linker: fix varying linking if SSO program has only gs and fs

Previously linker did not take in to account case where one would
have only gs and fs (with SSO), patch adds the case by refactoring
code around assign_varying_locations. This makes sure locations for
gs get populated correctly.

This was found with some of the SSO subtests of Martin's upcoming
GetProgramInterfaceiv Piglit test which passes with the patch, no
Piglit regressions.

v2: code cleanups (Martin Peres)

Signed-off-by: Tapani Pälli <[email protected]>
Reviewed-by: Martin Peres <[email protected]>

1 files changed, 17 insertions, 12 deletions

diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index 85830e680ed..118614bdd80 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -2726,10 +2726,18 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
       goto done;
    }
 
-   unsigned first;
-   for (first = 0; first <= MESA_SHADER_FRAGMENT; first++) {
-      if (prog->_LinkedShaders[first] != NULL)
-	 break;
+   unsigned first, last;
+
+   first = MESA_SHADER_STAGES;
+   last = 0;
+
+   /* Determine first and last stage. */
+   for (unsigned i = 0; i < MESA_SHADER_STAGES; i++) {
+      if (!prog->_LinkedShaders[i])
+         continue;
+      if (first == MESA_SHADER_STAGES)
+         first = i;
+      last = i;
    }
 
    if (num_tfeedback_decls != 0) {
@@ -2758,13 +2766,9 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
     * ensures that inter-shader outputs written to in an earlier stage are
     * eliminated if they are (transitively) not used in a later stage.
     */
-   int last, next;
-   for (last = MESA_SHADER_FRAGMENT; last >= 0; last--) {
-      if (prog->_LinkedShaders[last] != NULL)
-         break;
-   }
+   int next;
 
-   if (last >= 0 && last < MESA_SHADER_FRAGMENT) {
+   if (first < MESA_SHADER_FRAGMENT) {
       gl_shader *const sh = prog->_LinkedShaders[last];
 
       if (first == MESA_SHADER_GEOMETRY) {
@@ -2776,13 +2780,14 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
           * MESA_SHADER_GEOMETRY.
           */
          if (!assign_varying_locations(ctx, mem_ctx, prog,
-                                       NULL, sh,
+                                       NULL, prog->_LinkedShaders[first],
                                        num_tfeedback_decls, tfeedback_decls,
                                        prog->Geom.VerticesIn))
             goto done;
       }
 
-      if (num_tfeedback_decls != 0 || prog->SeparateShader) {
+      if (last != MESA_SHADER_FRAGMENT &&
+         (num_tfeedback_decls != 0 || prog->SeparateShader)) {
          /* There was no fragment shader, but we still have to assign varying
           * locations for use by transform feedback.
           */