Re: [PATCH] Cleanup strcpy/stpcpy no nul warning code

[Jeff Law <law at redhat dot com>]

On 9/16/18 1:58 PM, Bernd Edlinger wrote:
> Hi,
> 
> this is a cleanup of the recently added strlen/strcpy/stpcpy
> no nul warning code.
> 
> Most importantly it moves the SSA_NAME handling from
> unterminated_array to string_constant, thereby fixing
> another round of xfails in the strlen and stpcpy test cases.
> 
> I need to say that the fix for bug 86622 is relying in
> type info on the pointer which is probably not safe in
> GIMPLE in the light of the recent discussion.
> 
> I had to add two further exceptions, which should
> be safe in general: that is a pointer arithmentic on a string
> literal is okay, and arithmetic on a string constant
> that is exactly the size of the whole DECL, cannot
> access an adjacent member.
> 
> 
> Bootstrapped and reg-tested on x86_64-pc-linux-gnu.
> Is it OK for trunk?
> 
> 
> Thanks
> Bernd.
> 
> 
> patch-cleanup-no-nul.diff
> 
> gcc:
> 2018-09-16  Bernd Edlinger  <bernd.edlinger@hotmail.de>
> 
> 	* builtins.h (unterminated_array): Remove prototype.
>         * builtins.c (unterminated_array): Simplify.  Make static.
>         (expand_builtin_strcpy_args): Don't use TREE_NO_WARNING here.
> 	(expand_builtin_stpcpy_1): Remove warn_string_no_nul without effect.
> 	* expr.c (string_constant): Handle SSA_NAME.  Add more exceptions
> 	where pointer arithmetic is safe.
> 	* gimple-fold.c (get_range_strlen): Handle nonstr like in c_strlen.
> 	(get_max_strlen): Remove the unnecessary mynonstr handling.
> 	(gimple_fold_builtin_strcpy): Simplify.
> 	(gimple_fold_builtin_stpcpy): Simplify.
> 	(gimple_fold_builtin_sprintf): Remove NO_WARNING propagation
> 	without effect.
> 	(gimple_fold_builtin_strlen): Simplify.
> 
> testsuite:
> 2018-09-16  Bernd Edlinger  <bernd.edlinger@hotmail.de>
> 
> 	* gcc.dg/warn-stpcpy-no-nul.c: Remove xfails.
> 	* gcc.dg/warn-strlen-no-nul.c: Remove xfails.
> 
> Index: gcc/builtins.c
> ===================================================================
> --- gcc/builtins.c	(revision 264342)
> +++ gcc/builtins.c	(working copy)
> @@ -567,31 +567,12 @@ warn_string_no_nul (location_t loc, const char *fn
>     the declaration of the object of which the array is a member or
>     element.  Otherwise return null.  */
>  
> -tree
> +static tree
>  unterminated_array (tree exp)
>  {
> -  if (TREE_CODE (exp) == SSA_NAME)
> -    {
> -      gimple *stmt = SSA_NAME_DEF_STMT (exp);
> -      if (!is_gimple_assign (stmt))
> -	return NULL_TREE;
> -
> -      tree rhs1 = gimple_assign_rhs1 (stmt);
> -      tree_code code = gimple_assign_rhs_code (stmt);
> -      if (code == ADDR_EXPR
> -	  && TREE_CODE (TREE_OPERAND (rhs1, 0)) == ARRAY_REF)
> -	rhs1 = rhs1;
> -      else if (code != POINTER_PLUS_EXPR)
> -	return NULL_TREE;
> -
> -      exp = rhs1;
> -    }
> -
>    tree nonstr = NULL;
> -  if (c_strlen (exp, 1, &nonstr, 1) == NULL && nonstr)
> -    return nonstr;
> -
> -  return NULL_TREE;
> +  c_strlen (exp, 1, &nonstr);
> +  return nonstr;
>  }
Sigh.  This is going to conflict with patch #6 from Martin's kit.



>  
>  /* Compute the length of a null-terminated character string or wide
> @@ -3936,8 +3917,7 @@ expand_builtin_strcpy_args (tree exp, tree dest, t
>    if (tree nonstr = unterminated_array (src))
>      {
>        /* NONSTR refers to the non-nul terminated constant array.  */
> -      if (!TREE_NO_WARNING (exp))
> -	warn_string_no_nul (EXPR_LOCATION (exp), "strcpy", src, nonstr);
> +      warn_string_no_nul (EXPR_LOCATION (exp), "strcpy", src, nonstr);
>        return NULL_RTX;
>      }
There's also some target dependencies to be concerned about.  I'll have
to dig out the thread, but in general removing these TREE_NO_WARNING
checks is probably a bad idea -- you're likely introducing redundant
warnings on one or more targets (but not x86).


There may be things in there we want to take.  But my focus is going to
be on getting the #4 and #6 patches from Martin's kit resolved (while he
works on the string length range stuff).

Jeff