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From: "absoler at smail dot nju.edu.cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/114800] New: redundant set-zero when initiate
 a struct
Date: Mon, 22 Apr 2024 08:27:18 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 13.2.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: absoler at smail dot nju.edu.cn
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114800

            Bug ID: 114800
           Summary: redundant set-zero when initiate a struct
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: absoler at smail dot nju.edu.cn
  Target Milestone: ---

I found a weird case that
```
struct thresh_restart {
        int             *f0;
        int                     f1;
        int                     f2;
        int                     f3;
};

int arr[10];
void __attribute__((noinline)) foo(struct thresh_restart *p) {
    arr[0] =3D p->f3;
    arr[1] =3D p->f1;
}

void func(int *b) {
    struct thresh_restart tr =3D {
        .f0 =3D b,
        .f1 =3D 1,
        .f2     =3D 2,
        .f3     =3D 3,
    };
    foo(&tr);
}

```

such code is compiled as: (gcc-13.2.0 -O2, regression [11/12/13/trunk])
https://godbolt.org/z/rb4o6xc7E
```
func(int*):
 sub    $0x28,%rsp
 pxor   %xmm0,%xmm0
 mov    %rsp,%rdi
 movaps %xmm0,(%rsp)
 movq   $0x0,0x10(%rsp)   # redundancy
 movl   $0x1,0x8(%rsp)
 movl   $0x3,0x10(%rsp)
 call   401120 <foo(thresh_restart*)>
 add    $0x28,%rsp
 ret
```=