Why would a stack trace skip a function that obviously has to have been called for the following functions to have been reached?

Question

Given a setup like this, where DoFooStuff() is called:

class Foo {
public:
    void DoFooStuff(); // calls Bar::DoBarStuff()
}

class Bar {
public:
    void DoBarStuff(); // Calls Bar::DoInternalBarStuff()
protected:
    void DoInternalBarStuff();
}

What could make it possible that my stack trace could show exactly this?:

Type                   Function
void                   Bar::DoInternalBarStuff()
void                   Foo::DoFooStuff()

The only reference to DoInternalBarStuff() is in DoBarStuff(). DoInternalBarStuff() asserts on it's first line:

assert(false);

And that is the location where the stack trace is taken from.

None of these functions are declared as inline in the headers. Thanks for the suggestion though. Also I like your name :D — Kelsie, Jul 11 '13 at 02:21
The compiler is free to inline any function, even if not declared inline. Any compiler worth its salt will inline functions as a matter of course. — zindorsky, Jul 11 '13 at 02:35
@zindorsky: would that sort of behavior be limited to release/shipping builds? — Kelsie, Jul 11 '13 at 02:52
Nevermind, I found an answer to that question: http://stackoverflow.com/questions/1626248/does-gcc-inline-c-functions-without-the-inline-keyword — Kelsie, Jul 11 '13 at 02:59

score 4 · Accepted Answer · answered Jul 11 '13 at 03:04

4

Is the call to Bar::DoBarInternalStuff the last statement in Bar::DoBarStuff? If so, the compiler most likely replaced Bar::DoBarStuff's stack frame with Bar::DoBarInternalStuff's when Bar::DoBarInternalStuff was called.

This kind of tail call optimization is fairly common in C/C++ compilers. It reduces the stack depth required when a recursive function can be arranged such that the recursive call is the last call in the function.

answered Jul 11 '13 at 03:04

wrdieter

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Okay, yes, this is what happened. Thanks so much for helping me make sense of this! <3 – Kelsie Jul 11 '13 at 03:06

score 0 · Answer 2 · edited May 23 '17 at 12:05

0

So it turns out that the compiler does automatic inlining at certain optimization levels. Learn new things every day. :)

Does GCC inline C++ functions without the 'inline' keyword?

(Thanks for the helpful comments that showed me this.)

edited May 23 '17 at 12:05

Community

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answered Jul 11 '13 at 03:00

Kelsie

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Why would a stack trace skip a function that obviously has to have been called for the following functions to have been reached?

2 Answers2