i965/fs: Reduce restrictions on interference in register coalescing.

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%)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

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 b2ab386ab6631e5285d762b7d19bd35e092f3718..13b678afdc4d3574362a2fb08abec0a2b7e573b9 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
@@ -83,19 +83,6 @@ 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;