Re: [2/2] PR96463 -- changes to type checking vec_perm_expr in middle end

[Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org>]

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On Tue, 4 Jan 2022 at 19:12, Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> Richard Biener <rguenther@suse.de> writes:
> > On Tue, 4 Jan 2022, Richard Sandiford wrote:
> >
> >> Richard Biener <rguenther@suse.de> writes:
> >> > On Fri, 17 Dec 2021, Richard Sandiford wrote:
> >> >
> >> >> Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org> writes:
> >> >> > Hi,
> >> >> > The attached patch rearranges order of type-check for vec_perm_expr
> >> >> > and relaxes type checking for
> >> >> > lhs = vec_perm_expr<rhs1, rhs2, mask>
> >> >> >
> >> >> > when:
> >> >> > rhs1 == rhs2,
> >> >> > lhs is variable length vector,
> >> >> > rhs1 is fixed length vector,
> >> >> > TREE_TYPE (lhs) == TREE_TYPE (rhs1)
> >> >> >
> >> >> > I am not sure tho if this check is correct ? My intent was to capture
> >> >> > case when vec_perm_expr is used to "extend" fixed length vector to
> >> >> > it's VLA equivalent.
> >> >>
> >> >> VLAness isn't really the issue.  We want the same thing to work for
> >> >> -msve-vector-bits=256, -msve-vector-bits=512, etc., even though the
> >> >> vectors are fixed-length in that case.
> >> >>
> >> >> The principle is that for:
> >> >>
> >> >>   A = VEC_PERM_EXPR <B, C, D>;
> >> >>
> >> >> the requirements are:
> >> >>
> >> >> - A, B, C and D must be vectors
> >> >> - A, B and C must have the same element type
> >> >> - D must have an integer element type
> >> >> - A and D must have the same number of elements (NA)
> >> >> - B and C must have the same number of elements (NB)
> >> >>
> >> >> The semantics are that we create a joined vector BC (all elements of B
> >> >> followed by all element of C) and that:
> >> >>
> >> >>   A[i] = BC[D[i] % (NB+NB)]
> >> >>
> >> >> for 0 ≤ i < NA.
> >> >>
> >> >> This operation makes sense even if NA != NB.
> >> >
> >> > But note that we don't currently expect NA != NB and the optab just
> >> > has a single mode.
> >>
> >> True, but we only need this for constant permutes.  They are already
> >> special in that they allow the index elements to be wider than the data
> >> elements.
> >
> > OK, then we should reflect this in the stmt verification and only relax
> > the constant permute vector case and also amend the
> > TARGET_VECTORIZE_VEC_PERM_CONST accordingly.
>
> Sounds good.
>
> > For non-constant permutes the docs say the mode of vec_perm is
> > the common mode of operands 1 and 2 whilst the mode of operand 0
> > is unspecified - even unconstrained by the docs.  I'm not sure
> > if vec_perm expansion is expected to eventually FAIL.  Updating the
> > docs of vec_perm would be appreciated as well.
>
> Yeah, I guess de facto operand 0 has to be the same mode as operands
> 1 and 2.  Maybe that was just an oversight, or maybe it seemed obvious
> or self-explanatory at the time. :-)
>
> > As said I prefer to not mangle the existing stmt checking too much
> > at this stage so minimal adjustment is prefered there.
>
> The PR is only an enhancement request rather than a bug, so I think the
> patch would need to wait for GCC 13 whatever happens.
Hi,
In attached patch, the type checking is relaxed only if mask is constant.
Does this look OK ?

Thanks,
Prathamesh
>
> Thanks,
> Richard

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diff --git a/gcc/tree-cfg.cc b/gcc/tree-cfg.cc
index e321d929fd0..02b88f67855 100644
--- a/gcc/tree-cfg.cc
+++ b/gcc/tree-cfg.cc
@@ -4307,6 +4307,24 @@ verify_gimple_assign_ternary (gassign *stmt)
       break;
 
     case VEC_PERM_EXPR:
+      /* If permute is constant, then we allow for lhs and rhs
+	 to have different vector types, provided:
+	 (1) lhs, rhs1, rhs2, and rhs3 have same element type.
+	 (2) rhs3 vector has integer element type.
+	 (3) len(lhs) == len(rhs3) && len(rhs1) == len(rhs2).  */
+
+      if (TREE_CONSTANT (rhs3)
+	  && VECTOR_TYPE_P (lhs_type)
+	  && VECTOR_TYPE_P (rhs1_type)
+	  && VECTOR_TYPE_P (rhs2_type)
+	  && VECTOR_TYPE_P (rhs3_type)
+	  && TREE_TYPE (lhs_type) == TREE_TYPE (rhs1_type)
+	  && TREE_TYPE (lhs_type) == TREE_TYPE (rhs2_type)
+	  && INTEGRAL_TYPE_P (TREE_TYPE (rhs3_type))
+	  && known_eq (TYPE_VECTOR_SUBPARTS (lhs_type), TYPE_VECTOR_SUBPARTS (rhs3_type))
+	  && known_eq (TYPE_VECTOR_SUBPARTS (rhs1_type), TYPE_VECTOR_SUBPARTS (rhs2_type)))
+	return false;
+
       if (!useless_type_conversion_p (lhs_type, rhs1_type)
 	  || !useless_type_conversion_p (lhs_type, rhs2_type))
 	{