[llvm-dev] Is it valid to dereference a pointer that have undef bits in its offset?

[Juneyoung Lee via llvm-dev]

Hello all,

Is it valid to dereference a pointer that has undef bits in its offset?

For example,

%p = alloca [8 x i8]
%p2 = gep %p, (undef & 8)
store 0, %p2

undef & 8 is always less than 8, so technically it will store zero to one
of the array's elements.

The reason is that I want to improve no-undef analysis by suggesting that a
pointer that is passed to load/store is well-defined, by making it raise UB
when a pointer with undef bits is given.

A suggested patch is here: https://reviews.llvm.org/D87994

I wonder whether there is a case using this to do something that I'm not
aware.

Thanks,
Juneyoung
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