Re: [PATCH] Fix bool vs. unsigned:1 vectorization (PR tree-optimization/79284)

[Jakub Jelinek <jakub at redhat dot com>]

On Wed, Feb 01, 2017 at 11:07:18AM +0100, Richard Biener wrote:
> > On Wed, Feb 01, 2017 at 10:58:29AM +0100, Richard Biener wrote:
> > > > > +/* Nonzero if TYPE represents a (scalar) boolean type or type
> > > > > +   in the middle-end compatible with it.  */
> > > > > +
> > > > > +#define INTEGRAL_BOOLEAN_TYPE_P(TYPE) \
> > > > > +  (TREE_CODE (TYPE) == BOOLEAN_TYPE            \
> > > > > +   || ((TREE_CODE (TYPE) == INTEGER_TYPE       \
> > > > > +       || TREE_CODE (TYPE) == ENUMERAL_TYPE)   \
> > > > > +       && TYPE_PRECISION (TYPE) == 1           \
> > > > > +       && TYPE_UNSIGNED (TYPE)))
> > > > > 
> > > > > (just to quote what you proposed).
> > > > 
> > > > So would it help to use
> > > >   (TREE_CODE (TYPE) == BOOLEAN_TYPE
> > > >    || (INTEGRAL_TYPE_P (TYPE)
> > > >        && useless_type_conversion_p (boolean_type_node, TYPE)))
> > > > It would be much slower than the above, but would be less dependent
> > > > on useless_type_conversion_p details.
> > > 
> > > For the vectorizer it likely would break the larger logical type
> > > handling?
> > 
> > Why?  It is the same thing as the earlier macro above.
> > Any kind of boolean, plus anything that could be initially boolean
> > and the middle-end might have replaced it with.
> 
> boolean_type_node is QImode but logical(8) is DImode for example.
> Both have precision == 1 but they are not types_compatible_p
> (you probably missed the mode check in useless_type_conversion_p).

Then the earlier macro should have used also a TYPE_MODE check.
The latter macro is what I've been looking for in the patch, except that
I thought it is too expensive (plus might actually not DTRT if
boolean_type_node has > 1 precision, but some unsigned precision 1
BOOLEAN_TYPE exists too; as Fortran has changed, now it is only Ada that
doesn't have precision 1 boolean_type_node, but then it likely doesn't
have any precision 1 BOOLEAN_TYPEs).

> > > The question is really what the vectorizer and other places are looking
> > > for -- which isually is a 1-bit precision, eventually unsigned,
> > > integral type.
> > 
> > It is looking for any type where the only valid values are 0 (false) and 1
> > (true), so that it can actually vectorize it as a bitmask, or vector of
> > integers with -1 and 0 values.
> 
> That's INTEGRAL_TYPE_P && TYPE_PRECISION == 1 && TYPE_UNSIGNED.  The
> Ada types do not fall under this category as far as I understand as
> the exceptional values may exist in memory(?)

But the exceptional values are undefined behavior I believe.
Anyway, we've been vectorizing not just the 1-bit precision BOOLEAN_TYPEs
but other BOOLEAN_TYPEs (Ada and especially Fortran) for a couple of years
this way already and I'm not aware of issues with that.

So suddenly stopping doing that because we want to fix a bug related
to the fact that for 1-bit precision unsigned QImode BOOLEAN_TYPE the
middle-end considers other types to be compatible with those is strange
and very risky, especially at this point in GCC 7 development.

	Jakub