[PATCH] D38042: EmitAssemblyHelper: CodeGenOpts.DisableLLVMOpts should not overrule CodeGenOpts.VerifyModule.

[Chandler Carruth via Phabricator via cfe-commits]

chandlerc added a comment.

In https://reviews.llvm.org/D38042#875328, @aprantl wrote:

> In https://reviews.llvm.org/D38042#875303, @chandlerc wrote:
>
> > But, the verifier itself will just "crash". It won't print a stack trace, but I don't see why that's much better? And this flag is supposed to be a developer option and not a user facing one, so I'm somewhat confused at what the intent is here...
>
>
> No, it will report_fatal_error() instead of crashing the compiler later on.
>  In any case, that is not my primary motivation: The intent is exactly what is illustrated by the testcase, stripping malformed debug info metadata produced by older, buggy versions of clang. The backstory to this is that historically the Verifier was very weak when it came to verifying debug info. To allow us to make the Verifier better (stricter), while still supporting importing of older .bc files produced by older compilers, we added a mechanism that strips all debug info metadata if the verification of the debug info failed, but the bitcode is otherwise correct.


Ok, that use case makes way more sense. I'd replace the change description with some discussion of this use case.

My next question is -- why is this done by the verifier? It seems *really* bad that the verifier *changes the IR*. Don't get me wrong, what you're trying to do (strip malformed debug info) makes perfect sense. But I think that the thing which does that shouldn't be called a verifier. It might *use* the verifier of course.

Last but not least, I still suspect that this shouldn't be run here. If the user wants to disable LLVM passes *and emits LLVM IR*, they should get it unperturbed. The stripping of malformed debug info seems like it should happen later as part of the passes to emit code, and I'd actually expect the LLVM code generator to add the necessary pass rather than relying on every frontend remembering to do so?


https://reviews.llvm.org/D38042