st/mesa: only set primitive_restart when the restart index is in range

Even when enabled, primitive restart has no effect when the restart index
is larger than the representable values in the index buffer.

Fixes GL45-CTS.gtf31.GL3Tests.primitive_restart.primitive_restart_upconvert
for radeonsi VI.

v2: add an explanatory comment

Cc: "12.0 13.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Marek Olšák <marek.olsak@amd.com> (v1)

diff --git a/src/mesa/state_tracker/st_draw.c b/src/mesa/state_tracker/st_draw.c
index f4af23da97f36a258276ba158dba941d07d14c29..5dcaff09c03d20b16c248f7a643a41b4b44b1fd5 100644 (file)
--- a/src/mesa/state_tracker/st_draw.c
+++ b/src/mesa/state_tracker/st_draw.c
@@ -205,8 +205,19 @@ st_draw_vbo(struct gl_context *ctx,
       /* The VBO module handles restart for the non-indexed GLDrawArrays
        * so we only set these fields for indexed drawing:
        */
-      info.primitive_restart = ctx->Array._PrimitiveRestart;
-      info.restart_index = _mesa_primitive_restart_index(ctx, ib->type);
+      if (ctx->Array._PrimitiveRestart) {
+         info.restart_index = _mesa_primitive_restart_index(ctx, ib->type);
+
+         /* Enable primitive restart only when the restart index can have an
+          * effect. This is required for correctness in radeonsi VI support,
+          * though other hardware may also benefit from taking a faster,
+          * non-restart path when possible.
+          */
+         if ((ibuffer.index_size >= 4) ||
+             (ibuffer.index_size >= 2 && info.restart_index <= 0xffff) ||
+             (info.restart_index <= 0xff))
+            info.primitive_restart = true;
+      }
    }
    else {
       /* Transform feedback drawing is always non-indexed. */