| Issue |
99804
|
| Summary |
[clang] document default for `__GNUC__` macros
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
h-vetinari
|
While the [documentation](https://clang.llvm.org/docs/UsersManual.html#cmdoption-fgnuc-version) notes how to override GNU compatibility macros using `-fgnuc-version=`, it doesn't note that it's set by default (it is), nor what value it is set to.
It takes a far bit of [digging](https://github.com/llvm/llvm-project/issues/42162#issuecomment-2241520557) in the code to actually figure out that it's still at
```
__GNUC__=4
__GNUC_MINOR__=2
__GNUC_PATCHLEVEL__=1
```
which is ancient (cf. #42162). The consequence of this is that benign-looking code based on these macros will implicitly fall back to workarounds that shouldn't actually be necessary, and end up pessimizing clang-compiled code. Example: https://github.com/scipy/scipy/issues/20479
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