This patch canonicalizes constant expression GEPs to use i8 source
element type, aka ptradd. This is the ConstantFolding equivalent of the
InstCombine canonicalization introduced in #68882.
I believe all our optimizations working on constant expression GEPs
(like GlobalOpt etc) have already been switched to work on offsets, so I
don't expect any significant fallout from this change.
This is part of:
https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699
If `Mask` and `Amt` are not constants and `binop1` and `binop2` are
the same we can transform to:
`(binop (lshift (binop X, Y), Amt), Mask)`
If `binop` is `add`, `lshift` must be `shl`.
If `Mask` and `Amt` are constants `C` and `C1` respectively.
We can transform to:
`(lshift1 (binop1 (binop2 X, (inv_lshift1 C, C1), Y)), C1)`
Saving an instruction IFF:
`lshift1` is same opcode as `lshift2`
Either `bitwise1` and/or `bitwise2` is `and`.
Proofs(1/2): https://alive2.llvm.org/ce/z/BjN-m_
Proofs(2/2): https://alive2.llvm.org/ce/z/bZn5QB
This is to help fix the regression caused in D151807
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D152568
