[ConstantRange] makeGuaranteedNoWrapRegion(): `shl` support
If all the shifts amount are already poison-producing,
then we can add more poison-producing flags ontop:
Otherwise, we should only consider the possible range of shift amts that don't result in poison.
For unsigned range not not overflow, we must not shift out any set bits,
and the actual limit for `x` can be computed by backtransforming
the maximal value we could ever get out of the `shl` - `-1` through
`lshr`. If the `x` is any larger than that then it will overflow.
Likewise for signed range, but just in signed domain..
This is based on the general idea outlined by @nikic in https://reviews.llvm.org/D68672#1714990
Reviewers: nikic, sanjoy
Reviewed By: nikic
Subscribers: hiraditya, llvm-commits, nikic
Differential Revision: https://reviews.llvm.org/D69217
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375370 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed