[Bug tree-optimization/83867] [8 Regression] ICE: Segmentation fault in nested_in_vect_loop_p

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83867

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rsandifo at gcc dot gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
The issue is that vectorized stmts replacing scalar stmts via
vect_finish_replace_stmt leave the scalar stmt def dangling in no BB.  Here

9525      /* Handle inner-loop stmts whose DEF is used in the loop-nest that
9526         is being vectorized, but outside the immediately enclosing loop. 
*/
9527      if (vec_stmt
9528          && STMT_VINFO_LOOP_VINFO (stmt_info)
9529          && nested_in_vect_loop_p (LOOP_VINFO_LOOP (
9530                                    STMT_VINFO_LOOP_VINFO (stmt_info)),
stmt)

passes the dangling 'stmt' to nested_in_vect_loop_p.

Replacing the scalar def in this way is somewhat hacky given the caller still
has its hand on 'stmt' :/

We could fix this particular fallout but why do we need to re-use the original
SSA def?  This is from vectorize_fold_left_reduction.

Anyway, I see it is convenient but I do expect more fallout from this.

Index: gcc/tree-vect-stmts.c
===================================================================
--- gcc/tree-vect-stmts.c       (revision 256722)
+++ gcc/tree-vect-stmts.c       (working copy)
@@ -9426,6 +9426,11 @@ vect_transform_stmt (gimple *stmt, gimpl
   gcc_assert (slp_node || !PURE_SLP_STMT (stmt_info));
   gimple *old_vec_stmt = STMT_VINFO_VEC_STMT (stmt_info);

+  bool nested_p = (STMT_VINFO_LOOP_VINFO (stmt_info)
+                  && nested_in_vect_loop_p
+                       (LOOP_VINFO_LOOP (STMT_VINFO_LOOP_VINFO (stmt_info)),
+                        stmt));
+
   switch (STMT_VINFO_TYPE (stmt_info))
     {
     case type_demotion_vec_info_type:
@@ -9525,9 +9530,7 @@ vect_transform_stmt (gimple *stmt, gimpl
   /* Handle inner-loop stmts whose DEF is used in the loop-nest that
      is being vectorized, but outside the immediately enclosing loop.  */
   if (vec_stmt
-      && STMT_VINFO_LOOP_VINFO (stmt_info)
-      && nested_in_vect_loop_p (LOOP_VINFO_LOOP (
-                                STMT_VINFO_LOOP_VINFO (stmt_info)), stmt)
+      && nested_p
       && STMT_VINFO_TYPE (stmt_info) != reduc_vec_info_type
       && (STMT_VINFO_RELEVANT (stmt_info) == vect_used_in_outer
           || STMT_VINFO_RELEVANT (stmt_info) ==