Re: Fix ICE in use-after-scope w/ -fno-tree-dce (PR, sanitize/79783).

[Jakub Jelinek <jakub at redhat dot com>]

On Mon, Mar 06, 2017 at 08:59:09AM +0100, Martin Liška wrote:
> >> --- a/gcc/asan.c
> >> +++ b/gcc/asan.c
> >> @@ -3107,7 +3107,10 @@ asan_expand_poison_ifn (gimple_stmt_iterator *iter,
> >>  {
> >>    gimple *g = gsi_stmt (*iter);
> >>    tree poisoned_var = gimple_call_lhs (g);
> >> -  if (!poisoned_var)
> >> +
> >> +  /* It can happen with inlining and -fno-tree-dce that VAR_DECL for a SSA
> >> +     NAME was removed and thus the poisoning should not have any usage.  */
> >> +  if (!poisoned_var || SSA_NAME_VAR (poisoned_var) == NULL_TREE)
> > 
> > I wonder if it wouldn't be better to do:
> >   if (!poisoned_var || has_zero_uses (poisoned_var))
> > 
> > perhaps with -fno-tree-dce we could end up with SSA_NAME_VAR being
> > non-NULL, yet no uses; in that case there is nothing to warn about.
> > On the other side, in theory we could also end up with anonymous SSA_NAME
> > and some uses - in that case perhaps it would be better to warn.
> > So do:
> >   if (SSA_NAME_VAR (poisoned_var) == NULL_TREE)
> >     SSA_NAME_VAR (poisoned_var) = create_tmp_var (TREE_TYPE (poisoned_var));
> >   tree shadow_var = create_asan_shadow_var (SSA_NAME_VAR (poisoned_var),
> >                                             shadow_vars_mapping);
> > or so?  We'll need SSA_NAME_VAR non-NULL so that we can use a default def
> > later.
> 
> Ok, I've just prepared and tested following patch that does what Jakub suggested.Hi.
> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
> --- a/gcc/asan.c
> +++ b/gcc/asan.c

Can you please add also the suggested
 {   
   gimple *g = gsi_stmt (*iter);
   tree poisoned_var = gimple_call_lhs (g);
-  if (!poisoned_var)
+  if (!poisoned_var || has_zero_uses (poisoned_var))
     {
       gsi_remove (iter, true);
       return true;
hunk into the same function?  If we don't do DCE, we can end up with
ASAN_POISON with lhs but not really used anywhere.  If there are no uses,
it is a poisoned use.

> @@ -3113,6 +3113,10 @@ asan_expand_poison_ifn (gimple_stmt_iterator *iter,
>        return true;
>      }
>  
> +  if (SSA_NAME_VAR (poisoned_var) == NULL_TREE)
> +    SET_SSA_NAME_VAR_OR_IDENTIFIER (poisoned_var,
> +				    create_tmp_var (TREE_TYPE (poisoned_var)));
> +
>    tree shadow_var = create_asan_shadow_var (SSA_NAME_VAR (poisoned_var),
>  					    shadow_vars_mapping);
>  

Ok with that change.

	Jakub