glsl: move to compiler/

Signed-off-by: Emil Velikov <[email protected]>
Acked-by: Matt Turner <[email protected]>
Acked-by: Jose Fonseca <[email protected]>

1 files changed, 1888 insertions, 0 deletions

diff --git a/src/compiler/glsl/link_varyings.cpp b/src/compiler/glsl/link_varyings.cpp
new file mode 100644
index 00000000000..264b69ca619
--- /dev/null
+++ b/src/compiler/glsl/link_varyings.cpp
@@ -0,0 +1,1888 @@
+/*
+ * Copyright © 2012 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 link_varyings.cpp
+ *
+ * Linker functions related specifically to linking varyings between shader
+ * stages.
+ */
+
+
+#include "main/mtypes.h"
+#include "glsl_symbol_table.h"
+#include "glsl_parser_extras.h"
+#include "ir_optimization.h"
+#include "linker.h"
+#include "link_varyings.h"
+#include "main/macros.h"
+#include "program/hash_table.h"
+#include "program.h"
+
+
+/**
+ * Get the varying type stripped of the outermost array if we're processing
+ * a stage whose varyings are arrays indexed by a vertex number (such as
+ * geometry shader inputs).
+ */
+static const glsl_type *
+get_varying_type(const ir_variable *var, gl_shader_stage stage)
+{
+   const glsl_type *type = var->type;
+
+   if (!var->data.patch &&
+       ((var->data.mode == ir_var_shader_out &&
+         stage == MESA_SHADER_TESS_CTRL) ||
+        (var->data.mode == ir_var_shader_in &&
+         (stage == MESA_SHADER_TESS_CTRL || stage == MESA_SHADER_TESS_EVAL ||
+          stage == MESA_SHADER_GEOMETRY)))) {
+      assert(type->is_array());
+      type = type->fields.array;
+   }
+
+   return type;
+}
+
+/**
+ * Validate the types and qualifiers of an output from one stage against the
+ * matching input to another stage.
+ */
+static void
+cross_validate_types_and_qualifiers(struct gl_shader_program *prog,
+                                    const ir_variable *input,
+                                    const ir_variable *output,
+                                    gl_shader_stage consumer_stage,
+                                    gl_shader_stage producer_stage)
+{
+   /* Check that the types match between stages.
+    */
+   const glsl_type *type_to_match = input->type;
+
+   /* VS -> GS, VS -> TCS, VS -> TES, TES -> GS */
+   const bool extra_array_level = (producer_stage == MESA_SHADER_VERTEX &&
+                                   consumer_stage != MESA_SHADER_FRAGMENT) ||
+                                  consumer_stage == MESA_SHADER_GEOMETRY;
+   if (extra_array_level) {
+      assert(type_to_match->is_array());
+      type_to_match = type_to_match->fields.array;
+   }
+
+   if (type_to_match != output->type) {
+      /* There is a bit of a special case for gl_TexCoord.  This
+       * built-in is unsized by default.  Applications that variable
+       * access it must redeclare it with a size.  There is some
+       * language in the GLSL spec that implies the fragment shader
+       * and vertex shader do not have to agree on this size.  Other
+       * driver behave this way, and one or two applications seem to
+       * rely on it.
+       *
+       * Neither declaration needs to be modified here because the array
+       * sizes are fixed later when update_array_sizes is called.
+       *
+       * From page 48 (page 54 of the PDF) of the GLSL 1.10 spec:
+       *
+       *     "Unlike user-defined varying variables, the built-in
+       *     varying variables don't have a strict one-to-one
+       *     correspondence between the vertex language and the
+       *     fragment language."
+       */
+      if (!output->type->is_array() || !is_gl_identifier(output->name)) {
+         linker_error(prog,
+                      "%s shader output `%s' declared as type `%s', "
+                      "but %s shader input declared as type `%s'\n",
+                      _mesa_shader_stage_to_string(producer_stage),
+                      output->name,
+                      output->type->name,
+                      _mesa_shader_stage_to_string(consumer_stage),
+                      input->type->name);
+         return;
+      }
+   }
+
+   /* Check that all of the qualifiers match between stages.
+    */
+   if (input->data.centroid != output->data.centroid) {
+      linker_error(prog,
+                   "%s shader output `%s' %s centroid qualifier, "
+                   "but %s shader input %s centroid qualifier\n",
+                   _mesa_shader_stage_to_string(producer_stage),
+                   output->name,
+                   (output->data.centroid) ? "has" : "lacks",
+                   _mesa_shader_stage_to_string(consumer_stage),
+                   (input->data.centroid) ? "has" : "lacks");
+      return;
+   }
+
+   if (input->data.sample != output->data.sample) {
+      linker_error(prog,
+                   "%s shader output `%s' %s sample qualifier, "
+                   "but %s shader input %s sample qualifier\n",
+                   _mesa_shader_stage_to_string(producer_stage),
+                   output->name,
+                   (output->data.sample) ? "has" : "lacks",
+                   _mesa_shader_stage_to_string(consumer_stage),
+                   (input->data.sample) ? "has" : "lacks");
+      return;
+   }
+
+   if (input->data.patch != output->data.patch) {
+      linker_error(prog,
+                   "%s shader output `%s' %s patch qualifier, "
+                   "but %s shader input %s patch qualifier\n",
+                   _mesa_shader_stage_to_string(producer_stage),
+                   output->name,
+                   (output->data.patch) ? "has" : "lacks",
+                   _mesa_shader_stage_to_string(consumer_stage),
+                   (input->data.patch) ? "has" : "lacks");
+      return;
+   }
+
+   if (!prog->IsES && input->data.invariant != output->data.invariant) {
+      linker_error(prog,
+                   "%s shader output `%s' %s invariant qualifier, "
+                   "but %s shader input %s invariant qualifier\n",
+                   _mesa_shader_stage_to_string(producer_stage),
+                   output->name,
+                   (output->data.invariant) ? "has" : "lacks",
+                   _mesa_shader_stage_to_string(consumer_stage),
+                   (input->data.invariant) ? "has" : "lacks");
+      return;
+   }
+
+   /* GLSL >= 4.40 removes text requiring interpolation qualifiers
+    * to match cross stage, they must only match within the same stage.
+    *
+    * From page 84 (page 90 of the PDF) of the GLSL 4.40 spec:
+    *
+    *     "It is a link-time error if, within the same stage, the interpolation
+    *     qualifiers of variables of the same name do not match.
+    *
+    */
+   if (input->data.interpolation != output->data.interpolation &&
+       prog->Version < 440) {
+      linker_error(prog,
+                   "%s shader output `%s' specifies %s "
+                   "interpolation qualifier, "
+                   "but %s shader input specifies %s "
+                   "interpolation qualifier\n",
+                   _mesa_shader_stage_to_string(producer_stage),
+                   output->name,
+                   interpolation_string(output->data.interpolation),
+                   _mesa_shader_stage_to_string(consumer_stage),
+                   interpolation_string(input->data.interpolation));
+      return;
+   }
+}
+
+/**
+ * Validate front and back color outputs against single color input
+ */
+static void
+cross_validate_front_and_back_color(struct gl_shader_program *prog,
+                                    const ir_variable *input,
+                                    const ir_variable *front_color,
+                                    const ir_variable *back_color,
+                                    gl_shader_stage consumer_stage,
+                                    gl_shader_stage producer_stage)
+{
+   if (front_color != NULL && front_color->data.assigned)
+      cross_validate_types_and_qualifiers(prog, input, front_color,
+                                          consumer_stage, producer_stage);
+
+   if (back_color != NULL && back_color->data.assigned)
+      cross_validate_types_and_qualifiers(prog, input, back_color,
+                                          consumer_stage, producer_stage);
+}
+
+/**
+ * Validate that outputs from one stage match inputs of another
+ */
+void
+cross_validate_outputs_to_inputs(struct gl_shader_program *prog,
+				 gl_shader *producer, gl_shader *consumer)
+{
+   glsl_symbol_table parameters;
+   ir_variable *explicit_locations[MAX_VARYING] = { NULL, };
+
+   /* Find all shader outputs in the "producer" stage.
+    */
+   foreach_in_list(ir_instruction, node, producer->ir) {
+      ir_variable *const var = node->as_variable();
+
+      if ((var == NULL) || (var->data.mode != ir_var_shader_out))
+	 continue;
+
+      if (!var->data.explicit_location
+          || var->data.location < VARYING_SLOT_VAR0)
+         parameters.add_variable(var);
+      else {
+         /* User-defined varyings with explicit locations are handled
+          * differently because they do not need to have matching names.
+          */
+         const unsigned idx = var->data.location - VARYING_SLOT_VAR0;
+
+         if (explicit_locations[idx] != NULL) {
+            linker_error(prog,
+                         "%s shader has multiple outputs explicitly "
+                         "assigned to location %d\n",
+                         _mesa_shader_stage_to_string(producer->Stage),
+                         idx);
+            return;
+         }
+
+         explicit_locations[idx] = var;
+      }
+   }
+
+
+   /* Find all shader inputs in the "consumer" stage.  Any variables that have
+    * matching outputs already in the symbol table must have the same type and
+    * qualifiers.
+    *
+    * Exception: if the consumer is the geometry shader, then the inputs
+    * should be arrays and the type of the array element should match the type
+    * of the corresponding producer output.
+    */
+   foreach_in_list(ir_instruction, node, consumer->ir) {
+      ir_variable *const input = node->as_variable();
+
+      if ((input == NULL) || (input->data.mode != ir_var_shader_in))
+	 continue;
+
+      if (strcmp(input->name, "gl_Color") == 0 && input->data.used) {
+         const ir_variable *const front_color =
+            parameters.get_variable("gl_FrontColor");
+
+         const ir_variable *const back_color =
+            parameters.get_variable("gl_BackColor");
+
+         cross_validate_front_and_back_color(prog, input,
+                                             front_color, back_color,
+                                             consumer->Stage, producer->Stage);
+      } else if (strcmp(input->name, "gl_SecondaryColor") == 0 && input->data.used) {
+         const ir_variable *const front_color =
+            parameters.get_variable("gl_FrontSecondaryColor");
+
+         const ir_variable *const back_color =
+            parameters.get_variable("gl_BackSecondaryColor");
+
+         cross_validate_front_and_back_color(prog, input,
+                                             front_color, back_color,
+                                             consumer->Stage, producer->Stage);
+      } else {
+         /* The rules for connecting inputs and outputs change in the presence
+          * of explicit locations.  In this case, we no longer care about the
+          * names of the variables.  Instead, we care only about the
+          * explicitly assigned location.
+          */
+         ir_variable *output = NULL;
+         if (input->data.explicit_location
+             && input->data.location >= VARYING_SLOT_VAR0) {
+            output = explicit_locations[input->data.location - VARYING_SLOT_VAR0];
+
+            if (output == NULL) {
+               linker_error(prog,
+                            "%s shader input `%s' with explicit location "
+                            "has no matching output\n",
+                            _mesa_shader_stage_to_string(consumer->Stage),
+                            input->name);
+            }
+         } else {
+            output = parameters.get_variable(input->name);
+         }
+
+         if (output != NULL) {
+            cross_validate_types_and_qualifiers(prog, input, output,
+                                                consumer->Stage, producer->Stage);
+         } else {
+            /* Check for input vars with unmatched output vars in prev stage
+             * taking into account that interface blocks could have a matching
+             * output but with different name, so we ignore them.
+             */
+            assert(!input->data.assigned);
+            if (input->data.used && !input->get_interface_type() &&
+                !input->data.explicit_location && !prog->SeparateShader)
+               linker_error(prog,
+                            "%s shader input `%s' "
+                            "has no matching output in the previous stage\n",
+                            _mesa_shader_stage_to_string(consumer->Stage),
+                            input->name);
+         }
+      }
+   }
+}
+
+/**
+ * Demote shader inputs and outputs that are not used in other stages, and
+ * remove them via dead code elimination.
+ */
+void
+remove_unused_shader_inputs_and_outputs(bool is_separate_shader_object,
+                                        gl_shader *sh,
+                                        enum ir_variable_mode mode)
+{
+   if (is_separate_shader_object)
+      return;
+
+   foreach_in_list(ir_instruction, node, sh->ir) {
+      ir_variable *const var = node->as_variable();
+
+      if ((var == NULL) || (var->data.mode != int(mode)))
+	 continue;
+
+      /* A shader 'in' or 'out' variable is only really an input or output if
+       * its value is used by other shader stages. This will cause the
+       * variable to have a location assigned.
+       */
+      if (var->data.is_unmatched_generic_inout) {
+         assert(var->data.mode != ir_var_temporary);
+	 var->data.mode = ir_var_auto;
+      }
+   }
+
+   /* Eliminate code that is now dead due to unused inputs/outputs being
+    * demoted.
+    */
+   while (do_dead_code(sh->ir, false))
+      ;
+
+}
+
+/**
+ * Initialize this object based on a string that was passed to
+ * glTransformFeedbackVaryings.
+ *
+ * If the input is mal-formed, this call still succeeds, but it sets
+ * this->var_name to a mal-formed input, so tfeedback_decl::find_output_var()
+ * will fail to find any matching variable.
+ */
+void
+tfeedback_decl::init(struct gl_context *ctx, const void *mem_ctx,
+                     const char *input)
+{
+   /* We don't have to be pedantic about what is a valid GLSL variable name,
+    * because any variable with an invalid name can't exist in the IR anyway.
+    */
+
+   this->location = -1;
+   this->orig_name = input;
+   this->lowered_builtin_array_variable = none;
+   this->skip_components = 0;
+   this->next_buffer_separator = false;
+   this->matched_candidate = NULL;
+   this->stream_id = 0;
+
+   if (ctx->Extensions.ARB_transform_feedback3) {
+      /* Parse gl_NextBuffer. */
+      if (strcmp(input, "gl_NextBuffer") == 0) {
+         this->next_buffer_separator = true;
+         return;
+      }
+
+      /* Parse gl_SkipComponents. */
+      if (strcmp(input, "gl_SkipComponents1") == 0)
+         this->skip_components = 1;
+      else if (strcmp(input, "gl_SkipComponents2") == 0)
+         this->skip_components = 2;
+      else if (strcmp(input, "gl_SkipComponents3") == 0)
+         this->skip_components = 3;
+      else if (strcmp(input, "gl_SkipComponents4") == 0)
+         this->skip_components = 4;
+
+      if (this->skip_components)
+         return;
+   }
+
+   /* Parse a declaration. */
+   const char *base_name_end;
+   long subscript = parse_program_resource_name(input, &base_name_end);
+   this->var_name = ralloc_strndup(mem_ctx, input, base_name_end - input);
+   if (this->var_name == NULL) {
+      _mesa_error_no_memory(__func__);
+      return;
+   }
+
+   if (subscript >= 0) {
+      this->array_subscript = subscript;
+      this->is_subscripted = true;
+   } else {
+      this->is_subscripted = false;
+   }
+
+   /* For drivers that lower gl_ClipDistance to gl_ClipDistanceMESA, this
+    * class must behave specially to account for the fact that gl_ClipDistance
+    * is converted from a float[8] to a vec4[2].
+    */
+   if (ctx->Const.ShaderCompilerOptions[MESA_SHADER_VERTEX].LowerClipDistance &&
+       strcmp(this->var_name, "gl_ClipDistance") == 0) {
+      this->lowered_builtin_array_variable = clip_distance;
+   }
+
+   if (ctx->Const.LowerTessLevel &&
+       (strcmp(this->var_name, "gl_TessLevelOuter") == 0))
+      this->lowered_builtin_array_variable = tess_level_outer;
+   if (ctx->Const.LowerTessLevel &&
+       (strcmp(this->var_name, "gl_TessLevelInner") == 0))
+      this->lowered_builtin_array_variable = tess_level_inner;
+}
+
+
+/**
+ * Determine whether two tfeedback_decl objects refer to the same variable and
+ * array index (if applicable).
+ */
+bool
+tfeedback_decl::is_same(const tfeedback_decl &x, const tfeedback_decl &y)
+{
+   assert(x.is_varying() && y.is_varying());
+
+   if (strcmp(x.var_name, y.var_name) != 0)
+      return false;
+   if (x.is_subscripted != y.is_subscripted)
+      return false;
+   if (x.is_subscripted && x.array_subscript != y.array_subscript)
+      return false;
+   return true;
+}
+
+
+/**
+ * Assign a location and stream ID for this tfeedback_decl object based on the
+ * transform feedback candidate found by find_candidate.
+ *
+ * If an error occurs, the error is reported through linker_error() and false
+ * is returned.
+ */
+bool
+tfeedback_decl::assign_location(struct gl_context *ctx,
+                                struct gl_shader_program *prog)
+{
+   assert(this->is_varying());
+
+   unsigned fine_location
+      = this->matched_candidate->toplevel_var->data.location * 4
+      + this->matched_candidate->toplevel_var->data.location_frac
+      + this->matched_candidate->offset;
+
+   if (this->matched_candidate->type->is_array()) {
+      /* Array variable */
+      const unsigned matrix_cols =
+         this->matched_candidate->type->fields.array->matrix_columns;
+      const unsigned vector_elements =
+         this->matched_candidate->type->fields.array->vector_elements;
+      const unsigned dmul =
+         this->matched_candidate->type->fields.array->is_double() ? 2 : 1;
+      unsigned actual_array_size;
+      switch (this->lowered_builtin_array_variable) {
+      case clip_distance:
+         actual_array_size = prog->LastClipDistanceArraySize;
+         break;
+      case tess_level_outer:
+         actual_array_size = 4;
+         break;
+      case tess_level_inner:
+         actual_array_size = 2;
+         break;
+      case none:
+      default:
+         actual_array_size = this->matched_candidate->type->array_size();
+         break;
+      }
+
+      if (this->is_subscripted) {
+         /* Check array bounds. */
+         if (this->array_subscript >= actual_array_size) {
+            linker_error(prog, "Transform feedback varying %s has index "
+                         "%i, but the array size is %u.",
+                         this->orig_name, this->array_subscript,
+                         actual_array_size);
+            return false;
+         }
+         unsigned array_elem_size = this->lowered_builtin_array_variable ?
+            1 : vector_elements * matrix_cols * dmul;
+         fine_location += array_elem_size * this->array_subscript;
+         this->size = 1;
+      } else {
+         this->size = actual_array_size;
+      }
+      this->vector_elements = vector_elements;
+      this->matrix_columns = matrix_cols;
+      if (this->lowered_builtin_array_variable)
+         this->type = GL_FLOAT;
+      else
+         this->type = this->matched_candidate->type->fields.array->gl_type;
+   } else {
+      /* Regular variable (scalar, vector, or matrix) */
+      if (this->is_subscripted) {
+         linker_error(prog, "Transform feedback varying %s requested, "
+                      "but %s is not an array.",
+                      this->orig_name, this->var_name);
+         return false;
+      }
+      this->size = 1;
+      this->vector_elements = this->matched_candidate->type->vector_elements;
+      this->matrix_columns = this->matched_candidate->type->matrix_columns;
+      this->type = this->matched_candidate->type->gl_type;
+   }
+   this->location = fine_location / 4;
+   this->location_frac = fine_location % 4;
+
+   /* From GL_EXT_transform_feedback:
+    *   A program will fail to link if:
+    *
+    *   * the total number of components to capture in any varying
+    *     variable in <varyings> is greater than the constant
+    *     MAX_TRANSFORM_FEEDBACK_SEPARATE_COMPONENTS_EXT and the
+    *     buffer mode is SEPARATE_ATTRIBS_EXT;
+    */
+   if (prog->TransformFeedback.BufferMode == GL_SEPARATE_ATTRIBS &&
+       this->num_components() >
+       ctx->Const.MaxTransformFeedbackSeparateComponents) {
+      linker_error(prog, "Transform feedback varying %s exceeds "
+                   "MAX_TRANSFORM_FEEDBACK_SEPARATE_COMPONENTS.",
+                   this->orig_name);
+      return false;
+   }
+
+   /* Only transform feedback varyings can be assigned to non-zero streams,
+    * so assign the stream id here.
+    */
+   this->stream_id = this->matched_candidate->toplevel_var->data.stream;
+
+   return true;
+}
+
+
+unsigned
+tfeedback_decl::get_num_outputs() const
+{
+   if (!this->is_varying()) {
+      return 0;
+   }
+   return (this->num_components() + this->location_frac + 3)/4;
+}
+
+
+/**
+ * Update gl_transform_feedback_info to reflect this tfeedback_decl.
+ *
+ * If an error occurs, the error is reported through linker_error() and false
+ * is returned.
+ */
+bool
+tfeedback_decl::store(struct gl_context *ctx, struct gl_shader_program *prog,
+                      struct gl_transform_feedback_info *info,
+                      unsigned buffer, const unsigned max_outputs) const
+{
+   assert(!this->next_buffer_separator);
+
+   /* Handle gl_SkipComponents. */
+   if (this->skip_components) {
+      info->BufferStride[buffer] += this->skip_components;
+      return true;
+   }
+
+   /* From GL_EXT_transform_feedback:
+    *   A program will fail to link if:
+    *
+    *     * the total number of components to capture is greater than
+    *       the constant MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS_EXT
+    *       and the buffer mode is INTERLEAVED_ATTRIBS_EXT.
+    */
+   if (prog->TransformFeedback.BufferMode == GL_INTERLEAVED_ATTRIBS &&
+       info->BufferStride[buffer] + this->num_components() >
+       ctx->Const.MaxTransformFeedbackInterleavedComponents) {
+      linker_error(prog, "The MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS "
+                   "limit has been exceeded.");
+      return false;
+   }
+
+   unsigned location = this->location;
+   unsigned location_frac = this->location_frac;
+   unsigned num_components = this->num_components();
+   while (num_components > 0) {
+      unsigned output_size = MIN2(num_components, 4 - location_frac);
+      assert(info->NumOutputs < max_outputs);
+      info->Outputs[info->NumOutputs].ComponentOffset = location_frac;
+      info->Outputs[info->NumOutputs].OutputRegister = location;
+      info->Outputs[info->NumOutputs].NumComponents = output_size;
+      info->Outputs[info->NumOutputs].StreamId = stream_id;
+      info->Outputs[info->NumOutputs].OutputBuffer = buffer;
+      info->Outputs[info->NumOutputs].DstOffset = info->BufferStride[buffer];
+      ++info->NumOutputs;
+      info->BufferStride[buffer] += output_size;
+      info->BufferStream[buffer] = this->stream_id;
+      num_components -= output_size;
+      location++;
+      location_frac = 0;
+   }
+
+   info->Varyings[info->NumVarying].Name = ralloc_strdup(prog, this->orig_name);
+   info->Varyings[info->NumVarying].Type = this->type;
+   info->Varyings[info->NumVarying].Size = this->size;
+   info->NumVarying++;
+
+   return true;
+}
+
+
+const tfeedback_candidate *
+tfeedback_decl::find_candidate(gl_shader_program *prog,
+                               hash_table *tfeedback_candidates)
+{
+   const char *name = this->var_name;
+   switch (this->lowered_builtin_array_variable) {
+   case none:
+      name = this->var_name;
+      break;
+   case clip_distance:
+      name = "gl_ClipDistanceMESA";
+      break;
+   case tess_level_outer:
+      name = "gl_TessLevelOuterMESA";
+      break;
+   case tess_level_inner:
+      name = "gl_TessLevelInnerMESA";
+      break;
+   }
+   this->matched_candidate = (const tfeedback_candidate *)
+      hash_table_find(tfeedback_candidates, name);
+   if (!this->matched_candidate) {
+      /* From GL_EXT_transform_feedback:
+       *   A program will fail to link if:
+       *
+       *   * any variable name specified in the <varyings> array is not
+       *     declared as an output in the geometry shader (if present) or
+       *     the vertex shader (if no geometry shader is present);
+       */
+      linker_error(prog, "Transform feedback varying %s undeclared.",
+                   this->orig_name);
+   }
+   return this->matched_candidate;
+}
+
+
+/**
+ * Parse all the transform feedback declarations that were passed to
+ * glTransformFeedbackVaryings() and store them in tfeedback_decl objects.
+ *
+ * If an error occurs, the error is reported through linker_error() and false
+ * is returned.
+ */
+bool
+parse_tfeedback_decls(struct gl_context *ctx, struct gl_shader_program *prog,
+                      const void *mem_ctx, unsigned num_names,
+                      char **varying_names, tfeedback_decl *decls)
+{
+   for (unsigned i = 0; i < num_names; ++i) {
+      decls[i].init(ctx, mem_ctx, varying_names[i]);
+
+      if (!decls[i].is_varying())
+         continue;
+
+      /* From GL_EXT_transform_feedback:
+       *   A program will fail to link if:
+       *
+       *   * any two entries in the <varyings> array specify the same varying
+       *     variable;
+       *
+       * We interpret this to mean "any two entries in the <varyings> array
+       * specify the same varying variable and array index", since transform
+       * feedback of arrays would be useless otherwise.
+       */
+      for (unsigned j = 0; j < i; ++j) {
+         if (!decls[j].is_varying())
+            continue;
+
+         if (tfeedback_decl::is_same(decls[i], decls[j])) {
+            linker_error(prog, "Transform feedback varying %s specified "
+                         "more than once.", varying_names[i]);
+            return false;
+         }
+      }
+   }
+   return true;
+}
+
+
+/**
+ * Store transform feedback location assignments into
+ * prog->LinkedTransformFeedback based on the data stored in tfeedback_decls.
+ *
+ * If an error occurs, the error is reported through linker_error() and false
+ * is returned.
+ */
+bool
+store_tfeedback_info(struct gl_context *ctx, struct gl_shader_program *prog,
+                     unsigned num_tfeedback_decls,
+                     tfeedback_decl *tfeedback_decls)
+{
+   bool separate_attribs_mode =
+      prog->TransformFeedback.BufferMode == GL_SEPARATE_ATTRIBS;
+
+   ralloc_free(prog->LinkedTransformFeedback.Varyings);
+   ralloc_free(prog->LinkedTransformFeedback.Outputs);
+
+   memset(&prog->LinkedTransformFeedback, 0,
+          sizeof(prog->LinkedTransformFeedback));
+
+   prog->LinkedTransformFeedback.Varyings =
+      rzalloc_array(prog,
+		    struct gl_transform_feedback_varying_info,
+		    num_tfeedback_decls);
+
+   unsigned num_outputs = 0;
+   for (unsigned i = 0; i < num_tfeedback_decls; ++i)
+      num_outputs += tfeedback_decls[i].get_num_outputs();
+
+   prog->LinkedTransformFeedback.Outputs =
+      rzalloc_array(prog,
+                    struct gl_transform_feedback_output,
+                    num_outputs);
+
+   unsigned num_buffers = 0;
+
+   if (separate_attribs_mode) {
+      /* GL_SEPARATE_ATTRIBS */
+      for (unsigned i = 0; i < num_tfeedback_decls; ++i) {
+         if (!tfeedback_decls[i].store(ctx, prog, &prog->LinkedTransformFeedback,
+                                       num_buffers, num_outputs))
+            return false;
+
+         num_buffers++;
+      }
+   }
+   else {
+      /* GL_INVERLEAVED_ATTRIBS */
+      int buffer_stream_id = -1;
+      for (unsigned i = 0; i < num_tfeedback_decls; ++i) {
+         if (tfeedback_decls[i].is_next_buffer_separator()) {
+            num_buffers++;
+            buffer_stream_id = -1;
+            continue;
+         } else if (buffer_stream_id == -1)  {
+            /* First varying writing to this buffer: remember its stream */
+            buffer_stream_id = (int) tfeedback_decls[i].get_stream_id();
+         } else if (buffer_stream_id !=
+                    (int) tfeedback_decls[i].get_stream_id()) {
+            /* Varying writes to the same buffer from a different stream */
+            linker_error(prog,
+                         "Transform feedback can't capture varyings belonging "
+                         "to different vertex streams in a single buffer. "
+                         "Varying %s writes to buffer from stream %u, other "
+                         "varyings in the same buffer write from stream %u.",
+                         tfeedback_decls[i].name(),
+                         tfeedback_decls[i].get_stream_id(),
+                         buffer_stream_id);
+            return false;
+         }
+
+         if (!tfeedback_decls[i].store(ctx, prog,
+                                       &prog->LinkedTransformFeedback,
+                                       num_buffers, num_outputs))
+            return false;
+      }
+      num_buffers++;
+   }
+
+   assert(prog->LinkedTransformFeedback.NumOutputs == num_outputs);
+
+   prog->LinkedTransformFeedback.NumBuffers = num_buffers;
+   return true;
+}
+
+namespace {
+
+/**
+ * Data structure recording the relationship between outputs of one shader
+ * stage (the "producer") and inputs of another (the "consumer").
+ */
+class varying_matches
+{
+public:
+   varying_matches(bool disable_varying_packing,
+                   gl_shader_stage producer_stage,
+                   gl_shader_stage consumer_stage);
+   ~varying_matches();
+   void record(ir_variable *producer_var, ir_variable *consumer_var);
+   unsigned assign_locations(struct gl_shader_program *prog,
+                             uint64_t reserved_slots, bool separate_shader);
+   void store_locations() const;
+
+private:
+   /**
+    * If true, this driver disables varying packing, so all varyings need to
+    * be aligned on slot boundaries, and take up a number of slots equal to
+    * their number of matrix columns times their array size.
+    */
+   const bool disable_varying_packing;
+
+   /**
+    * Enum representing the order in which varyings are packed within a
+    * packing class.
+    *
+    * Currently we pack vec4's first, then vec2's, then scalar values, then
+    * vec3's.  This order ensures that the only vectors that are at risk of
+    * having to be "double parked" (split between two adjacent varying slots)
+    * are the vec3's.
+    */
+   enum packing_order_enum {
+      PACKING_ORDER_VEC4,
+      PACKING_ORDER_VEC2,
+      PACKING_ORDER_SCALAR,
+      PACKING_ORDER_VEC3,
+   };
+
+   static unsigned compute_packing_class(const ir_variable *var);
+   static packing_order_enum compute_packing_order(const ir_variable *var);
+   static int match_comparator(const void *x_generic, const void *y_generic);
+
+   /**
+    * Structure recording the relationship between a single producer output
+    * and a single consumer input.
+    */
+   struct match {
+      /**
+       * Packing class for this varying, computed by compute_packing_class().
+       */
+      unsigned packing_class;
+
+      /**
+       * Packing order for this varying, computed by compute_packing_order().
+       */
+      packing_order_enum packing_order;
+      unsigned num_components;
+
+      /**
+       * The output variable in the producer stage.
+       */
+      ir_variable *producer_var;
+
+      /**
+       * The input variable in the consumer stage.
+       */
+      ir_variable *consumer_var;
+
+      /**
+       * The location which has been assigned for this varying.  This is
+       * expressed in multiples of a float, with the first generic varying
+       * (i.e. the one referred to by VARYING_SLOT_VAR0) represented by the
+       * value 0.
+       */
+      unsigned generic_location;
+   } *matches;
+
+   /**
+    * The number of elements in the \c matches array that are currently in
+    * use.
+    */
+   unsigned num_matches;
+
+   /**
+    * The number of elements that were set aside for the \c matches array when
+    * it was allocated.
+    */
+   unsigned matches_capacity;
+
+   gl_shader_stage producer_stage;
+   gl_shader_stage consumer_stage;
+};
+
+} /* anonymous namespace */
+
+varying_matches::varying_matches(bool disable_varying_packing,
+                                 gl_shader_stage producer_stage,
+                                 gl_shader_stage consumer_stage)
+   : disable_varying_packing(disable_varying_packing),
+     producer_stage(producer_stage),
+     consumer_stage(consumer_stage)
+{
+   /* Note: this initial capacity is rather arbitrarily chosen to be large
+    * enough for many cases without wasting an unreasonable amount of space.
+    * varying_matches::record() will resize the array if there are more than
+    * this number of varyings.
+    */
+   this->matches_capacity = 8;
+   this->matches = (match *)
+      malloc(sizeof(*this->matches) * this->matches_capacity);
+   this->num_matches = 0;
+}
+
+
+varying_matches::~varying_matches()
+{
+   free(this->matches);
+}
+
+
+/**
+ * Record the given producer/consumer variable pair in the list of variables
+ * that should later be assigned locations.
+ *
+ * It is permissible for \c consumer_var to be NULL (this happens if a
+ * variable is output by the producer and consumed by transform feedback, but
+ * not consumed by the consumer).
+ *
+ * If \c producer_var has already been paired up with a consumer_var, or
+ * producer_var is part of fixed pipeline functionality (and hence already has
+ * a location assigned), this function has no effect.
+ *
+ * Note: as a side effect this function may change the interpolation type of
+ * \c producer_var, but only when the change couldn't possibly affect
+ * rendering.
+ */
+void
+varying_matches::record(ir_variable *producer_var, ir_variable *consumer_var)
+{
+   assert(producer_var != NULL || consumer_var != NULL);
+
+   if ((producer_var && (!producer_var->data.is_unmatched_generic_inout ||
+       producer_var->data.explicit_location)) ||
+       (consumer_var && (!consumer_var->data.is_unmatched_generic_inout ||
+       consumer_var->data.explicit_location))) {
+      /* Either a location already exists for this variable (since it is part
+       * of fixed functionality), or it has already been recorded as part of a
+       * previous match.
+       */
+      return;
+   }
+
+   if ((consumer_var == NULL && producer_var->type->contains_integer()) ||
+       (consumer_stage != -1 && consumer_stage != MESA_SHADER_FRAGMENT)) {
+      /* Since this varying is not being consumed by the fragment shader, its
+       * interpolation type varying cannot possibly affect rendering.
+       * Also, this variable is non-flat and is (or contains) an integer.
+       * If the consumer stage is unknown, don't modify the interpolation
+       * type as it could affect rendering later with separate shaders.
+       *
+       * lower_packed_varyings requires all integer varyings to flat,
+       * regardless of where they appear.  We can trivially satisfy that
+       * requirement by changing the interpolation type to flat here.
+       */
+      if (producer_var) {
+         producer_var->data.centroid = false;
+         producer_var->data.sample = false;
+         producer_var->data.interpolation = INTERP_QUALIFIER_FLAT;
+      }
+
+      if (consumer_var) {
+         consumer_var->data.centroid = false;
+         consumer_var->data.sample = false;
+         consumer_var->data.interpolation = INTERP_QUALIFIER_FLAT;
+      }
+   }
+
+   if (this->num_matches == this->matches_capacity) {
+      this->matches_capacity *= 2;
+      this->matches = (match *)
+         realloc(this->matches,
+                 sizeof(*this->matches) * this->matches_capacity);
+   }
+
+   const ir_variable *const var = (producer_var != NULL)
+      ? producer_var : consumer_var;
+   const gl_shader_stage stage = (producer_var != NULL)
+      ? producer_stage : consumer_stage;
+   const glsl_type *type = get_varying_type(var, stage);
+
+   this->matches[this->num_matches].packing_class
+      = this->compute_packing_class(var);
+   this->matches[this->num_matches].packing_order
+      = this->compute_packing_order(var);
+   if (this->disable_varying_packing) {
+      unsigned slots = type->count_attribute_slots(false);
+      this->matches[this->num_matches].num_components = slots * 4;
+   } else {
+      this->matches[this->num_matches].num_components
+         = type->component_slots();
+   }
+   this->matches[this->num_matches].producer_var = producer_var;
+   this->matches[this->num_matches].consumer_var = consumer_var;
+   this->num_matches++;
+   if (producer_var)
+      producer_var->data.is_unmatched_generic_inout = 0;
+   if (consumer_var)
+      consumer_var->data.is_unmatched_generic_inout = 0;
+}
+
+
+/**
+ * Choose locations for all of the variable matches that were previously
+ * passed to varying_matches::record().
+ */
+unsigned
+varying_matches::assign_locations(struct gl_shader_program *prog,
+                                  uint64_t reserved_slots,
+                                  bool separate_shader)
+{
+   /* We disable varying sorting for separate shader programs for the
+    * following reasons:
+    *
+    * 1/ All programs must sort the code in the same order to guarantee the
+    *    interface matching. However varying_matches::record() will change the
+    *    interpolation qualifier of some stages.
+    *
+    * 2/ GLSL version 4.50 removes the matching constrain on the interpolation
+    *    qualifier.
+    *
+    * From Section 4.5 (Interpolation Qualifiers) of the GLSL 4.40 spec:
+    *
+    *    "The type and presence of interpolation qualifiers of variables with
+    *    the same name declared in all linked shaders for the same cross-stage
+    *    interface must match, otherwise the link command will fail.
+    *
+    *    When comparing an output from one stage to an input of a subsequent
+    *    stage, the input and output don't match if their interpolation
+    *    qualifiers (or lack thereof) are not the same."
+    *
+    *    "It is a link-time error if, within the same stage, the interpolation
+    *    qualifiers of variables of the same name do not match."
+    */
+   if (!separate_shader) {
+      /* Sort varying matches into an order that makes them easy to pack. */
+      qsort(this->matches, this->num_matches, sizeof(*this->matches),
+            &varying_matches::match_comparator);
+   }
+
+   unsigned generic_location = 0;
+   unsigned generic_patch_location = MAX_VARYING*4;
+
+   for (unsigned i = 0; i < this->num_matches; i++) {
+      unsigned *location = &generic_location;
+
+      const ir_variable *var;
+      const glsl_type *type;
+      bool is_vertex_input = false;
+      if (matches[i].consumer_var) {
+         var = matches[i].consumer_var;
+         type = get_varying_type(var, consumer_stage);
+         if (consumer_stage == MESA_SHADER_VERTEX)
+            is_vertex_input = true;
+      } else {
+         var = matches[i].producer_var;
+         type = get_varying_type(var, producer_stage);
+      }
+
+      if (var->data.patch)
+         location = &generic_patch_location;
+
+      /* Advance to the next slot if this varying has a different packing
+       * class than the previous one, and we're not already on a slot
+       * boundary.
+       */
+      if (i > 0 &&
+          this->matches[i - 1].packing_class
+          != this->matches[i].packing_class) {
+         *location = ALIGN(*location, 4);
+      }
+
+      unsigned num_elements =  type->count_attribute_slots(is_vertex_input);
+      unsigned slot_end = this->disable_varying_packing ? 4 :
+         type->without_array()->vector_elements;
+      slot_end += *location - 1;
+
+      /* FIXME: We could be smarter in the below code and loop back over
+       * trying to fill any locations that we skipped because we couldn't pack
+       * the varying between an explicit location. For now just let the user
+       * hit the linking error if we run out of room and suggest they use
+       * explicit locations.
+       */
+      for (unsigned j = 0; j < num_elements; j++) {
+         while ((slot_end < MAX_VARYING * 4u) &&
+                ((reserved_slots & (UINT64_C(1) << *location / 4u) ||
+                 (reserved_slots & (UINT64_C(1) << slot_end / 4u))))) {
+
+            *location = ALIGN(*location + 1, 4);
+            slot_end = *location;
+
+            /* reset the counter and try again */
+            j = 0;
+         }
+
+         /* Increase the slot to make sure there is enough room for next
+          * array element.
+          */
+         if (this->disable_varying_packing)
+            slot_end += 4;
+         else
+            slot_end += type->without_array()->vector_elements;
+      }
+
+      if (!var->data.patch && *location >= MAX_VARYING * 4u) {
+         linker_error(prog, "insufficient contiguous locations available for "
+                      "%s it is possible an array or struct could not be "
+                      "packed between varyings with explicit locations. Try "
+                      "using an explicit location for arrays and structs.",
+                      var->name);
+      }
+
+      this->matches[i].generic_location = *location;
+
+      *location += this->matches[i].num_components;
+   }
+
+   return (generic_location + 3) / 4;
+}
+
+
+/**
+ * Update the producer and consumer shaders to reflect the locations
+ * assignments that were made by varying_matches::assign_locations().
+ */
+void
+varying_matches::store_locations() const
+{
+   for (unsigned i = 0; i < this->num_matches; i++) {
+      ir_variable *producer_var = this->matches[i].producer_var;
+      ir_variable *consumer_var = this->matches[i].consumer_var;
+      unsigned generic_location = this->matches[i].generic_location;
+      unsigned slot = generic_location / 4;
+      unsigned offset = generic_location % 4;
+
+      if (producer_var) {
+         producer_var->data.location = VARYING_SLOT_VAR0 + slot;
+         producer_var->data.location_frac = offset;
+      }
+
+      if (consumer_var) {
+         assert(consumer_var->data.location == -1);
+         consumer_var->data.location = VARYING_SLOT_VAR0 + slot;
+         consumer_var->data.location_frac = offset;
+      }
+   }
+}
+
+
+/**
+ * Compute the "packing class" of the given varying.  This is an unsigned
+ * integer with the property that two variables in the same packing class can
+ * be safely backed into the same vec4.
+ */
+unsigned
+varying_matches::compute_packing_class(const ir_variable *var)
+{
+   /* Without help from the back-end, there is no way to pack together
+    * variables with different interpolation types, because
+    * lower_packed_varyings must choose exactly one interpolation type for
+    * each packed varying it creates.
+    *
+    * However, we can safely pack together floats, ints, and uints, because:
+    *
+    * - varyings of base type "int" and "uint" must use the "flat"
+    *   interpolation type, which can only occur in GLSL 1.30 and above.
+    *
+    * - On platforms that support GLSL 1.30 and above, lower_packed_varyings
+    *   can store flat floats as ints without losing any information (using
+    *   the ir_unop_bitcast_* opcodes).
+    *
+    * Therefore, the packing class depends only on the interpolation type.
+    */
+   unsigned packing_class = var->data.centroid | (var->data.sample << 1) |
+                            (var->data.patch << 2);
+   packing_class *= 4;
+   packing_class += var->data.interpolation;
+   return packing_class;
+}
+
+
+/**
+ * Compute the "packing order" of the given varying.  This is a sort key we
+ * use to determine when to attempt to pack the given varying relative to
+ * other varyings in the same packing class.
+ */
+varying_matches::packing_order_enum
+varying_matches::compute_packing_order(const ir_variable *var)
+{
+   const glsl_type *element_type = var->type;
+
+   while (element_type->base_type == GLSL_TYPE_ARRAY) {
+      element_type = element_type->fields.array;
+   }
+
+   switch (element_type->component_slots() % 4) {
+   case 1: return PACKING_ORDER_SCALAR;
+   case 2: return PACKING_ORDER_VEC2;
+   case 3: return PACKING_ORDER_VEC3;
+   case 0: return PACKING_ORDER_VEC4;
+   default:
+      assert(!"Unexpected value of vector_elements");
+      return PACKING_ORDER_VEC4;
+   }
+}
+
+
+/**
+ * Comparison function passed to qsort() to sort varyings by packing_class and
+ * then by packing_order.
+ */
+int
+varying_matches::match_comparator(const void *x_generic, const void *y_generic)
+{
+   const match *x = (const match *) x_generic;
+   const match *y = (const match *) y_generic;
+
+   if (x->packing_class != y->packing_class)
+      return x->packing_class - y->packing_class;
+   return x->packing_order - y->packing_order;
+}
+
+
+/**
+ * Is the given variable a varying variable to be counted against the
+ * limit in ctx->Const.MaxVarying?
+ * This includes variables such as texcoords, colors and generic
+ * varyings, but excludes variables such as gl_FrontFacing and gl_FragCoord.
+ */
+static bool
+var_counts_against_varying_limit(gl_shader_stage stage, const ir_variable *var)
+{
+   /* Only fragment shaders will take a varying variable as an input */
+   if (stage == MESA_SHADER_FRAGMENT &&
+       var->data.mode == ir_var_shader_in) {
+      switch (var->data.location) {
+      case VARYING_SLOT_POS:
+      case VARYING_SLOT_FACE:
+      case VARYING_SLOT_PNTC:
+         return false;
+      default:
+         return true;
+      }
+   }
+   return false;
+}
+
+
+/**
+ * Visitor class that generates tfeedback_candidate structs describing all
+ * possible targets of transform feedback.
+ *
+ * tfeedback_candidate structs are stored in the hash table
+ * tfeedback_candidates, which is passed to the constructor.  This hash table
+ * maps varying names to instances of the tfeedback_candidate struct.
+ */
+class tfeedback_candidate_generator : public program_resource_visitor
+{
+public:
+   tfeedback_candidate_generator(void *mem_ctx,
+                                 hash_table *tfeedback_candidates)
+      : mem_ctx(mem_ctx),
+        tfeedback_candidates(tfeedback_candidates),
+        toplevel_var(NULL),
+        varying_floats(0)
+   {
+   }
+
+   void process(ir_variable *var)
+   {
+      /* All named varying interface blocks should be flattened by now */
+      assert(!var->is_interface_instance());
+
+      this->toplevel_var = var;
+      this->varying_floats = 0;
+      program_resource_visitor::process(var);
+   }
+
+private:
+   virtual void visit_field(const glsl_type *type, const char *name,
+                            bool row_major)
+   {
+      assert(!type->without_array()->is_record());
+      assert(!type->without_array()->is_interface());
+
+      (void) row_major;
+
+      tfeedback_candidate *candidate
+         = rzalloc(this->mem_ctx, tfeedback_candidate);
+      candidate->toplevel_var = this->toplevel_var;
+      candidate->type = type;
+      candidate->offset = this->varying_floats;
+      hash_table_insert(this->tfeedback_candidates, candidate,
+                        ralloc_strdup(this->mem_ctx, name));
+      this->varying_floats += type->component_slots();
+   }
+
+   /**
+    * Memory context used to allocate hash table keys and values.
+    */
+   void * const mem_ctx;
+
+   /**
+    * Hash table in which tfeedback_candidate objects should be stored.
+    */
+   hash_table * const tfeedback_candidates;
+
+   /**
+    * Pointer to the toplevel variable that is being traversed.
+    */
+   ir_variable *toplevel_var;
+
+   /**
+    * Total number of varying floats that have been visited so far.  This is
+    * used to determine the offset to each varying within the toplevel
+    * variable.
+    */
+   unsigned varying_floats;
+};
+
+
+namespace linker {
+
+bool
+populate_consumer_input_sets(void *mem_ctx, exec_list *ir,
+                             hash_table *consumer_inputs,
+                             hash_table *consumer_interface_inputs,
+                             ir_variable *consumer_inputs_with_locations[VARYING_SLOT_TESS_MAX])
+{
+   memset(consumer_inputs_with_locations,
+          0,
+          sizeof(consumer_inputs_with_locations[0]) * VARYING_SLOT_TESS_MAX);
+
+   foreach_in_list(ir_instruction, node, ir) {
+      ir_variable *const input_var = node->as_variable();
+
+      if ((input_var != NULL) && (input_var->data.mode == ir_var_shader_in)) {
+         if (input_var->type->is_interface())
+            return false;
+
+         if (input_var->data.explicit_location) {
+            /* assign_varying_locations only cares about finding the
+             * ir_variable at the start of a contiguous location block.
+             *
+             *     - For !producer, consumer_inputs_with_locations isn't used.
+             *
+             *     - For !consumer, consumer_inputs_with_locations is empty.
+             *
+             * For consumer && producer, if you were trying to set some
+             * ir_variable to the middle of a location block on the other side
+             * of producer/consumer, cross_validate_outputs_to_inputs() should
+             * be link-erroring due to either type mismatch or location
+             * overlaps.  If the variables do match up, then they've got a
+             * matching data.location and you only looked at
+             * consumer_inputs_with_locations[var->data.location], not any
+             * following entries for the array/structure.
+             */
+            consumer_inputs_with_locations[input_var->data.location] =
+               input_var;
+         } else if (input_var->get_interface_type() != NULL) {
+            char *const iface_field_name =
+               ralloc_asprintf(mem_ctx, "%s.%s",
+                               input_var->get_interface_type()->name,
+                               input_var->name);
+            hash_table_insert(consumer_interface_inputs, input_var,
+                              iface_field_name);
+         } else {
+            hash_table_insert(consumer_inputs, input_var,
+                              ralloc_strdup(mem_ctx, input_var->name));
+         }
+      }
+   }
+
+   return true;
+}
+
+/**
+ * Find a variable from the consumer that "matches" the specified variable
+ *
+ * This function only finds inputs with names that match.  There is no
+ * validation (here) that the types, etc. are compatible.
+ */
+ir_variable *
+get_matching_input(void *mem_ctx,
+                   const ir_variable *output_var,
+                   hash_table *consumer_inputs,
+                   hash_table *consumer_interface_inputs,
+                   ir_variable *consumer_inputs_with_locations[VARYING_SLOT_TESS_MAX])
+{
+   ir_variable *input_var;
+
+   if (output_var->data.explicit_location) {
+      input_var = consumer_inputs_with_locations[output_var->data.location];
+   } else if (output_var->get_interface_type() != NULL) {
+      char *const iface_field_name =
+         ralloc_asprintf(mem_ctx, "%s.%s",
+                         output_var->get_interface_type()->name,
+                         output_var->name);
+      input_var =
+         (ir_variable *) hash_table_find(consumer_interface_inputs,
+                                         iface_field_name);
+   } else {
+      input_var =
+         (ir_variable *) hash_table_find(consumer_inputs, output_var->name);
+   }
+
+   return (input_var == NULL || input_var->data.mode != ir_var_shader_in)
+      ? NULL : input_var;
+}
+
+}
+
+static int
+io_variable_cmp(const void *_a, const void *_b)
+{
+   const ir_variable *const a = *(const ir_variable **) _a;
+   const ir_variable *const b = *(const ir_variable **) _b;
+
+   if (a->data.explicit_location && b->data.explicit_location)
+      return b->data.location - a->data.location;
+
+   if (a->data.explicit_location && !b->data.explicit_location)
+      return 1;
+
+   if (!a->data.explicit_location && b->data.explicit_location)
+      return -1;
+
+   return -strcmp(a->name, b->name);
+}
+
+/**
+ * Sort the shader IO variables into canonical order
+ */
+static void
+canonicalize_shader_io(exec_list *ir, enum ir_variable_mode io_mode)
+{
+   ir_variable *var_table[MAX_PROGRAM_OUTPUTS * 4];
+   unsigned num_variables = 0;
+
+   foreach_in_list(ir_instruction, node, ir) {
+      ir_variable *const var = node->as_variable();
+
+      if (var == NULL || var->data.mode != io_mode)
+         continue;
+
+      /* If we have already encountered more I/O variables that could
+       * successfully link, bail.
+       */
+      if (num_variables == ARRAY_SIZE(var_table))
+         return;
+
+      var_table[num_variables++] = var;
+   }
+
+   if (num_variables == 0)
+      return;
+
+   /* Sort the list in reverse order (io_variable_cmp handles this).  Later
+    * we're going to push the variables on to the IR list as a stack, so we
+    * want the last variable (in canonical order) to be first in the list.
+    */
+   qsort(var_table, num_variables, sizeof(var_table[0]), io_variable_cmp);
+
+   /* Remove the variable from it's current location in the IR, and put it at
+    * the front.
+    */
+   for (unsigned i = 0; i < num_variables; i++) {
+      var_table[i]->remove();
+      ir->push_head(var_table[i]);
+   }
+}
+
+/**
+ * Generate a bitfield map of the explicit locations for shader varyings.
+ *
+ * In theory a 32 bits value will be enough but a 64 bits value is future proof.
+ */
+uint64_t
+reserved_varying_slot(struct gl_shader *stage, ir_variable_mode io_mode)
+{
+   assert(io_mode == ir_var_shader_in || io_mode == ir_var_shader_out);
+   assert(MAX_VARYING <= 64); /* avoid an overflow of the returned value */
+
+   uint64_t slots = 0;
+   int var_slot;
+
+   if (!stage)
+      return slots;
+
+   foreach_in_list(ir_instruction, node, stage->ir) {
+      ir_variable *const var = node->as_variable();
+
+      if (var == NULL || var->data.mode != io_mode ||
+          !var->data.explicit_location ||
+          var->data.location < VARYING_SLOT_VAR0)
+         continue;
+
+      var_slot = var->data.location - VARYING_SLOT_VAR0;
+
+      unsigned num_elements = get_varying_type(var, stage->Stage)
+         ->count_attribute_slots(stage->Stage == MESA_SHADER_VERTEX);
+      for (unsigned i = 0; i < num_elements; i++) {
+         if (var_slot >= 0 && var_slot < MAX_VARYING)
+            slots |= UINT64_C(1) << var_slot;
+         var_slot += 1;
+      }
+   }
+
+   return slots;
+}
+
+
+/**
+ * Assign locations for all variables that are produced in one pipeline stage
+ * (the "producer") and consumed in the next stage (the "consumer").
+ *
+ * Variables produced by the producer may also be consumed by transform
+ * feedback.
+ *
+ * \param num_tfeedback_decls is the number of declarations indicating
+ *        variables that may be consumed by transform feedback.
+ *
+ * \param tfeedback_decls is a pointer to an array of tfeedback_decl objects
+ *        representing the result of parsing the strings passed to
+ *        glTransformFeedbackVaryings().  assign_location() will be called for
+ *        each of these objects that matches one of the outputs of the
+ *        producer.
+ *
+ * When num_tfeedback_decls is nonzero, it is permissible for the consumer to
+ * be NULL.  In this case, varying locations are assigned solely based on the
+ * requirements of transform feedback.
+ */
+bool
+assign_varying_locations(struct gl_context *ctx,
+			 void *mem_ctx,
+			 struct gl_shader_program *prog,
+			 gl_shader *producer, gl_shader *consumer,
+                         unsigned num_tfeedback_decls,
+                         tfeedback_decl *tfeedback_decls)
+{
+   if (ctx->Const.DisableVaryingPacking) {
+      /* Transform feedback code assumes varyings are packed, so if the driver
+       * has disabled varying packing, make sure it does not support transform
+       * feedback.
+       */
+      assert(!ctx->Extensions.EXT_transform_feedback);
+   }
+
+   /* Tessellation shaders treat inputs and outputs as shared memory and can
+    * access inputs and outputs of other invocations.
+    * Therefore, they can't be lowered to temps easily (and definitely not
+    * efficiently).
+    */
+   bool disable_varying_packing =
+      ctx->Const.DisableVaryingPacking ||
+      (consumer && consumer->Stage == MESA_SHADER_TESS_EVAL) ||
+      (consumer && consumer->Stage == MESA_SHADER_TESS_CTRL) ||
+      (producer && producer->Stage == MESA_SHADER_TESS_CTRL);
+
+   varying_matches matches(disable_varying_packing,
+                           producer ? producer->Stage : (gl_shader_stage)-1,
+                           consumer ? consumer->Stage : (gl_shader_stage)-1);
+   hash_table *tfeedback_candidates
+      = hash_table_ctor(0, hash_table_string_hash, hash_table_string_compare);
+   hash_table *consumer_inputs
+      = hash_table_ctor(0, hash_table_string_hash, hash_table_string_compare);
+   hash_table *consumer_interface_inputs
+      = hash_table_ctor(0, hash_table_string_hash, hash_table_string_compare);
+   ir_variable *consumer_inputs_with_locations[VARYING_SLOT_TESS_MAX] = {
+      NULL,
+   };
+
+   unsigned consumer_vertices = 0;
+   if (consumer && consumer->Stage == MESA_SHADER_GEOMETRY)
+      consumer_vertices = prog->Geom.VerticesIn;
+
+   /* Operate in a total of four passes.
+    *
+    * 1. Sort inputs / outputs into a canonical order.  This is necessary so
+    *    that inputs / outputs of separable shaders will be assigned
+    *    predictable locations regardless of the order in which declarations
+    *    appeared in the shader source.
+    *
+    * 2. Assign locations for any matching inputs and outputs.
+    *
+    * 3. Mark output variables in the producer that do not have locations as
+    *    not being outputs.  This lets the optimizer eliminate them.
+    *
+    * 4. Mark input variables in the consumer that do not have locations as
+    *    not being inputs.  This lets the optimizer eliminate them.
+    */
+   if (consumer)
+      canonicalize_shader_io(consumer->ir, ir_var_shader_in);
+
+   if (producer)
+      canonicalize_shader_io(producer->ir, ir_var_shader_out);
+
+   if (consumer
+       && !linker::populate_consumer_input_sets(mem_ctx,
+                                                consumer->ir,
+                                                consumer_inputs,
+                                                consumer_interface_inputs,
+                                                consumer_inputs_with_locations)) {
+      assert(!"populate_consumer_input_sets failed");
+      hash_table_dtor(tfeedback_candidates);
+      hash_table_dtor(consumer_inputs);
+      hash_table_dtor(consumer_interface_inputs);
+      return false;
+   }
+
+   if (producer) {
+      foreach_in_list(ir_instruction, node, producer->ir) {
+         ir_variable *const output_var = node->as_variable();
+
+         if ((output_var == NULL) ||
+             (output_var->data.mode != ir_var_shader_out))
+            continue;
+
+         /* Only geometry shaders can use non-zero streams */
+         assert(output_var->data.stream == 0 ||
+                (output_var->data.stream < MAX_VERTEX_STREAMS &&
+                 producer->Stage == MESA_SHADER_GEOMETRY));
+
+         tfeedback_candidate_generator g(mem_ctx, tfeedback_candidates);
+         g.process(output_var);
+
+         ir_variable *const input_var =
+            linker::get_matching_input(mem_ctx, output_var, consumer_inputs,
+                                       consumer_interface_inputs,
+                                       consumer_inputs_with_locations);
+
+         /* If a matching input variable was found, add this ouptut (and the
+          * input) to the set.  If this is a separable program and there is no
+          * consumer stage, add the output.
+          *
+          * Always add TCS outputs. They are shared by all invocations
+          * within a patch and can be used as shared memory.
+          */
+         if (input_var || (prog->SeparateShader && consumer == NULL) ||
+             producer->Type == GL_TESS_CONTROL_SHADER) {
+            matches.record(output_var, input_var);
+         }
+
+         /* Only stream 0 outputs can be consumed in the next stage */
+         if (input_var && output_var->data.stream != 0) {
+            linker_error(prog, "output %s is assigned to stream=%d but "
+                         "is linked to an input, which requires stream=0",
+                         output_var->name, output_var->data.stream);
+            return false;
+         }
+      }
+   } else {
+      /* If there's no producer stage, then this must be a separable program.
+       * For example, we may have a program that has just a fragment shader.
+       * Later this program will be used with some arbitrary vertex (or
+       * geometry) shader program.  This means that locations must be assigned
+       * for all the inputs.
+       */
+      foreach_in_list(ir_instruction, node, consumer->ir) {
+         ir_variable *const input_var = node->as_variable();
+
+         if ((input_var == NULL) ||
+             (input_var->data.mode != ir_var_shader_in))
+            continue;
+
+         matches.record(NULL, input_var);
+      }
+   }
+
+   for (unsigned i = 0; i < num_tfeedback_decls; ++i) {
+      if (!tfeedback_decls[i].is_varying())
+         continue;
+
+      const tfeedback_candidate *matched_candidate
+         = tfeedback_decls[i].find_candidate(prog, tfeedback_candidates);
+
+      if (matched_candidate == NULL) {
+         hash_table_dtor(tfeedback_candidates);
+         hash_table_dtor(consumer_inputs);
+         hash_table_dtor(consumer_interface_inputs);
+         return false;
+      }
+
+      if (matched_candidate->toplevel_var->data.is_unmatched_generic_inout)
+         matches.record(matched_candidate->toplevel_var, NULL);
+   }
+
+   const uint64_t reserved_slots =
+      reserved_varying_slot(producer, ir_var_shader_out) |
+      reserved_varying_slot(consumer, ir_var_shader_in);
+
+   const unsigned slots_used = matches.assign_locations(prog, reserved_slots,
+                                                        prog->SeparateShader);
+   matches.store_locations();
+
+   for (unsigned i = 0; i < num_tfeedback_decls; ++i) {
+      if (!tfeedback_decls[i].is_varying())
+         continue;
+
+      if (!tfeedback_decls[i].assign_location(ctx, prog)) {
+         hash_table_dtor(tfeedback_candidates);
+         hash_table_dtor(consumer_inputs);
+         hash_table_dtor(consumer_interface_inputs);
+         return false;
+      }
+   }
+
+   hash_table_dtor(tfeedback_candidates);
+   hash_table_dtor(consumer_inputs);
+   hash_table_dtor(consumer_interface_inputs);
+
+   if (consumer && producer) {
+      foreach_in_list(ir_instruction, node, consumer->ir) {
+         ir_variable *const var = node->as_variable();
+
+         if (var && var->data.mode == ir_var_shader_in &&
+             var->data.is_unmatched_generic_inout) {
+            if (prog->IsES) {
+               /*
+                * On Page 91 (Page 97 of the PDF) of the GLSL ES 1.0 spec:
+                *
+                *     If the vertex shader declares but doesn't write to a
+                *     varying and the fragment shader declares and reads it,
+                *     is this an error?
+                *
+                *     RESOLUTION: No.
+                */
+               linker_warning(prog, "%s shader varying %s not written "
+                              "by %s shader\n.",
+                              _mesa_shader_stage_to_string(consumer->Stage),
+                              var->name,
+                              _mesa_shader_stage_to_string(producer->Stage));
+            } else if (prog->Version <= 120) {
+               /* On page 25 (page 31 of the PDF) of the GLSL 1.20 spec:
+                *
+                *     Only those varying variables used (i.e. read) in
+                *     the fragment shader executable must be written to
+                *     by the vertex shader executable; declaring
+                *     superfluous varying variables in a vertex shader is
+                *     permissible.
+                *
+                * We interpret this text as meaning that the VS must
+                * write the variable for the FS to read it.  See
+                * "glsl1-varying read but not written" in piglit.
+                */
+               linker_error(prog, "%s shader varying %s not written "
+                            "by %s shader\n.",
+                            _mesa_shader_stage_to_string(consumer->Stage),
+			    var->name,
+                            _mesa_shader_stage_to_string(producer->Stage));
+            }
+         }
+      }
+
+      /* Now that validation is done its safe to remove unused varyings. As
+       * we have both a producer and consumer its safe to remove unused
+       * varyings even if the program is a SSO because the stages are being
+       * linked together i.e. we have a multi-stage SSO.
+       */
+      remove_unused_shader_inputs_and_outputs(false, producer,
+                                              ir_var_shader_out);
+      remove_unused_shader_inputs_and_outputs(false, consumer,
+                                              ir_var_shader_in);
+   }
+
+   if (!disable_varying_packing) {
+      if (producer) {
+         lower_packed_varyings(mem_ctx, slots_used, ir_var_shader_out,
+                               0, producer);
+      }
+      if (consumer) {
+         lower_packed_varyings(mem_ctx, slots_used, ir_var_shader_in,
+                               consumer_vertices, consumer);
+      }
+   }
+
+   return true;
+}
+
+bool
+check_against_output_limit(struct gl_context *ctx,
+                           struct gl_shader_program *prog,
+                           gl_shader *producer)
+{
+   unsigned output_vectors = 0;
+
+   foreach_in_list(ir_instruction, node, producer->ir) {
+      ir_variable *const var = node->as_variable();
+
+      if (var && var->data.mode == ir_var_shader_out &&
+          var_counts_against_varying_limit(producer->Stage, var)) {
+         /* outputs for fragment shader can't be doubles */
+         output_vectors += var->type->count_attribute_slots(false);
+      }
+   }
+
+   assert(producer->Stage != MESA_SHADER_FRAGMENT);
+   unsigned max_output_components =
+      ctx->Const.Program[producer->Stage].MaxOutputComponents;
+
+   const unsigned output_components = output_vectors * 4;
+   if (output_components > max_output_components) {
+      if (ctx->API == API_OPENGLES2 || prog->IsES)
+         linker_error(prog, "%s shader uses too many output vectors "
+                      "(%u > %u)\n",
+                      _mesa_shader_stage_to_string(producer->Stage),
+                      output_vectors,
+                      max_output_components / 4);
+      else
+         linker_error(prog, "%s shader uses too many output components "
+                      "(%u > %u)\n",
+                      _mesa_shader_stage_to_string(producer->Stage),
+                      output_components,
+                      max_output_components);
+
+      return false;
+   }
+
+   return true;
+}
+
+bool
+check_against_input_limit(struct gl_context *ctx,
+                          struct gl_shader_program *prog,
+                          gl_shader *consumer)
+{
+   unsigned input_vectors = 0;
+
+   foreach_in_list(ir_instruction, node, consumer->ir) {
+      ir_variable *const var = node->as_variable();
+
+      if (var && var->data.mode == ir_var_shader_in &&
+          var_counts_against_varying_limit(consumer->Stage, var)) {
+         /* vertex inputs aren't varying counted */
+         input_vectors += var->type->count_attribute_slots(false);
+      }
+   }
+
+   assert(consumer->Stage != MESA_SHADER_VERTEX);
+   unsigned max_input_components =
+      ctx->Const.Program[consumer->Stage].MaxInputComponents;
+
+   const unsigned input_components = input_vectors * 4;
+   if (input_components > max_input_components) {
+      if (ctx->API == API_OPENGLES2 || prog->IsES)
+         linker_error(prog, "%s shader uses too many input vectors "
+                      "(%u > %u)\n",
+                      _mesa_shader_stage_to_string(consumer->Stage),
+                      input_vectors,
+                      max_input_components / 4);
+      else
+         linker_error(prog, "%s shader uses too many input components "
+                      "(%u > %u)\n",
+                      _mesa_shader_stage_to_string(consumer->Stage),
+                      input_components,
+                      max_input_components);
+
+      return false;
+   }
+
+   return true;
+}