[mlir][Interfaces][WIP] ValueBoundsOpInterface: Variable

Author: matthias-springer

mlir/include/mlir/Interfaces/ValueBoundsOpInterface.h

@@ -15,6 +15,7 @@
 #include "mlir/IR/Value.h"
 #include "mlir/Interfaces/DestinationStyleOpInterface.h"
 #include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/ExtensibleRTTI.h"
 
 #include <queue>
@@ -111,6 +112,39 @@ class ValueBoundsConstraintSet
 public:
   static char ID;
 
+  /// A variable that can be added to the constraint set as a "column". The
+  /// value bounds infrastructure can compute bounds for variables and compare
+  /// two variables.
+  ///
+  /// Internally, a variable is represented as an affine map and operands.
+  class Variable {
+  public:
+    /// Construct a variable for an index-typed attribute or SSA value.
+    Variable(OpFoldResult ofr);
+
+    /// Construct a variable for an index-typed SSA value.
+    Variable(Value indexValue);
+
+    /// Construct a variable for a dimension of a shaped value.
+    Variable(Value shapedValue, int64_t dim);
+
+    /// Construct a variable for an index-typed attribute/SSA value or for a
+    /// dimension of a shaped value. A non-null dimension must be provided if
+    /// and only if `ofr` is a shaped value.
+    Variable(OpFoldResult ofr, std::optional<int64_t> dim);
+
+    /// Construct a variable for a map and its operands.
+    Variable(AffineMap map, ArrayRef<Variable> mapOperands);
+    Variable(AffineMap map, ArrayRef<Value> mapOperands);
+
+    MLIRContext *getContext() const { return map.getContext(); }
+
+  private:
+    friend class ValueBoundsConstraintSet;
+    AffineMap map;
+    ValueDimList mapOperands;
+  };
+
   /// The stop condition when traversing the backward slice of a shaped value/
   /// index-type value. The traversal continues until the stop condition
   /// evaluates to "true" for a value.
@@ -121,35 +155,31 @@ class ValueBoundsConstraintSet
   using StopConditionFn = std::function<bool(
       Value, std::optional<int64_t> /*dim*/, ValueBoundsConstraintSet &cstr)>;
 
-  /// Compute a bound for the given index-typed value or shape dimension size.
-  /// The computed bound is stored in `resultMap`. The operands of the bound are
-  /// stored in `mapOperands`. An operand is either an index-type SSA value
-  /// or a shaped value and a dimension.
+  /// Compute a bound for the given variable. The computed bound is stored in
+  /// `resultMap`. The operands of the bound are stored in `mapOperands`. An
+  /// operand is either an index-type SSA value or a shaped value and a
+  /// dimension.
   ///
-  /// `dim` must be `nullopt` if and only if `value` is index-typed. The bound
-  /// is computed in terms of values/dimensions for which `stopCondition`
-  /// evaluates to "true". To that end, the backward slice (reverse use-def
-  /// chain) of the given value is visited in a worklist-driven manner and the
-  /// constraint set is populated according to `ValueBoundsOpInterface` for each
-  /// visited value.
+  /// The bound is computed in terms of values/dimensions for which
+  /// `stopCondition` evaluates to "true". To that end, the backward slice
+  /// (reverse use-def chain) of the given value is visited in a worklist-driven
+  /// manner and the constraint set is populated according to
+  /// `ValueBoundsOpInterface` for each visited value.
   ///
   /// By default, lower/equal bounds are closed and upper bounds are open. If
   /// `closedUB` is set to "true", upper bounds are also closed.
-  static LogicalResult computeBound(AffineMap &resultMap,
-                                    ValueDimList &mapOperands,
-                                    presburger::BoundType type, Value value,
-                                    std::optional<int64_t> dim,
-                                    StopConditionFn stopCondition,
-                                    bool closedUB = false);
+  static LogicalResult
+  computeBound(AffineMap &resultMap, ValueDimList &mapOperands,
+               presburger::BoundType type, const Variable &var,
+               StopConditionFn stopCondition, bool closedUB = false);
 
   /// Compute a bound in terms of the values/dimensions in `dependencies`. The
   /// computed bound consists of only constant terms and dependent values (or
   /// dimension sizes thereof).
   static LogicalResult
   computeDependentBound(AffineMap &resultMap, ValueDimList &mapOperands,
-                        presburger::BoundType type, Value value,
-                        std::optional<int64_t> dim, ValueDimList dependencies,
-                        bool closedUB = false);
+                        presburger::BoundType type, const Variable &var,
+                        ValueDimList dependencies, bool closedUB = false);
 
   /// Compute a bound in that is independent of all values in `independencies`.
   ///
@@ -161,13 +191,10 @@ class ValueBoundsConstraintSet
   /// appear in the computed bound.
   static LogicalResult
   computeIndependentBound(AffineMap &resultMap, ValueDimList &mapOperands,
-                          presburger::BoundType type, Value value,
-                          std::optional<int64_t> dim, ValueRange independencies,
-                          bool closedUB = false);
+                          presburger::BoundType type, const Variable &var,
+                          ValueRange independencies, bool closedUB = false);
 
-  /// Compute a constant bound for the given affine map, where dims and symbols
-  /// are bound to the given operands. The affine map must have exactly one
-  /// result.
+  /// Compute a constant bound for the given variable.
   ///
   /// This function traverses the backward slice of the given operands in a
   /// worklist-driven manner until `stopCondition` evaluates to "true". The
@@ -182,16 +209,9 @@ class ValueBoundsConstraintSet
   /// By default, lower/equal bounds are closed and upper bounds are open. If
   /// `closedUB` is set to "true", upper bounds are also closed.
   static FailureOr<int64_t>
-  computeConstantBound(presburger::BoundType type, Value value,
-                       std::optional<int64_t> dim = std::nullopt,
+  computeConstantBound(presburger::BoundType type, const Variable &var,
                        StopConditionFn stopCondition = nullptr,
                        bool closedUB = false);
-  static FailureOr<int64_t> computeConstantBound(
-      presburger::BoundType type, AffineMap map, ValueDimList mapOperands,
-      StopConditionFn stopCondition = nullptr, bool closedUB = false);
-  static FailureOr<int64_t> computeConstantBound(
-      presburger::BoundType type, AffineMap map, ArrayRef<Value> mapOperands,
-      StopConditionFn stopCondition = nullptr, bool closedUB = false);
 
   /// Compute a constant delta between the given two values. Return "failure"
   /// if a constant delta could not be determined.
@@ -221,9 +241,7 @@ class ValueBoundsConstraintSet
   /// proven. This could be because the specified relation does in fact not hold
   /// or because there is not enough information in the constraint set. In other
   /// words, if we do not know for sure, this function returns "false".
-  bool populateAndCompare(OpFoldResult lhs, std::optional<int64_t> lhsDim,
-                          ComparisonOperator cmp, OpFoldResult rhs,
-                          std::optional<int64_t> rhsDim);
+  bool populateAndCompare(Variable lhs, ComparisonOperator cmp, Variable rhs);
 
   /// Return "true" if "lhs cmp rhs" was proven to hold. Return "false" if the
   /// specified relation could not be proven. This could be because the
@@ -233,24 +251,11 @@ class ValueBoundsConstraintSet
   ///
   /// This function keeps traversing the backward slice of lhs/rhs until could
   /// prove the relation or until it ran out of IR.
-  static bool compare(OpFoldResult lhs, std::optional<int64_t> lhsDim,
-                      ComparisonOperator cmp, OpFoldResult rhs,
-                      std::optional<int64_t> rhsDim);
-  static bool compare(AffineMap lhs, ValueDimList lhsOperands,
-                      ComparisonOperator cmp, AffineMap rhs,
-                      ValueDimList rhsOperands);
-  static bool compare(AffineMap lhs, ArrayRef<Value> lhsOperands,
-                      ComparisonOperator cmp, AffineMap rhs,
-                      ArrayRef<Value> rhsOperands);
-
-  /// Compute whether the given values/dimensions are equal. Return "failure" if
+  static bool compare(Variable lhs, ComparisonOperator cmp, Variable rhs);
+
+  /// Compute whether the given variables are equal. Return "failure" if
   /// equality could not be determined.
-  ///
-  /// `dim1`/`dim2` must be `nullopt` if and only if `value1`/`value2` are
-  /// index-typed.
-  static FailureOr<bool> areEqual(OpFoldResult value1, OpFoldResult value2,
-                                  std::optional<int64_t> dim1 = std::nullopt,
-                                  std::optional<int64_t> dim2 = std::nullopt);
+  static FailureOr<bool> areEqual(Variable var1, Variable var2);
 
   /// Return "true" if the given slices are guaranteed to be overlapping.
   /// Return "false" if the given slices are guaranteed to be non-overlapping.
@@ -317,9 +322,6 @@ class ValueBoundsConstraintSet
   ///
   /// This function does not analyze any IR and does not populate any additional
   /// constraints.
-  bool compareValueDims(OpFoldResult lhs, std::optional<int64_t> lhsDim,
-                        ComparisonOperator cmp, OpFoldResult rhs,
-                        std::optional<int64_t> rhsDim);
   bool comparePos(int64_t lhsPos, ComparisonOperator cmp, int64_t rhsPos);
 
   /// Given an affine map with a single result (and map operands), add a new
@@ -374,13 +376,16 @@ class ValueBoundsConstraintSet
   /// constraint system. Return the position of the new column. Any operands
   /// that were not analyzed yet are put on the worklist.
   int64_t insert(AffineMap map, ValueDimList operands, bool isSymbol = true);
+  int64_t insert(const Variable &var, bool isSymbol = true);
 
   /// Project out the given column in the constraint set.
   void projectOut(int64_t pos);
 
   /// Project out all columns for which the condition holds.
   void projectOut(function_ref<bool(ValueDim)> condition);
 
+  void projectOutAnonymous(std::optional<int64_t> except = std::nullopt);
+
   /// Mapping of columns to values/shape dimensions.
   SmallVector<std::optional<ValueDim>> positionToValueDim;
   /// Reverse mapping of values/shape dimensions to columns.

mlir/lib/Dialect/Affine/IR/ValueBoundsOpInterfaceImpl.cpp

@@ -120,9 +120,7 @@ mlir::affine::fullyComposeAndComputeConstantDelta(Value value1, Value value2) {
   mapOperands.push_back(value1);
   mapOperands.push_back(value2);
   affine::fullyComposeAffineMapAndOperands(&map, &mapOperands);
-  ValueDimList valueDims;
-  for (Value v : mapOperands)
-    valueDims.push_back({v, std::nullopt});
   return ValueBoundsConstraintSet::computeConstantBound(
-      presburger::BoundType::EQ, map, valueDims);
+      presburger::BoundType::EQ,
+      ValueBoundsConstraintSet::Variable(map, mapOperands));
 }

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

@@ -25,7 +25,7 @@ reifyValueBound(OpBuilder &b, Location loc, presburger::BoundType type,
   AffineMap boundMap;
   ValueDimList mapOperands;
   if (failed(ValueBoundsConstraintSet::computeBound(
-          boundMap, mapOperands, type, value, dim, stopCondition, closedUB)))
+          boundMap, mapOperands, type, {value, dim}, stopCondition, closedUB)))
     return failure();
 
   // Reify bound.

mlir/lib/Dialect/Arith/IR/ValueBoundsOpInterfaceImpl.cpp

@@ -75,6 +75,75 @@ struct MulIOpInterface
   }
 };
 
+struct SelectOpInterface
+    : public ValueBoundsOpInterface::ExternalModel<SelectOpInterface,
+                                                   SelectOp> {
+
+  static void populateBounds(SelectOp selectOp, std::optional<int64_t> dim,
+                             ValueBoundsConstraintSet &cstr) {
+    Value value = selectOp.getResult();
+    Value condition = selectOp.getCondition();
+    Value trueValue = selectOp.getTrueValue();
+    Value falseValue = selectOp.getFalseValue();
+
+    if (isa<ShapedType>(condition.getType())) {
+      // If the condition is a shaped type, the condition is applied
+      // element-wise. All three operands must have the same shape.
+      cstr.bound(value)[*dim] == cstr.getExpr(trueValue, dim);
+      cstr.bound(value)[*dim] == cstr.getExpr(falseValue, dim);
+      cstr.bound(value)[*dim] == cstr.getExpr(condition, dim);
+      return;
+    }
+
+    // Populate constraints for the true/false values (and all values on the
+    // backward slice, as long as the current stop condition is not satisfied).
+    cstr.populateConstraints(trueValue, dim);
+    cstr.populateConstraints(falseValue, dim);
+    auto boundsBuilder = cstr.bound(value);
+    if (dim)
+      boundsBuilder[*dim];
+
+    // Compare yielded values.
+    // If trueValue <= falseValue:
+    // * result <= falseValue
+    // * result >= trueValue
+    if (cstr.compare(/*lhs=*/{trueValue, dim},
+                     ValueBoundsConstraintSet::ComparisonOperator::LE,
+                     /*rhs=*/{falseValue, dim})) {
+      if (dim) {
+        cstr.bound(value)[*dim] >= cstr.getExpr(trueValue, dim);
+        cstr.bound(value)[*dim] <= cstr.getExpr(falseValue, dim);
+      } else {
+        cstr.bound(value) >= trueValue;
+        cstr.bound(value) <= falseValue;
+      }
+    }
+    // If falseValue <= trueValue:
+    // * result <= trueValue
+    // * result >= falseValue
+    if (cstr.compare(/*lhs=*/{falseValue, dim},
+                     ValueBoundsConstraintSet::ComparisonOperator::LE,
+                     /*rhs=*/{trueValue, dim})) {
+      if (dim) {
+        cstr.bound(value)[*dim] >= cstr.getExpr(falseValue, dim);
+        cstr.bound(value)[*dim] <= cstr.getExpr(trueValue, dim);
+      } else {
+        cstr.bound(value) >= falseValue;
+        cstr.bound(value) <= trueValue;
+      }
+    }
+  }
+
+  void populateBoundsForIndexValue(Operation *op, Value value,
+                                   ValueBoundsConstraintSet &cstr) const {
+    populateBounds(cast<SelectOp>(op), /*dim=*/std::nullopt, cstr);
+  }
+
+  void populateBoundsForShapedValueDim(Operation *op, Value value, int64_t dim,
+                                       ValueBoundsConstraintSet &cstr) const {
+    populateBounds(cast<SelectOp>(op), dim, cstr);
+  }
+};
 } // namespace
 } // namespace arith
 } // namespace mlir

mlir/lib/Dialect/Arith/Transforms/IntNarrowing.cpp

@@ -449,7 +449,7 @@ struct IndexCastPattern final : NarrowingPattern<CastOp> {
       return failure();
 
     FailureOr<int64_t> ub = ValueBoundsConstraintSet::computeConstantBound(
-        presburger::BoundType::UB, in, /*dim=*/std::nullopt,
+        presburger::BoundType::UB, in,
         /*stopCondition=*/nullptr, /*closedUB=*/true);
     if (failed(ub))
       return failure();

mlir/lib/Dialect/Arith/Transforms/ReifyValueBounds.cpp

@@ -70,7 +70,9 @@ reifyValueBound(OpBuilder &b, Location loc, presburger::BoundType type,
   AffineMap boundMap;
   ValueDimList mapOperands;
   if (failed(ValueBoundsConstraintSet::computeBound(
-          boundMap, mapOperands, type, value, dim, stopCondition, closedUB)))
+          boundMap, mapOperands, type,
+          ValueBoundsConstraintSet::Variable(value, dim), stopCondition,
+          closedUB)))
     return failure();
 
   // Materialize tensor.dim/memref.dim ops.

mlir/lib/Dialect/Linalg/Transforms/Padding.cpp

@@ -72,8 +72,10 @@ static LogicalResult computePaddedShape(linalg::LinalgOp opToPad,
     // Otherwise, try to compute a constant upper bound for the size value.
     FailureOr<int64_t> upperBound =
         ValueBoundsConstraintSet::computeConstantBound(
-            presburger::BoundType::UB, opOperand->get(),
-            /*dim=*/i, /*stopCondition=*/nullptr, /*closedUB=*/true);
+            presburger::BoundType::UB,
+            {opOperand->get(),
+             /*dim=*/i},
+            /*stopCondition=*/nullptr, /*closedUB=*/true);
     if (failed(upperBound)) {
       LLVM_DEBUG(DBGS() << "----could not compute a bounding box for padding");
       return failure();

mlir/lib/Dialect/Linalg/Transforms/Promotion.cpp

@@ -257,14 +257,12 @@ FailureOr<PromotionInfo> mlir::linalg::promoteSubviewAsNewBuffer(
     if (auto attr = llvm::dyn_cast_if_present<Attribute>(rangeValue.size)) {
       size = getValueOrCreateConstantIndexOp(b, loc, rangeValue.size);
     } else {
-      Value materializedSize =
-          getValueOrCreateConstantIndexOp(b, loc, rangeValue.size);
       FailureOr<int64_t> upperBound =
           ValueBoundsConstraintSet::computeConstantBound(
-              presburger::BoundType::UB, materializedSize, /*dim=*/std::nullopt,
+              presburger::BoundType::UB, rangeValue.size,
               /*stopCondition=*/nullptr, /*closedUB=*/true);
       size = failed(upperBound)
-                 ? materializedSize
+                 ? getValueOrCreateConstantIndexOp(b, loc, rangeValue.size)
                  : b.create<arith::ConstantIndexOp>(loc, *upperBound);
     }
     LLVM_DEBUG(llvm::dbgs() << "Extracted tightest: " << size << "\n");

mlir/lib/Dialect/MemRef/Transforms/IndependenceTransforms.cpp

@@ -23,12 +23,11 @@ static FailureOr<OpFoldResult> makeIndependent(OpBuilder &b, Location loc,
                                                ValueRange independencies) {
   if (ofr.is<Attribute>())
     return ofr;
-  Value value = ofr.get<Value>();
   AffineMap boundMap;
   ValueDimList mapOperands;
   if (failed(ValueBoundsConstraintSet::computeIndependentBound(
-          boundMap, mapOperands, presburger::BoundType::UB, value,
-          /*dim=*/std::nullopt, independencies, /*closedUB=*/true)))
+          boundMap, mapOperands, presburger::BoundType::UB, ofr, independencies,
+          /*closedUB=*/true)))
     return failure();
   return affine::materializeComputedBound(b, loc, boundMap, mapOperands);
 }