loop-manip: Avoid -fcompare-debug issues in create_iv [PR94285]

The following testcase FAILs with -fcompare-debug.  The problem is that
create_iv behaves differently when inserting after into an empty bb (in that
case sets location to goto_locus), or when inserting before gsi_end_p (i.e.
at the end of bb; in that case it will not set location, otherwise it will
set it to the location of next stmt).
This isn't -fcompare-debug friendly, because if inserting after and the
bb contains only debug stmts, then the location will not be set with -g
and will be with -g0, or when inserting before, the location might either
be set from the following debug stmt rather than some non-debug stmt after
that, or might not be set with -g0 if it is to be inserted at the end of bb,
while with -g would be set to location of debug stmt.

2020-03-24  Jakub Jelinek  <jakub@redhat.com>

	PR debug/94285
	* tree-ssa-loop-manip.c (create_iv): If after, set stmt location to
	e->goto_locus even if gsi_bb (*incr_pos) contains only debug stmts.
	If not after and at *incr_pos is a debug stmt, set stmt location to
	location of next non-debug stmt after it if any.

	* gfortran.dg/pr94285.f90: New test.

gcc/ChangeLog

 2020-03-24  Jakub Jelinek  <jakub@redhat.com>
 
+	PR debug/94285
+	* tree-ssa-loop-manip.c (create_iv): If after, set stmt location to
+	e->goto_locus even if gsi_bb (*incr_pos) contains only debug stmts.
+	If not after and at *incr_pos is a debug stmt, set stmt location to
+	location of next non-debug stmt after it if any.
+
 	PR debug/94283
 	* tree-if-conv.c (ifcvt_local_dce): For gimple debug stmts, just set
 	GF_PLF_2, but don't add them to worklist.  Don't add an assigment to

gcc/testsuite/ChangeLog

 2020-03-24  Jakub Jelinek  <jakub@redhat.com>
 
+	PR debug/94285
+	* gfortran.dg/pr94285.f90: New test.
+
 	PR debug/94283
 	* gcc.target/i386/pr94283.c: New test.
 

gcc/testsuite/gfortran.dg/pr94285.f90

+! PR debug/94285
+! { dg-do compile }
+! { dg-options "-Os -fno-tree-dominator-opts -fno-tree-vrp -fcompare-debug" }
+
+include 'array_constructor_40.f90'

gcc/tree-ssa-loop-manip.c

@@ -129,7 +129,10 @@ create_iv (tree base, tree step, tree var, class loop *loop,
      immediately after a statement whose location is known.  */
   if (after)
     {
-      if (gsi_end_p (*incr_pos))
+      if (gsi_end_p (*incr_pos)
+	  || (is_gimple_debug (gsi_stmt (*incr_pos))
+	      && gsi_bb (*incr_pos)
+	      && gsi_end_p (gsi_last_nondebug_bb (gsi_bb (*incr_pos)))))
 	{
 	  edge e = single_succ_edge (gsi_bb (*incr_pos));
 	  gimple_set_location (stmt, e->goto_locus);
@@ -138,8 +141,11 @@ create_iv (tree base, tree step, tree var, class loop *loop,
     }
   else
     {
-      if (!gsi_end_p (*incr_pos))
-	gimple_set_location (stmt, gimple_location (gsi_stmt (*incr_pos)));
+      gimple_stmt_iterator gsi = *incr_pos;
+      if (!gsi_end_p (gsi) && is_gimple_debug (gsi_stmt (gsi)))
+	gsi_next_nondebug (&gsi);
+      if (!gsi_end_p (gsi))
+	gimple_set_location (stmt, gimple_location (gsi_stmt (gsi)));
       gsi_insert_before (incr_pos, stmt, GSI_NEW_STMT);
     }