[Bug tree-optimization/42586] load-modify-store on x86 should be a single instruction

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42586

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.6.0
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #21 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC 4.6.0 was when the fix was included for this.
Cyc_string_ungetc:
.LFB0:
        .cfi_startproc
        movl    8(%esp), %eax
        subl    $1, (%eax)
        xorl    %eax, %eax
        ret

Note the trunk's sra does not need to handle the extra copy any more.
Before esra:
```
  _T2 = *sptr_3(D); // unused
  _ans = *sptr_3(D);
  _1 = _ans.curr;
  _2 = _1 + 4294967295;
  _ans.curr = _2;
  *sptr_3(D) = _ans;
  _T2 ={v} {CLOBBER(eos)};
  _ans ={v} {CLOBBER(eos)};
```

ESRA does now:
```
  _T2 = *sptr_3(D);
  _ans$curr_13 = sptr_3(D)->curr;
  _ans$base_10 = MEM <unsigned char *> [(struct _fat_ptr *)sptr_3(D) + 4B];
  _ans$last_plus_one_8 = MEM <unsigned char *> [(struct _fat_ptr *)sptr_3(D) +
8B];
  _1 = _ans$curr_13;
  _2 = _1 + 4294967295;
  _ans$curr_5 = _2;
  sptr_3(D)->curr = _ans$curr_5;
  MEM <unsigned char *> [(struct _fat_ptr *)sptr_3(D) + 4B] = _ans$base_10;
  MEM <unsigned char *> [(struct _fat_ptr *)sptr_3(D) + 8B] =
_ans$last_plus_one_8;
  _T2 ={v} {CLOBBER(eos)};
```

In GCC 15 it was:
```
  _T2$curr_13 = MEM <unsigned char *> [(struct _fat_ptr *)sptr_3(D)];
  _T2$base_10 = MEM <unsigned char *> [(struct _fat_ptr *)sptr_3(D) + 4B];
  _T2$last_plus_one_8 = MEM <unsigned char *> [(struct _fat_ptr *)sptr_3(D) +
8B];
  _ans$curr_5 = _T2$curr_13;
  _ans$base_4 = _T2$base_10;
  _ans$last_plus_one_16 = _T2$last_plus_one_8;
  _1 = _ans$curr_5;
  _2 = _1 + 4294967295;
  _ans$curr_17 = _2;
  sptr_3(D)->curr = _ans$curr_17;
  MEM <unsigned char *> [(struct _fat_ptr *)sptr_3(D) + 4B] = _ans$base_4;
  MEM <unsigned char *> [(struct _fat_ptr *)sptr_3(D) + 8B] =
_ans$last_plus_one_16;
  return 0;
```