MitalAshok marked an inline comment as not done.
MitalAshok added inline comments.
================
Comment at: clang/test/SemaCXX/varargs.cpp:34
enum Unscoped1 { One = 0x7FFFFFFF };
- (void)__builtin_va_arg(ap, Unscoped1); // ok
+ (void)__builtin_va_arg(ap, Unscoped1); // expected-warning {{second argument
to 'va_arg' is of promotable type 'Unscoped1'; this va_arg has undefined
behavior because arguments will be promoted to 'int'}}
----------------
MitalAshok wrote:
> Unscoped1 is promoted to int when passed to a variadic function.
>
> The underlying type for Unscoped1 is unsigned int, so only Unscoped1 and
> unsigned int are compatible, not Unscoped1 and int. An Unscoped1 passed to a
> variadic function must be retrieved via va_arg(ap, int).
>
Although I guess the warning is now wrong because even though `void f(int x,
...) { std::va_list ap; va_start(ap, x); va_arg(ap, Unscoped1); }` `f(0,
Unscoped1{2})` would be UB, `f(0, 2u)` would not be UB.
The user still should be warned about it, so I could create a new warning
"second argument to 'va_arg' is of promotable enumeration type 'Unscoped1';
this va_arg may have undefined behavior because arguments of this enumeration
type will be promoted to 'int', not the underlying type 'unsigned int'", and
maybe suggest a fix `Unscoped1{va_arg(ap, unsigned)}`.
Or we could ignore it and pretend that int and enums with underlying types
unsigned are compatible for the purposes of va_arg
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D156054/new/
https://reviews.llvm.org/D156054
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