Re: [PATCH] c++: Fix bogus -Wparentheses warning [PR95344]

[Jason Merrill <jason@redhat.com>]

On 5/26/20 8:25 PM, Marek Polacek wrote:
> Since r267272, which added location wrappers, cp_fold loses
> TREE_NO_WARNING on a MODIFY_EXPR that finish_parenthesized_expr set, and
> that results in a bogus -Wparentheses warning.
> 
> I.e., previously we had "b = 1" but now we have "VIEW_CONVERT_EXPR<bool>(b) = 1"
> and cp_fold_maybe_rvalue folds away the location wrapper and so we do
> 2718             x = fold_build2_loc (loc, code, TREE_TYPE (x), op0, op1);
> in cp_fold and the flag is lost.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/10/9?
> 
> 	PR c++/95344
> 	* cp-gimplify.c (cp_fold) <case MODIFY_EXPR>: Set TREE_NO_WARNING.
> 
> 	* c-c++-common/Wparentheses-2.c: New test.
> ---
>   gcc/cp/cp-gimplify.c                        |  5 ++++-
>   gcc/testsuite/c-c++-common/Wparentheses-2.c | 18 ++++++++++++++++++
>   2 files changed, 22 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/c-c++-common/Wparentheses-2.c
> 
> diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
> index 53d715dcd89..8b505dd878c 100644
> --- a/gcc/cp/cp-gimplify.c
> +++ b/gcc/cp/cp-gimplify.c
> @@ -2745,7 +2745,10 @@ cp_fold (tree x)
>   	    x = org_x;
>   	}
>         if (code == MODIFY_EXPR && TREE_CODE (x) == MODIFY_EXPR)
> -	TREE_THIS_VOLATILE (x) = TREE_THIS_VOLATILE (org_x);
> +	{
> +	  TREE_THIS_VOLATILE (x) = TREE_THIS_VOLATILE (org_x);
> +	  TREE_NO_WARNING (x) = TREE_NO_WARNING (org_x);
> +	}

I wonder if we want to copy these flags lower down for any EXPR_P (x) 
where TREE_CODE (x) == code?

Jason