glsl: make a copy of array indices that are used to deref a function out param

Fixes new piglit test:
tests/spec/glsl-1.20/execution/qualifiers/vs-out-conversion-int-to-float-vec4-index.shader_test

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/compiler/glsl/ast_function.cpp

@@ -348,6 +348,49 @@ verify_parameter_modes(_mesa_glsl_parse_state *state,
    return true;
 }
 
+struct copy_index_deref_data {
+   void *mem_ctx;
+   exec_list *before_instructions;
+};
+
+static void
+copy_index_derefs_to_temps(ir_instruction *ir, void *data)
+{
+   struct copy_index_deref_data *d = (struct copy_index_deref_data *)data;
+
+   if (ir->ir_type == ir_type_dereference_array) {
+      ir_dereference_array *a = (ir_dereference_array *) ir;
+      ir = a->array->as_dereference();
+
+      ir_rvalue *idx = a->array_index;
+      if (idx->as_dereference_variable()) {
+         ir_variable *var = idx->variable_referenced();
+
+         /* If the index is read only it cannot change so there is no need
+          * to copy it.
+          */
+         if (var->data.read_only || var->data.memory_read_only)
+            return;
+
+         ir_variable *tmp = new(d->mem_ctx) ir_variable(idx->type, "idx_tmp",
+                                                        ir_var_temporary);
+         d->before_instructions->push_tail(tmp);
+
+         ir_dereference_variable *const deref_tmp_1 =
+            new(d->mem_ctx) ir_dereference_variable(tmp);
+         ir_assignment *const assignment =
+            new(d->mem_ctx) ir_assignment(deref_tmp_1,
+                                          idx->clone(d->mem_ctx, NULL));
+         d->before_instructions->push_tail(assignment);
+
+         /* Replace the array index with a dereference of the new temporary */
+         ir_dereference_variable *const deref_tmp_2 =
+            new(d->mem_ctx) ir_dereference_variable(tmp);
+         a->array_index = deref_tmp_2;
+      }
+   }
+}
+
 static void
 fix_parameter(void *mem_ctx, ir_rvalue *actual, const glsl_type *formal_type,
               exec_list *before_instructions, exec_list *after_instructions,
@@ -362,6 +405,17 @@ fix_parameter(void *mem_ctx, ir_rvalue *actual, const glsl_type *formal_type,
        && (expr == NULL || expr->operation != ir_binop_vector_extract))
       return;
 
+   /* An array index could also be an out variable so we need to make a copy
+    * of them before the function is called.
+    */
+   if (!actual->as_dereference_variable()) {
+      struct copy_index_deref_data data;
+      data.mem_ctx = mem_ctx;
+      data.before_instructions = before_instructions;
+
+      visit_tree(actual, copy_index_derefs_to_temps, &data);
+   }
+
    /* To convert an out parameter, we need to create a temporary variable to
     * hold the value before conversion, and then perform the conversion after
     * the function call returns.