+ if (shader_stage == MESA_SHADER_TESS_CTRL &&
+ deref->variable_referenced()->data.mode == ir_var_shader_out) {
+ /* Tessellation control shader outputs act as if they have memory
+ * backing them and if we have writes from multiple threads
+ * targeting the same vec4 (this can happen for patch outputs), the
+ * load-vec-store pattern of ir_triop_vector_insert doesn't work.
+ * Instead, we have to lower to a series of conditional write-masked
+ * assignments.
+ */
+ ir_variable *const src_temp =
+ factory.make_temp(ir->rhs->type, "scalar_tmp");
+
+ /* The newly created variable declaration goes before the assignment
+ * because we're going to set it as the new LHS.
+ */
+ ir->insert_before(factory.instructions);
+ ir->set_lhs(new(mem_ctx) ir_dereference_variable(src_temp));
+
+ ir_variable *const arr_index =
+ factory.make_temp(deref->array_index->type, "index_tmp");
+ factory.emit(assign(arr_index, deref->array_index));
+
+ for (unsigned i = 0; i < new_lhs->type->vector_elements; i++) {
+ ir_constant *const cmp_index =
+ ir_constant::zero(factory.mem_ctx, deref->array_index->type);
+ cmp_index->value.u[0] = i;
+
+ ir_rvalue *const lhs_clone = new_lhs->clone(factory.mem_ctx, NULL);
+ ir_dereference_variable *const src_temp_deref =
+ new(mem_ctx) ir_dereference_variable(src_temp);
+
+ if (new_lhs->ir_type != ir_type_swizzle) {
+ assert(lhs_clone->as_dereference());
+ ir_assignment *cond_assign =
+ new(mem_ctx) ir_assignment(lhs_clone->as_dereference(),
+ src_temp_deref,
+ equal(arr_index, cmp_index),
+ WRITEMASK_X << i);
+ factory.emit(cond_assign);
+ } else {
+ ir_assignment *cond_assign =
+ new(mem_ctx) ir_assignment(swizzle(lhs_clone, i, 1),
+ src_temp_deref,
+ equal(arr_index, cmp_index));
+ factory.emit(cond_assign);
+ }
+ }
+ ir->insert_after(factory.instructions);
+ } else {
+ ir->rhs = new(mem_ctx) ir_expression(ir_triop_vector_insert,
+ new_lhs->type,
+ new_lhs->clone(mem_ctx, NULL),
+ ir->rhs,
+ deref->array_index);
+ ir->write_mask = (1 << new_lhs->type->vector_elements) - 1;
+ ir->set_lhs(new_lhs);
+ }