[llvm] [SimplifyCFG] Add optimization for switches of powers of two (PR #70977)

[via llvm-commits]

================
@@ -0,0 +1,90 @@
+; RUN: opt %s -passes='simplifycfg<switch-to-lookup>' -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s
----------------
DianQK wrote:

You can use `llvm/utils/update_test_checks.py` to generate tests.

https://github.com/llvm/llvm-project/pull/70977