i965: Avoid branch instructions while in single program flow mode.

There is an errata for Broadwater that threads don't have the instruction/loop
mask stacks initialized on thread spawn.  In single program flow mode, those
stacks are not writable, so we can't initialize them.  However, they do get
read during ELSE and ENDIF instructions.  So, instead, replace branch
instructions in single program flow mode with predicated jumps (ADD to the ip
register), avoiding use of the more complicated branch instructions that may
fail.  This is also a minor optimization as no ENDIF equivalent is necessary.

Signed-off-by: Keith Packard <keithp@neko.keithp.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_clip.c b/src/mesa/drivers/dri/i965/brw_clip.c
index 0e8591aaa8..3bec153075 100644
--- a/src/mesa/drivers/dri/i965/brw_clip.c
+++ b/src/mesa/drivers/dri/i965/brw_clip.c
@@ -62,6 +62,8 @@ static void compile_clip_prog( struct brw_context *brw,
     */
    brw_init_compile(&c.func);
 
+   c.func.single_program_flow = 1;
+
    c.key = *key;