[Diffusion] rGc93f93b2e3f2: Revert "Revert "Recommit "Revert "[CVP] processSwitch: Remove default case when…

[Alexander Kornienko via Phabricator via cfe-commits]

alexfh added a comment.

In rGc93f93b2e3f28997f794265089fb8138dd5b5f13#1039669 <https://reviews.llvm.org/rGc93f93b2e3f28997f794265089fb8138dd5b5f13#1039669>, @bgraur wrote:

> Early heads up that this revision causes a large regression in compilation time for some of our internal source files: we are seeing an almost 20x increase in compilation times for some files (from 42s to 728s).
>
> I'm working on a reproducer which I'm going to upload when ready.

We're still reducing it, but the test case is a different one as the one I posted in https://reviews.llvm.org/D106056#3023708. Similar to https://reviews.llvm.org/D106056, adding `-mllvm -disable-early-taildup=true` reduces the compilation time to normal.

`perf record --call-graph lbr clang -xc++ -std=gnu++17 -c -O3 test.ii` results in the profile below:

  -   99.28%     0.00%  clang    clang               [.] llvm::FPPassManager::runOnFunction                                                                                                                      ◆
     - 99.27% llvm::FPPassManager::runOnFunction                                                                                                                                                                 ▒
        - 99.24% llvm::MachineFunctionPass::runOnFunction                                                                                                                                                        ▒
           - 97.51% (anonymous namespace)::MachineBlockPlacement::runOnMachineFunction                                                                                                                           ▒
              - 97.51% (anonymous namespace)::MachineBlockPlacement::buildCFGChains                                                                                                                              ▒
                 - 97.45% (anonymous namespace)::MachineBlockPlacement::buildChain                                                                                                                               ▒
                    - 96.82% (anonymous namespace)::MachineBlockPlacement::canTailDuplicateUnplacedPreds                                                                                                         ▒
                         94.66% hasSameSuccessors                                                                                                                                                                ▒

Hope this helps finding out the cause of the problem.

It would be helpful, if you could revert the commit while you're investigating.


BRANCHES
  fix_asan, main

Users:
  junparser (Author)

https://reviews.llvm.org/rGc93f93b2e3f2