https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80730
--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot
com> ---
I think it should be understood implicitly that it's the initializer *as
converted* that must be a constant expression (and, thus, to be an address
constant, must be of pointer type). Thus "unsigned int x = -2.0;" at file
scope is invalid (while -2.0 is a constant expression, the conversion to
unsigned int would involve runtime undefined behavior, so makes it not a
constant expression). And that where part of a constant expression is an
address constant, that can only be related to an overall address constant
as an initializer in the obvious way (effectively, through operations that
add constants to it, and conditional expressions with integer constant
expression conditions). Thus address constants converted to _Bool are not
valid initializers, and nor is ("" ? "" : "") an address constant, because
of the truth-value test of the first "" making an invalid condition.
That is, this is an issue about the unclear standard wording regarding
constant expressions where I think the compiler is behaving appropriately.
A question about appropriate conditions and array indices in address
constants (whether they must be integer or just arithmetic constant
expressions) is point 7 in my old list of constant expressions issues
<https://www.polyomino.org.uk/computer/c/const-exprs-issues.txt>. _Bool
initializers with address constants and such constants controlling ?: are
on my notes of further constant expression issues (the former probably
based on
<https://groups.google.com/forum/#!original/comp.std.c/ez822gwxxYA/k1OpYXFy90wJ>
and
<https://groups.google.com/forum/#!original/comp.std.c/mIh1ej_mkrc/vbbp9UQ7zDoJ>,
the latter with the date 2007-10-24 but I'm not sure where the discussion
was).
