[Bug c/55217] New: False -Wstrict-overflow warning

[mattiase at acm dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55217



             Bug #: 55217

           Summary: False -Wstrict-overflow warning

    Classification: Unclassified

           Product: gcc

           Version: 4.7.2

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: c

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: matti...@acm.org





This code yields a false -Wstrict-overflow warning in gcc 4.7.2:



void h(int *s);

void f(int n, int s)

{

        int r = 1;

        for (int i = 1; i < n; i++)

                if (r)

                        r++;

        if (r * s >= s + 3)       // warning here

                for (int j = 0; j < r; j++)

                        h(&s);

}



beta.c:8:12: warning: assuming signed overflow does not occur when assuming

that (X + c) < X is always false [-Wstrict-overflow]



The condition is not on the form X+c<X, and can legitimately go either way.



Here is a variant with s hard-wired to 0. The call to g() seems necessary:



void g(void);

void h(int *s);

void f(int n)

{

        int s = 0;

        int r = 1;

        g();

        for (int i = 1; i < n; i++)

                if (r)

                        r++;

        if (r * s >= s + 3)      // warning here

                for (int j = 0; j < r; j++)

                        h(&s);

}