[Mesa-dev] [PATCH 2/2] i965/cfg: Ignore non-CF instructions in unreachable blocks.

[Matt Turner]

The basic block following a control flow structure like an infinite loop
will be unreachable. Ignore any non-control-flow instructions in it
since they can have no effect on the program.

Avoids a segmentation fault in cfg_t::intersect(a, b) when called on an
unreachable block. By avoiding ever putting code in an unreachable
block, we never attempt to optimize code in an unreachable block.
---
 src/mesa/drivers/dri/i965/brw_cfg.cpp | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_cfg.cpp b/src/mesa/drivers/dri/i965/brw_cfg.cpp
index 53b32be..2fa4e3d 100644
--- a/src/mesa/drivers/dri/i965/brw_cfg.cpp
+++ b/src/mesa/drivers/dri/i965/brw_cfg.cpp
@@ -312,6 +312,11 @@ cfg_t::cfg_t(exec_list *instructions)
 	 break;
 
       default:
+         if (cur->num != 0 && cur->parents.is_empty()) {
+            ip--;
+            continue;
+         }
+
          cur->instructions.push_tail(inst);
 	 break;
       }
@@ -319,6 +324,12 @@ cfg_t::cfg_t(exec_list *instructions)
 
    cur->end_ip = ip - 1;
 
+   /* If the last block was empty (because it was unreachable) drop it. */
+   if (cur->instructions.is_empty()) {
+      cur->link.remove();
+      num_blocks--;
+   }
+
    make_block_array();
 }
 
-- 
2.7.3