https://gcc.gnu.org/bugzilla/show_bug.cgi?id=22326
--- Comment #15 from rguenther at suse dot de <rguenther at suse dot de> --- On Fri, 27 Nov 2020, luoxhu at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=22326 > > --- Comment #14 from luoxhu at gcc dot gnu.org --- > (In reply to luoxhu from comment #13) > > > > 2) mad2.c > > > > float foo (double x, float y, float z) > > { > > return ( y * fabs (x) + z ); > > } > > > > > > mad2.c.098t.cunrolli: > > > > foo (double x, float y, float z) > > { > > double _1; > > double _2; > > double _3; > > double _4; > > double _5; > > float _9; > > > > <bb 2> [local count: 1073741824]: > > _1 = (double) y_6(D); > > _2 = ABS_EXPR <x_7(D)>; > > _3 = _1 * _2; > > _4 = (double) z_8(D); > > _5 = _3 + _4; > > _9 = (float) _5; > > return _9; > > > > } > > > > Maybe should use forward propagation here to save [_1, _2, _3 ... _9] to > m_vars > and set ignore_convert status in usage_info if rhs of the expression could > remove double conversion, for stmt which has two rhs, need intersect status > with AND operation of rhs1 ignore_convert and rhs2 ignore_convert, also clear > the ignore_convert status if any of it is false. Not sure whether this works, > also a bit more complicated then expected... I think backprop would need a way to "materialize" necessary converts on select arms of expressions so that double + (double)float can continue as "unneeded" on the arm to the float? So basically you do a optimistic back-propagation followed by a forward propagation step cancelling optimistic assumptions that didn't work out. Maybe it already works that way.
