i965: Don't use the head sentinel as an fs_inst in Gen4 workaround code.

When walking backwards, we want to stop at the head sentinel, which is
where scan_inst->prev->prev == NULL, not scan_inst->prev == NULL.

Fixes random crashes, as well as valgrind errors.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: mesa-stable@lists.freedesktop.org

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index a8ca9bc..b485e65 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -2355,7 +2355,7 @@ fs_visitor::insert_gen4_pre_send_dependency_workarounds(fs_inst *inst)
     * program.
     */
    for (fs_inst *scan_inst = (fs_inst *)inst->prev;
-        scan_inst != NULL;
+        !scan_inst->is_head_sentinel();
         scan_inst = (fs_inst *)scan_inst->prev) {
 
       /* If we hit control flow, assume that there *are* outstanding