CODEWITHSUNDEEP
c++visual-studioassembly
Ghita
Ghita

Reputation: 4505

investigating visual studio assembly output

While using /FA option for compiling code that uses this dummy class

class A  {
public:
    A() {}
    int Initialize() {
        return 0;
    }
};

I looked over the generated asm file where this was defined and also used and saw this in the asm file

PUBLIC  ?Initialize@A@@QEAAHXZ              ; A::Initialize
PUBLIC  ??0A@@QEAA@H@Z                  ; A::A

??0A@@QEAA@H@Z PROC                 ; A::A, COMDAT
; File d:\dev\temp\consoleapplication1\consoleapplication1\consoleapp2.cpp
; Line 7
    mov rax, rcx
    ret 0
??0A@@QEAA@H@Z ENDP                 ; A::A
_TEXT   ENDS
; Function compile flags: /Ogtpy
;   COMDAT ?Initialize@A@@QEAAHXZ
_TEXT   SEGMENT
this$dead$ = 8
?Initialize@A@@QEAAHXZ PROC             ; A::Initialize, COMDAT
; File d:\dev\temp\consoleapplication1\consoleapplication1\consoleapp2.cpp
; Line 9
    xor eax, eax
; Line 10
    ret 0
?Initialize@A@@QEAAHXZ ENDP             ; A::Initialize

As you can see there is generated "trivial" implementation functions for both constructor and Initialize function.

At first I thought that this non inline implementation was going to be used where class A is used but debugging showed that this was not the case (code seemed to be inlined). Class A is not used anywhere else except this asm file so why are those functions generated if not used ?

Whole program optimization was in place.

Upvotes: 1

Views: 92

Answers (1)

πάντα ῥεῖ
πάντα ῥεῖ

Reputation: 1

"so why are those functions generated if not used ?"

You are inspecting assembly code generated for a single translation unit, not the final assembly after linking.

The linker will strip out any unused functions finally.

Upvotes: 3

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