mesa/src/glsl/ir_set_program_inouts.cpp

/*
 * Copyright © 2010 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

/**
 * \file ir_set_program_inouts.cpp
 *
 * Sets the InputsRead and OutputsWritten of Mesa programs.
 *
 * Additionally, for fragment shaders, sets the InterpQualifier array, the
 * IsCentroid bitfield, and the UsesDFdy flag.
 *
 * Mesa programs (gl_program, not gl_shader_program) have a set of
 * flags indicating which varyings are read and written.  Computing
 * which are actually read from some sort of backend code can be
 * tricky when variable array indexing involved.  So this pass
 * provides support for setting InputsRead and OutputsWritten right
 * from the GLSL IR.
 */

#include "main/core.h" /* for struct gl_program */
#include "ir.h"
#include "ir_visitor.h"
#include "glsl_types.h"

class ir_set_program_inouts_visitor : public ir_hierarchical_visitor {
public:
   ir_set_program_inouts_visitor(struct gl_program *prog, GLenum shader_type)
   {
      this->prog = prog;
      this->shader_type = shader_type;
   }
   ~ir_set_program_inouts_visitor()
   {
   }

   virtual ir_visitor_status visit_enter(ir_dereference_array *);
   virtual ir_visitor_status visit_enter(ir_function_signature *);
   virtual ir_visitor_status visit_enter(ir_expression *);
   virtual ir_visitor_status visit_enter(ir_discard *);
   virtual ir_visitor_status visit(ir_dereference_variable *);

private:
   void mark_whole_variable(ir_variable *var);
   bool try_mark_partial_variable(ir_variable *var, ir_rvalue *index);

   struct gl_program *prog;
   GLenum shader_type;
};

static inline bool
is_shader_inout(ir_variable *var)
{
   return var->mode == ir_var_shader_in ||
          var->mode == ir_var_shader_out ||
          var->mode == ir_var_system_value;
}

static void
mark(struct gl_program *prog, ir_variable *var, int offset, int len,
     bool is_fragment_shader)
{
   /* As of GLSL 1.20, varyings can only be floats, floating-point
    * vectors or matrices, or arrays of them.  For Mesa programs using
    * InputsRead/OutputsWritten, everything but matrices uses one
    * slot, while matrices use a slot per column.  Presumably
    * something doing a more clever packing would use something other
    * than InputsRead/OutputsWritten.
    */

   for (int i = 0; i < len; i++) {
      GLbitfield64 bitfield = BITFIELD64_BIT(var->location + var->index + offset + i);
      if (var->mode == ir_var_shader_in) {
	 prog->InputsRead |= bitfield;
         if (is_fragment_shader) {
            gl_fragment_program *fprog = (gl_fragment_program *) prog;
            fprog->InterpQualifier[var->location + var->index + offset + i] =
               (glsl_interp_qualifier) var->interpolation;
            if (var->centroid)
               fprog->IsCentroid |= bitfield;
         }
      } else if (var->mode == ir_var_system_value) {
         prog->SystemValuesRead |= bitfield;
      } else {
         assert(var->mode == ir_var_shader_out);
	 prog->OutputsWritten |= bitfield;
      }
   }
}

/**
 * Mark an entire variable as used.  Caller must ensure that the variable
 * represents a shader input or output.
 */
void
ir_set_program_inouts_visitor::mark_whole_variable(ir_variable *var)
{
   mark(this->prog, var, 0, var->type->count_attribute_slots(),
        this->shader_type == GL_FRAGMENT_SHADER);
}

/* Default handler: Mark all the locations in the variable as used. */
ir_visitor_status
ir_set_program_inouts_visitor::visit(ir_dereference_variable *ir)
{
   if (!is_shader_inout(ir->var))
      return visit_continue;

   mark_whole_variable(ir->var);

   return visit_continue;
}

/**
 * Try to mark a portion of the given variable as used.  Caller must ensure
 * that the variable represents a shader input or output which can be indexed
 * into in array fashion (an array or matrix).
 *
 * If the index can't be interpreted as a constant, or some other problem
 * occurs, then nothing will be marked and false will be returned.
 */
bool
ir_set_program_inouts_visitor::try_mark_partial_variable(ir_variable *var,
                                                         ir_rvalue *index)
{
   const glsl_type *type = var->type;

   /* The code below only handles:
    *
    * - Indexing into matrices
    * - Indexing into arrays of (matrices, vectors, or scalars)
    *
    * All other possibilities are either prohibited by GLSL (vertex inputs and
    * fragment outputs can't be structs) or should have been eliminated by
    * lowering passes (do_vec_index_to_swizzle() gets rid of indexing into
    * vectors, and lower_packed_varyings() gets rid of structs that occur in
    * varyings).
    */
   if (!(type->is_matrix() ||
        (type->is_array() &&
         (type->fields.array->is_numeric() ||
          type->fields.array->is_boolean())))) {
      assert(!"Unexpected indexing in ir_set_program_inouts");

      /* For safety in release builds, in case we ever encounter unexpected
       * indexing, give up and let the caller mark the whole variable as used.
       */
      return false;
   }

   ir_constant *index_as_constant = index->as_constant();
   if (!index_as_constant)
      return false;

   unsigned elem_width;
   unsigned num_elems;
   if (type->is_array()) {
      num_elems = type->length;
      if (type->fields.array->is_matrix())
         elem_width = type->fields.array->matrix_columns;
      else
         elem_width = 1;
   } else {
      num_elems = type->matrix_columns;
      elem_width = 1;
   }

   if (index_as_constant->value.u[0] >= num_elems) {
      /* Constant index outside the bounds of the matrix/array.  This could
       * arise as a result of constant folding of a legal GLSL program.
       *
       * Even though the spec says that indexing outside the bounds of a
       * matrix/array results in undefined behaviour, we don't want to pass
       * out-of-range values to mark() (since this could result in slots that
       * don't exist being marked as used), so just let the caller mark the
       * whole variable as used.
       */
      return false;
   }

   mark(this->prog, var, index_as_constant->value.u[0] * elem_width,
        elem_width, this->shader_type == GL_FRAGMENT_SHADER);
   return true;
}

ir_visitor_status
ir_set_program_inouts_visitor::visit_enter(ir_dereference_array *ir)
{
   ir_dereference_variable *deref_var;
   deref_var = ir->array->as_dereference_variable();
   ir_variable *var = deref_var ? deref_var->var : NULL;

   /* Check that we're dereferencing a shader in or out */
   if (!var || !is_shader_inout(var))
      return visit_continue;

   if (try_mark_partial_variable(var, ir->array_index))
      return visit_continue_with_parent;

   return visit_continue;
}

ir_visitor_status
ir_set_program_inouts_visitor::visit_enter(ir_function_signature *ir)
{
   /* We don't want to descend into the function parameters and
    * consider them as shader inputs or outputs.
    */
   visit_list_elements(this, &ir->body);
   return visit_continue_with_parent;
}

ir_visitor_status
ir_set_program_inouts_visitor::visit_enter(ir_expression *ir)
{
   if (this->shader_type == GL_FRAGMENT_SHADER &&
       ir->operation == ir_unop_dFdy) {
      gl_fragment_program *fprog = (gl_fragment_program *) prog;
      fprog->UsesDFdy = true;
   }
   return visit_continue;
}

ir_visitor_status
ir_set_program_inouts_visitor::visit_enter(ir_discard *)
{
   /* discards are only allowed in fragment shaders. */
   assert(this->shader_type == GL_FRAGMENT_SHADER);

   gl_fragment_program *fprog = (gl_fragment_program *) prog;
   fprog->UsesKill = true;

   return visit_continue;
}

void
do_set_program_inouts(exec_list *instructions, struct gl_program *prog,
                      GLenum shader_type)
{
   ir_set_program_inouts_visitor v(prog, shader_type);

   prog->InputsRead = 0;
   prog->OutputsWritten = 0;
   prog->SystemValuesRead = 0;
   if (shader_type == GL_FRAGMENT_SHADER) {
      gl_fragment_program *fprog = (gl_fragment_program *) prog;
      memset(fprog->InterpQualifier, 0, sizeof(fprog->InterpQualifier));
      fprog->IsCentroid = 0;
      fprog->UsesDFdy = false;
      fprog->UsesKill = false;
   }
   visit_list_elements(&v, instructions);
}