Mesa (master): glsl: re-enable varying packing in GL4.4+

[Timothy Arceri]

Module: Mesa
Branch: master
Commit: 91dde3ddcaf6ca5a7aa2d2e9815236ce2ddf698f
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=91dde3ddcaf6ca5a7aa2d2e9815236ce2ddf698f

Author: Timothy Arceri <timothy.arceri at collabora.com>
Date:   Thu May 26 14:50:43 2016 +1000

glsl: re-enable varying packing in GL4.4+

We can still do packing we just need to get the packing type from the consumer
rather than the producer.

Reviewed-by: Iago Toral Quiroga <itoral at igalia.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97033

---

 src/compiler/glsl/link_varyings.cpp | 54 +++++++++++++++++--------------------
 1 file changed, 24 insertions(+), 30 deletions(-)

diff --git a/src/compiler/glsl/link_varyings.cpp b/src/compiler/glsl/link_varyings.cpp
index 29362c4..f6778b6 100644
--- a/src/compiler/glsl/link_varyings.cpp
+++ b/src/compiler/glsl/link_varyings.cpp
@@ -1405,10 +1405,26 @@ varying_matches::record(ir_variable *producer_var, ir_variable *consumer_var)
                  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;
+   /* We must use the consumer to compute the packing class because in GL4.4+
+    * there is no guarantee interpolation qualifiers will match across stages.
+    *
+    * From Section 4.5 (Interpolation Qualifiers) of the GLSL 4.30 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."
+    *
+    * This text was also in at least revison 7 of the 4.40 spec but is no
+    * longer in revision 9 and not in the 4.50 spec.
+    */
+   const ir_variable *const var = (consumer_var != NULL)
+      ? consumer_var : producer_var;
+   const gl_shader_stage stage = (consumer_var != NULL)
+      ? consumer_stage : producer_stage;
    const glsl_type *type = get_varying_type(var, stage);
 
    this->matches[this->num_matches].packing_class
@@ -2023,40 +2039,18 @@ assign_varying_locations(struct gl_context *ctx,
    bool xfb_enabled =
       ctx->Extensions.EXT_transform_feedback && !unpackable_tess;
 
-   /* Disable varying packing for GL 4.4+ as there is no guarantee
-    * that interpolation qualifiers will match between shaders in these
-    * versions. We also disable packing on outward facing interfaces for
-    * SSO because in ES we need to retain the unpacked varying information
-    * for draw time validation. For desktop GL we could allow packing for
-    * versions < 4.4 but it's just safer not to do packing.
+   /* Disable packing on outward facing interfaces for SSO because in ES we
+    * need to retain the unpacked varying information for draw time
+    * validation.
     *
     * Packing is still enabled on individual arrays, structs, and matrices as
     * these are required by the transform feedback code and it is still safe
     * to do so. We also enable packing when a varying is only used for
     * transform feedback and its not a SSO.
-    *
-    * Varying packing currently only packs together varyings with matching
-    * interpolation qualifiers as the backends assume all packed components
-    * are to be processed in the same way. Therefore we cannot do packing in
-    * these versions of GL without the risk of mismatching interfaces.
-    *
-    * From Section 4.5 (Interpolation Qualifiers) of the GLSL 4.30 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."
-    *
-    * This text was also in at least revison 7 of the 4.40 spec but is no
-    * longer in revision 9 and not in the 4.50 spec.
     */
    bool disable_varying_packing =
       ctx->Const.DisableVaryingPacking || unpackable_tess;
-   if ((ctx->API == API_OPENGL_CORE && ctx->Version >= 44) ||
-       (prog->SeparateShader && (producer == NULL || consumer == NULL)))
+   if (prog->SeparateShader && (producer == NULL || consumer == NULL))
       disable_varying_packing = true;
 
    varying_matches matches(disable_varying_packing, xfb_enabled,