[Bug tree-optimization/22326] promotions (from float to double) are not removed when they should be able to

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=22326

--- Comment #17 from luoxhu at gcc dot gnu.org ---
(In reply to rsandifo@gcc.gnu.org from comment #16)
> > 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;
> > 
> > }
> > 
> > mad2.c.099t.backprop:
> > 
> > [USE] _9 in return _9;
> > [USE] _5 in _9 = (float) _5;
> >   _5: convert from float to double not important
> > [DEF] Recording new information for _5 = _3 + _4;
> >   _5: convert from float to double not important
> > [USE] _4 in _5 = _3 + _4;
> >   _4: convert from float to double not important
> > [DEF] Recording new information for _4 = (double) z_8(D);
> >   _4: convert from float to double not important
> > [USE] _3 in _5 = _3 + _4;
> >   _3: convert from float to double not important
> > [DEF] Recording new information for _3 = _1 * _2;
> >   _3: convert from float to double not important
> > [USE] _2 in _3 = _1 * _2;
> >   _2: convert from float to double not important
> > [DEF] Recording new information for _2 = ABS_EXPR <x_7(D)>;
> >   _2: convert from float to double not important
> > [USE] _1 in _3 = _1 * _2;
> >   _1: convert from float to double not important
> > [DEF] Recording new information for _1 = (double) y_6(D);
> >   _1: convert from float to double not important
> > 
> > Deleting _4 = (double) z_8(D);
> > Deleting _1 = (double) y_6(D);
> > 
> > 
> > EMERGENCY DUMP:
> > 
> > __attribute__((noinline))
> > foo (double x, float y, float z)
> > {
> >   double _2;
> >   double _3;
> >   double _5;
> >   float _9;
> > 
> >   <bb 2> [local count: 1073741824]:
> >   _2 = ABS_EXPR <x_7(D)>;
> >   _3 = _2 * y_6(D);
> >   _5 = _3 + z_8(D);
> >   _9 = (float) _5;
> >   return _9;
> > 
> > }
> Maybe I'm misunderstanding the point, but isn't this
> just an issue with the way that the results of the
> analysis are applied to the IL, rather than a problem
> in the analysis itself?

Yes, the optimize operations on Gimple is a bit uncertain.
Do you mean add convert from double to float at proper place
like below to avoid ICE caused by type mismatch ICE in verify_ssa?
Which one will be better, and whether it is correct for all kind
of math operations like pow/exp, etc under fast-math?  If so, no
cancelling is needed again as Richi mentioned?

1) convert before ABS_EXPR:

foo (double x, float y, float z)
{
  float _9;
  float _11;
  float _12;
  float _13;
  float _14;

  <bb 2> [local count: 1073741824]:
  _11 = (float) x_6(D);
  _12 = ABS_EXPR <_11>;
  _13 = y_7(D) * _12;
  _14 = z_8(D) + _13;
  _9 = _14;
  return _9;

}

foo:
.LFB0:
        .cfi_startproc
        frsp 0,1
        fabs 0,0
        fmadds 1,2,0,3
        blr


2) OR convert after ABS_EXPR:

foo (double x, float y, float z)
{
  double _1;
  float _9;
  float _11;
  float _12;
  float _13;

  <bb 2> [local count: 1073741824]:
  _1 = ABS_EXPR <x_6(D)>;
  _11 = (float) _1;
  _12 = y_7(D) * _11;
  _13 = z_8(D) + _12;
  _9 = _13;
  return _9;

}

foo:
.LFB0:
        .cfi_startproc
        fabs 0,1
        frsp 0,0
        fmadds 1,2,0,3
        blr