[Bug c++/82476] New: C++: Inlining fails for a simple function

[arun11299 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82476

            Bug ID: 82476
           Summary: C++: Inlining fails for a simple function
           Product: gcc
           Version: 7.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arun11299 at gmail dot com
  Target Milestone: ---

Hello Folks,
I was just trying to figure out if a particular code of mine would provide me
with optimized code or not at O2 optimization level.

The code is:

{code}

#include <cstdio>
#include <utility>

class Object
{
public:
    Object()                    { puts("Cons\n");        }
    Object(const Object&)       { puts("Copy Cons\n");   }
    Object& operator=(Object&)  { puts("Assign Cons\n"); return *this; }
    Object(Object&&)            { puts("Move Cons\n");   }
    Object& operator=(Object&&) { puts("Move Assign\n"); return *this; }
    ~Object()                   { puts("Destructor\n");  }
};

struct result_type
{
    Object obj;
    unsigned val;
};

Object create_object() 
{
    Object obj;
    return obj;
}

result_type get_result()
{
    auto obj = create_object();
    return {std::move(obj), 42};
    //return std::pair<Object, unsigned>{obj, 42};
}

int main() {
    auto res = get_result();
    return 0;
}

{code}

Nothing fancy in here. Just a function returning an object by value.

The assembly generated (seen via https://godbolt.org/g/nvg1o4)

{code}

.LC0:
        .string "Cons\n"
create_object():
        push    rbx
        mov     rbx, rdi
        mov     edi, OFFSET FLAT:.LC0
        call    puts
        mov     rax, rbx
        pop     rbx
        ret
.LC1:
        .string "Move Cons\n"
.LC2:
        .string "Destructor\n"
get_result():
        push    rbx
        mov     rbx, rdi
        mov     edi, OFFSET FLAT:.LC0
        call    puts
        mov     edi, OFFSET FLAT:.LC1
        call    puts
        mov     DWORD PTR [rbx+4], 42
        mov     edi, OFFSET FLAT:.LC2
        call    puts
        mov     rax, rbx
        pop     rbx
        ret
        mov     rbx, rax
        mov     edi, OFFSET FLAT:.LC2
        call    puts
        mov     rdi, rbx
        call    _Unwind_Resume
main:
        sub     rsp, 24
        lea     rdi, [rsp+8]
        call    get_result()
        mov     edi, OFFSET FLAT:.LC2
        call    puts
        xor     eax, eax
        add     rsp, 24
        ret

{code}

As can be seen in the 'main' subroutine, "get_result" function call is not
getting inlined. Though it does get inlined if I add the "inline" keyword to
the function, but I dont think it should be required. Clang 5.0 is able to
inline the function call.

Compilation arguments: -O2 -std=c++14 -finline-functions
G++ version : 7.2
Ran on: Compiler explorer https://godbolt.org/g/nvg1o4


Thanks guys.