Notice that I have tried this with several 32-bit native and
cross GCC compilers including versions 3.2.2, 3.3, and 4.0.2.
In the test-case that follows, I get the warning in spite of the
fact that the conditional is constant and "bitNumber" must always
be less than 8 to execute the conditional.
I discovered this feature while trying to write a generic C++
template where the "bitNumber" is a template parameter.
I expected the constant conditional statement to be optimized
with a "smart-enough" compiler.
Since I always compile with -Werror, this warning is causing
me a bit of grief.
Note that the targets which I have tested all have 32-bit
unsigned long integers.
enum{ bitNumber = 15};
void test(unsigned long* p)
{
if(bitNumber < 8){
*p = (((unsigned long)0x01) << (bitNumber*4));
}
}
% gcc -c biterr.c
biterr.c: In function `test':
biterr.c:6: warning: left shift count >= width of type
--
Summary: warning: left shift count >= width of type
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: mnmoran at bellsouth dot net
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26516
