[Mesa-dev] [PATCH 5/6] glsl: don't sort varying in separate shader mode

[Timothy Arceri]

From: Gregory Hainaut <gregory.hainaut at gmail.com>

This fixes an issue where the addition of the FLAT qualifier in
varying_matches::record() can break the expected varying order.

It also avoids a future issue with the relaxing of interpolation
qualifier matching constraints in GLSL 4.50.

V2: (by Timothy Arceri)
* reworked comment slightly

Signed-off-by: Gregory Hainaut <gregory.hainaut at gmail.com>
Reviewed-by: Timothy Arceri <timothy.arceri at collabora.com>
---
 src/glsl/link_varyings.cpp | 38 ++++++++++++++++++++++++++++++++------
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/src/glsl/link_varyings.cpp b/src/glsl/link_varyings.cpp
index ac2755f..71750d1 100644
--- a/src/glsl/link_varyings.cpp
+++ b/src/glsl/link_varyings.cpp
@@ -766,7 +766,7 @@ public:
                    gl_shader_stage consumer_stage);
    ~varying_matches();
    void record(ir_variable *producer_var, ir_variable *consumer_var);
-   unsigned assign_locations(uint64_t reserved_slots);
+   unsigned assign_locations(uint64_t reserved_slots, bool separate_shader);
    void store_locations() const;
 
 private:
@@ -988,11 +988,36 @@ varying_matches::record(ir_variable *producer_var, ir_variable *consumer_var)
  * passed to varying_matches::record().
  */
 unsigned
-varying_matches::assign_locations(uint64_t reserved_slots)
+varying_matches::assign_locations(uint64_t reserved_slots, bool 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);
+   /* 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;
@@ -1592,7 +1617,8 @@ assign_varying_locations(struct gl_context *ctx,
       reserved_varying_slot(producer, ir_var_shader_out) |
       reserved_varying_slot(consumer, ir_var_shader_in);
 
-   const unsigned slots_used = matches.assign_locations(reserved_slots);
+   const unsigned slots_used = matches.assign_locations(reserved_slots,
+                                                        prog->SeparateShader);
    matches.store_locations();
 
    for (unsigned i = 0; i < num_tfeedback_decls; ++i) {
-- 
2.4.3