On 9/1/20 6:23 PM, Marek Polacek wrote:
This patch nails down the remaining P0960 case in PR92812:struct A { int ar[2]; A(): ar(1, 2) {} // doesn't work without this patch }; Note that when the target object is not of array type, this already works: struct S { int x, y; }; struct A { S s; A(): s(1, 2) { } // OK in C++20 }; because build_new_method_call_1 takes care of the P0960 magic. It proved to be quite hairy. When the ()-list has more than one element, we can always create a CONSTRUCTOR, because the code was previously invalid. But when the ()-list has just one element, it gets all kinds of difficult. As usual, we have to handle a("foo") so as not to wrap the STRING_CST in a CONSTRUCTOR. Always turning x(e) into x{e} would run into trouble as in c++/93790. Another issue was what to do about x({e}): previously, this would trigger "list-initializer for non-class type must not be parenthesized". I figured I'd make this work in C++20, so that given struct S { int x, y; }; you can do S a[2]; [...] A(): a({1, 2}) // initialize a[0] with {1, 2} and a[1] with {} It also turned out that, as an extension, we support compound literals: F (): m((S[1]) { 1, 2 }) so this has to keep working as before. Moreover, make sure not to trigger in compiler-generated code, like =default, where array assignment is allowed. paren-init35.C also tests this with vector types. Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? gcc/cp/ChangeLog: PR c++/92812 * init.c (do_paren_init_for_array_p): New. (perform_member_init): Use it. If true, build up a CONSTRUCTOR from the list of arguments. gcc/testsuite/ChangeLog: PR c++/92812 * g++.dg/cpp0x/constexpr-array23.C: Adjust dg-error. * g++.dg/cpp0x/initlist69.C: Likewise. * g++.dg/diagnostic/mem-init1.C: Likewise. * g++.dg/init/array28.C: Likewise. * g++.dg/cpp2a/paren-init33.C: New test. * g++.dg/cpp2a/paren-init34.C: New test. * g++.dg/cpp2a/paren-init35.C: New test. * g++.old-deja/g++.brendan/crash60.C: Adjust dg-error. * g++.old-deja/g++.law/init10.C: Likewise. * g++.old-deja/g++.other/array3.C: Likewise. --- gcc/cp/init.c | 64 ++++++++- .../g++.dg/cpp0x/constexpr-array23.C | 6 +- gcc/testsuite/g++.dg/cpp0x/initlist69.C | 4 +- gcc/testsuite/g++.dg/cpp2a/paren-init33.C | 128 ++++++++++++++++++ gcc/testsuite/g++.dg/cpp2a/paren-init34.C | 25 ++++ gcc/testsuite/g++.dg/cpp2a/paren-init35.C | 21 +++ gcc/testsuite/g++.dg/diagnostic/mem-init1.C | 4 +- gcc/testsuite/g++.dg/init/array28.C | 2 +- .../g++.old-deja/g++.brendan/crash60.C | 2 +- gcc/testsuite/g++.old-deja/g++.law/init10.C | 2 +- gcc/testsuite/g++.old-deja/g++.other/array3.C | 3 +- 11 files changed, 243 insertions(+), 18 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init33.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init34.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init35.C diff --git a/gcc/cp/init.c b/gcc/cp/init.c index d4540db3605..2edc9651ad6 100644 --- a/gcc/cp/init.c +++ b/gcc/cp/init.c @@ -756,6 +756,41 @@ maybe_warn_list_ctor (tree member, tree init) "of the underlying array", member, begin); }+/* Return true if we should attempt to perform the P0960 magic when+ initializing an array TYPE from a parenthesized list of values LIST. */ + +static bool +do_paren_init_for_array_p (tree list, tree type) +{ + if (cxx_dialect < cxx20) + /* P0960 is a C++20 feature. */ + return false; + + const int len = list_length (list); + if (len == 0) + /* Value-initialization. */ + return false; + else if (len > 1) + /* If the list had more than one element, the code is ill-formed + pre-C++20, so we should attempt to ()-init. */ + return true; + + /* Lists with one element are trickier. */ + tree elt = TREE_VALUE (list); + + /* For a("foo"), don't wrap the STRING_CST in { }. */ + if (char_type_p (TYPE_MAIN_VARIANT (TREE_TYPE (type))) + && TREE_CODE (tree_strip_any_location_wrapper (elt)) == STRING_CST) + return false;
Hmm, yet another place we need to implement the special treatment of strings? Can't we factor this better? Could there be a general e.g. maybe_aggregate_paren_init function to turn a list into a CONSTRUCTOR that's used in various places?
+ /* Don't trigger in compiler-generated code for = default. */ + if (current_function_decl && DECL_DEFAULTED_FN (current_function_decl)) + return false; + + /* Handle non-standard extensions like compound literals. */ + return !same_type_ignoring_top_level_qualifiers_p (type, TREE_TYPE (elt));
Isn't the defaulted function case caught by the same-type check? Jason
