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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/105030] store motion if-change flag causes
 if-conversion optimization can't be taken.
Date: Thu, 24 Mar 2022 07:22:52 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105030

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
something like

void *bar (void *x)
{
  *(double *)x =3D 1.;
}

void foo(int n)
{
   double atemp;
   pthread_create (..., bar, &atemp);
   for (int i =3D 0; i < n; i++)
     if (a[i] < atemp)
       atemp =3D a[i];
   pthread_join (...);
   if (atemp !=3D 1.)
     abort ();
}

if it is ensured the store to atemp in the loop never takes place then
we have created a store data race when applying store motion.  Of course
thread creation/join can be hidden in other functions called from foo()
as long as 'atemp' escapes to callers.=