[Bug c/104288] New: Null pointer check invalidly deleted

["nrk at disroot dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104288

            Bug ID: 104288
           Summary: Null pointer check invalidly deleted
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nrk at disroot dot org
  Target Milestone: ---

Hi,

In the following code, the null checks are removed when compiled with `-O2` on
gcc v11.2.1. Compiling with `-O2 -fno-delete-null-pointer-checks` produces
proper result.

        #include <stdbool.h>
        #include <stdio.h>
        #include <stdlib.h>
        #include <string.h>


        #define RESULT_PASS "PASS"
        #define RESULT_FAIL "FAIL"


        void test_assert(bool result)
        {
            printf("Assert: %s\n", result ? RESULT_PASS : RESULT_FAIL);

            if (!result)
                exit(EXIT_FAILURE);
        }


        void test_strcmp(const char *value_1, const char *value_2)
        {
            test_assert(value_1 != NULL);
            test_assert(value_2 != NULL);

            bool result = !strcmp(value_1, value_2);

            printf("Test equal: %s\n", result ? RESULT_PASS : RESULT_FAIL);
        }


        int main()
        {
            test_strcmp(NULL, "value 1");
        }

(code snippet taken from:
https://gist.github.com/novns/c84d6e1efd6304b3076811fef34096fd )