[llvm] r191393 - Teach DAGCombiner how to canonicalize dags according to the rule

[Rafael Espíndola]

This causes llc to crash on

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define void @g(i32 %a) {
  %b = lshr i32 %a, 2
  %c = zext i32 %b to i64
  %d = add i64 %c, 1
  %e = shl i64 %c, 2
  tail call void @f(i64 %e)
  ret void
}

declare void @f(i64)
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which is pr17380.

Could you please take a look?

Thanks,
Rafael