Mesa (master): Revert "i965/fs: Reduce restrictions on interference in register coalescing."

[Matt Turner]

Module: Mesa
Branch: master
Commit: ccb1ea8a1502286124b48030dac9b898a6c7caaa
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=ccb1ea8a1502286124b48030dac9b898a6c7caaa

Author: Matt Turner <mattst88 at gmail.com>
Date:   Mon May 26 11:44:09 2014 -0700

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

This reverts commit f770123f58b46459e8dbd27525162ee8ba89f30b.

Cc: "10.2" <mesa-stable at lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=78692

---

 src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp |   13 +++++++++++++
 1 file changed, 13 insertions(+)

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 13b678a..b2ab386 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
@@ -83,6 +83,19 @@ 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;