[InstCombine] Add transform `(icmp pred (shl {nsw and/or nuw} X, Y), C)` -> `(icmp pred X, C)`
Three new transforms:
1) `(icmp pred (shl nsw nuw X, Y), C)` [if `C <= 0`] -> `(icmp pred X, C)`
- ugt: https://alive2.llvm.org/ce/z/K_57J_
- sgt: https://alive2.llvm.org/ce/z/BL8u_a
- sge: https://alive2.llvm.org/ce/z/yZZVYz
- uge: https://alive2.llvm.org/ce/z/R4jwwJ
- ule: https://alive2.llvm.org/ce/z/-gbmth
- sle: https://alive2.llvm.org/ce/z/ycZVsh
- slt: https://alive2.llvm.org/ce/z/4MzHYm
- sle: https://alive2.llvm.org/ce/z/fgNfex
- ult: https://alive2.llvm.org/ce/z/cXfvH5
- eq : https://alive2.llvm.org/ce/z/sZh_Ti
- ne : https://alive2.llvm.org/ce/z/UrqSWA
2) `(icmp eq/ne (shl {nsw|nuw} X, Y), 0)` -> `(icmp eq/ne X, 0)`
- eq+nsw: https://alive2.llvm.org/ce/z/aSJN6D
- eq+nuw: https://alive2.llvm.org/ce/z/r2_-br
- ne+nuw: https://alive2.llvm.org/ce/z/RkETtu
- ne+nsw: https://alive2.llvm.org/ce/z/8iSfW3
3) `(icmp slt (shl nsw X, Y), 0/1)` -> `(icmp pred X, 0/1)`
`(icmp sgt (shl nsw X, Y), 0/-1)` -> `(icmp pred X, 0/-1)`
- slt: https://alive2.llvm.org/ce/z/eZYRan
- sgt: https://alive2.llvm.org/ce/z/QQeP26
Transform 3) is really sle/slt/sge/sgt with 0, but sle/sge
canonicalize to slt/sgt respectively so its implemented as such.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D145341