glsl: add a NIR based varying linker

With a NIR based linker we get better xfb packing, and we no longer
depend on the GLSL IR optimisations to be able to link shaders
with a large amount of dead input/outputs.

Acked-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15731>

src/compiler/glsl/gl_nir_link_varyings.h

@@ -0,0 +1,220 @@
+/*
+ * Copyright © 2012 Intel Corporation
+ * Copyright © 2022 Valve 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.
+ */
+
+#ifndef GLSL_LINK_VARYINGS_H
+#define GLSL_LINK_VARYINGS_H
+
+/**
+ * Linker functions related specifically to linking varyings between shader
+ * stages.
+ */
+
+
+#include "main/glheader.h"
+#include "program/prog_parameter.h"
+#include "util/bitset.h"
+
+#include "nir.h"
+
+struct gl_shader_program;
+struct gl_shader_stage;
+struct gl_shader;
+struct gl_type;
+
+
+/**
+ * Data structure describing a varying which is available for use in transform
+ * feedback.
+ *
+ * For example, if the vertex shader contains:
+ *
+ *     struct S {
+ *       vec4 foo;
+ *       float[3] bar;
+ *     };
+ *
+ *     varying S[2] v;
+ *
+ * Then there would be tfeedback_candidate objects corresponding to the
+ * following varyings:
+ *
+ *     v[0].foo
+ *     v[0].bar
+ *     v[1].foo
+ *     v[1].bar
+ */
+struct tfeedback_candidate
+{
+   /**
+    * Toplevel variable containing this varying.  In the above example, this
+    * would point to the declaration of the varying v.
+    */
+   nir_variable *toplevel_var;
+
+   /**
+    * Type of this varying.  In the above example, this would point to the
+    * glsl_type for "vec4" or "float[3]".
+    */
+   const struct glsl_type *type;
+
+   /**
+    * Offset within the toplevel variable where this varying occurs.
+    * Counted in floats.
+    */
+   unsigned struct_offset_floats;
+
+   /**
+    * Offset within the xfb with respect to alignment requirements.
+    * Counted in floats.
+    */
+   unsigned xfb_offset_floats;
+
+   /* Used to match varyings and update toplevel_var pointer after NIR
+    * optimisations have been performed.
+    */
+   unsigned initial_location;
+   unsigned initial_location_frac;
+};
+
+enum lowered_builtin_array_var {
+   none,
+   clip_distance,
+   cull_distance,
+   tess_level_outer,
+   tess_level_inner,
+};
+
+/**
+ * Data structure tracking information about a transform feedback declaration
+ * during linking.
+ */
+struct xfb_decl
+{
+   /**
+    * The name that was supplied to glTransformFeedbackVaryings.  Used for
+    * error reporting and glGetTransformFeedbackVarying().
+    */
+   const char *orig_name;
+
+   /**
+    * The name of the variable, parsed from orig_name.
+    */
+   const char *var_name;
+
+   /**
+    * True if the declaration in orig_name represents an array.
+    */
+   bool is_subscripted;
+
+   /**
+    * If is_subscripted is true, the subscript that was specified in orig_name.
+    */
+   unsigned array_subscript;
+
+   /**
+    * Non-zero if the variable is gl_ClipDistance, glTessLevelOuter or
+    * gl_TessLevelInner and the driver lowers it to gl_*MESA.
+    */
+   enum lowered_builtin_array_var lowered_builtin_array_variable;
+
+   /**
+    * The vertex shader output location that the linker assigned for this
+    * variable.  -1 if a location hasn't been assigned yet.
+    */
+   int location;
+
+   /**
+    * Used to store the buffer assigned by xfb_buffer.
+    */
+   unsigned buffer;
+
+   /**
+    * Used to store the offset assigned by xfb_offset.
+    */
+   unsigned offset;
+
+   /**
+    * If non-zero, then this variable may be packed along with other variables
+    * into a single varying slot, so this offset should be applied when
+    * accessing components.  For example, an offset of 1 means that the x
+    * component of this variable is actually stored in component y of the
+    * location specified by \c location.
+    *
+    * Only valid if location != -1.
+    */
+   unsigned location_frac;
+
+   /**
+    * 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;
+
+   /** Type of the varying returned by glGetTransformFeedbackVarying() */
+   GLenum type;
+
+   /**
+    * If location != -1, the size that should be returned by
+    * glGetTransformFeedbackVarying().
+    */
+   unsigned size;
+
+   /**
+    * How many components to skip. If non-zero, this is
+    * gl_SkipComponents{1,2,3,4} from ARB_transform_feedback3.
+    */
+   unsigned skip_components;
+
+   /**
+    * Whether this is gl_NextBuffer from ARB_transform_feedback3.
+    */
+   bool next_buffer_separator;
+
+   /**
+    * If find_candidate() has been called, pointer to the tfeedback_candidate
+    * data structure that was found.  Otherwise NULL.
+    */
+   struct tfeedback_candidate *matched_candidate;
+
+   /**
+    * StreamId assigned to this varying (defaults to 0). Can only be set to
+    * values other than 0 in geometry shaders that use the stream layout
+    * modifier. Accepted values must be in the range [0, MAX_VERTEX_STREAMS-1].
+    */
+   unsigned stream_id;
+};
+
+static inline bool
+xfb_decl_is_varying(const struct xfb_decl *xfb_decl)
+{
+   return !xfb_decl->next_buffer_separator && !xfb_decl->skip_components;
+}
+
+#endif /* GLSL_LINK_VARYINGS_H */

src/compiler/glsl/gl_nir_linker.h

@@ -25,6 +25,7 @@
 #define GL_NIR_LINKER_H
 
 #include "main/glheader.h"
+#include "main/menums.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -58,6 +59,10 @@ bool gl_nir_link_uniforms(const struct gl_constants *consts,
                           struct gl_shader_program *prog,
                           bool fill_parameters);
 
+bool gl_nir_link_varyings(const struct gl_constants *consts,
+                          const struct gl_extensions *exts,
+                          gl_api api, struct gl_shader_program *prog);
+
 void gl_nir_set_uniform_initializers(const struct gl_constants *consts,
                                      struct gl_shader_program *prog);
 

src/compiler/glsl/meson.build

@@ -93,6 +93,8 @@ files_libglsl = files(
   'gl_nir_link_uniform_blocks.c',
   'gl_nir_link_uniform_initializers.c',
   'gl_nir_link_uniforms.c',
+  'gl_nir_link_varyings.c',
+  'gl_nir_link_varyings.h',
   'gl_nir_link_xfb.c',
   'gl_nir_linker.c',
   'gl_nir_linker.h',