Hi,
The following file foo.c is a simplified version of a subtler bug I
found in my code.
int b;void bar(int a);void foo(int a){ bar(a); a = 42;}
The line a = 42 is in fact a typo in my code: I meant b = 42. I do
*not* expect the compiler to detect that I made a typo, but I would
like the get a warning that I am assigning to a local variable (or a
function parameter) that is not going to be used anymore. If I compile
this file with
% gcc-4.6 -Wall -Wextra -pedantic -O3 -c foo.c
I get absolutely no warning. Inspecting the generated code shows that
the assignment a = 42 is not performed, so gcc is perfectly well aware
that this instruction is useless (hence potentially bogus). Commenting
the call to bar(a); does produce a "warning: parameter ‘a’ set but not
used [-Wunused-but-set-parameter]", so it seems like gcc will not warn
as long as variable a is used somewhere in the function, even if it is
before the assignment.
My questions:
1. Is there a way to tell gcc to produce a warning for such case?2. Is
there a reason for the actual behavior? I.e, some cases were it is
actually desirable to assign to local variables that will be thrown
away by the optimizer?
Thanks
--
Alexandre Duret-Lutz
