glsl: Add a lowering pass for packing varyings.

This lowering pass generates GLSL code that manually packs varyings
into vec4 slots, for the benefit of back-ends that don't support
packed varyings natively.

No functional change--the lowering pass is not yet used.

Reviewed-by: Eric Anholt <eric@anholt.net>

v2: Don't use ir_hierarchical_visitor--just loop over instructions
directly.  Also, make the names of the packed varyings include the
names of the original varyings that were packed into them.

1 files changed, 364 insertions, 0 deletions

diff --git a/src/glsl/lower_packed_varyings.cpp b/src/glsl/lower_packed_varyings.cpp
new file mode 100644
index 00000000000..09c551c4e63
--- /dev/null
+++ b/src/glsl/lower_packed_varyings.cpp
@@ -0,0 +1,364 @@
+/*
+ * Copyright © 2011 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 lower_varyings_to_packed.cpp
+ *
+ * This lowering pass generates GLSL code that manually packs varyings into
+ * vec4 slots, for the benefit of back-ends that don't support packed varyings
+ * natively.
+ *
+ * For example, the following shader:
+ *
+ *   out mat3x2 foo;  // location=4, location_frac=0
+ *   out vec3 bar[2]; // location=5, location_frac=2
+ *
+ *   main()
+ *   {
+ *     ...
+ *   }
+ *
+ * Is rewritten to:
+ *
+ *   mat3x2 foo;
+ *   vec3 bar[2];
+ *   out vec4 packed4; // location=4, location_frac=0
+ *   out vec4 packed5; // location=5, location_frac=0
+ *   out vec4 packed6; // location=6, location_frac=0
+ *
+ *   main()
+ *   {
+ *     ...
+ *     packed4.xy = foo[0];
+ *     packed4.zw = foo[1];
+ *     packed5.xy = foo[2];
+ *     packed5.zw = bar[0].xy;
+ *     packed6.x = bar[0].z;
+ *     packed6.yzw = bar[1];
+ *   }
+ *
+ * This lowering pass properly handles "double parking" of a varying vector
+ * across two varying slots.  For example, in the code above, two of the
+ * components of bar[0] are stored in packed5, and the remaining component is
+ * stored in packed6.
+ *
+ * Note that in theory, the extra instructions may cause some loss of
+ * performance.  However, hopefully in most cases the performance loss will
+ * either be absorbed by a later optimization pass, or it will be offset by
+ * memory bandwidth savings (because fewer varyings are used).
+ */
+
+#include "glsl_symbol_table.h"
+#include "ir.h"
+#include "ir_optimization.h"
+
+/**
+ * Visitor that performs varying packing.  For each varying declared in the
+ * shader, this visitor determines whether it needs to be packed.  If so, it
+ * demotes it to an ordinary global, creates new packed varyings, and
+ * generates assignments to convert between the original varying and the
+ * packed varying.
+ */
+class lower_packed_varyings_visitor
+{
+public:
+   lower_packed_varyings_visitor(void *mem_ctx, unsigned location_base,
+                                 unsigned locations_used,
+                                 ir_variable_mode mode,
+                                 exec_list *main_instructions);
+
+   void run(exec_list *instructions);
+
+private:
+   unsigned lower_rvalue(ir_rvalue *rvalue, unsigned fine_location,
+                         ir_variable *unpacked_var, const char *name);
+   unsigned lower_arraylike(ir_rvalue *rvalue, unsigned array_size,
+                            unsigned fine_location,
+                            ir_variable *unpacked_var, const char *name);
+   ir_variable *get_packed_varying(unsigned location,
+                                   ir_variable *unpacked_var,
+                                   const char *name);
+   bool needs_lowering(ir_variable *var);
+
+   /**
+    * Memory context used to allocate new instructions for the shader.
+    */
+   void * const mem_ctx;
+
+   /**
+    * Location representing the first generic varying slot for this shader
+    * stage (e.g. VERT_RESULT_VAR0 if we are packing vertex shader outputs).
+    * Varyings whose location is less than this value are assumed to
+    * correspond to special fixed function hardware, so they are not lowered.
+    */
+   const unsigned location_base;
+
+   /**
+    * Number of generic varying slots which are used by this shader.  This is
+    * used to allocate temporary intermediate data structures.  If any any
+    * varying used by this shader has a location greater than or equal to
+    * location_base + locations_used, an assertion will fire.
+    */
+   const unsigned locations_used;
+
+   /**
+    * Array of pointers to the packed varyings that have been created for each
+    * generic varying slot.  NULL entries in this array indicate varying slots
+    * for which a packed varying has not been created yet.
+    */
+   ir_variable **packed_varyings;
+
+   /**
+    * Type of varying which is being lowered in this pass (either ir_var_in or
+    * ir_var_out).
+    */
+   const ir_variable_mode mode;
+
+   /**
+    * List of instructions corresponding to the main() function.  This is
+    * where we add instructions to pack or unpack the varyings.
+    */
+   exec_list *main_instructions;
+};
+
+lower_packed_varyings_visitor::lower_packed_varyings_visitor(
+      void *mem_ctx, unsigned location_base, unsigned locations_used,
+      ir_variable_mode mode, exec_list *main_instructions)
+   : mem_ctx(mem_ctx),
+     location_base(location_base),
+     locations_used(locations_used),
+     packed_varyings((ir_variable **)
+                     rzalloc_array_size(mem_ctx, sizeof(*packed_varyings),
+                                        locations_used)),
+     mode(mode),
+     main_instructions(main_instructions)
+{
+}
+
+void
+lower_packed_varyings_visitor::run(exec_list *instructions)
+{
+   foreach_list (node, instructions) {
+      ir_variable *var = ((ir_instruction *) node)->as_variable();
+      if (var == NULL)
+         continue;
+
+      if (var->mode != this->mode ||
+          var->location < (int) this->location_base ||
+          !this->needs_lowering(var))
+         continue;
+
+      /* Change the old varying into an ordinary global. */
+      var->mode = ir_var_auto;
+
+      /* Create a reference to the old varying. */
+      ir_dereference_variable *deref
+         = new(this->mem_ctx) ir_dereference_variable(var);
+
+      /* Recursively pack or unpack it. */
+      this->lower_rvalue(deref, var->location * 4 + var->location_frac, var,
+                         var->name);
+   }
+}
+
+/**
+ * Recursively pack or unpack the given varying (or portion of a varying) by
+ * traversing all of its constituent vectors.
+ *
+ * \param fine_location is the location where the first constituent vector
+ * should be packed--the word "fine" indicates that this location is expressed
+ * in multiples of a float, rather than multiples of a vec4 as is used
+ * elsewhere in Mesa.
+ *
+ * \return the location where the next constituent vector (after this one)
+ * should be packed.
+ */
+unsigned
+lower_packed_varyings_visitor::lower_rvalue(ir_rvalue *rvalue,
+                                            unsigned fine_location,
+                                            ir_variable *unpacked_var,
+                                            const char *name)
+{
+   /* FINISHME: Support for "varying" records in GLSL 1.50. */
+   assert(!rvalue->type->is_record());
+
+   if (rvalue->type->is_array()) {
+      /* Arrays are packed/unpacked by considering each array element in
+       * sequence.
+       */
+      return this->lower_arraylike(rvalue, rvalue->type->array_size(),
+                                   fine_location, unpacked_var, name);
+   } else if (rvalue->type->is_matrix()) {
+      /* Matrices are packed/unpacked by considering each column vector in
+       * sequence.
+       */
+      return this->lower_arraylike(rvalue, rvalue->type->matrix_columns,
+                                   fine_location, unpacked_var, name);
+   } else if (rvalue->type->vector_elements + fine_location % 4 > 4) {
+      /* This vector is going to be "double parked" across two varying slots,
+       * so handle it as two separate assignments.
+       */
+      unsigned left_components = 4 - fine_location % 4;
+      unsigned right_components
+         = rvalue->type->vector_elements - left_components;
+      unsigned left_swizzle_values[4] = { 0, 0, 0, 0 };
+      unsigned right_swizzle_values[4] = { 0, 0, 0, 0 };
+      char left_swizzle_name[4] = { 0, 0, 0, 0 };
+      char right_swizzle_name[4] = { 0, 0, 0, 0 };
+      for (unsigned i = 0; i < left_components; i++) {
+         left_swizzle_values[i] = i;
+         left_swizzle_name[i] = "xyzw"[i];
+      }
+      for (unsigned i = 0; i < right_components; i++) {
+         right_swizzle_values[i] = i + left_components;
+         right_swizzle_name[i] = "xyzw"[i + left_components];
+      }
+      ir_swizzle *left_swizzle = new(this->mem_ctx)
+         ir_swizzle(rvalue, left_swizzle_values, left_components);
+      ir_swizzle *right_swizzle = new(this->mem_ctx)
+         ir_swizzle(rvalue->clone(this->mem_ctx, NULL), right_swizzle_values,
+                    right_components);
+      char *left_name
+         = ralloc_asprintf(this->mem_ctx, "%s.%s", name, left_swizzle_name);
+      char *right_name
+         = ralloc_asprintf(this->mem_ctx, "%s.%s", name, right_swizzle_name);
+      fine_location = this->lower_rvalue(left_swizzle, fine_location,
+                                         unpacked_var, left_name);
+      return this->lower_rvalue(right_swizzle, fine_location, unpacked_var,
+                                right_name);
+   } else {
+      /* No special handling is necessary; pack the rvalue into the
+       * varying.
+       */
+      unsigned swizzle_values[4] = { 0, 0, 0, 0 };
+      unsigned components = rvalue->type->vector_elements;
+      unsigned location = fine_location / 4;
+      unsigned location_frac = fine_location % 4;
+      for (unsigned i = 0; i < components; ++i)
+         swizzle_values[i] = i + location_frac;
+      ir_dereference_variable *packed_deref = new(this->mem_ctx)
+         ir_dereference_variable(this->get_packed_varying(location,
+                                                          unpacked_var, name));
+      ir_swizzle *swizzle = new(this->mem_ctx)
+         ir_swizzle(packed_deref, swizzle_values, components);
+      if (this->mode == ir_var_out) {
+         ir_assignment *assignment = new(this->mem_ctx)
+            ir_assignment(swizzle, rvalue);
+         this->main_instructions->push_tail(assignment);
+      } else {
+         ir_assignment *assignment = new(this->mem_ctx)
+            ir_assignment(rvalue, swizzle);
+         this->main_instructions->push_head(assignment);
+      }
+      return fine_location + components;
+   }
+}
+
+/**
+ * Recursively pack or unpack a varying for which we need to iterate over its
+ * constituent elements, accessing each one using an ir_dereference_array.
+ * This takes care of both arrays and matrices, since ir_dereference_array
+ * treats a matrix like an array of its column vectors.
+ */
+unsigned
+lower_packed_varyings_visitor::lower_arraylike(ir_rvalue *rvalue,
+                                               unsigned array_size,
+                                               unsigned fine_location,
+                                               ir_variable *unpacked_var,
+                                               const char *name)
+{
+   for (unsigned i = 0; i < array_size; i++) {
+      if (i != 0)
+         rvalue = rvalue->clone(this->mem_ctx, NULL);
+      ir_constant *constant = new(this->mem_ctx) ir_constant(i);
+      ir_dereference_array *dereference_array = new(this->mem_ctx)
+         ir_dereference_array(rvalue, constant);
+      char *subscripted_name
+         = ralloc_asprintf(this->mem_ctx, "%s[%d]", name, i);
+      fine_location = this->lower_rvalue(dereference_array, fine_location,
+                                         unpacked_var, subscripted_name);
+   }
+   return fine_location;
+}
+
+/**
+ * Retrieve the packed varying corresponding to the given varying location.
+ * If no packed varying has been created for the given varying location yet,
+ * create it and add it to the shader before returning it.
+ *
+ * The newly created varying inherits its base type (float, uint, or int) and
+ * interpolation parameters from \c unpacked_var.
+ */
+ir_variable *
+lower_packed_varyings_visitor::get_packed_varying(unsigned location,
+                                                  ir_variable *unpacked_var,
+                                                  const char *name)
+{
+   unsigned slot = location - this->location_base;
+   assert(slot < locations_used);
+   if (this->packed_varyings[slot] == NULL) {
+      char *packed_name = ralloc_asprintf(this->mem_ctx, "packed:%s", name);
+      const glsl_type *packed_type = glsl_type::get_instance(
+            unpacked_var->type->get_scalar_type()->base_type, 4, 1);
+      ir_variable *packed_var = new(this->mem_ctx)
+         ir_variable(packed_type, packed_name, this->mode);
+      packed_var->centroid = unpacked_var->centroid;
+      packed_var->interpolation = unpacked_var->interpolation;
+      packed_var->location = location;
+      unpacked_var->insert_before(packed_var);
+      this->packed_varyings[slot] = packed_var;
+   } else {
+      ralloc_asprintf_append((char **) &this->packed_varyings[slot]->name,
+                             ",%s", name);
+   }
+   return this->packed_varyings[slot];
+}
+
+bool
+lower_packed_varyings_visitor::needs_lowering(ir_variable *var)
+{
+   /* Things composed of vec4's don't need lowering.  Everything else does. */
+   const glsl_type *type = var->type;
+   if (type->is_array())
+      type = type->fields.array;
+   if (type->vector_elements == 4)
+      return false;
+   return true;
+}
+
+void
+lower_packed_varyings(void *mem_ctx, unsigned location_base,
+                      unsigned locations_used, ir_variable_mode mode,
+                      gl_shader *shader)
+{
+   exec_list *instructions = shader->ir;
+   ir_function *main_func = shader->symbols->get_function("main");
+   exec_list void_parameters;
+   ir_function_signature *main_func_sig
+      = main_func->matching_signature(&void_parameters);
+   exec_list *main_instructions = &main_func_sig->body;
+   lower_packed_varyings_visitor visitor(mem_ctx, location_base,
+                                         locations_used, mode,
+                                         main_instructions);
+   visitor.run(instructions);
+}