[Bug tree-optimization/127495] New: push_back twice to a new std::vector still has two operator new rather than one

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127495

            Bug ID: 127495
           Summary: push_back twice to a new std::vector still has two
                    operator new rather than one
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
            Blocks: 118130
  Target Milestone: ---

Take:
```
#include <vector>
std::vector<int> f()
{
    std::vector<int> a;
    a.push_back(1);
    a.push_back(1);
    return a;
}
```

In optimized we have:
```
  _46 = operator new (4);
  *_46 = 1;
  _71 = operator new (8);
  MEM <unsigned long> [(void *)_71] = 4294967297;
  __new_finish_61 = _71 + 8;
  operator delete (_46, 4);
  a_2(D)->D.34495._M_impl.D.33792._M_start = _71;
  a_2(D)->D.34495._M_impl.D.33792._M_finish = __new_finish_61;
  a_2(D)->D.34495._M_impl.D.33792._M_end_of_storage = __new_finish_61;
  return a_2(D);
```

Notice the first operator new is dead/unused?


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118130
[Bug 118130] std::vector code quality issues