[PATCH] D122485: [SimplifyCFG] Fold mutil cases to And mask

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

Let's add the baseline tests as an NFC commit now, so it is easier to see the diffs.

The order of the transforms creates an interesting trade-off, so we need a test like this (and probably even more tests):

  define i8 @same_value_two_case(i32 %i) {
  entry:
    switch i32 %i, label %default [
    i32 -3, label %end
    i32 5, label %end
    ]
  
  default:
    br label %end
  
  end:
    %t0 = phi i8 [ 42, %default ], [ 3, %entry ], [ 3, %entry ]
    ret i8 %t0
  }

This patch creates a difference that survives all the way through codegen - instcombine does not recognize the equivalence between the 2 patterns:
https://alive2.llvm.org/ce/z/mqo87Z

It's not clear to me if there is a universal better form (depends on target?) or even which one is better for IR. To avoid those questions, you can re-order the transforms, so we do not have to answer it in this patch (add a TODO comment though).


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D122485/new/

https://reviews.llvm.org/D122485