Index: flang/lib/Optimizer/Transforms/SimplifyIntrinsics.cpp
===================================================================
--- flang/lib/Optimizer/Transforms/SimplifyIntrinsics.cpp
+++ flang/lib/Optimizer/Transforms/SimplifyIntrinsics.cpp
@@ -617,8 +617,18 @@
   auto genBodyOp = [](fir::FirOpBuilder builder, mlir::Location loc,
                       mlir::Type elementType, mlir::Value elem1,
                       mlir::Value elem2) -> mlir::Value {
-    if (elementType.isa<mlir::FloatType>())
-      return builder.create<mlir::arith::MaxFOp>(loc, elem1, elem2);
+    if (elementType.isa<mlir::FloatType>()) {
+      // arith.maxf later converted to llvm.intr.maxnum does not work
+      // correctly for NaNs and -0.0 (see maxnum/minnum pattern matching
+      // in LLVM's InstCombine pass). Moreover, llvm.intr.maxnum
+      // for F128 operands is lowered into fmaxl call by LLVM.
+      // This libm function may not work properly for F128 arguments
+      // on targets where long double is not F128. It is an LLVM issue,
+      // but we just use normal select here to resolve all the cases.
+      auto compare = builder.create<mlir::arith::CmpFOp>(
+          loc, mlir::arith::CmpFPredicate::OGT, elem1, elem2);
+      return builder.create<mlir::arith::SelectOp>(loc, compare, elem1, elem2);
+    }
     if (elementType.isa<mlir::IntegerType>())
       return builder.create<mlir::arith::MaxSIOp>(loc, elem1, elem2);
 
Index: flang/test/Transforms/simplifyintrinsics.fir
===================================================================
--- flang/test/Transforms/simplifyintrinsics.fir
+++ flang/test/Transforms/simplifyintrinsics.fir
@@ -899,7 +899,8 @@
 // CHECK:           %[[RES:.*]] = fir.do_loop %[[ITER:.*]] = %[[CINDEX_0]] to %[[EXTENT]] step %[[CINDEX_1]] iter_args(%[[MAX]] = %[[NEG_DBL_MAX]]) -> (f64) {
 // CHECK:             %[[ITEM:.*]] = fir.coordinate_of %[[ARR_BOX_F64]], %[[ITER]] : (!fir.box<!fir.array<?xf64>>, index) -> !fir.ref<f64>
 // CHECK:             %[[ITEM_VAL:.*]] = fir.load %[[ITEM]] : !fir.ref<f64>
-// CHECK:             %[[NEW_MAX:.*]] = arith.maxf %[[ITEM_VAL]], %[[MAX]] : f64
+// CHECK:             %[[CMP:.*]] = arith.cmpf ogt, %[[ITEM_VAL]], %[[MAX]] : f64
+// CHECK:             %[[NEW_MAX:.*]] = arith.select %[[CMP]], %[[ITEM_VAL]], %[[MAX]] : f64
 // CHECK:             fir.result %[[NEW_MAX]] : f64
 // CHECK:           }
 // CHECK:           return %[[RES]] : f64