| Message ID | 20200416175331.2019448-1-ppalka@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | c++: Non-type-dependent variadic lambda init-capture [PR94483] | expand |
On 4/16/20 1:53 PM, Patrick Palka wrote: > In this PR (which I think is misclassified as ice-on-invalid instead of > ice-on-valid), we're ICEing on a use of an 'int... a' template parameter pack as > part of the variadic lambda init-capture [...z=a]. > > The unexpected thing about this variadic init-capture is that it is not > type-dependent, and so when we call do_auto_deduction from > lambda_capture_field_type it actually resolves its type to 'int' instead of > exiting early like it would do for a type-dependent variadic initializer. This > later confuses add_capture which, according to one of its comments, assumes that > 'type' is always 'auto' for a variadic init-capture. > > The simplest fix, and the approach that this patch takes, seems to be to avoid > doing auto deduction in lambda_capture_field_type when the initializer uses > parameter packs, so that we always return 'auto' even in the non-type-dependent > case. Hmm, that will make 'z' more dependent than necessary, but I suppose its packness will tend to make uses dependent anyway, so OK. > Passes 'make check-c++', does this look OK to commit after full > bootstrap/regtesting? > > gcc/cp/ChangeLog: > > PR c++/94483 > * lambda.c (lambda_capture_field_type): Avoid doing auto deduction if > the explicit initializer has parameter packs. > > gcc/testsuite/ChangeLog: > > PR c++/94483 > * g++.dg/cpp2a/lambda-pack-init5.C: New test. > --- > gcc/cp/lambda.c | 5 ++++- > gcc/testsuite/g++.dg/cpp2a/lambda-pack-init5.C | 18 ++++++++++++++++++ > 2 files changed, 22 insertions(+), 1 deletion(-) > create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-pack-init5.C > > diff --git a/gcc/cp/lambda.c b/gcc/cp/lambda.c > index 4f39f99756b..b55c2f85d27 100644 > --- a/gcc/cp/lambda.c > +++ b/gcc/cp/lambda.c > @@ -223,7 +223,10 @@ lambda_capture_field_type (tree expr, bool explicit_init_p, > /* Add the reference now, so deduction doesn't lose > outermost CV qualifiers of EXPR. */ > type = build_reference_type (type); > - type = do_auto_deduction (type, expr, auto_node); > + if (uses_parameter_packs (expr)) > + /* Stick with 'auto' even if the type could be deduced. */; > + else > + type = do_auto_deduction (type, expr, auto_node); > } > else if (!is_this && type_dependent_expression_p (expr)) > { > diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-pack-init5.C b/gcc/testsuite/g++.dg/cpp2a/lambda-pack-init5.C > new file mode 100644 > index 00000000000..492fc479e94 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp2a/lambda-pack-init5.C > @@ -0,0 +1,18 @@ > +// PR c++/94483 > +// { dg-do compile { target c++2a } } > + > +template<int... a> constexpr auto x1 > + = [...z = -a] (auto F) { return F(z...); }; > + > +template<const int&... a> constexpr auto x2 > + = [&...z = a] (auto F) { return F(z...); }; > + > +template<int... a> constexpr auto x3 > + = [z = -a] (auto F) { return F(z); }; // { dg-error "packs not expanded" } > + > + > +constexpr auto sum = [] (auto... xs) { return (xs + ... + 0); }; > +const int y1 = 1, y2 = 2, y3 = 3; > + > +static_assert(x1<1,2,3>(sum) == -6); > +static_assert(x2<y1,y2,y3>(sum) == 6); >
diff --git a/gcc/cp/lambda.c b/gcc/cp/lambda.c index 4f39f99756b..b55c2f85d27 100644 --- a/gcc/cp/lambda.c +++ b/gcc/cp/lambda.c @@ -223,7 +223,10 @@ lambda_capture_field_type (tree expr, bool explicit_init_p, /* Add the reference now, so deduction doesn't lose outermost CV qualifiers of EXPR. */ type = build_reference_type (type); - type = do_auto_deduction (type, expr, auto_node); + if (uses_parameter_packs (expr)) + /* Stick with 'auto' even if the type could be deduced. */; + else + type = do_auto_deduction (type, expr, auto_node); } else if (!is_this && type_dependent_expression_p (expr)) { diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-pack-init5.C b/gcc/testsuite/g++.dg/cpp2a/lambda-pack-init5.C new file mode 100644 index 00000000000..492fc479e94 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/lambda-pack-init5.C @@ -0,0 +1,18 @@ +// PR c++/94483 +// { dg-do compile { target c++2a } } + +template<int... a> constexpr auto x1 + = [...z = -a] (auto F) { return F(z...); }; + +template<const int&... a> constexpr auto x2 + = [&...z = a] (auto F) { return F(z...); }; + +template<int... a> constexpr auto x3 + = [z = -a] (auto F) { return F(z); }; // { dg-error "packs not expanded" } + + +constexpr auto sum = [] (auto... xs) { return (xs + ... + 0); }; +const int y1 = 1, y2 = 2, y3 = 3; + +static_assert(x1<1,2,3>(sum) == -6); +static_assert(x2<y1,y2,y3>(sum) == 6);