[Mlir-commits] [mlir] [MLIR][arith] Fold or(a, or(a, b)) to or(a, b) (PR #228386)

[Chibuoyim Ogbonna]

https://github.com/bruteforceboy created https://github.com/llvm/llvm-project/pull/228386

`arith.andi` already folds `and(a, and(a, b))` to `and(a, b)`, but `arith.ori` doesn't perform the equivalent fold, so using canonicalize misses this opportunity.

Generalize the existing helper and use it for both ops.

>From 32b715c377e5907ebbf3ca49e437ea5b8c698fb4 Mon Sep 17 00:00:00 2001
From: bruteforceboy <chibuoyim.faith.ogbonna at huawei.com>
Date: Fri, 2 Oct 2026 11:22:22 +0100
Subject: [PATCH] [MLIR][arith] Fold or(a, or(a, b)) to or(a, b)

---
 mlir/lib/Dialect/Arith/IR/ArithOps.cpp    | 14 ++++--
 mlir/test/Dialect/Arith/canonicalize.mlir | 54 +++++++++++++++++++++++
 2 files changed, 64 insertions(+), 4 deletions(-)

diff --git a/mlir/lib/Dialect/Arith/IR/ArithOps.cpp b/mlir/lib/Dialect/Arith/IR/ArithOps.cpp
index 01d0c18670cb8..be02143ea2771 100644
--- a/mlir/lib/Dialect/Arith/IR/ArithOps.cpp
+++ b/mlir/lib/Dialect/Arith/IR/ArithOps.cpp
@@ -1132,11 +1132,13 @@ Speculation::Speculatability arith::RemSIOp::getSpeculatability() {
 // AndIOp
 //===----------------------------------------------------------------------===//
 
-/// Fold `and(a, and(a, b))` to `and(a, b)`
-static Value foldAndIofAndI(arith::AndIOp op) {
+/// Fold `op(a, op(a, b))` to `op(a, b)` for an associative, commutative and
+/// idempotent `op` (e.g. `and`, `or`).
+template <typename OpTy>
+static Value foldIdempotentOfSameOp(OpTy op) {
   for (bool reversePrev : {false, true}) {
     auto prev = (reversePrev ? op.getRhs() : op.getLhs())
-                    .getDefiningOp<arith::AndIOp>();
+                    .template getDefiningOp<OpTy>();
     if (!prev)
       continue;
 
@@ -1170,7 +1172,7 @@ OpFoldResult arith::AndIOp::fold(FoldAdaptor adaptor) {
     return Builder(getContext()).getZeroAttr(getType());
 
   /// and(a, and(a, b)) -> and(a, b)
-  if (Value result = foldAndIofAndI(*this))
+  if (Value result = foldIdempotentOfSameOp(*this))
     return result;
 
   return constFoldBinaryOp<IntegerAttr>(
@@ -1204,6 +1206,10 @@ OpFoldResult arith::OrIOp::fold(FoldAdaptor adaptor) {
       intValue.isAllOnes())
     return getLhs().getDefiningOp<XOrIOp>().getRhs();
 
+  /// or(a, or(a, b)) -> or(a, b)
+  if (Value result = foldIdempotentOfSameOp(*this))
+    return result;
+
   return constFoldBinaryOp<IntegerAttr>(
       adaptor.getOperands(),
       [](APInt a, const APInt &b) { return std::move(a) | b; });
diff --git a/mlir/test/Dialect/Arith/canonicalize.mlir b/mlir/test/Dialect/Arith/canonicalize.mlir
index 8a46c963f02d7..9c512cd605d7d 100644
--- a/mlir/test/Dialect/Arith/canonicalize.mlir
+++ b/mlir/test/Dialect/Arith/canonicalize.mlir
@@ -4437,6 +4437,60 @@ func.func @andand3(%a : i32, %b : i32) -> i32 {
 
 // -----
 
+/// or(a, or(a, b)) -> or(a, b)
+
+// CHECK-LABEL: @oror0
+//  CHECK-SAME:   (%[[A:.*]]: i32, %[[B:.*]]: i32)
+//       CHECK:   %[[RES:.*]] = arith.ori %[[A]], %[[B]] : i32
+//       CHECK:   return %[[RES]]
+func.func @oror0(%a : i32, %b : i32) -> i32 {
+  %c = arith.ori %a, %b : i32
+  %res = arith.ori %a, %c : i32
+  return %res : i32
+}
+
+// CHECK-LABEL: @oror1
+//  CHECK-SAME:   (%[[A:.*]]: i32, %[[B:.*]]: i32)
+//       CHECK:   %[[RES:.*]] = arith.ori %[[A]], %[[B]] : i32
+//       CHECK:   return %[[RES]]
+func.func @oror1(%a : i32, %b : i32) -> i32 {
+  %c = arith.ori %a, %b : i32
+  %res = arith.ori %c, %a : i32
+  return %res : i32
+}
+
+// CHECK-LABEL: @oror2
+//  CHECK-SAME:   (%[[A:.*]]: i32, %[[B:.*]]: i32)
+//       CHECK:   %[[RES:.*]] = arith.ori %[[A]], %[[B]] : i32
+//       CHECK:   return %[[RES]]
+func.func @oror2(%a : i32, %b : i32) -> i32 {
+  %c = arith.ori %a, %b : i32
+  %res = arith.ori %b, %c : i32
+  return %res : i32
+}
+
+// CHECK-LABEL: @oror3
+//  CHECK-SAME:   (%[[A:.*]]: i32, %[[B:.*]]: i32)
+//       CHECK:   %[[RES:.*]] = arith.ori %[[A]], %[[B]] : i32
+//       CHECK:   return %[[RES]]
+func.func @oror3(%a : i32, %b : i32) -> i32 {
+  %c = arith.ori %a, %b : i32
+  %res = arith.ori %c, %b : i32
+  return %res : i32
+}
+
+// CHECK-LABEL: @oror_vector
+//  CHECK-SAME:   (%[[A:.*]]: vector<4xi32>, %[[B:.*]]: vector<4xi32>)
+//       CHECK:   %[[RES:.*]] = arith.ori %[[A]], %[[B]] : vector<4xi32>
+//       CHECK:   return %[[RES]]
+func.func @oror_vector(%a : vector<4xi32>, %b : vector<4xi32>) -> vector<4xi32> {
+  %c = arith.ori %a, %b : vector<4xi32>
+  %res = arith.ori %c, %a : vector<4xi32>
+  return %res : vector<4xi32>
+}
+
+// -----
+
 // CHECK-LABEL: @truncIShrSIToTrunciShrUI
 //  CHECK-SAME:   (%[[A:.+]]: i64)
 //  CHECK-NEXT:   %[[C32:.+]] = arith.constant 32 : i64