From aa088438784dd76a859eee229ddaec17e0cb0651 Mon Sep 17 00:00:00 2001 From: Louis Dionne Date: Wed, 21 Aug 2024 09:05:55 -0400 Subject: [PATCH] [libc++] Avoid -Wzero-as-null-pointer-constant in operator<=> (#79465) Issue #43670 describes a situation where the following comparison will issue a warning when -Wzero-as-null-pointer-constant is enabled: #include auto b = (1 <=> 2) < 0; This code uses operator<(strong_ordering, Unspecified), which is specified by the Standard to only work with a literal 0. In the library, this is achieved by constructing Unspecified from a pointer, which works but has the downside of triggering the warning. This patch uses an alternative implementation where we require that the operator is used exactly with an int of value 0 (known at compile-time), however that value can technically be an expression like `1 - 1`, which makes us a bit less strict than what's specified in the Standard. Fixes #43670 --- libcxx/include/__compare/ordering.h | 23 ++++-- .../reject-other-than-literal-zero.verify.cpp | 74 +++++++++++++++++++ .../cmp.categories.pre/zero_type.verify.cpp | 57 -------------- 3 files changed, 89 insertions(+), 65 deletions(-) create mode 100644 libcxx/test/std/language.support/cmp/cmp.categories.pre/reject-other-than-literal-zero.verify.cpp delete mode 100644 libcxx/test/std/language.support/cmp/cmp.categories.pre/zero_type.verify.cpp diff --git a/libcxx/include/__compare/ordering.h b/libcxx/include/__compare/ordering.h index 2995d381304f0e..379f3459c681dd 100644 --- a/libcxx/include/__compare/ordering.h +++ b/libcxx/include/__compare/ordering.h @@ -30,14 +30,20 @@ class partial_ordering; class weak_ordering; class strong_ordering; -template -inline constexpr bool __one_of_v = (is_same_v<_Tp, _Args> || ...); - struct _CmpUnspecifiedParam { - _LIBCPP_HIDE_FROM_ABI constexpr _CmpUnspecifiedParam(int _CmpUnspecifiedParam::*) noexcept {} - - template >> - _CmpUnspecifiedParam(_Tp) = delete; + // If anything other than a literal 0 is provided, the behavior is undefined by the Standard. + // + // The alternative to the `__enable_if__` attribute would be to use the fact that a pointer + // can be constructed from literal 0, but this conflicts with `-Wzero-as-null-pointer-constant`. + template > > + _LIBCPP_HIDE_FROM_ABI consteval _CmpUnspecifiedParam(_Tp __zero) noexcept +# if __has_attribute(__enable_if__) + __attribute__((__enable_if__( + __zero == 0, "Only literal 0 is allowed as the operand of a comparison with one of the ordering types"))) +# endif + { + (void)__zero; + } }; class partial_ordering { @@ -269,7 +275,8 @@ inline constexpr strong_ordering strong_ordering::greater(_OrdResult::__greater) /// The types partial_ordering, weak_ordering, and strong_ordering are /// collectively termed the comparison category types. template -concept __comparison_category = __one_of_v<_Tp, partial_ordering, weak_ordering, strong_ordering>; +concept __comparison_category = + is_same_v<_Tp, partial_ordering> || is_same_v<_Tp, weak_ordering> || is_same_v<_Tp, strong_ordering>; #endif // _LIBCPP_STD_VER >= 20 diff --git a/libcxx/test/std/language.support/cmp/cmp.categories.pre/reject-other-than-literal-zero.verify.cpp b/libcxx/test/std/language.support/cmp/cmp.categories.pre/reject-other-than-literal-zero.verify.cpp new file mode 100644 index 00000000000000..b6bc4dd4f097a4 --- /dev/null +++ b/libcxx/test/std/language.support/cmp/cmp.categories.pre/reject-other-than-literal-zero.verify.cpp @@ -0,0 +1,74 @@ +//===----------------------------------------------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// + +// UNSUPPORTED: c++03, c++11, c++14, c++17 + +// + +// Ensure we reject all cases where an argument other than a literal 0 is used +// for a comparison against a comparison category type. + +// Also ensure that we don't warn about providing a null pointer constant when +// comparing an ordering type against literal 0, since one of the common +// implementation strategies is to use a pointer as the "unspecified type". +// ADDITIONAL_COMPILE_FLAGS: -Wzero-as-null-pointer-constant + +#include + +#include "test_macros.h" + +#define TEST_FAIL(v, op) \ + do { \ + /* invalid types */ \ + void(v op 0L); \ + void(0L op v); \ + void(v op 0.0); \ + void(0.0 op v); \ + void(v op nullptr); \ + void(nullptr op v); \ + /* invalid value */ \ + void(v op 1); \ + void(1 op v); \ + /* value not known at compile-time */ \ + int i = 0; \ + void(v op i); \ + void(i op v); \ + } while (false) + +#define TEST_PASS(v, op) \ + do { \ + void(v op 0); \ + void(0 op v); \ + LIBCPP_ONLY(void(v op(1 - 1))); \ + LIBCPP_ONLY(void((1 - 1) op v)); \ + } while (false) + +template +void test_category(T v) { + TEST_FAIL(v, ==); // expected-error 30 {{invalid operands to binary expression}} + TEST_FAIL(v, !=); // expected-error 30 {{invalid operands to binary expression}} + TEST_FAIL(v, <); // expected-error 30 {{invalid operands to binary expression}} + TEST_FAIL(v, <=); // expected-error 30 {{invalid operands to binary expression}} + TEST_FAIL(v, >); // expected-error 30 {{invalid operands to binary expression}} + TEST_FAIL(v, >=); // expected-error 30 {{invalid operands to binary expression}} + TEST_FAIL(v, <=>); // expected-error 30 {{invalid operands to binary expression}} + + TEST_PASS(v, ==); + TEST_PASS(v, !=); + TEST_PASS(v, <); + TEST_PASS(v, >); + TEST_PASS(v, <=); + TEST_PASS(v, >=); + TEST_PASS(v, <=>); +} + +void f() { + test_category(std::strong_ordering::equivalent); + test_category(std::weak_ordering::equivalent); + test_category(std::partial_ordering::equivalent); +} diff --git a/libcxx/test/std/language.support/cmp/cmp.categories.pre/zero_type.verify.cpp b/libcxx/test/std/language.support/cmp/cmp.categories.pre/zero_type.verify.cpp deleted file mode 100644 index 8e3c793de4b92a..00000000000000 --- a/libcxx/test/std/language.support/cmp/cmp.categories.pre/zero_type.verify.cpp +++ /dev/null @@ -1,57 +0,0 @@ -//===----------------------------------------------------------------------===// -// -// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. -// See https://llvm.org/LICENSE.txt for license information. -// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception -// -//===----------------------------------------------------------------------===// - -// UNSUPPORTED: c++03, c++11, c++14, c++17 - -// In MSVC mode, there's a slightly different number of errors printed for -// each of these, so it doesn't add up to the exact expected count of 18. -// XFAIL: msvc - -// - -// Ensure we reject all cases where an argument other than a literal 0 is used -// for a comparison against a comparison category type. - -#include - -#define TEST_FAIL(v, op) \ - void(v op 0L); \ - void(0L op v); \ - void(v op nullptr); \ - void(nullptr op v); \ - void(v op(1 - 1)); \ - void((1 - 1) op v) - -#define TEST_PASS(v, op) \ - void(v op 0); \ - void(0 op v) - -template -void test_category(T v) { - TEST_FAIL(v, ==); // expected-error 18 {{}} - TEST_FAIL(v, !=); // expected-error 18 {{}} - TEST_FAIL(v, <); // expected-error 18 {{}} - TEST_FAIL(v, <=); // expected-error 18 {{}} - TEST_FAIL(v, >); // expected-error 18 {{}} - TEST_FAIL(v, >=); // expected-error 18 {{}} - TEST_FAIL(v, <=>); // expected-error 18 {{}} - - TEST_PASS(v, ==); - TEST_PASS(v, !=); - TEST_PASS(v, <); - TEST_PASS(v, >); - TEST_PASS(v, <=); - TEST_PASS(v, >=); - TEST_PASS(v, <=>); -} - -void f() { - test_category(std::strong_ordering::equivalent); - test_category(std::weak_ordering::equivalent); - test_category(std::partial_ordering::equivalent); -}