[Bug rtl-optimization/82103] New: spurious stringop-overflow warning

[arnd at linaro dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82103

            Bug ID: 82103
           Summary: spurious stringop-overflow warning
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arnd at linaro dot org
  Target Milestone: ---

On a current snapshot (tested with r251683), I get a warning that seems
unhelpful and probably should not be there.

This happened in exactly one file from the Linux kernel so far, on any 32-bit
target:

$ arm-linux-gnueabi-gcc-8.0.0 -Werror -O2 -march=armv7-a -c -Wall
hns_ethtool-b.c

hns_ethtool-b.c: In function 'g':
hns_ethtool-b.c:9:7: error: 'memset' specified size 4294967295 exceeds maximum
object size 2147483647 [-Werror=stringop-overflow=]
       memset(__p, v, __n);           \
       ^~~~~~~~~~~~~~~~~~~
hns_ethtool-b.c:18:2: note: in expansion of macro 'memset'
  memset(&data[frame_size / 2], 0, frame_size / 2 - 1);
  ^~~~~~

---
extern void f(void);
extern void *memset();

#define memset(p, v, n)              \
  ({                                 \
    void *__p = p;                   \
    unsigned int __n = n;            \
    if (__n != 0)                    \
      memset(__p, v, __n);           \
    (__p);                           \
  })

void g(char *data, unsigned int frame_size, _Bool c)
{
        memset(data, 5, frame_size);
        if (c)
                f();
        memset(&data[frame_size / 2], 0, frame_size / 2 - 1);
        memset(&data[frame_size / 2 + 0], 4, frame_size / 2 - 11);
}