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. Should we play some ugly games with maybe_undo_parenthesized_ref? Marek