0b3ec8f48f
In order for std::less<T*> etc. to meet the total order requirements of [comparisons] p2 we need to cast unrelated pointers to uintptr_t before comparing them. Those casts aren't allowed in constant expressions, so only cast when __builtin_constant_p says the result of the comparison is not a compile-time constant (because the arguments are not constants, or the result of the comparison is unspecified). When the result is constant just compare the pointers directly without casting. This ensures that the function can be called in constant expressions with suitable arguments, but still yields a total order even for otherwise unspecified pointer comparisons. For std::less<void> etc. add new overloads for pointers, which use std::less<common_type_t<T*,U*>> directly. Also change the generic overloads to detect when the comparison would call a built-in relational operator with pointer operands, and dispatch that case to the corresponding specialization for void pointers. PR libstdc++/78420 * include/bits/stl_function.h (greater<_Tp*>, less<_Tp*>) (greater_equal<_Tp*>, less_equal<_Tp>*): Add partial specializations to ensure total order for pointers. (greater<void>, less<void>, greater_equal<void>, less_equal<void>): Add operator() overloads for pointer arguments and make generic overloads dispatch to new _S_cmp functions when comparisons would use built-in operators for pointers. * testsuite/20_util/function_objects/comparisons_pointer.cc: New. From-SVN: r258540 |
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README
file: libstdc++-v3/README New users may wish to point their web browsers to the file index.html in the 'doc/html' subdirectory. It contains brief building instructions and notes on how to configure the library in interesting ways.