On Tue, Jul 25, 2023 at 03:25:57PM -0400, Drew Ross wrote:
> > With that fixed I think for non-vector integrals the above is the most
> suitable
> > canonical form of a sign-extension. Note it should also work for any
> other
> > constant shift amount - just use the appropriate intermediate precision
> for
> > the truncating type.
> > We _might_ want
> > to consider to only use the converts when the intermediate type has
> > mode precision (and as a special case allow one bit as in your above case)
> > so it can expand to (sign_extend:<outer> (subreg:<inner> reg)).
>
> Here is a pattern that that only matches to truncations that result in mode
> precision (or precision of 1):
>
> (simplify
> (rshift (nop_convert? (lshift @0 INTEGER_CST@1)) @@1)
> (if (INTEGRAL_TYPE_P (type)
> && !TYPE_UNSIGNED (type)
> && wi::gt_p (element_precision (type), wi::to_wide (@1), TYPE_SIGN
> (TREE_TYPE (@1))))
I'd use
&& wi::ltu_p (wi::to_wide (@1), element_precision (type))
If the shift count would be negative, you'd otherwise ICE in tree_to_uhwi on
it (sure, that is UB at runtime, but compiler shouldn't ICE on it).
> (with {
> int width = element_precision (type) - tree_to_uhwi (@1);
> tree stype = build_nonstandard_integer_type (width, 0);
> }
> (if (TYPE_PRECISION (stype) == 1 || type_has_mode_precision_p (stype))
> (convert (convert:stype @0))))))
Jakub
