[Bug c++/103827] New: function which takes an argument via (hidden) reference should assume the argument does not escape or is only read from

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103827

            Bug ID: 103827
           Summary: function which takes an argument via (hidden)
                    reference should assume the argument does not escape
                    or is only read from
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: alias, missed-optimization
          Severity: enhancement
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
#include <string>

extern void foo (const std::string );

void
bar ()
{
  foo ("abc");
  foo (std::string("abc"));
}

---- CUT ----
Right now we get:
  MEM[(struct _Alloc_hider *)&D.33220]._M_p = &D.33220.D.26223._M_local_buf;
  __builtin_memcpy (&D.33220.D.26223._M_local_buf, "abc", 3);
  D.33220._M_string_length = 3;
  MEM[(char_type &)&D.33220 + 19] = 0;
  foo (&D.33220);

  <bb 6> [local count: 1073741824]:
  _5 = D.33220._M_dataplus._M_p;
  if (&D.33220.D.26223._M_local_buf != _5)

But the address of what was passed to foo cannot escape and foo cannot change
the content of D.33220. So the read of D.33220._M_dataplus._M_p should always
return &D.33220.D.26223._M_local_buf.