[Mesa-dev] [PATCH 6/6] i965/fs: Reduce restrictions on interference in register coalescing.

[Matt Turner]

We previously only allowed coalescing registers that interfere (i.e.,
whose live ranges overlap) if the destination register's live range was
entirely inside the source's live range. This is unnecessary -- we only
need to check for interfering writes in the intersection of their live
ranges.

total instructions in shared programs: 1639470 -> 1638453 (-0.06%)
instructions in affected programs:     84751 -> 83734 (-1.20%)
---
 src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp b/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
index ca7a6a8..b056e9c 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
@@ -79,19 +79,6 @@ can_coalesce_vars(brw::fs_live_variables *live_intervals,
    if (!live_intervals->vars_interfere(var_from, var_to))
       return true;
 
-   /* We know that the live ranges of A (var_from) and B (var_to)
-    * interfere because of the ->vars_interfere() call above. If the end
-    * of B's live range is after the end of A's range, then we know two
-    * things:
-    *  - the start of B's live range must be in A's live range (since we
-    *    already know the two ranges interfere, this is the only remaining
-    *    possibility)
-    *  - the interference isn't of the form we're looking for (where B is
-    *    entirely inside A)
-    */
-   if (live_intervals->end[var_to] > live_intervals->end[var_from])
-      return false;
-
    assert(ip >= live_intervals->start[var_to]);
 
    fs_inst *scan_inst;
-- 
1.8.3.2