` and not handled here.
- if (!sliceBound || sliceBound.getNumResults() != 1)
- return failure(); // No or multiple bounds found.
- // Recover the inclusive UB in the case of an `affine.min`.
- AffineMap boundMap = isMin ? addConstToResults(sliceBound, -1) : sliceBound;
-
- // Add an equality: Set dimOpBound to computed bound.
- // Add back dimension for op. (Was removed by `getSliceBounds`.)
- AffineMap alignedBoundMap = boundMap.shiftDims(/*shift=*/1, /*offset=*/dimOp);
- if (failed(constraints.addBound(FlatAffineConstraints::EQ, dimOpBound,
- alignedBoundMap)))
- return failure();
-
- // If the constraint system is empty, there is an inconsistency. (E.g., this
- // can happen if loop lb > ub.)
- if (constraints.isEmpty())
- return failure();
-
- // In the case of `isMin` (`!isMin` is inversed):
- // Prove that each result of `map` has a lower bound that is equal to (or
- // greater than) the upper bound of `op` (`dimOpBound`). In that case, `op`
- // can be replaced with the bound. I.e., prove that for each result
- // expr_i (represented by dimension r_i):
- //
- // r_i >= opBound
- //
- // To prove this inequality, add its negation to the constraint set and prove
- // that the constraint set is empty.
- for (unsigned i = resultDimStart; i < resultDimStart + numResults; ++i) {
- FlatAffineValueConstraints newConstr(constraints);
-
- // Add an equality: r_i = expr_i
- // Note: These equalities could have been added earlier and used to express
- // minOp <= expr_i. However, then we run the risk that `getSliceBounds`
- // computes minOpUb in terms of r_i dims, which is not desired.
- if (failed(alignAndAddBound(newConstr, FlatAffineConstraints::EQ, i,
- map.getSubMap({i - resultDimStart}), operands)))
- return failure();
-
- // If `isMin`: Add inequality: r_i < opBound
- // equiv.: opBound - r_i - 1 >= 0
- // If `!isMin`: Add inequality: r_i > opBound
- // equiv.: -opBound + r_i - 1 >= 0
- SmallVector<int64_t> ineq(newConstr.getNumCols(), 0);
- ineq[dimOpBound] = isMin ? 1 : -1;
- ineq[i] = isMin ? -1 : 1;
- ineq[newConstr.getNumCols() - 1] = -1;
- newConstr.addInequality(ineq);
- if (!newConstr.isEmpty())
- return failure();
- }
-
- // Lower and upper bound of `op` are equal. Replace `minOp` with its bound.
- AffineMap newMap = alignedBoundMap;
- SmallVector<Value> newOperands;
- unpackOptionalValues(constraints.getMaybeDimAndSymbolValues(), newOperands);
- mlir::canonicalizeMapAndOperands(&newMap, &newOperands);
- rewriter.setInsertionPoint(op);
- rewriter.replaceOpWithNewOp<AffineApplyOp>(op, newMap, newOperands);
- return success();
-}
-
-/// Try to simplify a min/max operation `op` after loop peeling. This function
-/// can simplify min/max operations such as (ub is the previous upper bound of
-/// the unpeeled loop):
-/// ```
-/// #map = affine_map<(d0)[s0, s1] -> (s0, -d0 + s1)>
-/// %r = affine.min #affine.min #map(%iv)[%step, %ub]
-/// ```
-/// and rewrites them into (in the case the peeled loop):
-/// ```
-/// %r = %step
-/// ```
-/// min/max operations inside the partial iteration are rewritten in a similar
-/// way.
-///
-/// This function builds up a set of constraints, capable of proving that:
-/// * Inside the peeled loop: min(step, ub - iv) == step
-/// * Inside the partial iteration: min(step, ub - iv) == ub - iv
-///
-/// Returns `success` if the given operation was replaced by a new operation;
-/// `failure` otherwise.
-///
-/// Note: `ub` is the previous upper bound of the loop (before peeling).
-/// `insideLoop` must be true for min/max ops inside the loop and false for
-/// affine.min ops inside the partial iteration. For an explanation of the other
-/// parameters, see comment of `canonicalizeMinMaxOpInLoop`.
-LogicalResult mlir::scf::rewritePeeledMinMaxOp(RewriterBase &rewriter,
- Operation *op, AffineMap map,
- ValueRange operands, bool isMin,
- Value iv, Value ub, Value step,
- bool insideLoop) {
- FlatAffineValueConstraints constraints;
- constraints.appendDimId({iv, ub, step});
- if (auto constUb = getConstantIntValue(ub))
- constraints.addBound(FlatAffineConstraints::EQ, 1, *constUb);
- if (auto constStep = getConstantIntValue(step))
- constraints.addBound(FlatAffineConstraints::EQ, 2, *constStep);
-
- // Add loop peeling invariant. This is the main piece of knowledge that
- // enables AffineMinOp simplification.
- if (insideLoop) {
- // ub - iv >= step (equiv.: -iv + ub - step + 0 >= 0)
- // Intuitively: Inside the peeled loop, every iteration is a "full"
- // iteration, i.e., step divides the iteration space `ub - lb` evenly.
- constraints.addInequality({-1, 1, -1, 0});
- } else {
- // ub - iv < step (equiv.: iv + -ub + step - 1 >= 0)
- // Intuitively: `iv` is the split bound here, i.e., the iteration variable
- // value of the very last iteration (in the unpeeled loop). At that point,
- // there are less than `step` elements remaining. (Otherwise, the peeled
- // loop would run for at least one more iteration.)
- constraints.addInequality({1, -1, 1, -1});
- }
-
- return canonicalizeMinMaxOp(rewriter, op, map, operands, isMin, constraints);
-}
-
template <typename OpTy, bool IsMin>
static void rewriteAffineOpAfterPeeling(RewriterBase &rewriter, ForOp forOp,
ForOp partialIteration,
@@ -409,78 +189,6 @@ LogicalResult mlir::scf::peelAndCanonicalizeForLoop(RewriterBase &rewriter,
return success();
}
-/// Canonicalize min/max operations in the context of for loops with a known
-/// range. Call `canonicalizeMinMaxOp` and add the following constraints to
-/// the constraint system (along with the missing dimensions):
-///
-/// * iv >= lb
-/// * iv < lb + step * ((ub - lb - 1) floorDiv step) + 1
-///
-/// Note: Due to limitations of FlatAffineConstraints, only constant step sizes
-/// are currently supported.
-LogicalResult
-mlir::scf::canonicalizeMinMaxOpInLoop(RewriterBase &rewriter, Operation *op,
- AffineMap map, ValueRange operands,
- bool isMin, LoopMatcherFn loopMatcher) {
- FlatAffineValueConstraints constraints;
- DenseSet<Value> allIvs;
-
- // Find all iteration variables among `minOp`'s operands add constrain them.
- for (Value operand : operands) {
- // Skip duplicate ivs.
- if (llvm::find(allIvs, operand) != allIvs.end())
- continue;
-
- // If `operand` is an iteration variable: Find corresponding loop
- // bounds and step.
- Value iv = operand;
- Value lb, ub, step;
- if (failed(loopMatcher(operand, lb, ub, step)))
- continue;
- allIvs.insert(iv);
-
- // FlatAffineConstraints does not support semi-affine expressions.
- // Therefore, only constant step values are supported.
- auto stepInt = getConstantIntValue(step);
- if (!stepInt)
- continue;
-
- unsigned dimIv = constraints.appendDimId(iv);
- unsigned dimLb = constraints.appendDimId(lb);
- unsigned dimUb = constraints.appendDimId(ub);
-
- // If loop lower/upper bounds are constant: Add EQ constraint.
- Optional<int64_t> lbInt = getConstantIntValue(lb);
- Optional<int64_t> ubInt = getConstantIntValue(ub);
- if (lbInt)
- constraints.addBound(FlatAffineConstraints::EQ, dimLb, *lbInt);
- if (ubInt)
- constraints.addBound(FlatAffineConstraints::EQ, dimUb, *ubInt);
-
- // 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)));
- auto map = AffineMap::get(
- /*dimCount=*/constraints.getNumDimIds(),
- /*symbolCount=*/constraints.getNumSymbolIds(), /*result=*/ivUb);
-
- if (failed(constraints.addBound(FlatAffineConstraints::UB, dimIv, map)))
- return failure();
- }
-
- return canonicalizeMinMaxOp(rewriter, op, map, operands, isMin, constraints);
-}
-
static constexpr char kPeeledLoopLabel[] = "__peeled_loop__";
static constexpr char kPartialIterationLabel[] = "__partial_iteration__";
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