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From: "rsandifo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/96974] [10/11 Regression] ICE in
 vect_get_vector_types_for_stmt compiling for SVE
Date: Thu, 28 Jan 2021 11:59:17 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96974

--- Comment #9 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.or=
g> ---
(In reply to Stam Markianos-Wright from comment #8)
> I have a liiitle bit more progress here, but I have a question about
> vect_get_smallest_scalar_type.
>=20
> If we look at the comment before the function:
>=20
> >/* Return the smallest scalar part of STMT_INFO.
> >   This is used to determine the vectype of the stmt.  We generally set =
the
> >   vectype according to the type of the result (lhs).  For stmts whose
> >   result-type is different than the type of the arguments (e.g., demoti=
on,
> >   promotion), vectype will be reset appropriately (later).  Note that w=
e have
> >   to visit the smallest datatype in this function, because that determi=
nes the
> >   VF.  If the smallest datatype in the loop is present only as the rhs =
of a
> >   promotion operation - we'd miss it.
>=20
> Would this be "smallest datatype in all cases", or is this more like "the
> smallest
> datatype within the same promotion/demotion chain"?
>=20
> i.e. how should we react if we detect a smallest datatype on the rhs of
> "float"
> when everything else in the stmt has been in the integer chain (int or,
> like in this case, long int)?
Not sure if this is really answering the question (let me know if it's not),
but: for an lhs of int and an rhs of float, the choice doesn't really matte=
r,
since they're the same size.  But for an lhs of long int and an rhs of floa=
t,
the smallest vectype has to be taken from the float.=