[Bug c++/86590] New: Codegen regression when passing std::string by value in C++ 17 and C++ 20

[s_gccbugzilla at nedprod dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86590

            Bug ID: 86590
           Summary: Codegen regression when passing std::string by value
                    in C++ 17 and C++ 20
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: s_gccbugzilla at nedprod dot com
  Target Milestone: ---

If compiled as C++ 14:

#include <string>

inline size_t calc(std::string a, std::string b)
{
    return a.size() + b.size();
}

int foo()
{
    std::string a = "Hello world", b = "Goodbye world";
    return calc(a, b);
}

...one gets:

foo():
        mov     eax, 24
        ret

But if compiled as C++ 17 or later, one gets lots of spew:
https://godbolt.org/g/jCzpAS

Using std::move() generates the right result in C++ 17 or later:
https://godbolt.org/g/tHXpyy. I think it should also work by value, like it did
in C++ 11 and C++ 14.