glsl: Add parser/compiler support for unsized array's length()

The unsized array length is computed with the following formula:

array.length() =
   max((buffer_object_size - offset_of_array) / stride_of_array, 0)

Of these, only the buffer size needs to be provided by the backends, the
frontend already knows the values of the two other variables.

This patch identifies the cases where we need to get the length of an
unsized array, injecting ir_unop_ssbo_unsized_array_length expressions
that will be lowered (in a later patch) to inject the formula mentioned
above.

It also adds the ir_unop_get_buffer_size expression that drivers will
implement to provide the buffer length.

v2:
- Do not define a triop that will force backends to implement the
  entire formula, they should only need to provide the buffer size
  since the other values are known by the frontend (Curro).

v3:
- Call state->has_shader_storage_buffer_objects() in ast_function.cpp instead
  of using state->ARB_shader_storage_buffer_object_enable (Tapani).

Signed-off-by: Samuel Iglesias Gonsalvez <[email protected]>
Reviewed-by: Kristian Høgsberg <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/mesa/program/ir_to_mesa.cpp b/src/mesa/program/ir_to_mesa.cpp
index afb400f714c..4201a80cf62 100644
--- a/src/mesa/program/ir_to_mesa.cpp
+++ b/src/mesa/program/ir_to_mesa.cpp
@@ -1344,9 +1344,11 @@ ir_to_mesa_visitor::visit(ir_expression *ir)
    case ir_unop_dFdy_coarse:
    case ir_unop_dFdy_fine:
    case ir_unop_subroutine_to_int:
+   case ir_unop_get_buffer_size:
       assert(!"not supported");
       break;
 
+   case ir_unop_ssbo_unsized_array_length:
    case ir_quadop_vector:
       /* This operation should have already been handled.
        */