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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 middle-end/107047] load introduced of struct/union fields after
 assigning it to a local variable
Date: Wed, 26 Oct 2022 08:31:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107047

--- Comment #3 from absoler at smail dot nju.edu.cn ---
and for union there's similar behavior:

union U2 {
    long long  f0;
    unsigned short  f2;
    int  f4;
};

void  func_17(union U2  p_20);
void  func_1() {
    func_17(g_39[0]);
}

void func_17(union U2 e) {
  int *f =3D &g_30;
  if (e.f0 || e.f2)
    *f =3D e.f2;
}

are compiled with gcc-12.1 -O1 to:

0000000000402020 <func_1>:
func_17():
/home/csmith-2.3.0/test/output2.c:87
  402020:       48 83 3d 68 3e 00 00    cmpq   $0x0,0x3e68(%rip)        #
405e90 <g_39>
  402027:       00=20
  402028:       74 0d                   je     402037 <func_1+0x17>
/home/csmith-2.3.0/test/output2.c:88
  40202a:       0f b7 05 5f 3e 00 00    movzwl 0x3e5f(%rip),%eax        #
405e90 <g_39>
  402031:       89 05 71 3e 00 00       mov    %eax,0x3e71(%rip)        #
405ea8 <g_30>

uses of e.f0 and e.f2 are replaced by g_39[0]=