From b0e515c9a00c25b6606d784fea6feca1e8705891 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Markus=20B=C3=B6ck?= <markus.boeck02@gmail.com>
Date: Wed, 24 Aug 2022 13:09:46 +0200
Subject: [PATCH] [mlir][arith] Fold `andi x, not(x)` to zero

A bitwise and with the bitwise negate of itself is always 0, regardless of the integer type. This patch adds detection of such a pattern in `arith.andi`s `fold` method.

Differential Revision: https://reviews.llvm.org/D131860
---
 mlir/lib/Dialect/Arithmetic/IR/ArithmeticOps.cpp | 10 +++++++++
 mlir/test/Dialect/Arithmetic/canonicalize.mlir   | 27 ++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/mlir/lib/Dialect/Arithmetic/IR/ArithmeticOps.cpp b/mlir/lib/Dialect/Arithmetic/IR/ArithmeticOps.cpp
index 8546a37..11e64ff 100644
--- a/mlir/lib/Dialect/Arithmetic/IR/ArithmeticOps.cpp
+++ b/mlir/lib/Dialect/Arithmetic/IR/ArithmeticOps.cpp
@@ -574,6 +574,16 @@ OpFoldResult arith::AndIOp::fold(ArrayRef<Attribute> operands) {
   APInt intValue;
   if (matchPattern(getRhs(), m_ConstantInt(&intValue)) && intValue.isAllOnes())
     return getLhs();
+  /// and(x, not(x)) -> 0
+  if (matchPattern(getRhs(), m_Op<XOrIOp>(matchers::m_Val(getLhs()),
+                                          m_ConstantInt(&intValue))) &&
+      intValue.isAllOnes())
+    return IntegerAttr::get(getType(), 0);
+  /// and(not(x), x) -> 0
+  if (matchPattern(getLhs(), m_Op<XOrIOp>(matchers::m_Val(getRhs()),
+                                          m_ConstantInt(&intValue))) &&
+      intValue.isAllOnes())
+    return IntegerAttr::get(getType(), 0);
 
   return constFoldBinaryOp<IntegerAttr>(
       operands, [](APInt a, const APInt &b) { return std::move(a) & b; });
diff --git a/mlir/test/Dialect/Arithmetic/canonicalize.mlir b/mlir/test/Dialect/Arithmetic/canonicalize.mlir
index f99a070..a1ab1be 100644
--- a/mlir/test/Dialect/Arithmetic/canonicalize.mlir
+++ b/mlir/test/Dialect/Arithmetic/canonicalize.mlir
@@ -1532,3 +1532,30 @@ func.func @test_remf_vec() -> (vector<4xf32>) {
   %0 = arith.remf %v1, %v2 : vector<4xf32>
   return %0 : vector<4xf32>
 }
+
+// -----
+
+// CHECK-LABEL: @test_andi_not_fold_rhs(
+// CHECK-SAME: %[[ARG0:[[:alnum:]]+]]
+// CHECK: %[[C:.*]] = arith.constant 0 : index
+// CHECK: return %[[C]]
+
+func.func @test_andi_not_fold_rhs(%arg0 : index) -> index {
+    %0 = arith.constant -1 : index
+    %1 = arith.xori %arg0, %0 : index
+    %2 = arith.andi %arg0, %1 : index
+    return %2 : index
+}
+
+
+// CHECK-LABEL: @test_andi_not_fold_lhs(
+// CHECK-SAME: %[[ARG0:[[:alnum:]]+]]
+// CHECK: %[[C:.*]] = arith.constant 0 : index
+// CHECK: return %[[C]]
+
+func.func @test_andi_not_fold_lhs(%arg0 : index) -> index {
+    %0 = arith.constant -1 : index
+    %1 = arith.xori %arg0, %0 : index
+    %2 = arith.andi %1, %arg0 : index
+    return %2 : index
+}
-- 
2.7.4