[Bug ipa/68470] [4.9/5/6 Regression] Internal Compiler Error observed by g++-4.9.2 and a few other versions (reported to Debian)

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68470

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ok, so the issue is the non-split part doesn't return but we keep and wire
the original return block (duplicated into the split part) into the
split-return
part of the main function.  That leaves us with stmts that have no defs for
their uses.  The following works for me.

Index: gcc/ipa-split.c
===================================================================
--- gcc/ipa-split.c     (revision 230998)
+++ gcc/ipa-split.c     (working copy)
@@ -1205,7 +1205,6 @@ split_function (basic_block return_bb, s
   edge e;
   edge_iterator ei;
   tree retval = NULL, real_retval = NULL, retbnd = NULL;
-  bool split_part_return_p = false;
   bool with_bounds = chkp_function_instrumented_p (current_function_decl);
   gimple *last_stmt = NULL;
   unsigned int i;
@@ -1246,12 +1245,16 @@ split_function (basic_block return_bb, s
        args_to_pass.safe_push (arg);
       }

-  /* See if the split function will return.  */
+  /* See if the split function or the main part will return.  */
+  bool main_part_return_p = false;
+  bool split_part_return_p = false;
   FOR_EACH_EDGE (e, ei, return_bb->preds)
-    if (bitmap_bit_p (split_point->split_bbs, e->src->index))
-      break;
-  if (e)
-    split_part_return_p = true;
+    {
+      if (bitmap_bit_p (split_point->split_bbs, e->src->index))
+       split_part_return_p = true;
+      else
+       main_part_return_p = true;
+    }

   /* Add return block to what will become the split function.
      We do not return; no return block is needed.  */
@@ -1295,6 +1298,11 @@ split_function (basic_block return_bb, s
   else
     bitmap_set_bit (split_point->split_bbs, return_bb->index);

+  /* If the main part doesn't return pretend the return block wasn't
+     found for all of the following.  */
+  if (! main_part_return_p)
+    return_bb = EXIT_BLOCK_PTR_FOR_FN (cfun);
+
   /* If RETURN_BB has virtual operand PHIs, they must be removed and the
      virtual operand marked for renaming as we change the CFG in a way that
      tree-inline is not able to compensate for.