[Flang][Runtime] Fix implicit conversion warning when targeting 32bit architecture

On 32 bit systems, TypeParameterValue is 64bit wide while CFI_index_t is 32bit wide.

Author: serge-sans-paille

flang/runtime/derived.cpp

@@ -23,10 +23,16 @@ static RT_API_ATTRS void GetComponentExtents(SubscriptValue (&extents)[maxRank],
     const typeInfo::Component &comp, const Descriptor &derivedInstance) {
   const typeInfo::Value *bounds{comp.bounds()};
   for (int dim{0}; dim < comp.rank(); ++dim) {
-    SubscriptValue lb{bounds[2 * dim].GetValue(&derivedInstance).value_or(0)};
-    SubscriptValue ub{
-        bounds[2 * dim + 1].GetValue(&derivedInstance).value_or(0)};
-    extents[dim] = ub >= lb ? ub - lb + 1 : 0;
+    auto lb = bounds[2 * dim].GetValue(&derivedInstance).value_or(0);
+    auto ub = bounds[2 * dim + 1].GetValue(&derivedInstance).value_or(0);
+    if (ub >= lb) {
+      auto bound_diff = ub - lb;
+      assert(bound_diff <= std::numeric_limits<SubscriptValue>::max() &&
+          "array bound overflow");
+      extents[dim] = bound_diff;
+    } else {
+      extents[dim] = 0;
+    }
   }
 }