Hi,
Here's an updated version of the patch which warns the user if the
removing of redundant exits results in an infinite loop. I have added
an additional flag in struct loop called external_exits to record if
an exit edge is moved outside the loop body. This currently happens in
the loop-unswitch pass and was the root cause of the regression in
torture/pr49518.c that I talked about earlier. The patch now passes all
regression tests except a mudflap case (fail37-frag). The test is
already broken due to removal of all exits so I haven't attempted to
fix it as part of this patch. How does this version look?
Regards,
Siddhesh
gcc/ChangeLog:
* cfgloop.h (struct loop): New member EXTERNAL_EXITS.
* tree-ssa-loop-ivcanon.c (remove_redundant_iv_tests) Warn when
loop is left without any exits.
* tree-ssa-loop-unswitch.c (tree_unswitch_single_loop): Set
EXTERNAL_EXITS when moving a statement with an exit edge out of
the loop body.
diff --git a/gcc/cfgloop.h b/gcc/cfgloop.h
index 5cd62b3..dab3565 100644
--- a/gcc/cfgloop.h
+++ b/gcc/cfgloop.h
@@ -173,6 +173,9 @@ struct GTY ((chain_next ("%h.next"))) loop {
/* Head of the cyclic list of the exits of the loop. */
struct loop_exit *exits;
+
+ /* True if an exit branch was moved out of the loop. */
+ bool external_exits;
};
/* Flags for state of loop structure. */
diff --git a/gcc/tree-ssa-loop-ivcanon.c b/gcc/tree-ssa-loop-ivcanon.c
index 601223b..8448234 100644
--- a/gcc/tree-ssa-loop-ivcanon.c
+++ b/gcc/tree-ssa-loop-ivcanon.c
@@ -50,6 +50,8 @@ along with GCC; see the file COPYING3. If not see
#include "flags.h"
#include "tree-inline.h"
#include "target.h"
+#include "diagnostic.h"
+#include "intl.h"
/* Specifies types of loops that may be unrolled. */
@@ -525,10 +527,21 @@ static bool
remove_redundant_iv_tests (struct loop *loop)
{
struct nb_iter_bound *elt;
- bool changed = false;
+ loop_exit *exit;
+ VEC(gimple, stack) *exit_stmts = VEC_alloc (gimple, stack, 16);
+ int exits_left = 0, num_exits = 0;
if (!loop->any_upper_bound)
- return false;
+ goto out;
+
+ /* Count our exits. */
+ for (exit = loop->exits->next; exit->e; exit = exit->next)
+ num_exits++;
+
+ if (num_exits == 0)
+ goto out;
+
+ exits_left = num_exits;
for (elt = loop->bounds; elt; elt = elt->next)
{
/* Exit is pointless if it won't be taken before loop reaches
@@ -555,7 +568,11 @@ remove_redundant_iv_tests (struct loop *loop)
|| !loop->nb_iterations_upper_bound.ult
(tree_to_double_int (niter.niter)))
continue;
-
+
+ exits_left--;
+
+ VEC_safe_push (gimple, stack, exit_stmts, elt->stmt);
+
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "Removed pointless exit: ");
@@ -566,10 +583,31 @@ remove_redundant_iv_tests (struct loop *loop)
else
gimple_cond_make_true (elt->stmt);
update_stmt (elt->stmt);
- changed = true;
}
}
- return changed;
+
+ /* We removed all exit points, so tell the user. */
+ if (exits_left == 0 && !loop->external_exits)
+ {
+ gimple stmt;
+ const char *wording;
+ unsigned i;
+ location_t loc;
+
+ FOR_EACH_VEC_ELT (gimple, exit_stmts, i, stmt)
+ {
+ loc = gimple_location (stmt);
+ wording = N_("Loop behavior is undefined before exit condition; "
+ "turned into infinite loop");
+ warning_at ((LOCATION_LINE (loc) > 0) ? loc : input_location, 0,
+ gettext (wording));
+ }
+ }
+
+out:
+ VEC_free (gimple, stack, exit_stmts);
+
+ return exits_left < num_exits;
}
/* Stores loops that will be unlooped after we process whole loop tree. */
diff --git a/gcc/tree-ssa-loop-unswitch.c b/gcc/tree-ssa-loop-unswitch.c
index b24f3d7..fb95ab7 100644
--- a/gcc/tree-ssa-loop-unswitch.c
+++ b/gcc/tree-ssa-loop-unswitch.c
@@ -234,6 +234,14 @@ tree_unswitch_single_loop (struct loop *loop, int num)
cond = simplify_using_entry_checks (loop, cond);
stmt = last_stmt (bbs[i]);
+
+ /* We're switching out an exit point, so note that the loop has exits
+ outside its body. */
+ if (loop_exit_edge_p (loop, EDGE_SUCC (bbs[i], 0))
+ || loop_exit_edge_p (loop, EDGE_SUCC (bbs[i], 1)))
+ loop->external_exits = true;
+
+ /* TODO If this is a loop exit statement then note it. */
if (integer_nonzerop (cond))
{
/* Remove false path. */
