[Bug c/84764] Wrong warning "so large that it is unsigned" for __int128 constant

["daniel.lundin.mail at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84764

Daniel Lundin <daniel.lundin.mail at gmail dot com> changed:

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--- Comment #3 from Daniel Lundin <daniel.lundin.mail at gmail dot com> ---
This is a bug as in the wrong text is displayed in the diagnostic message. gcc
picks `__int128` and it is not an unsigned type.

Decimal integer constants use the the quoted list in 6.4.4.1: `int` then `long`
then `long long`. Therefore this normative text (from C99 to C23) applies: "If
all of the types in the list for the constant are signed, the extended integer
type shall be signed."

gcc behaves just like required too, since `__int128` ought to be one of the
extended integer types and it is signed.

I would guess this message is some remain from C90 where extended integer types
didn't exist. Compiling with -std=c90 adds an additional warning "warning: this
decimal constant is unsigned only in ISO C90". It would appear that this is the
correct warning that should always be displayed. Seems to be a minor bug that
occurred during the switch (gcc 5.0.0) from gnu90 to gnu11 as default option.