[Bug tree-optimization/82129] [8 Regression] ICE in compute_antic, at tree-ssa-pre.c:2447

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82129

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Not yet analyzed but I see LIM performs store-motion on

   <bb 8> [0.00%] [count: INV] [loop 5 header]:
-  *h5_26(D) = tv_24(D);
+  h5__lsm.7_18 = tv_24(D);

where I think stores from undefined SSA names could be turned into CLOBBERs.

"Fixes" the testcase.

Index: gcc/gimple-fold.c
===================================================================
--- gcc/gimple-fold.c   (revision 252002)
+++ gcc/gimple-fold.c   (working copy)
@@ -410,6 +410,16 @@ fold_gimple_assign (gimple_stmt_iterator

        else if (DECL_P (rhs))
          return get_symbol_constant_value (rhs);
+
+       else if (TREE_CODE (rhs) == SSA_NAME
+                && SSA_NAME_IS_DEFAULT_DEF (rhs)
+                && ! ssa_defined_default_def_p (rhs)
+                && gimple_store_p (stmt))
+         {
+           tree clobber = build_constructor (TREE_TYPE (rhs), NULL);
+           TREE_THIS_VOLATILE (clobber) = true;
+           return clobber;
+         }
       }
       break;