C++ PATCH to fix static init with () in a template (PR c++/84582)
Marek Polacek
polacek@redhat.com
Thu Mar 1 21:40:00 GMT 2018
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
More information about the Gcc-patches
mailing list