[Bug c/97982] New: integer casting after abs() causes undefined behavior

[mytbk920423 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97982

            Bug ID: 97982
           Summary: integer casting after abs() causes undefined behavior
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mytbk920423 at gmail dot com
  Target Milestone: ---

The following code has different result when compiling with -O0/-O1 and -O2.
Also, ubsan will report an error. But I don't know why the
signed(INT_MIN)->unsigned data conversion is undefined. It's found in GCC
10.2.0 and 4.8.5.
clang does fine with both -O0 and -O2 and reports no ubsan errors.

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

int main()
{
        char str[20];
        scanf("%s", str);
        int32_t x = strtol(str, NULL, 0);
        uint32_t u = abs(x); // x=0x80000000 will trigger an undefined behavior
        uint64_t val = u;
        printf("0x%lx\n", val);
}