[Bug tree-optimization/34825] [4.2/4.3 regression] ICE with -funsafe-math-optimizations

["rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #4 from rguenth at gcc dot gnu dot org  2008-01-17 10:45 -------
So, we enter the recip pass with

<bb 2>:
  if (x_2(D) == y_3(D))
    goto <bb 3>;
  else
    goto <bb 4>;

<bb 3>:
  D.1547_4 = x_2(D) / x_2(D);
  D.1548_5 = D.1547_4 * x_2(D);
  D.1545_6 = D.1548_5 / x_2(D);

<bb 4>:
  # D.1545_1 = PHI <D.1545_6(3), 0.0(2)>
  return D.1545_1;

that is, we compute x/x*x/x.  Recip now 'optimizes' this to

  reciptmp.6_10 = 1.0e+0 / x_2(D);
  D.1547_4 = __builtin_pow (reciptmp.6_10, 2.0e+0);
  D.1548_5 = D.1547_4 * x_2(D);
  D.1545_6 = D.1548_5 * reciptmp.6_10;

which is bogus anyway.  But the ICE is gone :P

Well, it registers the division x_2(D)/x_2(D) twice, which also makes
it a wrong-code regression.

The easiest thing is probably to just not do reciprocal optimization
for x / x.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
           Priority|P3                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34825