[ValueTracking] Out of range shifts might be undef
If it is possible for the RHS of a shift operation to be greater than or equal
to the bit-width, then the result might be undef, and we can't report any known
bits.
In some cases, this was allowing a transformation in instcombine which widened
an undef value from i1 to i32, increasing the range of values that a function
could return.
Differential revision: https://reviews.llvm.org/D30781
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297724
91177308-0d34-0410-b5e6-
96231b3b80d8
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