Missed optimization in gcc 3.4?

[Martin Reinecke]

Hi,

the piece of code below shows a case where the loop optimizer and/or inliner
of gcc 3.4 does a suboptimal job.


------- snip

class RNG
   {
   private:
     unsigned int x,y,z,w;

   public:
     /*! initializes the generator with 1 to 4 seed values. */
     RNG (unsigned int x1=123456789, unsigned int y1=362436069,
          unsigned int z1=521288629, unsigned int w1=88675123)
       : x(x1), y(y1), z(z1), w(w1)  {}


     unsigned int int_rand_uni()
       {
       unsigned int t = x^(x<<11);
       x = y;
       y = z;
       z = w;

       return w=(w^(w>>19))^(t^(t>>8));
       }

     void skip()
       {
       for (int m=0; m<100000000; ++m)
         int_rand_uni();
       }
   };

int main()
   {
   RNG rng;

#ifdef OUTER_LOOP

   for (int m=0; m<100000000; ++m)
     rng.int_rand_uni();

#else

   rng.skip();

#endif

   return rng.int_rand_uni()%255;
   }

------- snip

When compiling with -O3, the runtime of the resulting executable
is about three times as long when OUTER_LOOP is defined
than when it is undefined, despite the fact that int_rand_uni()
is inlined in both cases. Is there a way to generate the same,
efficient code in both cases, or is this an inherent limitation of
gcc's optimizer?

Thanks,
   Martin