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QRunnable: fix Coverity dead-code warnings in create()

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Coverity complained about the call to warnNullCallable() being dead
code for most instantiations of the create() function template. It's
right, of course, even though warning in a template that clearly has
instantations where it's not dead code isn't exactly helpful.

Nonetheless, take the opportinity to avoid the dead code warning at
the expense of a bit or un-DRY-ing:

- because we now use them more than once, cache the result of
  is_*function_* predicates in constexpr variables

- then scope the is_null variable such that its use is not subject to
  dead-code removal anymore (at instantiation time; it may still be
  removed by the optimizer)

As drive-bys, add a comment about the reinterpret_cast, and make the
custom template predicates variable- instead of class templates.

Coverity-Id: 407640
Change-Id: I272223042c2aae9d814e82c466e1d29e1c42bfa1
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
This commit is contained in:
Marc Mutz 2023-05-08 11:42:32 +02:00
parent 5ddfa8bbe6
commit 6da9662143
1 changed files with 20 additions and 12 deletions
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22
src/corelib/thread/qrunnable.h
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@ -101,27 +101,35 @@ public:
namespace QtPrivate {
template <typename T>
using is_function_pointer = std::conjunction<std::is_pointer<T>, std::is_function<std::remove_pointer_t<T>>>;
constexpr inline bool is_function_pointer_v = std::conjunction_v<
std::is_pointer<T>,
std::is_function<std::remove_pointer_t<T>>
>;
template <typename T>
struct is_std_function : std::false_type {};
constexpr inline bool is_std_function_v = false;
template <typename T>
struct is_std_function<std::function<T>> : std::true_type {};
constexpr inline bool is_std_function_v<std::function<T>> = true;
} // namespace QtPrivate
template <typename Callable, QRunnable::if_callable<Callable>>
QRunnable *QRunnable::create(Callable &&functionToRun)
{
bool is_null = false;
if constexpr(QtPrivate::is_std_function<std::decay_t<Callable>>::value)
using F = std::decay_t<Callable>;
constexpr bool is_std_function = QtPrivate::is_std_function_v<F>;
constexpr bool is_function_pointer = QtPrivate::is_function_pointer_v<F>;
if constexpr (is_std_function || is_function_pointer) {
bool is_null;
if constexpr (is_std_function) {
is_null = !functionToRun;
if constexpr(QtPrivate::is_function_pointer<std::decay_t<Callable>>::value) {
} else if constexpr (is_function_pointer) {
// shut up warnings about functions always having a non-null address:
const void *functionPtr = reinterpret_cast<void *>(functionToRun);
is_null = !functionPtr;
}
if (is_null)
return warnNullCallable();
}
return new QGenericRunnable(std::forward<Callable>(functionToRun));
}