llvmpipe,draw,gallivm: Ensure we don't walk beyond the end of the shader variant list.

u_simple_list.h uses a sentinel element, and not a NULL element. So
ensure list is not empty when reducing the list of shader variants.

Something I noticed while trying to free variants more aggressively.

Reviewed-by: Brian Paul <[email protected]>

1 files changed, 7 insertions, 2 deletions

diff --git a/src/gallium/auxiliary/draw/draw_pt_fetch_shade_pipeline_llvm.c b/src/gallium/auxiliary/draw/draw_pt_fetch_shade_pipeline_llvm.c
index 7698f5ff2af..de6ce7fad40 100644
--- a/src/gallium/auxiliary/draw/draw_pt_fetch_shade_pipeline_llvm.c
+++ b/src/gallium/auxiliary/draw/draw_pt_fetch_shade_pipeline_llvm.c
@@ -160,8 +160,13 @@ llvm_middle_end_prepare( struct draw_pt_middle_end *middle,
           * XXX: should we flush here ?
           */
          for (i = 0; i < DRAW_MAX_SHADER_VARIANTS / 4; i++) {
-            struct draw_llvm_variant_list_item *item =
-               last_elem(&fpme->llvm->vs_variants_list);
+            struct draw_llvm_variant_list_item *item;
+            if (is_empty_list(&fpme->llvm->vs_variants_list)) {
+               break;
+            }
+            item = last_elem(&fpme->llvm->vs_variants_list);
+            assert(item);
+            assert(item->base);
             draw_llvm_destroy_variant(item->base);
          }
       }