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