Fix bug in visitDivExpr, visitMulExpr and visitModExpr

Whenever the result of a div or mod affine expression is a
constant expression, place the value in the constant index of the
flattened expression instead of adding it as a local expression.

Author: arnab-polymage

mlir/include/mlir/IR/AffineExprVisitor.h

@@ -418,6 +418,14 @@ class SimpleAffineExprFlattener
                                              AffineExpr localExpr);
 
 private:
+  /// Flatten `expr` and it to `result`. If `expr` is dimension, symbol or
+  /// constant, we add it to appropriate index in `result`. Otherwise we add it
+  /// in local variable section.
+  LogicalResult addExprToFlattenedList(ArrayRef<int64_t> lhs,
+                                       ArrayRef<int64_t> rhs,
+                                       SmallVectorImpl<int64_t> &result,
+                                       AffineExpr expr);
+
   /// Adds `localExpr`, which may be mod, ceildiv, floordiv or mod expression
   /// representing the affine expression corresponding to the quantifier
   /// introduced as the local variable corresponding to `localExpr`. If the

mlir/lib/IR/AffineExpr.cpp

@@ -19,6 +19,7 @@
 #include "mlir/Support/TypeID.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/raw_ostream.h"
 #include <numeric>
 #include <optional>
 
@@ -1177,10 +1178,9 @@ static AffineExpr getSemiAffineExprFromFlatForm(ArrayRef<int64_t> flatExprs,
     if (flatExprs[numDims + numSymbols + it.index()] == 0)
       continue;
     AffineExpr expr = it.value();
-    auto binaryExpr = dyn_cast<AffineBinaryOpExpr>(expr);
-    if (!binaryExpr)
-      continue;
-
+    // A Local expression cannot be a dimension, symbol or a constant -- it
+    // should be a binary op expression.
+    auto binaryExpr = cast<AffineBinaryOpExpr>(expr);
     AffineExpr lhs = binaryExpr.getLHS();
     AffineExpr rhs = binaryExpr.getRHS();
     if (!((isa<AffineDimExpr>(lhs) || isa<AffineSymbolExpr>(lhs)) &&
@@ -1295,7 +1295,8 @@ LogicalResult SimpleAffineExprFlattener::visitMulExpr(AffineBinaryOpExpr expr) {
                                              localExprs, context);
     AffineExpr b = getAffineExprFromFlatForm(rhs, numDims, numSymbols,
                                              localExprs, context);
-    return addLocalVariableSemiAffine(mulLhs, rhs, a * b, lhs, lhs.size());
+    AffineExpr mulExpr = a * b;
+    return addExprToFlattenedList(mulLhs, rhs, lhs, mulExpr);
   }
 
   // Get the RHS constant.
@@ -1348,7 +1349,7 @@ LogicalResult SimpleAffineExprFlattener::visitModExpr(AffineBinaryOpExpr expr) {
     AffineExpr divisorExpr = getAffineExprFromFlatForm(rhs, numDims, numSymbols,
                                                        localExprs, context);
     AffineExpr modExpr = dividendExpr % divisorExpr;
-    return addLocalVariableSemiAffine(modLhs, rhs, modExpr, lhs, lhs.size());
+    return addExprToFlattenedList(modLhs, rhs, lhs, modExpr);
   }
 
   int64_t rhsConst = rhs[getConstantIndex()];
@@ -1450,6 +1451,27 @@ LogicalResult SimpleAffineExprFlattener::addLocalVariableSemiAffine(
   return success();
 }
 
+LogicalResult SimpleAffineExprFlattener::addExprToFlattenedList(
+    ArrayRef<int64_t> lhs, ArrayRef<int64_t> rhs,
+    SmallVectorImpl<int64_t> &result, AffineExpr expr) {
+  if (auto constExpr = dyn_cast<AffineConstantExpr>(expr)) {
+    std::fill(result.begin(), result.end(), 0);
+    result[getConstantIndex()] = constExpr.getValue();
+    return success();
+  }
+  if (auto dimExpr = dyn_cast<AffineDimExpr>(expr)) {
+    std::fill(result.begin(), result.end(), 0);
+    result[getDimStartIndex() + dimExpr.getPosition()] = 1;
+    return success();
+  }
+  if (auto symExpr = dyn_cast<AffineSymbolExpr>(expr)) {
+    std::fill(result.begin(), result.end(), 0);
+    result[getSymbolStartIndex() + symExpr.getPosition()] = 1;
+    return success();
+  }
+  return addLocalVariableSemiAffine(lhs, rhs, expr, result, result.size());
+}
+
 // t = expr floordiv c   <=> t = q, c * q <= expr <= c * q + c - 1
 // A floordiv is thus flattened by introducing a new local variable q, and
 // replacing that expression with 'q' while adding the constraints
@@ -1482,7 +1504,7 @@ LogicalResult SimpleAffineExprFlattener::visitDivExpr(AffineBinaryOpExpr expr,
     AffineExpr b = getAffineExprFromFlatForm(rhs, numDims, numSymbols,
                                              localExprs, context);
     AffineExpr divExpr = isCeil ? a.ceilDiv(b) : a.floorDiv(b);
-    return addLocalVariableSemiAffine(divLhs, rhs, divExpr, lhs, lhs.size());
+    return addExprToFlattenedList(divLhs, rhs, lhs, divExpr);
   }
 
   // This is a pure affine expr; the RHS is a positive constant.

mlir/test/Dialect/Affine/simplify-structures.mlir

@@ -595,16 +595,33 @@ func.func @semiaffine_modulo_dim(%arg0: index, %arg1: index, %arg2: index) -> in
 
 // -----
 
-// CHECK-LABEL: func @semiaffine_simplification_floordiv_and_ceildiv_const
-func.func @semiaffine_simplification_floordiv_and_ceildiv_const(%arg0: tensor<?xf32>) -> (index, index) {
+// CHECK-DAG: #[[$MAP:.*]] = affine_map<()[s0] -> (13 mod s0)>
+// CHECK-DAG: #[[$MAP1:.*]] = affine_map<(d0) -> (d0 * 2)>
+// CHECK-LABEL: semiaffine_simplification_local_expr_folded_into_non_binary_expr
+func.func @semiaffine_simplification_local_expr_folded_into_non_binary_expr(%arg0: memref<?x?xf32>) -> (index, index, index, index) {
   %c0 = arith.constant 0 : index
   %c1 = arith.constant 1 : index
+  %c4 = arith.constant 4 : index
   %c13 = arith.constant 13 : index
-  %dim = tensor.dim %arg0, %c0 : tensor<?xf32>
+  // CHECK: %[[DIM:.*]] = memref.dim
+  %dim = memref.dim %arg0, %c0 : memref<?x?xf32>
+  // CHECK-DAG: %[[C6:.*]] = arith.constant 6 : index
+  // CHECK-DAG: %[[C7:.*]] = arith.constant 7 : index
   %a = affine.apply affine_map<()[s0, s1, s2] -> (s0 floordiv (s1 + (-s1 + 2) * (-s1 + s1 * s2 + 1)))>()[%c13, %dim, %c1]
   %b = affine.apply affine_map<()[s0, s1, s2] -> (s0 ceildiv (s1 + (-s1 + 2) * (-s1 + s1 * s2 + 1)))>()[%c13, %dim, %c1]
-  // CHECK:      %[[C6:.*]] = arith.constant 6 : index
-  // CHECK-NEXT: %[[C7:.*]] = arith.constant 7 : index
-  // CHECK-NEXT: return %[[C6]], %[[C7]]
-  return %a, %b : index, index
+  // CHECK: %[[VAL0:.*]] = affine.apply #[[$MAP]]()[%[[DIM]]]
+  %c = affine.apply affine_map<()[s0, s1, s2, s3] -> (s0 mod (s1 + (-s1 + s3) * (-s1 + s1 * s2 + 1)))>()[%c13, %dim, %c1, %dim]
+  %alloc = memref.alloc() : memref<1xindex>
+  affine.for %iv = 0 to 1 {
+    %d = affine.apply affine_map<(d0)[s1, s2] -> ((d0 - s1 + s1 * s2) * (s1 + (-s1 + 2) * (-s1 + s1 * s2 + 1)))>(%iv)[%dim, %c1]
+    affine.store %d, %alloc[0] : memref<1xindex>
+  }
+  // CHECK:      affine.for %[[IV:.*]] = 0 to 1 {
+  // CHECK-NEXT:   %[[VAL:.*]] = affine.apply #[[$MAP1]](%[[IV]])
+  // CHECK-NEXT:   affine.store %[[VAL]], %{{.*}}[0] : memref<1xindex>
+  // CHECK-NEXT: }
+  // CHECK: %[[VAL1:.*]] = affine.load %{{.*}}[0]
+  %d = affine.load %alloc[0] : memref<1xindex>
+  // CHECK: return %[[C6]], %[[C7]], %[[VAL0]], %[[VAL1]]
+  return %a, %b, %c, %d : index, index, index, index
 }