On Fri, Jul 15, 2022 at 3:49 PM Prathamesh Kulkarni
<prathamesh.kulka...@linaro.org> wrote:
>
> On Thu, 14 Jul 2022 at 17:22, Richard Sandiford
> <richard.sandif...@arm.com> wrote:
> >
> > Richard Biener <richard.guent...@gmail.com> writes:
> > > On Thu, Jul 14, 2022 at 9:55 AM Prathamesh Kulkarni
> > > <prathamesh.kulka...@linaro.org> wrote:
> > >>
> > >> On Wed, 13 Jul 2022 at 12:22, Richard Biener
> > >> <richard.guent...@gmail.com> wrote:
> > >> >
> > >> > On Tue, Jul 12, 2022 at 9:12 PM Prathamesh Kulkarni via Gcc-patches
> > >> > <gcc-patches@gcc.gnu.org> wrote:
> > >> > >
> > >> > > Hi Richard,
> > >> > > For the following test:
> > >> > >
> > >> > > svint32_t f2(int a, int b, int c, int d)
> > >> > > {
> > >> > > int32x4_t v = (int32x4_t) {a, b, c, d};
> > >> > > return svld1rq_s32 (svptrue_b8 (), &v[0]);
> > >> > > }
> > >> > >
> > >> > > The compiler emits following ICE with -O3 -mcpu=generic+sve:
> > >> > > foo.c: In function ‘f2’:
> > >> > > foo.c:4:11: error: non-trivial conversion in ‘view_convert_expr’
> > >> > > 4 | svint32_t f2(int a, int b, int c, int d)
> > >> > > | ^~
> > >> > > svint32_t
> > >> > > __Int32x4_t
> > >> > > _7 = VIEW_CONVERT_EXPR<__Int32x4_t>(_8);
> > >> > > during GIMPLE pass: forwprop
> > >> > > dump file: foo.c.109t.forwprop2
> > >> > > foo.c:4:11: internal compiler error: verify_gimple failed
> > >> > > 0xfda04a verify_gimple_in_cfg(function*, bool)
> > >> > > ../../gcc/gcc/tree-cfg.cc:5568
> > >> > > 0xe9371f execute_function_todo
> > >> > > ../../gcc/gcc/passes.cc:2091
> > >> > > 0xe93ccb execute_todo
> > >> > > ../../gcc/gcc/passes.cc:2145
> > >> > >
> > >> > > This happens because, after folding svld1rq_s32 to vec_perm_expr, we
> > >> > > have:
> > >> > > int32x4_t v;
> > >> > > __Int32x4_t _1;
> > >> > > svint32_t _9;
> > >> > > vector(4) int _11;
> > >> > >
> > >> > > <bb 2> :
> > >> > > _1 = {a_3(D), b_4(D), c_5(D), d_6(D)};
> > >> > > v_12 = _1;
> > >> > > _11 = v_12;
> > >> > > _9 = VEC_PERM_EXPR <_11, _11, { 0, 1, 2, 3, ... }>;
> > >> > > return _9;
> > >> > >
> > >> > > During forwprop, simplify_permutation simplifies vec_perm_expr to
> > >> > > view_convert_expr,
> > >> > > and the end result becomes:
> > >> > > svint32_t _7;
> > >> > > __Int32x4_t _8;
> > >> > >
> > >> > > ;; basic block 2, loop depth 0
> > >> > > ;; pred: ENTRY
> > >> > > _8 = {a_2(D), b_3(D), c_4(D), d_5(D)};
> > >> > > _7 = VIEW_CONVERT_EXPR<__Int32x4_t>(_8);
> > >> > > return _7;
> > >> > > ;; succ: EXIT
> > >> > >
> > >> > > which causes the error duing verify_gimple since VIEW_CONVERT_EXPR
> > >> > > has incompatible types (svint32_t, int32x4_t).
> > >> > >
> > >> > > The attached patch disables simplification of VEC_PERM_EXPR
> > >> > > in simplify_permutation, if lhs and rhs have non compatible types,
> > >> > > which resolves ICE, but am not sure if it's the correct approach ?
> > >> >
> > >> > It for sure papers over the issue. I think the error happens earlier,
> > >> > the V_C_E should have been built with the type of the VEC_PERM_EXPR
> > >> > which is the type of the LHS. But then you probably run into the
> > >> > different sizes ICE (VLA vs constant size). I think for this case you
> > >> > want a BIT_FIELD_REF instead of a VIEW_CONVERT_EXPR,
> > >> > selecting the "low" part of the VLA vector.
> > >> Hi Richard,
> > >> Sorry I don't quite follow. In this case, we use VEC_PERM_EXPR to
> > >> represent dup operation
> > >> from fixed width to VLA vector. I am not sure how folding it to
> > >> BIT_FIELD_REF will work.
> > >> Could you please elaborate ?
> > >>
> > >> Also, the issue doesn't seem restricted to this case.
> > >> The following test case also ICE's during forwprop:
> > >> svint32_t foo()
> > >> {
> > >> int32x4_t v = (int32x4_t) {1, 2, 3, 4};
> > >> svint32_t v2 = svld1rq_s32 (svptrue_b8 (), &v[0]);
> > >> return v2;
> > >> }
> > >>
> > >> foo2.c: In function ‘foo’:
> > >> foo2.c:9:1: error: non-trivial conversion in ‘vector_cst’
> > >> 9 | }
> > >> | ^
> > >> svint32_t
> > >> int32x4_t
> > >> v2_4 = { 1, 2, 3, 4 };
> > >>
> > >> because simplify_permutation folds
> > >> VEC_PERM_EXPR< {1, 2, 3, 4}, {1, 2, 3, 4}, {0, 1, 2, 3, ...} >
> > >> into:
> > >> vector_cst {1, 2, 3, 4}
> > >>
> > >> and it complains during verify_gimple_assign_single because we don't
> > >> support assignment of vector_cst to VLA vector.
> > >>
> > >> I guess the issue really is that currently, only VEC_PERM_EXPR
> > >> supports lhs and rhs
> > >> to have vector types with differing lengths, and simplifying it to
> > >> other tree codes, like above,
> > >> will result in type errors ?
> > >
> > > That might be the case - Richard should know.
> >
> > I don't see anything particularly special about VEC_PERM_EXPR here,
> > or about the VLA vs. VLS thing. We would have the same issue trying
> > to build a 128-bit vector from 2 64-bit vectors. And there are other
> > tree codes whose input types are/can be different from their output
> > types.
> >
> > So it just seems like a normal type correctness issue: a VEC_PERM_EXPR
> > of type T needs to be replaced by something of type T. Whether T has a
> > constant size or a variable size doesn't matter.
> >
> > > If so your type check
> > > is still too late, you should instead recognize that we are permuting
> > > a VLA vector and then refuse to go any of the non-VEC_PERM generating
> > > paths - that probably means just allowing the code == VEC_PERM_EXPR
> > > case and not any of the CTOR/CST/VIEW_CONVERT_EXPR cases?
> >
> > Yeah. If we're talking about the match.pd code, I think only:
> >
> > (if (sel.series_p (0, 1, 0, 1))
> > { op0; }
> > (if (sel.series_p (0, 1, nelts, 1))
> > { op1; }
> >
> > need a type compatibility check. For fold_vec_perm I think
> > we should just rearrange:
> >
> > gcc_assert (known_eq (TYPE_VECTOR_SUBPARTS (type), nelts)
> > && known_eq (TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg0)), nelts)
> > && known_eq (TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg1)), nelts));
> > if (TREE_TYPE (TREE_TYPE (arg0)) != TREE_TYPE (type)
> > || TREE_TYPE (TREE_TYPE (arg1)) != TREE_TYPE (type))
> > return NULL_TREE;
> >
> > so that the assert comes after the early-out.
> >
> > It would be good at some point to relax fold_vec_perm to cases where the
> > outputs are a different length from the inputs, since the all-constant
> > VEC_PERM_EXPR above could be folded to a VECTOR_CST.
> Hi,
> For the above case, I think the issue is that simplify_permutation
> uses TREE_TYPE (arg0) for res_type,
> while it should now use type for lhs.
>
> /* Shuffle of a constructor. */
> bool ret = false;
> tree res_type = TREE_TYPE (arg0);
> tree opt = fold_ternary (VEC_PERM_EXPR, res_type, arg0, arg1, op2);
>
> Using, res_type = TREE_TYPE (gimple_get_lhs (stmt)),
> resolves the ICE, and emits all constant VEC_PERM_EXPR:
>
> v2_4 = VEC_PERM_EXPR <{ 1, 2, 3, 4 }, { 1, 2, 3, 4 }, { 0, 1, 2, 3, ... }>;
> return v2_4;
>
> Does the patch look OK to commit after bootstrap+test ?
Ok with using gimple_assign_lhs (stmt) instead of gimple_get_lhs (stmt).
> I will try to address the folding for above VEC_PERM_EXPR in follow-up patch.
>
> Thanks,
> Prathamesh
> >
> > Thanks,
> > Richard
