| Issue |
64296
|
| Summary |
`__builtin_ctz` does not work at compile time if the argument is 0
|
| Labels |
good first issue,
clang:frontend,
consteval
|
| Assignees |
|
| Reporter |
tbaederr
|
```c++
constexpr int a = __builtin_ctz(0);
```
Clang refuses to [compile this](https://godbolt.org/z/nqM4sKvKb):
```console
<source>:3:19: error: constexpr variable 'a' must be initialized by a constant _expression_
3 | constexpr int a = __builtin_ctz(0);
| ^~~~~~~~~~~~~~~~
```
Both GCC and ICC compile this just fine and I don't see a reason why the argument should be rejected if it's 0?
`APInt::countr_zero` even states in its documentation:
```
Returns
BitWidth if the value is zero, otherwise returns the number of zeros from the least significant bit to the first one bit.
```
so returns what I would expect for 0.
This should be easy to fix, just remove the extra `if (!Val)` check in `ExprConstant.cpp` and adjust (or add) test cases.
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