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.
>
> Alternatively, should we allow assignments from fixed-width to SVE
> vector, so the above
> VIEW_CONVERT_EXPR would result in dup ?
>
> Thanks,
> Prathamesh
