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@Hardcode84 Hardcode84 commented Jul 3, 2025

Order symbol/dim arguments by position and put dims before symbols. This is to help affine simplifications.

Order symbol/dim arguments by position, put dims before symbols and put constants to the right.
This is to help affine simplefications.
@Hardcode84 Hardcode84 requested a review from ftynse July 3, 2025 14:08
@llvmbot llvmbot added mlir:core MLIR Core Infrastructure mlir:affine mlir labels Jul 3, 2025
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llvmbot commented Jul 3, 2025

@llvm/pr-subscribers-mlir-affine

Author: Ivan Butygin (Hardcode84)

Changes

Order symbol/dim arguments by position, put dims before symbols and put constants to the right. This is to help affine simplifications.


Full diff: https://github.com/llvm/llvm-project/pull/146895.diff

4 Files Affected:

  • (modified) mlir/lib/IR/AffineExpr.cpp (+36-2)
  • (modified) mlir/test/Dialect/Affine/simplify-structures.mlir (+2-2)
  • (modified) mlir/test/IR/affine-map.mlir (+1-1)
  • (modified) mlir/unittests/IR/AffineExprTest.cpp (+23)
diff --git a/mlir/lib/IR/AffineExpr.cpp b/mlir/lib/IR/AffineExpr.cpp
index cc81f9d19aca7..856b29125602d 100644
--- a/mlir/lib/IR/AffineExpr.cpp
+++ b/mlir/lib/IR/AffineExpr.cpp
@@ -784,6 +784,36 @@ static AffineExpr simplifyAdd(AffineExpr lhs, AffineExpr rhs) {
   return nullptr;
 }
 
+static std::pair<AffineExpr, AffineExpr>
+orderCommutativeArgs(AffineExpr expr1, AffineExpr expr2) {
+  auto sym1 = dyn_cast<AffineSymbolExpr>(expr1);
+  auto sym2 = dyn_cast<AffineSymbolExpr>(expr2);
+  // Try to order by symbol/dim position first
+  if (sym1 && sym2)
+    return sym1.getPosition() < sym2.getPosition() ? std::pair{expr1, expr2}
+                                                   : std::pair{expr2, expr1};
+
+  auto dim1 = dyn_cast<AffineDimExpr>(expr1);
+  auto dim2 = dyn_cast<AffineDimExpr>(expr2);
+  if (dim1 && dim2)
+    return dim1.getPosition() < dim2.getPosition() ? std::pair{expr1, expr2}
+                                                   : std::pair{expr2, expr1};
+
+  // Put dims before symbols
+  if (dim1 && sym2)
+    return {dim1, sym2};
+
+  if (sym1 && dim2)
+    return {dim2, sym1};
+
+  // Move constants to the right
+  if (isa<AffineConstantExpr>(expr1) && !isa<AffineConstantExpr>(expr2))
+    return {expr2, expr1};
+
+  // Otherwise, keep original order
+  return {expr1, expr2};
+}
+
 AffineExpr AffineExpr::operator+(int64_t v) const {
   return *this + getAffineConstantExpr(v, getContext());
 }
@@ -791,9 +821,11 @@ AffineExpr AffineExpr::operator+(AffineExpr other) const {
   if (auto simplified = simplifyAdd(*this, other))
     return simplified;
 
+  auto [lhs, rhs] = orderCommutativeArgs(*this, other);
+
   StorageUniquer &uniquer = getContext()->getAffineUniquer();
   return uniquer.get<AffineBinaryOpExprStorage>(
-      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Add), *this, other);
+      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Add), lhs, rhs);
 }
 
 /// Simplify a multiply expression. Return nullptr if it can't be simplified.
@@ -856,9 +888,11 @@ AffineExpr AffineExpr::operator*(AffineExpr other) const {
   if (auto simplified = simplifyMul(*this, other))
     return simplified;
 
+  auto [lhs, rhs] = orderCommutativeArgs(*this, other);
+
   StorageUniquer &uniquer = getContext()->getAffineUniquer();
   return uniquer.get<AffineBinaryOpExprStorage>(
-      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Mul), *this, other);
+      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Mul), lhs, rhs);
 }
 
 // Unary minus, delegate to operator*.
diff --git a/mlir/test/Dialect/Affine/simplify-structures.mlir b/mlir/test/Dialect/Affine/simplify-structures.mlir
index 6f2737a982752..653c2cb521637 100644
--- a/mlir/test/Dialect/Affine/simplify-structures.mlir
+++ b/mlir/test/Dialect/Affine/simplify-structures.mlir
@@ -508,7 +508,7 @@ func.func @test_not_trivially_true_or_false_returning_three_results() -> (index,
 // -----
 
 // Test simplification of mod expressions.
-// CHECK-DAG:   #[[$MOD:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s3 + s4 * s1 + (s0 - s1) mod s2)>
+// CHECK-DAG:   #[[$MOD:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s1 * s4 + s3 + (s0 - s1) mod s2)>
 // CHECK-DAG:   #[[$SIMPLIFIED_MOD_RHS:.*]] = affine_map<()[s0, s1, s2, s3] -> (s3 mod (s2 - s0 * s1))>
 // CHECK-DAG:   #[[$MODULO_AND_PRODUCT:.*]] = affine_map<()[s0, s1, s2, s3] -> (s0 * s1 + s3 - (-s0 + s3) mod s2)>
 // CHECK-LABEL: func @semiaffine_simplification_mod
@@ -547,7 +547,7 @@ func.func @semiaffine_simplification_floordiv_and_ceildiv(%arg0: index, %arg1: i
 
 // Test simplification of product expressions.
 // CHECK-DAG:   #[[$PRODUCT:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s3 + s4 + (s0 - s1) * s2)>
-// CHECK-DAG:   #[[$SUM_OF_PRODUCTS:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s2 + s2 * s0 + s3 + s3 * s0 + s3 * s1 + s4 + s4 * s1)>
+// CHECK-DAG:   #[[$SUM_OF_PRODUCTS:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s0 * s2 + s0 * s3 + s1 * s3 + s1 * s4 + s2 + s3 + s4)>
 // CHECK-LABEL: func @semiaffine_simplification_product
 // CHECK-SAME:  (%[[ARG0:.*]]: index, %[[ARG1:.*]]: index, %[[ARG2:.*]]: index, %[[ARG3:.*]]: index, %[[ARG4:.*]]: index, %[[ARG5:.*]]: index)
 func.func @semiaffine_simplification_product(%arg0: index, %arg1: index, %arg2: index, %arg3: index, %arg4: index, %arg5: index) -> (index, index) {
diff --git a/mlir/test/IR/affine-map.mlir b/mlir/test/IR/affine-map.mlir
index 977aec2536b1e..6277b28561f36 100644
--- a/mlir/test/IR/affine-map.mlir
+++ b/mlir/test/IR/affine-map.mlir
@@ -139,7 +139,7 @@
 #map44 = affine_map<(i, j) -> (i - 2*j, j * 6 floordiv 4)>
 
 // Simplifications
-// CHECK: #map{{[0-9]*}} = affine_map<(d0, d1, d2)[s0] -> (d0 + d1 + d2 + 1, d2 + d1, (d0 * s0) * 8)>
+// CHECK: #map{{[0-9]*}} = affine_map<(d0, d1, d2)[s0] -> (d0 + d1 + d2 + 1, d1 + d2, (d0 * s0) * 8)>
 #map45 = affine_map<(i, j, k) [N] -> (1 + i + 3 + j - 3 + k, k + 5 + j - 5, 2*i*4*N)>
 
 // CHECK: #map{{[0-9]*}} = affine_map<(d0, d1, d2) -> (0, d1, d0 * 2, 0)>
diff --git a/mlir/unittests/IR/AffineExprTest.cpp b/mlir/unittests/IR/AffineExprTest.cpp
index 8a2d697540d5c..f8494ecb971c2 100644
--- a/mlir/unittests/IR/AffineExprTest.cpp
+++ b/mlir/unittests/IR/AffineExprTest.cpp
@@ -84,6 +84,20 @@ TEST(AffineExprTest, constantFolding) {
   ASSERT_EQ(cminfloordivcn1.getKind(), AffineExprKind::FloorDiv);
 }
 
+TEST(AffineExprTest, commutative) {
+  MLIRContext ctx;
+  OpBuilder b(&ctx);
+  auto c2 = b.getAffineConstantExpr(1);
+  auto d0 = b.getAffineDimExpr(0);
+  auto d1 = b.getAffineDimExpr(1);
+  auto s0 = b.getAffineSymbolExpr(0);
+  auto s1 = b.getAffineSymbolExpr(1);
+
+  ASSERT_EQ(d0 * d1, d1 * d0);
+  ASSERT_EQ(s0 + s1, s1 + s0);
+  ASSERT_EQ(s0 * c2, c2 * s0);
+}
+
 TEST(AffineExprTest, divisionSimplification) {
   MLIRContext ctx;
   OpBuilder b(&ctx);
@@ -147,3 +161,12 @@ TEST(AffineExprTest, simpleAffineExprFlattenerRegression) {
   ASSERT_TRUE(isa<AffineConstantExpr>(result));
   ASSERT_EQ(cast<AffineConstantExpr>(result).getValue(), 7);
 }
+
+TEST(AffineExprTest, simplifyCommutative) {
+  MLIRContext ctx;
+  OpBuilder b(&ctx);
+  auto s0 = b.getAffineSymbolExpr(0);
+  auto s1 = b.getAffineSymbolExpr(1);
+
+  ASSERT_EQ(s0 * s1 - s1 * s0 + 1, 1);
+}

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llvmbot commented Jul 3, 2025

@llvm/pr-subscribers-mlir-core

Author: Ivan Butygin (Hardcode84)

Changes

Order symbol/dim arguments by position, put dims before symbols and put constants to the right. This is to help affine simplifications.


Full diff: https://github.com/llvm/llvm-project/pull/146895.diff

4 Files Affected:

  • (modified) mlir/lib/IR/AffineExpr.cpp (+36-2)
  • (modified) mlir/test/Dialect/Affine/simplify-structures.mlir (+2-2)
  • (modified) mlir/test/IR/affine-map.mlir (+1-1)
  • (modified) mlir/unittests/IR/AffineExprTest.cpp (+23)
diff --git a/mlir/lib/IR/AffineExpr.cpp b/mlir/lib/IR/AffineExpr.cpp
index cc81f9d19aca7..856b29125602d 100644
--- a/mlir/lib/IR/AffineExpr.cpp
+++ b/mlir/lib/IR/AffineExpr.cpp
@@ -784,6 +784,36 @@ static AffineExpr simplifyAdd(AffineExpr lhs, AffineExpr rhs) {
   return nullptr;
 }
 
+static std::pair<AffineExpr, AffineExpr>
+orderCommutativeArgs(AffineExpr expr1, AffineExpr expr2) {
+  auto sym1 = dyn_cast<AffineSymbolExpr>(expr1);
+  auto sym2 = dyn_cast<AffineSymbolExpr>(expr2);
+  // Try to order by symbol/dim position first
+  if (sym1 && sym2)
+    return sym1.getPosition() < sym2.getPosition() ? std::pair{expr1, expr2}
+                                                   : std::pair{expr2, expr1};
+
+  auto dim1 = dyn_cast<AffineDimExpr>(expr1);
+  auto dim2 = dyn_cast<AffineDimExpr>(expr2);
+  if (dim1 && dim2)
+    return dim1.getPosition() < dim2.getPosition() ? std::pair{expr1, expr2}
+                                                   : std::pair{expr2, expr1};
+
+  // Put dims before symbols
+  if (dim1 && sym2)
+    return {dim1, sym2};
+
+  if (sym1 && dim2)
+    return {dim2, sym1};
+
+  // Move constants to the right
+  if (isa<AffineConstantExpr>(expr1) && !isa<AffineConstantExpr>(expr2))
+    return {expr2, expr1};
+
+  // Otherwise, keep original order
+  return {expr1, expr2};
+}
+
 AffineExpr AffineExpr::operator+(int64_t v) const {
   return *this + getAffineConstantExpr(v, getContext());
 }
@@ -791,9 +821,11 @@ AffineExpr AffineExpr::operator+(AffineExpr other) const {
   if (auto simplified = simplifyAdd(*this, other))
     return simplified;
 
+  auto [lhs, rhs] = orderCommutativeArgs(*this, other);
+
   StorageUniquer &uniquer = getContext()->getAffineUniquer();
   return uniquer.get<AffineBinaryOpExprStorage>(
-      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Add), *this, other);
+      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Add), lhs, rhs);
 }
 
 /// Simplify a multiply expression. Return nullptr if it can't be simplified.
@@ -856,9 +888,11 @@ AffineExpr AffineExpr::operator*(AffineExpr other) const {
   if (auto simplified = simplifyMul(*this, other))
     return simplified;
 
+  auto [lhs, rhs] = orderCommutativeArgs(*this, other);
+
   StorageUniquer &uniquer = getContext()->getAffineUniquer();
   return uniquer.get<AffineBinaryOpExprStorage>(
-      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Mul), *this, other);
+      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Mul), lhs, rhs);
 }
 
 // Unary minus, delegate to operator*.
diff --git a/mlir/test/Dialect/Affine/simplify-structures.mlir b/mlir/test/Dialect/Affine/simplify-structures.mlir
index 6f2737a982752..653c2cb521637 100644
--- a/mlir/test/Dialect/Affine/simplify-structures.mlir
+++ b/mlir/test/Dialect/Affine/simplify-structures.mlir
@@ -508,7 +508,7 @@ func.func @test_not_trivially_true_or_false_returning_three_results() -> (index,
 // -----
 
 // Test simplification of mod expressions.
-// CHECK-DAG:   #[[$MOD:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s3 + s4 * s1 + (s0 - s1) mod s2)>
+// CHECK-DAG:   #[[$MOD:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s1 * s4 + s3 + (s0 - s1) mod s2)>
 // CHECK-DAG:   #[[$SIMPLIFIED_MOD_RHS:.*]] = affine_map<()[s0, s1, s2, s3] -> (s3 mod (s2 - s0 * s1))>
 // CHECK-DAG:   #[[$MODULO_AND_PRODUCT:.*]] = affine_map<()[s0, s1, s2, s3] -> (s0 * s1 + s3 - (-s0 + s3) mod s2)>
 // CHECK-LABEL: func @semiaffine_simplification_mod
@@ -547,7 +547,7 @@ func.func @semiaffine_simplification_floordiv_and_ceildiv(%arg0: index, %arg1: i
 
 // Test simplification of product expressions.
 // CHECK-DAG:   #[[$PRODUCT:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s3 + s4 + (s0 - s1) * s2)>
-// CHECK-DAG:   #[[$SUM_OF_PRODUCTS:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s2 + s2 * s0 + s3 + s3 * s0 + s3 * s1 + s4 + s4 * s1)>
+// CHECK-DAG:   #[[$SUM_OF_PRODUCTS:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s0 * s2 + s0 * s3 + s1 * s3 + s1 * s4 + s2 + s3 + s4)>
 // CHECK-LABEL: func @semiaffine_simplification_product
 // CHECK-SAME:  (%[[ARG0:.*]]: index, %[[ARG1:.*]]: index, %[[ARG2:.*]]: index, %[[ARG3:.*]]: index, %[[ARG4:.*]]: index, %[[ARG5:.*]]: index)
 func.func @semiaffine_simplification_product(%arg0: index, %arg1: index, %arg2: index, %arg3: index, %arg4: index, %arg5: index) -> (index, index) {
diff --git a/mlir/test/IR/affine-map.mlir b/mlir/test/IR/affine-map.mlir
index 977aec2536b1e..6277b28561f36 100644
--- a/mlir/test/IR/affine-map.mlir
+++ b/mlir/test/IR/affine-map.mlir
@@ -139,7 +139,7 @@
 #map44 = affine_map<(i, j) -> (i - 2*j, j * 6 floordiv 4)>
 
 // Simplifications
-// CHECK: #map{{[0-9]*}} = affine_map<(d0, d1, d2)[s0] -> (d0 + d1 + d2 + 1, d2 + d1, (d0 * s0) * 8)>
+// CHECK: #map{{[0-9]*}} = affine_map<(d0, d1, d2)[s0] -> (d0 + d1 + d2 + 1, d1 + d2, (d0 * s0) * 8)>
 #map45 = affine_map<(i, j, k) [N] -> (1 + i + 3 + j - 3 + k, k + 5 + j - 5, 2*i*4*N)>
 
 // CHECK: #map{{[0-9]*}} = affine_map<(d0, d1, d2) -> (0, d1, d0 * 2, 0)>
diff --git a/mlir/unittests/IR/AffineExprTest.cpp b/mlir/unittests/IR/AffineExprTest.cpp
index 8a2d697540d5c..f8494ecb971c2 100644
--- a/mlir/unittests/IR/AffineExprTest.cpp
+++ b/mlir/unittests/IR/AffineExprTest.cpp
@@ -84,6 +84,20 @@ TEST(AffineExprTest, constantFolding) {
   ASSERT_EQ(cminfloordivcn1.getKind(), AffineExprKind::FloorDiv);
 }
 
+TEST(AffineExprTest, commutative) {
+  MLIRContext ctx;
+  OpBuilder b(&ctx);
+  auto c2 = b.getAffineConstantExpr(1);
+  auto d0 = b.getAffineDimExpr(0);
+  auto d1 = b.getAffineDimExpr(1);
+  auto s0 = b.getAffineSymbolExpr(0);
+  auto s1 = b.getAffineSymbolExpr(1);
+
+  ASSERT_EQ(d0 * d1, d1 * d0);
+  ASSERT_EQ(s0 + s1, s1 + s0);
+  ASSERT_EQ(s0 * c2, c2 * s0);
+}
+
 TEST(AffineExprTest, divisionSimplification) {
   MLIRContext ctx;
   OpBuilder b(&ctx);
@@ -147,3 +161,12 @@ TEST(AffineExprTest, simpleAffineExprFlattenerRegression) {
   ASSERT_TRUE(isa<AffineConstantExpr>(result));
   ASSERT_EQ(cast<AffineConstantExpr>(result).getValue(), 7);
 }
+
+TEST(AffineExprTest, simplifyCommutative) {
+  MLIRContext ctx;
+  OpBuilder b(&ctx);
+  auto s0 = b.getAffineSymbolExpr(0);
+  auto s1 = b.getAffineSymbolExpr(1);
+
+  ASSERT_EQ(s0 * s1 - s1 * s0 + 1, 1);
+}

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llvmbot commented Jul 3, 2025

@llvm/pr-subscribers-mlir

Author: Ivan Butygin (Hardcode84)

Changes

Order symbol/dim arguments by position, put dims before symbols and put constants to the right. This is to help affine simplifications.


Full diff: https://github.com/llvm/llvm-project/pull/146895.diff

4 Files Affected:

  • (modified) mlir/lib/IR/AffineExpr.cpp (+36-2)
  • (modified) mlir/test/Dialect/Affine/simplify-structures.mlir (+2-2)
  • (modified) mlir/test/IR/affine-map.mlir (+1-1)
  • (modified) mlir/unittests/IR/AffineExprTest.cpp (+23)
diff --git a/mlir/lib/IR/AffineExpr.cpp b/mlir/lib/IR/AffineExpr.cpp
index cc81f9d19aca7..856b29125602d 100644
--- a/mlir/lib/IR/AffineExpr.cpp
+++ b/mlir/lib/IR/AffineExpr.cpp
@@ -784,6 +784,36 @@ static AffineExpr simplifyAdd(AffineExpr lhs, AffineExpr rhs) {
   return nullptr;
 }
 
+static std::pair<AffineExpr, AffineExpr>
+orderCommutativeArgs(AffineExpr expr1, AffineExpr expr2) {
+  auto sym1 = dyn_cast<AffineSymbolExpr>(expr1);
+  auto sym2 = dyn_cast<AffineSymbolExpr>(expr2);
+  // Try to order by symbol/dim position first
+  if (sym1 && sym2)
+    return sym1.getPosition() < sym2.getPosition() ? std::pair{expr1, expr2}
+                                                   : std::pair{expr2, expr1};
+
+  auto dim1 = dyn_cast<AffineDimExpr>(expr1);
+  auto dim2 = dyn_cast<AffineDimExpr>(expr2);
+  if (dim1 && dim2)
+    return dim1.getPosition() < dim2.getPosition() ? std::pair{expr1, expr2}
+                                                   : std::pair{expr2, expr1};
+
+  // Put dims before symbols
+  if (dim1 && sym2)
+    return {dim1, sym2};
+
+  if (sym1 && dim2)
+    return {dim2, sym1};
+
+  // Move constants to the right
+  if (isa<AffineConstantExpr>(expr1) && !isa<AffineConstantExpr>(expr2))
+    return {expr2, expr1};
+
+  // Otherwise, keep original order
+  return {expr1, expr2};
+}
+
 AffineExpr AffineExpr::operator+(int64_t v) const {
   return *this + getAffineConstantExpr(v, getContext());
 }
@@ -791,9 +821,11 @@ AffineExpr AffineExpr::operator+(AffineExpr other) const {
   if (auto simplified = simplifyAdd(*this, other))
     return simplified;
 
+  auto [lhs, rhs] = orderCommutativeArgs(*this, other);
+
   StorageUniquer &uniquer = getContext()->getAffineUniquer();
   return uniquer.get<AffineBinaryOpExprStorage>(
-      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Add), *this, other);
+      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Add), lhs, rhs);
 }
 
 /// Simplify a multiply expression. Return nullptr if it can't be simplified.
@@ -856,9 +888,11 @@ AffineExpr AffineExpr::operator*(AffineExpr other) const {
   if (auto simplified = simplifyMul(*this, other))
     return simplified;
 
+  auto [lhs, rhs] = orderCommutativeArgs(*this, other);
+
   StorageUniquer &uniquer = getContext()->getAffineUniquer();
   return uniquer.get<AffineBinaryOpExprStorage>(
-      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Mul), *this, other);
+      /*initFn=*/{}, static_cast<unsigned>(AffineExprKind::Mul), lhs, rhs);
 }
 
 // Unary minus, delegate to operator*.
diff --git a/mlir/test/Dialect/Affine/simplify-structures.mlir b/mlir/test/Dialect/Affine/simplify-structures.mlir
index 6f2737a982752..653c2cb521637 100644
--- a/mlir/test/Dialect/Affine/simplify-structures.mlir
+++ b/mlir/test/Dialect/Affine/simplify-structures.mlir
@@ -508,7 +508,7 @@ func.func @test_not_trivially_true_or_false_returning_three_results() -> (index,
 // -----
 
 // Test simplification of mod expressions.
-// CHECK-DAG:   #[[$MOD:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s3 + s4 * s1 + (s0 - s1) mod s2)>
+// CHECK-DAG:   #[[$MOD:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s1 * s4 + s3 + (s0 - s1) mod s2)>
 // CHECK-DAG:   #[[$SIMPLIFIED_MOD_RHS:.*]] = affine_map<()[s0, s1, s2, s3] -> (s3 mod (s2 - s0 * s1))>
 // CHECK-DAG:   #[[$MODULO_AND_PRODUCT:.*]] = affine_map<()[s0, s1, s2, s3] -> (s0 * s1 + s3 - (-s0 + s3) mod s2)>
 // CHECK-LABEL: func @semiaffine_simplification_mod
@@ -547,7 +547,7 @@ func.func @semiaffine_simplification_floordiv_and_ceildiv(%arg0: index, %arg1: i
 
 // Test simplification of product expressions.
 // CHECK-DAG:   #[[$PRODUCT:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s3 + s4 + (s0 - s1) * s2)>
-// CHECK-DAG:   #[[$SUM_OF_PRODUCTS:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s2 + s2 * s0 + s3 + s3 * s0 + s3 * s1 + s4 + s4 * s1)>
+// CHECK-DAG:   #[[$SUM_OF_PRODUCTS:.*]] = affine_map<()[s0, s1, s2, s3, s4] -> (s0 * s2 + s0 * s3 + s1 * s3 + s1 * s4 + s2 + s3 + s4)>
 // CHECK-LABEL: func @semiaffine_simplification_product
 // CHECK-SAME:  (%[[ARG0:.*]]: index, %[[ARG1:.*]]: index, %[[ARG2:.*]]: index, %[[ARG3:.*]]: index, %[[ARG4:.*]]: index, %[[ARG5:.*]]: index)
 func.func @semiaffine_simplification_product(%arg0: index, %arg1: index, %arg2: index, %arg3: index, %arg4: index, %arg5: index) -> (index, index) {
diff --git a/mlir/test/IR/affine-map.mlir b/mlir/test/IR/affine-map.mlir
index 977aec2536b1e..6277b28561f36 100644
--- a/mlir/test/IR/affine-map.mlir
+++ b/mlir/test/IR/affine-map.mlir
@@ -139,7 +139,7 @@
 #map44 = affine_map<(i, j) -> (i - 2*j, j * 6 floordiv 4)>
 
 // Simplifications
-// CHECK: #map{{[0-9]*}} = affine_map<(d0, d1, d2)[s0] -> (d0 + d1 + d2 + 1, d2 + d1, (d0 * s0) * 8)>
+// CHECK: #map{{[0-9]*}} = affine_map<(d0, d1, d2)[s0] -> (d0 + d1 + d2 + 1, d1 + d2, (d0 * s0) * 8)>
 #map45 = affine_map<(i, j, k) [N] -> (1 + i + 3 + j - 3 + k, k + 5 + j - 5, 2*i*4*N)>
 
 // CHECK: #map{{[0-9]*}} = affine_map<(d0, d1, d2) -> (0, d1, d0 * 2, 0)>
diff --git a/mlir/unittests/IR/AffineExprTest.cpp b/mlir/unittests/IR/AffineExprTest.cpp
index 8a2d697540d5c..f8494ecb971c2 100644
--- a/mlir/unittests/IR/AffineExprTest.cpp
+++ b/mlir/unittests/IR/AffineExprTest.cpp
@@ -84,6 +84,20 @@ TEST(AffineExprTest, constantFolding) {
   ASSERT_EQ(cminfloordivcn1.getKind(), AffineExprKind::FloorDiv);
 }
 
+TEST(AffineExprTest, commutative) {
+  MLIRContext ctx;
+  OpBuilder b(&ctx);
+  auto c2 = b.getAffineConstantExpr(1);
+  auto d0 = b.getAffineDimExpr(0);
+  auto d1 = b.getAffineDimExpr(1);
+  auto s0 = b.getAffineSymbolExpr(0);
+  auto s1 = b.getAffineSymbolExpr(1);
+
+  ASSERT_EQ(d0 * d1, d1 * d0);
+  ASSERT_EQ(s0 + s1, s1 + s0);
+  ASSERT_EQ(s0 * c2, c2 * s0);
+}
+
 TEST(AffineExprTest, divisionSimplification) {
   MLIRContext ctx;
   OpBuilder b(&ctx);
@@ -147,3 +161,12 @@ TEST(AffineExprTest, simpleAffineExprFlattenerRegression) {
   ASSERT_TRUE(isa<AffineConstantExpr>(result));
   ASSERT_EQ(cast<AffineConstantExpr>(result).getValue(), 7);
 }
+
+TEST(AffineExprTest, simplifyCommutative) {
+  MLIRContext ctx;
+  OpBuilder b(&ctx);
+  auto s0 = b.getAffineSymbolExpr(0);
+  auto s1 = b.getAffineSymbolExpr(1);
+
+  ASSERT_EQ(s0 * s1 - s1 * s0 + 1, 1);
+}

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LGTM with comment addressed.

Comment on lines 809 to 811
// Move constants to the right
if (isa<AffineConstantExpr>(expr1) && !isa<AffineConstantExpr>(expr2))
return {expr2, expr1};
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Could you double-check composition with special cases. IIRC, in multiplication, we wanted to put the constant on the LHS, and there was something special about -1 as well.

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Looks like simplifyMul/simplifyAdd already handles it, so I can just drop this case.

@kuhar kuhar requested a review from qedawkins July 3, 2025 22:24
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Rather than swapping while constructing expressions, can we do this during simplifyAdd/simplifyMul? Having the operands of an expression you just created get swapped sounds surprising to me.

@Hardcode84
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Rather than swapping while constructing expressions, can we do this during simplifyAdd/simplifyMul? Having the operands of an expression you just created get swapped sounds surprising to me.

I kind of don't like how simplifyMul calls constructor (and thus itself) recursively, you can end up with infinite recursion if not careful.

@Hardcode84
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Hardcode84 commented Jul 4, 2025

Actually, I can try to canonicalize longer chains, let me check something.

@Hardcode84
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I've tried to rearrange dims/symbols order across nested bin ops (AffineExpr is already doing this for the constants), but it's probably not worth it (and also, more unbounded recursion in constructor)
Hardcode84@ba6bb3f

Let's keep this simple version for now.

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Rather than swapping while constructing expressions, can we do this during simplifyAdd/simplifyMul? Having the operands of an expression you just created get swapped sounds surprising to me.

I kind of don't like how simplifyMul calls constructor (and thus itself) recursively, you can end up with infinite recursion if not careful.

Ouch, that does sounds bad, ok makes sense to me.

@Hardcode84 Hardcode84 merged commit 454e4e3 into llvm:main Jul 4, 2025
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@Hardcode84 Hardcode84 deleted the order-affine-expr branch July 4, 2025 20:34
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4 participants