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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/90710] Bogus Wmaybe-uninitialized caused by
 __builtin_expect when compiled with -Og
Date: Tue, 06 Apr 2021 23:16:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D90710

--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
Here's a smaller test case showing both the problem (first gcc invocation) =
and
how it can be avoided (second invocation):

$ (set -x && cat pr90710.c && gcc -Og -S -Wall pr90710.c && gcc -Dint=3Dlon=
g -Og
-S -Wall pr90710.c)
+ cat pr90710.c
static inline int f (int x, int *p)
{
  if (x =3D=3D 0)
    return 0;

  *p =3D x;
  return 1;
}

volatile int z;

void g (int x)
{
  int b, a =3D f (x, &b);

  if (a)
    z =3D b;

  if (__builtin_expect (a, 1))
    z =3D b;
}
+ gcc -Og -S -Wall pr90710.c
pr90710.c: In function =E2=80=98g=E2=80=99:
pr90710.c:20:7: warning: =E2=80=98b=E2=80=99 may be used uninitialized in t=
his function
[-Wmaybe-uninitialized]
   20 |     z =3D b;
      |     ~~^~~
pr90710.c:14:7: note: =E2=80=98b=E2=80=99 was declared here
   14 |   int b, a =3D f (x, &b);
      |       ^
+ gcc -Dint=3Dlong -Og -S -Wall pr90710.c=