GCC issues warnings like "division by zero" or "right shift count >= width of
type" even though the corresponding code will never be executed (under a
condition that is always false); it shouldn't do this, at least by default. For
instance:
int tst (void)
{
int x;
x = 0 ? 1 / 0 : 0;
return x;
if (0)
{
x = 1 / 0;
x = 1 >> 128;
}
return x;
}
$ gcc-snapshot -std=c99 -O2 -c tst.c
tst.c: In function 'tst':
tst.c:8:13: warning: division by zero [-Wdiv-by-zero]
tst.c:9:7: warning: right shift count >= width of type [enabled by default]
One can see that GCC detects neither the first "return x;" nor the always-false
condition, and issues spurious warnings for the lines:
x = 1 / 0;
x = 1 >> 128;
On the other hand, GCC could successfully detect that the 1 / 0 in
x = 0 ? 1 / 0 : 0;
would never be executed.
Note: always-false conditions occur in practice for platform-dependent code,
e.g. by doing a test on integer types.
--
Summary: gcc should not issue warnings for code that will never
be executed
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: vincent at vinc17 dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44842
