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author | Dodji Seketeli <dodji@redhat.com> | 2013-05-16 06:14:49 +0000 |
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committer | Dodji Seketeli <dodji@gcc.gnu.org> | 2013-05-16 08:14:49 +0200 |
commit | f5b6d0d1d2cf80e685084eedd5ce68370a6f4248 (patch) | |
tree | c6b464617b7d00a515b81b19e8d79595d99f21d2 /gcc | |
parent | ad56ed7ebca514b172e13172f2486951218d3c8b (diff) | |
download | gcc-f5b6d0d1d2cf80e685084eedd5ce68370a6f4248.zip gcc-f5b6d0d1d2cf80e685084eedd5ce68370a6f4248.tar.gz gcc-f5b6d0d1d2cf80e685084eedd5ce68370a6f4248.tar.bz2 |
PR c++/56782 - Regression with empty pack expansions
In the example of the patch below, during the instantiation of
is_convertible at #1, we see at some point Tuple<>. (Let's note '{}'
an empty argument pack.) In that context, during the partial
specialization the member template
template<class... U>
Tuple<>::Tuple<U,
typename enable_if<and_<is_convertible<U, {}>...
>::value,
int
>::type
>
Let's look at what happens to the expansion "is_convertible<U, {}>...."
To express the result of that expansion tsubst_pack_expansion receives
the expansion is_convertible<U, T>, with the argument list [{}]. This
function should detect that we have an empty argument pack for the
parameter pack T and no argument pack for the parameter pack U. It
should thus return a pack expansion "is_convertible<U,T>..." that has this
information: "I have gotten an argument list, that is not complete
because U doesn't have any argument pack; the argument pack for T is
'{}', so I'll wait for the next time I am passed to
tsubst_pack_expansion with enough additional argument packs, to really
perform the substitution". That information is conveyed by attaching
the the '{}' to the PACK_EXPANSION_EXTRA property of the pack expansion
returned by tsubst_pack_expansion.
The problem in this report is that we are not setting
PACK_EXPANSION_EXTRA when the non-complete argument pack list is made
of an empty argument pack, because use_pack_expansion_extra_args_p
doesn't detect this case.
Fixed thus.
gcc/cp/
* pt.c (use_pack_expansion_extra_args_p): When at least a
parameter pack has an empty argument pack, and another parameter
pack has no argument pack at all, use the PACK_EXPANSION_EXTRA
mechanism.
From-SVN: r198956
Diffstat (limited to 'gcc')
-rw-r--r-- | gcc/cp/ChangeLog | 8 | ||||
-rw-r--r-- | gcc/cp/pt.c | 15 | ||||
-rw-r--r-- | gcc/testsuite/g++.dg/cpp0x/variadic143.C | 63 |
3 files changed, 79 insertions, 7 deletions
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog index a602af3..3609fa5 100644 --- a/gcc/cp/ChangeLog +++ b/gcc/cp/ChangeLog @@ -1,3 +1,11 @@ +2013-05-16 Dodji Seketeli <dodji@redhat.com> + + PR c++/56782 - Regression with empty pack expansions + * pt.c (use_pack_expansion_extra_args_p): When at least a + parameter pack has an empty argument pack, and another parameter + pack has no argument pack at all, use the PACK_EXPANSION_EXTRA + mechanism. + 2013-05-15 Paolo Carlini <paolo.carlini@oracle.com> * name-lookup.c (pushdecl_maybe_friend_1): Replace pairs of diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index 04dc4fc..b0be950 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -9202,8 +9202,15 @@ use_pack_expansion_extra_args_p (tree parm_packs, int arg_pack_len, bool has_empty_arg) { + /* If one pack has an expansion and another pack has a normal + argument or if one pack has an empty argument and an another + one hasn't then tsubst_pack_expansion cannot perform the + substitution and need to fall back on the + PACK_EXPANSION_EXTRA mechanism. */ if (parm_packs == NULL_TREE) return false; + else if (has_empty_arg) + return true; bool has_expansion_arg = false; for (int i = 0 ; i < arg_pack_len; ++i) @@ -9221,13 +9228,7 @@ use_pack_expansion_extra_args_p (tree parm_packs, has_non_expansion_arg = true; } - /* If one pack has an expansion and another pack has a normal - argument or if one pack has an empty argument another one - hasn't then tsubst_pack_expansion cannot perform the - substitution and need to fall back on the - PACK_EXPANSION_EXTRA mechanism. */ - if ((has_expansion_arg && has_non_expansion_arg) - || (has_empty_arg && (has_expansion_arg || has_non_expansion_arg))) + if (has_expansion_arg && has_non_expansion_arg) return true; } return false; diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic143.C b/gcc/testsuite/g++.dg/cpp0x/variadic143.C new file mode 100644 index 0000000..7737b4c --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/variadic143.C @@ -0,0 +1,63 @@ +// PR c++/56782 +// { dg-options -std=c++0x } + +template<class T> +T&& declval(); + +struct is_convertible_impl { + template<class T> + static void sink(T); + + template<class T, class U, class = decltype(sink<U>(declval<T>()))> + static auto test(int) -> char; + + template<class, class> + static auto test(...) -> char(&)[2]; +}; + +template<class T, class U> +struct is_convertible : is_convertible_impl +{ + static const bool value = sizeof(test<T, U>(0)) == 1; +}; + +template<bool, class> +struct enable_if {}; + +template<class T> +struct enable_if<true, T> { typedef T type; }; + +template<bool, class If, class Else> +struct conditional { typedef If type; }; + +template<class If, class Else> +struct conditional<false, If, Else> { typedef Else type; }; + +template<class...> +struct and_; + +template<> +struct and_<> +{ + static const bool value = true; +}; + +template<class P> +struct and_<P> : P +{ +}; + +template<class P1, class P2> +struct and_<P1, P2> : conditional<P1::value, P2, P1>::type +{ +}; + +template<class... T> +struct Tuple { + template<class... U, + class = typename enable_if<and_<is_convertible<U, T>... >::value, int>::type + > + Tuple(U&&...){} +}; + +static_assert(is_convertible<Tuple<>, Tuple<>>::value, "Ouch"); //#1 |