forked from OSchip/llvm-project
607f8ced39
This fixes the assertion failure "Loop in the Block Graph!". SIMachineScheduler groups instructions into blocks (also referred to as coloring or groups) and then performs a two-level scheduling: inter-block scheduling, and intra-block scheduling. This approach requires that the dependency graph on the blocks which is obtained by contracting the blocks in the original dependency graph is acyclic. In other words: Whenever A and B end up in the same block, all vertices on a path from A to B must be in the same block. When compiling an example consisting of an export followed by a buffer store, we see a dependency between these two. This dependency may be false, but that is a different issue. This dependency was not correctly accounted for by SiMachineScheduler. A new test case si-scheduler-exports.ll demonstrating this is also added in this commit. The problematic part of SiMachineScheduler was a post-optimization of the block assignment that tried to group all export instructions into a separate export block for better execution performance. This routine correctly checked that any paths from exports to exports did not contain any non-exports, but not vice-versa: In case of an export with a non-export successor dependency, that single export was moved to a separate block, which could then be both a successor and a predecessor block of a non-export block. As fix, we now skip export grouping if there are exports with direct non-export successor dependencies. This fixes the issue at hand, but is slightly pessimistic: We *could* group all exports into a separate block that have neither direct nor indirect export successor dependencies. We will review the potential performance impact and potentially revisit with a more sophisticated implementation. Note that just grouping all exports without direct non-export successor dependencies could still lead to illegal blocks, since non-export A could depend on export B that depends on export C. In that case, export C has no non-export successor, but still may not be grouped into an export block. |
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| lib | ||
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| runtimes | ||
| test | ||
| tools | ||
| unittests | ||
| utils | ||
| .clang-format | ||
| .clang-tidy | ||
| .gitattributes | ||
| .gitignore | ||
| CMakeLists.txt | ||
| CODE_OWNERS.TXT | ||
| CREDITS.TXT | ||
| LICENSE.TXT | ||
| README.txt | ||
| RELEASE_TESTERS.TXT | ||
| configure | ||
| llvm.spec.in | ||
README.txt
The LLVM Compiler Infrastructure ================================ 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.