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1 //===- SimpleLoopUnswitch.h - Hoist loop-invariant control flow -*- C++ -*-===//
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2 //
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3 // The LLVM Compiler Infrastructure
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4 //
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5 // This file is distributed under the University of Illinois Open Source
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6 // License. See LICENSE.TXT for details.
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7 //
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8 //===----------------------------------------------------------------------===//
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9
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10 #ifndef LLVM_TRANSFORMS_SCALAR_SIMPLELOOPUNSWITCH_H
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11 #define LLVM_TRANSFORMS_SCALAR_SIMPLELOOPUNSWITCH_H
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12
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13 #include "llvm/Analysis/LoopAnalysisManager.h"
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14 #include "llvm/Analysis/LoopInfo.h"
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15 #include "llvm/IR/PassManager.h"
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16 #include "llvm/Transforms/Scalar/LoopPassManager.h"
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17
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18 namespace llvm {
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19
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20 /// This pass transforms loops that contain branches on loop-invariant
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21 /// conditions to have multiple loops. For example, it turns the left into the
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22 /// right code:
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23 ///
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24 /// for (...) if (lic)
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25 /// A for (...)
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26 /// if (lic) A; B; C
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27 /// B else
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28 /// C for (...)
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29 /// A; C
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30 ///
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31 /// This can increase the size of the code exponentially (doubling it every time
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32 /// a loop is unswitched) so we only unswitch if the resultant code will be
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33 /// smaller than a threshold.
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34 ///
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35 /// This pass expects LICM to be run before it to hoist invariant conditions out
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36 /// of the loop, to make the unswitching opportunity obvious.
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37 ///
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38 class SimpleLoopUnswitchPass : public PassInfoMixin<SimpleLoopUnswitchPass> {
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39 public:
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40 SimpleLoopUnswitchPass() = default;
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41
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42 PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM,
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43 LoopStandardAnalysisResults &AR, LPMUpdater &U);
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44 };
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45
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46 /// Create the legacy pass object for the simple loop unswitcher.
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47 ///
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48 /// See the documentaion for `SimpleLoopUnswitchPass` for details.
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49 Pass *createSimpleLoopUnswitchLegacyPass();
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50
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51 } // end namespace llvm
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52
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53 #endif // LLVM_TRANSFORMS_SCALAR_SIMPLELOOPUNSWITCH_H
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