On Wed, 2 Nov 2016, Richard Biener wrote:
>
> The following fixes PR78185 by properly honoring possibly infinite child
> loops when computing what blocks are always executed during loop invariant
> motion. Such loops behave as if the loop would exit at this point.
>
> Both GIMPLE and RTL level passes have that very same issue and the
> following fixes the GIMPLE one and simply disables hoisting of possibly
> trapping or faulting instructions in the RTL pass ... Eric seems to
> remember this might regress gzip so I'm going to put this on one of
> our SPEC testers for tonights run as well. Maybe somebody else
Nothing popped out, but ...
> wants to check the performance impact (I'm interested in both,
> GIMPLE and RTL change fallout for performance).
>
> Bootstrap and regtest running on x86_64-unknown-linux-gnu.
>
> If all goes well I'll followup with the obvious removal of no longer
> needed stuff in loop-invariant.c.
>
> Another variant for RTL would be to simply treat all edges entering
> a child loop (not only those entering possibly infinitely looping ones)
> as an exit. I think finite_loop_p has no RTL level variant (yet).
... that was easy enough to implement and should be slightly less
conservative.
Re-bootstrap / regtest running on x86_64-unknown-linux-gnu. I'll
commit that if nobody objects until tomorrow.
Richard.
2016-11-03 Richard Biener <rguent...@suse.de>
PR middle-end/78185
* loop-invariant.c (find_exits): Record entering inner
loops as possibly exiting to handle infinite sub-loops.
* tree-ssa-loop-im.c: Include tree-ssa-loop-niter.h.
(fill_always_executed_in_1): Honor infinite child loops.
* gcc.dg/pr78185.c: New testcase.
Index: gcc/tree-ssa-loop-im.c
===================================================================
--- gcc/tree-ssa-loop-im.c (revision 241795)
+++ gcc/tree-ssa-loop-im.c (working copy)
@@ -44,6 +44,7 @@ along with GCC; see the file COPYING3.
#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 *
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;
Index: gcc/loop-invariant.c
===================================================================
--- gcc/loop-invariant.c (revision 241795)
+++ gcc/loop-invariant.c (working copy)
@@ -598,13 +598,17 @@ find_exits (struct loop *loop, basic_blo
FOR_EACH_EDGE (e, ei, body[i]->succs)
{
- if (flow_bb_inside_loop_p (loop, e->dest))
- continue;
-
- bitmap_set_bit (may_exit, i);
- bitmap_set_bit (has_exit, i);
- outermost_exit = find_common_loop (outermost_exit,
- e->dest->loop_father);
+ if (! flow_bb_inside_loop_p (loop, e->dest))
+ {
+ bitmap_set_bit (may_exit, i);
+ bitmap_set_bit (has_exit, i);
+ outermost_exit = find_common_loop (outermost_exit,
+ e->dest->loop_father);
+ }
+ /* If we enter a subloop that might never terminate treat
+ it like a possible exit. */
+ if (flow_loop_nested_p (loop, e->dest->loop_father))
+ bitmap_set_bit (may_exit, i);
}
continue;
}
Index: gcc/testsuite/gcc.dg/pr78185.c
===================================================================
--- gcc/testsuite/gcc.dg/pr78185.c (revision 0)
+++ gcc/testsuite/gcc.dg/pr78185.c (revision 0)
@@ -0,0 +1,28 @@
+/* { dg-do run { target *-*-linux* *-*-gnu* } } */
+/* { dg-options "-O" } */
+
+#include <unistd.h>
+#include <signal.h>
+#include <stdlib.h>
+
+static char var1 = 0L;
+static char *var2 = &var1;
+
+void do_exit (int i)
+{
+ exit (0);
+}
+
+int main(void)
+{
+ struct sigaction s;
+ sigemptyset (&s.sa_mask);
+ s.sa_handler = do_exit;
+ s.sa_flags = 0;
+ sigaction (SIGALRM, &s, NULL);
+ alarm (1);
+ /* The following loop is infinite, the division by zero should not
+ be hoisted out of it. */
+ for (; (var1 == 0 ? 0 : (100 / var1)) == *var2; );
+ return 0;
+}
