From 2ec803e768a820c9208fea2e8b144ee359379139 Mon Sep 17 00:00:00 2001 From: Marek Polacek Date: Fri, 10 Jul 2020 17:39:54 -0400 Subject: [PATCH] c++: Fixing the wording of () aggregate-init [PR92812] P1975R0 tweaks the static_cast wording: it says that "An expression e can be explicitly converted to a type T if [...] T is an aggregate type having a first element x and there is an implicit conversion sequence from e to the type of x." This already works for classes, e.g.: struct Aggr { int x; int y; }; Aggr a = static_cast(1); for which we create TARGET_EXPR . The proposal also mentions "If T is ``array of unknown bound of U'', this direct-initialization defines the type of the expression as U[1]" which suggest that this should work for arrays (they're aggregates too, after all): int (&&r)[3] = static_cast(42); int (&&r2)[1] = static_cast(42); So I handled that specifically in build_static_cast_1: wrap the expression in { } and initialize from that. For the 'r' case above this creates TARGET_EXPR . There are multiple things in play, as usual, so the tests test brace elision, narrowing, explicit constructors, and lifetime extension too. I think it's in line with what we discussed on the core reflector. gcc/cp/ChangeLog: PR c++/92812 * typeck.c (build_static_cast_1): Implement P1975R0 by allowing static_cast to aggregate type. gcc/testsuite/ChangeLog: PR c++/92812 * g++.dg/cpp2a/paren-init27.C: New test. * g++.dg/cpp2a/paren-init28.C: New test. * g++.dg/cpp2a/paren-init29.C: New test. * g++.dg/cpp2a/paren-init30.C: New test. * g++.dg/cpp2a/paren-init31.C: New test. * g++.dg/cpp2a/paren-init32.C: New test. --- gcc/cp/typeck.c | 14 ++++++++++++++ gcc/testsuite/g++.dg/cpp2a/paren-init27.C | 24 ++++++++++++++++++++++++ gcc/testsuite/g++.dg/cpp2a/paren-init28.C | 15 +++++++++++++++ gcc/testsuite/g++.dg/cpp2a/paren-init29.C | 15 +++++++++++++++ gcc/testsuite/g++.dg/cpp2a/paren-init30.C | 23 +++++++++++++++++++++++ gcc/testsuite/g++.dg/cpp2a/paren-init31.C | 10 ++++++++++ gcc/testsuite/g++.dg/cpp2a/paren-init32.C | 21 +++++++++++++++++++++ 7 files changed, 122 insertions(+) create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init27.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init28.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init29.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init30.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init31.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init32.C diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c index a557f34..9166156 100644 --- a/gcc/cp/typeck.c +++ b/gcc/cp/typeck.c @@ -7480,6 +7480,20 @@ build_static_cast_1 (location_t loc, tree type, tree expr, bool c_cast_p, t. */ result = perform_direct_initialization_if_possible (type, expr, c_cast_p, complain); + /* P1975 allows static_cast(42), as well as static_cast(42), + which initialize the first element of the aggregate. We need to handle + the array case specifically. */ + if (result == NULL_TREE + && cxx_dialect >= cxx20 + && TREE_CODE (type) == ARRAY_TYPE) + { + /* Create { EXPR } and perform direct-initialization from it. */ + tree e = build_constructor_single (init_list_type_node, NULL_TREE, expr); + CONSTRUCTOR_IS_DIRECT_INIT (e) = true; + CONSTRUCTOR_IS_PAREN_INIT (e) = true; + result = perform_direct_initialization_if_possible (type, e, c_cast_p, + complain); + } if (result) { if (processing_template_decl) diff --git a/gcc/testsuite/g++.dg/cpp2a/paren-init27.C b/gcc/testsuite/g++.dg/cpp2a/paren-init27.C new file mode 100644 index 0000000..0b8cbe3 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/paren-init27.C @@ -0,0 +1,24 @@ +// PR c++/92812 +// P1975R0 +// { dg-do run { target c++20 } } +// { dg-options "-Wall -Wextra" } + +struct Aggr { int x; int y; }; +struct Base { int i; Base(int i_) : i{i_} { } }; +struct BaseAggr : Base { }; +struct X { }; +struct AggrSDM { static X x; int i; int j; }; + +int +main () +{ + Aggr a = static_cast(42); // { dg-warning "missing initializer" } + if (a.x != 42 || a.y != 0) + __builtin_abort (); + BaseAggr b = static_cast(42); + if (b.i != 42) + __builtin_abort (); + AggrSDM s = static_cast(42); // { dg-warning "missing initializer" } + if (s.i != 42 || s.j != 0) + __builtin_abort (); +} diff --git a/gcc/testsuite/g++.dg/cpp2a/paren-init28.C b/gcc/testsuite/g++.dg/cpp2a/paren-init28.C new file mode 100644 index 0000000..8c57dc8 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/paren-init28.C @@ -0,0 +1,15 @@ +// PR c++/92812 +// P1975R0 +// { dg-do compile { target c++20 } } + +// In both cases the reference declarations lifetime-extend the array +// temporary. +int (&&r)[3] = static_cast(42); +int (&&r2)[1] = static_cast(42); + +// Make sure we've lifetime-extended. +// { dg-final { scan-assembler "_ZGR1r_" } } +// { dg-final { scan-assembler "_ZGR2r2_" } } + +// Narrowing is probably OK here. +int (&&r3)[1] = static_cast(1.3); diff --git a/gcc/testsuite/g++.dg/cpp2a/paren-init29.C b/gcc/testsuite/g++.dg/cpp2a/paren-init29.C new file mode 100644 index 0000000..c39cd8c --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/paren-init29.C @@ -0,0 +1,15 @@ +// PR c++/92812 +// P1975R0 +// { dg-do run { target c++20 } } + +int (&&r)[3] = static_cast(42); +int (&&r2)[1] = static_cast(42); + +int +main () +{ + if (r[0] != 42 || r[1] != 0 || r[2] != 0) + __builtin_abort (); + if (r2[0] != 42 || sizeof (r2) != sizeof (int)) + __builtin_abort (); +} diff --git a/gcc/testsuite/g++.dg/cpp2a/paren-init30.C b/gcc/testsuite/g++.dg/cpp2a/paren-init30.C new file mode 100644 index 0000000..6b2e86f --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/paren-init30.C @@ -0,0 +1,23 @@ +// PR c++/92812 +// P1975R0 +// { dg-do compile { target c++20 } } + +struct S1 { + int i; + int j; +}; + +struct S2 { + S1 s[4]; +}; + +struct S3 { + S2 s2; +}; + +void +f () +{ + // Brace elision not allowed. + auto s3 = static_cast(1); // { dg-error "could not convert" } +} diff --git a/gcc/testsuite/g++.dg/cpp2a/paren-init31.C b/gcc/testsuite/g++.dg/cpp2a/paren-init31.C new file mode 100644 index 0000000..3600c49 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/paren-init31.C @@ -0,0 +1,10 @@ +// PR c++/92812 +// P1975R0 +// { dg-do compile { target c++20 } } +// Test we don't lifetime-extend the int temporary. + +struct A { const int &r; }; +A a(42); +auto a2 = static_cast(42); + +// { dg-final { scan-assembler-not "_ZGR" } } diff --git a/gcc/testsuite/g++.dg/cpp2a/paren-init32.C b/gcc/testsuite/g++.dg/cpp2a/paren-init32.C new file mode 100644 index 0000000..bf7833e --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/paren-init32.C @@ -0,0 +1,21 @@ +// PR c++/92812 +// P1975R0 +// { dg-do compile { target c++20 } } + +struct A { int i; }; +struct A2 { int i; A2(int); }; +struct A3 { int i; explicit A3(int); }; + +struct X { A a; }; +auto x = static_cast(42); // { dg-error "could not convert" } + +struct X2 { A2 a; }; +auto x2 = static_cast(42); + +struct X3 { A3 a; }; +// Aggregate-initialization copy-initializes, so the explicit ctor +// isn't considered. +auto x3 = static_cast(42); // { dg-error "could not convert" } + +struct NonAggr { int i; virtual void foo (); }; +auto x4 = static_cast(42); // { dg-error "no matching" } -- 2.7.4