[mlir][affine|ValueBounds] Add transform to simplify affine min max ops with ValueBoundsOpInterface

mlir/include/mlir/Dialect/Affine/TransformOps/AffineTransformOps.td

@@ -63,4 +63,35 @@ def SimplifyBoundedAffineOpsOp
   }];
 }
 
+def SimplifyMinMaxAffineOpsOp :
+  Op<Transform_Dialect, "affine.simplify_min_max_affine_ops", [
+    DeclareOpInterfaceMethods<TransformOpInterface>,
+    DeclareOpInterfaceMethods<MemoryEffectsOpInterface>
+  ]> {
+  let description = [{
+    Simplify the targeted `affine.min` / `affine.max` ops using the
+    `mlir::affine::simplifyAffineMinMaxOps` transform.
+
+    Example:
+    ```
+    %0 = transform.structured.match ops{["affine.max"]} in %arg1
+    transform.affine.simplify_min_max_affine_ops %0 : !transform.any_op
+    ```
+
+    #### Return modes
+
+    This transform consumes the target handle and does not produce any results.
+    This transforms definitely fails if any of the targeted operations is not an
+    `affine.min` or `affine.max` operation, or if the canonicalization patterns
+    failed to converge.
+    This transform silently fails if none of the operations were simplified.
+    Otherwise, it succeeds.
+  }];
+  let arguments = (ins TransformHandleTypeInterface:$target);
+  let results = (outs);
+  let assemblyFormat = [{
+      $target attr-dict `:` type($target)
+  }];
+}
+
 #endif // Affine_TRANSFORM_OPS

mlir/include/mlir/Dialect/Affine/Transforms/Transforms.h

@@ -34,6 +34,8 @@ namespace affine {
 class AffineApplyOp;
 class AffineDelinearizeIndexOp;
 class AffineLinearizeIndexOp;
+class AffineMaxOp;
+class AffineMinOp;
 
 /// Lowers `affine.delinearize_index` into a sequence of division and remainder
 /// operations.
@@ -127,6 +129,37 @@ OpFoldResult materializeComputedBound(
     OpBuilder &b, Location loc, AffineMap boundMap,
     ArrayRef<std::pair<Value, std::optional<int64_t>>> mapOperands);
 
+/// This transform tries to simplify the affine min operation `op`, by finding a
+/// common lower bound for a set of expressions in the affine map results. It
+/// returns whether the transform updated `op`'s affine map.
+///
+/// In concrete terms, given an operation like:
+/// `affine.min affine_map<(d0)[s0, s1] -> (d0, s1, s0, 128)>(%i)[%s0, %s1]`
+/// If `d0 < 128` and `128 < s1 < s0`, the transform will update `op` to:
+/// `affine.min affine_map<(d0)[s0, s1] -> (d0, 128)>(%i)[%s0, %s1]`.
+bool simplifyAffineMinOp(RewriterBase &rewriter, AffineMinOp op);
+
+/// This transform tries to simplify the affine max operation `op`, by finding a
+/// common upper bound for a set of expressions in the affine map results. It
+/// returns whether the transform updated `op`'s affine map.
+///
+/// In concrete terms, given an operation like:
+/// `affine.max affine_map<(d0)[s0, s1] -> (d0, s1, s0, 128)>(%i)[%s0, %s1]`
+/// If `d0 > 128` and `s0 > s1 > 128`, the transform will update `op` to:
+/// `affine.max affine_map<(d0)[s0, s1] -> (d0, s0)>(%i)[%s0, %s1]`.
+bool simplifyAffineMaxOp(RewriterBase &rewriter, AffineMaxOp op);
+
+/// This transform applies `simplifyAffineMinOp` and `simplifyAffineMaxOp` to
+/// all the `affine.min` or `affine.max` operations in `ops`. After
+/// simplification, it invokes the `affine.min/max` canonicalization patterns on
+/// `ops`.
+///
+/// This transform returns failure if the greedy pattern rewriter failed to
+/// converge during canonicalization, otherwise it returns success. If provided,
+/// `modified` is set to `true` if the IR was modified in any way.
+LogicalResult simplifyAffineMinMaxOps(RewriterBase &rewriter,
+                                      ArrayRef<Operation *> ops,
+                                      bool *modified = nullptr);
 } // namespace affine
 } // namespace mlir
 

mlir/include/mlir/Interfaces/ValueBoundsOpInterface.h

@@ -135,10 +135,17 @@ class ValueBoundsConstraintSet
 
     /// Construct a variable for a map and its operands.
     Variable(AffineMap map, ArrayRef<Variable> mapOperands);
-    Variable(AffineMap map, ArrayRef<Value> mapOperands);
+    Variable(AffineMap map, ValueRange mapOperands);
 
     MLIRContext *getContext() const { return map.getContext(); }
 
+    /// Returns the affine map.
+    AffineMap getMap() const { return map; }
+
+    /// Returns the map operands.
+    ValueDimList &getOperands() { return mapOperands; }
+    const ValueDimList &getOperands() const { return mapOperands; }
+
   private:
     friend class ValueBoundsConstraintSet;
     AffineMap map;
@@ -254,6 +261,12 @@ class ValueBoundsConstraintSet
   /// prove the relation or until it ran out of IR.
   static bool compare(const Variable &lhs, ComparisonOperator cmp,
                       const Variable &rhs);
+  /// This function is similar to `ValueBoundsConstraintSet::compare`, except
+  /// that it returns false if `!(lhs cmp rhs)`, and `failure` if neither the
+  /// relation nor its inverse relation could be proven.
+  static llvm::FailureOr<bool> strongCompare(const Variable &lhs,
+                                             ComparisonOperator cmp,
+                                             const Variable &rhs);
 
   /// Compute whether the given variables are equal. Return "failure" if
   /// equality could not be determined.
@@ -327,6 +340,16 @@ class ValueBoundsConstraintSet
   /// constraints.
   bool comparePos(int64_t lhsPos, ComparisonOperator cmp, int64_t rhsPos);
 
+  /// Return "true" if, based on the current state of the constraint system,
+  /// "lhs cmp rhs" was proven to hold. It returns "false" if "!(lhs cmp rhs)"
+  /// can be proven. Otherwise, it returns `failure` if neither the relation nor
+  /// its inverse relation could be proven.
+  ///
+  /// This function does not analyze any IR and does not populate any additional
+  /// constraints.
+  llvm::FailureOr<bool> strongComparePos(int64_t lhsPos, ComparisonOperator cmp,
+                                         int64_t rhsPos);
+
   /// Given an affine map with a single result (and map operands), add a new
   /// column to the constraint set that represents the result of the map.
   /// Traverse additional IR starting from the map operands as needed (as long

mlir/lib/Dialect/Affine/TransformOps/AffineTransformOps.cpp

@@ -12,6 +12,7 @@
 #include "mlir/Dialect/Affine/IR/AffineOps.h"
 #include "mlir/Dialect/Affine/IR/AffineValueMap.h"
 #include "mlir/Dialect/Affine/LoopUtils.h"
+#include "mlir/Dialect/Affine/Transforms/Transforms.h"
 #include "mlir/Dialect/Transform/IR/TransformDialect.h"
 #include "mlir/Dialect/Transform/Interfaces/TransformInterfaces.h"
 #include "mlir/Transforms/GreedyPatternRewriteDriver.h"
@@ -112,7 +113,7 @@ SimplifyBoundedAffineOpsOp::apply(transform::TransformRewriter &rewriter,
     }
     if (boundedOps.contains(target)) {
       auto diag = emitDefiniteFailure()
-                  << "target op result must not be constrainted";
+                  << "target op result must not be constrained";
       diag.attachNote(target->getLoc()) << "target/constrained op";
       return diag;
     }
@@ -148,6 +149,42 @@ void SimplifyBoundedAffineOpsOp::getEffects(
   modifiesPayload(effects);
 }
 
+//===----------------------------------------------------------------------===//
+// SimplifyMinMaxAffineOpsOp
+//===----------------------------------------------------------------------===//
+DiagnosedSilenceableFailure
+SimplifyMinMaxAffineOpsOp::apply(transform::TransformRewriter &rewriter,
+                                 TransformResults &results,
+                                 TransformState &state) {
+  SmallVector<Operation *> targets;
+  for (Operation *target : state.getPayloadOps(getTarget())) {
+    if (!isa<AffineMinOp, AffineMaxOp>(target)) {
+      auto diag = emitDefiniteFailure()
+                  << "target must be affine.min or affine.max";
+      diag.attachNote(target->getLoc()) << "target op";
+      return diag;
+    }
+    targets.push_back(target);
+  }
+  bool modified = false;
+  if (failed(mlir::affine::simplifyAffineMinMaxOps(rewriter, targets,
+                                                   &modified))) {
+    return emitDefiniteFailure()
+           << "affine.min/max simplification did not converge";
+  }
+  if (!modified) {
+    return emitSilenceableError()
+           << "the transform failed to simplify any of the target operations";
+  }
+  return DiagnosedSilenceableFailure::success();
+}
+
+void SimplifyMinMaxAffineOpsOp::getEffects(
+    SmallVectorImpl<MemoryEffects::EffectInstance> &effects) {
+  consumesHandle(getTargetMutable(), effects);
+  modifiesPayload(effects);
+}
+
 //===----------------------------------------------------------------------===//
 // Transform op registration
 //===----------------------------------------------------------------------===//

mlir/lib/Dialect/Affine/Transforms/CMakeLists.txt

@@ -17,6 +17,7 @@ add_mlir_dialect_library(MLIRAffineTransforms
   ReifyValueBounds.cpp
   SuperVectorize.cpp
   SimplifyAffineStructures.cpp
+  SimplifyAffineMinMax.cpp
 
   ADDITIONAL_HEADER_DIRS
   ${MLIR_MAIN_INCLUDE_DIR}/mlir/Dialect/Affine

mlir/lib/Dialect/Affine/Transforms/SimplifyAffineMinMax.cpp

@@ -0,0 +1,174 @@
+//===- SimplifyAffineMinMax.cpp - Simplify affine min/max ops -------------===//
+//
+// 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 file implements a transform to simplify mix/max affine operations.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Dialect/Affine/IR/AffineOps.h"
+#include "mlir/Dialect/Affine/Transforms/Transforms.h"
+#include "mlir/IR/PatternMatch.h"
+#include "mlir/Interfaces/ValueBoundsOpInterface.h"
+#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
+#include "llvm/ADT/IntEqClasses.h"
+#include "llvm/Support/Debug.h"
+
+#define DEBUG_TYPE "affine-min-max"
+#define DBGS() (llvm::dbgs() << "[" DEBUG_TYPE << "]: ")
+
+using namespace mlir;
+using namespace mlir::affine;
+
+/// Simplifies an affine min/max operation by proving there's a lower or upper
+/// bound.
+template <typename AffineOp>
+static bool simplifyAffineMinMaxOp(RewriterBase &rewriter, AffineOp affineOp) {
+  using Variable = ValueBoundsConstraintSet::Variable;
+  using ComparisonOperator = ValueBoundsConstraintSet::ComparisonOperator;
+
+  AffineMap affineMap = affineOp.getMap();
+  ValueRange operands = affineOp.getOperands();
+  static constexpr bool isMin = std::is_same_v<AffineOp, AffineMinOp>;
+
+  LLVM_DEBUG({ DBGS() << "analyzing value: `" << affineOp << "`\n"; });
+
+  // Create a `Variable` list with values corresponding to each of the results
+  // in the affine affineMap.
+  SmallVector<Variable> variables = llvm::map_to_vector(
+      llvm::iota_range<unsigned>(0u, affineMap.getNumResults(), false),
+      [&](unsigned i) {
+        return Variable(affineMap.getSliceMap(i, 1), operands);
+      });
+
+  // Get the comparison operation.
+  ComparisonOperator cmpOp =
+      isMin ? ComparisonOperator::LT : ComparisonOperator::GT;
+
+  // Find disjoint sets bounded by a common value.
+  llvm::IntEqClasses boundedClasses(variables.size());
+  DenseMap<unsigned, Variable *> bounds;
+  for (auto &&[i, v] : llvm::enumerate(variables)) {
+    unsigned eqClass = boundedClasses.findLeader(i);
+
+    // If the class already has a bound continue.
+    if (bounds.contains(eqClass))
+      continue;
+
+    // Initialize the bound.
+    Variable *bound = &v;
+
+    LLVM_DEBUG({
+      DBGS() << "- inspecting variable: #" << i << ", with map: `" << v.getMap()
+             << "`\n";
+    });
+
+    // Check against the other variables.
+    for (size_t j = i + 1; j < variables.size(); ++j) {
+      unsigned jEqClass = boundedClasses.findLeader(j);
+      // Skip if the class is the same.
+      if (jEqClass == eqClass)
+        continue;
+
+      // Get the bound of the equivalence class or itself.
+      Variable *nv = bounds.lookup_or(jEqClass, &variables[j]);
+
+      LLVM_DEBUG({
+        DBGS() << "- comparing with variable: #" << jEqClass
+               << ", with map: " << nv->getMap() << "\n";
+      });
+
+      // Compare the variables.
+      FailureOr<bool> cmpResult =
+          ValueBoundsConstraintSet::strongCompare(*bound, cmpOp, *nv);
+
+      // The variables cannot be compared.
+      if (failed(cmpResult)) {
+        LLVM_DEBUG({
+          DBGS() << "-- classes: #" << i << ", #" << jEqClass
+                 << " cannot be merged\n";
+        });
+        continue;
+      }
+
+      // Join the equivalent classes and update the bound if necessary.
+      LLVM_DEBUG({
+        DBGS() << "-- merging classes: #" << i << ", #" << jEqClass
+               << ", is cmp(lhs, rhs): " << *cmpResult << "`\n";
+      });
+      if (*cmpResult) {
+        boundedClasses.join(eqClass, jEqClass);
+      } else {
+        // In this case we have lhs > rhs if isMin == true, or lhs < rhs if
+        // isMin == false.
+        bound = nv;
+        boundedClasses.join(eqClass, jEqClass);
+      }
+    }
+    bounds[boundedClasses.findLeader(i)] = bound;
+  }
+
+  // Return if there's no simplification.
+  if (bounds.size() >= affineMap.getNumResults()) {
+    LLVM_DEBUG(
+        { DBGS() << "- the affine operation couldn't get simplified\n"; });
+    return false;
+  }
+
+  // Construct the new affine affineMap.
+  SmallVector<AffineExpr> results;
+  results.reserve(bounds.size());
+  for (auto [k, bound] : bounds)
+    results.push_back(bound->getMap().getResult(0));
+
+  affineMap = AffineMap::get(affineMap.getNumDims(), affineMap.getNumSymbols(),
+                             results, rewriter.getContext());
+
+  // Update the affine op.
+  rewriter.modifyOpInPlace(affineOp, [&]() { affineOp.setMap(affineMap); });
+  LLVM_DEBUG({ DBGS() << "- simplified affine op: `" << affineOp << "`\n"; });
+  return true;
+}
+
+bool mlir::affine::simplifyAffineMinOp(RewriterBase &rewriter, AffineMinOp op) {
+  return simplifyAffineMinMaxOp(rewriter, op);
+}
+
+bool mlir::affine::simplifyAffineMaxOp(RewriterBase &rewriter, AffineMaxOp op) {
+  return simplifyAffineMinMaxOp(rewriter, op);
+}
+
+LogicalResult mlir::affine::simplifyAffineMinMaxOps(RewriterBase &rewriter,
+                                                    ArrayRef<Operation *> ops,
+                                                    bool *modified) {
+  bool changed = false;
+  for (Operation *op : ops) {
+    if (auto minOp = dyn_cast<AffineMinOp>(op))
+      changed = simplifyAffineMinOp(rewriter, minOp) || changed;
+    else if (auto maxOp = cast<AffineMaxOp>(op))
+      changed = simplifyAffineMaxOp(rewriter, maxOp) || changed;
+  }
+  RewritePatternSet patterns(rewriter.getContext());
+  AffineMaxOp::getCanonicalizationPatterns(patterns, rewriter.getContext());
+  AffineMinOp::getCanonicalizationPatterns(patterns, rewriter.getContext());
+  FrozenRewritePatternSet frozenPatterns(std::move(patterns));
+  if (modified)
+    *modified = changed;
+  // Canonicalize to a fixpoint.
+  if (failed(applyOpPatternsGreedily(
+          ops, frozenPatterns,
+          GreedyRewriteConfig()
+              .setListener(
+                  static_cast<RewriterBase::Listener *>(rewriter.getListener()))
+              .setStrictness(GreedyRewriteStrictness::ExistingAndNewOps),
+          &changed))) {
+    return failure();
+  }
+  if (modified)
+    *modified = changed;
+  return success();
+}