078d214672
https://github.com/llvm/llvm-project/pull/114990 allowed more aggressive tail duplication for computed-gotos in both pre- and post-regalloc tail duplication. In some cases, performing tail-duplication too early can lead to worse results, especially if we duplicate blocks with a number of phi nodes. This is causing a ~3% performance regression in some workloads using Python 3.12. This patch updates TailDup to delay aggressive tail-duplication for computed gotos to after register allocation. This means we can keep the non-duplicated version for a bit longer throughout the backend, which should reduce compile-time as well as allowing a number of optimizations and simplifications to trigger before drastically expanding the CFG. For the case in https://github.com/llvm/llvm-project/issues/106846, I get the same performance with and without this patch on Skylake. PR: https://github.com/llvm/llvm-project/pull/150911