forked from OSchip/llvm-project
b01fff06ed
This is a last fix for the corner case of PR32214. Actually this is not really corner case in general. We should not do a loop rotation if we create an additional branch due to it. Consider the case where we have a loop chain H, M, B, C , where H is header with viable fallthrough from pre-header and exit from the loop M - some middle block B - backedge to Header but with exit from the loop also. C - some cold block of the loop. Let's H is determined as a best exit. If we do a loop rotation M, B, C, H we can introduce the extra branch. Let's compute the change in number of branches: +1 branch from pre-header to header -1 branch from header to exit +1 branch from header to middle block if there is such -1 branch from cold bock to header if there is one So if C is not a predecessor of H then we introduce extra branch. This change actually prohibits rotation of the loop if both true 1) Best Exit has next element in chain as successor. 2) Last element in chain is not a predecessor of first element of chain. Reviewers: iteratee, xur Reviewed By: iteratee Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D34271 llvm-svn: 306272 |
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README.txt
Low Level Virtual Machine (LLVM) ================================ This directory and its subdirectories contain source code for LLVM, 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 are writing a package for LLVM, see docs/Packaging.rst for our suggestions.