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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/102951] New: failure to optimize MIN_EXPR of
 subobject addresses of the same object
Date: Tue, 26 Oct 2021 15:24:15 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102951

            Bug ID: 102951
           Summary: failure to optimize MIN_EXPR of subobject addresses of
                    the same object
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

GCC fails to fold the MIN_EXPR below to the lower address.  The test case
affects C because the C front end emits a MIN_EXPR but not C++ because the =
C++
front end emits an if statement.

$ cat z.c && gcc -O2 -S -Wall -fdump-tree-optimized=3D/dev/stdout z.c
extern int a[];

void f (void)
{
  int *p1 =3D &a[1];
  int *p2 =3D &a[2];

  int *d =3D p1 < p2 ? p1 : p2;
  *d =3D 0;
}

;; Function f (f, funcdef_no=3D0, decl_uid=3D1979, cgraph_uid=3D1, symbol_o=
rder=3D0)

void f ()
{
  int * d;

  <bb 2> [local count: 1073741824]:
  d_1 =3D MIN_EXPR <&a[2], &a[1]>;   // the two statements can be folded in=
to
  *d_1 =3D 0;                        //   MEM[(int *)&a + 4B] =3D 0
  return;

}=