Re: [PATCH] c++: ICE with template NEW_EXPR [PR105803]

[Patrick Palka <ppalka@redhat.com>]

On Wed, 1 Jun 2022, Marek Polacek via Gcc-patches wrote:

> Here we ICE because value_dependent_expression_p gets a NEW_EXPR
> whose operand is a type, and we go to the default case which just
> calls v_d_e_p on each operand of the NEW_EXPR.  Since one of them
> is a type, we crash on the new assert in t_d_e_p.

Looks like NEW_EXPR is considered to be not potentially constant
according to potential_constant_expression.  I thought we shouldn't
be calling value_dependent_expression_p on such exprs?

> 
> t_d_e_p has code to handle {,VEC_}NEW_EXPR, which at this point
> was already performed, so I think we can handle these two codes
> specifically and skip the second operand, which is always going
> to be a type.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> 
> 	PR c++/105803
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (value_dependent_expression_p): Handle {,VEC_}NEW_EXPR
> 	in the switch.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/template/new13.C: New test.
> ---
>  gcc/cp/pt.cc                          |  8 ++++++++
>  gcc/testsuite/g++.dg/template/new13.C | 11 +++++++++++
>  2 files changed, 19 insertions(+)
>  create mode 100644 gcc/testsuite/g++.dg/template/new13.C
> 
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 6de8e496859..836861e1039 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -27643,6 +27643,14 @@ value_dependent_expression_p (tree expression)
>  	 under instantiate_non_dependent_expr; it can't be constant.  */
>        return true;
>  
> +    case NEW_EXPR:
> +    case VEC_NEW_EXPR:
> +      /* The second operand is a type, which type_dependent_expression_p
> +	 (and therefore value_dependent_expression_p) doesn't want to see.  */
> +      return (value_dependent_expression_p (TREE_OPERAND (expression, 0))
> +	      || value_dependent_expression_p (TREE_OPERAND (expression, 2))
> +	      || value_dependent_expression_p (TREE_OPERAND (expression, 3)));
> +
>      default:
>        /* A constant expression is value-dependent if any subexpression is
>  	 value-dependent.  */
> diff --git a/gcc/testsuite/g++.dg/template/new13.C b/gcc/testsuite/g++.dg/template/new13.C
> new file mode 100644
> index 00000000000..3168374b26d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/new13.C
> @@ -0,0 +1,11 @@
> +// PR c++/105803
> +// { dg-do compile }
> +// { dg-additional-options "-fchecking=2" }
> +
> +namespace std {
> +template <typename> class shared_ptr;
> +}
> +struct S {};
> +template <int> void build_matrices() {
> +  std::shared_ptr<S>(new S);
> +}

I think this testcase might be IFNDR since shared_ptr<S> is incomplete
at the point of its non-dependent use.

> 
> base-commit: 2d546ff69455f7deadab65309de89d19380a8864
> -- 
> 2.36.1
> 
>