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[coroutine] Suppress unreachable-code warning on coroutine statements. (
#77454) This fixes #69219. Consider an example: ``` CoTask my_coroutine() { std::abort(); co_return 1; // unreachable code warning. } ``` Clang emits a CFG-based unreachable warning on the `co_return` statement (precisely the `1` subexpr). If we remove this statement, the program semantic is changed (my_coroutine is not a coroutine anymore). This patch fixes this issue by never considering coroutine statements as dead statements.
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// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -std=c++20 -fsyntax-only -verify -Wunreachable-code | ||
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#include "Inputs/std-coroutine.h" | ||
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extern void abort(void) __attribute__((__noreturn__)); | ||
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struct task { | ||
struct promise_type { | ||
std::suspend_always initial_suspend(); | ||
std::suspend_always final_suspend() noexcept; | ||
void return_void(); | ||
std::suspend_always yield_value(int) { return {}; } | ||
task get_return_object(); | ||
void unhandled_exception(); | ||
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struct Awaiter { | ||
bool await_ready(); | ||
void await_suspend(auto); | ||
int await_resume(); | ||
}; | ||
auto await_transform(const int& x) { return Awaiter{}; } | ||
}; | ||
}; | ||
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task test1() { | ||
abort(); | ||
co_yield 1; | ||
} | ||
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task test2() { | ||
abort(); | ||
1; // expected-warning {{code will never be executed}} | ||
co_yield 1; | ||
} | ||
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task test3() { | ||
abort(); | ||
co_return; | ||
} | ||
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task test4() { | ||
abort(); | ||
1; // expected-warning {{code will never be executed}} | ||
co_return; | ||
} | ||
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task test5() { | ||
abort(); | ||
co_await 1; | ||
} | ||
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task test6() { | ||
abort(); | ||
1; // expected-warning {{code will never be executed}} | ||
co_await 3; | ||
} | ||
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task test7() { | ||
// coroutine statements are not considered unreachable. | ||
co_await 1; | ||
abort(); | ||
co_await 2; | ||
} | ||
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task test8() { | ||
// coroutine statements are not considered unreachable. | ||
abort(); | ||
co_return; | ||
1 + 1; // expected-warning {{code will never be executed}} | ||
} | ||
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task test9() { | ||
abort(); | ||
// This warning is emitted on the declaration itself, rather the coroutine substmt. | ||
int x = co_await 1; // expected-warning {{code will never be executed}} | ||
} |