__builtin_constant_p to stop constant folding

[Sylvain Pion <Sylvain dot Pion at sophia dot inria dot fr>]

It seems that with GCC 3, __builtin_constant_p sometimes answers 0, even when
GCC actually does some constant folding (in a later pass ?).  It's
annoying for me since I used to use __builtin_constant_p to stop constant
folding on certain variables using something like :

inline double stop_cprop(double d)
{
  volatile double e = d;
  return e;
}

#define STOP_CPROP(x) (__builtin_constant_p(x) ? stop_cprop(x) : (x))

inline double div (double a, double b)
{
  return a / STOP_CPROP(b);
}

div(1.0, 3.0); // return value depends on current rounding mode.


It's hard to extract a test case from my code, but it worked for me with GCC
2.95, so it's a performance regression since I will be forced to call
stop_cprop() everytime now.

I guess the right way to do what I want is to use "#pragma STDC FENV_ACCESS",
but it's not supported by GCC 3 :(.

Is there a possibility to restore this old __builtin_constant_p property ?

-- 
Sylvain