nir: fix sampler lowering pass for arrays

This fixes bugs with special cases where we have arrays of
structures containing samplers or arrays of samplers.

I've verified that patch results in calculating same index value as
returned by _mesa_get_sampler_uniform_value for IR. Patch makes
following ES3 conformance test pass:

	ES3-CTS.shaders.struct.uniform.sampler_array_fragment

v2: remove unnecessary comment (Topi)
    simplify changes and the overall code (Jason)

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90114

src/glsl/nir/nir_lower_samplers.cpp

@@ -70,19 +70,22 @@ lower_sampler(nir_tex_instr *instr, const struct gl_shader_program *shader_progr
       case nir_deref_type_array: {
          nir_deref_array *deref_array = nir_deref_as_array(deref->child);
 
+         assert(deref_array->deref_array_type != nir_deref_array_type_wildcard);
+
+         if (deref_array->deref.child) {
+            ralloc_asprintf_append(&name, "[%u]",
+               deref_array->deref_array_type == nir_deref_array_type_direct ?
+                  deref_array->base_offset : 0);
+         } else {
+            assert(deref->child->type->base_type == GLSL_TYPE_SAMPLER);
+            instr->sampler_index = deref_array->base_offset;
+         }
+
          /* XXX: We're assuming here that the indirect is the last array
           * thing we have.  This should be ok for now as we don't support
           * arrays_of_arrays yet.
           */
-
-         instr->sampler_index *= glsl_get_length(deref->type);
-         switch (deref_array->deref_array_type) {
-         case nir_deref_array_type_direct:
-            instr->sampler_index += deref_array->base_offset;
-            if (deref_array->deref.child)
-               ralloc_asprintf_append(&name, "[%u]", deref_array->base_offset);
-            break;
-         case nir_deref_array_type_indirect: {
+         if (deref_array->deref_array_type == nir_deref_array_type_indirect) {
             /* First, we have to resize the array of texture sources */
             nir_tex_src *new_srcs = rzalloc_array(instr, nir_tex_src,
                                                   instr->num_srcs + 1);
@@ -106,16 +109,6 @@ lower_sampler(nir_tex_instr *instr, const struct gl_shader_program *shader_progr
                                &deref_array->indirect);
 
             instr->sampler_array_size = glsl_get_length(deref->type);
-
-            if (deref_array->deref.child)
-               ralloc_strcat(&name, "[0]");
-            break;
-         }
-
-         case nir_deref_array_type_wildcard:
-            unreachable("Cannot copy samplers");
-         default:
-            unreachable("Invalid deref array type");
          }
          break;
       }