middle-end: skip checking loop exits if loop malformed [PR111878]

Before my refactoring if the loop->latch was incorrect then find_loop_location
skipped checking the edges and would eventually return a dummy location.

It turns out that a loop can have
loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS) but also not have a latch
in which case get_loop_exit_edges traps.

This restores the old behavior.

gcc/ChangeLog:

	PR tree-optimization/111878
	* tree-vect-loop-manip.cc (find_loop_location): Skip edges check if
	latch incorrect.

gcc/testsuite/ChangeLog:

	PR tree-optimization/111878
	* gcc.dg/graphite/pr111878.c: New test.

gcc/testsuite/gcc.dg/graphite/pr111878.c

@@ -0,0 +1,19 @@
+/* { dg-options "-O3 -fgraphite-identity -fsave-optimization-record" } */
+
+int long_c2i_ltmp;
+int *long_c2i_cont;
+
+void
+long_c2i (long utmp, int i)
+{
+  int neg = 1;
+  switch (long_c2i_cont[0])
+    case 0:
+    neg = 0;
+  for (; i; i++)
+    if (neg)
+      utmp |= long_c2i_cont[i] ^ 5;
+    else
+      utmp |= long_c2i_cont[i];
+  long_c2i_ltmp = utmp;
+}

gcc/tree-vect-loop-manip.cc

@@ -1792,6 +1792,10 @@ find_loop_location (class loop *loop)
   if (!loop)
     return dump_user_location_t ();
 
+  /* For the root of the loop tree return the function location.  */
+  if (!loop_outer (loop))
+    return dump_user_location_t::from_function_decl (cfun->decl);
+
   if (loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
     {
       /* We only care about the loop location, so use any exit with location