https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69960
--- Comment #23 from Daniel Lundin <daniel.lundin.mail at gmail dot com> --- (In reply to jos...@codesourcery.com from comment #21) > On Wed, 22 Feb 2023, daniel.lundin.mail at gmail dot com via Gcc-bugs wrote: > > > First of all, it is questionable if gcc is still conforming after the change > > discussed here and implemented as per gcc 8.0. Yes "an implementation may > > accept other forms of constant expressions" but that doesn't mean that a > > compiler is allowed to ignore the constraints in C17 6.7.9/4 nor the > > definition > > of an integer constant expression. So this ought to explicitly be a compiler > > extension and we ought to have a way to reliably compile strictly conforming > > programs with gcc without constraint violations silently getting ignored. > > "integer constant expression" does not mean the same thing as "constant > expression of integer type". Yes, who said otherwise? Rather, this is the problem. Please check out the link I gave for the full reasoning including quotes. https://stackoverflow.com/questions/68252570/why-are-const-qualified-variables-accepted-as-initializers-on-gcc Specifically (C17 6.6): "An integer constant expression shall have integer type and shall only have operands that are integer constants, enumeration constants, character constants, sizeof expressions whose results are integer constants, _Alignof expressions, and floating constants that are the immediate operands of casts." In this code static const int y = 1; static int x = y; y is not an integer constant expression, nor is it an integer constant in the meaning that ISO 9899 defines it. Therefore an initializer was given which is not a constant expression. Therefore this is a constraint violation of C17 6.7.9/4 and a diagnostic must be issued. Therefore gcc is not conforming because of the "bug fix" carried out above. "an implementation may accept other forms of constant expressions" does not mean that an implementation can throw out any constraints it pleases out the window. Also the text "however, they are not an integer constant expression" added in C23 must have been added for a reason, such as misbehaving compilers.
