[Bug tree-optimization/126696] Fold a fused multiply-add by one into an addition

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126696

--- Comment #2 from Drea Pinski <pinskia at gcc dot gnu.org> ---
  double fadd (double x, double y) { return __builtin_fma (x, y, -0.0); }

can also be folded into just x*y (clang handles that too).

Maybe these only valid to do without signaling nans.


Note:
  double fmul1 (double x, double y) { return __builtin_fma (1.0, x, y); }

operands 0 and 1 are swapped for Canonicalization so we only need to handle the
1.0 in operand 1.