Make sure warning is present before assignment

Author: clementval

flang/lib/Common/Fortran.cpp

@@ -138,7 +138,7 @@ bool AreCompatibleCUDADataAttrs(std::optional<CUDADataAttr> x,
                 (*y == CUDADataAttr::Managed || *y == CUDADataAttr::Unified ||
                     *y == CUDADataAttr::Shared)) ||
             (!y && (isCudaUnified || isCudaManaged))) {
-          if (y && *y == CUDADataAttr::Shared) {
+          if (y && *y == CUDADataAttr::Shared && warning) {
             *warning = "SHARED attribute ignored"s;
           }
           return true;

flang/lib/Evaluate/characteristics.cpp

@@ -1762,7 +1762,6 @@ bool DistinguishUtils::Distinguishable(
 bool DistinguishUtils::Distinguishable(
     const DummyDataObject &x, const DummyDataObject &y) const {
   using Attr = DummyDataObject::Attr;
-  std::optional<std::string> warning;
   if (Distinguishable(x.type, y.type, x.ignoreTKR | y.ignoreTKR)) {
     return true;
   } else if (x.attrs.test(Attr::Allocatable) && y.attrs.test(Attr::Pointer) &&
@@ -1772,7 +1771,7 @@ bool DistinguishUtils::Distinguishable(
       x.intent != common::Intent::In) {
     return true;
   } else if (!common::AreCompatibleCUDADataAttrs(x.cudaDataAttr, y.cudaDataAttr,
-                 x.ignoreTKR | y.ignoreTKR, &warning,
+                 x.ignoreTKR | y.ignoreTKR, nullptr,
                  /*allowUnifiedMatchingRule=*/false)) {
     return true;
   } else if (features_.IsEnabled(