https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106797
Bug ID: 106797
Summary: Improvement: diagnose undefined behavior: not all
declarations that refer to the same object or function
have compatible type
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: pavel.morozkin at gmail dot com
Target Milestone: ---
This code:
static int (*x)[];
void f1(void)
{
extern int (*x)[3];
}
void f2(void)
{
extern int (*x)[5];
}
compiled with -std=c11 -pedantic -Wall -Wextra -Wno-unused-variable triggers UB
(see below) and leads to no diagnostics. It is proposed to produce this (or
similar) diagnostics: "not all declarations that refer to the same object x
have compatible type" OR "declarations that refer to the same object x have
types 'int (*)[5]' and 'int (*)[3]' which are not compatible".
Relevant quote from C11, 6.2.7 Compatible type and composite type, 2:
> All declarations that refer to the same object or function shall have
> compatible type; otherwise, the behavior is undefined.
In the program above types 'int (*)[5]' and 'int (*)[3]' are not compatible. It
is useful to diagnose that.
