search for: eg0p_

...R intrinsic that implements the same semantic, namely `call void @llvm.memcpy.p0i8.p0i8.i64` (e.g. https://godbolt.org/z/0y1Yqh). This is a problem when designing a libc's memory function as the compiler may choose to replace the implementation with a call to itself (e.g. https://godbolt.org/z/eg0p_E) Using `-fno-builtin-memcpy` prevents the compiler from understanding that an expression has memory copy semantic, effectively removing `@llvm.memcpy` at the IR level : https://godbolt.org/z/lnCIIh. In this specific example, the vectorizer kicks in and the generated code is quite good. Unfortunat...