[ET][Portable] Add util to check for overflow when casting scalar

Differential Revision: [D77382647](https://our.internmc.facebook.com/intern/diff/D77382647/)

[ghstack-poisoned]

Author: manuelcandales

kernels/portable/cpu/scalar_utils.h

@@ -11,6 +11,7 @@
 #include <cmath>
 #include <limits>
 
+#include <c10/util/overflows.h>
 #include <executorch/kernels/portable/cpu/selective_build.h>
 #include <executorch/runtime/core/exec_aten/exec_aten.h>
 #include <executorch/runtime/core/exec_aten/util/scalar_type_util.h>
@@ -287,6 +288,29 @@ inline int64_t scalar_to<int64_t>(const Scalar& s) {
                              : s.to<int64_t>();
 }
 
+namespace internal {
+
+template <typename To, typename From>
+std::optional<To> check_overflow_cast(From in) {
+  // Converting to bool can't overflow so we exclude this case from checking.
+  if (!std::is_same_v<To, bool> && c10::overflows<To, From>(in)) {
+    return std::nullopt;
+  }
+  return static_cast<To>(in);
+}
+
+template <typename To>
+std::optional<To> check_overflow_scalar_cast(const Scalar& in) {
+  if (in.isBoolean()) {
+    return check_overflow_cast<To>(in.to<bool>());
+  } else if (in.isFloatingPoint()) {
+    return check_overflow_cast<To>(in.to<double>());
+  } else {
+    return check_overflow_cast<To>(in.to<int64_t>());
+  }
+}
+
+} // namespace internal
 } // namespace utils
 } // namespace native
 } // namespace executor