C++ PATCH to fix missing warning (PR c++/70194)

[Jakub Jelinek]

On Tue, Mar 15, 2016 at 11:41:20AM +0100, Marek Polacek wrote:
> This is to fix missing "address of %qD will never be NULL" warning that went
> away since the delayed folding merge.  The problem was that cp_build_binary_op
> was getting unfolded ops so in the constexpr case it saw "(int *) p" instead of
> "&i" (in this particular testcase).  Fixed by calling fold_non_dependent_expr
> as is done elsewhere.
> (It doesn't seem like the "if (CONVERT_EXPR_P (op?)" blocks need to use cop?
> too.)
> 
> I did not try to address the other issues Martin has raised in the PR yet.
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
> 
> 2016-03-15  Marek Polacek  <polacek@redhat.com>
> 
> 	PR c++/70194
> 	* typeck.c (cp_build_binary_op): Call fold_non_dependent_expr before
> 	warning about an address not being null.
> 
> 	* g++.dg/warn/constexpr-70194.C: New test.
> 
> diff --git gcc/cp/typeck.c gcc/cp/typeck.c
> index 20f0afc..a789c7a 100644
> --- gcc/cp/typeck.c
> +++ gcc/cp/typeck.c
> @@ -4520,14 +4520,16 @@ cp_build_binary_op (location_t location,
>  	  else
>  	    result_type = type0;
>  
> -	  if (TREE_CODE (op0) == ADDR_EXPR
> -	      && decl_with_nonnull_addr_p (TREE_OPERAND (op0, 0)))
> +	  tree cop0 = fold_non_dependent_expr (op0);
> +
> +	  if (TREE_CODE (cop0) == ADDR_EXPR
> +	      && decl_with_nonnull_addr_p (TREE_OPERAND (cop0, 0)))

>From compile time perspective, I wonder if it wouldn't be better to do
the cheap tests early, like:
	if (warn_address
	    && (complain & tf_warning)
	    && c_inhibit_evaluation_warnings == 0
	    && !TREE_NO_WARNING (op0))
	  {
	    tree cop0 = fold_non_dependent_expr (op0);

	    if (TREE_CODE (cop0) == ADDR_EXPR
		&& decl_with_nonnull_addr_p (TREE_OPERAND (cop0, 0))
		&& !TREE_NO_WARNING (cop0))
	      warning (OPT_waddress, "the address of %qD will never be NULL",
		       TREE_OPERAND (cop0, 0));
	  }

thus perform fold_non_dependent_expr only if it is needed.
Furthermore, I wonder if it isn't preferrable to %qD the non-folded
expression (if it is ADDR_EXPR, that is), so perhaps:
TREE_OPERAND (TREE_CODE (op0) == ADDR_EXPR ? op0 : cop0, 0)
?

	Jakub