On Thu, 10 Jul 2025 at 09:06, Jakub Jelinek wrote:
>
> On Wed, Jul 09, 2025 at 06:45:41PM -0400, Jason Merrill wrote:
> > > + && reduced_constant_expression_p (val))
> >
> > And a value doesn't need to be constant to be printable, we should be able
> > to print it unconditionally.
>
> Sure, the question is if printing non-constant value is better for users.
> The change to do unconditionally the %qE results in
> /usr/src/gcc/gcc/testsuite/g++.dg/cpp26/constexpr-eh12.C:71:49: error:
> uncaught exception '(E*)(& heap )'
> while previously it was
> /usr/src/gcc/gcc/testsuite/g++.dg/cpp26/constexpr-eh12.C:71:49: error:
> uncaught exception of type 'E*'
> I've kept the conditional for now but if you really want that change, can
> remove it
> in the 2 spots and tweak constexpr-eh12.C test's expectations.
>
> > Is there a reason not to add it to heap_vars here?
>
> In the earlier patch I had:
>
> > > + case CXA_ALLOCATE_EXCEPTION:
> ...
> > > + tree var = cxa_allocate_exception (loc, type, size_zero_node);
> > > + ctx->global->heap_vars.safe_push (var);
> > > + ctx->global->put_value (var, NULL_TREE);
> vs.
> > > + case CXA_BAD_CAST:
> > > + case CXA_BAD_TYPEID:
> > > + case CXA_THROW_BAD_ARRAY_NEW_LENGTH:
> ...
> > > + tree var = cxa_allocate_exception (loc, type, size_one_node);
> > > + tree ctor
> > > + = build_special_member_call (var, complete_ctor_identifier,
> > > + NULL, type, LOOKUP_NORMAL,
> > > + ctx->quiet ? tf_none
> > > + : tf_warning_or_error);
> > > + if (ctor == error_mark_node)
> > > + {
> > > + *non_constant_p = true;
> > > + return call;
> > > + }
> > > + ctx->global->heap_vars.safe_push (var);
>
> and so it wasn't added to heap_vars if build_special_member_call failed.
> But thinking about it now, we really don't care about what is in heap_vars
> if *non_constant_p, so I've made the change.
>
> The rest incorporated into the following version of the patch, passes
> GXX_TESTSUITE_STDS=98,11,14,17,20,23,26 make check-g++
> RUNTESTFLAGS="--target_board=unix/-fpie dg.exp='constexpr-eh*
> constexpr-asm-5.C static_assert1.C feat-cxx26.C constexpr-throw.C
> constexpr-84192.C constexpr-dynamic*.C consteval34.C constexpr-new27.C
> consteval-memfn1.C constexpr-typeid5.C constexpr-ellipsis*'"
> so far.
>
> 2025-07-10 Jakub Jelinek <ja...@redhat.com>
>
> PR c++/117785
> gcc/c-family/
> * c-cppbuiltin.cc (c_cpp_builtins): Predefine
> __cpp_constexpr_exceptions=202411L for C++26.
> gcc/cp/
> * constexpr.cc: Implement C++26 P3068R5 - constexpr exceptions.
> (class constexpr_global_ctx): Add caught_exceptions and
> uncaught_exceptions members.
> (constexpr_global_ctx::constexpr_global_ctx): Initialize
> uncaught_exceptions.
> (returns, breaks, continues, switches): Move earlier.
> (throws): New function.
> (exception_what_str, diagnose_std_terminate,
> diagnose_uncaught_exception): New functions.
> (enum cxa_builtin): New type.
> (cxx_cxa_builtin_fn_p, cxx_eval_cxa_builtin_fn): New functions.
> (cxx_eval_builtin_function_call): Add jump_target argument. Call
> cxx_eval_cxa_builtin_fn for __builtin_eh_ptr_adjust_ref. Adjust
> cxx_eval_constant_expression calls, if it results in jmp_target,
> set *jump_target to it and return.
> (cxx_bind_parameters_in_call): Add jump_target argument. Pass
> it through to cxx_eval_constant_expression. If it sets *jump_target,
> break.
> (fold_operand): Adjust cxx_eval_constant_expression caller.
> (cxx_eval_assert): Likewise. If it set jmp_target, return true.
> (cxx_eval_internal_function): Add jump_target argument. Pass it
> through to cxx_eval_constant_expression. Return early if
> *jump_target after recursing on args.
> (cxx_eval_dynamic_cast_fn): Likewise. Don't set reference_p for
> C++26 with -fexceptions.
> (cxx_eval_thunk_call): Add jump_target argument. Pass it through
> to cxx_eval_constant_expression.
> (cxx_set_object_constness): Likewise. Don't set TREE_READONLY if
> throws (jump_target).
> (cxx_eval_call_expression): Add jump_target argument. Pass it
> through to cxx_eval_internal_function, cxx_eval_builtin_function_call,
> cxx_eval_thunk_call, cxx_eval_dynamic_cast_fn and
> cxx_set_object_constness. Pass it through also
> cxx_eval_constant_expression on arguments, cxx_bind_parameters_in_call
> and cxx_fold_indirect_ref and for those cases return early if
> *jump_target. Call cxx_eval_cxa_builtin_fn for cxx_cxa_builtin_fn_p
> functions. For cxx_eval_constant_expression on body, pass address of
> cleared jmp_target automatic variable, if it throws propagate to
> *jump_target and make it non-cacheable. For C++26 don't diagnose
> calls to non-constexpr functions before cxx_bind_parameters_in_call
> could report some argument throwing an exception.
> (cxx_eval_unary_expression): Add jump_target argument. Pass it
> through to cxx_eval_constant_expression and return early if
> *jump_target after the call.
> (cxx_fold_pointer_plus_expression): Likewise.
> (cxx_eval_binary_expression): Likewise and similarly for
> cxx_fold_pointer_plus_expression call.
> (cxx_eval_conditional_expression): Pass jump_target to
> cxx_eval_constant_expression on first operand and return early if
> *jump_target after the call.
> (cxx_eval_vector_conditional_expression): Add jump_target argument.
> Pass it through to cxx_eval_constant_expression for all 3 arguments
> and return early if *jump_target after any of those calls.
> (get_array_or_vector_nelts): Add jump_target argument. Pass it
> through to cxx_eval_constant_expression.
> (eval_and_check_array_index): Add jump_target argument. Pass it
> through to cxx_eval_constant_expression calls and return early after
> each of them if *jump_target.
> (cxx_eval_array_reference): Likewise.
> (cxx_eval_component_reference): Likewise.
> (cxx_eval_bit_field_ref): Likewise.
> (cxx_eval_bit_cast): Likewise. Assert CHECKING_P call doesn't
> throw or return.
> (cxx_eval_logical_expression): Add jump_target argument. Pass it
> through to cxx_eval_constant_expression calls and return early after
> each of them if *jump_target.
> (cxx_eval_bare_aggregate): Likewise.
> (cxx_eval_vec_init_1): Add jump_target argument. Pass it through
> to cxx_eval_bare_aggregate and recursive call. Pass it through
> to get_array_or_vector_nelts and cxx_eval_constant_expression
> and return early after it if *jump_target.
> (cxx_eval_vec_init): Add jump_target argument. Pass it through
> to cxx_eval_constant_expression and cxx_eval_vec_init_1.
> (cxx_union_active_member): Add jump_target argument. Pass it
> through to cxx_eval_constant_expression and return early after it
> if *jump_target.
> (cxx_fold_indirect_ref_1): Add jump_target argument. Pass it
> through to cxx_union_active_member and recursive calls.
> (cxx_eval_indirect_ref): Add jump_target argument. Pass it through
> to cxx_fold_indirect_ref_1 calls and to recursive call, in which
> case return early after it if *jump_target.
> (cxx_fold_indirect_ref): Add jump_target argument. Pass it through
> to cxx_fold_indirect_ref and cxx_eval_constant_expression calls and
> return early after those if *jump_target.
> (cxx_eval_trinary_expression): Add jump_target argument. Pass it
> through to cxx_eval_constant_expression calls and return early after
> those if *jump_target.
> (cxx_eval_store_expression): Add jump_target argument. Pass it
> through to cxx_eval_constant_expression and eval_and_check_array_index
> calls and return early after those if *jump_target.
> (cxx_eval_increment_expression): Add jump_target argument. Pass it
> through to cxx_eval_constant_expression calls and return early after
> those if *jump_target.
> (label_matches): Handle VAR_DECL case.
> (cxx_eval_statement_list): Remove local_target variable and
> !jump_target handling. Handle throws (jump_target) like returns or
> breaks.
> (cxx_eval_loop_expr): Remove local_target variable and !jump_target
> handling. Pass it through to cxx_eval_constant_expression. Handle
> throws (jump_target) like returns.
> (cxx_eval_switch_expr): Pass jump_target through to
> cxx_eval_constant_expression on cond, return early after it if
> *jump_target.
> (build_new_constexpr_heap_type): Add jump_target argument. Pass it
> through to cxx_eval_constant_expression calls, return early after
> those if *jump_target.
> (merge_jump_target): New function.
> (cxx_eval_constant_expression): Make jump_target argument no longer
> defaulted, don't test jump_target for NULL. Pass jump_target
> through to recursive calls, cxx_eval_call_expression,
> cxx_eval_store_expression, cxx_eval_indirect_ref,
> cxx_eval_unary_expression, cxx_eval_binary_expression,
> cxx_eval_logical_expression, cxx_eval_array_reference,
> cxx_eval_component_reference, cxx_eval_bit_field_ref,
> cxx_eval_vector_conditional_expression, cxx_eval_bare_aggregate,
> cxx_eval_vec_init, cxx_eval_trinary_expression, cxx_fold_indirect_ref,
> build_new_constexpr_heap_type, cxx_eval_increment_expression,
> cxx_eval_bit_cast and return earlyu after some of those if
> *jump_target as needed.
> (cxx_eval_constant_expression) <case TARGET_EXPR>: For C++26 push
> also CLEANUP_EH_ONLY cleanups, with NULL_TREE marker after them.
> (cxx_eval_constant_expression) <case RETURN_EXPR>: Don't override
> *jump_target if throws (jump_target).
> (cxx_eval_constant_expression) <case TRY_CATCH_EXPR, case TRY_BLOCK,
> case MUST_NOT_THROW_EXPR, case TRY_FINALLY_EXPR, case CLEANUP_STMT>:
> Handle C++26 constant expressions.
> (cxx_eval_constant_expression) <case CLEANUP_POINT_EXPR>: For C++26
> with throws (jump_target) evaluate the CLEANUP_EH_ONLY cleanups as
> well, and if not throws (jump_target) skip those. Set *jump_target
> if some of the cleanups threw.
> (cxx_eval_constant_expression) <case THROW_EXPR>: Recurse on operand
> for C++26.
> (cxx_eval_outermost_constant_expr): Diagnose uncaught exceptions both
> from main expression and cleanups, diagnose also
> break/continue/returns from the main expression. Handle
> CLEANUP_EH_ONLY cleanup markers. Don't diagnose mutable poison stuff
> if non_constant_p. Use different diagnostics for non-deleted heap
> allocations if they were allocated by __cxa_allocate_exception.
> (callee_might_throw): New function.
> (struct check_for_return_continue_data): Add could_throw field.
> (check_for_return_continue): Handle AGGR_INIT_EXPR and CALL_EXPR and
> set d->could_throw if they could throw.
> (potential_constant_expression_1): For CALL_EXPR allow
> cxx_dynamic_cast_fn_p calls. For C++26 set *jump_target to void_node
> for calls that could throw. For C++26 if call to non-constexpr call
> is seen, try to evaluate arguments first and if they could throw,
> don't diagnose call to non-constexpr function nor return false.
> Adjust check_for_return_continue_data initializers and set
> *jump_target to void_node if data.could_throw_p. For C++26 recurse on
> THROW_EXPR argument. Add comment explaining TRY_BLOCK handling with
> C++26 exceptions. Handle throws like returns in some cases.
> * cp-tree.h (MUST_NOT_THROW_NOEXCEPT_P, MUST_NOT_THROW_THROW_P,
> MUST_NOT_THROW_CATCH_P, DECL_EXCEPTION_REFCOUNT): Define.
> (DECL_LOCAL_DECL_P): Fix comment typo, VARIABLE_DECL -> VAR_DECL.
> (enum cp_built_in_function): Add CP_BUILT_IN_EH_PTR_ADJUST_REF,
> (handler_match_for_exception_type): Declare.
> * call.cc (handler_match_for_exception_type): New function.
> * except.cc (initialize_handler_parm): Set MUST_NOT_THROW_CATCH_P
> on newly created MUST_NOT_THROW_EXPR.
> (begin_eh_spec_block): Set MUST_NOT_THROW_NOEXCEPT_P.
> (wrap_cleanups_r): Set MUST_NOT_THROW_THROW_P.
> (build_throw): Add another TARGET_EXPR whose scope spans
> until after the __cxa_throw call and copy pointer value from ptr
> to it and use it in __cxa_throw argument.
> * tree.cc (builtin_valid_in_constant_expr_p): Handle
> CP_BUILT_IN_EH_PTR_ADJUST_REF.
> * decl.cc (cxx_init_decl_processing): Initialize
> __builtin_eh_ptr_adjust_ref FE builtin.
> * pt.cc (tsubst_stmt) <case MUST_NOT_THROW_EXPR>: Copy the
> MUST_NOT_THROW_NOEXCEPT_P, MUST_NOT_THROW_THROW_P and
> MUST_NOT_THROW_CATCH_P flags.
> * cp-gimplify.cc (cp_gimplify_expr) <case CALL_EXPR>: Error on
> non-folded CP_BUILT_IN_EH_PTR_ADJUST_REF calls.
> gcc/testsuite/
> * g++.dg/cpp0x/constexpr-ellipsis2.C: Expect different diagnostics for
> C++26.
> * g++.dg/cpp0x/constexpr-throw.C: Likewise.
> * g++.dg/cpp1y/constexpr-84192.C: Expect different diagnostics.
> * g++.dg/cpp1y/constexpr-throw.C: Expect different diagnostics for
> C++26.
> * g++.dg/cpp1z/constexpr-asm-5.C: Likewise.
> * g++.dg/cpp26/constexpr-eh1.C: New test.
> * g++.dg/cpp26/constexpr-eh2.C: New test.
> * g++.dg/cpp26/constexpr-eh3.C: New test.
> * g++.dg/cpp26/constexpr-eh4.C: New test.
> * g++.dg/cpp26/constexpr-eh5.C: New test.
> * g++.dg/cpp26/constexpr-eh6.C: New test.
> * g++.dg/cpp26/constexpr-eh7.C: New test.
> * g++.dg/cpp26/constexpr-eh8.C: New test.
> * g++.dg/cpp26/constexpr-eh9.C: New test.
> * g++.dg/cpp26/constexpr-eh10.C: New test.
> * g++.dg/cpp26/constexpr-eh11.C: New test.
> * g++.dg/cpp26/constexpr-eh12.C: New test.
> * g++.dg/cpp26/constexpr-eh13.C: New test.
> * g++.dg/cpp26/constexpr-eh14.C: New test.
> * g++.dg/cpp26/constexpr-eh15.C: New test.
> * g++.dg/cpp26/feat-cxx26.C: Change formatting in __cpp_pack_indexing
> and __cpp_pp_embed test. Add __cpp_constexpr_exceptions test.
> * g++.dg/cpp26/static_assert1.C: Expect different diagnostics for
> C++26.
> * g++.dg/cpp2a/consteval34.C: Likewise.
> * g++.dg/cpp2a/consteval-memfn1.C: Likewise.
> * g++.dg/cpp2a/constexpr-dynamic4.C: For C++26 add std::exception and
> std::bad_cast definitions and expect different diagnostics.
> * g++.dg/cpp2a/constexpr-dynamic6.C: Likewise.
> * g++.dg/cpp2a/constexpr-dynamic7.C: Likewise.
> * g++.dg/cpp2a/constexpr-dynamic8.C: Likewise.
> * g++.dg/cpp2a/constexpr-dynamic9.C: Likewise.
> * g++.dg/cpp2a/constexpr-dynamic11.C: Likewise.
> * g++.dg/cpp2a/constexpr-dynamic14.C: Likewise.
> * g++.dg/cpp2a/constexpr-dynamic18.C: Likewise.
> * g++.dg/cpp2a/constexpr-new27.C: New test.
> * g++.dg/cpp2a/constexpr-typeid5.C: New test.
> libstdc++-v3/
> * include/bits/version.def (constexpr_exceptions): New.
> * include/bits/version.h: Regenerate.
> * libsupc++/exception (std::bad_exception::bad_exception): Add
> _GLIBCXX26_CONSTEXPR.
> (std::bad_exception::~bad_exception, std::bad_exception::what): For
> C++26 add constexpr and define inline.
> * libsupc++/exception.h (std::exception::exception,
> std::exception::operator=): Add _GLIBCXX26_CONSTEXPR.
> (std::exception::~exception, std::exception::what): For C++26 add
> constexpr and define inline.
> * libsupc++/exception_ptr.h (std::make_exception_ptr): Add
> _GLIBCXX26_CONSTEXPR. For if consteval use just throw with
> current_exception() in catch.
> (std::exception_ptr::exception_ptr(void*)): For C++26 add constexpr
> and define inline.
> (std::exception_ptr::exception_ptr()): Add _GLIBCXX26_CONSTEXPR.
> (std::exception_ptr::exception_ptr(const exception_ptr&)): Likewise.
> Use __builtin_eh_ptr_adjust_ref if consteval and compiler has it
> instead of _M_addref.
> (std::exception_ptr::exception_ptr(nullptr_t)): Add
> _GLIBCXX26_CONSTEXPR.
> (std::exception_ptr::exception_ptr(exception_ptr&&)): Likewise.
> (std::exception_ptr::operator=): Likewise.
> (std::exception_ptr::~exception_ptr): Likewise. Use
> __builtin_eh_ptr_adjust_ref if consteval and compiler has it
> instead of _M_release.
> (std::exception_ptr::swap): Add _GLIBCXX26_CONSTEXPR.
> (std::exception_ptr::operator bool): Likewise.
> (std::exception_ptr::operator==): Likewise.
> * libsupc++/nested_exception.h
> (std::nested_exception::nested_exception): Add _GLIBCXX26_CONSTEXPR.
> (std::nested_exception::operator=): Likewise.
> (std::nested_exception::~nested_exception): For C++26 add constexpr
> and define inline.
> (std::nested_exception::rethrow_if_nested): Add _GLIBCXX26_CONSTEXPR.
> (std::nested_exception::nested_ptr): Likewise.
> (std::_Nested_exception::_Nested_exception): Likewise.
> (std::throw_with_nested, std::rethrow_if_nested): Likewise.
> * libsupc++/new (std::bad_alloc::bad_alloc): Likewise.
> (std::bad_alloc::operator=): Likewise.
> (std::bad_alloc::~bad_alloc): For C++26 add constexpr and define
> inline.
> (std::bad_alloc::what): Likewise.
> (std::bad_array_new_length::bad_array_new_length): Add
> _GLIBCXX26_CONSTEXPR.
> (std::bad_array_new_length::~bad_array_new_length): For C++26 add
> constexpr and define inline.
> (std::bad_array_new_length::what): Likewise.
> * libsupc++/typeinfo (std::bad_cast::bad_cast): Add
> _GLIBCXX26_CONSTEXPR.
> (std::bad_cast::~bad_cast): For C++26 add constexpr and define inline.
> (std::bad_cast::what): Likewise.
> (std::bad_typeid::bad_typeid): Add _GLIBCXX26_CONSTEXPR.
> (std::bad_typeid::~bad_typeid): For C++26 add constexpr and define
> inline.
> (std::bad_typeid::what): Likewise.
>
I'm seeing some unexpected libstdc++ test failures since this commit
(confirmed by bisection).
$ export GLIBCXX_TESTSUITE_STDS=26
$ make check RUNTESTFLAGS="conformance.exp=25_algo*debug/constexpr*neg.cc
--target_board=unix/-D_GLIBCXX_DEBUG"
FAIL: 25_algorithms/copy/debug/constexpr_neg.cc -std=gnu++26 (test
for errors, line )
FAIL: 25_algorithms/copy/debug/constexpr_neg.cc -std=gnu++26 (test
for excess errors)
FAIL: 25_algorithms/copy_backward/debug/constexpr_neg.cc -std=gnu++26
(test for excess errors)
FAIL: 25_algorithms/equal/debug/constexpr_neg.cc -std=gnu++26 (test
for errors, line )
FAIL: 25_algorithms/equal/debug/constexpr_neg.cc -std=gnu++26 (test
for excess errors)
FAIL: 25_algorithms/lower_bound/debug/constexpr_partitioned_neg.cc
-std=gnu++26 (test for excess errors)
FAIL: 25_algorithms/lower_bound/debug/constexpr_partitioned_pred_neg.cc
-std=gnu++26 (test for excess errors)
FAIL: 25_algorithms/lower_bound/debug/constexpr_valid_range_neg.cc
-std=gnu++26 (test for excess errors)
FAIL: 25_algorithms/upper_bound/debug/constexpr_partitioned_neg.cc
-std=gnu++26 (test for excess errors)
FAIL: 25_algorithms/upper_bound/debug/constexpr_partitioned_pred_neg.cc
-std=gnu++26 (test for excess errors)
FAIL: 25_algorithms/upper_bound/debug/constexpr_valid_range_neg.cc
-std=gnu++26 (test for excess errors)
The difference is in the diagnostic we get from the expansion of this macro:
#define _GLIBCXX_DEBUG_VERIFY_AT_F(_Cond,_ErrMsg,_File,_Line,_Func) \
do { \
if (__builtin_expect(!bool(_Cond), false)) \
__gnu_debug::_Error_formatter::_S_at(_File, _Line, _Func) \
._ErrMsg._M_error(); \
} while (false)
The dg-error lines in the tests expect a "non-constant condition"
error and the location to match:
// { dg-error "_Error_formatter::_M_error()" "" { target *-*-* } 0 }
but now the error points to the _Error_formatter::_S_at(...) function.
The diagnostic only changed for C++26, and I'm not sure why (the _S_at
function isn't constexpr, so why wasn't it failing there before?)
Is this change in diagnostics expected?
I already have a patch to make the necessary changes to the tests, but
I wanted to understand why it is required.
The fixes are all of this form:
-// { dg-error "_Error_formatter::_M_error()" "" { target *-*-* } 0 }
+// { dg-error "_Error_formatter::(_M_error|_S_at)" "" { target *-*-* } 0 }
