Re: tail call optimization vs. debugging

[dan@cgsoftware.com (Daniel Berlin+list.gcc)]

Bruno Haible <haible@ilog.fr> writes:


> For each optimized tail call, in the debugger, there is a stack
>frame missing.
Given, AFAIK.

> Example:
>          A () { B (); }
>          B () { C (); }
>          C () { D (); ... }
> Here gdb will only display the stack frames of A and D. That is, the tail
> call elimination makes debugging very hard.

Maybe, i don't know yet.
> 
> Many GNU programs are compiled with "-O2 -g" by default, which has been
> up to now a good compromise between speed and ease of debugging.
> 
Sure.
> May I suggest:
> 
> 1. that tail call elimination be disabled/enabled by a particular command
>    line option,

Not my call.
> 
> 2. that this command line option be "-fomit-frame-pointer", which is the
>    other optimization which makes debugging impossible. Since -O2 does
>    not imply "-fomit-frame-pointer", "-O2 -g" would continue to produce
>    reasonably debuggable code.
Here's where i have a problem.
-fomit-frame-pointer does not make code undebuggable.
In the past it did have trouble, but it's had frame pointerless
debugging for over a year now, i believe.
When is the last time you tried to debug code with
-fomit-frame-pointer on?

--Dan

> 
> Bruno