| Message ID | 20210624151538.2495141-1-ppalka@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | c++: alias CTAD and aggregate deduction cand [PR98832] | expand |
On 6/24/21 11:15 AM, Patrick Palka wrote: > During alias CTAD, we're accidentally ignoring the aggregate deduction > candidate of the underlying template because it's added to the candidate > set separately via maybe_aggr_guide (which doesn't yet handle alias > templates) rather than via deduction_guides_for (which does). This > patch makes maybe_aggr_guide handle alias templates in a manner similar > to deduction_guides_for. > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for > trunk? OK. > PR c++/98832 > > gcc/cp/ChangeLog: > > * pt.c (maybe_aggr_guide): Handle an alias template. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp2a/class-deduction-alias9.C: New test. > --- > gcc/cp/pt.c | 11 +++++++++++ > gcc/testsuite/g++.dg/cpp2a/class-deduction-alias9.C | 6 ++++++ > 2 files changed, 17 insertions(+) > create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias9.C > > diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c > index aeb1e8a6f97..db15e4714d5 100644 > --- a/gcc/cp/pt.c > +++ b/gcc/cp/pt.c > @@ -28880,6 +28880,8 @@ is_spec_or_derived (tree etype, tree tmpl) > return !err; > } > > +static tree alias_ctad_tweaks (tree, tree); > + > /* Return a C++20 aggregate deduction candidate for TYPE initialized from > INIT. */ > > @@ -28892,6 +28894,15 @@ maybe_aggr_guide (tree tmpl, tree init, vec<tree,va_gc> *args) > if (init == NULL_TREE) > return NULL_TREE; > > + if (DECL_ALIAS_TEMPLATE_P (tmpl)) > + { > + tree under = DECL_ORIGINAL_TYPE (DECL_TEMPLATE_RESULT (tmpl)); > + tree tinfo = get_template_info (under); > + if (tree guide = maybe_aggr_guide (TI_TEMPLATE (tinfo), init, args)) > + return alias_ctad_tweaks (tmpl, guide); > + return NULL_TREE; > + } > + > /* We might be creating a guide for a class member template, e.g., > > template<typename U> struct A { > diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias9.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias9.C > new file mode 100644 > index 00000000000..0aaf203639a > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias9.C > @@ -0,0 +1,6 @@ > +// PR c++/98832 > +// { dg-do compile { target c++20 } } > + > +template<class T, class U> struct X{ U u; }; > +template<class T> using Y = X<int, T>; > +Y y{0}; >
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index aeb1e8a6f97..db15e4714d5 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -28880,6 +28880,8 @@ is_spec_or_derived (tree etype, tree tmpl) return !err; } +static tree alias_ctad_tweaks (tree, tree); + /* Return a C++20 aggregate deduction candidate for TYPE initialized from INIT. */ @@ -28892,6 +28894,15 @@ maybe_aggr_guide (tree tmpl, tree init, vec<tree,va_gc> *args) if (init == NULL_TREE) return NULL_TREE; + if (DECL_ALIAS_TEMPLATE_P (tmpl)) + { + tree under = DECL_ORIGINAL_TYPE (DECL_TEMPLATE_RESULT (tmpl)); + tree tinfo = get_template_info (under); + if (tree guide = maybe_aggr_guide (TI_TEMPLATE (tinfo), init, args)) + return alias_ctad_tweaks (tmpl, guide); + return NULL_TREE; + } + /* We might be creating a guide for a class member template, e.g., template<typename U> struct A { diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias9.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias9.C new file mode 100644 index 00000000000..0aaf203639a --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias9.C @@ -0,0 +1,6 @@ +// PR c++/98832 +// { dg-do compile { target c++20 } } + +template<class T, class U> struct X{ U u; }; +template<class T> using Y = X<int, T>; +Y y{0};