[PATCH] D104547: [langref] attempt to clarify semantics of inttoptr/ptrtoint for non-integral types

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


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Comment at: llvm/docs/LangRef.rst:623
+need to either ensure that a) all possible values are valid, or b)
+appropriate fencing is inserted.  Since the appropriate fencing is
+implementation defined, the optimizer can't do the latter.  The former is
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mkazantsev wrote:
> I think it should clearly be stated what happens if a new cast is inserted (for some reason) and the corresponding rules are not fulfuilled. Does a new cast returns undef, or some other cast (e.g. that goes after it) returns undef, of the entire program has undefined behavior? It's not clear to me how exactly it may break.
It is also not clear from the text if it's safe to insert new dynamic casts if their results are not used. Their result is state-dependent - fine. I don't care what they return. But if they don't *change* the state, they should not have impact on any further casts. So it's not obvious why it should be illegal to make such insertion.


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