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[libc++] Avoid -Wzero-as-null-pointer-constant in operator<=> (llvm#7…
…9465) Issue llvm#43670 describes a situation where the following comparison will issue a warning when -Wzero-as-null-pointer-constant is enabled: #include <compare> 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 llvm#43670
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74 changes: 74 additions & 0 deletions
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...est/std/language.support/cmp/cmp.categories.pre/reject-other-than-literal-zero.verify.cpp
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//===----------------------------------------------------------------------===// | ||
// | ||
// 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 | ||
// | ||
//===----------------------------------------------------------------------===// | ||
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// UNSUPPORTED: c++03, c++11, c++14, c++17 | ||
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// <compare> | ||
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// Ensure we reject all cases where an argument other than a literal 0 is used | ||
// for a comparison against a comparison category type. | ||
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// 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 | ||
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#include <compare> | ||
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#include "test_macros.h" | ||
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#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) | ||
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#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) | ||
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template <typename T> | ||
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}} | ||
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TEST_PASS(v, ==); | ||
TEST_PASS(v, !=); | ||
TEST_PASS(v, <); | ||
TEST_PASS(v, >); | ||
TEST_PASS(v, <=); | ||
TEST_PASS(v, >=); | ||
TEST_PASS(v, <=>); | ||
} | ||
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void f() { | ||
test_category(std::strong_ordering::equivalent); | ||
test_category(std::weak_ordering::equivalent); | ||
test_category(std::partial_ordering::equivalent); | ||
} |
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libcxx/test/std/language.support/cmp/cmp.categories.pre/zero_type.verify.cpp
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