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 ?

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

Thanks,
Prathamesh