Spurious lint warning about assigned variable never used

Question

I'm getting a lint warning "assigned value never used" (and another one "set but not used in function")
that seems to be spurious. Test case included below. Can someone either confirm that this is a bug or explain to me why
this warning is legitimate.
marten 229% cc -V
cc: Sun C 5.9 SunOS_sparc Patch 124867-01 2007/07/12
marten 230% uname -a
SunOS marten.isi.edu 5.10 Generic_127111-11 sun4u sparc SUNW,Sun-Blade-1000 Solaris
marten 231% cat test93.c
static long value;
long get_value (void) {
value++;
return value;
int main (int argc, char ** argv) {
long k, val;
value = 0;
k = 0;
while ((val = get_value()) != 47) {
k++;
return 0;
marten 249% lint -u -m -x -Ncheck=%all test93.c
argument unused in function
(9) argc in main
(9) argv in main
set but not used in function
(10) val in main
.c file has no corresponding .h file
/nfs/m_usr/dhollen/junk/test93.c
assigned value never used
val defined at test93.c(10) :: set at test93.c(14)

Answer 1

The value of variable "val" is never actually used in function main.
You could delete its declaration and the assignment to it in the while-loop header without affecting the program.
Maybe you are thinking that the line
while ((val = get_value()) != 47)
uses the value of val. An assignment-expression has the type and value that is stored in the left operand, and is not an lvalue. The actual storage into the variable is a side effect that need not occur before the value of the assignment is used.
Reference: C99 Standard, section 6.5.16 "Assignment operators", paragraph 3.
In this example, the storage into val must occur before entering or skipping the loop body, but need not occur before evaluating the control expression. Variable val is therefore not used in the function.
We can go further and notice that since storing into val is not an "observable side effect", a compiler is free to omit allocating the variable or storing into it.