Fix PR c++/70822 (bogus error with parenthesized SCOPE_REF)

The problem here is that some code paths are not prepared to handle a
non-dependent PAREN_EXPR, which my fix for PR c++/70106 introduced.  In
particular lvalue_kind() returns clk_none for a PAREN_EXPR which makes
build_x_unary_op() emit a bogus error for an expression like &(A::b).
(If the PAREN_EXPR were dependent then lvalue_kind() wouldn't get called
in the first place, build_x_unary_op() would exit early.)

This patch replaces the 70106 fix.  Instead of wrapping a SCOPE_REF in a
PAREN_EXPR, this patch overloads the REF_PARENTHESIZED_P to apply to
SCOPE_REFs too.  This makes sense to me because the two tree codes are
closely related (e.g. a SCOPE_REF before instantiation may become a
COMPONENT_REF after instantiation) so they should be treated similarly
by force_paren_expr().

There are two rather simpler ways to fix this PR.  One is to make
lvalue_kind() recurse into PAREN_EXPRs (although other parts of the FE
may be mishandling non-dependent PAREN_EXPRs as well), and the other is
to make force_paren_expr() never return a non-dependent PAREN_EXPR,
which can be achieved by building the PAREN_EXPR with build_nt().  I am
not sure which approach is best for GCC 7 and for GCC 6.

Somewhat unrelated the fix: I couldn't find an existing test that
checked that force_paren_expr handles SCOPE_REFs properly wrt auto
deduction so I added one.

Bootstrap and regtesting in progress on x86_64-pc-linux-gnu.

gcc/cp/ChangeLog:

	PR c++/70822
	PR c++/70106
	* cp-tree.h (REF_PARENTHESIZED_P): Make this flag apply to
	SCOPE_REFs too.
	* pt.c (tsubst_qualified_id): If REF_PARENTHESIZED_P is set
	on the qualified_id then propagate it to the resulting
	expression.
	(do_auto_deduction): Check REF_PARENTHESIZED_P on SCOPE_REFs
	too.
	* semantics.c (force_paren_expr): If given a SCOPE_REF, just set
	its REF_PARENTHESIZED_P flag.

gcc/testsuite/ChangeLog:

	PR c++/70822
	PR c++/70106
	* g++.dg/cpp1y/auto-fn31.C: New test.
	* g++.dg/cpp1y/paren4.C: New test.
---
 gcc/cp/cp-tree.h                       |  4 ++--
 gcc/cp/pt.c                            | 15 +++++++++++----
 gcc/cp/semantics.c                     | 13 +++----------
 gcc/testsuite/g++.dg/cpp1y/auto-fn31.C | 33 +++++++++++++++++++++++++++++++++
 gcc/testsuite/g++.dg/cpp1y/paren4.C    | 14 ++++++++++++++
 5 files changed, 63 insertions(+), 16 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/auto-fn31.C
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/paren4.C

On Fri, Apr 29, 2016 at 11:55 AM, Patrick Palka <patrick@parcs.ath.cx> wrote:
> The problem here is that some code paths are not prepared to handle a
> non-dependent PAREN_EXPR, which my fix for PR c++/70106 introduced.  In
> particular lvalue_kind() returns clk_none for a PAREN_EXPR which makes
> build_x_unary_op() emit a bogus error for an expression like &(A::b).
> (If the PAREN_EXPR were dependent then lvalue_kind() wouldn't get called
> in the first place, build_x_unary_op() would exit early.)
>
> This patch replaces the 70106 fix.  Instead of wrapping a SCOPE_REF in a
> PAREN_EXPR, this patch overloads the REF_PARENTHESIZED_P to apply to
> SCOPE_REFs too.  This makes sense to me because the two tree codes are
> closely related (e.g. a SCOPE_REF before instantiation may become a
> COMPONENT_REF after instantiation) so they should be treated similarly
> by force_paren_expr().
>
> There are two rather simpler ways to fix this PR.  One is to make
> lvalue_kind() recurse into PAREN_EXPRs (although other parts of the FE
> may be mishandling non-dependent PAREN_EXPRs as well), and the other is
> to make force_paren_expr() never return a non-dependent PAREN_EXPR,
> which can be achieved by building the PAREN_EXPR with build_nt().  I am
> not sure which approach is best for GCC 7 and for GCC 6.
>
> Somewhat unrelated the fix: I couldn't find an existing test that
> checked that force_paren_expr handles SCOPE_REFs properly wrt auto
> deduction so I added one.
>
> Bootstrap and regtesting in progress on x86_64-pc-linux-gnu.
>
> gcc/cp/ChangeLog:
>
>         PR c++/70822
>         PR c++/70106
>         * cp-tree.h (REF_PARENTHESIZED_P): Make this flag apply to
>         SCOPE_REFs too.
>         * pt.c (tsubst_qualified_id): If REF_PARENTHESIZED_P is set
>         on the qualified_id then propagate it to the resulting
>         expression.
>         (do_auto_deduction): Check REF_PARENTHESIZED_P on SCOPE_REFs
>         too.
>         * semantics.c (force_paren_expr): If given a SCOPE_REF, just set
>         its REF_PARENTHESIZED_P flag.
>
> gcc/testsuite/ChangeLog:
>
>         PR c++/70822
>         PR c++/70106
>         * g++.dg/cpp1y/auto-fn31.C: New test.
>         * g++.dg/cpp1y/paren4.C: New test.
> ---
>  gcc/cp/cp-tree.h                       |  4 ++--
>  gcc/cp/pt.c                            | 15 +++++++++++----
>  gcc/cp/semantics.c                     | 13 +++----------
>  gcc/testsuite/g++.dg/cpp1y/auto-fn31.C | 33 +++++++++++++++++++++++++++++++++
>  gcc/testsuite/g++.dg/cpp1y/paren4.C    | 14 ++++++++++++++
>  5 files changed, 63 insertions(+), 16 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/cpp1y/auto-fn31.C
>  create mode 100644 gcc/testsuite/g++.dg/cpp1y/paren4.C
>
> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> index 2caf7ce..0df5953 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -170,7 +170,7 @@ operator == (const cp_expr &lhs, tree rhs)
>        TARGET_EXPR_DIRECT_INIT_P (in TARGET_EXPR)
>        FNDECL_USED_AUTO (in FUNCTION_DECL)
>        DECLTYPE_FOR_LAMBDA_PROXY (in DECLTYPE_TYPE)
> -      REF_PARENTHESIZED_P (in COMPONENT_REF, INDIRECT_REF)
> +      REF_PARENTHESIZED_P (in COMPONENT_REF, INDIRECT_REF, SCOPE_REF)
>        AGGR_INIT_ZERO_FIRST (in AGGR_INIT_EXPR)
>        CONSTRUCTOR_MUTABLE_POISON (in CONSTRUCTOR)
>     3: (TREE_REFERENCE_EXPR) (in NON_LVALUE_EXPR) (commented-out).
> @@ -3403,7 +3403,7 @@ extern void decl_shadowed_for_var_insert (tree, tree);
>     some of the time in C++14 mode.  */
>
>  #define REF_PARENTHESIZED_P(NODE) \
> -  TREE_LANG_FLAG_2 (TREE_CHECK2 ((NODE), COMPONENT_REF, INDIRECT_REF))
> +  TREE_LANG_FLAG_2 (TREE_CHECK3 ((NODE), COMPONENT_REF, INDIRECT_REF, SCOPE_REF))
>
>  /* Nonzero if this AGGR_INIT_EXPR provides for initialization via a
>     constructor call, rather than an ordinary function call.  */
> diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
> index e7ec629..7adf308 100644
> --- a/gcc/cp/pt.c
> +++ b/gcc/cp/pt.c
> @@ -13741,8 +13741,10 @@ tsubst_qualified_id (tree qualified_id, tree args,
>      {
>        if (is_template)
>         expr = build_min_nt_loc (loc, TEMPLATE_ID_EXPR, expr, template_args);
> -      return build_qualified_name (NULL_TREE, scope, expr,
> -                                  QUALIFIED_NAME_IS_TEMPLATE (qualified_id));
> +      tree r = build_qualified_name (NULL_TREE, scope, expr,
> +                                    QUALIFIED_NAME_IS_TEMPLATE (qualified_id));
> +      REF_PARENTHESIZED_P (r) = REF_PARENTHESIZED_P (qualified_id);
> +      return r;
>      }
>
>    if (!BASELINK_P (name) && !DECL_P (expr))
> @@ -13822,6 +13824,9 @@ tsubst_qualified_id (tree qualified_id, tree args,
>        && TREE_CODE (expr) != OFFSET_REF)
>      expr = convert_from_reference (expr);
>
> +  if (REF_PARENTHESIZED_P (qualified_id))
> +    expr = force_paren_expr (expr);
> +
>    return expr;
>  }
>
> @@ -23966,8 +23971,10 @@ do_auto_deduction (tree type, tree init, tree auto_node,
>
>    if (AUTO_IS_DECLTYPE (auto_node))
>      {
> -      bool id = (DECL_P (init) || (TREE_CODE (init) == COMPONENT_REF
> -                                  && !REF_PARENTHESIZED_P (init)));
> +      bool id = (DECL_P (init)
> +                || ((TREE_CODE (init) == COMPONENT_REF
> +                     || TREE_CODE (init) == SCOPE_REF)
> +                    && !REF_PARENTHESIZED_P (init)));
>        targs = make_tree_vec (1);
>        TREE_VEC_ELT (targs, 0)
>         = finish_decltype_type (init, id, tf_warning_or_error);
> diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
> index bb13fad..89da773 100644
> --- a/gcc/cp/semantics.c
> +++ b/gcc/cp/semantics.c
> @@ -1647,17 +1647,10 @@ force_paren_expr (tree expr)
>        && TREE_CODE (expr) != SCOPE_REF)
>      return expr;
>
> -  if (TREE_CODE (expr) == COMPONENT_REF)
> +  if (TREE_CODE (expr) == COMPONENT_REF
> +      || TREE_CODE (expr) == SCOPE_REF)
>      REF_PARENTHESIZED_P (expr) = true;
> -  else if (type_dependent_expression_p (expr)
> -          /* When processing_template_decl, a SCOPE_REF may actually be
> -             referring to a non-static data member of the current class, in
> -             which case its TREE_TYPE may not be properly cv-qualified (the
> -             cv-qualifiers of the implicit *this object haven't yet been taken
> -             into account) so we have to delay building a static_cast until
> -             instantiation.  */
> -          || (processing_template_decl
> -              && TREE_CODE (expr) == SCOPE_REF))
> +  else if (type_dependent_expression_p (expr))
>      expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);
>    else if (VAR_P (expr) && DECL_HARD_REGISTER (expr))
>      /* We can't bind a hard register variable to a reference.  */;
> diff --git a/gcc/testsuite/g++.dg/cpp1y/auto-fn31.C b/gcc/testsuite/g++.dg/cpp1y/auto-fn31.C
> new file mode 100644
> index 0000000..0a5dafc
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/auto-fn31.C
> @@ -0,0 +1,33 @@
> +// { dg-do compile { target c++14 } }
> +
> +template<class,class> struct same_type;
> +template<class T> struct same_type<T,T> {};
> +
> +struct A
> +{
> +  static int b;
> +  int c;
> +
> +  template <int>
> +  decltype(auto) f() { return A::c; }
> +
> +  template <int>
> +  decltype(auto) g() { return (A::c); }
> +};
> +
> +A a;
> +
> +template <int>
> +decltype(auto) f() { return A::b; }
> +
> +template <int>
> +decltype(auto) g() { return (A::b); }
> +
> +int main()
> +{
> +  same_type<decltype(f<0>()), int>();
> +  same_type<decltype(g<0>()), int&>();
> +
> +  same_type<decltype(a.f<0>()), int>();
> +  same_type<decltype(a.g<0>()), int&>();
> +}
> diff --git a/gcc/testsuite/g++.dg/cpp1y/paren4.C b/gcc/testsuite/g++.dg/cpp1y/paren4.C
> new file mode 100644
> index 0000000..71abe84
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/paren4.C
> @@ -0,0 +1,14 @@
> +// PR c++/70822
> +// { dg-do compile { target c++14 } }
> +
> +struct a
> +{
> +  static int b;
> +};
> +
> +template <typename>
> +void
> +foo ()
> +{
> +  &(a::b);
> +}
> --
> 2.8.1.361.g2fbef4c
>

Ping.

OK.

Jason