[Bug tree-optimization/78185] Wrong branch optimization with -O1 on x86/x86_64

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78185

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Better patch (question answered, we walk all BBs of each loop, thus BBs in
sub-loop multiple times, and no, finite_loop_p would not catch infinite
subloops):

diff --git a/gcc/tree-ssa-loop-im.c b/gcc/tree-ssa-loop-im.c
index 463db04..0524e57 100644
--- a/gcc/tree-ssa-loop-im.c
+++ b/gcc/tree-ssa-loop-im.c
@@ -44,6 +44,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "trans-mem.h"
 #include "gimple-fold.h"
 #include "tree-scalar-evolution.h"
+#include "tree-ssa-loop-niter.h"

 /* TODO:  Support for predicated code motion.  I.e.

@@ -2369,8 +2370,16 @@ fill_always_executed_in_1 (struct loop *loop, sbitmap
contains_call)
            break;

          FOR_EACH_EDGE (e, ei, bb->succs)
-           if (!flow_bb_inside_loop_p (loop, e->dest))
-             break;
+           {
+             /* If there is an exit from this BB.  */
+             if (!flow_bb_inside_loop_p (loop, e->dest))
+               break;
+             /* Or we enter a possibly non-finite loop.  */
+             if (flow_loop_nested_p (bb->loop_father,
+                                     e->dest->loop_father)
+                 && ! finite_loop_p (e->dest->loop_father))
+               break;
+           }
          if (e)
            break;