[flang] Impose DATA initialization size limit to avoid crashing

[klausler]

Summary

Impose a large but finite limit on the size of a variable being
initialized in a DATA statement to provide a readable error message
for artificial test cases that's better than a memory allocation
failure crash.

flang/lib/Semantics/data-to-inits.cpp

 // done in lowering, so don't do it here in semantics; but the code remains here
 // in case we change our minds.
 static constexpr bool makeDefaultInitializationExplicit{false};
 
 // Whether to delete the original "init()" initializers from storage-associated
 // objects and pointers.
 static constexpr bool removeOriginalInits{false};
 
+// Impose a hard limit that's more than large enough for real applications but
+// small enough to cause artificial stress tests to fail reasonably instead of
+// crashing the compiler with a memory allocation failure.
+static constexpr auto maxDataInitBytes{std::size_t{1000000000}}; // 1GiB
+
 namespace Fortran::semantics {
 
 // Steps through a list of values in a DATA statement set; implements
 // repetition.
 template <typename DSV = parser::DataStmtValue> class ValueListIterator {
 public:
   ValueListIterator(SemanticsContext &context, const std::list<DSV> &list)
       : context_{context}, end_{list.end()}, at_{list.begin()} {
return false;
                  offsetSymbol.offset() + offsetSymbol.size()) > symbol.size()) {
     OutOfRangeError();
     return false;
   }
 
   const SomeExpr *expr{*values_};
   if (!expr) {
     CHECK(exprAnalyzer_.context().AnyFatalError());
+  } else if (symbol.size() > maxDataInitBytes) {
+    evaluate::AttachDeclaration(
+        exprAnalyzer_.context().Say(
+            "'%s' is too large to initialize with a DATA statement"_todo_en_US,
+            symbol.name()),
+        symbol);
+    return false;
   } else if (isPointer) {
     if (static_cast<std::size_t>(offsetSymbol.offset() + offsetSymbol.size()) >
         symbol.size()) {
       OutOfRangeError();
     } else if (evaluate::IsNullPointer(*expr)) {
       // nothing to do; rely on zero initialization
       return true;
     } else if (isProcPointer) {

flang/lib/Semantics/expression.cpp

if (const Symbol *sym{sc.component.symbol}) {
                 *sc.component.symbol, pair.second, isSubroutine);
             return std::nullopt;
           }
         }
         std::optional<DataRef> dataRef{ExtractDataRef(std::move(*dtExpr))};
         if (dataRef && !CheckDataRef(*dataRef)) {
           return std::nullopt;
         }
+        if (dataRef && dataRef->Rank() > 0 && sym->attrs().test(semantics::Attr::NOPASS)) {
+          // C1529 seems unnecessary and most compilers don't enforce it.
+          Say(sc.component.source,
+            "Base of procedure component reference should be scalar when NOPASS component or binding '%s' is referenced"_port_en_US, sc.component.source);
+        }
         if (const Symbol *resolution{
                 GetBindingResolution(dtExpr->GetType(), *sym)}) {
           AddPassArg(arguments, std::move(*dtExpr), *sym, false);
           return CalleeAndArguments{
               ProcedureDesignator{*resolution}, std::move(arguments)};
         } else if (dataRef.has_value()) {
           if (sym->attrs().test(semantics::Attr::NOPASS)) {
             return CalleeAndArguments{