[Bug middle-end/71614] ppc __gcc_qmul is mis-optimized not to be commutative

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71614

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The fix would then put a barrier to force GCC not to do contracting.

Something like:
  v = a*d;
  w = b*c;
  asm("":"+f"(v));
  asm("":"+f"(w));
  tau += v + w;     /* Add in other second-order terms.  */