Taken from:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=323

---
import std.stdio;

void test(double x, double y)
{
  double y2 = x + 1.0;
  if (y != y2)
    writeln("error");
}

void main()
{
  immutable double x = .012;  // Remove 'immutable', and 'error' is not printed.
  double y = x + 1.0;

  test(x, y);
}
---


This is a GCC bug with a front-end fix.  It may be a good idea to conform to this behaviour in D (GDC) too.  If not at least because the reference compiler doesn't appear to optimise aggressively enough to get this problem.