Re: gcc warn unreached else {}

Martin Sebor via Gcc-help <gcc-help@xxxxxxxxxxx> · Thu, 9 Jul 2020 10:15:17 -0600

On 7/9/20 3:45 AM, Jonny Grant wrote:
Hello!

There is an example below, (my code is not like this example below). I'm reporting a possible issue, and asking if there is a way to detect it in code bases. If it's a real issue I can file a bug report on Bugzilla.

Can gcc warn where code will not get to the 'return 3;' below?

-Wduplicated-branches detects a related problem.  It's implemented
entirely in the front end and quite simplistic.  It just looks at
the chain of expressions controlling the if statements and compares
them for equality.  I think it could be enhanced with not too much
effort to detect a subset of this problem as well by considering
the operator as well as its operands.

Here's the function that does the checking and issues the warning:
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/c-family/c-warn.c#l2491

Martin

Cheers, Jonny

int main(void)
{
     const int i = 1;
     if(1 == i)
     {
         return 1;
     }
     else if(1 != i)
     {
         return 2;
     }
     else
     {
         return 3;
     }
}