[cfe-users] Unexpected (IMO) constant-conversion warning

David Blaikie via cfe-users cfe-users at lists.llvm.org
Mon Jun 25 10:20:28 PDT 2018

Yeah, the problem is that '~a' is an expression of type 'int' due to
something called "the usual arithmetic conversions" - basically in almost
any arithmetic expression in C++, all the smaller int types get promoted up
to int (this is oversimplifying a bit - but sufficient here - if you look
up that phrase you'll find a more detailed description) and then the
arithmetic is done. So there's an implicit widening from uint8_t to int of
the 'a' before the ~ is done. So you have to cast back down.

On Wed, Jun 20, 2018 at 6:35 PM Szymon Zimnowoda via cfe-users <
cfe-users at lists.llvm.org> wrote:

> Hello, consider following code:
> https://godbolt.org/g/UN8xTy <https://godbolt.org/g/n3Rt9D>
> I do not understand, why overflow warning is here, there is no explicite
> int in this code.
> When removing constexpr, warning disappears, when changing to:
> static constexpr uint8_t b = uint8_t{~a};
> warning disappears.
> Could someone explain it to me?
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