glsl: move to compiler/

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Matt Turner <mattst88@gmail.com>
Acked-by: Jose Fonseca <jfonseca@vmware.com>

1 files changed, 749 insertions, 0 deletions

diff --git a/src/compiler/glsl/lower_packed_varyings.cpp b/src/compiler/glsl/lower_packed_varyings.cpp
new file mode 100644
index 0000000..8d1eb17
--- /dev/null
+++ b/src/compiler/glsl/lower_packed_varyings.cpp
@@ -0,0 +1,749 @@
+/*
+ * 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).
+ *
+ * This lowering pass also packs flat floats, ints, and uints together, by
+ * using ivec4 as the base type of flat "varyings", and using appropriate
+ * casts to convert floats and uints into ints.
+ *
+ * This lowering pass also handles varyings whose type is a struct or an array
+ * of struct.  Structs are packed in order and with no gaps, so there may be a
+ * performance penalty due to structure elements being double-parked.
+ *
+ * Lowering of geometry shader inputs is slightly more complex, since geometry
+ * inputs are always arrays, so we need to lower arrays to arrays.  For
+ * example, the following input:
+ *
+ *   in struct Foo {
+ *     float f;
+ *     vec3 v;
+ *     vec2 a[2];
+ *   } arr[3];         // location=4, location_frac=0
+ *
+ * Would get lowered like this if it occurred in a fragment shader:
+ *
+ *   struct Foo {
+ *     float f;
+ *     vec3 v;
+ *     vec2 a[2];
+ *   } arr[3];
+ *   in vec4 packed4;  // location=4, location_frac=0
+ *   in vec4 packed5;  // location=5, location_frac=0
+ *   in vec4 packed6;  // location=6, location_frac=0
+ *   in vec4 packed7;  // location=7, location_frac=0
+ *   in vec4 packed8;  // location=8, location_frac=0
+ *   in vec4 packed9;  // location=9, location_frac=0
+ *
+ *   main()
+ *   {
+ *     arr[0].f = packed4.x;
+ *     arr[0].v = packed4.yzw;
+ *     arr[0].a[0] = packed5.xy;
+ *     arr[0].a[1] = packed5.zw;
+ *     arr[1].f = packed6.x;
+ *     arr[1].v = packed6.yzw;
+ *     arr[1].a[0] = packed7.xy;
+ *     arr[1].a[1] = packed7.zw;
+ *     arr[2].f = packed8.x;
+ *     arr[2].v = packed8.yzw;
+ *     arr[2].a[0] = packed9.xy;
+ *     arr[2].a[1] = packed9.zw;
+ *     ...
+ *   }
+ *
+ * But it would get lowered like this if it occurred in a geometry shader:
+ *
+ *   struct Foo {
+ *     float f;
+ *     vec3 v;
+ *     vec2 a[2];
+ *   } arr[3];
+ *   in vec4 packed4[3];  // location=4, location_frac=0
+ *   in vec4 packed5[3];  // location=5, location_frac=0
+ *
+ *   main()
+ *   {
+ *     arr[0].f = packed4[0].x;
+ *     arr[0].v = packed4[0].yzw;
+ *     arr[0].a[0] = packed5[0].xy;
+ *     arr[0].a[1] = packed5[0].zw;
+ *     arr[1].f = packed4[1].x;
+ *     arr[1].v = packed4[1].yzw;
+ *     arr[1].a[0] = packed5[1].xy;
+ *     arr[1].a[1] = packed5[1].zw;
+ *     arr[2].f = packed4[2].x;
+ *     arr[2].v = packed4[2].yzw;
+ *     arr[2].a[0] = packed5[2].xy;
+ *     arr[2].a[1] = packed5[2].zw;
+ *     ...
+ *   }
+ */
+
+#include "glsl_symbol_table.h"
+#include "ir.h"
+#include "ir_builder.h"
+#include "ir_optimization.h"
+#include "program/prog_instruction.h"
+
+using namespace ir_builder;
+
+namespace {
+
+/**
+ * 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 locations_used,
+                                 ir_variable_mode mode,
+                                 unsigned gs_input_vertices,
+                                 exec_list *out_instructions,
+                                 exec_list *out_variables);
+
+   void run(struct gl_shader *shader);
+
+private:
+   void bitwise_assign_pack(ir_rvalue *lhs, ir_rvalue *rhs);
+   void bitwise_assign_unpack(ir_rvalue *lhs, ir_rvalue *rhs);
+   unsigned lower_rvalue(ir_rvalue *rvalue, unsigned fine_location,
+                         ir_variable *unpacked_var, const char *name,
+                         bool gs_input_toplevel, unsigned vertex_index);
+   unsigned lower_arraylike(ir_rvalue *rvalue, unsigned array_size,
+                            unsigned fine_location,
+                            ir_variable *unpacked_var, const char *name,
+                            bool gs_input_toplevel, unsigned vertex_index);
+   ir_dereference *get_packed_varying_deref(unsigned location,
+                                            ir_variable *unpacked_var,
+                                            const char *name,
+                                            unsigned vertex_index);
+   bool needs_lowering(ir_variable *var);
+
+   /**
+    * Memory context used to allocate new instructions for the shader.
+    */
+   void * const mem_ctx;
+
+   /**
+    * Number of generic varying slots which are used by this shader.  This is
+    * used to allocate temporary intermediate data structures.  If any varying
+    * used by this shader has a location greater than or equal to
+    * VARYING_SLOT_VAR0 + 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_shader_in or ir_var_shader_out).
+    */
+   const ir_variable_mode mode;
+
+   /**
+    * If we are currently lowering geometry shader inputs, the number of input
+    * vertices the geometry shader accepts.  Otherwise zero.
+    */
+   const unsigned gs_input_vertices;
+
+   /**
+    * Exec list into which the visitor should insert the packing instructions.
+    * Caller provides this list; it should insert the instructions into the
+    * appropriate place in the shader once the visitor has finished running.
+    */
+   exec_list *out_instructions;
+
+   /**
+    * Exec list into which the visitor should insert any new variables.
+    */
+   exec_list *out_variables;
+};
+
+} /* anonymous namespace */
+
+lower_packed_varyings_visitor::lower_packed_varyings_visitor(
+      void *mem_ctx, unsigned locations_used, ir_variable_mode mode,
+      unsigned gs_input_vertices, exec_list *out_instructions,
+      exec_list *out_variables)
+   : mem_ctx(mem_ctx),
+     locations_used(locations_used),
+     packed_varyings((ir_variable **)
+                     rzalloc_array_size(mem_ctx, sizeof(*packed_varyings),
+                                        locations_used)),
+     mode(mode),
+     gs_input_vertices(gs_input_vertices),
+     out_instructions(out_instructions),
+     out_variables(out_variables)
+{
+}
+
+void
+lower_packed_varyings_visitor::run(struct gl_shader *shader)
+{
+   foreach_in_list(ir_instruction, node, shader->ir) {
+      ir_variable *var = node->as_variable();
+      if (var == NULL)
+         continue;
+
+      if (var->data.mode != this->mode ||
+          var->data.location < VARYING_SLOT_VAR0 ||
+          !this->needs_lowering(var))
+         continue;
+
+      /* This lowering pass is only capable of packing floats and ints
+       * together when their interpolation mode is "flat".  Therefore, to be
+       * safe, caller should ensure that integral varyings always use flat
+       * interpolation, even when this is not required by GLSL.
+       */
+      assert(var->data.interpolation == INTERP_QUALIFIER_FLAT ||
+             !var->type->contains_integer());
+
+      /* Clone the variable for program resource list before
+       * it gets modified and lost.
+       */
+      if (!shader->packed_varyings)
+         shader->packed_varyings = new (shader) exec_list;
+
+      shader->packed_varyings->push_tail(var->clone(shader, NULL));
+
+      /* Change the old varying into an ordinary global. */
+      assert(var->data.mode != ir_var_temporary);
+      var->data.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->data.location * 4 + var->data.location_frac, var,
+                         var->name, this->gs_input_vertices != 0, 0);
+   }
+}
+
+#define SWIZZLE_ZWZW MAKE_SWIZZLE4(SWIZZLE_Z, SWIZZLE_W, SWIZZLE_Z, SWIZZLE_W)
+
+/**
+ * Make an ir_assignment from \c rhs to \c lhs, performing appropriate
+ * bitcasts if necessary to match up types.
+ *
+ * This function is called when packing varyings.
+ */
+void
+lower_packed_varyings_visitor::bitwise_assign_pack(ir_rvalue *lhs,
+                                                   ir_rvalue *rhs)
+{
+   if (lhs->type->base_type != rhs->type->base_type) {
+      /* Since we only mix types in flat varyings, and we always store flat
+       * varyings as type ivec4, we need only produce conversions from (uint
+       * or float) to int.
+       */
+      assert(lhs->type->base_type == GLSL_TYPE_INT);
+      switch (rhs->type->base_type) {
+      case GLSL_TYPE_UINT:
+         rhs = new(this->mem_ctx)
+            ir_expression(ir_unop_u2i, lhs->type, rhs);
+         break;
+      case GLSL_TYPE_FLOAT:
+         rhs = new(this->mem_ctx)
+            ir_expression(ir_unop_bitcast_f2i, lhs->type, rhs);
+         break;
+      case GLSL_TYPE_DOUBLE:
+         assert(rhs->type->vector_elements <= 2);
+         if (rhs->type->vector_elements == 2) {
+            ir_variable *t = new(mem_ctx) ir_variable(lhs->type, "pack", ir_var_temporary);
+
+            assert(lhs->type->vector_elements == 4);
+            this->out_variables->push_tail(t);
+            this->out_instructions->push_tail(
+                  assign(t, u2i(expr(ir_unop_unpack_double_2x32, swizzle_x(rhs->clone(mem_ctx, NULL)))), 0x3));
+            this->out_instructions->push_tail(
+                  assign(t,  u2i(expr(ir_unop_unpack_double_2x32, swizzle_y(rhs))), 0xc));
+            rhs = deref(t).val;
+         } else {
+            rhs = u2i(expr(ir_unop_unpack_double_2x32, rhs));
+         }
+         break;
+      default:
+         assert(!"Unexpected type conversion while lowering varyings");
+         break;
+      }
+   }
+   this->out_instructions->push_tail(new (this->mem_ctx) ir_assignment(lhs, rhs));
+}
+
+
+/**
+ * Make an ir_assignment from \c rhs to \c lhs, performing appropriate
+ * bitcasts if necessary to match up types.
+ *
+ * This function is called when unpacking varyings.
+ */
+void
+lower_packed_varyings_visitor::bitwise_assign_unpack(ir_rvalue *lhs,
+                                                     ir_rvalue *rhs)
+{
+   if (lhs->type->base_type != rhs->type->base_type) {
+      /* Since we only mix types in flat varyings, and we always store flat
+       * varyings as type ivec4, we need only produce conversions from int to
+       * (uint or float).
+       */
+      assert(rhs->type->base_type == GLSL_TYPE_INT);
+      switch (lhs->type->base_type) {
+      case GLSL_TYPE_UINT:
+         rhs = new(this->mem_ctx)
+            ir_expression(ir_unop_i2u, lhs->type, rhs);
+         break;
+      case GLSL_TYPE_FLOAT:
+         rhs = new(this->mem_ctx)
+            ir_expression(ir_unop_bitcast_i2f, lhs->type, rhs);
+         break;
+      case GLSL_TYPE_DOUBLE:
+         assert(lhs->type->vector_elements <= 2);
+         if (lhs->type->vector_elements == 2) {
+            ir_variable *t = new(mem_ctx) ir_variable(lhs->type, "unpack", ir_var_temporary);
+            assert(rhs->type->vector_elements == 4);
+            this->out_variables->push_tail(t);
+            this->out_instructions->push_tail(
+                  assign(t, expr(ir_unop_pack_double_2x32, i2u(swizzle_xy(rhs->clone(mem_ctx, NULL)))), 0x1));
+            this->out_instructions->push_tail(
+                  assign(t, expr(ir_unop_pack_double_2x32, i2u(swizzle(rhs->clone(mem_ctx, NULL), SWIZZLE_ZWZW, 2))), 0x2));
+            rhs = deref(t).val;
+         } else {
+            rhs = expr(ir_unop_pack_double_2x32, i2u(rhs));
+         }
+         break;
+      default:
+         assert(!"Unexpected type conversion while lowering varyings");
+         break;
+      }
+   }
+   this->out_instructions->push_tail(new(this->mem_ctx) ir_assignment(lhs, rhs));
+}
+
+
+/**
+ * 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.
+ *
+ * \param gs_input_toplevel should be set to true if we are lowering geometry
+ * shader inputs, and we are currently lowering the whole input variable
+ * (i.e. we are lowering the array whose index selects the vertex).
+ *
+ * \param vertex_index: if we are lowering geometry shader inputs, and the
+ * level of the array that we are currently lowering is *not* the top level,
+ * then this indicates which vertex we are currently lowering.  Otherwise it
+ * is ignored.
+ *
+ * \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,
+                                            bool gs_input_toplevel,
+                                            unsigned vertex_index)
+{
+   unsigned dmul = rvalue->type->is_double() ? 2 : 1;
+   /* When gs_input_toplevel is set, we should be looking at a geometry shader
+    * input array.
+    */
+   assert(!gs_input_toplevel || rvalue->type->is_array());
+
+   if (rvalue->type->is_record()) {
+      for (unsigned i = 0; i < rvalue->type->length; i++) {
+         if (i != 0)
+            rvalue = rvalue->clone(this->mem_ctx, NULL);
+         const char *field_name = rvalue->type->fields.structure[i].name;
+         ir_dereference_record *dereference_record = new(this->mem_ctx)
+            ir_dereference_record(rvalue, field_name);
+         char *deref_name
+            = ralloc_asprintf(this->mem_ctx, "%s.%s", name, field_name);
+         fine_location = this->lower_rvalue(dereference_record, fine_location,
+                                            unpacked_var, deref_name, false,
+                                            vertex_index);
+      }
+      return fine_location;
+   } else 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,
+                                   gs_input_toplevel, vertex_index);
+   } 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,
+                                   false, vertex_index);
+   } else if (rvalue->type->vector_elements * dmul +
+              fine_location % 4 > 4) {
+      /* This vector is going to be "double parked" across two varying slots,
+       * so handle it as two separate assignments. For doubles, a dvec3/dvec4
+       * can end up being spread over 3 slots. However the second splitting
+       * will happen later, here we just always want to split into 2.
+       */
+      unsigned left_components, right_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 };
+
+      left_components = 4 - fine_location % 4;
+      if (rvalue->type->is_double()) {
+         /* We might actually end up with 0 left components! */
+         left_components /= 2;
+      }
+      right_components = rvalue->type->vector_elements - left_components;
+
+      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);
+      if (left_components)
+         fine_location = this->lower_rvalue(left_swizzle, fine_location,
+                                            unpacked_var, left_name, false,
+                                            vertex_index);
+      else
+         /* Top up the fine location to the next slot */
+         fine_location++;
+      return this->lower_rvalue(right_swizzle, fine_location, unpacked_var,
+                                right_name, false, vertex_index);
+   } 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 * dmul;
+      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 *packed_deref =
+         this->get_packed_varying_deref(location, unpacked_var, name,
+                                        vertex_index);
+      ir_swizzle *swizzle = new(this->mem_ctx)
+         ir_swizzle(packed_deref, swizzle_values, components);
+      if (this->mode == ir_var_shader_out) {
+         this->bitwise_assign_pack(swizzle, rvalue);
+      } else {
+         this->bitwise_assign_unpack(rvalue, swizzle);
+      }
+      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.
+ *
+ * \param gs_input_toplevel should be set to true if we are lowering geometry
+ * shader inputs, and we are currently lowering the whole input variable
+ * (i.e. we are lowering the array whose index selects the vertex).
+ *
+ * \param vertex_index: if we are lowering geometry shader inputs, and the
+ * level of the array that we are currently lowering is *not* the top level,
+ * then this indicates which vertex we are currently lowering.  Otherwise it
+ * is ignored.
+ */
+unsigned
+lower_packed_varyings_visitor::lower_arraylike(ir_rvalue *rvalue,
+                                               unsigned array_size,
+                                               unsigned fine_location,
+                                               ir_variable *unpacked_var,
+                                               const char *name,
+                                               bool gs_input_toplevel,
+                                               unsigned vertex_index)
+{
+   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);
+      if (gs_input_toplevel) {
+         /* Geometry shader inputs are a special case.  Instead of storing
+          * each element of the array at a different location, all elements
+          * are at the same location, but with a different vertex index.
+          */
+         (void) this->lower_rvalue(dereference_array, fine_location,
+                                   unpacked_var, name, false, i);
+      } else {
+         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,
+                               false, vertex_index);
+      }
+   }
+   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 interpolation parameters from \c
+ * unpacked_var.  Its base type is ivec4 if we are lowering a flat varying,
+ * vec4 otherwise.
+ *
+ * \param vertex_index: if we are lowering geometry shader inputs, then this
+ * indicates which vertex we are currently lowering.  Otherwise it is ignored.
+ */
+ir_dereference *
+lower_packed_varyings_visitor::get_packed_varying_deref(
+      unsigned location, ir_variable *unpacked_var, const char *name,
+      unsigned vertex_index)
+{
+   unsigned slot = location - VARYING_SLOT_VAR0;
+   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;
+      if (unpacked_var->data.interpolation == INTERP_QUALIFIER_FLAT)
+         packed_type = glsl_type::ivec4_type;
+      else
+         packed_type = glsl_type::vec4_type;
+      if (this->gs_input_vertices != 0) {
+         packed_type =
+            glsl_type::get_array_instance(packed_type,
+                                          this->gs_input_vertices);
+      }
+      ir_variable *packed_var = new(this->mem_ctx)
+         ir_variable(packed_type, packed_name, this->mode);
+      if (this->gs_input_vertices != 0) {
+         /* Prevent update_array_sizes() from messing with the size of the
+          * array.
+          */
+         packed_var->data.max_array_access = this->gs_input_vertices - 1;
+      }
+      packed_var->data.centroid = unpacked_var->data.centroid;
+      packed_var->data.sample = unpacked_var->data.sample;
+      packed_var->data.patch = unpacked_var->data.patch;
+      packed_var->data.interpolation = unpacked_var->data.interpolation;
+      packed_var->data.location = location;
+      packed_var->data.precision = unpacked_var->data.precision;
+      packed_var->data.always_active_io = unpacked_var->data.always_active_io;
+      unpacked_var->insert_before(packed_var);
+      this->packed_varyings[slot] = packed_var;
+   } else {
+      /* For geometry shader inputs, only update the packed variable name the
+       * first time we visit each component.
+       */
+      if (this->gs_input_vertices == 0 || vertex_index == 0) {
+         ralloc_asprintf_append((char **) &this->packed_varyings[slot]->name,
+                                ",%s", name);
+      }
+   }
+
+   ir_dereference *deref = new(this->mem_ctx)
+      ir_dereference_variable(this->packed_varyings[slot]);
+   if (this->gs_input_vertices != 0) {
+      /* When lowering GS inputs, the packed variable is an array, so we need
+       * to dereference it using vertex_index.
+       */
+      ir_constant *constant = new(this->mem_ctx) ir_constant(vertex_index);
+      deref = new(this->mem_ctx) ir_dereference_array(deref, constant);
+   }
+   return deref;
+}
+
+bool
+lower_packed_varyings_visitor::needs_lowering(ir_variable *var)
+{
+   /* Things composed of vec4's and varyings with explicitly assigned
+    * locations don't need lowering.  Everything else does.
+    */
+   if (var->data.explicit_location)
+      return false;
+
+   const glsl_type *type = var->type->without_array();
+   if (type->vector_elements == 4 && !type->is_double())
+      return false;
+   return true;
+}
+
+
+/**
+ * Visitor that splices varying packing code before every use of EmitVertex()
+ * in a geometry shader.
+ */
+class lower_packed_varyings_gs_splicer : public ir_hierarchical_visitor
+{
+public:
+   explicit lower_packed_varyings_gs_splicer(void *mem_ctx,
+                                             const exec_list *instructions);
+
+   virtual ir_visitor_status visit_leave(ir_emit_vertex *ev);
+
+private:
+   /**
+    * Memory context used to allocate new instructions for the shader.
+    */
+   void * const mem_ctx;
+
+   /**
+    * Instructions that should be spliced into place before each EmitVertex()
+    * call.
+    */
+   const exec_list *instructions;
+};
+
+
+lower_packed_varyings_gs_splicer::lower_packed_varyings_gs_splicer(
+      void *mem_ctx, const exec_list *instructions)
+   : mem_ctx(mem_ctx), instructions(instructions)
+{
+}
+
+
+ir_visitor_status
+lower_packed_varyings_gs_splicer::visit_leave(ir_emit_vertex *ev)
+{
+   foreach_in_list(ir_instruction, ir, this->instructions) {
+      ev->insert_before(ir->clone(this->mem_ctx, NULL));
+   }
+   return visit_continue;
+}
+
+
+void
+lower_packed_varyings(void *mem_ctx, unsigned locations_used,
+                      ir_variable_mode mode, unsigned gs_input_vertices,
+                      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(NULL, &void_parameters, false);
+   exec_list new_instructions, new_variables;
+   lower_packed_varyings_visitor visitor(mem_ctx, locations_used, mode,
+                                         gs_input_vertices,
+                                         &new_instructions,
+                                         &new_variables);
+   visitor.run(shader);
+   if (mode == ir_var_shader_out) {
+      if (shader->Stage == MESA_SHADER_GEOMETRY) {
+         /* For geometry shaders, outputs need to be lowered before each call
+          * to EmitVertex()
+          */
+         lower_packed_varyings_gs_splicer splicer(mem_ctx, &new_instructions);
+
+         /* Add all the variables in first. */
+         main_func_sig->body.head->insert_before(&new_variables);
+
+         /* Now update all the EmitVertex instances */
+         splicer.run(instructions);
+      } else {
+         /* For other shader types, outputs need to be lowered at the end of
+          * main()
+          */
+         main_func_sig->body.append_list(&new_variables);
+         main_func_sig->body.append_list(&new_instructions);
+      }
+   } else {
+      /* Shader inputs need to be lowered at the beginning of main() */
+      main_func_sig->body.head->insert_before(&new_instructions);
+      main_func_sig->body.head->insert_before(&new_variables);
+   }
+}