On Wed, Jan 28, 2026 at 02:34:48PM +0800, Jason Merrill wrote: > > > This is so close to build_range_temp that I think it should get > > > a "bool expansion_stmt_p" parm so that we can reuse the do_auto_deduction > > > and further code. > > > > Perhaps, it looked small enough for me, just 4 function calls and two flag > > setting stmts, the rest is different. But can change sure, or part of > > build_range_temp could be outlined to finish_range_temp that this could use. > > I think I agree with Marek's suggestion. OK with that change.
Here is what I'm going to test tonight, so far tested with GXX_TESTSUITE_STDS=98,11,14,17,20,23,26 make check-g++ -j32 -k RUNTESTFLAGS="dg.exp='reflection/* expansion-stmt*'" I've kept the paren expr construction in the caller because it later needs that value, so build_range_temp is just auto &&__for_range = range_expr; vs. const decltype(auto) __for_range = range_expr; for now (and guess later on for CWG3140 we'll also need to tell it whether it should do const or not, but that will need to be done in cp_build_range_for_decls too). 2026-01-28 Jakub Jelinek <[email protected]> * cp-tree.h (build_range_temp): Implement CWG3131 - Value categories and types for the range in iterable expansion statements. Add bool argument defaulted to false. * parser.cc (build_range_temp): Add expansion_stmt_p argument, if true build const decltype(auto) __for_range = range_expr instead of auto &&__for_range = range_expr. (cp_build_range_for_decls): For expansion stmts build __for_range as static constexpr decltype(auto) __for_range = (range_expr); rather than static constexpr auto &&__for_range = range_expr;. * g++.dg/cpp26/expansion-stmt1.C (N::begin, N::end, O::begin, O::end): Change argument type from B & to const B & or from D & to const D &. * g++.dg/cpp26/expansion-stmt2.C (N::begin, N::end, O::begin, O::end): Likewise. * g++.dg/cpp26/expansion-stmt3.C (N::begin, N::end, O::begin, O::end): Likewise. * g++.dg/cpp26/expansion-stmt16.C: Expect different diagnostics for C++11. * g++.dg/cpp26/expansion-stmt18.C (N::begin, N::end): Change argument type from B & to const B &. * g++.dg/cpp26/expansion-stmt25.C (N::begin, N::end): Likewise. * g++.dg/cpp26/expansion-stmt26.C: New test. * g++.dg/reflect/p3491-2.C (baz): Move workaround to a new function garply, use the previously #if 0 guarded implementation. (garply): New function. --- gcc/cp/cp-tree.h.jj 2026-01-28 09:50:17.238775416 +0100 +++ gcc/cp/cp-tree.h 2026-01-28 12:27:52.252582912 +0100 @@ -7995,7 +7995,7 @@ extern bool maybe_clone_body (tree); extern tree cp_build_range_for_decls (location_t, tree, tree *, bool); extern tree cp_convert_range_for (tree, tree, tree, cp_decomp *, bool, tree, bool); -extern tree build_range_temp (tree); +extern tree build_range_temp (tree, bool = false); extern tree cp_perform_range_for_lookup (tree, tree *, tree *, tsubst_flags_t = tf_warning_or_error); extern void cp_convert_omp_range_for (tree &, tree &, tree &, --- gcc/cp/parser.cc.jj 2026-01-28 10:20:25.783446142 +0100 +++ gcc/cp/parser.cc 2026-01-28 12:48:38.974311063 +0100 @@ -15855,12 +15855,24 @@ cp_parser_range_for (cp_parser *parser, builds up the range temporary. */ tree -build_range_temp (tree range_expr) +build_range_temp (tree range_expr, bool expansion_stmt_p /* = false */) { - /* Find out the type deduced by the declaration - `auto &&__range = range_expr'. */ - tree auto_node = make_auto (); - tree range_type = cp_build_reference_type (auto_node, true); + tree range_type, auto_node; + + if (expansion_stmt_p) + { + /* Build const decltype(auto) __range = range_expr; + - range_expr provided by the caller already is (range_expr). */ + auto_node = make_decltype_auto (); + range_type = cp_build_qualified_type (auto_node, TYPE_QUAL_CONST); + } + else + { + /* Find out the type deduced by the declaration + `auto &&__range = range_expr'. */ + auto_node = make_auto (); + range_type = cp_build_reference_type (auto_node, true); + } range_type = do_auto_deduction (range_type, range_expr, auto_node); /* Create the __range variable. */ @@ -16019,13 +16031,17 @@ cp_build_range_for_decls (location_t loc range_temp = range_expr; else { - range_temp = build_range_temp (range_expr); if (expansion_stmt_p) { - /* Depending on CWG3044 resolution, we might want to remove - these 3 sets of TREE_STATIC (on range_temp, begin and end). - Although it can only be done when P2686R4 is fully - implemented. */ + /* Build constexpr decltype(auto) __for_range = (range_expr); */ + location_t range_loc = cp_expr_loc_or_loc (range_expr, loc); + range_expr + = finish_parenthesized_expr (cp_expr (range_expr, range_loc)); + range_temp = build_range_temp (range_expr, true); + + /* When P2686R4 is fully implemented, these 3 sets of TREE_STATIC + (on range_temp, begin and end) should be removed as per + CWG3044. */ TREE_STATIC (range_temp) = 1; TREE_PUBLIC (range_temp) = 0; DECL_COMMON (range_temp) = 0; @@ -16033,6 +16049,10 @@ cp_build_range_for_decls (location_t loc DECL_DECLARED_CONSTEXPR_P (range_temp) = 1; TREE_READONLY (range_temp) = 1; } + else + /* Build auto &&__for_range = range_expr; */ + range_temp = build_range_temp (range_expr); + pushdecl (range_temp); cp_finish_decl (range_temp, range_expr, /*is_constant_init*/false, NULL_TREE, --- gcc/testsuite/g++.dg/cpp26/expansion-stmt1.C.jj 2026-01-28 09:54:50.584498257 +0100 +++ gcc/testsuite/g++.dg/cpp26/expansion-stmt1.C 2026-01-28 12:27:22.289326150 +0100 @@ -40,15 +40,15 @@ struct C namespace N { struct B { constexpr B () {} }; - constexpr A begin (B &) { return A (0); } - constexpr A end (B &) { return A (6); } + constexpr A begin (const B &) { return A (0); } + constexpr A end (const B &) { return A (6); } } namespace O { struct D { constexpr D () {} }; - constexpr C begin (D &) { return C (0, 42, 5); } - constexpr C end (D &) { return C (6, 36, 11); } + constexpr C begin (const D &) { return C (0, 42, 5); } + constexpr C end (const D &) { return C (6, 36, 11); } } long long --- gcc/testsuite/g++.dg/cpp26/expansion-stmt2.C.jj 2026-01-28 09:54:50.586659034 +0100 +++ gcc/testsuite/g++.dg/cpp26/expansion-stmt2.C 2026-01-28 12:27:22.289479158 +0100 @@ -40,15 +40,15 @@ struct C namespace N { struct B { constexpr B () {} }; - constexpr A begin (B &) { return A (0); } - constexpr A end (B &) { return A (6); } + constexpr A begin (const B &) { return A (0); } + constexpr A end (const B &) { return A (6); } } namespace O { struct D { constexpr D () {} }; - constexpr C begin (D &) { return C (0, 42, 5); } - constexpr C end (D &) { return C (6, 36, 11); } + constexpr C begin (const D &) { return C (0, 42, 5); } + constexpr C end (const D &) { return C (6, 36, 11); } } #if __cpp_nontype_template_parameter_class >= 201806L --- gcc/testsuite/g++.dg/cpp26/expansion-stmt3.C.jj 2026-01-28 09:54:50.587177815 +0100 +++ gcc/testsuite/g++.dg/cpp26/expansion-stmt3.C 2026-01-28 12:27:22.289594999 +0100 @@ -40,15 +40,15 @@ struct C namespace N { struct B { constexpr B () {} }; - constexpr A begin (B &) { return A (0); } - constexpr A end (B &) { return A (6); } + constexpr A begin (const B &) { return A (0); } + constexpr A end (const B &) { return A (6); } } namespace O { struct D { constexpr D () {} }; - constexpr C begin (D &) { return C (0, 42, 5); } - constexpr C end (D &) { return C (6, 36, 11); } + constexpr C begin (const D &) { return C (0, 42, 5); } + constexpr C end (const D &) { return C (6, 36, 11); } } template <int N> --- gcc/testsuite/g++.dg/cpp26/expansion-stmt16.C.jj 2026-01-20 01:13:20.349260041 +0100 +++ gcc/testsuite/g++.dg/cpp26/expansion-stmt16.C 2026-01-28 12:27:22.289706924 +0100 @@ -43,23 +43,26 @@ foo () { B c = { 3 }; template for (constexpr auto g : c) // { dg-warning "'template for' only available with" "" { target c++23_down } } - ; // { dg-error "'c' is not a constant expression" "" { target *-*-* } .-1 } + ; // { dg-error "'c' is not a constant expression" "" { target c++14 } .-1 } + // { dg-error "the value of 'c' is not usable in a constant expression" "" { target c++11_down } .-1 } C d = { 3 }; template for (constexpr auto g : d) // { dg-warning "'template for' only available with" "" { target c++23_down } } - ; // { dg-error "'d' is not a constant expression" "" { target *-*-* } .-1 } + ; // { dg-error "'d' is not a constant expression" "" { target c++14 } .-1 } // { dg-error "call to non-'constexpr' function 'const A\\\* C::begin\\\(\\\) const'" "" { target c++11_down } .-1 } // { dg-error "call to non-'constexpr' function 'const A\\\* C::end\\\(\\\) const'" "" { target c++11_down } .-2 } + // { dg-error "the type 'const C' of 'constexpr' variable '__for_range ' is not literal" "" { target c++11_down } .-3 } constexpr D e = { 3 }; template for (constexpr auto g : e) // { dg-warning "'template for' only available with" "" { target c++23_down } } - ; // { dg-error "'e' is not a constant expression" "" { target *-*-* } .-1 } + ; // { dg-error "'e' is not a constant expression" "" { target c++14 } .-1 } // { dg-error "call to non-'constexpr' function 'const A\\\* D::end\\\(\\\) const'" "" { target *-*-* } .-1 } constexpr E f = { 3 }; template for (constexpr auto g : f) // { dg-warning "'template for' only available with" "" { target c++23_down } } - ; // { dg-error "'f' is not a constant expression" "" { target *-*-* } .-1 } + ; // { dg-error "'f' is not a constant expression" "" { target c++14 } .-1 } // { dg-error "call to non-'constexpr' function 'const A\\\* E::begin\\\(\\\) const'" "" { target *-*-* } .-1 } constexpr G h = { 3 }; template for (constexpr auto g : h) // { dg-warning "'template for' only available with" "" { target c++23_down } } - ; // { dg-error "'h' is not a constant expression" "" { target *-*-* } .-1 } + ; // { dg-error "'h' is not a constant expression" "" { target c++14 } .-1 } + // { dg-error "the type 'const F' of 'constexpr' variable 'g' is not literal" "" { target c++11_down } .-2 } template for (constexpr auto g : { 1, 2, F { 3 }, 4L }) // { dg-warning "'template for' only available with" "" { target c++23_down } } ; // { dg-error "the type 'const F' of 'constexpr' variable 'g' is not literal" "" { target *-*-* } .-1 } template for (constexpr auto g : H {})// { dg-warning "'template for' only available with" "" { target c++23_down } } --- gcc/testsuite/g++.dg/cpp26/expansion-stmt18.C.jj 2026-01-28 09:54:50.587619229 +0100 +++ gcc/testsuite/g++.dg/cpp26/expansion-stmt18.C 2026-01-28 12:27:22.289840511 +0100 @@ -17,8 +17,8 @@ struct A namespace N { struct B { constexpr B () {} }; - constexpr A begin (B &) { return A (0); } - constexpr A end (B &) { return A (6); } + constexpr A begin (const B &) { return A (0); } + constexpr A end (const B &) { return A (6); } } void --- gcc/testsuite/g++.dg/cpp26/expansion-stmt25.C.jj 2026-01-28 09:54:50.587756365 +0100 +++ gcc/testsuite/g++.dg/cpp26/expansion-stmt25.C 2026-01-28 12:27:22.289942910 +0100 @@ -15,8 +15,8 @@ struct A namespace N { struct B { constexpr B () {} }; - constexpr A begin (B &) { return A (0); } - constexpr A end (B &) { return A (6); } + constexpr A begin (const B &) { return A (0); } + constexpr A end (const B &) { return A (6); } } void --- gcc/testsuite/g++.dg/cpp26/expansion-stmt26.C.jj 2026-01-28 12:27:22.290040084 +0100 +++ gcc/testsuite/g++.dg/cpp26/expansion-stmt26.C 2026-01-28 12:27:22.290040084 +0100 @@ -0,0 +1,18 @@ +// C++26 P1306R5 - Expansion statements +// { dg-do run { target c++23 } } +// { dg-options "" } + +#include <span> + +constexpr int arr[3] = { 1, 2, 3 }; +consteval std::span <const int> foo () { return std::span <const int> (arr); } + +int +main () +{ + int r = 0; + template for (constexpr auto m : foo ()) // { dg-warning "'template for' only available with" "" { target c++23_down } } + r += m; + if (r != 6) + __builtin_abort (); +} --- gcc/testsuite/g++.dg/reflect/p3491-2.C.jj 2026-01-15 16:33:47.014097840 +0100 +++ gcc/testsuite/g++.dg/reflect/p3491-2.C 2026-01-28 13:04:13.083366251 +0100 @@ -17,17 +17,9 @@ consteval void bar() { consteval int baz() { int r = 0; -#if 0 - // TODO: This doesn't work yet. template for (constexpr int I : std::define_static_array(foo())) { r += I; } -#else - // Ugly workaround for that. - template for (constexpr int I : (const std::span<const int>)std::define_static_array(foo())) { - r += I; - } -#endif return r; } @@ -45,6 +37,15 @@ consteval int fred() { return (... + m); } +consteval int garply() { + int r = 0; + template for (constexpr int I : (const std::span<const int>)std::define_static_array(foo())) { + r += I; + } + return r; +} + static_assert (baz() == 6); static_assert (qux() == 6); static_assert (fred<int>() == 6); +static_assert (garply() == 6); Jakub
