glsl: Assign transform feedback varying slots in linker.

This patch modifies the GLSL linker to assign additional slots for
varying variables used by transform feedback, and record the varying
slots used by transform feedback for use by the driver back-end.

This required modifying assign_varying_locations() so that it assigns
a varying location if either (a) the varying is used by the next stage
of the GL pipeline, or (b) the varying is required by transform
feedback.  In order to avoid duplicating the code to assign a single
varying location, I moved it into its own function,
assign_varying_location().

In addition, to support transform feedback in the case where there is
no fragment shader, it is now possible to call
assign_varying_locations() with a consumer of NULL.

Reviewed-by: Marek Olšák <[email protected]>
Tested-by: Marek Olšák <[email protected]>

1 files changed, 490 insertions, 63 deletions

diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index 0306b7a1b5f..351680d43fc 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -1369,10 +1369,359 @@ demote_shader_inputs_and_outputs(gl_shader *sh, enum ir_variable_mode mode)
 }
 
 
+/**
+ * Data structure tracking information about a transform feedback declaration
+ * during linking.
+ */
+class tfeedback_decl
+{
+public:
+   bool init(struct gl_shader_program *prog, const void *mem_ctx,
+             const char *input);
+   static bool is_same(const tfeedback_decl &x, const tfeedback_decl &y);
+   bool assign_location(struct gl_context *ctx, struct gl_shader_program *prog,
+                        ir_variable *output_var);
+   bool store(struct gl_shader_program *prog,
+              struct gl_transform_feedback_info *info, unsigned buffer) const;
+
+
+   /**
+    * True if assign_location() has been called for this object.
+    */
+   bool is_assigned() const
+   {
+      return this->location != -1;
+   }
+
+   /**
+    * Determine whether this object refers to the variable var.
+    */
+   bool matches_var(ir_variable *var) const
+   {
+      return strcmp(var->name, this->var_name) == 0;
+   }
+
+   /**
+    * The total number of varying components taken up by this variable.  Only
+    * valid if is_assigned() is true.
+    */
+   unsigned num_components() const
+   {
+      return this->vector_elements * this->matrix_columns;
+   }
+
+private:
+   /**
+    * The name that was supplied to glTransformFeedbackVaryings.  Used for
+    * error reporting.
+    */
+   const char *orig_name;
+
+   /**
+    * The name of the variable, parsed from orig_name.
+    */
+   char *var_name;
+
+   /**
+    * True if the declaration in orig_name represents an array.
+    */
+   bool is_array;
+
+   /**
+    * If is_array is true, the array index that was specified in orig_name.
+    */
+   unsigned array_index;
+
+   /**
+    * The vertex shader output location that the linker assigned for this
+    * variable.  -1 if a location hasn't been assigned yet.
+    */
+   int location;
+
+   /**
+    * If location != -1, the number of vector elements in this variable, or 1
+    * if this variable is a scalar.
+    */
+   unsigned vector_elements;
+
+   /**
+    * If location != -1, the number of matrix columns in this variable, or 1
+    * if this variable is not a matrix.
+    */
+   unsigned matrix_columns;
+};
+
+
+/**
+ * Initialize this object based on a string that was passed to
+ * glTransformFeedbackVaryings.  If there is a parse error, the error is
+ * reported using linker_error(), and false is returned.
+ */
+bool
+tfeedback_decl::init(struct gl_shader_program *prog, 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;
+
+   const char *bracket = strrchr(input, '[');
+
+   if (bracket) {
+      this->var_name = ralloc_strndup(mem_ctx, input, bracket - input);
+      if (sscanf(bracket, "[%u]", &this->array_index) == 1) {
+         this->is_array = true;
+         return true;
+      }
+   } else {
+      this->var_name = ralloc_strdup(mem_ctx, input);
+      this->is_array = false;
+      return true;
+   }
+
+   linker_error(prog, "Cannot parse transform feedback varying %s", input);
+   return false;
+}
+
+
+/**
+ * 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)
+{
+   if (strcmp(x.var_name, y.var_name) != 0)
+      return false;
+   if (x.is_array != y.is_array)
+      return false;
+   if (x.is_array && x.array_index != y.array_index)
+      return false;
+   return true;
+}
+
+
+/**
+ * Assign a location for this tfeedback_decl object based on the location
+ * assignment in output_var.
+ *
+ * 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,
+                                ir_variable *output_var)
+{
+   if (output_var->type->is_array()) {
+      /* Array variable */
+      if (!this->is_array) {
+         linker_error(prog, "Transform feedback varying %s found, "
+                      "but it's not an array ([] not expected).",
+                      this->orig_name);
+         return false;
+      }
+      /* Check array bounds. */
+      if (this->array_index >=
+          (unsigned) output_var->type->array_size()) {
+         linker_error(prog, "Transform feedback varying %s has index "
+                      "%i, but the array size is %i.",
+                      this->orig_name, this->array_index,
+                      output_var->type->array_size());
+         return false;
+      }
+      const unsigned matrix_cols =
+         output_var->type->fields.array->matrix_columns;
+      this->location = output_var->location + this->array_index * matrix_cols;
+      this->vector_elements = output_var->type->fields.array->vector_elements;
+      this->matrix_columns = matrix_cols;
+   } else {
+      /* Regular variable (scalar, vector, or matrix) */
+      if (this->is_array) {
+         linker_error(prog, "Transform feedback varying %s found, "
+                      "but it's an array ([] expected).",
+                      this->orig_name);
+         return false;
+      }
+      this->location = output_var->location;
+      this->vector_elements = output_var->type->vector_elements;
+      this->matrix_columns = output_var->type->matrix_columns;
+   }
+   /* 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;
+   }
+
+   return true;
+}
+
+
+/**
+ * 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_shader_program *prog,
+                      struct gl_transform_feedback_info *info,
+                      unsigned buffer) const
+{
+   if (!this->is_assigned()) {
+      /* 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 false;
+   }
+   for (unsigned v = 0; v < this->matrix_columns; ++v) {
+      info->Outputs[info->NumOutputs].OutputRegister = this->location + v;
+      info->Outputs[info->NumOutputs].NumComponents = this->vector_elements;
+      info->Outputs[info->NumOutputs].OutputBuffer = buffer;
+      ++info->NumOutputs;
+   }
+   return true;
+}
+
+
+/**
+ * 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.
+ */
+static bool
+parse_tfeedback_decls(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) {
+      if (!decls[i].init(prog, mem_ctx, varying_names[i]))
+         return false;
+      /* 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 (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;
+}
+
+
+/**
+ * Assign a location for a variable that is produced in one pipeline stage
+ * (the "producer") and consumed in the next stage (the "consumer").
+ *
+ * \param input_var is the input variable declaration in the consumer.
+ *
+ * \param output_var is the output variable declaration in the producer.
+ *
+ * \param input_index is the counter that keeps track of assigned input
+ *        locations in the consumer.
+ *
+ * \param output_index is the counter that keeps track of assigned output
+ *        locations in the producer.
+ *
+ * It is permissible for \c input_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 the variable has already been assigned a location, this function has no
+ * effect.
+ */
+void
+assign_varying_location(ir_variable *input_var, ir_variable *output_var,
+                        unsigned *input_index, unsigned *output_index)
+{
+   if (output_var->location != -1) {
+      /* Location already assigned. */
+      return;
+   }
+
+   if (input_var) {
+      assert(input_var->location == -1);
+      input_var->location = *input_index;
+   }
+
+   output_var->location = *output_index;
+
+   /* FINISHME: Support for "varying" records in GLSL 1.50. */
+   assert(!output_var->type->is_record());
+
+   if (output_var->type->is_array()) {
+      const unsigned slots = output_var->type->length
+         * output_var->type->fields.array->matrix_columns;
+
+      *output_index += slots;
+      *input_index += slots;
+   } else {
+      const unsigned slots = output_var->type->matrix_columns;
+
+      *output_index += slots;
+      *input_index += 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,
 			 struct gl_shader_program *prog,
-			 gl_shader *producer, gl_shader *consumer)
+			 gl_shader *producer, gl_shader *consumer,
+                         unsigned num_tfeedback_decls,
+                         tfeedback_decl *tfeedback_decls)
 {
    /* FINISHME: Set dynamically when geometry shader support is added. */
    unsigned output_index = VERT_RESULT_VAR0;
@@ -1390,79 +1739,77 @@ assign_varying_locations(struct gl_context *ctx,
     */
 
    link_invalidate_variable_locations(producer, ir_var_out, VERT_RESULT_VAR0);
-   link_invalidate_variable_locations(consumer, ir_var_in, FRAG_ATTRIB_VAR0);
+   if (consumer)
+      link_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))
+      if ((output_var == NULL) || (output_var->mode != ir_var_out))
 	 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);
-
-      output_var->location = output_index;
-      input_var->location = input_index;
-
-      /* FINISHME: Support for "varying" records in GLSL 1.50. */
-      assert(!output_var->type->is_record());
+      ir_variable *input_var =
+	 consumer ? consumer->symbols->get_variable(output_var->name) : NULL;
 
-      if (output_var->type->is_array()) {
-	 const unsigned slots = output_var->type->length
-	    * output_var->type->fields.array->matrix_columns;
+      if (input_var && input_var->mode != ir_var_in)
+         input_var = NULL;
 
-	 output_index += slots;
-	 input_index += slots;
-      } else {
-	 const unsigned slots = output_var->type->matrix_columns;
+      if (input_var) {
+         assign_varying_location(input_var, output_var, &input_index,
+                                 &output_index);
+      }
 
-	 output_index += slots;
-	 input_index += slots;
+      for (unsigned i = 0; i < num_tfeedback_decls; ++i) {
+         if (!tfeedback_decls[i].is_assigned() &&
+             tfeedback_decls[i].matches_var(output_var)) {
+            if (output_var->location == -1) {
+               assign_varying_location(input_var, output_var, &input_index,
+                                       &output_index);
+            }
+            if (!tfeedback_decls[i].assign_location(ctx, prog, output_var))
+               return false;
+         }
       }
    }
 
    unsigned varying_vectors = 0;
 
-   foreach_list(node, consumer->ir) {
-      ir_variable *const var = ((ir_instruction *) node)->as_variable();
-
-      if ((var == NULL) || (var->mode != ir_var_in))
-	 continue;
-
-      if (var->location == -1) {
-	 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, "fragment shader varying %s not written "
-			 "by vertex shader\n.", var->name);
-	 }
+   if (consumer) {
+      foreach_list(node, consumer->ir) {
+         ir_variable *const var = ((ir_instruction *) node)->as_variable();
+
+         if ((var == NULL) || (var->mode != ir_var_in))
+            continue;
+
+         if (var->location == -1) {
+            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, "fragment shader varying %s not written "
+                            "by vertex shader\n.", var->name);
+            }
 
-	 /* An 'in' variable is only really a shader input if its
-	  * value is written by the previous stage.
-	  */
-	 var->mode = ir_var_auto;
-      } else {
-	 /* The packing rules are used for vertex shader inputs are also used
-	  * for fragment shader inputs.
-	  */
-	 varying_vectors += count_attribute_slots(var->type);
+            /* An 'in' variable is only really a shader input if its
+             * value is written by the previous stage.
+             */
+            var->mode = ir_var_auto;
+         } else {
+            /* The packing rules are used for vertex shader inputs are also
+             * used for fragment shader inputs.
+             */
+            varying_vectors += count_attribute_slots(var->type);
+         }
       }
    }
 
@@ -1487,9 +1834,54 @@ assign_varying_locations(struct gl_context *ctx,
 }
 
 
+/**
+ * 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.
+ */
+static bool
+store_tfeedback_info(struct gl_context *ctx, struct gl_shader_program *prog,
+                     unsigned num_tfeedback_decls,
+                     tfeedback_decl *tfeedback_decls)
+{
+   unsigned total_tfeedback_components = 0;
+   prog->LinkedTransformFeedback.NumOutputs = 0;
+   for (unsigned i = 0; i < num_tfeedback_decls; ++i) {
+      unsigned buffer =
+         prog->TransformFeedback.BufferMode == GL_SEPARATE_ATTRIBS ? i : 0;
+      if (!tfeedback_decls[i].store(prog, &prog->LinkedTransformFeedback,
+                                    buffer))
+         return false;
+      total_tfeedback_components += tfeedback_decls[i].num_components();
+   }
+
+   /* 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 &&
+       total_tfeedback_components >
+       ctx->Const.MaxTransformFeedbackInterleavedComponents) {
+      linker_error(prog, "The MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS "
+                   "limit has been exceeded.");
+      return false;
+   }
+
+   return true;
+}
+
+
 void
 link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
 {
+   tfeedback_decl *tfeedback_decls = NULL;
+   unsigned num_tfeedback_decls = prog->TransformFeedback.NumVarying;
+
    void *mem_ctx = ralloc_context(NULL); // temporary linker context
 
    prog->LinkStatus = false;
@@ -1656,19 +2048,54 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
 	 break;
    }
 
+   if (num_tfeedback_decls != 0) {
+      /* From GL_EXT_transform_feedback:
+       *   A program will fail to link if:
+       *
+       *   * the <count> specified by TransformFeedbackVaryingsEXT is
+       *     non-zero, but the program object has no vertex or geometry
+       *     shader;
+       */
+      if (prev >= MESA_SHADER_FRAGMENT) {
+         linker_error(prog, "Transform feedback varyings specified, but "
+                      "no vertex or geometry shader is present.");
+         goto done;
+      }
+
+      tfeedback_decls = ralloc_array(mem_ctx, tfeedback_decl,
+                                     prog->TransformFeedback.NumVarying);
+      if (!parse_tfeedback_decls(prog, mem_ctx, num_tfeedback_decls,
+                                 prog->TransformFeedback.VaryingNames,
+                                 tfeedback_decls))
+         goto done;
+   }
+
    for (unsigned i = prev + 1; i < MESA_SHADER_TYPES; i++) {
       if (prog->_LinkedShaders[i] == NULL)
 	 continue;
 
-      if (!assign_varying_locations(ctx, prog,
-				    prog->_LinkedShaders[prev],
-				    prog->_LinkedShaders[i])) {
+      if (!assign_varying_locations(
+             ctx, prog, prog->_LinkedShaders[prev], prog->_LinkedShaders[i],
+             i == MESA_SHADER_FRAGMENT ? num_tfeedback_decls : 0,
+             tfeedback_decls))
 	 goto done;
-      }
 
       prev = i;
    }
 
+   if (prev != MESA_SHADER_FRAGMENT && num_tfeedback_decls != 0) {
+      /* There was no fragment shader, but we still have to assign varying
+       * locations for use by transform feedback.
+       */
+      if (!assign_varying_locations(
+             ctx, prog, prog->_LinkedShaders[prev], NULL, num_tfeedback_decls,
+             tfeedback_decls))
+         goto done;
+   }
+
+   if (!store_tfeedback_info(ctx, prog, num_tfeedback_decls, tfeedback_decls))
+      goto done;
+
    if (prog->_LinkedShaders[MESA_SHADER_VERTEX] != NULL) {
       demote_shader_inputs_and_outputs(prog->_LinkedShaders[MESA_SHADER_VERTEX],
 				       ir_var_out);