[PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[Patrick Palka]

Here we're incorrectly deeming the templated call a.g() inside b's
initializer as potentially constant, despite g being non-constexpr,
which leads to us wastefully instantiating the initializer ahead of time
and triggering a bug in access checking deferral (which will get fixed
in the subsequent patch).

This patch fixes this by calling get_fns earlier during potentiality
checking so that we also handle the templated form of a member function
call (whose overall callee is a COMPONENT_REF) when checking if the called
function is constexpr etc.

	PR c++/109480

gcc/cp/ChangeLog:

	* constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
	Reorganize to call get_fns sooner.  Remove dead store to 'fun'.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the
	expected "without object" diagnostic isn't replaced by a
	"call to non-constexpr function" diagnostic.
	* g++.dg/template/non-dependent25.C: New test.
---
 gcc/cp/constexpr.cc                             | 16 ++++++++--------
 gcc/testsuite/g++.dg/cpp0x/noexcept59.C         |  2 +-
 gcc/testsuite/g++.dg/template/non-dependent25.C | 14 ++++++++++++++
 3 files changed, 23 insertions(+), 9 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index d1097764b10..29d872d0a5e 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
 
 	if (fun && is_overloaded_fn (fun))
 	  {
+	    if (!RECUR (fun, true))
+	      return false;
+	    fun = get_fns (fun);
+
 	    if (TREE_CODE (fun) == FUNCTION_DECL)
 	      {
 		if (builtin_valid_in_constant_expr_p (fun))
@@ -9167,7 +9171,8 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
 		   expression the address will be folded away, so look
 		   through it now.  */
 		if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun)
-		    && !DECL_CONSTRUCTOR_P (fun))
+		    && !DECL_CONSTRUCTOR_P (fun)
+		    && !processing_template_decl)
 		  {
 		    tree x = get_nth_callarg (t, 0);
 		    if (is_this_parameter (x))
@@ -9182,16 +9187,11 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
 		    i = 1;
 		  }
 	      }
-	    else
-	      {
-		if (!RECUR (fun, true))
-		  return false;
-		fun = get_first_fn (fun);
-	      }
+
+	    fun = OVL_FIRST (fun);
 	    /* Skip initial arguments to base constructors.  */
 	    if (DECL_BASE_CONSTRUCTOR_P (fun))
 	      i = num_artificial_parms_for (fun);
-	    fun = DECL_ORIGIN (fun);
 	  }
 	else if (fun)
           {
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
index c752601ba09..1dc826d3111 100644
--- a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
@@ -3,7 +3,7 @@
 
 template <class ...Ts> class A
 {
-  void e ();
+  constexpr bool e () { return true; };
   bool f (int() noexcept(this->e())); // { dg-error "this" }
   bool g (int() noexcept(e()));	      // { dg-error "without object" }
 };
diff --git a/gcc/testsuite/g++.dg/template/non-dependent25.C b/gcc/testsuite/g++.dg/template/non-dependent25.C
new file mode 100644
index 00000000000..a2f9801e11f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent25.C
@@ -0,0 +1,14 @@
+// PR c++/109480
+
+template<class T>
+struct A {
+  void f() {
+    A<int> a;
+    const bool b = a.g();
+  }
+
+private:
+  bool g() const;
+};
+
+template struct A<int>;
-- 
2.40.1.459.g48d89b51b3

[PATCH 2/2] c++: non-dep init folding and access checking [PR109480]

[Patrick Palka]

enforce_access currently inspects processing_template_decl to determine
whether to defer the given access check until instantiation time.  But
using this flag is unreliable because it gets cleared during e.g.
non-dependent initializer folding, and can lead to premature access
check failures as in the below testcase.  It seems better to inspect
current_template_parms instead.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
for trunk?

	PR c++/109480

gcc/cp/ChangeLog:

	* semantics.cc (enforce_access): Check current_template_parms
	instead of processing_template_decl when determining whether
	to defer the access check.

gcc/testsuite/ChangeLog:

	* g++.dg/template/non-dependent25a.C: New test.
---
 gcc/cp/semantics.cc                             |  2 +-
 .../g++.dg/template/non-dependent25a.C          | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25a.C

diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 9ba316ab3be..474da71bff6 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -346,7 +346,7 @@ enforce_access (tree basetype_path, tree decl, tree diag_decl,
     }
 
   tree cs = current_scope ();
-  if (processing_template_decl
+  if (current_template_parms
       && (CLASS_TYPE_P (cs) || TREE_CODE (cs) == FUNCTION_DECL))
     if (tree template_info = get_template_info (cs))
       {
diff --git a/gcc/testsuite/g++.dg/template/non-dependent25a.C b/gcc/testsuite/g++.dg/template/non-dependent25a.C
new file mode 100644
index 00000000000..902e537ec09
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent25a.C
@@ -0,0 +1,17 @@
+// PR c++/109480
+// A version of non-dependent25.C where b's initializer is a constant
+// expression.
+// { dg-do compile { target c++11 } }
+
+template<class T>
+struct A {
+  void f() {
+    constexpr A<int> a;
+    const bool b = a.g(); // { dg-bogus "private" }
+  }
+
+private:
+  constexpr bool g() const { return true; }
+};
+
+template struct A<int>;
-- 
2.40.1.459.g48d89b51b3

Re: [PATCH 2/2] c++: non-dep init folding and access checking [PR109480]

[Jason Merrill]

On 5/1/23 15:59, Patrick Palka wrote:
> enforce_access currently inspects processing_template_decl to determine
> whether to defer the given access check until instantiation time.  But
> using this flag is unreliable because it gets cleared during e.g.
> non-dependent initializer folding, and can lead to premature access
> check failures as in the below testcase.  It seems better to inspect
> current_template_parms instead.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
> for trunk?

OK.

> 	PR c++/109480
> 
> gcc/cp/ChangeLog:
> 
> 	* semantics.cc (enforce_access): Check current_template_parms
> 	instead of processing_template_decl when determining whether
> 	to defer the access check.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/template/non-dependent25a.C: New test.
> ---
>   gcc/cp/semantics.cc                             |  2 +-
>   .../g++.dg/template/non-dependent25a.C          | 17 +++++++++++++++++
>   2 files changed, 18 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25a.C
> 
> diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> index 9ba316ab3be..474da71bff6 100644
> --- a/gcc/cp/semantics.cc
> +++ b/gcc/cp/semantics.cc
> @@ -346,7 +346,7 @@ enforce_access (tree basetype_path, tree decl, tree diag_decl,
>       }
>   
>     tree cs = current_scope ();
> -  if (processing_template_decl
> +  if (current_template_parms
>         && (CLASS_TYPE_P (cs) || TREE_CODE (cs) == FUNCTION_DECL))
>       if (tree template_info = get_template_info (cs))
>         {
> diff --git a/gcc/testsuite/g++.dg/template/non-dependent25a.C b/gcc/testsuite/g++.dg/template/non-dependent25a.C
> new file mode 100644
> index 00000000000..902e537ec09
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/non-dependent25a.C
> @@ -0,0 +1,17 @@
> +// PR c++/109480
> +// A version of non-dependent25.C where b's initializer is a constant
> +// expression.
> +// { dg-do compile { target c++11 } }
> +
> +template<class T>
> +struct A {
> +  void f() {
> +    constexpr A<int> a;
> +    const bool b = a.g(); // { dg-bogus "private" }
> +  }
> +
> +private:
> +  constexpr bool g() const { return true; }
> +};
> +
> +template struct A<int>;

Re: [PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[Jason Merrill]

On 5/1/23 15:59, Patrick Palka wrote:
> Here we're incorrectly deeming the templated call a.g() inside b's
> initializer as potentially constant, despite g being non-constexpr,
> which leads to us wastefully instantiating the initializer ahead of time
> and triggering a bug in access checking deferral (which will get fixed
> in the subsequent patch).
> 
> This patch fixes this by calling get_fns earlier during potentiality
> checking so that we also handle the templated form of a member function
> call (whose overall callee is a COMPONENT_REF) when checking if the called
> function is constexpr etc.
> 
> 	PR c++/109480
> 
> gcc/cp/ChangeLog:
> 
> 	* constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
> 	Reorganize to call get_fns sooner.  Remove dead store to 'fun'.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the
> 	expected "without object" diagnostic isn't replaced by a
> 	"call to non-constexpr function" diagnostic.
> 	* g++.dg/template/non-dependent25.C: New test.
> ---
>   gcc/cp/constexpr.cc                             | 16 ++++++++--------
>   gcc/testsuite/g++.dg/cpp0x/noexcept59.C         |  2 +-
>   gcc/testsuite/g++.dg/template/non-dependent25.C | 14 ++++++++++++++
>   3 files changed, 23 insertions(+), 9 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C
> 
> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> index d1097764b10..29d872d0a5e 100644
> --- a/gcc/cp/constexpr.cc
> +++ b/gcc/cp/constexpr.cc
> @@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
>   
>   	if (fun && is_overloaded_fn (fun))
>   	  {
> +	    if (!RECUR (fun, true))
> +	      return false;
> +	    fun = get_fns (fun);
> +
>   	    if (TREE_CODE (fun) == FUNCTION_DECL)
>   	      {
>   		if (builtin_valid_in_constant_expr_p (fun))
> @@ -9167,7 +9171,8 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
>   		   expression the address will be folded away, so look
>   		   through it now.  */
>   		if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun)
> -		    && !DECL_CONSTRUCTOR_P (fun))
> +		    && !DECL_CONSTRUCTOR_P (fun)
> +		    && !processing_template_decl)

I don't see any rationale for this hunk?

>   		  {
>   		    tree x = get_nth_callarg (t, 0);
>   		    if (is_this_parameter (x))
> @@ -9182,16 +9187,11 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
>   		    i = 1;
>   		  }
>   	      }
> -	    else
> -	      {
> -		if (!RECUR (fun, true))
> -		  return false;
> -		fun = get_first_fn (fun);
> -	      }
> +
> +	    fun = OVL_FIRST (fun);
>   	    /* Skip initial arguments to base constructors.  */
>   	    if (DECL_BASE_CONSTRUCTOR_P (fun))
>   	      i = num_artificial_parms_for (fun);
> -	    fun = DECL_ORIGIN (fun);
>   	  }
>   	else if (fun)
>             {
> diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> index c752601ba09..1dc826d3111 100644
> --- a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> @@ -3,7 +3,7 @@
>   
>   template <class ...Ts> class A
>   {
> -  void e ();
> +  constexpr bool e () { return true; };
>     bool f (int() noexcept(this->e())); // { dg-error "this" }
>     bool g (int() noexcept(e()));	      // { dg-error "without object" }
>   };
> diff --git a/gcc/testsuite/g++.dg/template/non-dependent25.C b/gcc/testsuite/g++.dg/template/non-dependent25.C
> new file mode 100644
> index 00000000000..a2f9801e11f
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/non-dependent25.C
> @@ -0,0 +1,14 @@
> +// PR c++/109480
> +
> +template<class T>
> +struct A {
> +  void f() {
> +    A<int> a;
> +    const bool b = a.g();
> +  }
> +
> +private:
> +  bool g() const;
> +};
> +
> +template struct A<int>;

Re: [PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[Patrick Palka]

On Tue, 2 May 2023, Jason Merrill wrote:

> On 5/1/23 15:59, Patrick Palka wrote:
> > Here we're incorrectly deeming the templated call a.g() inside b's
> > initializer as potentially constant, despite g being non-constexpr,
> > which leads to us wastefully instantiating the initializer ahead of time
> > and triggering a bug in access checking deferral (which will get fixed
> > in the subsequent patch).
> > 
> > This patch fixes this by calling get_fns earlier during potentiality
> > checking so that we also handle the templated form of a member function
> > call (whose overall callee is a COMPONENT_REF) when checking if the called
> > function is constexpr etc.
> > 
> > 	PR c++/109480
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
> > 	Reorganize to call get_fns sooner.  Remove dead store to 'fun'.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	* g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the
> > 	expected "without object" diagnostic isn't replaced by a
> > 	"call to non-constexpr function" diagnostic.
> > 	* g++.dg/template/non-dependent25.C: New test.
> > ---
> >   gcc/cp/constexpr.cc                             | 16 ++++++++--------
> >   gcc/testsuite/g++.dg/cpp0x/noexcept59.C         |  2 +-
> >   gcc/testsuite/g++.dg/template/non-dependent25.C | 14 ++++++++++++++
> >   3 files changed, 23 insertions(+), 9 deletions(-)
> >   create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C
> > 
> > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> > index d1097764b10..29d872d0a5e 100644
> > --- a/gcc/cp/constexpr.cc
> > +++ b/gcc/cp/constexpr.cc
> > @@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool
> > want_rval, bool strict, bool now,
> >     	if (fun && is_overloaded_fn (fun))
> >   	  {
> > +	    if (!RECUR (fun, true))
> > +	      return false;
> > +	    fun = get_fns (fun);
> > +
> >   	    if (TREE_CODE (fun) == FUNCTION_DECL)
> >   	      {
> >   		if (builtin_valid_in_constant_expr_p (fun))
> > @@ -9167,7 +9171,8 @@ potential_constant_expression_1 (tree t, bool
> > want_rval, bool strict, bool now,
> >   		   expression the address will be folded away, so look
> >   		   through it now.  */
> >   		if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun)
> > -		    && !DECL_CONSTRUCTOR_P (fun))
> > +		    && !DECL_CONSTRUCTOR_P (fun)
> > +		    && !processing_template_decl)
> 
> I don't see any rationale for this hunk?

Now that we call get_fns earlier, we can reach this code path with a
templated non-static memfn call, but the code that follows assumes
non-templated form.

I tried teaching it to handle the templated form too, but there's
apparently two different templated forms for non-static memfn calls,
one with a COMPONENT_REF callee and one with an ordinary BASELINK
callee (without a implicit object argument).  In the former the implict
object argument is inside the COMPONENT_REF (and is a reference instead
of a pointer), and in the latter we don't even have an implicit object
argument to inspect.

FWIW I think which form we use depends on whether we know if the called
function is a member of the current instantiation, e.g

  struct A { void f(); };

  template<class T> struct B;

  template<class T>
  struct C : B<T> {
    void g();

    void h() {
      A::f(); // templated form has BASELINK callee, no object arg
      C::g(); // templated form has COMPONENT_REF callee
    }
  };

So it seemed best to punt on templated non-static memfn calls here for
now and treat that as a separate enhancement.

> 
> >   		  {
> >   		    tree x = get_nth_callarg (t, 0);
> >   		    if (is_this_parameter (x))
> > @@ -9182,16 +9187,11 @@ potential_constant_expression_1 (tree t, bool
> > want_rval, bool strict, bool now,
> >   		    i = 1;
> >   		  }
> >   	      }
> > -	    else
> > -	      {
> > -		if (!RECUR (fun, true))
> > -		  return false;
> > -		fun = get_first_fn (fun);
> > -	      }
> > +
> > +	    fun = OVL_FIRST (fun);
> >   	    /* Skip initial arguments to base constructors.  */
> >   	    if (DECL_BASE_CONSTRUCTOR_P (fun))
> >   	      i = num_artificial_parms_for (fun);
> > -	    fun = DECL_ORIGIN (fun);
> >   	  }
> >   	else if (fun)
> >             {
> > diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> > b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> > index c752601ba09..1dc826d3111 100644
> > --- a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> > +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> > @@ -3,7 +3,7 @@
> >     template <class ...Ts> class A
> >   {
> > -  void e ();
> > +  constexpr bool e () { return true; };
> >     bool f (int() noexcept(this->e())); // { dg-error "this" }
> >     bool g (int() noexcept(e()));	      // { dg-error "without object" }
> >   };
> > diff --git a/gcc/testsuite/g++.dg/template/non-dependent25.C
> > b/gcc/testsuite/g++.dg/template/non-dependent25.C
> > new file mode 100644
> > index 00000000000..a2f9801e11f
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/template/non-dependent25.C
> > @@ -0,0 +1,14 @@
> > +// PR c++/109480
> > +
> > +template<class T>
> > +struct A {
> > +  void f() {
> > +    A<int> a;
> > +    const bool b = a.g();
> > +  }
> > +
> > +private:
> > +  bool g() const;
> > +};
> > +
> > +template struct A<int>;
> 
> 

Re: [PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[Patrick Palka]

on Tue, 2 May 2023, Patrick Palka wrote:

> On Tue, 2 May 2023, Jason Merrill wrote:
> 
> > On 5/1/23 15:59, Patrick Palka wrote:
> > > Here we're incorrectly deeming the templated call a.g() inside b's
> > > initializer as potentially constant, despite g being non-constexpr,
> > > which leads to us wastefully instantiating the initializer ahead of time
> > > and triggering a bug in access checking deferral (which will get fixed
> > > in the subsequent patch).
> > > 
> > > This patch fixes this by calling get_fns earlier during potentiality
> > > checking so that we also handle the templated form of a member function
> > > call (whose overall callee is a COMPONENT_REF) when checking if the called
> > > function is constexpr etc.
> > > 
> > > 	PR c++/109480
> > > 
> > > gcc/cp/ChangeLog:
> > > 
> > > 	* constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
> > > 	Reorganize to call get_fns sooner.  Remove dead store to 'fun'.
> > > 
> > > gcc/testsuite/ChangeLog:
> > > 
> > > 	* g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the
> > > 	expected "without object" diagnostic isn't replaced by a
> > > 	"call to non-constexpr function" diagnostic.
> > > 	* g++.dg/template/non-dependent25.C: New test.
> > > ---
> > >   gcc/cp/constexpr.cc                             | 16 ++++++++--------
> > >   gcc/testsuite/g++.dg/cpp0x/noexcept59.C         |  2 +-
> > >   gcc/testsuite/g++.dg/template/non-dependent25.C | 14 ++++++++++++++
> > >   3 files changed, 23 insertions(+), 9 deletions(-)
> > >   create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C
> > > 
> > > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> > > index d1097764b10..29d872d0a5e 100644
> > > --- a/gcc/cp/constexpr.cc
> > > +++ b/gcc/cp/constexpr.cc
> > > @@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool
> > > want_rval, bool strict, bool now,
> > >     	if (fun && is_overloaded_fn (fun))
> > >   	  {
> > > +	    if (!RECUR (fun, true))
> > > +	      return false;
> > > +	    fun = get_fns (fun);
> > > +
> > >   	    if (TREE_CODE (fun) == FUNCTION_DECL)
> > >   	      {
> > >   		if (builtin_valid_in_constant_expr_p (fun))
> > > @@ -9167,7 +9171,8 @@ potential_constant_expression_1 (tree t, bool
> > > want_rval, bool strict, bool now,
> > >   		   expression the address will be folded away, so look
> > >   		   through it now.  */
> > >   		if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun)
> > > -		    && !DECL_CONSTRUCTOR_P (fun))
> > > +		    && !DECL_CONSTRUCTOR_P (fun)
> > > +		    && !processing_template_decl)
> > 
> > I don't see any rationale for this hunk?
> 
> Now that we call get_fns earlier, we can reach this code path with a
> templated non-static memfn call, but the code that follows assumes
> non-templated form.
> 
> I tried teaching it to handle the templated form too, but there's
> apparently two different templated forms for non-static memfn calls,
> one with a COMPONENT_REF callee and one with an ordinary BASELINK
> callee (without a implicit object argument).  In the former the implict
> object argument is inside the COMPONENT_REF (and is a reference instead
> of a pointer), and in the latter we don't even have an implicit object
> argument to inspect.
> 
> FWIW I think which form we use depends on whether we know if the called
> function is a member of the current instantiation, e.g
> 
>   struct A { void f(); };
> 
>   template<class T> struct B;
> 
>   template<class T>
>   struct C : B<T> {
>     void g();
> 
>     void h() {
>       A::f(); // templated form has BASELINK callee, no object arg
>       C::g(); // templated form has COMPONENT_REF callee
>     }
>   };
> 
> So it seemed best to punt on templated non-static memfn calls here for
> now and treat that as a separate enhancement.

And I'm not even sure if the code path in question is necessary at all
anymore: disabling it outright doesn't cause any regressions in the testsuite.
It seems effectively equivalent to the body of the loop over the args a few
lines later:

  for (; i < nargs; ++i)
    {
      tree x = get_nth_callarg (t, i);
      /* In a template, reference arguments haven't been converted to
         REFERENCE_TYPE and we might not even know if the parameter
         is a reference, so accept lvalue constants too.  */
      bool rv = processing_template_decl ? any : rval;
      /* Don't require an immediately constant value, as constexpr
         substitution might not use the value of the argument.  */
      bool sub_now = false;
      if (!potential_constant_expression_1 (x, rv, strict,
                                            sub_now, fundef_p, flags,
                                            jump_target))
        return false;
    }

> 
> > 
> > >   		  {
> > >   		    tree x = get_nth_callarg (t, 0);
> > >   		    if (is_this_parameter (x))
> > > @@ -9182,16 +9187,11 @@ potential_constant_expression_1 (tree t, bool
> > > want_rval, bool strict, bool now,
> > >   		    i = 1;
> > >   		  }
> > >   	      }
> > > -	    else
> > > -	      {
> > > -		if (!RECUR (fun, true))
> > > -		  return false;
> > > -		fun = get_first_fn (fun);
> > > -	      }
> > > +
> > > +	    fun = OVL_FIRST (fun);
> > >   	    /* Skip initial arguments to base constructors.  */
> > >   	    if (DECL_BASE_CONSTRUCTOR_P (fun))
> > >   	      i = num_artificial_parms_for (fun);
> > > -	    fun = DECL_ORIGIN (fun);
> > >   	  }
> > >   	else if (fun)
> > >             {
> > > diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> > > b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> > > index c752601ba09..1dc826d3111 100644
> > > --- a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> > > +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> > > @@ -3,7 +3,7 @@
> > >     template <class ...Ts> class A
> > >   {
> > > -  void e ();
> > > +  constexpr bool e () { return true; };
> > >     bool f (int() noexcept(this->e())); // { dg-error "this" }
> > >     bool g (int() noexcept(e()));	      // { dg-error "without object" }
> > >   };
> > > diff --git a/gcc/testsuite/g++.dg/template/non-dependent25.C
> > > b/gcc/testsuite/g++.dg/template/non-dependent25.C
> > > new file mode 100644
> > > index 00000000000..a2f9801e11f
> > > --- /dev/null
> > > +++ b/gcc/testsuite/g++.dg/template/non-dependent25.C
> > > @@ -0,0 +1,14 @@
> > > +// PR c++/109480
> > > +
> > > +template<class T>
> > > +struct A {
> > > +  void f() {
> > > +    A<int> a;
> > > +    const bool b = a.g();
> > > +  }
> > > +
> > > +private:
> > > +  bool g() const;
> > > +};
> > > +
> > > +template struct A<int>;
> > 
> > 
> 

Re: [PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[Jason Merrill]

On 5/2/23 15:53, Patrick Palka wrote:
> on Tue, 2 May 2023, Patrick Palka wrote:
> 
>> On Tue, 2 May 2023, Jason Merrill wrote:
>>
>>> On 5/1/23 15:59, Patrick Palka wrote:
>>>> Here we're incorrectly deeming the templated call a.g() inside b's
>>>> initializer as potentially constant, despite g being non-constexpr,
>>>> which leads to us wastefully instantiating the initializer ahead of time
>>>> and triggering a bug in access checking deferral (which will get fixed
>>>> in the subsequent patch).
>>>>
>>>> This patch fixes this by calling get_fns earlier during potentiality
>>>> checking so that we also handle the templated form of a member function
>>>> call (whose overall callee is a COMPONENT_REF) when checking if the called
>>>> function is constexpr etc.
>>>>
>>>> 	PR c++/109480
>>>>
>>>> gcc/cp/ChangeLog:
>>>>
>>>> 	* constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
>>>> 	Reorganize to call get_fns sooner.  Remove dead store to 'fun'.
>>>>
>>>> gcc/testsuite/ChangeLog:
>>>>
>>>> 	* g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the
>>>> 	expected "without object" diagnostic isn't replaced by a
>>>> 	"call to non-constexpr function" diagnostic.
>>>> 	* g++.dg/template/non-dependent25.C: New test.
>>>> ---
>>>>    gcc/cp/constexpr.cc                             | 16 ++++++++--------
>>>>    gcc/testsuite/g++.dg/cpp0x/noexcept59.C         |  2 +-
>>>>    gcc/testsuite/g++.dg/template/non-dependent25.C | 14 ++++++++++++++
>>>>    3 files changed, 23 insertions(+), 9 deletions(-)
>>>>    create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C
>>>>
>>>> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
>>>> index d1097764b10..29d872d0a5e 100644
>>>> --- a/gcc/cp/constexpr.cc
>>>> +++ b/gcc/cp/constexpr.cc
>>>> @@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool
>>>> want_rval, bool strict, bool now,
>>>>      	if (fun && is_overloaded_fn (fun))
>>>>    	  {
>>>> +	    if (!RECUR (fun, true))
>>>> +	      return false;
>>>> +	    fun = get_fns (fun);
>>>> +
>>>>    	    if (TREE_CODE (fun) == FUNCTION_DECL)
>>>>    	      {
>>>>    		if (builtin_valid_in_constant_expr_p (fun))
>>>> @@ -9167,7 +9171,8 @@ potential_constant_expression_1 (tree t, bool
>>>> want_rval, bool strict, bool now,
>>>>    		   expression the address will be folded away, so look
>>>>    		   through it now.  */
>>>>    		if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun)
>>>> -		    && !DECL_CONSTRUCTOR_P (fun))
>>>> +		    && !DECL_CONSTRUCTOR_P (fun)
>>>> +		    && !processing_template_decl)
>>>
>>> I don't see any rationale for this hunk?
>>
>> Now that we call get_fns earlier, we can reach this code path with a
>> templated non-static memfn call, but the code that follows assumes
>> non-templated form.
>>
>> I tried teaching it to handle the templated form too, but there's
>> apparently two different templated forms for non-static memfn calls,
>> one with a COMPONENT_REF callee and one with an ordinary BASELINK
>> callee (without a implicit object argument).  In the former the implict
>> object argument is inside the COMPONENT_REF (and is a reference instead
>> of a pointer), and in the latter we don't even have an implicit object
>> argument to inspect.
>>
>> FWIW I think which form we use depends on whether we know if the called
>> function is a member of the current instantiation, e.g
>>
>>    struct A { void f(); };
>>
>>    template<class T> struct B;
>>
>>    template<class T>
>>    struct C : B<T> {
>>      void g();
>>
>>      void h() {
>>        A::f(); // templated form has BASELINK callee, no object arg
>>        C::g(); // templated form has COMPONENT_REF callee
>>      }
>>    };
>>
>> So it seemed best to punt on templated non-static memfn calls here for
>> now and treat that as a separate enhancement.
> 
> And I'm not even sure if the code path in question is necessary at all
> anymore: disabling it outright doesn't cause any regressions in the testsuite.
> It seems effectively equivalent to the body of the loop over the args a few
> lines later:

If removing that hunk doesn't regress anything, let's do it.  Probably 
that should have happened in r13-55-ge9d2adc17d0dbe

>    for (; i < nargs; ++i)
>      {
>        tree x = get_nth_callarg (t, i);
>        /* In a template, reference arguments haven't been converted to
>           REFERENCE_TYPE and we might not even know if the parameter
>           is a reference, so accept lvalue constants too.  */
>        bool rv = processing_template_decl ? any : rval;
>        /* Don't require an immediately constant value, as constexpr
>           substitution might not use the value of the argument.  */
>        bool sub_now = false;
>        if (!potential_constant_expression_1 (x, rv, strict,
>                                              sub_now, fundef_p, flags,
>                                              jump_target))
>          return false;
>      }
> 
>>
>>>
>>>>    		  {
>>>>    		    tree x = get_nth_callarg (t, 0);
>>>>    		    if (is_this_parameter (x))
>>>> @@ -9182,16 +9187,11 @@ potential_constant_expression_1 (tree t, bool
>>>> want_rval, bool strict, bool now,
>>>>    		    i = 1;
>>>>    		  }
>>>>    	      }
>>>> -	    else
>>>> -	      {
>>>> -		if (!RECUR (fun, true))
>>>> -		  return false;
>>>> -		fun = get_first_fn (fun);
>>>> -	      }
>>>> +
>>>> +	    fun = OVL_FIRST (fun);
>>>>    	    /* Skip initial arguments to base constructors.  */
>>>>    	    if (DECL_BASE_CONSTRUCTOR_P (fun))
>>>>    	      i = num_artificial_parms_for (fun);
>>>> -	    fun = DECL_ORIGIN (fun);
>>>>    	  }
>>>>    	else if (fun)
>>>>              {
>>>> diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
>>>> b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
>>>> index c752601ba09..1dc826d3111 100644
>>>> --- a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
>>>> +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
>>>> @@ -3,7 +3,7 @@
>>>>      template <class ...Ts> class A
>>>>    {
>>>> -  void e ();
>>>> +  constexpr bool e () { return true; };
>>>>      bool f (int() noexcept(this->e())); // { dg-error "this" }
>>>>      bool g (int() noexcept(e()));	      // { dg-error "without object" }
>>>>    };
>>>> diff --git a/gcc/testsuite/g++.dg/template/non-dependent25.C
>>>> b/gcc/testsuite/g++.dg/template/non-dependent25.C
>>>> new file mode 100644
>>>> index 00000000000..a2f9801e11f
>>>> --- /dev/null
>>>> +++ b/gcc/testsuite/g++.dg/template/non-dependent25.C
>>>> @@ -0,0 +1,14 @@
>>>> +// PR c++/109480
>>>> +
>>>> +template<class T>
>>>> +struct A {
>>>> +  void f() {
>>>> +    A<int> a;
>>>> +    const bool b = a.g();
>>>> +  }
>>>> +
>>>> +private:
>>>> +  bool g() const;
>>>> +};
>>>> +
>>>> +template struct A<int>;
>>>
>>>
>>
> 

Re: [PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[Patrick Palka]

On Wed, 3 May 2023, Jason Merrill wrote:

> On 5/2/23 15:53, Patrick Palka wrote:
> > on Tue, 2 May 2023, Patrick Palka wrote:
> > 
> > > On Tue, 2 May 2023, Jason Merrill wrote:
> > > 
> > > > On 5/1/23 15:59, Patrick Palka wrote:
> > > > > Here we're incorrectly deeming the templated call a.g() inside b's
> > > > > initializer as potentially constant, despite g being non-constexpr,
> > > > > which leads to us wastefully instantiating the initializer ahead of
> > > > > time
> > > > > and triggering a bug in access checking deferral (which will get fixed
> > > > > in the subsequent patch).
> > > > > 
> > > > > This patch fixes this by calling get_fns earlier during potentiality
> > > > > checking so that we also handle the templated form of a member
> > > > > function
> > > > > call (whose overall callee is a COMPONENT_REF) when checking if the
> > > > > called
> > > > > function is constexpr etc.
> > > > > 
> > > > > 	PR c++/109480
> > > > > 
> > > > > gcc/cp/ChangeLog:
> > > > > 
> > > > > 	* constexpr.cc (potential_constant_expression_1) <case
> > > > > CALL_EXPR>:
> > > > > 	Reorganize to call get_fns sooner.  Remove dead store to
> > > > > 'fun'.
> > > > > 
> > > > > gcc/testsuite/ChangeLog:
> > > > > 
> > > > > 	* g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the
> > > > > 	expected "without object" diagnostic isn't replaced by a
> > > > > 	"call to non-constexpr function" diagnostic.
> > > > > 	* g++.dg/template/non-dependent25.C: New test.
> > > > > ---
> > > > >    gcc/cp/constexpr.cc                             | 16
> > > > > ++++++++--------
> > > > >    gcc/testsuite/g++.dg/cpp0x/noexcept59.C         |  2 +-
> > > > >    gcc/testsuite/g++.dg/template/non-dependent25.C | 14 ++++++++++++++
> > > > >    3 files changed, 23 insertions(+), 9 deletions(-)
> > > > >    create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C
> > > > > 
> > > > > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> > > > > index d1097764b10..29d872d0a5e 100644
> > > > > --- a/gcc/cp/constexpr.cc
> > > > > +++ b/gcc/cp/constexpr.cc
> > > > > @@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool
> > > > > want_rval, bool strict, bool now,
> > > > >      	if (fun && is_overloaded_fn (fun))
> > > > >    	  {
> > > > > +	    if (!RECUR (fun, true))
> > > > > +	      return false;
> > > > > +	    fun = get_fns (fun);
> > > > > +
> > > > >    	    if (TREE_CODE (fun) == FUNCTION_DECL)
> > > > >    	      {
> > > > >    		if (builtin_valid_in_constant_expr_p (fun))
> > > > > @@ -9167,7 +9171,8 @@ potential_constant_expression_1 (tree t, bool
> > > > > want_rval, bool strict, bool now,
> > > > >    		   expression the address will be folded away, so look
> > > > >    		   through it now.  */
> > > > >    		if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun)
> > > > > -		    && !DECL_CONSTRUCTOR_P (fun))
> > > > > +		    && !DECL_CONSTRUCTOR_P (fun)
> > > > > +		    && !processing_template_decl)
> > > > 
> > > > I don't see any rationale for this hunk?
> > > 
> > > Now that we call get_fns earlier, we can reach this code path with a
> > > templated non-static memfn call, but the code that follows assumes
> > > non-templated form.
> > > 
> > > I tried teaching it to handle the templated form too, but there's
> > > apparently two different templated forms for non-static memfn calls,
> > > one with a COMPONENT_REF callee and one with an ordinary BASELINK
> > > callee (without a implicit object argument).  In the former the implict
> > > object argument is inside the COMPONENT_REF (and is a reference instead
> > > of a pointer), and in the latter we don't even have an implicit object
> > > argument to inspect.
> > > 
> > > FWIW I think which form we use depends on whether we know if the called
> > > function is a member of the current instantiation, e.g
> > > 
> > >    struct A { void f(); };
> > > 
> > >    template<class T> struct B;
> > > 
> > >    template<class T>
> > >    struct C : B<T> {
> > >      void g();
> > > 
> > >      void h() {
> > >        A::f(); // templated form has BASELINK callee, no object arg
> > >        C::g(); // templated form has COMPONENT_REF callee
> > >      }
> > >    };
> > > 
> > > So it seemed best to punt on templated non-static memfn calls here for
> > > now and treat that as a separate enhancement.
> > 
> > And I'm not even sure if the code path in question is necessary at all
> > anymore: disabling it outright doesn't cause any regressions in the
> > testsuite.
> > It seems effectively equivalent to the body of the loop over the args a few
> > lines later:
> 
> If removing that hunk doesn't regress anything, let's do it.  Probably that
> should have happened in r13-55-ge9d2adc17d0dbe

Sounds good, here's the combined patch which I'm bootstrapping for good
measure.  Does it look OK for trunk if bootstrap+regtest succeeds?

-- >8 --

Subject: [PATCH] c++: potentiality of templated memfn call [PR109480]

Here we're incorrectly deeming the templated call a.g() inside b's
initializer as potentially constant, despite g being non-constexpr,
which leads to us wastefully instantiating the initializer ahead of time,
which incidentally tiggers a bug in access checking deferral (to be
fixed by the subsequent patch).

This patch fixes this by calling get_fns earlier during CALL_EXPR
potentiality checking so that we're able to extract a FUNCTION_DECL out
of a templated member function call (whose overall is typically a
COMPONENT_REF) and to the usual checking if the called function is
constexpr etc.

In passing, I noticed potential_constant_expression_1's special handling
of the object argument of a non-static member function call is effectively
the same as the generic argument handling a few lines later.  So this
patch just gets rid of this special handling; otherwise we'd have to adapt
it to handle templated versions of such calls.

	PR c++/109480

gcc/cp/ChangeLog:

	* constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
	Reorganize to call get_fns sooner.  Remove special handling of
	the object argument of a non-static member function call.  Remove
	dead store to 'fun'.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the
	expected "without object" diagnostic isn't replaced by a
	"call to non-constexpr function" diagnostic.
	* g++.dg/template/non-dependent25.C: New test.
---
 gcc/cp/constexpr.cc                           | 32 ++++---------------
 gcc/testsuite/g++.dg/cpp0x/noexcept59.C       |  2 +-
 .../g++.dg/template/non-dependent25.C         | 14 ++++++++
 3 files changed, 21 insertions(+), 27 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index d1097764b10..075339f7f62 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
 
 	if (fun && is_overloaded_fn (fun))
 	  {
+	    if (!RECUR (fun, true))
+	      return false;
+	    fun = get_fns (fun);
+
 	    if (TREE_CODE (fun) == FUNCTION_DECL)
 	      {
 		if (builtin_valid_in_constant_expr_p (fun))
@@ -9162,36 +9166,12 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
 		      explain_invalid_constexpr_fn (fun);
 		    return false;
 		  }
-		/* A call to a non-static member function takes the address
-		   of the object as the first argument.  But in a constant
-		   expression the address will be folded away, so look
-		   through it now.  */
-		if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun)
-		    && !DECL_CONSTRUCTOR_P (fun))
-		  {
-		    tree x = get_nth_callarg (t, 0);
-		    if (is_this_parameter (x))
-		      return true;
-		    /* Don't require an immediately constant value, as
-		       constexpr substitution might not use the value.  */
-		    bool sub_now = false;
-		    if (!potential_constant_expression_1 (x, rval, strict,
-							  sub_now, fundef_p,
-							  flags, jump_target))
-		      return false;
-		    i = 1;
-		  }
-	      }
-	    else
-	      {
-		if (!RECUR (fun, true))
-		  return false;
-		fun = get_first_fn (fun);
 	      }
+
+	    fun = OVL_FIRST (fun);
 	    /* Skip initial arguments to base constructors.  */
 	    if (DECL_BASE_CONSTRUCTOR_P (fun))
 	      i = num_artificial_parms_for (fun);
-	    fun = DECL_ORIGIN (fun);
 	  }
 	else if (fun)
           {
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
index c752601ba09..1dc826d3111 100644
--- a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
@@ -3,7 +3,7 @@
 
 template <class ...Ts> class A
 {
-  void e ();
+  constexpr bool e () { return true; };
   bool f (int() noexcept(this->e())); // { dg-error "this" }
   bool g (int() noexcept(e()));	      // { dg-error "without object" }
 };
diff --git a/gcc/testsuite/g++.dg/template/non-dependent25.C b/gcc/testsuite/g++.dg/template/non-dependent25.C
new file mode 100644
index 00000000000..c00e44532b0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent25.C
@@ -0,0 +1,14 @@
+// PR c++/109480
+
+template<class T>
+struct A {
+  void f() {
+    A<int> a;
+    const bool b = a.g(); // { dg-bogus "private" }
+  }
+
+private:
+  bool g() const;
+};
+
+template struct A<int>;
-- 
2.40.1.476.g69c786637d

Re: [PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[Jason Merrill]

On 5/3/23 16:50, Patrick Palka wrote:
> On Wed, 3 May 2023, Jason Merrill wrote:
> 
>> On 5/2/23 15:53, Patrick Palka wrote:
>>> on Tue, 2 May 2023, Patrick Palka wrote:
>>>
>>>> On Tue, 2 May 2023, Jason Merrill wrote:
>>>>
>>>>> On 5/1/23 15:59, Patrick Palka wrote:
>>>>>> Here we're incorrectly deeming the templated call a.g() inside b's
>>>>>> initializer as potentially constant, despite g being non-constexpr,
>>>>>> which leads to us wastefully instantiating the initializer ahead of
>>>>>> time
>>>>>> and triggering a bug in access checking deferral (which will get fixed
>>>>>> in the subsequent patch).
>>>>>>
>>>>>> This patch fixes this by calling get_fns earlier during potentiality
>>>>>> checking so that we also handle the templated form of a member
>>>>>> function
>>>>>> call (whose overall callee is a COMPONENT_REF) when checking if the
>>>>>> called
>>>>>> function is constexpr etc.
>>>>>>
>>>>>> 	PR c++/109480
>>>>>>
>>>>>> gcc/cp/ChangeLog:
>>>>>>
>>>>>> 	* constexpr.cc (potential_constant_expression_1) <case
>>>>>> CALL_EXPR>:
>>>>>> 	Reorganize to call get_fns sooner.  Remove dead store to
>>>>>> 'fun'.
>>>>>>
>>>>>> gcc/testsuite/ChangeLog:
>>>>>>
>>>>>> 	* g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the
>>>>>> 	expected "without object" diagnostic isn't replaced by a
>>>>>> 	"call to non-constexpr function" diagnostic.
>>>>>> 	* g++.dg/template/non-dependent25.C: New test.
>>>>>> ---
>>>>>>     gcc/cp/constexpr.cc                             | 16
>>>>>> ++++++++--------
>>>>>>     gcc/testsuite/g++.dg/cpp0x/noexcept59.C         |  2 +-
>>>>>>     gcc/testsuite/g++.dg/template/non-dependent25.C | 14 ++++++++++++++
>>>>>>     3 files changed, 23 insertions(+), 9 deletions(-)
>>>>>>     create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C
>>>>>>
>>>>>> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
>>>>>> index d1097764b10..29d872d0a5e 100644
>>>>>> --- a/gcc/cp/constexpr.cc
>>>>>> +++ b/gcc/cp/constexpr.cc
>>>>>> @@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool
>>>>>> want_rval, bool strict, bool now,
>>>>>>       	if (fun && is_overloaded_fn (fun))
>>>>>>     	  {
>>>>>> +	    if (!RECUR (fun, true))
>>>>>> +	      return false;
>>>>>> +	    fun = get_fns (fun);
>>>>>> +
>>>>>>     	    if (TREE_CODE (fun) == FUNCTION_DECL)
>>>>>>     	      {
>>>>>>     		if (builtin_valid_in_constant_expr_p (fun))
>>>>>> @@ -9167,7 +9171,8 @@ potential_constant_expression_1 (tree t, bool
>>>>>> want_rval, bool strict, bool now,
>>>>>>     		   expression the address will be folded away, so look
>>>>>>     		   through it now.  */
>>>>>>     		if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun)
>>>>>> -		    && !DECL_CONSTRUCTOR_P (fun))
>>>>>> +		    && !DECL_CONSTRUCTOR_P (fun)
>>>>>> +		    && !processing_template_decl)
>>>>>
>>>>> I don't see any rationale for this hunk?
>>>>
>>>> Now that we call get_fns earlier, we can reach this code path with a
>>>> templated non-static memfn call, but the code that follows assumes
>>>> non-templated form.
>>>>
>>>> I tried teaching it to handle the templated form too, but there's
>>>> apparently two different templated forms for non-static memfn calls,
>>>> one with a COMPONENT_REF callee and one with an ordinary BASELINK
>>>> callee (without a implicit object argument).  In the former the implict
>>>> object argument is inside the COMPONENT_REF (and is a reference instead
>>>> of a pointer), and in the latter we don't even have an implicit object
>>>> argument to inspect.
>>>>
>>>> FWIW I think which form we use depends on whether we know if the called
>>>> function is a member of the current instantiation, e.g
>>>>
>>>>     struct A { void f(); };
>>>>
>>>>     template<class T> struct B;
>>>>
>>>>     template<class T>
>>>>     struct C : B<T> {
>>>>       void g();
>>>>
>>>>       void h() {
>>>>         A::f(); // templated form has BASELINK callee, no object arg
>>>>         C::g(); // templated form has COMPONENT_REF callee
>>>>       }
>>>>     };
>>>>
>>>> So it seemed best to punt on templated non-static memfn calls here for
>>>> now and treat that as a separate enhancement.
>>>
>>> And I'm not even sure if the code path in question is necessary at all
>>> anymore: disabling it outright doesn't cause any regressions in the
>>> testsuite.
>>> It seems effectively equivalent to the body of the loop over the args a few
>>> lines later:
>>
>> If removing that hunk doesn't regress anything, let's do it.  Probably that
>> should have happened in r13-55-ge9d2adc17d0dbe
> 
> Sounds good, here's the combined patch which I'm bootstrapping for good
> measure.  Does it look OK for trunk if bootstrap+regtest succeeds?

OK.

> -- >8 --
> 
> Subject: [PATCH] c++: potentiality of templated memfn call [PR109480]
> 
> Here we're incorrectly deeming the templated call a.g() inside b's
> initializer as potentially constant, despite g being non-constexpr,
> which leads to us wastefully instantiating the initializer ahead of time,
> which incidentally tiggers a bug in access checking deferral (to be
> fixed by the subsequent patch).
> 
> This patch fixes this by calling get_fns earlier during CALL_EXPR
> potentiality checking so that we're able to extract a FUNCTION_DECL out
> of a templated member function call (whose overall is typically a
> COMPONENT_REF) and to the usual checking if the called function is
> constexpr etc.
> 
> In passing, I noticed potential_constant_expression_1's special handling
> of the object argument of a non-static member function call is effectively
> the same as the generic argument handling a few lines later.  So this
> patch just gets rid of this special handling; otherwise we'd have to adapt
> it to handle templated versions of such calls.
> 
> 	PR c++/109480
> 
> gcc/cp/ChangeLog:
> 
> 	* constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
> 	Reorganize to call get_fns sooner.  Remove special handling of
> 	the object argument of a non-static member function call.  Remove
> 	dead store to 'fun'.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the
> 	expected "without object" diagnostic isn't replaced by a
> 	"call to non-constexpr function" diagnostic.
> 	* g++.dg/template/non-dependent25.C: New test.
> ---
>   gcc/cp/constexpr.cc                           | 32 ++++---------------
>   gcc/testsuite/g++.dg/cpp0x/noexcept59.C       |  2 +-
>   .../g++.dg/template/non-dependent25.C         | 14 ++++++++
>   3 files changed, 21 insertions(+), 27 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C
> 
> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> index d1097764b10..075339f7f62 100644
> --- a/gcc/cp/constexpr.cc
> +++ b/gcc/cp/constexpr.cc
> @@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
>   
>   	if (fun && is_overloaded_fn (fun))
>   	  {
> +	    if (!RECUR (fun, true))
> +	      return false;
> +	    fun = get_fns (fun);
> +
>   	    if (TREE_CODE (fun) == FUNCTION_DECL)
>   	      {
>   		if (builtin_valid_in_constant_expr_p (fun))
> @@ -9162,36 +9166,12 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
>   		      explain_invalid_constexpr_fn (fun);
>   		    return false;
>   		  }
> -		/* A call to a non-static member function takes the address
> -		   of the object as the first argument.  But in a constant
> -		   expression the address will be folded away, so look
> -		   through it now.  */
> -		if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun)
> -		    && !DECL_CONSTRUCTOR_P (fun))
> -		  {
> -		    tree x = get_nth_callarg (t, 0);
> -		    if (is_this_parameter (x))
> -		      return true;
> -		    /* Don't require an immediately constant value, as
> -		       constexpr substitution might not use the value.  */
> -		    bool sub_now = false;
> -		    if (!potential_constant_expression_1 (x, rval, strict,
> -							  sub_now, fundef_p,
> -							  flags, jump_target))
> -		      return false;
> -		    i = 1;
> -		  }
> -	      }
> -	    else
> -	      {
> -		if (!RECUR (fun, true))
> -		  return false;
> -		fun = get_first_fn (fun);
>   	      }
> +
> +	    fun = OVL_FIRST (fun);
>   	    /* Skip initial arguments to base constructors.  */
>   	    if (DECL_BASE_CONSTRUCTOR_P (fun))
>   	      i = num_artificial_parms_for (fun);
> -	    fun = DECL_ORIGIN (fun);
>   	  }
>   	else if (fun)
>             {
> diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> index c752601ba09..1dc826d3111 100644
> --- a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
> @@ -3,7 +3,7 @@
>   
>   template <class ...Ts> class A
>   {
> -  void e ();
> +  constexpr bool e () { return true; };
>     bool f (int() noexcept(this->e())); // { dg-error "this" }
>     bool g (int() noexcept(e()));	      // { dg-error "without object" }
>   };
> diff --git a/gcc/testsuite/g++.dg/template/non-dependent25.C b/gcc/testsuite/g++.dg/template/non-dependent25.C
> new file mode 100644
> index 00000000000..c00e44532b0
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/non-dependent25.C
> @@ -0,0 +1,14 @@
> +// PR c++/109480
> +
> +template<class T>
> +struct A {
> +  void f() {
> +    A<int> a;
> +    const bool b = a.g(); // { dg-bogus "private" }
> +  }
> +
> +private:
> +  bool g() const;
> +};
> +
> +template struct A<int>;

Re: [PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[Martin Jambor]

Hello Patrick,

On Wed, May 03 2023, Patrick Palka via Gcc-patches wrote:
>
[...]
>
> Subject: [PATCH] c++: potentiality of templated memfn call [PR109480]
>
> Here we're incorrectly deeming the templated call a.g() inside b's
> initializer as potentially constant, despite g being non-constexpr,
> which leads to us wastefully instantiating the initializer ahead of time,
> which incidentally tiggers a bug in access checking deferral (to be
> fixed by the subsequent patch).
>
> This patch fixes this by calling get_fns earlier during CALL_EXPR
> potentiality checking so that we're able to extract a FUNCTION_DECL out
> of a templated member function call (whose overall is typically a
> COMPONENT_REF) and to the usual checking if the called function is
> constexpr etc.
>
> In passing, I noticed potential_constant_expression_1's special handling
> of the object argument of a non-static member function call is effectively
> the same as the generic argument handling a few lines later.  So this
> patch just gets rid of this special handling; otherwise we'd have to adapt
> it to handle templated versions of such calls.
>
> 	PR c++/109480
>
> gcc/cp/ChangeLog:
>
> 	* constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
> 	Reorganize to call get_fns sooner.  Remove special handling of
> 	the object argument of a non-static member function call.  Remove
> 	dead store to 'fun'.
>

This patch makes g++ no longer accept the following, complaining that
get_subsys is non-constexpr (with just -std=c++17 -S), which is of
course auto-reduced from a much larger source file from Ceph:

----------------------------------- 8< -----------------------------------
struct {
  void get_subsys();
} PriorSet_dpp;
struct PriorSet {
  template <typename> PriorSet();
};
template <typename> PriorSet::PriorSet() {
  [](auto cctX) { cctX.template should_gather<PriorSet_dpp.get_subsys()>; };
}
----------------------------------- 8< -----------------------------------

I assume that is intentional and am actually somewhat surprised it was
accepted before, but can you please confirm?

Thanks,

Martin

Re: [PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[Patrick Palka]

Hi Martin,

On Fri, May 12, 2023 at 12:13 PM Martin Jambor <mjambor@suse.cz> wrote:
>
> Hello Patrick,
>
> On Wed, May 03 2023, Patrick Palka via Gcc-patches wrote:
> >
> [...]
> >
> > Subject: [PATCH] c++: potentiality of templated memfn call [PR109480]
> >
> > Here we're incorrectly deeming the templated call a.g() inside b's
> > initializer as potentially constant, despite g being non-constexpr,
> > which leads to us wastefully instantiating the initializer ahead of time,
> > which incidentally tiggers a bug in access checking deferral (to be
> > fixed by the subsequent patch).
> >
> > This patch fixes this by calling get_fns earlier during CALL_EXPR
> > potentiality checking so that we're able to extract a FUNCTION_DECL out
> > of a templated member function call (whose overall is typically a
> > COMPONENT_REF) and to the usual checking if the called function is
> > constexpr etc.
> >
> > In passing, I noticed potential_constant_expression_1's special handling
> > of the object argument of a non-static member function call is effectively
> > the same as the generic argument handling a few lines later.  So this
> > patch just gets rid of this special handling; otherwise we'd have to adapt
> > it to handle templated versions of such calls.
> >
> >       PR c++/109480
> >
> > gcc/cp/ChangeLog:
> >
> >       * constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
> >       Reorganize to call get_fns sooner.  Remove special handling of
> >       the object argument of a non-static member function call.  Remove
> >       dead store to 'fun'.
> >
>
> This patch makes g++ no longer accept the following, complaining that
> get_subsys is non-constexpr (with just -std=c++17 -S), which is of
> course auto-reduced from a much larger source file from Ceph:
>
> ----------------------------------- 8< -----------------------------------
> struct {
>   void get_subsys();
> } PriorSet_dpp;
> struct PriorSet {
>   template <typename> PriorSet();
> };
> template <typename> PriorSet::PriorSet() {
>   [](auto cctX) { cctX.template should_gather<PriorSet_dpp.get_subsys()>; };
> }
> ----------------------------------- 8< -----------------------------------
>
> I assume that is intentional and am actually somewhat surprised it was
> accepted before, but can you please confirm?

Yes, this seems correct/intentional to me-- no instantiation of the
template would be valid because it's trying to use a non-constant
expression (which we now correctly identify as such) as a template
argument, so this snippet is IFNDR.

I don't think we have testsuite coverage for this QoI diagnostic, I'll add one.

>
> Thanks,
>
> Martin
>

Re: [PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[Jason Merrill]

On 5/12/23 13:02, Patrick Palka wrote:
> Hi Martin,
> 
> On Fri, May 12, 2023 at 12:13 PM Martin Jambor <mjambor@suse.cz> wrote:
>>
>> Hello Patrick,
>>
>> On Wed, May 03 2023, Patrick Palka via Gcc-patches wrote:
>>>
>> [...]
>>>
>>> Subject: [PATCH] c++: potentiality of templated memfn call [PR109480]
>>>
>>> Here we're incorrectly deeming the templated call a.g() inside b's
>>> initializer as potentially constant, despite g being non-constexpr,
>>> which leads to us wastefully instantiating the initializer ahead of time,
>>> which incidentally tiggers a bug in access checking deferral (to be
>>> fixed by the subsequent patch).
>>>
>>> This patch fixes this by calling get_fns earlier during CALL_EXPR
>>> potentiality checking so that we're able to extract a FUNCTION_DECL out
>>> of a templated member function call (whose overall is typically a
>>> COMPONENT_REF) and to the usual checking if the called function is
>>> constexpr etc.
>>>
>>> In passing, I noticed potential_constant_expression_1's special handling
>>> of the object argument of a non-static member function call is effectively
>>> the same as the generic argument handling a few lines later.  So this
>>> patch just gets rid of this special handling; otherwise we'd have to adapt
>>> it to handle templated versions of such calls.
>>>
>>>        PR c++/109480
>>>
>>> gcc/cp/ChangeLog:
>>>
>>>        * constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
>>>        Reorganize to call get_fns sooner.  Remove special handling of
>>>        the object argument of a non-static member function call.  Remove
>>>        dead store to 'fun'.
>>>
>>
>> This patch makes g++ no longer accept the following, complaining that
>> get_subsys is non-constexpr (with just -std=c++17 -S), which is of
>> course auto-reduced from a much larger source file from Ceph:
>>
>> ----------------------------------- 8< -----------------------------------
>> struct {
>>    void get_subsys();
>> } PriorSet_dpp;
>> struct PriorSet {
>>    template <typename> PriorSet();
>> };
>> template <typename> PriorSet::PriorSet() {
>>    [](auto cctX) { cctX.template should_gather<PriorSet_dpp.get_subsys()>; };
>> }
>> ----------------------------------- 8< -----------------------------------
>>
>> I assume that is intentional and am actually somewhat surprised it was
>> accepted before, but can you please confirm?
> 
> Yes, this seems correct/intentional to me-- no instantiation of the
> template would be valid because it's trying to use a non-constant
> expression (which we now correctly identify as such) as a template
> argument, so this snippet is IFNDR.
> 
> I don't think we have testsuite coverage for this QoI diagnostic, I'll add one.

Incidentally, I wonder about trying to make IFNDR diags in general 
permerrors or default-error pedwarns, but that doesn't need to happen now.

Jason