[PATCH] D156497: [BPF] report fatal error rather than miscompile

[Tamir Duberstein via Phabricator via llvm-commits]

tamird added a comment.

In D156497#4555836 <https://reviews.llvm.org/D156497#4555836>, @ast wrote:

> Agree with Eduard. Doing report_fatal_error() in fail() is cleaner. Proceeding with miscompiled code can only cause further issues in other parts of the backend.
> Not sure why we didn't do this earlier.

Counterpoint: D98471 <https://reviews.llvm.org/D98471>. @yonghong-song can you weigh in please?

It's not apparent that there's an obviously right thing to do here. The standard error emitting mechanisms seem to always involve a risk of miscompilation. Does anyone know how other backends deal with this situation, where code generation cannot reasonably proceed? Looks like other backends use `UNDEF` in at least some similar cases (https://github.com/llvm/llvm-project/blob/cd328c10ad503b243cc333f813c0c6ee66598ffc/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp#L1265-L1269). From my perspective, as long as we miscompile more severely - that is we produce code that definitely doesn't work, rather than code that might work but do the wrong thing - then I'm happy. @ast I believe you suggested constant zeroes rather than UNDEF in earlier reviews -- can you shed some light on why that was deemed preferable?


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