[Issue 9387] Compiler switch -O changes behavior of correct code

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=9387


Don <clugdbug at yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code


--- Comment #12 from Don <clugdbug at yahoo.com.au> 2013-01-29 15:13:51 PST ---
Here is a more reduced test case (still enormous):
Without -O, it returns on the first pass through the loop. With -O, one of two
things happen:
(a) it hits the assert(0) on the first pass through the loop; or
(b) it generates an alignment hardware exception.

It looks as though it is a issue with misalignment of SSE registers.
Removing the assert(0) causes an ICE.

---
import std.math : abs;

void minimize()
{
    double a,b,d=0.0,etemp,fu,fv,fw,fx;
    double p;
    double q,r,tol1,tol2,u,v,w,x,xm;
    double e=0.0;
    double ax,bx,cx,fa,fb,fc;
    double tol;
  ax = 2.8541;
  bx = 3;
  cx = 3.0458;
  fa = 0.145898;
  fb = 0;
  fc = 0.381966;
 tol = 3.0e-8;

    a= ax;
    b= cx;
    v = bx;
    w = bx;
    x = bx;
    fx = 0;
    fv = fx;
    fw = fx;

  a = 2.97871347812973974456; b = 3.0458; v =2.9442711606; w =2.9787134781;
  x = 3;  fx= 0; fv = 0.00310570354087098691;
  fw = 0.00045311601333306815;
  e =-0.0557288394;
  d = -0.0212865219;
    for (int iter=0;iter<1;iter++) {
      xm=0.5*(a+b);
      tol1=tol*abs(x);
      tol2=2.0*(tol1);
      if (abs(x-xm) <= (tol2-0.5*(b-a))) {
        return;
      }
      if (abs(e) > tol1) {
       r=(x-w)*(fx-fv);
        q=(x-v)*(fx-fw);
        p=(x-v)*q-(x-w)*r;
        q=2.0*(q-r);
        if (q > 0.0) p = -p;
        q=abs(q);
        etemp=e;
        e=d;
        if (abs(p) >= abs(0.5*q*etemp) || q < p) {
          d= b-x;
        }
        else {
          d=p/q;
          u=x+d;
          if (u-a < tol2 || b-u < tol2)
            d = xm - x;
        }
      }
      else { d= (e=(x >= xm ? a-x : b-x)); }
      u= (abs(d) >= tol1) ? x+d : x+3.0e-8;

     if (u < 3.01) return;
     else
        assert(0);  // FAILS HERE

      fu = (u-3.0)*(u-3.0);

      if (fu <= fx) {
        assert(0);
      }
    }
}

void main() {
  minimize();
}

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