>
> The effect is that a pedantic compilation sees an add of the variable
> where a non-pedantic compilation sees an add of the constant 1. This
> then leads to slightly different generated code, which causes the
> non-pedantic compilation to fail to see that it can generate a tail
> call.
>
A curious effect.
It seems that a transformation that is supposed to help optimization
(seeing j as a constant value instead of a variable) has a negative
effect. I've tried to simplify the code in order to isolate the issue
and I've produced the following functions:
int recur_1(int i)
{
if (i-- <= 0) return 0;
return (i + 1) + recur_1(i);
}
int recur_2(int i)
{
if (i-- <= 0) return 0;
{
int j = i + 1;
return j + recur_2(i);
}
}
The optimizer (gcc version is 4.1.2) behaves much better with the
second function. I'm wondering what mysterious beast lurks in the
optimization routines... :)
Dario
