nir/opt_varyings: handle user barycentrics

This failed an assertion because the barycentric src wasn't an intrinsic.

v2: also do it in backward_inter_shader_code_motion

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com> (v1)
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33024>

src/compiler/nir/nir_opt_varyings.c

@@ -2599,8 +2599,10 @@ get_input_qualifier(struct linkage_info *linkage, unsigned i)
    }
 
    assert(load->intrinsic == nir_intrinsic_load_interpolated_input);
-   nir_intrinsic_instr *baryc =
-      nir_instr_as_intrinsic(load->src[0].ssa->parent_instr);
+
+   nir_instr *baryc_instr = load->src[0].ssa->parent_instr;
+   nir_intrinsic_instr *baryc = baryc_instr->type == nir_instr_type_intrinsic ?
+                                   nir_instr_as_intrinsic(baryc_instr) : NULL;
 
    if (linkage->has_flexible_interp) {
       if (is_color) {
@@ -2611,6 +2613,12 @@ get_input_qualifier(struct linkage_info *linkage, unsigned i)
       }
    }
 
+   /* This is either lowered barycentric_at_offset/at_sample or user
+    * barycentrics. Treat it like barycentric_at_offset.
+    */
+   if (!baryc)
+      return QUAL_SKIP;
+
    /* If interpolateAt{Centroid,Offset,Sample} is used, see if there is
     * another load that doesn't use those, so that we get the real qualifier.
     */
@@ -3903,8 +3911,15 @@ backward_inter_shader_code_motion(struct linkage_info *linkage,
          switch (load->intrinsic) {
          case nir_intrinsic_load_interpolated_input: {
             assert(linkage->consumer_stage == MESA_SHADER_FRAGMENT);
-            nir_intrinsic_instr *baryc =
-               nir_instr_as_intrinsic(load->src[0].ssa->parent_instr);
+            nir_instr *baryc_instr = load->src[0].ssa->parent_instr;
+
+            /* This is either lowered barycentric_at_offset/at_sample or user
+             * barycentrics. Treat it like barycentric_at_offset.
+             */
+            if (baryc_instr->type != nir_instr_type_intrinsic)
+               continue;
+
+            nir_intrinsic_instr *baryc = nir_instr_as_intrinsic(baryc_instr);
             nir_intrinsic_op op = baryc->intrinsic;
             enum glsl_interp_mode interp = nir_intrinsic_interp_mode(baryc);
             bool linear = interp == INTERP_MODE_NOPERSPECTIVE;