nir/opt_deref: Fix the vector bitcast optimization

It assumes the parent is a vector or scalar so we need to fail if it
isn't.

Fixes: 9190f82d57 "nir/opt_deref: Add an optimization for bitcasts"
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7064>

.gitlab-ci/piglit/cl.txt

@@ -358,7 +358,6 @@ program/execute/vload/vload-ulong-private: fail
 program/execute/vload/vload-ushort-global: fail
 program/execute/vload/vload-ushort-local: fail
 program/execute/vload/vload-ushort-private: fail
-program/execute/vload/vload_half-float-local: crash
 program/execute/vload/vload_half-float-private: crash
 program/execute/vload/vloada_half-float-private: crash
 program/execute/vstore/vstore-char-global: fail
@@ -405,9 +404,9 @@ program/execute/vstore/vstorea_half-float-private: crash
 summary:
        name:  results
        ----  --------
-       pass:     1418
+       pass:     1430
        fail:      296
-      crash:       29
+      crash:       28
        skip:       79
     timeout:        0
        warn:        0
@@ -417,4 +416,4 @@ summary:
     changes:        0
       fixes:        0
 regressions:        0
-      total:     1822
+      total:     1833

src/compiler/nir/nir_deref.c

@@ -1123,6 +1123,10 @@ is_vector_bitcast_deref(nir_deref_instr *cast,
    if (parent == NULL)
       return false;
 
+   /* The parent has to be a vector or scalar */
+   if (!glsl_type_is_vector_or_scalar(parent->type))
+      return false;
+
    /* Don't bother with 1-bit types */
    unsigned cast_bit_size = glsl_get_bit_size(cast->type);
    unsigned parent_bit_size = glsl_get_bit_size(parent->type);