RE: [PATCH 1/2]middle-end: Fix wrong overmatching of div-bitmask by using new optabs [PR108583]

[Tamar Christina <Tamar.Christina@arm.com>]

> > >>> In any case, if you disagree I don’t' really see a way forward
> > >>> aside from making this its own pattern running it before the
> > >>> overwidening
> > pattern.
> > >> I think we should look to see if ranger can be persuaded to provide
> > >> the range of the 16-bit addition, even though the statement that
> > >> produces it isn't part of a BB.  It shouldn't matter that the
> > >> addition originally came from a 32-bit one: the range follows
> > >> directly from the ranges of the operands (i.e. the fact that the
> > >> operands are the results of widening conversions).
> > > I think you can ask ranger on operations on names defined in the IL,
> > > so you can work yourself through the sequence of operations in the
> > > pattern sequence to compute ranges on their defs (and possibly even
> > > store them in the SSA info).  You just need to pick the correct
> > > ranger API for this…. Andrew CCed
> > >
> > >
> > Its not clear to me whats being asked...
> >
> > Expressions don't need to be in the IL to do range calculations.. I
> > believe we support arbitrary tree expressions via range_of_expr.
> >
> > if you have 32 bit ranges that you want to do 16 bit addition on, you
> > can also cast those ranges to a 16bit type,
> >
> > my32bitrange.cast (my16bittype);
> >
> > then invoke range-ops directly via getting the handler:
> >
> > handler = range_op_handler (PLUS_EXPR, 16bittype_tree); if (handler)
> >     handler->fold (result, my16bittype, mycasted32bitrange,
> > myothercasted32bitrange)
> >
> > There are higher level APIs if what you have on hand is closer to IL
> > than random ranges
> >
> > Describe exactly what it is you want to do... and I'll try to direct
> > you to the best way to do it.
> 
> The vectorizer has  a pattern matcher that runs at startup on the scalar code.
> This pattern matcher can replace one or more statements with alternative
> ones, these can be either existing tree_code or new internal functions.
> 
> One of the patterns here is a overwidening detection pattern which reduces
> the precision that an operation is to be done in during vectorization.
> 
> Another one is widening multiplication, which replaced PLUS_EXPR with
> WIDEN_PLUS_EXPR.
> 
> These can be chained, so e.g. a widening addition done on ints can be
> reduced to a widen addition done on shorts.
> 
> The question is whether given the new expression that the vectorizer has
> created whether ranger can tell what the precision is.  get_range_query fails
> because presumably it has no idea about the new operations created  and
> also doesn't know about any new IFNs.

Hi,

I have been trying to use ranger as requested. I've tried:

	  gimple_ranger ranger;
	  int_range_max r;
	  /* Check that no overflow will occur.  If we don't have range
	     information we can't perform the optimization.  */
	  if (ranger.range_of_expr (r, oprnd0, stmt))
	    {
	      wide_int max = r.upper_bound ();
                    ....

Which works for non-patterns, but still doesn't work for patterns.
On a stmt:
patt_27 = (_3) w+ (level_15(D));

it gives me a range:

$2 = {
  <wide_int_storage> = {
    val = {[0x0] = 0xffffffffffffffff, [0x1] = 0x7fff95bd8b00, [0x2] = 0x7fff95bd78b0, [0x3] = 0x3fa1dd0, [0x4] = 0x3fa1dd0, [0x5] = 0x344a706f832d4f00, [0x6] = 0x7fff95bd7950, [0x7] = 0x1ae7f11, [0x8] = 0x7fff95bd79f8},
    len = 0x1,
    precision = 0x10
  },
  members of generic_wide_int<wide_int_storage>:
  static is_sign_extended = 0x1
}

The precision is fine, but range seems to be -1?

Should I use range_op_handler (WIDEN_PLUS_EXPR, ...) in this case?

Thanks,
Tamar

> 
> Thanks,
> Tamar
> 
> >
> > Andrew
> >
> >