[Bug tree-optimization/85175] New: [8 regression] false-positive -Wformat-overflow= warning with gcc-8 -Os

[arnd at linaro dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85175

            Bug ID: 85175
           Summary: [8 regression] false-positive -Wformat-overflow=
                    warning with gcc-8 -Os
           Product: gcc
           Version: 8.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arnd at linaro dot org
  Target Milestone: ---

This snippet from the Linux kernel produces a bogus warning when built with gcc
-Os, using a recent snapshot (20180402) A two months older version did not
produce the warning, and building with -O2 is also fine. Reduced test case:

$ gcc-8.0.1 -Os -Wall -c test.c

int of_property_read_u32(int *out_value);
int imx_ldb_bind(void)
{
        int i;
        for (i = 0; i < 4; i++) {
                char clkname[16];
                __builtin_sprintf(clkname, "di%d_sel", i);
        }
        return of_property_read_u32(&i);
}

imx-ldb.i: In function 'imx_ldb_bind':
imx-ldb.i:7:35: warning: '_sel' directive writing 4 bytes into a region of size
between 3 and 13 [-Wformat-overflow=]
   __builtin_sprintf(clkname, "di%d_sel", i);