[Bug tree-optimization/101186] New: predictable comparison of integer variables not folded

["dizhao at os dot amperecomputing.com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101186

            Bug ID: 101186
           Summary: predictable comparison of integer variables not folded
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dizhao at os dot amperecomputing.com
  Target Milestone: ---

GCC fail to remove dead codes for following cases:

#include <stdio.h>

void f (unsigned int a, unsigned int b, unsigned int c)
// if a,b,c are signed, VRP can remove dead code
{
  if (a == b)
    {
      printf ("a");
      if (c < a)
        {
          printf ("b");
          if (c >= b)
            printf ("Unreachable!");
        }
    }
}

void g (int a, int b, int x, int y)
{
  int c = y;
  if (a != 0)
    c = x;
  while (b < 1000)
  // without this loop, jump thread & VRP can remove dead code
    {
      if (a != 0)
        {
          if (c > x)
            printf ("Unreachable!");
        }
      else
        printf ("a\n");
      b++;
    }
}