Re: Doubt regarding a tail optimized code under ‘gdb’

[Amit Saha <amitsaha.in@gmail.com>]

Hello Paul,

On Mon, May 18, 2009 at 11:13 PM, Paul Pluzhnikov
<ppluzhnikov@google.com> wrote:
> On Mon, May 18, 2009 at 9:46 AM, Amit Saha <amitsaha.in@gmail.com> wrote:
>
>> Out of sheer curiosity, I tried to run a tail optimised code under
>> 'gdb'. Consider a tail recursive factorial implementation in C:
>
> Debugging optimized code is tricky; you need to know what you are doing
> and know how to read disassembly :-)
>
>> I place a breakpoint in 'factorial' and I run the above under 'gdb'.
>> The breakpoint is never hit. Assuming that its tail call optimised (I
>> have compiled it using gcc -O2), it should hit the breakpoint, at
>> least once. I get the final result without hitting any breakpoint.
>
> I can reproduce this with gcc-4.3.1 on i386, but not with gcc-4.4.0.
> This doesn't have anything to do with tail-recursion though: gcc-4.3.1
> simply inlines factorial() into main: looking at disassembly, the only
> CALLs from main are to scanf and printf. Compiling with -fno-inline makes
> it work as expected under gcc-4.3.1 as well.

Yes. Yes. Now I remember. In the assembly code (I obtained by gcc
--S), I remember the CALL to only printf and scanf.  So that explains
the behavior. Thanks!

Now, I will look into why the inlining takes place :)

Thanks a ton!

Best,
Amit


>
> Cheers,
> --
> Paul Pluzhnikov
>



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