[PATCH] D140689: [DFSan] Add `zeroext` attribute for callbacks with 8bit shadow variable arguments

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

> Some platforms' ABI including LoongArch and RISCV requires unsigned integer data types (except unsigned int) are zero-extended when stored in general-purpose register. So we need to add the zeroext attribute when declaring and calling them.

This is not precise. First, most architectures zero-extend unsigned integer data types... So you change "some" to "many" and drop LoongArch/RISCV.
Second, the problem is that compiler optimization may assume the arguments are zero-extended and, if not, misbehave, e.g. it uses an `i8` argument to index into a jump table. If the argument has non-zero high bits, the output will be wrong.


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https://reviews.llvm.org/D140689