[COMMITTED] Avoid using unavailable objects in jt_state.

[Aldy Hernandez <aldyh@redhat.com>]

[Jeff: I'm going to go out on a limb here and commit this under the
obvious rule.  If I am overstepping my obvious powers, please let me
know.]

The jump threading state is about to get more interesting, and it may
get with a ranger or with the const_copies/etc helpers.  This patch
makes sure we have an object before we attempt to call push_marker or
pop_to_marker.

Tested on x86-64 Linux.

gcc/ChangeLog:

	* tree-ssa-threadedge.c (jt_state::push): Only call methods for
	which objects are available.
	(jt_state::pop): Same.
	(jt_state::register_equiv): Same.
	(jt_state::register_equivs_on_edge): Same.
---
 gcc/tree-ssa-threadedge.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c
index 8a485125ff5..e57f6d3e39c 100644
--- a/gcc/tree-ssa-threadedge.c
+++ b/gcc/tree-ssa-threadedge.c
@@ -1323,8 +1323,10 @@ jt_state::jt_state (const_and_copies *copies,
 void
 jt_state::push (edge)
 {
-  m_copies->push_marker ();
-  m_exprs->push_marker ();
+  if (m_copies)
+    m_copies->push_marker ();
+  if (m_exprs)
+    m_exprs->push_marker ();
   if (m_evrp)
     m_evrp->push_marker ();
 }
@@ -1334,8 +1336,10 @@ jt_state::push (edge)
 void
 jt_state::pop ()
 {
-  m_copies->pop_to_marker ();
-  m_exprs->pop_to_marker ();
+  if (m_copies)
+    m_copies->pop_to_marker ();
+  if (m_exprs)
+    m_exprs->pop_to_marker ();
   if (m_evrp)
     m_evrp->pop_to_marker ();
 }
@@ -1346,7 +1350,8 @@ jt_state::pop ()
 void
 jt_state::register_equiv (tree dst, tree src, bool update_range)
 {
-  m_copies->record_const_or_copy (dst, src);
+  if (m_copies)
+    m_copies->record_const_or_copy (dst, src);
 
   /* If requested, update the value range associated with DST, using
      the range from SRC.  */
@@ -1396,7 +1401,8 @@ jt_state::record_ranges_from_stmt (gimple *stmt, bool temporary)
 void
 jt_state::register_equivs_on_edge (edge e)
 {
-  record_temporary_equivalences (e, m_copies, m_exprs);
+  if (m_copies && m_exprs)
+    record_temporary_equivalences (e, m_copies, m_exprs);
 }
 
 jump_threader_simplifier::jump_threader_simplifier (vr_values *v)
-- 
2.31.1