nir/xfb: sort varyings too

Right now we are only re-sorting outputs. But it is better to sort too
varyings, as linker expect them to be sorted out (as it was done on
GLSL). For varyings, and to make easier to compute buffer_index, we
sort also by buffer. We could do the same for outputs, but we lack a
reason for that, so we left it as it is (just offset).

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/compiler/nir/nir_gather_xfb_info.c

@@ -122,10 +122,22 @@ add_var_xfb_outputs(nir_xfb_info *xfb,
    }
 }
 
+static int
+compare_xfb_varying_offsets(const void *_a, const void *_b)
+{
+   const nir_xfb_varying_info *a = _a, *b = _b;
+
+   if (a->buffer != b->buffer)
+      return a->buffer - b->buffer;
+
+   return a->offset - b->offset;
+}
+
 static int
 compare_xfb_output_offsets(const void *_a, const void *_b)
 {
    const nir_xfb_output_info *a = _a, *b = _b;
+
    return a->offset - b->offset;
 }
 
@@ -199,12 +211,15 @@ nir_gather_xfb_info(const nir_shader *shader, void *mem_ctx)
       }
    }
 
-   /* Everything is easier in the state setup code if the list is sorted in
-    * order of output offset.
+   /* Everything is easier in the state setup code if outputs and varyings are
+    * sorted in order of output offset (and buffer for varyings).
     */
    qsort(xfb->outputs, xfb->output_count, sizeof(xfb->outputs[0]),
          compare_xfb_output_offsets);
 
+   qsort(xfb->varyings, xfb->varying_count, sizeof(xfb->varyings[0]),
+         compare_xfb_varying_offsets);
+
 #ifndef NDEBUG
    /* Finally, do a sanity check */
    unsigned max_offset[NIR_MAX_XFB_BUFFERS] = {0};