Re: [PATCH] c++: -Wdangling-reference not suppressed in template [PR109774]

[Jason Merrill <jason@redhat.com>]

On 5/16/23 15:13, Marek Polacek wrote:
> In check_return_expr, we suppress the -Wdangling-reference warning when
> we're sure it would be a false positive.  It wasn't working in a
> template, though, because the suppress_warning call was never reached.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk and 13.2?

OK.

> 	PR c++/109774
> 
> gcc/cp/ChangeLog:
> 
> 	* typeck.cc (check_return_expr): In a template, return only after
> 	suppressing -Wdangling-reference.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/warn/Wdangling-reference13.C: New test.
> ---
>   gcc/cp/typeck.cc                              |  6 ++---
>   .../g++.dg/warn/Wdangling-reference13.C       | 23 +++++++++++++++++++
>   2 files changed, 26 insertions(+), 3 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wdangling-reference13.C
> 
> diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
> index 53ac925a092..c225c4e2423 100644
> --- a/gcc/cp/typeck.cc
> +++ b/gcc/cp/typeck.cc
> @@ -11236,9 +11236,6 @@ check_return_expr (tree retval, bool *no_warning)
>   			 build_zero_cst (TREE_TYPE (retval)));
>       }
>   
> -  if (processing_template_decl)
> -    return saved_retval;
> -
>     /* A naive attempt to reduce the number of -Wdangling-reference false
>        positives: if we know that this function can return a variable with
>        static storage duration rather than one of its parameters, suppress
> @@ -11250,6 +11247,9 @@ check_return_expr (tree retval, bool *no_warning)
>         && TREE_STATIC (bare_retval))
>       suppress_warning (current_function_decl, OPT_Wdangling_reference);
>   
> +  if (processing_template_decl)
> +    return saved_retval;
> +
>     /* Actually copy the value returned into the appropriate location.  */
>     if (retval && retval != result)
>       {
> diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference13.C b/gcc/testsuite/g++.dg/warn/Wdangling-reference13.C
> new file mode 100644
> index 00000000000..bc09fbae22b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference13.C
> @@ -0,0 +1,23 @@
> +// PR c++/109774
> +// { dg-do compile }
> +// { dg-options "-Wdangling-reference" }
> +
> +int y;
> +
> +template<typename T>
> +int& get(const char& )
> +{
> +    return y;
> +}
> +
> +int& get2(const char&)
> +{
> +    return y;
> +}
> +
> +int stuff(void)
> +{
> +    const int &h = get<void>(0); // { dg-bogus "dangling reference" }
> +    const int &k = get2(0); // { dg-bogus "dangling reference" }
> +    return h+k;
> +}
> 
> base-commit: 94a311abf783de754f0f1b2d4c1f00a9788e795b