Merge branch 'glsl2-head' into glsl2

This brings in the standalone GLSL compiler that we are planning on
replacing the existing Mesa GLSL compiler.  It currently targets GLSL
1.20 and the Mesa IR.

1 files changed, 871 insertions, 0 deletions

diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
new file mode 100644
index 0000000000..ba382fe881
--- /dev/null
+++ b/src/glsl/linker.cpp
@@ -0,0 +1,871 @@
+/*
+ * Copyright © 2010 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+/**
+ * \file linker.cpp
+ * GLSL linker implementation
+ *
+ * Given a set of shaders that are to be linked to generate a final program,
+ * there are three distinct stages.
+ *
+ * In the first stage shaders are partitioned into groups based on the shader
+ * type.  All shaders of a particular type (e.g., vertex shaders) are linked
+ * together.
+ *
+ *   - Undefined references in each shader are resolve to definitions in
+ *     another shader.
+ *   - Types and qualifiers of uniforms, outputs, and global variables defined
+ *     in multiple shaders with the same name are verified to be the same.
+ *   - Initializers for uniforms and global variables defined
+ *     in multiple shaders with the same name are verified to be the same.
+ *
+ * The result, in the terminology of the GLSL spec, is a set of shader
+ * executables for each processing unit.
+ *
+ * After the first stage is complete, a series of semantic checks are performed
+ * on each of the shader executables.
+ *
+ *   - Each shader executable must define a \c main function.
+ *   - Each vertex shader executable must write to \c gl_Position.
+ *   - Each fragment shader executable must write to either \c gl_FragData or
+ *     \c gl_FragColor.
+ *
+ * In the final stage individual shader executables are linked to create a
+ * complete exectuable.
+ *
+ *   - Types of uniforms defined in multiple shader stages with the same name
+ *     are verified to be the same.
+ *   - Initializers for uniforms defined in multiple shader stages with the
+ *     same name are verified to be the same.
+ *   - Types and qualifiers of outputs defined in one stage are verified to
+ *     be the same as the types and qualifiers of inputs defined with the same
+ *     name in a later stage.
+ *
+ * \author Ian Romanick <ian.d.romanick@intel.com>
+ */
+#include <cstdlib>
+#include <cstdio>
+#include <cstdarg>
+
+extern "C" {
+#include <talloc.h>
+}
+
+#include "main/mtypes.h"
+#include "glsl_symbol_table.h"
+#include "glsl_parser_extras.h"
+#include "ir.h"
+#include "ir_optimization.h"
+#include "program.h"
+#include "hash_table.h"
+
+/**
+ * Visitor that determines whether or not a variable is ever written.
+ */
+class find_assignment_visitor : public ir_hierarchical_visitor {
+public:
+   find_assignment_visitor(const char *name)
+      : name(name), found(false)
+   {
+      /* empty */
+   }
+
+   virtual ir_visitor_status visit_enter(ir_assignment *ir)
+   {
+      ir_variable *const var = ir->lhs->variable_referenced();
+
+      if (strcmp(name, var->name) == 0) {
+	 found = true;
+	 return visit_stop;
+      }
+
+      return visit_continue_with_parent;
+   }
+
+   bool variable_found()
+   {
+      return found;
+   }
+
+private:
+   const char *name;       /**< Find writes to a variable with this name. */
+   bool found;             /**< Was a write to the variable found? */
+};
+
+
+void
+linker_error_printf(glsl_program *prog, const char *fmt, ...)
+{
+   va_list ap;
+
+   prog->InfoLog = talloc_strdup_append(prog->InfoLog, "error: ");
+   va_start(ap, fmt);
+   prog->InfoLog = talloc_vasprintf_append(prog->InfoLog, fmt, ap);
+   va_end(ap);
+}
+
+
+void
+invalidate_variable_locations(glsl_shader *sh, enum ir_variable_mode mode,
+			      int generic_base)
+{
+   foreach_list(node, &sh->ir) {
+      ir_variable *const var = ((ir_instruction *) node)->as_variable();
+
+      if ((var == NULL) || (var->mode != (unsigned) mode))
+	 continue;
+
+      /* Only assign locations for generic attributes / varyings / etc.
+       */
+      if (var->location >= generic_base)
+	  var->location = -1;
+   }
+}
+
+
+/**
+ * Determine the number of attribute slots required for a particular type
+ *
+ * This code is here because it implements the language rules of a specific
+ * GLSL version.  Since it's a property of the language and not a property of
+ * types in general, it doesn't really belong in glsl_type.
+ */
+unsigned
+count_attribute_slots(const glsl_type *t)
+{
+   /* From page 31 (page 37 of the PDF) of the GLSL 1.50 spec:
+    *
+    *     "A scalar input counts the same amount against this limit as a vec4,
+    *     so applications may want to consider packing groups of four
+    *     unrelated float inputs together into a vector to better utilize the
+    *     capabilities of the underlying hardware. A matrix input will use up
+    *     multiple locations.  The number of locations used will equal the
+    *     number of columns in the matrix."
+    *
+    * The spec does not explicitly say how arrays are counted.  However, it
+    * should be safe to assume the total number of slots consumed by an array
+    * is the number of entries in the array multiplied by the number of slots
+    * consumed by a single element of the array.
+    */
+
+   if (t->is_array())
+      return t->array_size() * count_attribute_slots(t->element_type());
+
+   if (t->is_matrix())
+      return t->matrix_columns;
+
+   return 1;
+}
+
+
+/**
+ * Verify that a vertex shader executable meets all semantic requirements
+ *
+ * \param shader  Vertex shader executable to be verified
+ */
+bool
+validate_vertex_shader_executable(struct glsl_program *prog,
+				  struct glsl_shader *shader)
+{
+   if (shader == NULL)
+      return true;
+
+   if (!shader->symbols->get_function("main")) {
+      linker_error_printf(prog, "vertex shader lacks `main'\n");
+      return false;
+   }
+
+   find_assignment_visitor find("gl_Position");
+   find.run(&shader->ir);
+   if (!find.variable_found()) {
+      linker_error_printf(prog,
+			  "vertex shader does not write to `gl_Position'\n");
+      return false;
+   }
+
+   return true;
+}
+
+
+/**
+ * Verify that a fragment shader executable meets all semantic requirements
+ *
+ * \param shader  Fragment shader executable to be verified
+ */
+bool
+validate_fragment_shader_executable(struct glsl_program *prog,
+				    struct glsl_shader *shader)
+{
+   if (shader == NULL)
+      return true;
+
+   if (!shader->symbols->get_function("main")) {
+      linker_error_printf(prog, "fragment shader lacks `main'\n");
+      return false;
+   }
+
+   find_assignment_visitor frag_color("gl_FragColor");
+   find_assignment_visitor frag_data("gl_FragData");
+
+   frag_color.run(&shader->ir);
+   frag_data.run(&shader->ir);
+
+   if (!frag_color.variable_found() && !frag_data.variable_found()) {
+      linker_error_printf(prog, "fragment shader does not write to "
+			  "`gl_FragColor' or `gl_FragData'\n");
+      return false;
+   }
+
+   if (frag_color.variable_found() && frag_data.variable_found()) {
+      linker_error_printf(prog,  "fragment shader writes to both "
+			  "`gl_FragColor' and `gl_FragData'\n");
+      return false;
+   }
+
+   return true;
+}
+
+
+/**
+ * Perform validation of uniforms used across multiple shader stages
+ */
+bool
+cross_validate_uniforms(struct glsl_program *prog)
+{
+   /* Examine all of the uniforms in all of the shaders and cross validate
+    * them.
+    */
+   glsl_symbol_table uniforms;
+   for (unsigned i = 0; i < prog->_NumLinkedShaders; i++) {
+      foreach_list(node, &prog->_LinkedShaders[i]->ir) {
+	 ir_variable *const var = ((ir_instruction *) node)->as_variable();
+
+	 if ((var == NULL) || (var->mode != ir_var_uniform))
+	    continue;
+
+	 /* If a uniform with this name has already been seen, verify that the
+	  * new instance has the same type.  In addition, if the uniforms have
+	  * initializers, the values of the initializers must be the same.
+	  */
+	 ir_variable *const existing = uniforms.get_variable(var->name);
+	 if (existing != NULL) {
+	    if (var->type != existing->type) {
+	       linker_error_printf(prog, "uniform `%s' declared as type "
+				   "`%s' and type `%s'\n",
+				   var->name, var->type->name,
+				   existing->type->name);
+	       return false;
+	    }
+
+	    if (var->constant_value != NULL) {
+	       if (existing->constant_value != NULL) {
+		  if (!var->constant_value->has_value(existing->constant_value)) {
+		     linker_error_printf(prog, "initializers for uniform "
+					 "`%s' have differing values\n",
+					 var->name);
+		     return false;
+		  }
+	       } else
+		  /* If the first-seen instance of a particular uniform did not
+		   * have an initializer but a later instance does, copy the
+		   * initializer to the version stored in the symbol table.
+		   */
+		  existing->constant_value =
+		     (ir_constant *)var->constant_value->clone(NULL);
+	    }
+	 } else
+	    uniforms.add_variable(var->name, var);
+      }
+   }
+
+   return true;
+}
+
+
+/**
+ * Validate that outputs from one stage match inputs of another
+ */
+bool
+cross_validate_outputs_to_inputs(struct glsl_program *prog,
+				 glsl_shader *producer, glsl_shader *consumer)
+{
+   glsl_symbol_table parameters;
+   /* FINISHME: Figure these out dynamically. */
+   const char *const producer_stage = "vertex";
+   const char *const consumer_stage = "fragment";
+
+   /* Find all shader outputs in the "producer" stage.
+    */
+   foreach_list(node, &producer->ir) {
+      ir_variable *const var = ((ir_instruction *) node)->as_variable();
+
+      /* FINISHME: For geometry shaders, this should also look for inout
+       * FINISHME: variables.
+       */
+      if ((var == NULL) || (var->mode != ir_var_out))
+	 continue;
+
+      parameters.add_variable(var->name, 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.
+    */
+   foreach_list(node, &consumer->ir) {
+      ir_variable *const input = ((ir_instruction *) node)->as_variable();
+
+      /* FINISHME: For geometry shaders, this should also look for inout
+       * FINISHME: variables.
+       */
+      if ((input == NULL) || (input->mode != ir_var_in))
+	 continue;
+
+      ir_variable *const output = parameters.get_variable(input->name);
+      if (output != NULL) {
+	 /* Check that the types match between stages.
+	  */
+	 if (input->type != output->type) {
+	    linker_error_printf(prog,
+				"%s shader output `%s' delcared as "
+				"type `%s', but %s shader input declared "
+				"as type `%s'\n",
+				producer_stage, output->name,
+				output->type->name,
+				consumer_stage, input->type->name);
+	    return false;
+	 }
+
+	 /* Check that all of the qualifiers match between stages.
+	  */
+	 if (input->centroid != output->centroid) {
+	    linker_error_printf(prog,
+				"%s shader output `%s' %s centroid qualifier, "
+				"but %s shader input %s centroid qualifier\n",
+				producer_stage,
+				output->name,
+				(output->centroid) ? "has" : "lacks",
+				consumer_stage,
+				(input->centroid) ? "has" : "lacks");
+	    return false;
+	 }
+
+	 if (input->invariant != output->invariant) {
+	    linker_error_printf(prog,
+				"%s shader output `%s' %s invariant qualifier, "
+				"but %s shader input %s invariant qualifier\n",
+				producer_stage,
+				output->name,
+				(output->invariant) ? "has" : "lacks",
+				consumer_stage,
+				(input->invariant) ? "has" : "lacks");
+	    return false;
+	 }
+
+	 if (input->interpolation != output->interpolation) {
+	    linker_error_printf(prog,
+				"%s shader output `%s' specifies %s "
+				"interpolation qualifier, "
+				"but %s shader input specifies %s "
+				"interpolation qualifier\n",
+				producer_stage,
+				output->name,
+				output->interpolation_string(),
+				consumer_stage,
+				input->interpolation_string());
+	    return false;
+	 }
+      }
+   }
+
+   return true;
+}
+
+
+struct uniform_node {
+   exec_node link;
+   struct gl_uniform *u;
+   unsigned slots;
+};
+
+void
+assign_uniform_locations(struct glsl_program *prog)
+{
+   /* */
+   exec_list uniforms;
+   unsigned total_uniforms = 0;
+   hash_table *ht = hash_table_ctor(32, hash_table_string_hash,
+				    hash_table_string_compare);
+
+   for (unsigned i = 0; i < prog->_NumLinkedShaders; i++) {
+      unsigned next_position = 0;
+
+      foreach_list(node, &prog->_LinkedShaders[i]->ir) {
+	 ir_variable *const var = ((ir_instruction *) node)->as_variable();
+
+	 if ((var == NULL) || (var->mode != ir_var_uniform))
+	    continue;
+
+	 const unsigned vec4_slots = (var->component_slots() + 3) / 4;
+	 assert(vec4_slots != 0);
+
+	 uniform_node *n = (uniform_node *) hash_table_find(ht, var->name);
+	 if (n == NULL) {
+	    n = (uniform_node *) calloc(1, sizeof(struct uniform_node));
+	    n->u = (gl_uniform *) calloc(vec4_slots, sizeof(struct gl_uniform));
+	    n->slots = vec4_slots;
+
+	    n->u[0].Name = strdup(var->name);
+	    for (unsigned j = 1; j < vec4_slots; j++)
+	       n->u[j].Name = n->u[0].Name;
+
+	    hash_table_insert(ht, n, n->u[0].Name);
+	    uniforms.push_tail(& n->link);
+	    total_uniforms += vec4_slots;
+	 }
+
+	 if (var->constant_value != NULL)
+	    for (unsigned j = 0; j < vec4_slots; j++)
+	       n->u[j].Initialized = true;
+
+	 var->location = next_position;
+
+	 for (unsigned j = 0; j < vec4_slots; j++) {
+	    switch (prog->_LinkedShaders[i]->Type) {
+	    case GL_VERTEX_SHADER:
+	       n->u[j].VertPos = next_position;
+	       break;
+	    case GL_FRAGMENT_SHADER:
+	       n->u[j].FragPos = next_position;
+	       break;
+	    case GL_GEOMETRY_SHADER:
+	       /* FINISHME: Support geometry shaders. */
+	       assert(prog->_LinkedShaders[i]->Type != GL_GEOMETRY_SHADER);
+	       break;
+	    }
+
+	    next_position++;
+	 }
+      }
+   }
+
+   gl_uniform_list *ul = (gl_uniform_list *)
+      calloc(1, sizeof(gl_uniform_list));
+
+   ul->Size = total_uniforms;
+   ul->NumUniforms = total_uniforms;
+   ul->Uniforms = (gl_uniform *) calloc(total_uniforms, sizeof(gl_uniform));
+
+   unsigned idx = 0;
+   uniform_node *next;
+   for (uniform_node *node = (uniform_node *) uniforms.head
+	   ; node->link.next != NULL
+	   ; node = next) {
+      next = (uniform_node *) node->link.next;
+
+      node->link.remove();
+      memcpy(&ul->Uniforms[idx], node->u, sizeof(gl_uniform) * node->slots);
+      idx += node->slots;
+
+      free(node->u);
+      free(node);
+   }
+
+   hash_table_dtor(ht);
+
+   prog->Uniforms = ul;
+}
+
+
+/**
+ * Find a contiguous set of available bits in a bitmask
+ *
+ * \param used_mask     Bits representing used (1) and unused (0) locations
+ * \param needed_count  Number of contiguous bits needed.
+ *
+ * \return
+ * Base location of the available bits on success or -1 on failure.
+ */
+int
+find_available_slots(unsigned used_mask, unsigned needed_count)
+{
+   unsigned needed_mask = (1 << needed_count) - 1;
+   const int max_bit_to_test = (8 * sizeof(used_mask)) - needed_count;
+
+   /* The comparison to 32 is redundant, but without it GCC emits "warning:
+    * cannot optimize possibly infinite loops" for the loop below.
+    */
+   if ((needed_count == 0) || (max_bit_to_test < 0) || (max_bit_to_test > 32))
+      return -1;
+
+   for (int i = 0; i <= max_bit_to_test; i++) {
+      if ((needed_mask & ~used_mask) == needed_mask)
+	 return i;
+
+      needed_mask <<= 1;
+   }
+
+   return -1;
+}
+
+
+bool
+assign_attribute_locations(glsl_program *prog, unsigned max_attribute_index)
+{
+   /* Mark invalid attribute locations as being used.
+    */
+   unsigned used_locations = (max_attribute_index >= 32)
+      ? ~0 : ~((1 << max_attribute_index) - 1);
+
+   glsl_shader *const sh = prog->_LinkedShaders[0];
+   assert(sh->Type == GL_VERTEX_SHADER);
+
+   /* Operate in a total of four passes.
+    *
+    * 1. Invalidate the location assignments for all vertex shader inputs.
+    *
+    * 2. Assign locations for inputs that have user-defined (via
+    *    glBindVertexAttribLocation) locatoins.
+    *
+    * 3. Sort the attributes without assigned locations by number of slots
+    *    required in decreasing order.  Fragmentation caused by attribute
+    *    locations assigned by the application may prevent large attributes
+    *    from having enough contiguous space.
+    *
+    * 4. Assign locations to any inputs without assigned locations.
+    */
+
+   invalidate_variable_locations(sh, ir_var_in, VERT_ATTRIB_GENERIC0);
+
+   if (prog->Attributes != NULL) {
+      for (unsigned i = 0; i < prog->Attributes->NumParameters; i++) {
+	 ir_variable *const var =
+	    sh->symbols->get_variable(prog->Attributes->Parameters[i].Name);
+
+	 /* Note: attributes that occupy multiple slots, such as arrays or
+	  * matrices, may appear in the attrib array multiple times.
+	  */
+	 if ((var == NULL) || (var->location != -1))
+	    continue;
+
+	 /* From page 61 of the OpenGL 4.0 spec:
+	  *
+	  *     "LinkProgram will fail if the attribute bindings assigned by
+	  *     BindAttribLocation do not leave not enough space to assign a
+	  *     location for an active matrix attribute or an active attribute
+	  *     array, both of which require multiple contiguous generic
+	  *     attributes."
+	  *
+	  * Previous versions of the spec contain similar language but omit the
+	  * bit about attribute arrays.
+	  *
+	  * Page 61 of the OpenGL 4.0 spec also says:
+	  *
+	  *     "It is possible for an application to bind more than one
+	  *     attribute name to the same location. This is referred to as
+	  *     aliasing. This will only work if only one of the aliased
+	  *     attributes is active in the executable program, or if no path
+	  *     through the shader consumes more than one attribute of a set
+	  *     of attributes aliased to the same location. A link error can
+	  *     occur if the linker determines that every path through the
+	  *     shader consumes multiple aliased attributes, but
+	  *     implementations are not required to generate an error in this
+	  *     case."
+	  *
+	  * These two paragraphs are either somewhat contradictory, or I don't
+	  * fully understand one or both of them.
+	  */
+	 /* FINISHME: The code as currently written does not support attribute
+	  * FINISHME: location aliasing (see comment above).
+	  */
+	 const int attr = prog->Attributes->Parameters[i].StateIndexes[0];
+	 const unsigned slots = count_attribute_slots(var->type);
+
+	 /* Mask representing the contiguous slots that will be used by this
+	  * attribute.
+	  */
+	 const unsigned use_mask = (1 << slots) - 1;
+
+	 /* Generate a link error if the set of bits requested for this
+	  * attribute overlaps any previously allocated bits.
+	  */
+	 if ((~(use_mask << attr) & used_locations) != used_locations) {
+	    linker_error_printf(prog,
+				"insufficient contiguous attribute locations "
+				"available for vertex shader input `%s'",
+				var->name);
+	    return false;
+	 }
+
+	 var->location = VERT_ATTRIB_GENERIC0 + attr;
+	 used_locations |= (use_mask << attr);
+      }
+   }
+
+   /* Temporary storage for the set of attributes that need locations assigned.
+    */
+   struct temp_attr {
+      unsigned slots;
+      ir_variable *var;
+
+      /* Used below in the call to qsort. */
+      static int compare(const void *a, const void *b)
+      {
+	 const temp_attr *const l = (const temp_attr *) a;
+	 const temp_attr *const r = (const temp_attr *) b;
+
+	 /* Reversed because we want a descending order sort below. */
+	 return r->slots - l->slots;
+      }
+   } to_assign[16];
+
+   unsigned num_attr = 0;
+
+   foreach_list(node, &sh->ir) {
+      ir_variable *const var = ((ir_instruction *) node)->as_variable();
+
+      if ((var == NULL) || (var->mode != ir_var_in))
+	 continue;
+
+      /* The location was explicitly assigned, nothing to do here.
+       */
+      if (var->location != -1)
+	 continue;
+
+      to_assign[num_attr].slots = count_attribute_slots(var->type);
+      to_assign[num_attr].var = var;
+      num_attr++;
+   }
+
+   /* If all of the attributes were assigned locations by the application (or
+    * are built-in attributes with fixed locations), return early.  This should
+    * be the common case.
+    */
+   if (num_attr == 0)
+      return true;
+
+   qsort(to_assign, num_attr, sizeof(to_assign[0]), temp_attr::compare);
+
+   for (unsigned i = 0; i < num_attr; i++) {
+      /* Mask representing the contiguous slots that will be used by this
+       * attribute.
+       */
+      const unsigned use_mask = (1 << to_assign[i].slots) - 1;
+
+      int location = find_available_slots(used_locations, to_assign[i].slots);
+
+      if (location < 0) {
+	 linker_error_printf(prog,
+			     "insufficient contiguous attribute locations "
+			     "available for vertex shader input `%s'",
+			     to_assign[i].var->name);
+	 return false;
+      }
+
+      to_assign[i].var->location = VERT_ATTRIB_GENERIC0 + location;
+      used_locations |= (use_mask << location);
+   }
+
+   return true;
+}
+
+
+void
+assign_varying_locations(glsl_shader *producer, glsl_shader *consumer)
+{
+   /* FINISHME: Set dynamically when geometry shader support is added. */
+   unsigned output_index = VERT_RESULT_VAR0;
+   unsigned input_index = FRAG_ATTRIB_VAR0;
+
+   /* Operate in a total of three passes.
+    *
+    * 1. Assign locations for any matching inputs and outputs.
+    *
+    * 2. Mark output variables in the producer that do not have locations as
+    *    not being outputs.  This lets the optimizer eliminate them.
+    *
+    * 3. Mark input variables in the consumer that do not have locations as
+    *    not being inputs.  This lets the optimizer eliminate them.
+    */
+
+   invalidate_variable_locations(producer, ir_var_out, VERT_RESULT_VAR0);
+   invalidate_variable_locations(consumer, ir_var_in, FRAG_ATTRIB_VAR0);
+
+   foreach_list(node, &producer->ir) {
+      ir_variable *const output_var = ((ir_instruction *) node)->as_variable();
+
+      if ((output_var == NULL) || (output_var->mode != ir_var_out)
+	  || (output_var->location != -1))
+	 continue;
+
+      ir_variable *const input_var =
+	 consumer->symbols->get_variable(output_var->name);
+
+      if ((input_var == NULL) || (input_var->mode != ir_var_in))
+	 continue;
+
+      assert(input_var->location == -1);
+
+      /* FINISHME: Location assignment will need some changes when arrays,
+       * FINISHME: matrices, and structures are allowed as shader inputs /
+       * FINISHME: outputs.
+       */
+      output_var->location = output_index;
+      input_var->location = input_index;
+
+      output_index++;
+      input_index++;
+   }
+
+   foreach_list(node, &producer->ir) {
+      ir_variable *const var = ((ir_instruction *) node)->as_variable();
+
+      if ((var == NULL) || (var->mode != ir_var_out))
+	 continue;
+
+      /* An 'out' variable is only really a shader output if its value is read
+       * by the following stage.
+       */
+      var->shader_out = (var->location != -1);
+   }
+
+   foreach_list(node, &consumer->ir) {
+      ir_variable *const var = ((ir_instruction *) node)->as_variable();
+
+      if ((var == NULL) || (var->mode != ir_var_in))
+	 continue;
+
+      /* An 'in' variable is only really a shader input if its value is written
+       * by the previous stage.
+       */
+      var->shader_in = (var->location != -1);
+   }
+}
+
+
+void
+link_shaders(struct glsl_program *prog)
+{
+   prog->LinkStatus = false;
+   prog->Validated = false;
+   prog->_Used = false;
+
+   if (prog->InfoLog != NULL)
+      talloc_free(prog->InfoLog);
+
+   prog->InfoLog = talloc_strdup(NULL, "");
+
+   /* Separate the shaders into groups based on their type.
+    */
+   struct glsl_shader **vert_shader_list;
+   unsigned num_vert_shaders = 0;
+   struct glsl_shader **frag_shader_list;
+   unsigned num_frag_shaders = 0;
+
+   vert_shader_list = (struct glsl_shader **)
+      calloc(2 * prog->NumShaders, sizeof(struct glsl_shader *));
+   frag_shader_list =  &vert_shader_list[prog->NumShaders];
+
+   for (unsigned i = 0; i < prog->NumShaders; i++) {
+      switch (prog->Shaders[i]->Type) {
+      case GL_VERTEX_SHADER:
+	 vert_shader_list[num_vert_shaders] = prog->Shaders[i];
+	 num_vert_shaders++;
+	 break;
+      case GL_FRAGMENT_SHADER:
+	 frag_shader_list[num_frag_shaders] = prog->Shaders[i];
+	 num_frag_shaders++;
+	 break;
+      case GL_GEOMETRY_SHADER:
+	 /* FINISHME: Support geometry shaders. */
+	 assert(prog->Shaders[i]->Type != GL_GEOMETRY_SHADER);
+	 break;
+      }
+   }
+
+   /* FINISHME: Implement intra-stage linking. */
+   assert(num_vert_shaders <= 1);
+   assert(num_frag_shaders <= 1);
+
+   /* Verify that each of the per-target executables is valid.
+    */
+   if (!validate_vertex_shader_executable(prog, vert_shader_list[0])
+       || !validate_fragment_shader_executable(prog, frag_shader_list[0]))
+      goto done;
+
+
+   prog->_LinkedShaders = (struct glsl_shader **)
+      calloc(2, sizeof(struct glsl_shader *));
+   prog->_NumLinkedShaders = 0;
+
+   if (num_vert_shaders > 0) {
+      prog->_LinkedShaders[prog->_NumLinkedShaders] = vert_shader_list[0];
+      prog->_NumLinkedShaders++;
+   }
+
+   if (num_frag_shaders > 0) {
+      prog->_LinkedShaders[prog->_NumLinkedShaders] = frag_shader_list[0];
+      prog->_NumLinkedShaders++;
+   }
+
+   /* Here begins the inter-stage linking phase.  Some initial validation is
+    * performed, then locations are assigned for uniforms, attributes, and
+    * varyings.
+    */
+   if (cross_validate_uniforms(prog)) {
+      /* Validate the inputs of each stage with the output of the preceeding
+       * stage.
+       */
+      for (unsigned i = 1; i < prog->_NumLinkedShaders; i++) {
+	 if (!cross_validate_outputs_to_inputs(prog,
+					       prog->_LinkedShaders[i - 1],
+					       prog->_LinkedShaders[i]))
+	    goto done;
+      }
+
+      prog->LinkStatus = true;
+   }
+
+   /* FINISHME: Perform whole-program optimization here. */
+
+   assign_uniform_locations(prog);
+
+   if (prog->_LinkedShaders[0]->Type == GL_VERTEX_SHADER)
+      /* FINISHME: The value of the max_attribute_index parameter is
+       * FINISHME: implementation dependent based on the value of
+       * FINISHME: GL_MAX_VERTEX_ATTRIBS.  GL_MAX_VERTEX_ATTRIBS must be
+       * FINISHME: at least 16, so hardcode 16 for now.
+       */
+      if (!assign_attribute_locations(prog, 16))
+	 goto done;
+
+   for (unsigned i = 1; i < prog->_NumLinkedShaders; i++)
+      assign_varying_locations(prog->_LinkedShaders[i - 1],
+			       prog->_LinkedShaders[i]);
+
+   /* FINISHME: Assign fragment shader output locations. */
+
+done:
+   free(vert_shader_list);
+}