| Issue |
146401
|
| Summary |
Clang does not recognize hand-written buffer aliasing checks
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
davidben
|
Clang (and GCC) don't seem to recognize the `__fh_overlap` macro in https://godbolt.org/z/EqjKe716r as a buffer aliasing check.
The sample was adapted from https://github.com/jvoisin/fortify-headers/blob/master/include/string.h, which is reportedly used in Musl-based Linux distributions like Alpine.
In this case, since `r` was just allocated, the compiler should be able to reason that `r` cannot overlap with `a` and delete the `__fh_overlap` check. It's also important to be able to optimize this because `memcpy` is the usual pattern to load memory without tripping strict aliasing issues.
CC @andres-erbsen
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