C++ PATCH to fix static init with () in a template (PR c++/84582)

C++ PATCH to fix static init with () in a template (PR c++/84582)

[Marek Polacek]

My recent change introducing cxx_constant_init caused this code

template <class> class A {
  static const long b = 0;
  static const unsigned c = (b);
};

to be rejected.  The reason is that force_paren_expr turns "b" into "*(const
long int &) &b", where the former is not value-dependent but the latter is
value-dependent.  So when we get to maybe_constant_init_1:
5147   if (!is_nondependent_static_init_expression (t))
5148     /* Don't try to evaluate it.  */;
it's not evaluated and we get the non-constant initialization error.
(Before we'd always evaluated the expression.)

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2018-02-27  Marek Polacek  <polacek@redhat.com>

	PR c++/84582
	* semantics.c (force_paren_expr): Avoid creating a static cast
	when processing a template.

	* g++.dg/cpp1z/static1.C: New test.
	* g++.dg/template/static37.C: New test.

diff --git gcc/cp/semantics.c gcc/cp/semantics.c
index 35569d0cb0d..b48de2df4e2 100644
--- gcc/cp/semantics.c
+++ gcc/cp/semantics.c
@@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
-  else
+  else if (!processing_template_decl)
     {
       cp_lvalue_kind kind = lvalue_kind (expr);
       if ((kind & ~clk_class) != clk_none)
diff --git gcc/testsuite/g++.dg/cpp1z/static1.C gcc/testsuite/g++.dg/cpp1z/static1.C
index e69de29bb2d..cb872997c5a 100644
--- gcc/testsuite/g++.dg/cpp1z/static1.C
+++ gcc/testsuite/g++.dg/cpp1z/static1.C
@@ -0,0 +1,19 @@
+// PR c++/84582
+// { dg-options -std=c++17 }
+
+class C {
+  static inline const long b = 0;
+  static inline const unsigned c = (b);
+};
+class D {
+  static inline const long b = 0;
+  static inline const unsigned c = b;
+};
+template <class> class A {
+  static inline const long b = 0;
+  static inline const unsigned c = (b);
+};
+template <class> class B {
+  static inline const long b = 0;
+  static inline const unsigned c = b;
+};
diff --git gcc/testsuite/g++.dg/template/static37.C gcc/testsuite/g++.dg/template/static37.C
index e69de29bb2d..90bc65d2fbc 100644
--- gcc/testsuite/g++.dg/template/static37.C
+++ gcc/testsuite/g++.dg/template/static37.C
@@ -0,0 +1,18 @@
+// PR c++/84582
+
+class C {
+  static const long b = 0;
+  static const unsigned c = (b);
+};
+class D {
+  static const long b = 0;
+  static const unsigned c = b;
+};
+template <class> class A {
+  static const long b = 0;
+  static const unsigned c = (b);
+};
+template <class> class B {
+  static const long b = 0;
+  static const unsigned c = b;
+};

	Marek

Re: C++ PATCH to fix static init with () in a template (PR c++/84582)

[Jason Merrill]

[-- Attachment #1: Type: text/plain, Size: 1708 bytes --]

On 02/27/2018 02:13 PM, Marek Polacek wrote:
> My recent change introducing cxx_constant_init caused this code
> 
> template <class> class A {
>    static const long b = 0;
>    static const unsigned c = (b);
> };
> 
> to be rejected.  The reason is that force_paren_expr turns "b" into "*(const
> long int &) &b", where the former is not value-dependent but the latter is
> value-dependent.  So when we get to maybe_constant_init_1:
> 5147   if (!is_nondependent_static_init_expression (t))
> 5148     /* Don't try to evaluate it.  */;
> it's not evaluated and we get the non-constant initialization error.
> (Before we'd always evaluated the expression.)
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
> 
> 2018-02-27  Marek Polacek  <polacek@redhat.com>
> 
> 	PR c++/84582
> 	* semantics.c (force_paren_expr): Avoid creating a static cast
> 	when processing a template.
> 
> 	* g++.dg/cpp1z/static1.C: New test.
> 	* g++.dg/template/static37.C: New test.
> 
> diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> index 35569d0cb0d..b48de2df4e2 100644
> --- gcc/cp/semantics.c
> +++ gcc/cp/semantics.c
> @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
> -  else
> +  else if (!processing_template_decl)

Hmm, this means that we forget about the parentheses in a template.  I'm 
surprised that this didn't break anything in the testsuite.  In 
particular, auto-fn15.C.  I've attached an addition to auto-fn15.C to 
catch this issue.

Can we use PAREN_EXPR instead of the static_cast in a template?

Jason

[-- Attachment #2: auto-fn15.diff --]
[-- Type: text/x-patch, Size: 619 bytes --]

diff --git a/gcc/testsuite/g++.dg/cpp1y/auto-fn15.C b/gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
index ba9f3579f62..0db428f7270 100644
--- a/gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
+++ b/gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
@@ -22,6 +22,8 @@ template <class T>
 decltype(auto) h5(T t) { return t.i; }
 template <class T>
 decltype(auto) h6(T t) { return (t.i); }
+template <class T>
+decltype(auto) h7(T t) { return (i); }
 
 int main()
 {
@@ -48,4 +50,5 @@ int main()
   same_type<decltype(h4()),int&>();
   same_type<decltype(h5(a)),int>();
   same_type<decltype(h6(a)),int&>();
+  same_type<decltype(h7(a)),int&>();
 }

Re: C++ PATCH to fix static init with () in a template (PR c++/84582)

[Marek Polacek]

On Tue, Feb 27, 2018 at 04:16:31PM -0500, Jason Merrill wrote:
> On 02/27/2018 02:13 PM, Marek Polacek wrote:
> > My recent change introducing cxx_constant_init caused this code
> > 
> > template <class> class A {
> >    static const long b = 0;
> >    static const unsigned c = (b);
> > };
> > 
> > to be rejected.  The reason is that force_paren_expr turns "b" into "*(const
> > long int &) &b", where the former is not value-dependent but the latter is
> > value-dependent.  So when we get to maybe_constant_init_1:
> > 5147   if (!is_nondependent_static_init_expression (t))
> > 5148     /* Don't try to evaluate it.  */;
> > it's not evaluated and we get the non-constant initialization error.
> > (Before we'd always evaluated the expression.)
> > 
> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> > 
> > 2018-02-27  Marek Polacek  <polacek@redhat.com>
> > 
> > 	PR c++/84582
> > 	* semantics.c (force_paren_expr): Avoid creating a static cast
> > 	when processing a template.
> > 
> > 	* g++.dg/cpp1z/static1.C: New test.
> > 	* g++.dg/template/static37.C: New test.
> > 
> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> > index 35569d0cb0d..b48de2df4e2 100644
> > --- gcc/cp/semantics.c
> > +++ gcc/cp/semantics.c
> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
> > -  else
> > +  else if (!processing_template_decl)
> 
> Hmm, this means that we forget about the parentheses in a template.  I'm
> surprised that this didn't break anything in the testsuite.  In particular,
> auto-fn15.C.  I've attached an addition to auto-fn15.C to catch this issue.

Thanks, you're right.  I'll use it.

> Can we use PAREN_EXPR instead of the static_cast in a template?

I don't think so, it would fix the issue you pointed out in auto-fn15.C but
it wouldn't fix the original test.  The problem with using PAREN_EXPR in a
template is that instantiate_non_dependent_expr will turn in into the
static cast anyway; tsubst_copy_and_build has
    case PAREN_EXPR:
      RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND (t, 0))));
so it calls force_paren_expr and this time we're not in a template.  And
then when calling cxx_constant_init we have the same issue.

Should we play some ugly games with maybe_undo_parenthesized_ref?

	Marek

Re: C++ PATCH to fix static init with () in a template (PR c++/84582)

[Jason Merrill]

On Wed, Feb 28, 2018 at 9:32 AM, Marek Polacek <polacek@redhat.com> wrote:
> On Tue, Feb 27, 2018 at 04:16:31PM -0500, Jason Merrill wrote:
>> On 02/27/2018 02:13 PM, Marek Polacek wrote:
>> > My recent change introducing cxx_constant_init caused this code
>> >
>> > template <class> class A {
>> >    static const long b = 0;
>> >    static const unsigned c = (b);
>> > };
>> >
>> > to be rejected.  The reason is that force_paren_expr turns "b" into "*(const
>> > long int &) &b", where the former is not value-dependent but the latter is
>> > value-dependent.  So when we get to maybe_constant_init_1:
>> > 5147   if (!is_nondependent_static_init_expression (t))
>> > 5148     /* Don't try to evaluate it.  */;
>> > it's not evaluated and we get the non-constant initialization error.
>> > (Before we'd always evaluated the expression.)
>> >
>> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
>> >
>> > 2018-02-27  Marek Polacek  <polacek@redhat.com>
>> >
>> >     PR c++/84582
>> >     * semantics.c (force_paren_expr): Avoid creating a static cast
>> >     when processing a template.
>> >
>> >     * g++.dg/cpp1z/static1.C: New test.
>> >     * g++.dg/template/static37.C: New test.
>> >
>> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
>> > index 35569d0cb0d..b48de2df4e2 100644
>> > --- gcc/cp/semantics.c
>> > +++ gcc/cp/semantics.c
>> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
>> > -  else
>> > +  else if (!processing_template_decl)
>>
>> Hmm, this means that we forget about the parentheses in a template.  I'm
>> surprised that this didn't break anything in the testsuite.  In particular,
>> auto-fn15.C.  I've attached an addition to auto-fn15.C to catch this issue.
>
> Thanks, you're right.  I'll use it.
>
>> Can we use PAREN_EXPR instead of the static_cast in a template?
>
> I don't think so, it would fix the issue you pointed out in auto-fn15.C but
> it wouldn't fix the original test.  The problem with using PAREN_EXPR in a
> template is that instantiate_non_dependent_expr will turn in into the
> static cast anyway; tsubst_copy_and_build has
>     case PAREN_EXPR:
>       RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND (t, 0))));
> so it calls force_paren_expr and this time we're not in a template.  And
> then when calling cxx_constant_init we have the same issue.

Then maybe we need something like fold_non_dependent_expr, which
checks for dependency before substitution and then immediately
evaluates the result.

Jason

Re: C++ PATCH to fix static init with () in a template (PR c++/84582)

[Marek Polacek]

On Wed, Feb 28, 2018 at 10:51:17AM -0500, Jason Merrill wrote:
> On Wed, Feb 28, 2018 at 9:32 AM, Marek Polacek <polacek@redhat.com> wrote:
> > On Tue, Feb 27, 2018 at 04:16:31PM -0500, Jason Merrill wrote:
> >> On 02/27/2018 02:13 PM, Marek Polacek wrote:
> >> > My recent change introducing cxx_constant_init caused this code
> >> >
> >> > template <class> class A {
> >> >    static const long b = 0;
> >> >    static const unsigned c = (b);
> >> > };
> >> >
> >> > to be rejected.  The reason is that force_paren_expr turns "b" into "*(const
> >> > long int &) &b", where the former is not value-dependent but the latter is
> >> > value-dependent.  So when we get to maybe_constant_init_1:
> >> > 5147   if (!is_nondependent_static_init_expression (t))
> >> > 5148     /* Don't try to evaluate it.  */;
> >> > it's not evaluated and we get the non-constant initialization error.
> >> > (Before we'd always evaluated the expression.)
> >> >
> >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> >> >
> >> > 2018-02-27  Marek Polacek  <polacek@redhat.com>
> >> >
> >> >     PR c++/84582
> >> >     * semantics.c (force_paren_expr): Avoid creating a static cast
> >> >     when processing a template.
> >> >
> >> >     * g++.dg/cpp1z/static1.C: New test.
> >> >     * g++.dg/template/static37.C: New test.
> >> >
> >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> >> > index 35569d0cb0d..b48de2df4e2 100644
> >> > --- gcc/cp/semantics.c
> >> > +++ gcc/cp/semantics.c
> >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
> >> > -  else
> >> > +  else if (!processing_template_decl)
> >>
> >> Hmm, this means that we forget about the parentheses in a template.  I'm
> >> surprised that this didn't break anything in the testsuite.  In particular,
> >> auto-fn15.C.  I've attached an addition to auto-fn15.C to catch this issue.
> >
> > Thanks, you're right.  I'll use it.
> >
> >> Can we use PAREN_EXPR instead of the static_cast in a template?
> >
> > I don't think so, it would fix the issue you pointed out in auto-fn15.C but
> > it wouldn't fix the original test.  The problem with using PAREN_EXPR in a
> > template is that instantiate_non_dependent_expr will turn in into the
> > static cast anyway; tsubst_copy_and_build has
> >     case PAREN_EXPR:
> >       RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND (t, 0))));
> > so it calls force_paren_expr and this time we're not in a template.  And
> > then when calling cxx_constant_init we have the same issue.
> 
> Then maybe we need something like fold_non_dependent_expr, which
> checks for dependency before substitution and then immediately
> evaluates the result.

I hope you meant something like this.  Further testing also revealed that
maybe_undo_parenthesized_ref should be able to unwrap PAREN_EXPR (so that
(fn1)(); in paren2.C is handled correctly), and that lvalue_kind should look
into PAREN_EXPR so as to give the correct answer regarding lvalueness: we
should accept

template<typename T>
void foo (int i)
{
  ++(i);
}

Apologies if I'm on the wrong track.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2018-02-28  Marek Polacek  <polacek@redhat.com>
	    Jason Merrill  <jason@redhat.com>

	PR c++/84582
	* semantics.c (force_paren_expr): Avoid creating the static cast
	when in a template.  Create a PAREN_EXPR when in a template.
	(maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
	* typeck2.c (store_init_value): Call fold_non_dependent_expr instead
	of instantiate_non_dependent_expr.
	* tree.c (lvalue_kind): Handle PAREN_EXPR like NON_DEPENDENT_EXPR.

	* g++.dg/cpp1y/auto-fn15.C: Extend testing.
	* g++.dg/cpp1z/static1.C: New test.
	* g++.dg/template/static37.C: New test.

diff --git gcc/cp/semantics.c gcc/cp/semantics.c
index 35569d0cb0d..722e3718a14 100644
--- gcc/cp/semantics.c
+++ gcc/cp/semantics.c
@@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
-  else
+  else if (!processing_template_decl)
     {
       cp_lvalue_kind kind = lvalue_kind (expr);
       if ((kind & ~clk_class) != clk_none)
@@ -1713,6 +1713,8 @@ force_paren_expr (tree expr)
 	    REF_PARENTHESIZED_P (expr) = true;
 	}
     }
+  else
+    expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);
 
   return expr;
 }
@@ -1724,9 +1726,10 @@ force_paren_expr (tree expr)
 tree
 maybe_undo_parenthesized_ref (tree t)
 {
-  if (cxx_dialect >= cxx14
-      && INDIRECT_REF_P (t)
-      && REF_PARENTHESIZED_P (t))
+  if (cxx_dialect < cxx14)
+    return t;
+
+  if (INDIRECT_REF_P (t) && REF_PARENTHESIZED_P (t))
     {
       t = TREE_OPERAND (t, 0);
       while (TREE_CODE (t) == NON_LVALUE_EXPR
@@ -1737,6 +1740,8 @@ maybe_undo_parenthesized_ref (tree t)
 		  || TREE_CODE (t) == STATIC_CAST_EXPR);
       t = TREE_OPERAND (t, 0);
     }
+  else if (TREE_CODE (t) == PAREN_EXPR)
+    t = TREE_OPERAND (t, 0);
 
   return t;
 }
diff --git gcc/cp/tree.c gcc/cp/tree.c
index 9b9e36a1173..19f1c0629c9 100644
--- gcc/cp/tree.c
+++ gcc/cp/tree.c
@@ -239,6 +239,7 @@ lvalue_kind (const_tree ref)
       return lvalue_kind (BASELINK_FUNCTIONS (CONST_CAST_TREE (ref)));
 
     case NON_DEPENDENT_EXPR:
+    case PAREN_EXPR:
       return lvalue_kind (TREE_OPERAND (ref, 0));
 
     case VIEW_CONVERT_EXPR:
diff --git gcc/cp/typeck2.c gcc/cp/typeck2.c
index 153b46cca77..583c65d4d0a 100644
--- gcc/cp/typeck2.c
+++ gcc/cp/typeck2.c
@@ -822,7 +822,7 @@ store_init_value (tree decl, tree init, vec<tree, va_gc>** cleanups, int flags)
   if (decl_maybe_constant_var_p (decl) || TREE_STATIC (decl))
     {
       bool const_init;
-      value = instantiate_non_dependent_expr (value);
+      value = fold_non_dependent_expr (value);
       if (DECL_DECLARED_CONSTEXPR_P (decl)
 	  || (DECL_IN_AGGR_P (decl) && !DECL_VAR_DECLARED_INLINE_P (decl)))
 	{
diff --git gcc/testsuite/g++.dg/cpp1y/auto-fn15.C gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
index ba9f3579f62..0db428f7270 100644
--- gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
+++ gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
@@ -22,6 +22,8 @@ template <class T>
 decltype(auto) h5(T t) { return t.i; }
 template <class T>
 decltype(auto) h6(T t) { return (t.i); }
+template <class T>
+decltype(auto) h7(T t) { return (i); }
 
 int main()
 {
@@ -48,4 +50,5 @@ int main()
   same_type<decltype(h4()),int&>();
   same_type<decltype(h5(a)),int>();
   same_type<decltype(h6(a)),int&>();
+  same_type<decltype(h7(a)),int&>();
 }
diff --git gcc/testsuite/g++.dg/cpp1z/static1.C gcc/testsuite/g++.dg/cpp1z/static1.C
index e69de29bb2d..cb872997c5a 100644
--- gcc/testsuite/g++.dg/cpp1z/static1.C
+++ gcc/testsuite/g++.dg/cpp1z/static1.C
@@ -0,0 +1,19 @@
+// PR c++/84582
+// { dg-options -std=c++17 }
+
+class C {
+  static inline const long b = 0;
+  static inline const unsigned c = (b);
+};
+class D {
+  static inline const long b = 0;
+  static inline const unsigned c = b;
+};
+template <class> class A {
+  static inline const long b = 0;
+  static inline const unsigned c = (b);
+};
+template <class> class B {
+  static inline const long b = 0;
+  static inline const unsigned c = b;
+};
diff --git gcc/testsuite/g++.dg/template/static37.C gcc/testsuite/g++.dg/template/static37.C
index e69de29bb2d..90bc65d2fbc 100644
--- gcc/testsuite/g++.dg/template/static37.C
+++ gcc/testsuite/g++.dg/template/static37.C
@@ -0,0 +1,18 @@
+// PR c++/84582
+
+class C {
+  static const long b = 0;
+  static const unsigned c = (b);
+};
+class D {
+  static const long b = 0;
+  static const unsigned c = b;
+};
+template <class> class A {
+  static const long b = 0;
+  static const unsigned c = (b);
+};
+template <class> class B {
+  static const long b = 0;
+  static const unsigned c = b;
+};

	Marek

Re: C++ PATCH to fix static init with () in a template (PR c++/84582)

[Jason Merrill]

On Wed, Feb 28, 2018 at 4:19 PM, Marek Polacek <polacek@redhat.com> wrote:
> On Wed, Feb 28, 2018 at 10:51:17AM -0500, Jason Merrill wrote:
>> On Wed, Feb 28, 2018 at 9:32 AM, Marek Polacek <polacek@redhat.com> wrote:
>> > On Tue, Feb 27, 2018 at 04:16:31PM -0500, Jason Merrill wrote:
>> >> On 02/27/2018 02:13 PM, Marek Polacek wrote:
>> >> > My recent change introducing cxx_constant_init caused this code
>> >> >
>> >> > template <class> class A {
>> >> >    static const long b = 0;
>> >> >    static const unsigned c = (b);
>> >> > };
>> >> >
>> >> > to be rejected.  The reason is that force_paren_expr turns "b" into "*(const
>> >> > long int &) &b", where the former is not value-dependent but the latter is
>> >> > value-dependent.  So when we get to maybe_constant_init_1:
>> >> > 5147   if (!is_nondependent_static_init_expression (t))
>> >> > 5148     /* Don't try to evaluate it.  */;
>> >> > it's not evaluated and we get the non-constant initialization error.
>> >> > (Before we'd always evaluated the expression.)
>> >> >
>> >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
>> >> >
>> >> > 2018-02-27  Marek Polacek  <polacek@redhat.com>
>> >> >
>> >> >     PR c++/84582
>> >> >     * semantics.c (force_paren_expr): Avoid creating a static cast
>> >> >     when processing a template.
>> >> >
>> >> >     * g++.dg/cpp1z/static1.C: New test.
>> >> >     * g++.dg/template/static37.C: New test.
>> >> >
>> >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
>> >> > index 35569d0cb0d..b48de2df4e2 100644
>> >> > --- gcc/cp/semantics.c
>> >> > +++ gcc/cp/semantics.c
>> >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
>> >> > -  else
>> >> > +  else if (!processing_template_decl)
>> >>
>> >> Hmm, this means that we forget about the parentheses in a template.  I'm
>> >> surprised that this didn't break anything in the testsuite.  In particular,
>> >> auto-fn15.C.  I've attached an addition to auto-fn15.C to catch this issue.
>> >
>> > Thanks, you're right.  I'll use it.
>> >
>> >> Can we use PAREN_EXPR instead of the static_cast in a template?
>> >
>> > I don't think so, it would fix the issue you pointed out in auto-fn15.C but
>> > it wouldn't fix the original test.  The problem with using PAREN_EXPR in a
>> > template is that instantiate_non_dependent_expr will turn in into the
>> > static cast anyway; tsubst_copy_and_build has
>> >     case PAREN_EXPR:
>> >       RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND (t, 0))));
>> > so it calls force_paren_expr and this time we're not in a template.  And
>> > then when calling cxx_constant_init we have the same issue.
>>
>> Then maybe we need something like fold_non_dependent_expr, which
>> checks for dependency before substitution and then immediately
>> evaluates the result.
>
> I hope you meant something like this.  Further testing also revealed that
> maybe_undo_parenthesized_ref should be able to unwrap PAREN_EXPR (so that
> (fn1)(); in paren2.C is handled correctly), and that lvalue_kind should look
> into PAREN_EXPR so as to give the correct answer regarding lvalueness: we
> should accept
>
> template<typename T>
> void foo (int i)
> {
>   ++(i);
> }
>
> Apologies if I'm on the wrong track.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2018-02-28  Marek Polacek  <polacek@redhat.com>
>             Jason Merrill  <jason@redhat.com>
>
>         PR c++/84582
>         * semantics.c (force_paren_expr): Avoid creating the static cast
>         when in a template.  Create a PAREN_EXPR when in a template.
>         (maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
>         * typeck2.c (store_init_value): Call fold_non_dependent_expr instead
>         of instantiate_non_dependent_expr.
>         * tree.c (lvalue_kind): Handle PAREN_EXPR like NON_DEPENDENT_EXPR.
>
>         * g++.dg/cpp1y/auto-fn15.C: Extend testing.
>         * g++.dg/cpp1z/static1.C: New test.
>         * g++.dg/template/static37.C: New test.
>
> diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> index 35569d0cb0d..722e3718a14 100644
> --- gcc/cp/semantics.c
> +++ gcc/cp/semantics.c
> @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
> -  else
> +  else if (!processing_template_decl)
>      {
>        cp_lvalue_kind kind = lvalue_kind (expr);
>        if ((kind & ~clk_class) != clk_none)
> @@ -1713,6 +1713,8 @@ force_paren_expr (tree expr)
>             REF_PARENTHESIZED_P (expr) = true;
>         }
>      }
> +  else
> +    expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);

There's already a branch for building PAREN_EXPR, let's just replace
its condition.

> -      value = instantiate_non_dependent_expr (value);
> +      value = fold_non_dependent_expr (value);

I was thinking that we want a parallel fold_non_dependent_init (that
hopefully shares most of the implementation).  Then we shouldn't need
the call to maybe_constant_init anymore.

Jason

Re: C++ PATCH to fix static init with () in a template (PR c++/84582)

[Marek Polacek]

On Wed, Feb 28, 2018 at 04:50:39PM -0500, Jason Merrill wrote:
> On Wed, Feb 28, 2018 at 4:19 PM, Marek Polacek <polacek@redhat.com> wrote:
> > On Wed, Feb 28, 2018 at 10:51:17AM -0500, Jason Merrill wrote:
> >> On Wed, Feb 28, 2018 at 9:32 AM, Marek Polacek <polacek@redhat.com> wrote:
> >> > On Tue, Feb 27, 2018 at 04:16:31PM -0500, Jason Merrill wrote:
> >> >> On 02/27/2018 02:13 PM, Marek Polacek wrote:
> >> >> > My recent change introducing cxx_constant_init caused this code
> >> >> >
> >> >> > template <class> class A {
> >> >> >    static const long b = 0;
> >> >> >    static const unsigned c = (b);
> >> >> > };
> >> >> >
> >> >> > to be rejected.  The reason is that force_paren_expr turns "b" into "*(const
> >> >> > long int &) &b", where the former is not value-dependent but the latter is
> >> >> > value-dependent.  So when we get to maybe_constant_init_1:
> >> >> > 5147   if (!is_nondependent_static_init_expression (t))
> >> >> > 5148     /* Don't try to evaluate it.  */;
> >> >> > it's not evaluated and we get the non-constant initialization error.
> >> >> > (Before we'd always evaluated the expression.)
> >> >> >
> >> >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> >> >> >
> >> >> > 2018-02-27  Marek Polacek  <polacek@redhat.com>
> >> >> >
> >> >> >     PR c++/84582
> >> >> >     * semantics.c (force_paren_expr): Avoid creating a static cast
> >> >> >     when processing a template.
> >> >> >
> >> >> >     * g++.dg/cpp1z/static1.C: New test.
> >> >> >     * g++.dg/template/static37.C: New test.
> >> >> >
> >> >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> >> >> > index 35569d0cb0d..b48de2df4e2 100644
> >> >> > --- gcc/cp/semantics.c
> >> >> > +++ gcc/cp/semantics.c
> >> >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
> >> >> > -  else
> >> >> > +  else if (!processing_template_decl)
> >> >>
> >> >> Hmm, this means that we forget about the parentheses in a template.  I'm
> >> >> surprised that this didn't break anything in the testsuite.  In particular,
> >> >> auto-fn15.C.  I've attached an addition to auto-fn15.C to catch this issue.
> >> >
> >> > Thanks, you're right.  I'll use it.
> >> >
> >> >> Can we use PAREN_EXPR instead of the static_cast in a template?
> >> >
> >> > I don't think so, it would fix the issue you pointed out in auto-fn15.C but
> >> > it wouldn't fix the original test.  The problem with using PAREN_EXPR in a
> >> > template is that instantiate_non_dependent_expr will turn in into the
> >> > static cast anyway; tsubst_copy_and_build has
> >> >     case PAREN_EXPR:
> >> >       RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND (t, 0))));
> >> > so it calls force_paren_expr and this time we're not in a template.  And
> >> > then when calling cxx_constant_init we have the same issue.
> >>
> >> Then maybe we need something like fold_non_dependent_expr, which
> >> checks for dependency before substitution and then immediately
> >> evaluates the result.
> >
> > I hope you meant something like this.  Further testing also revealed that
> > maybe_undo_parenthesized_ref should be able to unwrap PAREN_EXPR (so that
> > (fn1)(); in paren2.C is handled correctly), and that lvalue_kind should look
> > into PAREN_EXPR so as to give the correct answer regarding lvalueness: we
> > should accept
> >
> > template<typename T>
> > void foo (int i)
> > {
> >   ++(i);
> > }
> >
> > Apologies if I'm on the wrong track.
> >
> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> >
> > 2018-02-28  Marek Polacek  <polacek@redhat.com>
> >             Jason Merrill  <jason@redhat.com>
> >
> >         PR c++/84582
> >         * semantics.c (force_paren_expr): Avoid creating the static cast
> >         when in a template.  Create a PAREN_EXPR when in a template.
> >         (maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
> >         * typeck2.c (store_init_value): Call fold_non_dependent_expr instead
> >         of instantiate_non_dependent_expr.
> >         * tree.c (lvalue_kind): Handle PAREN_EXPR like NON_DEPENDENT_EXPR.
> >
> >         * g++.dg/cpp1y/auto-fn15.C: Extend testing.
> >         * g++.dg/cpp1z/static1.C: New test.
> >         * g++.dg/template/static37.C: New test.
> >
> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> > index 35569d0cb0d..722e3718a14 100644
> > --- gcc/cp/semantics.c
> > +++ gcc/cp/semantics.c
> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
> > -  else
> > +  else if (!processing_template_decl)
> >      {
> >        cp_lvalue_kind kind = lvalue_kind (expr);
> >        if ((kind & ~clk_class) != clk_none)
> > @@ -1713,6 +1713,8 @@ force_paren_expr (tree expr)
> >             REF_PARENTHESIZED_P (expr) = true;
> >         }
> >      }
> > +  else
> > +    expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);
> 
> There's already a branch for building PAREN_EXPR, let's just replace
> its condition.

Sure.

> > -      value = instantiate_non_dependent_expr (value);
> > +      value = fold_non_dependent_expr (value);
> 
> I was thinking that we want a parallel fold_non_dependent_init (that
> hopefully shares most of the implementation).  Then we shouldn't need
> the call to maybe_constant_init anymore.

If you mean fold_non_dependent_init that would be like fold_non_dependent_expr
but with maybe_constant_init and not maybe_constant_value, then that would
break e.g.

const double d = 9.0;   // missing constexpr
constexpr double j = d; // should give error

because maybe_constant_value checks is_nondependent_constant_expression, and
"d" in the example above is not a constant expression, so we don't evaluate,
and "d" stays "d", so require_constant_expression gives the error.  On the
other hand, maybe_constant_init checks is_nondependent_static_init_expression,
and "d" is that, so we evaluate "d" to "9.0".  Then require_constant_expression
doesn't complain.

What problem do you see with using fold_non_dependent_expr?

Thanks,

	Marek

Re: C++ PATCH to fix static init with () in a template (PR c++/84582)

[Jason Merrill]

On Thu, Mar 1, 2018 at 8:17 AM, Marek Polacek <polacek@redhat.com> wrote:
> On Wed, Feb 28, 2018 at 04:50:39PM -0500, Jason Merrill wrote:
>> On Wed, Feb 28, 2018 at 4:19 PM, Marek Polacek <polacek@redhat.com> wrote:
>> > On Wed, Feb 28, 2018 at 10:51:17AM -0500, Jason Merrill wrote:
>> >> On Wed, Feb 28, 2018 at 9:32 AM, Marek Polacek <polacek@redhat.com> wrote:
>> >> > On Tue, Feb 27, 2018 at 04:16:31PM -0500, Jason Merrill wrote:
>> >> >> On 02/27/2018 02:13 PM, Marek Polacek wrote:
>> >> >> > My recent change introducing cxx_constant_init caused this code
>> >> >> >
>> >> >> > template <class> class A {
>> >> >> >    static const long b = 0;
>> >> >> >    static const unsigned c = (b);
>> >> >> > };
>> >> >> >
>> >> >> > to be rejected.  The reason is that force_paren_expr turns "b" into "*(const
>> >> >> > long int &) &b", where the former is not value-dependent but the latter is
>> >> >> > value-dependent.  So when we get to maybe_constant_init_1:
>> >> >> > 5147   if (!is_nondependent_static_init_expression (t))
>> >> >> > 5148     /* Don't try to evaluate it.  */;
>> >> >> > it's not evaluated and we get the non-constant initialization error.
>> >> >> > (Before we'd always evaluated the expression.)
>> >> >> >
>> >> >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
>> >> >> >
>> >> >> > 2018-02-27  Marek Polacek  <polacek@redhat.com>
>> >> >> >
>> >> >> >     PR c++/84582
>> >> >> >     * semantics.c (force_paren_expr): Avoid creating a static cast
>> >> >> >     when processing a template.
>> >> >> >
>> >> >> >     * g++.dg/cpp1z/static1.C: New test.
>> >> >> >     * g++.dg/template/static37.C: New test.
>> >> >> >
>> >> >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
>> >> >> > index 35569d0cb0d..b48de2df4e2 100644
>> >> >> > --- gcc/cp/semantics.c
>> >> >> > +++ gcc/cp/semantics.c
>> >> >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
>> >> >> > -  else
>> >> >> > +  else if (!processing_template_decl)
>> >> >>
>> >> >> Hmm, this means that we forget about the parentheses in a template.  I'm
>> >> >> surprised that this didn't break anything in the testsuite.  In particular,
>> >> >> auto-fn15.C.  I've attached an addition to auto-fn15.C to catch this issue.
>> >> >
>> >> > Thanks, you're right.  I'll use it.
>> >> >
>> >> >> Can we use PAREN_EXPR instead of the static_cast in a template?
>> >> >
>> >> > I don't think so, it would fix the issue you pointed out in auto-fn15.C but
>> >> > it wouldn't fix the original test.  The problem with using PAREN_EXPR in a
>> >> > template is that instantiate_non_dependent_expr will turn in into the
>> >> > static cast anyway; tsubst_copy_and_build has
>> >> >     case PAREN_EXPR:
>> >> >       RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND (t, 0))));
>> >> > so it calls force_paren_expr and this time we're not in a template.  And
>> >> > then when calling cxx_constant_init we have the same issue.
>> >>
>> >> Then maybe we need something like fold_non_dependent_expr, which
>> >> checks for dependency before substitution and then immediately
>> >> evaluates the result.
>> >
>> > I hope you meant something like this.  Further testing also revealed that
>> > maybe_undo_parenthesized_ref should be able to unwrap PAREN_EXPR (so that
>> > (fn1)(); in paren2.C is handled correctly), and that lvalue_kind should look
>> > into PAREN_EXPR so as to give the correct answer regarding lvalueness: we
>> > should accept
>> >
>> > template<typename T>
>> > void foo (int i)
>> > {
>> >   ++(i);
>> > }
>> >
>> > Apologies if I'm on the wrong track.
>> >
>> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
>> >
>> > 2018-02-28  Marek Polacek  <polacek@redhat.com>
>> >             Jason Merrill  <jason@redhat.com>
>> >
>> >         PR c++/84582
>> >         * semantics.c (force_paren_expr): Avoid creating the static cast
>> >         when in a template.  Create a PAREN_EXPR when in a template.
>> >         (maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
>> >         * typeck2.c (store_init_value): Call fold_non_dependent_expr instead
>> >         of instantiate_non_dependent_expr.
>> >         * tree.c (lvalue_kind): Handle PAREN_EXPR like NON_DEPENDENT_EXPR.
>> >
>> >         * g++.dg/cpp1y/auto-fn15.C: Extend testing.
>> >         * g++.dg/cpp1z/static1.C: New test.
>> >         * g++.dg/template/static37.C: New test.
>> >
>> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
>> > index 35569d0cb0d..722e3718a14 100644
>> > --- gcc/cp/semantics.c
>> > +++ gcc/cp/semantics.c
>> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
>> > -  else
>> > +  else if (!processing_template_decl)
>> >      {
>> >        cp_lvalue_kind kind = lvalue_kind (expr);
>> >        if ((kind & ~clk_class) != clk_none)
>> > @@ -1713,6 +1713,8 @@ force_paren_expr (tree expr)
>> >             REF_PARENTHESIZED_P (expr) = true;
>> >         }
>> >      }
>> > +  else
>> > +    expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);
>>
>> There's already a branch for building PAREN_EXPR, let's just replace
>> its condition.
>
> Sure.
>
>> > -      value = instantiate_non_dependent_expr (value);
>> > +      value = fold_non_dependent_expr (value);
>>
>> I was thinking that we want a parallel fold_non_dependent_init (that
>> hopefully shares most of the implementation).  Then we shouldn't need
>> the call to maybe_constant_init anymore.
>
> If you mean fold_non_dependent_init that would be like fold_non_dependent_expr
> but with maybe_constant_init and not maybe_constant_value

And is_nondependent_static_init_expression, and different arguments to
cxx_eval_outermost_constant_expression, yes.

> then that would break e.g.
>
> const double d = 9.0;   // missing constexpr
> constexpr double j = d; // should give error
>
> because maybe_constant_value checks is_nondependent_constant_expression, and
> "d" in the example above is not a constant expression, so we don't evaluate,
> and "d" stays "d", so require_constant_expression gives the error.  On the
> other hand, maybe_constant_init checks is_nondependent_static_init_expression,
> and "d" is that, so we evaluate "d" to "9.0".  Then require_constant_expression
> doesn't complain.

Ah, I see.  You're right, let's stick with fold_non_dependent_expr.

Jason

Re: C++ PATCH to fix static init with () in a template (PR c++/84582)

[Marek Polacek]

On Thu, Mar 01, 2018 at 01:56:50PM -0500, Jason Merrill wrote:
> On Thu, Mar 1, 2018 at 8:17 AM, Marek Polacek <polacek@redhat.com> wrote:
> > On Wed, Feb 28, 2018 at 04:50:39PM -0500, Jason Merrill wrote:
> >> On Wed, Feb 28, 2018 at 4:19 PM, Marek Polacek <polacek@redhat.com> wrote:
> >> > On Wed, Feb 28, 2018 at 10:51:17AM -0500, Jason Merrill wrote:
> >> >> On Wed, Feb 28, 2018 at 9:32 AM, Marek Polacek <polacek@redhat.com> wrote:
> >> >> > On Tue, Feb 27, 2018 at 04:16:31PM -0500, Jason Merrill wrote:
> >> >> >> On 02/27/2018 02:13 PM, Marek Polacek wrote:
> >> >> >> > My recent change introducing cxx_constant_init caused this code
> >> >> >> >
> >> >> >> > template <class> class A {
> >> >> >> >    static const long b = 0;
> >> >> >> >    static const unsigned c = (b);
> >> >> >> > };
> >> >> >> >
> >> >> >> > to be rejected.  The reason is that force_paren_expr turns "b" into "*(const
> >> >> >> > long int &) &b", where the former is not value-dependent but the latter is
> >> >> >> > value-dependent.  So when we get to maybe_constant_init_1:
> >> >> >> > 5147   if (!is_nondependent_static_init_expression (t))
> >> >> >> > 5148     /* Don't try to evaluate it.  */;
> >> >> >> > it's not evaluated and we get the non-constant initialization error.
> >> >> >> > (Before we'd always evaluated the expression.)
> >> >> >> >
> >> >> >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> >> >> >> >
> >> >> >> > 2018-02-27  Marek Polacek  <polacek@redhat.com>
> >> >> >> >
> >> >> >> >     PR c++/84582
> >> >> >> >     * semantics.c (force_paren_expr): Avoid creating a static cast
> >> >> >> >     when processing a template.
> >> >> >> >
> >> >> >> >     * g++.dg/cpp1z/static1.C: New test.
> >> >> >> >     * g++.dg/template/static37.C: New test.
> >> >> >> >
> >> >> >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> >> >> >> > index 35569d0cb0d..b48de2df4e2 100644
> >> >> >> > --- gcc/cp/semantics.c
> >> >> >> > +++ gcc/cp/semantics.c
> >> >> >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
> >> >> >> > -  else
> >> >> >> > +  else if (!processing_template_decl)
> >> >> >>
> >> >> >> Hmm, this means that we forget about the parentheses in a template.  I'm
> >> >> >> surprised that this didn't break anything in the testsuite.  In particular,
> >> >> >> auto-fn15.C.  I've attached an addition to auto-fn15.C to catch this issue.
> >> >> >
> >> >> > Thanks, you're right.  I'll use it.
> >> >> >
> >> >> >> Can we use PAREN_EXPR instead of the static_cast in a template?
> >> >> >
> >> >> > I don't think so, it would fix the issue you pointed out in auto-fn15.C but
> >> >> > it wouldn't fix the original test.  The problem with using PAREN_EXPR in a
> >> >> > template is that instantiate_non_dependent_expr will turn in into the
> >> >> > static cast anyway; tsubst_copy_and_build has
> >> >> >     case PAREN_EXPR:
> >> >> >       RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND (t, 0))));
> >> >> > so it calls force_paren_expr and this time we're not in a template.  And
> >> >> > then when calling cxx_constant_init we have the same issue.
> >> >>
> >> >> Then maybe we need something like fold_non_dependent_expr, which
> >> >> checks for dependency before substitution and then immediately
> >> >> evaluates the result.
> >> >
> >> > I hope you meant something like this.  Further testing also revealed that
> >> > maybe_undo_parenthesized_ref should be able to unwrap PAREN_EXPR (so that
> >> > (fn1)(); in paren2.C is handled correctly), and that lvalue_kind should look
> >> > into PAREN_EXPR so as to give the correct answer regarding lvalueness: we
> >> > should accept
> >> >
> >> > template<typename T>
> >> > void foo (int i)
> >> > {
> >> >   ++(i);
> >> > }
> >> >
> >> > Apologies if I'm on the wrong track.
> >> >
> >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> >> >
> >> > 2018-02-28  Marek Polacek  <polacek@redhat.com>
> >> >             Jason Merrill  <jason@redhat.com>
> >> >
> >> >         PR c++/84582
> >> >         * semantics.c (force_paren_expr): Avoid creating the static cast
> >> >         when in a template.  Create a PAREN_EXPR when in a template.
> >> >         (maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
> >> >         * typeck2.c (store_init_value): Call fold_non_dependent_expr instead
> >> >         of instantiate_non_dependent_expr.
> >> >         * tree.c (lvalue_kind): Handle PAREN_EXPR like NON_DEPENDENT_EXPR.
> >> >
> >> >         * g++.dg/cpp1y/auto-fn15.C: Extend testing.
> >> >         * g++.dg/cpp1z/static1.C: New test.
> >> >         * g++.dg/template/static37.C: New test.
> >> >
> >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> >> > index 35569d0cb0d..722e3718a14 100644
> >> > --- gcc/cp/semantics.c
> >> > +++ gcc/cp/semantics.c
> >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
> >> > -  else
> >> > +  else if (!processing_template_decl)
> >> >      {
> >> >        cp_lvalue_kind kind = lvalue_kind (expr);
> >> >        if ((kind & ~clk_class) != clk_none)
> >> > @@ -1713,6 +1713,8 @@ force_paren_expr (tree expr)
> >> >             REF_PARENTHESIZED_P (expr) = true;
> >> >         }
> >> >      }
> >> > +  else
> >> > +    expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);
> >>
> >> There's already a branch for building PAREN_EXPR, let's just replace
> >> its condition.
> >
> > Sure.
> >
> >> > -      value = instantiate_non_dependent_expr (value);
> >> > +      value = fold_non_dependent_expr (value);
> >>
> >> I was thinking that we want a parallel fold_non_dependent_init (that
> >> hopefully shares most of the implementation).  Then we shouldn't need
> >> the call to maybe_constant_init anymore.
> >
> > If you mean fold_non_dependent_init that would be like fold_non_dependent_expr
> > but with maybe_constant_init and not maybe_constant_value
> 
> And is_nondependent_static_init_expression, and different arguments to
> cxx_eval_outermost_constant_expression, yes.

Ah.  Maybe it'll be useful sometime in the future.

> > then that would break e.g.
> >
> > const double d = 9.0;   // missing constexpr
> > constexpr double j = d; // should give error
> >
> > because maybe_constant_value checks is_nondependent_constant_expression, and
> > "d" in the example above is not a constant expression, so we don't evaluate,
> > and "d" stays "d", so require_constant_expression gives the error.  On the
> > other hand, maybe_constant_init checks is_nondependent_static_init_expression,
> > and "d" is that, so we evaluate "d" to "9.0".  Then require_constant_expression
> > doesn't complain.
> 
> Ah, I see.  You're right, let's stick with fold_non_dependent_expr.

Thanks, so this is the final patch then:

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2018-03-01  Marek Polacek  <polacek@redhat.com>
	    Jason Merrill  <jason@redhat.com>

	PR c++/84582
	* semantics.c (force_paren_expr): Create a PAREN_EXPR when in
	a template.
	(maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
	* typeck2.c (store_init_value): Call fold_non_dependent_expr instead
	of instantiate_non_dependent_expr.
	* tree.c (lvalue_kind): Handle PAREN_EXPR like NON_DEPENDENT_EXPR.

	* g++.dg/cpp1y/auto-fn15.C: Extend testing.
	* g++.dg/cpp1z/static1.C: New test.
	* g++.dg/template/static37.C: New test.

diff --git gcc/cp/semantics.c gcc/cp/semantics.c
index 87c5c669a55..1ac1d23e761 100644
--- gcc/cp/semantics.c
+++ gcc/cp/semantics.c
@@ -1693,7 +1693,8 @@ force_paren_expr (tree expr)
   if (TREE_CODE (expr) == COMPONENT_REF
       || TREE_CODE (expr) == SCOPE_REF)
     REF_PARENTHESIZED_P (expr) = true;
-  else if (type_dependent_expression_p (expr))
+  else if (type_dependent_expression_p (expr)
+	   || processing_template_decl)
     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.  */;
@@ -1724,9 +1725,10 @@ force_paren_expr (tree expr)
 tree
 maybe_undo_parenthesized_ref (tree t)
 {
-  if (cxx_dialect >= cxx14
-      && INDIRECT_REF_P (t)
-      && REF_PARENTHESIZED_P (t))
+  if (cxx_dialect < cxx14)
+    return t;
+
+  if (INDIRECT_REF_P (t) && REF_PARENTHESIZED_P (t))
     {
       t = TREE_OPERAND (t, 0);
       while (TREE_CODE (t) == NON_LVALUE_EXPR
@@ -1737,6 +1739,8 @@ maybe_undo_parenthesized_ref (tree t)
 		  || TREE_CODE (t) == STATIC_CAST_EXPR);
       t = TREE_OPERAND (t, 0);
     }
+  else if (TREE_CODE (t) == PAREN_EXPR)
+    t = TREE_OPERAND (t, 0);
 
   return t;
 }
diff --git gcc/cp/tree.c gcc/cp/tree.c
index 9b9e36a1173..19f1c0629c9 100644
--- gcc/cp/tree.c
+++ gcc/cp/tree.c
@@ -239,6 +239,7 @@ lvalue_kind (const_tree ref)
       return lvalue_kind (BASELINK_FUNCTIONS (CONST_CAST_TREE (ref)));
 
     case NON_DEPENDENT_EXPR:
+    case PAREN_EXPR:
       return lvalue_kind (TREE_OPERAND (ref, 0));
 
     case VIEW_CONVERT_EXPR:
diff --git gcc/cp/typeck2.c gcc/cp/typeck2.c
index 153b46cca77..583c65d4d0a 100644
--- gcc/cp/typeck2.c
+++ gcc/cp/typeck2.c
@@ -822,7 +822,7 @@ store_init_value (tree decl, tree init, vec<tree, va_gc>** cleanups, int flags)
   if (decl_maybe_constant_var_p (decl) || TREE_STATIC (decl))
     {
       bool const_init;
-      value = instantiate_non_dependent_expr (value);
+      value = fold_non_dependent_expr (value);
       if (DECL_DECLARED_CONSTEXPR_P (decl)
 	  || (DECL_IN_AGGR_P (decl) && !DECL_VAR_DECLARED_INLINE_P (decl)))
 	{
diff --git gcc/testsuite/g++.dg/cpp1y/auto-fn15.C gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
index ba9f3579f62..0db428f7270 100644
--- gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
+++ gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
@@ -22,6 +22,8 @@ template <class T>
 decltype(auto) h5(T t) { return t.i; }
 template <class T>
 decltype(auto) h6(T t) { return (t.i); }
+template <class T>
+decltype(auto) h7(T t) { return (i); }
 
 int main()
 {
@@ -48,4 +50,5 @@ int main()
   same_type<decltype(h4()),int&>();
   same_type<decltype(h5(a)),int>();
   same_type<decltype(h6(a)),int&>();
+  same_type<decltype(h7(a)),int&>();
 }
diff --git gcc/testsuite/g++.dg/cpp1z/static1.C gcc/testsuite/g++.dg/cpp1z/static1.C
index e69de29bb2d..cb872997c5a 100644
--- gcc/testsuite/g++.dg/cpp1z/static1.C
+++ gcc/testsuite/g++.dg/cpp1z/static1.C
@@ -0,0 +1,19 @@
+// PR c++/84582
+// { dg-options -std=c++17 }
+
+class C {
+  static inline const long b = 0;
+  static inline const unsigned c = (b);
+};
+class D {
+  static inline const long b = 0;
+  static inline const unsigned c = b;
+};
+template <class> class A {
+  static inline const long b = 0;
+  static inline const unsigned c = (b);
+};
+template <class> class B {
+  static inline const long b = 0;
+  static inline const unsigned c = b;
+};
diff --git gcc/testsuite/g++.dg/template/static37.C gcc/testsuite/g++.dg/template/static37.C
index e69de29bb2d..90bc65d2fbc 100644
--- gcc/testsuite/g++.dg/template/static37.C
+++ gcc/testsuite/g++.dg/template/static37.C
@@ -0,0 +1,18 @@
+// PR c++/84582
+
+class C {
+  static const long b = 0;
+  static const unsigned c = (b);
+};
+class D {
+  static const long b = 0;
+  static const unsigned c = b;
+};
+template <class> class A {
+  static const long b = 0;
+  static const unsigned c = (b);
+};
+template <class> class B {
+  static const long b = 0;
+  static const unsigned c = b;
+};

	Marek

Re: C++ PATCH to fix static init with () in a template (PR c++/84582)

[Jason Merrill]

Ok.

On Mar 1, 2018 4:40 PM, "Marek Polacek" <polacek@redhat.com> wrote:

> On Thu, Mar 01, 2018 at 01:56:50PM -0500, Jason Merrill wrote:
> > On Thu, Mar 1, 2018 at 8:17 AM, Marek Polacek <polacek@redhat.com>
> wrote:
> > > On Wed, Feb 28, 2018 at 04:50:39PM -0500, Jason Merrill wrote:
> > >> On Wed, Feb 28, 2018 at 4:19 PM, Marek Polacek <polacek@redhat.com>
> wrote:
> > >> > On Wed, Feb 28, 2018 at 10:51:17AM -0500, Jason Merrill wrote:
> > >> >> On Wed, Feb 28, 2018 at 9:32 AM, Marek Polacek <polacek@redhat.com>
> wrote:
> > >> >> > On Tue, Feb 27, 2018 at 04:16:31PM -0500, Jason Merrill wrote:
> > >> >> >> On 02/27/2018 02:13 PM, Marek Polacek wrote:
> > >> >> >> > My recent change introducing cxx_constant_init caused this
> code
> > >> >> >> >
> > >> >> >> > template <class> class A {
> > >> >> >> >    static const long b = 0;
> > >> >> >> >    static const unsigned c = (b);
> > >> >> >> > };
> > >> >> >> >
> > >> >> >> > to be rejected.  The reason is that force_paren_expr turns
> "b" into "*(const
> > >> >> >> > long int &) &b", where the former is not value-dependent but
> the latter is
> > >> >> >> > value-dependent.  So when we get to maybe_constant_init_1:
> > >> >> >> > 5147   if (!is_nondependent_static_init_expression (t))
> > >> >> >> > 5148     /* Don't try to evaluate it.  */;
> > >> >> >> > it's not evaluated and we get the non-constant initialization
> error.
> > >> >> >> > (Before we'd always evaluated the expression.)
> > >> >> >> >
> > >> >> >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> > >> >> >> >
> > >> >> >> > 2018-02-27  Marek Polacek  <polacek@redhat.com>
> > >> >> >> >
> > >> >> >> >     PR c++/84582
> > >> >> >> >     * semantics.c (force_paren_expr): Avoid creating a static
> cast
> > >> >> >> >     when processing a template.
> > >> >> >> >
> > >> >> >> >     * g++.dg/cpp1z/static1.C: New test.
> > >> >> >> >     * g++.dg/template/static37.C: New test.
> > >> >> >> >
> > >> >> >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> > >> >> >> > index 35569d0cb0d..b48de2df4e2 100644
> > >> >> >> > --- gcc/cp/semantics.c
> > >> >> >> > +++ gcc/cp/semantics.c
> > >> >> >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
> > >> >> >> > -  else
> > >> >> >> > +  else if (!processing_template_decl)
> > >> >> >>
> > >> >> >> Hmm, this means that we forget about the parentheses in a
> template.  I'm
> > >> >> >> surprised that this didn't break anything in the testsuite.  In
> particular,
> > >> >> >> auto-fn15.C.  I've attached an addition to auto-fn15.C to catch
> this issue.
> > >> >> >
> > >> >> > Thanks, you're right.  I'll use it.
> > >> >> >
> > >> >> >> Can we use PAREN_EXPR instead of the static_cast in a template?
> > >> >> >
> > >> >> > I don't think so, it would fix the issue you pointed out in
> auto-fn15.C but
> > >> >> > it wouldn't fix the original test.  The problem with using
> PAREN_EXPR in a
> > >> >> > template is that instantiate_non_dependent_expr will turn in
> into the
> > >> >> > static cast anyway; tsubst_copy_and_build has
> > >> >> >     case PAREN_EXPR:
> > >> >> >       RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND (t,
> 0))));
> > >> >> > so it calls force_paren_expr and this time we're not in a
> template.  And
> > >> >> > then when calling cxx_constant_init we have the same issue.
> > >> >>
> > >> >> Then maybe we need something like fold_non_dependent_expr, which
> > >> >> checks for dependency before substitution and then immediately
> > >> >> evaluates the result.
> > >> >
> > >> > I hope you meant something like this.  Further testing also
> revealed that
> > >> > maybe_undo_parenthesized_ref should be able to unwrap PAREN_EXPR
> (so that
> > >> > (fn1)(); in paren2.C is handled correctly), and that lvalue_kind
> should look
> > >> > into PAREN_EXPR so as to give the correct answer regarding
> lvalueness: we
> > >> > should accept
> > >> >
> > >> > template<typename T>
> > >> > void foo (int i)
> > >> > {
> > >> >   ++(i);
> > >> > }
> > >> >
> > >> > Apologies if I'm on the wrong track.
> > >> >
> > >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> > >> >
> > >> > 2018-02-28  Marek Polacek  <polacek@redhat.com>
> > >> >             Jason Merrill  <jason@redhat.com>
> > >> >
> > >> >         PR c++/84582
> > >> >         * semantics.c (force_paren_expr): Avoid creating the static
> cast
> > >> >         when in a template.  Create a PAREN_EXPR when in a template.
> > >> >         (maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
> > >> >         * typeck2.c (store_init_value): Call
> fold_non_dependent_expr instead
> > >> >         of instantiate_non_dependent_expr.
> > >> >         * tree.c (lvalue_kind): Handle PAREN_EXPR like
> NON_DEPENDENT_EXPR.
> > >> >
> > >> >         * g++.dg/cpp1y/auto-fn15.C: Extend testing.
> > >> >         * g++.dg/cpp1z/static1.C: New test.
> > >> >         * g++.dg/template/static37.C: New test.
> > >> >
> > >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> > >> > index 35569d0cb0d..722e3718a14 100644
> > >> > --- gcc/cp/semantics.c
> > >> > +++ gcc/cp/semantics.c
> > >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
> > >> > -  else
> > >> > +  else if (!processing_template_decl)
> > >> >      {
> > >> >        cp_lvalue_kind kind = lvalue_kind (expr);
> > >> >        if ((kind & ~clk_class) != clk_none)
> > >> > @@ -1713,6 +1713,8 @@ force_paren_expr (tree expr)
> > >> >             REF_PARENTHESIZED_P (expr) = true;
> > >> >         }
> > >> >      }
> > >> > +  else
> > >> > +    expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);
> > >>
> > >> There's already a branch for building PAREN_EXPR, let's just replace
> > >> its condition.
> > >
> > > Sure.
> > >
> > >> > -      value = instantiate_non_dependent_expr (value);
> > >> > +      value = fold_non_dependent_expr (value);
> > >>
> > >> I was thinking that we want a parallel fold_non_dependent_init (that
> > >> hopefully shares most of the implementation).  Then we shouldn't need
> > >> the call to maybe_constant_init anymore.
> > >
> > > If you mean fold_non_dependent_init that would be like
> fold_non_dependent_expr
> > > but with maybe_constant_init and not maybe_constant_value
> >
> > And is_nondependent_static_init_expression, and different arguments to
> > cxx_eval_outermost_constant_expression, yes.
>
> Ah.  Maybe it'll be useful sometime in the future.
>
> > > then that would break e.g.
> > >
> > > const double d = 9.0;   // missing constexpr
> > > constexpr double j = d; // should give error
> > >
> > > because maybe_constant_value checks is_nondependent_constant_expression,
> and
> > > "d" in the example above is not a constant expression, so we don't
> evaluate,
> > > and "d" stays "d", so require_constant_expression gives the error.  On
> the
> > > other hand, maybe_constant_init checks is_nondependent_static_init_
> expression,
> > > and "d" is that, so we evaluate "d" to "9.0".  Then
> require_constant_expression
> > > doesn't complain.
> >
> > Ah, I see.  You're right, let's stick with fold_non_dependent_expr.
>
> Thanks, so this is the final patch then:
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2018-03-01  Marek Polacek  <polacek@redhat.com>
>             Jason Merrill  <jason@redhat.com>
>
>         PR c++/84582
>         * semantics.c (force_paren_expr): Create a PAREN_EXPR when in
>         a template.
>         (maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
>         * typeck2.c (store_init_value): Call fold_non_dependent_expr
> instead
>         of instantiate_non_dependent_expr.
>         * tree.c (lvalue_kind): Handle PAREN_EXPR like NON_DEPENDENT_EXPR.
>
>         * g++.dg/cpp1y/auto-fn15.C: Extend testing.
>         * g++.dg/cpp1z/static1.C: New test.
>         * g++.dg/template/static37.C: New test.
>
> diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> index 87c5c669a55..1ac1d23e761 100644
> --- gcc/cp/semantics.c
> +++ gcc/cp/semantics.c
> @@ -1693,7 +1693,8 @@ force_paren_expr (tree expr)
>    if (TREE_CODE (expr) == COMPONENT_REF
>        || TREE_CODE (expr) == SCOPE_REF)
>      REF_PARENTHESIZED_P (expr) = true;
> -  else if (type_dependent_expression_p (expr))
> +  else if (type_dependent_expression_p (expr)
> +          || processing_template_decl)
>      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.  */;
> @@ -1724,9 +1725,10 @@ force_paren_expr (tree expr)
>  tree
>  maybe_undo_parenthesized_ref (tree t)
>  {
> -  if (cxx_dialect >= cxx14
> -      && INDIRECT_REF_P (t)
> -      && REF_PARENTHESIZED_P (t))
> +  if (cxx_dialect < cxx14)
> +    return t;
> +
> +  if (INDIRECT_REF_P (t) && REF_PARENTHESIZED_P (t))
>      {
>        t = TREE_OPERAND (t, 0);
>        while (TREE_CODE (t) == NON_LVALUE_EXPR
> @@ -1737,6 +1739,8 @@ maybe_undo_parenthesized_ref (tree t)
>                   || TREE_CODE (t) == STATIC_CAST_EXPR);
>        t = TREE_OPERAND (t, 0);
>      }
> +  else if (TREE_CODE (t) == PAREN_EXPR)
> +    t = TREE_OPERAND (t, 0);
>
>    return t;
>  }
> diff --git gcc/cp/tree.c gcc/cp/tree.c
> index 9b9e36a1173..19f1c0629c9 100644
> --- gcc/cp/tree.c
> +++ gcc/cp/tree.c
> @@ -239,6 +239,7 @@ lvalue_kind (const_tree ref)
>        return lvalue_kind (BASELINK_FUNCTIONS (CONST_CAST_TREE (ref)));
>
>      case NON_DEPENDENT_EXPR:
> +    case PAREN_EXPR:
>        return lvalue_kind (TREE_OPERAND (ref, 0));
>
>      case VIEW_CONVERT_EXPR:
> diff --git gcc/cp/typeck2.c gcc/cp/typeck2.c
> index 153b46cca77..583c65d4d0a 100644
> --- gcc/cp/typeck2.c
> +++ gcc/cp/typeck2.c
> @@ -822,7 +822,7 @@ store_init_value (tree decl, tree init, vec<tree,
> va_gc>** cleanups, int flags)
>    if (decl_maybe_constant_var_p (decl) || TREE_STATIC (decl))
>      {
>        bool const_init;
> -      value = instantiate_non_dependent_expr (value);
> +      value = fold_non_dependent_expr (value);
>        if (DECL_DECLARED_CONSTEXPR_P (decl)
>           || (DECL_IN_AGGR_P (decl) && !DECL_VAR_DECLARED_INLINE_P (decl)))
>         {
> diff --git gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
> gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
> index ba9f3579f62..0db428f7270 100644
> --- gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
> +++ gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
> @@ -22,6 +22,8 @@ template <class T>
>  decltype(auto) h5(T t) { return t.i; }
>  template <class T>
>  decltype(auto) h6(T t) { return (t.i); }
> +template <class T>
> +decltype(auto) h7(T t) { return (i); }
>
>  int main()
>  {
> @@ -48,4 +50,5 @@ int main()
>    same_type<decltype(h4()),int&>();
>    same_type<decltype(h5(a)),int>();
>    same_type<decltype(h6(a)),int&>();
> +  same_type<decltype(h7(a)),int&>();
>  }
> diff --git gcc/testsuite/g++.dg/cpp1z/static1.C
> gcc/testsuite/g++.dg/cpp1z/static1.C
> index e69de29bb2d..cb872997c5a 100644
> --- gcc/testsuite/g++.dg/cpp1z/static1.C
> +++ gcc/testsuite/g++.dg/cpp1z/static1.C
> @@ -0,0 +1,19 @@
> +// PR c++/84582
> +// { dg-options -std=c++17 }
> +
> +class C {
> +  static inline const long b = 0;
> +  static inline const unsigned c = (b);
> +};
> +class D {
> +  static inline const long b = 0;
> +  static inline const unsigned c = b;
> +};
> +template <class> class A {
> +  static inline const long b = 0;
> +  static inline const unsigned c = (b);
> +};
> +template <class> class B {
> +  static inline const long b = 0;
> +  static inline const unsigned c = b;
> +};
> diff --git gcc/testsuite/g++.dg/template/static37.C
> gcc/testsuite/g++.dg/template/static37.C
> index e69de29bb2d..90bc65d2fbc 100644
> --- gcc/testsuite/g++.dg/template/static37.C
> +++ gcc/testsuite/g++.dg/template/static37.C
> @@ -0,0 +1,18 @@
> +// PR c++/84582
> +
> +class C {
> +  static const long b = 0;
> +  static const unsigned c = (b);
> +};
> +class D {
> +  static const long b = 0;
> +  static const unsigned c = b;
> +};
> +template <class> class A {
> +  static const long b = 0;
> +  static const unsigned c = (b);
> +};
> +template <class> class B {
> +  static const long b = 0;
> +  static const unsigned c = b;
> +};
>
>         Marek
>

Re: C++ PATCH to fix static init with () in a template (PR c++/84582)

[Jason Merrill]

On Mar 1, 2018 4:57 PM, "Jason Merrill" <jason@redhat.com> wrote:

> Ok.
>
> On Mar 1, 2018 4:40 PM, "Marek Polacek" <polacek@redhat.com> wrote:
>
>> On Thu, Mar 01, 2018 at 01:56:50PM -0500, Jason Merrill wrote:
>> > On Thu, Mar 1, 2018 at 8:17 AM, Marek Polacek <polacek@redhat.com>
>> wrote:
>> > > On Wed, Feb 28, 2018 at 04:50:39PM -0500, Jason Merrill wrote:
>> > >> On Wed, Feb 28, 2018 at 4:19 PM, Marek Polacek <polacek@redhat.com>
>> wrote:
>> > >> > On Wed, Feb 28, 2018 at 10:51:17AM -0500, Jason Merrill wrote:
>> > >> >> On Wed, Feb 28, 2018 at 9:32 AM, Marek Polacek <
>> polacek@redhat.com> wrote:
>> > >> >> > On Tue, Feb 27, 2018 at 04:16:31PM -0500, Jason Merrill wrote:
>> > >> >> >> On 02/27/2018 02:13 PM, Marek Polacek wrote:
>> > >> >> >> > My recent change introducing cxx_constant_init caused this
>> code
>> > >> >> >> >
>> > >> >> >> > template <class> class A {
>> > >> >> >> >    static const long b = 0;
>> > >> >> >> >    static const unsigned c = (b);
>> > >> >> >> > };
>> > >> >> >> >
>> > >> >> >> > to be rejected.  The reason is that force_paren_expr turns
>> "b" into "*(const
>> > >> >> >> > long int &) &b", where the former is not value-dependent but
>> the latter is
>> > >> >> >> > value-dependent.  So when we get to maybe_constant_init_1:
>> > >> >> >> > 5147   if (!is_nondependent_static_init_expression (t))
>> > >> >> >> > 5148     /* Don't try to evaluate it.  */;
>> > >> >> >> > it's not evaluated and we get the non-constant
>> initialization error.
>> > >> >> >> > (Before we'd always evaluated the expression.)
>> > >> >> >> >
>> > >> >> >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
>> > >> >> >> >
>> > >> >> >> > 2018-02-27  Marek Polacek  <polacek@redhat.com>
>> > >> >> >> >
>> > >> >> >> >     PR c++/84582
>> > >> >> >> >     * semantics.c (force_paren_expr): Avoid creating a
>> static cast
>> > >> >> >> >     when processing a template.
>> > >> >> >> >
>> > >> >> >> >     * g++.dg/cpp1z/static1.C: New test.
>> > >> >> >> >     * g++.dg/template/static37.C: New test.
>> > >> >> >> >
>> > >> >> >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
>> > >> >> >> > index 35569d0cb0d..b48de2df4e2 100644
>> > >> >> >> > --- gcc/cp/semantics.c
>> > >> >> >> > +++ gcc/cp/semantics.c
>> > >> >> >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
>> > >> >> >> > -  else
>> > >> >> >> > +  else if (!processing_template_decl)
>> > >> >> >>
>> > >> >> >> Hmm, this means that we forget about the parentheses in a
>> template.  I'm
>> > >> >> >> surprised that this didn't break anything in the testsuite.
>> In particular,
>> > >> >> >> auto-fn15.C.  I've attached an addition to auto-fn15.C to
>> catch this issue.
>> > >> >> >
>> > >> >> > Thanks, you're right.  I'll use it.
>> > >> >> >
>> > >> >> >> Can we use PAREN_EXPR instead of the static_cast in a template?
>> > >> >> >
>> > >> >> > I don't think so, it would fix the issue you pointed out in
>> auto-fn15.C but
>> > >> >> > it wouldn't fix the original test.  The problem with using
>> PAREN_EXPR in a
>> > >> >> > template is that instantiate_non_dependent_expr will turn in
>> into the
>> > >> >> > static cast anyway; tsubst_copy_and_build has
>> > >> >> >     case PAREN_EXPR:
>> > >> >> >       RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND
>> (t, 0))));
>> > >> >> > so it calls force_paren_expr and this time we're not in a
>> template.  And
>> > >> >> > then when calling cxx_constant_init we have the same issue.
>> > >> >>
>> > >> >> Then maybe we need something like fold_non_dependent_expr, which
>> > >> >> checks for dependency before substitution and then immediately
>> > >> >> evaluates the result.
>> > >> >
>> > >> > I hope you meant something like this.  Further testing also
>> revealed that
>> > >> > maybe_undo_parenthesized_ref should be able to unwrap PAREN_EXPR
>> (so that
>> > >> > (fn1)(); in paren2.C is handled correctly), and that lvalue_kind
>> should look
>> > >> > into PAREN_EXPR so as to give the correct answer regarding
>> lvalueness: we
>> > >> > should accept
>> > >> >
>> > >> > template<typename T>
>> > >> > void foo (int i)
>> > >> > {
>> > >> >   ++(i);
>> > >> > }
>> > >> >
>> > >> > Apologies if I'm on the wrong track.
>> > >> >
>> > >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
>> > >> >
>> > >> > 2018-02-28  Marek Polacek  <polacek@redhat.com>
>> > >> >             Jason Merrill  <jason@redhat.com>
>> > >> >
>> > >> >         PR c++/84582
>> > >> >         * semantics.c (force_paren_expr): Avoid creating the
>> static cast
>> > >> >         when in a template.  Create a PAREN_EXPR when in a
>> template.
>> > >> >         (maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
>> > >> >         * typeck2.c (store_init_value): Call
>> fold_non_dependent_expr instead
>> > >> >         of instantiate_non_dependent_expr.
>> > >> >         * tree.c (lvalue_kind): Handle PAREN_EXPR like
>> NON_DEPENDENT_EXPR.
>> > >> >
>> > >> >         * g++.dg/cpp1y/auto-fn15.C: Extend testing.
>> > >> >         * g++.dg/cpp1z/static1.C: New test.
>> > >> >         * g++.dg/template/static37.C: New test.
>> > >> >
>> > >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
>> > >> > index 35569d0cb0d..722e3718a14 100644
>> > >> > --- gcc/cp/semantics.c
>> > >> > +++ gcc/cp/semantics.c
>> > >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree 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.  */;
>> > >> > -  else
>> > >> > +  else if (!processing_template_decl)
>> > >> >      {
>> > >> >        cp_lvalue_kind kind = lvalue_kind (expr);
>> > >> >        if ((kind & ~clk_class) != clk_none)
>> > >> > @@ -1713,6 +1713,8 @@ force_paren_expr (tree expr)
>> > >> >             REF_PARENTHESIZED_P (expr) = true;
>> > >> >         }
>> > >> >      }
>> > >> > +  else
>> > >> > +    expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);
>> > >>
>> > >> There's already a branch for building PAREN_EXPR, let's just replace
>> > >> its condition.
>> > >
>> > > Sure.
>> > >
>> > >> > -      value = instantiate_non_dependent_expr (value);
>> > >> > +      value = fold_non_dependent_expr (value);
>> > >>
>> > >> I was thinking that we want a parallel fold_non_dependent_init (that
>> > >> hopefully shares most of the implementation).  Then we shouldn't need
>> > >> the call to maybe_constant_init anymore.
>> > >
>> > > If you mean fold_non_dependent_init that would be like
>> fold_non_dependent_expr
>> > > but with maybe_constant_init and not maybe_constant_value
>> >
>> > And is_nondependent_static_init_expression, and different arguments to
>> > cxx_eval_outermost_constant_expression, yes.
>>
>> Ah.  Maybe it'll be useful sometime in the future.
>>
>> > > then that would break e.g.
>> > >
>> > > const double d = 9.0;   // missing constexpr
>> > > constexpr double j = d; // should give error
>> > >
>> > > because maybe_constant_value checks is_nondependent_constant_expression,
>> and
>> > > "d" in the example above is not a constant expression, so we don't
>> evaluate,
>> > > and "d" stays "d", so require_constant_expression gives the error.
>> On the
>> > > other hand, maybe_constant_init checks is_nondependent_static_init_ex
>> pression,
>> > > and "d" is that, so we evaluate "d" to "9.0".  Then
>> require_constant_expression
>> > > doesn't complain.
>> >
>> > Ah, I see.  You're right, let's stick with fold_non_dependent_expr.
>>
>> Thanks, so this is the final patch then:
>>
>> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>>
>> 2018-03-01  Marek Polacek  <polacek@redhat.com>
>>             Jason Merrill  <jason@redhat.com>
>>
>>         PR c++/84582
>>         * semantics.c (force_paren_expr): Create a PAREN_EXPR when in
>>         a template.
>>         (maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
>>         * typeck2.c (store_init_value): Call fold_non_dependent_expr
>> instead
>>         of instantiate_non_dependent_expr.
>>         * tree.c (lvalue_kind): Handle PAREN_EXPR like NON_DEPENDENT_EXPR.
>>
>>         * g++.dg/cpp1y/auto-fn15.C: Extend testing.
>>         * g++.dg/cpp1z/static1.C: New test.
>>         * g++.dg/template/static37.C: New test.
>>
>> diff --git gcc/cp/semantics.c gcc/cp/semantics.c
>> index 87c5c669a55..1ac1d23e761 100644
>> --- gcc/cp/semantics.c
>> +++ gcc/cp/semantics.c
>> @@ -1693,7 +1693,8 @@ force_paren_expr (tree expr)
>>    if (TREE_CODE (expr) == COMPONENT_REF
>>        || TREE_CODE (expr) == SCOPE_REF)
>>      REF_PARENTHESIZED_P (expr) = true;
>> -  else if (type_dependent_expression_p (expr))
>> +  else if (type_dependent_expression_p (expr)
>> +          || processing_template_decl)
>
>
Actually, this is redundant; an expression can only be dependent if
processing_template_decl.  I'll fix.

Jason

Re: C++ PATCH to fix static init with () in a template (PR c++/84582)

[Marek Polacek]

On Fri, Mar 02, 2018 at 01:17:55PM -0500, Jason Merrill wrote:
> Actually, this is redundant; an expression can only be dependent if
> processing_template_decl.  I'll fix.

Ah, that makes a lot of sense.  Thanks,

	Marek