[Bug tree-optimization/111394] Warning about uninitialized memory that is actually initialized

[aiya64bits at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111394

Sayu  changed:

   What|Removed |Added

 Status|RESOLVED|UNCONFIRMED
 Resolution|INVALID |---

--- Comment #3 from Sayu  ---
(In reply to Andrew Pinski from comment #1)
> N could be -1 which then would access out of bounds ..
> 
> I suspect if you add a check for n being negative in memoized_cut_rod the
> warning will go away and a security issue is solved too.

I see. I didn't realize that negative indexes are allowed in C, I always
assumed it was undefined behavior or just invalid. However, what does "*r_30 +
_122" mean in the warning?

[Bug c/111394] New: Warning about uninitialized memory that is actually initialized

[aiya64bits at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111394

Bug ID: 111394
   Summary: Warning about uninitialized memory that is actually
initialized
   Product: gcc
   Version: unknown
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
  Assignee: unassigned at gcc dot gnu.org
  Reporter: aiya64bits at gmail dot com
  Target Milestone: ---

#include 
#include 

int memoized_cut_rod_aux(const int p[], int n, int c, int r[]) {
if (r[n] >= 0)
return r[n];

int q = p[n - 1];
if (!n) {
q = 0;
} else {
for (int i = 1; i <= n / 2; ++i) {
const int v = p[i - 1] + memoized_cut_rod_aux(p, n - i, c, r) - c;
if (v > q)
q = v;
}
}
r[n] = q;
return q;
}

int memoized_cut_rod(const int p[], int n, int c) {
int result;

int *const r = malloc((n + 1) * sizeof(int));
if (!r) {
fprintf(stderr, "Out of memory.\n");
exit(1);
}

for (int i = 0; i < n + 1; ++i)
r[i] = -1;

result = memoized_cut_rod_aux(p, n, c, r);
free(r);
return result;
}

The above code when compiled with "gcc -Wall -O3 -o rod_cutting rod_cutting.c"
gives the following warning:

In function ‘memoized_cut_rod_aux’,
inlined from ‘memoized_cut_rod’ at rod_cutting.c:95:17:
rod_cutting.c:59:14: warning: ‘*r_30 + _122’ may be used uninitialized
[-Wmaybe-uninitialized]
   59 | if (r[n] >= 0)
  | ~^~~

But all the elements of r are initialized to -1 in the loop in
memoized_cut_rod. I got this warning with GCC 13.2.1 and then got the same
warning with the trunk branch.