Mastodawn

Ugh.. when people won't take fixes because in their opinion the C specification is wrong and their feeling about how compilers work should be how it works:
https://lore.kernel.org/lkml/CAADnVQJN[email protected]/

Re: [PATCH v1 1/2] libbpf: Fix strict aliasing violations in hashmap - Alexei Starovoitov

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Aiden Grossman Mar 22

@irogers Yeah, this is pretty frustrating.

I remember seeing a lot of this when looking at where people where people were passing -fno-lifetime-dse across OSS projects when implementing the optimization in clang. There were several comments complaining about compiler optimizations, with optimizations quoted for emphasis.

I guess the behavior of optimizations like -flifetime-dse and -fstrict-aliasing can be somewhat surprising for users. But the C/C++ standards are what they are and these rules do help the compiler optimize better.

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Ian Rogers

@boomanaiden154 when we transitioned Android to clang a common practice in Android was to have functions doing "this == NULL" particularly in helper cast functions, which would then just return NULL. Clang/llvm would remove these tests as "this" can never be NULL causing chaos. The reaction from senior engineers was clang was wrong and we needed our own C++ specification. 🤷