| Issue |
208531
|
| Summary |
Clang Analyzer reports initialized coroutine promise members as garbage in `await_transform`
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
snarkmaster
|
Clang Static Analyzer **incorrectly** reports `core.UndefinedBinaryOperatorResult` when `promise_type::await_transform` reads coroutine promise members initialized with in-class member initializers.
The expected behavior is "no warning", since the `storage_` promise member is always initialized to `0`.
This report is based on real warnings showing up in [folly/coro](https://github.com/facebook/folly/tree/main/folly/coro).
# Repro
Analyzing the following code ([on Godbolt](https://godbolt.org/z/TKrTaaGhK)) emits warnings:
```
clang++ --analyze -std=c++20 -Xanalyzer -analyzer-output=text repro.cpp
```
```cpp
#include <coroutine>
#include <cstdint>
struct Ready {
bool await_ready() noexcept { return true; }
void await_suspend(std::coroutine_handle<>) noexcept {}
void await_resume() noexcept {}
};
struct PointerTask {
struct promise_type {
std::uintptr_t storage_ = 0;
PointerTask get_return_object() noexcept { return {}; }
std::suspend_never initial_suspend() noexcept { return {}; }
std::suspend_never final_suspend() noexcept { return {}; }
void return_void() noexcept {}
void unhandled_exception() noexcept {}
Ready await_transform(Ready a) noexcept {
(void)(storage_ & ~std::uintptr_t{3});
return a;
}
};
};
PointerTask pointer_repro() { co_await Ready{}; }
```
This warning appears from Clang 15 through trunk:
```
<source>:21:29: warning: The left operand of '&' is a garbage value [core.UndefinedBinaryOperatorResult]
21 | (void)(storage_ & ~std::uintptr_t{3});
| ^
<source>:27:31: note: Calling 'promise_type::await_transform'
27 | PointerTask pointer_repro() { co_await Ready{}; }
| ^~~~~~~~~~~~~~~~
<source>:21:29: note: The left operand of '&' is a garbage value
21 | (void)(storage_ & ~std::uintptr_t{3});
| ~~~~~~~~ ^
```
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