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From: "kristerw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113703] ivopts miscompiles loop
Date: Thu, 01 Feb 2024 15:01:06 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113703

--- Comment #2 from Krister Walfridsson <kristerw at gcc dot gnu.org> ---
Here is a runtime testcase:

#include <sys/mman.h>
#include <unistd.h>
#include <stdint.h>

__attribute__((noipa))
void f1 (char *p, uintptr_t i, uintptr_t n)
{
  p +=3D i;
  do
    {
      *p =3D '\0';
      p +=3D 1;
      i++;
    }
  while (i < n);
}

int main()
{
  long pgsz =3D sysconf (_SC_PAGESIZE);
  void *p =3D mmap (NULL, pgsz * 2, PROT_READ|PROT_WRITE,
     MAP_ANONYMOUS|MAP_PRIVATE, 0, 0);
  if (p =3D=3D MAP_FAILED)
    return 0;
  mprotect (p+pgsz, pgsz, PROT_NONE);
  uintptr_t n =3D -3 - (uintptr_t)p;
  f1 (p+2, -2, n);
  return 0;
}=