[Mesa-dev] [PATCH 2/2] glsl: disable array splitting for AoA

[Timothy Arceri]

While it produces functioning code the pass creates worse code
for arrays of arrays. See the comment added in this patch for more
detail.
---
 src/compiler/glsl/opt_array_splitting.cpp | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/src/compiler/glsl/opt_array_splitting.cpp b/src/compiler/glsl/opt_array_splitting.cpp
index e3073b0..525953f 100644
--- a/src/compiler/glsl/opt_array_splitting.cpp
+++ b/src/compiler/glsl/opt_array_splitting.cpp
@@ -133,20 +133,46 @@ ir_array_reference_visitor::get_variable_entry(ir_variable *var)
 
    if (!(var->type->is_array() || var->type->is_matrix()))
       return NULL;
 
    /* If the array hasn't been sized yet, we can't split it.  After
     * linking, this should be resolved.
     */
    if (var->type->is_unsized_array())
       return NULL;
 
+   /* FIXME: arrays of arrays are not handled correctly by this pass so we
+    * skip it for now. While the pass will create functioning code it actually
+    * produces worse code.
+    *
+    * For example the array:
+    *
+    *    int[3][2] a;
+    *
+    * ends up being split up into:
+    *
+    *    int[3][2] a_0;
+    *    int[3][2] a_1;
+    *    int[3][2] a_2;
+    *
+    * And we end up referencing each of these new arrays for example:
+    *
+    *    a[0][1] will be turned into a_0[0][1]
+    *    a[1][0] will be turned into a_1[1][0]
+    *    a[2][0] will be turned into a_2[2][0]
+    *
+    * For now we continue to split AoA of matrices to avoid CTS regressions.
+    */
+   if (var->type->is_array() && var->type->fields.array->is_array() &&
+       !var->type->without_array()->is_matrix())
+      return NULL;
+
    foreach_in_list(variable_entry, entry, &this->variable_list) {
       if (entry->var == var)
          return entry;
    }
 
    variable_entry *entry = new(mem_ctx) variable_entry(var);
    this->variable_list.push_tail(entry);
    return entry;
 }
 
-- 
2.9.4