https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101645
Bug ID: 101645
Summary: -Wsign-conversion misses negation of unsigned int
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: matthew at wil dot cx
Target Milestone: ---
Test case:
unsigned long a(void);
void b(long);
void c(void) {
unsigned int x = a();
b(-x);
}
There is a missed warning in the call to b(). x is negated, but as an int. It
is then passed to b() which sees a very large positive number instead of a
small negative number. This has recently affected the Linux codebase, and it's
disappointing that gcc doesn't have a warning that we could enable to find it.
https://godbolt.org/z/xvaxh1rqr
shows that Clang does spot this with -Wsign-conversion, but GCC currently
doesn't (it only warns for line 4 and not line 5). Admittedly the Clang
diagnostic message isn't the greatest, but at least it says _something_.
