Playing with devirtualization in g++4.9

[Robert Matusewicz]

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Hi,

I found that g++4.9.0 have -fdevirtualize switch and wanted to play with
that feature for a while. I wrote simple, non-trivial program to check
how g++ will behave in obvious case:

==== SOURCE BEGIN ====
#include <iostream>

class B final
{
public:
    virtual void test() { std::cout << "Test" << std::endl;  }
};

int main()
{
    B test;
    test.test();
    return 0;
}
==== SOURCE ENDS ====

I compiled this code with

g++ -std=c++11 -fdevirtualize simple1.cpp

and then objdumped symbols:

objdump -t a.out | c++filt  | grep vtable

and noticed that vtable is present (I would expect it will be removed)
00000000006012c0  w    O .bss	0000000000000058              vtable for
__cxxabiv1::__class_type_info@@CXXABI_1.3
0000000000400b20  w    O .rodata	0000000000000018              vtable for B


I found some examples in testsuite (opt/ and ipa/) but for those
examples I checked, I can "reproduce" devirtualization.

Is there a documentation somewhere to see what is the current status of
devirtualiztion in g++ 4.9? I mean, beside the source code. Or maybe
someone could explain me why this case can't be devirtualized?

Best regards
Robert
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