forked from OSchip/llvm-project
5bdf72cef6
mapping from a basic block to an incoming value, either for removal or just lookup, is linear in the number of predecessors, and we were doing this for every entry in the 'Preds' list which is in many cases almost all of them! Unfortunately, the fixes are quite ugly. PHI nodes just don't make this operation easy. The efficient way to fix this is to have a clever 'remove_if' operation on PHI nodes that lets us do a single pass over all the incoming values of the original PHI node, extracting the ones we care about. Then we could quickly construct the new phi node from this list. This would remove the remaining underlying quadratic movement of unrelated incoming values and the need for silly backwards looping to "minimize" how often we hit the quadratic case. This is the last obvious fix for PR19499. It shaves another 20% off the compile time for me, and while UpdatePHINodes remains in the profile, most of the time is now stemming from the well known inefficiencies of LVI and jump threading. llvm-svn: 207409 |
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README.txt
Low Level Virtual Machine (LLVM) ================================ This directory and its subdirectories contain source code for the Low Level Virtual Machine, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments. LLVM is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. Please see the documentation provided in docs/ for further assistance with LLVM, and in particular docs/GettingStarted.rst for getting started with LLVM and docs/README.txt for an overview of LLVM's documentation setup. If you're writing a package for LLVM, see docs/Packaging.rst for our suggestions.