gallium/auxiliary: Handle count == 0 in u_vbuf_get_minmax_index_mapped

This makes u_vbuf_get_minmax_index_mapped return min = 0 / max = 0
when info->count == 0.

That should never happen anyway, but this commit makes it at least
return a sane value that callers expect, and also allows us - and
GCC - to assume count != 0 for optimization purposes.

Reviewed-by: Alyssa Rosenzweig <[email protected]>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3050>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3050>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/gallium/auxiliary/util/u_vbuf.c b/src/gallium/auxiliary/util/u_vbuf.c
index 40bdf1ed830..7f4248fa49c 100644
--- a/src/gallium/auxiliary/util/u_vbuf.c
+++ b/src/gallium/auxiliary/util/u_vbuf.c
@@ -1030,6 +1030,12 @@ u_vbuf_get_minmax_index_mapped(const struct pipe_draw_info *info,
                                const void *indices, unsigned *out_min_index,
                                unsigned *out_max_index)
 {
+   if (!info->count) {
+      *out_min_index = 0;
+      *out_max_index = 0;
+      return;
+   }
+
    switch (info->index_size) {
    case 4: {
       const unsigned *ui_indices = (const unsigned*)indices;