On Wed, Feb 28, 2018 at 10:51:17AM -0500, Jason Merrill wrote: > On Wed, Feb 28, 2018 at 9:32 AM, Marek Polacek <pola...@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 <pola...@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 <pola...@redhat.com> Jason Merrill <ja...@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