[Bug tree-optimization/113964] New: repeat copy of struct

[absoler at smail dot nju.edu.cn via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113964

            Bug ID: 113964
           Summary: repeat copy of struct
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: absoler at smail dot nju.edu.cn
  Target Milestone: ---

here's the code:
```
struct S1 {
   uint32_t  f0;
   uint8_t  f1;
   uint64_t  f2;
   uint64_t  f3;
   int32_t  f4;
};

union U8 {
   struct S1  f0;
   int32_t  f1;
   int64_t  f2;
   uint8_t  f3;
   const int64_t  f4;
};

/* --- GLOBAL VARIABLES --- */
struct S1 g_16 = {4294967293UL,1UL,1UL,0xA9C1C73B017290B1LL,0x5ADF851FL};
union U8 g_37 = {{1UL,1UL,0x2361AE7D51263067LL,0xEEFD7F9B64A47447LL,0L}};
struct S1 g_50 =
{0x0CFC2012L,1UL,0x43E1243B3BE7B8BBLL,0x03C5CEC10C1A6FE1LL,1L};


/* --- FORWARD DECLARATIONS --- */

void func_32(union U8 e) {
  e.f3 = e.f0.f4;
  g_16 = e.f0 = g_50;
}
```

and compiled with gcc-13.2.0 -O2, generated binary code is:

```
0000000000401400 <func_32>:
func_32():
/root/myCSmith/test/output2.c:54
  401400:       movzbl 0x2c79(%rip),%eax        # 404080 <g_50>
  401407:       movdqa 0x2c71(%rip),%xmm0        # 404080 <g_50>
  40140f:       movdqa 0x2c79(%rip),%xmm1        # 404090 <g_50+0x10>
  401417:       movups %xmm0,0x8(%rsp)
  40141c:       mov    %al,0x8(%rsp)
  401420:       mov    0x2c72(%rip),%eax        # 404098 <g_50+0x18>
  401426:       movups %xmm1,0x18(%rsp)
  40142b:       movdqu 0x8(%rsp),%xmm2
  401431:       mov    %eax,0x20(%rsp)
  401435:       movdqu 0x18(%rsp),%xmm3
  40143b:       movaps %xmm2,0x2c7e(%rip)        # 4040c0 <g_16>
  401442:       movaps %xmm3,0x2c87(%rip)        # 4040d0 <g_16+0x10>
/root/myCSmith/test/output2.c:55
  401449:       retq   
  40144a:       nopw   0x0(%rax,%rax,1)
```

we can see that g_50.f0 and g_50.f4 have been repeatedly copy to e.