[Bug rtl-optimization/105546] New: load introduction when copying a struct

["absoler at smail dot nju.edu.cn" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105546

            Bug ID: 105546
           Summary: load introduction when copying a struct
           Product: gcc
           Version: 11.3.0
            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: ---

Created attachment 52948
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52948&action=edit
case file

Hi, here's the code:

...

struct S0 {
   unsigned short  f0;
   unsigned short  f1;
   short  f2;
   unsigned char  f3;
   long long  f4;
   long long  f5;
};

short g_344 = 0xC307L;

struct S0  func_1(void)
{ 
    struct S0 l_346 = {65526UL,1UL,-8L,0xA1L,0x2F513C84A35AAE1BLL,-6L};


    if (g_344)
    { 
        struct S0 l_345 = {0x0AB2L,0x6D27L,-1L,0xABL,3L,0x3E72F31FF82C1E35LL};
        return l_345;
    }
    else
    { 
        return l_346;
    }
}

...

with option -O1, gcc-11.3.0 generate the following code:

Dump of assembler code for function func_1:
   0x0000000000401126 <+0>:     mov    %rdi,%rax
   0x0000000000401129 <+3>:     cmpw   $0x1,0x2eff(%rip)        # 0x404030
<g_344>
   0x0000000000401131 <+11>:    sbb    %edi,%edi
   0x0000000000401133 <+13>:    and    $0xf544,%di
   0x0000000000401138 <+18>:    add    $0xab2,%di
   0x000000000040113d <+23>:    cmpw   $0x1,0x2eeb(%rip)        # 0x404030
<g_344>
   0x0000000000401145 <+31>:    sbb    %esi,%esi
   0x0000000000401147 <+33>:    and    $0x92da,%si
   0x000000000040114c <+38>:    add    $0x6d27,%si
   0x0000000000401151 <+43>:    cmpw   $0x1,0x2ed7(%rip)        # 0x404030
<g_344>
   0x0000000000401159 <+51>:    sbb    %ecx,%ecx
   0x000000000040115b <+53>:    and    $0xfffffff9,%ecx
   0x000000000040115e <+56>:    sub    $0x1,%ecx
   0x0000000000401161 <+59>:    cmpw   $0x1,0x2ec7(%rip)        # 0x404030
<g_344>
   0x0000000000401169 <+67>:    sbb    %edx,%edx
   0x000000000040116b <+69>:    and    $0xfffffff6,%edx
   0x000000000040116e <+72>:    sub    $0x55,%edx
   0x0000000000401171 <+75>:    cmpw   $0x0,0x2eb7(%rip)        # 0x404030
<g_344>
   0x0000000000401179 <+83>:    movabs $0x2f513c84a35aae1b,%r9
   0x0000000000401183 <+93>:    mov    $0x3,%r8d
   0x0000000000401189 <+99>:    cmovne %r8,%r9
   0x000000000040118d <+103>:   movabs $0x3e72f31ff82c1e35,%r10
   0x0000000000401197 <+113>:   mov    $0xfffffffffffffffa,%r8
   0x000000000040119e <+120>:   cmovne %r10,%r8
   0x00000000004011a2 <+124>:   mov    %di,(%rax)
   0x00000000004011a5 <+127>:   mov    %si,0x2(%rax)
   0x00000000004011a9 <+131>:   mov    %cx,0x4(%rax)
   0x00000000004011ad <+135>:   mov    %dl,0x6(%rax)
   0x00000000004011b0 <+138>:   mov    %r9,0x8(%rax)
   0x00000000004011b4 <+142>:   mov    %r8,0x10(%rax)
   0x00000000004011b8 <+146>:   retq

it seems the last 4 loads are unneed and can be optimized away, which bring
vulnerabilities when facing concurrency and may decrease performance