[all-commits] [llvm/llvm-project] 00871e: [SimplifyCFG] Try to fold switch with single resul...

[chenglin.bi via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 00871e2f4f9fdebcfe84f998c17c47465079bc67
      https://github.com/llvm/llvm-project/commit/00871e2f4f9fdebcfe84f998c17c47465079bc67
  Author: chenglin.bi <chenglin.bi at cixcomputing.com>
  Date:   2022-04-15 (Fri, 15 Apr 2022)

  Changed paths:
    M llvm/lib/Transforms/Utils/SimplifyCFG.cpp
    M llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll

  Log Message:
  -----------
  [SimplifyCFG] Try to fold switch with single result value and power-of-2 cases to mask+select

When switch with 2^n cases go to one result, check if the 2^n cases can be covered by n bit masks.
If yes we can use "and condition, ~mask" to simplify the switch

case 0 2 4 6 -> and condition, -7
https://alive2.llvm.org/ce/z/jjH_0N

case 0 2 8 10 -> and condition, -11
https://alive2.llvm.org/ce/z/K7E-2V

case 2 4 8 12 -> and (sub condition, 2), -11
https://alive2.llvm.org/ce/z/CrxbYg

Fix one case of https://github.com/llvm/llvm-project/issues/39957

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D122485