Re: [patch] Fix dangling references in thunks at -O0

[Eric Botcazou]

> In fact I can probably reuse cfun->tail_call_marked for this purpose.

Like so.

        * cgraphunit.c (cgraph_node::expand_thunk): Make sure to set
        cfun->tail_call_marked when forcing a tail call.
        * function.c (assign_parm_setup_reg): Always use a register to
        retrieve a parameter passed by reference if cfun->tail_call_marked.

-- 
Eric Botcazou
diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
index 26d3995a0c0..bedb6e2eea1 100644
--- a/gcc/cgraphunit.c
+++ b/gcc/cgraphunit.c
@@ -2171,7 +2171,10 @@ cgraph_node::expand_thunk (bool output_asm_thunks, bool force_gimple_thunk)
 		}
 	    }
 	  else
-	    gimple_call_set_tail (call, true);
+	    {
+	      gimple_call_set_tail (call, true);
+	      cfun->tail_call_marked = true;
+	    }
 
 	  /* Build return value.  */
 	  if (!DECL_BY_REFERENCE (resdecl))
@@ -2184,6 +2187,7 @@ cgraph_node::expand_thunk (bool output_asm_thunks, bool force_gimple_thunk)
       else
 	{
 	  gimple_call_set_tail (call, true);
+	  cfun->tail_call_marked = true;
 	  remove_edge (single_succ_edge (bb));
 	}
 
diff --git a/gcc/function.c b/gcc/function.c
index 2c8fa217f1f..314fd01c195 100644
--- a/gcc/function.c
+++ b/gcc/function.c
@@ -3322,13 +3322,15 @@ assign_parm_setup_reg (struct assign_parm_data_all *all, tree parm,
   else
     emit_move_insn (parmreg, validated_mem);
 
-  /* If we were passed a pointer but the actual value can safely live
-     in a register, retrieve it and use it directly.  */
+  /* If we were passed a pointer but the actual value can live in a register,
+     retrieve it and use it directly.  Note that we cannot use nominal_mode,
+     because it will have been set to Pmode above, we must use the actual mode
+     of the parameter instead.  */
   if (data->arg.pass_by_reference && TYPE_MODE (TREE_TYPE (parm)) != BLKmode)
     {
-      /* We can't use nominal_mode, because it will have been set to
-	 Pmode above.  We must use the actual mode of the parm.  */
-      if (use_register_for_decl (parm))
+      /* Use a stack slot for debugging purposes, except if a tail call is
+	 involved because this would create a dangling reference.  */
+      if (use_register_for_decl (parm) || cfun->tail_call_marked)
 	{
 	  parmreg = gen_reg_rtx (TYPE_MODE (TREE_TYPE (parm)));
 	  mark_user_reg (parmreg);