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 <sigles...@igalia.com>
---
 src/glsl/ast_function.cpp                             | 13 +++++++++----
 src/glsl/ir.cpp                                       |  7 +++++++
 src/glsl/ir.h                                         | 19 ++++++++++++++++++-
 src/glsl/ir_validate.cpp                              | 11 +++++++++++
 src/glsl/link_uniforms.cpp                            | 10 ++++++++--
 .../drivers/dri/i965/brw_fs_channel_expressions.cpp   |  2 ++
 src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp        |  8 ++++++++
 src/mesa/program/ir_to_mesa.cpp                       |  2 ++
 src/mesa/state_tracker/st_glsl_to_tgsi.cpp            |  5 +++++
 9 files changed, 70 insertions(+), 7 deletions(-)

diff --git a/src/glsl/ast_function.cpp b/src/glsl/ast_function.cpp
index 803edf5..ff5ecb9 100644
--- a/src/glsl/ast_function.cpp
+++ b/src/glsl/ast_function.cpp
@@ -1593,11 +1593,16 @@ ast_function_expression::handle_method(exec_list 
*instructions,
 
       if (op->type->is_array()) {
          if (op->type->is_unsized_array()) {
-            _mesa_glsl_error(&loc, state, "length called on unsized array");
-            goto fail;
+            if (!state->has_shader_storage_buffer_objects()) {
+               _mesa_glsl_error(&loc, state, "length called on unsized array"
+                                             " only available with "
+                                             
"ARB_shader_storage_buffer_object");
+            }
+            /* Calculate length of an unsized array in run-time */
+            result = new(ctx) ir_expression(ir_unop_ssbo_unsized_array_length, 
op);
+         } else {
+            result = new(ctx) ir_constant(op->type->array_size());
          }
-
-         result = new(ctx) ir_constant(op->type->array_size());
       } else if (op->type->is_vector()) {
          if (state->ARB_shading_language_420pack_enable) {
             /* .length() returns int. */
diff --git a/src/glsl/ir.cpp b/src/glsl/ir.cpp
index b9df976..2c45b9e 100644
--- a/src/glsl/ir.cpp
+++ b/src/glsl/ir.cpp
@@ -342,6 +342,11 @@ ir_expression::ir_expression(int op, ir_rvalue *op0)
                                           op0->type->vector_elements, 1);
       break;
 
+   case ir_unop_get_buffer_size:
+   case ir_unop_ssbo_unsized_array_length:
+      this->type = glsl_type::int_type;
+      break;
+
    default:
       assert(!"not reached: missing automatic type setup for ir_expression");
       this->type = op0->type;
@@ -571,6 +576,8 @@ static const char *const operator_strs[] = {
    "noise",
    "subroutine_to_int",
    "interpolate_at_centroid",
+   "get_buffer_size",
+   "ssbo_unsized_array_length",
    "+",
    "-",
    "*",
diff --git a/src/glsl/ir.h b/src/glsl/ir.h
index 48b6795..43a2bf0 100644
--- a/src/glsl/ir.h
+++ b/src/glsl/ir.h
@@ -1425,9 +1425,26 @@ enum ir_expression_operation {
    ir_unop_interpolate_at_centroid,
 
    /**
+    * Ask the driver for the total size of a buffer block.
+    *
+    * operand0 is the ir_constant buffer block index in the linked shader.
+    */
+   ir_unop_get_buffer_size,
+
+   /**
+    * Calculate length of an unsized array inside a buffer block.
+    * This opcode is going to be replaced in a lowering pass inside
+    * the linker.
+    *
+    * operand0 is the unsized array's ir_value for the calculation
+    * of its length.
+    */
+   ir_unop_ssbo_unsized_array_length,
+
+   /**
     * A sentinel marking the last of the unary operations.
     */
-   ir_last_unop = ir_unop_interpolate_at_centroid,
+   ir_last_unop = ir_unop_ssbo_unsized_array_length,
 
    ir_binop_add,
    ir_binop_sub,
diff --git a/src/glsl/ir_validate.cpp b/src/glsl/ir_validate.cpp
index 3f0dea7..935571a 100644
--- a/src/glsl/ir_validate.cpp
+++ b/src/glsl/ir_validate.cpp
@@ -409,6 +409,17 @@ ir_validate::visit_leave(ir_expression *ir)
       assert(ir->operands[0]->type->is_float());
       break;
 
+   case ir_unop_get_buffer_size:
+      assert(ir->type == glsl_type::int_type);
+      assert(ir->operands[0]->type == glsl_type::uint_type);
+      break;
+
+   case ir_unop_ssbo_unsized_array_length:
+      assert(ir->type == glsl_type::int_type);
+      assert(ir->operands[0]->type->is_array());
+      assert(ir->operands[0]->type->is_unsized_array());
+      break;
+
    case ir_unop_d2f:
       assert(ir->operands[0]->type->base_type == GLSL_TYPE_DOUBLE);
       assert(ir->type->base_type == GLSL_TYPE_FLOAT);
diff --git a/src/glsl/link_uniforms.cpp b/src/glsl/link_uniforms.cpp
index 238546b..67a6e1b 100644
--- a/src/glsl/link_uniforms.cpp
+++ b/src/glsl/link_uniforms.cpp
@@ -231,9 +231,15 @@ program_resource_visitor::recursion(const glsl_type *t, 
char **name,
       if (record_type == NULL && t->fields.array->is_record())
          record_type = t->fields.array;
 
-      record_array_count *= t->length;
+      unsigned length = t->length;
+      /* Shader storage block unsized arrays: add subscript [0] to variable
+       * names */
+      if (t->is_unsized_array())
+         length = 1;
 
-      for (unsigned i = 0; i < t->length; i++) {
+      record_array_count *= length;
+
+      for (unsigned i = 0; i < length; i++) {
         size_t new_length = name_length;
 
         /* Append the subscript to the current variable name */
diff --git a/src/mesa/drivers/dri/i965/brw_fs_channel_expressions.cpp 
b/src/mesa/drivers/dri/i965/brw_fs_channel_expressions.cpp
index a8883a3..277b6cc 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_channel_expressions.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_channel_expressions.cpp
@@ -379,6 +379,7 @@ ir_channel_expressions_visitor::visit_leave(ir_assignment 
*ir)
    }
 
    case ir_binop_ubo_load:
+   case ir_unop_get_buffer_size:
       unreachable("not yet supported");
 
    case ir_triop_fma:
@@ -430,6 +431,7 @@ ir_channel_expressions_visitor::visit_leave(ir_assignment 
*ir)
    case ir_triop_vector_insert:
    case ir_quadop_bitfield_insert:
    case ir_quadop_vector:
+   case ir_unop_ssbo_unsized_array_length:
       unreachable("should have been lowered");
 
    case ir_unop_unpack_half_2x16_split_x:
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp 
b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index ac086a7..3443e5c 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -1585,6 +1585,10 @@ vec4_visitor::visit(ir_expression *ir)
       emit(MOV(result_dst, op[0]));
       break;
 
+   case ir_unop_ssbo_unsized_array_length:
+      unreachable("not reached: should be handled by lower_ubo_reference");
+      break;
+
    case ir_binop_add:
       emit(ADD(result_dst, op[0], op[1]));
       break;
@@ -1791,6 +1795,10 @@ vec4_visitor::visit(ir_expression *ir)
       emit(RNDE(result_dst, op[0]));
       break;
 
+   case ir_unop_get_buffer_size:
+      unreachable("not reached: not implemented");
+      break;
+
    case ir_binop_min:
       emit_minmax(BRW_CONDITIONAL_L, result_dst, op[0], op[1]);
       break;
diff --git a/src/mesa/program/ir_to_mesa.cpp b/src/mesa/program/ir_to_mesa.cpp
index afb400f..4201a80 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.
        */
diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp 
b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index c3a8c11..5c16541 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -2217,10 +2217,15 @@ glsl_to_tgsi_visitor::visit(ir_expression *ir)
    case ir_triop_vector_insert:
    case ir_binop_carry:
    case ir_binop_borrow:
+   case ir_unop_ssbo_unsized_array_length:
       /* This operation is not supported, or should have already been handled.
        */
       assert(!"Invalid ir opcode in glsl_to_tgsi_visitor::visit()");
       break;
+
+   case ir_unop_get_buffer_size:
+      assert(!"Not implemented yet");
+      break;
    }
 
    this->result = result_src;
-- 
2.1.4

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