| Message ID | YjT/2vcFRIYNVWgD@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] c++: ICE with template code in constexpr [PR104284] | expand |
On 3/18/22 17:55, Marek Polacek wrote: > On Fri, Mar 11, 2022 at 06:46:42PM -0500, Jason Merrill wrote: >> On 3/10/22 18:04, Marek Polacek wrote: >>> Since r9-6073 cxx_eval_store_expression preevaluates the value to >>> be stored, and that revealed a crash where a template code (here, >>> code=IMPLICIT_CONV_EXPR) leaks into cxx_eval*. >>> >>> It happens because we're performing build_vec_init while processing >>> a template >> >> Hmm, that seems like the bug. Where's that call coming from? > > From build_aggr_init. So we're handling e.g. > > template<class> > constexpr void g () { > constexpr S s2[]{{'a'}}; > } > > cp_finish_decl (decl=s2, init={{'a'}}) sees we're in processing_template_decl, > but also that we have a constexpr var which is not dependent, nor is its > initializer: > > else if (init > && (init_const_expr_p || DECL_DECLARED_CONSTEXPR_P (decl)) > && !TYPE_REF_P (type) > && decl_maybe_constant_var_p (decl) > && !(dep_init = value_dependent_init_p (init))) > { > /* This variable seems to be a non-dependent constant, so process > its initializer. If check_initializer returns non-null the > initialization wasn't constant after all. */ > tree init_code; > cleanups = make_tree_vector (); > init_code = check_initializer (decl, init, flags, &cleanups); > > so we call check_initializer, where we go down this path: > > init_code = build_aggr_init_full_exprs (decl, init, flags); > > build_aggr_init sees that the type of 's2' is ARRAY_TYPE, so it calls > build_vec_init. > > I now recall that we've discussed build_vec_init in a template in the > past, for example in the context of c++/93676. So I agree we ought to > make an effort to avoid calling build_vec_init in a template. Perhaps > like this: use an INIT_EXPR. With that, we should call build_vec_init > if needed while instantiating. Does that make any sense? Hmm. If we do that, then we get back to > if (TREE_CODE (init_code) == INIT_EXPR) in check_initializer, and pull out the same init again, and set LOOKUP_ALREADY_DIGESTED. But I think that's wrong, we haven't digested it yet. Maybe we could avoid entering the below block of check_initializer at all in this situation? > if (((type_build_ctor_call (type) || CLASS_TYPE_P (type)) > && !(flags & LOOKUP_ALREADY_DIGESTED) > && !(init && BRACE_ENCLOSED_INITIALIZER_P (init) > && CP_AGGREGATE_TYPE_P (type) > && (CLASS_TYPE_P (type) Maybe by adding || processing_template_decl here? > || !TYPE_NEEDS_CONSTRUCTING (type) > || type_has_extended_temps (type)))) > || (DECL_DECOMPOSITION_P (decl) && TREE_CODE (type) == ARRAY_TYPE)) Jason
diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc index 7575597c8fd..58e66adbfe1 100644 --- a/gcc/cp/init.cc +++ b/gcc/cp/init.cc @@ -2006,10 +2006,13 @@ build_aggr_init (tree exp, tree init, int flags, tsubst_flags_t complain) } } - stmt_expr = build_vec_init (exp, NULL_TREE, init, - /*explicit_value_init_p=*/false, - from_array, - complain); + /* build_vec_init is not meant to be used in templates. */ + if (processing_template_decl) + stmt_expr = build2 (INIT_EXPR, itype, exp, init); + else + stmt_expr = build_vec_init (exp, NULL_TREE, init, + /*explicit_value_init_p=*/false, + from_array, complain); TREE_READONLY (exp) = was_const; TREE_THIS_VOLATILE (exp) = was_volatile; TREE_TYPE (exp) = type; diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-1.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-1.C new file mode 100644 index 00000000000..809c26a6161 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-1.C @@ -0,0 +1,34 @@ +// PR c++/104284 +// { dg-do compile { target c++14 } } +// { dg-additional-options "-fchecking=2" } + +struct S { + char c{}; +}; + +auto x1 = [](auto) { constexpr S s[]{{}}; }; +auto x2 = [](auto) { constexpr S s[]{{'a'}}; }; +#if __cpp_designated_initializers >= 201707L +auto x3 = [](auto) { constexpr S s[]{{.c = 'a'}}; }; +#endif +auto x4 = [](auto) { constexpr S s[]{'a'}; }; +auto x5 = [](auto) { constexpr S s[]{{{}}}; }; + +template<class> +constexpr void g () +{ + constexpr S s1[]{{}}; + static_assert(s1[0].c == '\0', ""); + constexpr S s2[]{{'a'}}; + static_assert(s2[0].c == 'a', ""); +#if __cpp_designated_initializers >= 201707L + constexpr S s3[]{{.c = 'a'}}; + static_assert(s3[0].c == 'a', ""); +#endif + constexpr S s4[]{'a'}; + static_assert(s4[0].c == 'a', ""); + constexpr S s5[]{{{}}}; + static_assert(s5[0].c == '\0', ""); +} + +static_assert ((g<int>(), true), ""); diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-2.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-2.C new file mode 100644 index 00000000000..704d37de129 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-2.C @@ -0,0 +1,33 @@ +// PR c++/104284 +// { dg-do compile { target c++14 } } +// { dg-additional-options "-fchecking=2" } + +struct S { + char a; + constexpr S() : a{'a'} { } + constexpr S(char a_) : a{a_} { } +}; + +auto x1 = [](auto) { constexpr S s[]{{}}; }; +auto x2 = [](auto) { constexpr S s[]{{'a'}}; }; +auto x3 = [](auto) { constexpr S s[]{'a'}; }; +auto x4 = [](auto) { constexpr S s[]{{{}}}; }; + +template<typename> +constexpr void g() +{ + constexpr S s1[]{{}}; + static_assert(s1[0].a == 'a', ""); + constexpr S s2[]{{'a'}}; + static_assert(s2[0].a == 'a', ""); + constexpr S s3[]{'a'}; + static_assert(s3[0].a == 'a', ""); + constexpr S s4[]{{{}}}; + static_assert(s4[0].a == '\0', ""); +} + +void +f () +{ + g<int>(); +} diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-3.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-3.C new file mode 100644 index 00000000000..6f23b255f9c --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-3.C @@ -0,0 +1,33 @@ +// PR c++/104284 +// { dg-do compile { target c++14 } } +// { dg-additional-options "-fchecking=2" } +// Like constexpr-104284.C, but the function template is not +// constexpr. In that case, we were still calling build_vec_init +// in a template, just not crashing. + +struct S { + char c{}; +}; + +template<class> +void g () +{ + constexpr S s1[]{{}}; + static_assert(s1[0].c == '\0', ""); + constexpr S s2[]{{'a'}}; + static_assert(s2[0].c == 'a', ""); +#if __cpp_designated_initializers >= 201707L + constexpr S s3[]{{.c = 'a'}}; + static_assert(s3[0].c == 'a', ""); +#endif + constexpr S s4[]{'a'}; + static_assert(s4[0].c == 'a', ""); + constexpr S s5[]{{{}}}; + static_assert(s5[0].c == '\0', ""); +} + +void +f () +{ + g<int>(); +} diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-4.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-4.C new file mode 100644 index 00000000000..a99d3255a47 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-4.C @@ -0,0 +1,35 @@ +// PR c++/104284 +// { dg-do run { target c++14 } } +// { dg-additional-options "-fchecking=2" } + +struct S { + char c{}; +}; + +template<class> +constexpr void g () +{ + S s1[]{{}}; + if (s1[0].c != '\0') + __builtin_abort (); + S s2[]{{'a'}}; + if (s2[0].c != 'a') + __builtin_abort (); +#if __cpp_designated_initializers >= 201707L + S s3[]{{.c = 'a'}}; + if (s3[0].c != 'a') + __builtin_abort (); +#endif + S s4[]{'a'}; + if (s4[0].c != 'a') + __builtin_abort (); + S s5[]{{{}}}; + if (s5[0].c != '\0') + __builtin_abort (); +} + +int +main () +{ + g<int>(); +}