[llvm] [InstCombine] Canonicalize `switch(X^C)` expressions to `switch(X)` (PR #143677)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> From llvm-opt-benchmark, a potential problem is that this can something turn small switch values into very large ones -- the common case is a xor by INT_MIN. I haven't checked how this affects codegen.

When not invoking the middle-end (except for SimplifyCFG, was not expecting llc to invoke it), the codegen looks slightly worse both in the optimized and unoptimized case: https://llvm.godbolt.org/z/jceqnev4n. Not sure if we wish to proceed further with the canonicalization :(

https://github.com/llvm/llvm-project/pull/143677