[mlir][arith] Add neutral element support to arith.maxnumf/arith.minnumf

For maxnumf and minnumf, the result of calculations involving NaN will be
another value, so their neutral element is set to NaN.

Author: cxy-1993

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

@@ -2467,6 +2467,12 @@ TypedAttr mlir::arith::getIdentityValueAttr(AtomicRMWKind kind, Type resultType,
                            : APFloat::getInf(semantic, /*Negative=*/true);
     return builder.getFloatAttr(resultType, identity);
   }
+  case AtomicRMWKind::maxnumf: {
+    const llvm::fltSemantics &semantic =
+        llvm::cast<FloatType>(resultType).getFloatSemantics();
+    APFloat identity = APFloat::getNaN(semantic, /*Negative=*/true);
+    return builder.getFloatAttr(resultType, identity);
+  }
   case AtomicRMWKind::addf:
   case AtomicRMWKind::addi:
   case AtomicRMWKind::maxu:
@@ -2489,6 +2495,12 @@ TypedAttr mlir::arith::getIdentityValueAttr(AtomicRMWKind kind, Type resultType,
 
     return builder.getFloatAttr(resultType, identity);
   }
+  case AtomicRMWKind::minnumf: {
+    const llvm::fltSemantics &semantic =
+        llvm::cast<FloatType>(resultType).getFloatSemantics();
+    APFloat identity = APFloat::getNaN(semantic, /*Negative=*/false);
+    return builder.getFloatAttr(resultType, identity);
+  }
   case AtomicRMWKind::mins:
     return builder.getIntegerAttr(
         resultType, APInt::getSignedMaxValue(
@@ -2518,6 +2530,8 @@ std::optional<TypedAttr> mlir::arith::getNeutralElement(Operation *op) {
           .Case([](arith::MulFOp op) { return AtomicRMWKind::mulf; })
           .Case([](arith::MaximumFOp op) { return AtomicRMWKind::maximumf; })
           .Case([](arith::MinimumFOp op) { return AtomicRMWKind::minimumf; })
+          .Case([](arith::MaxNumFOp op) { return AtomicRMWKind::maxnumf; })
+          .Case([](arith::MinNumFOp op) { return AtomicRMWKind::minnumf; })
           // Integer operations.
           .Case([](arith::AddIOp op) { return AtomicRMWKind::addi; })
           .Case([](arith::OrIOp op) { return AtomicRMWKind::ori; })

mlir/test/Dialect/Linalg/transform-op-split-reduction.mlir

@@ -407,3 +407,50 @@ module attributes {transform.with_named_sequence} {
       transform.yield
   }
 }
+
+// -----
+
+// Checks we use nan as the neutral element for maxnumf op.
+func.func @generic_split_maxnumf(%in: tensor<32xf32>, %out: tensor<f32>) -> tensor<f32> {
+  %r = linalg.generic {indexing_maps = [affine_map<(d0) -> (d0)>,
+                                        affine_map<(d0) -> ()>],
+        iterator_types = ["reduction"]}
+  ins(%in : tensor<32xf32>)
+  outs(%out : tensor<f32>) {
+  ^bb0(%arg1: f32, %arg2: f32):
+    %y = arith.maxnumf %arg1, %arg2 : f32
+    linalg.yield %y : f32
+  } -> tensor<f32>
+  return %r : tensor<f32>
+}
+
+//  CHECK-DAG: #[[$MAP0:.*]] = affine_map<(d0, d1) -> (d0, d1)>
+//  CHECK-DAG: #[[$MAP1:.*]] = affine_map<(d0, d1) -> (d1)>
+//  CHECK-DAG: #[[$MAP2:.*]] = affine_map<(d0) -> (d0)>
+//  CHECK-DAG: #[[$MAP3:.*]] = affine_map<(d0) -> ()>
+// CHECK-LABEL:  func @generic_split_maxnumf
+//  The float value 0xFFC00000 that is filled into the init tensor represents NaN.
+//  CHECK-DAG: %[[ID:.*]] = arith.constant 0xFFC00000 : f32
+//  CHECK-DAG: %[[I1:.*]] = tensor.expand_shape %{{.*}}[0, 1]] output_shape [8, 4] : tensor<32xf32> into tensor<8x4xf32>
+//  CHECK-DAG: %[[INI:.*]] = tensor.empty() : tensor<4xf32>
+//      CHECK: %[[F:.*]] = linalg.fill ins(%[[ID]] : f32) outs(%[[INI]] : tensor<4xf32>) -> tensor<4xf32>
+//      CHECK: %[[G:.*]] = linalg.generic {indexing_maps = [#[[$MAP0]], #[[$MAP1]]], iterator_types = ["reduction", "parallel"]}
+// CHECK-SAME:   ins(%[[I1]] : tensor<8x4xf32>) outs(%[[F]] : tensor<4xf32>) {
+//      CHECK:   arith.maxnumf
+//      CHECK:   linalg.yield
+//      CHECK: } -> tensor<4xf32>
+//      CHECK: %[[R:.*]] = linalg.generic {indexing_maps = [#[[$MAP2]], #[[$MAP3]]], iterator_types = ["reduction"]}
+// CHECK-SAME:   ins(%[[G]] : tensor<4xf32>) outs(%{{.*}} : tensor<f32>) {
+//      CHECK:   arith.maxnumf {{.*}}
+//      CHECK:   linalg.yield
+//      CHECK:  } -> tensor<f32>
+//      CHECK: return %[[R]] : tensor<f32>
+
+module attributes {transform.with_named_sequence} {
+  transform.named_sequence @__transform_main(%arg1: !transform.any_op {transform.readonly}) {
+    %0 = transform.structured.match ops{["linalg.generic"]} in %arg1 : (!transform.any_op) -> !transform.any_op
+    %1:4 = transform.structured.split_reduction %0 { split_factor = 4, insert_split_dimension = 0, inner_parallel}
+      : (!transform.any_op) -> (!transform.any_op, !transform.any_op, !transform.any_op, !transform.any_op)
+      transform.yield
+  }
+}