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| 14 | pmbaty | 1 | //===- LoopSimplify.h - Loop Canonicalization Pass --------------*- C++ -*-===// |
| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | // |
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| 9 | // This pass performs several transformations to transform natural loops into a |
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| 10 | // simpler form, which makes subsequent analyses and transformations simpler and |
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| 11 | // more effective. |
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| 12 | // |
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| 13 | // Loop pre-header insertion guarantees that there is a single, non-critical |
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| 14 | // entry edge from outside of the loop to the loop header. This simplifies a |
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| 15 | // number of analyses and transformations, such as LICM. |
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| 16 | // |
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| 17 | // Loop exit-block insertion guarantees that all exit blocks from the loop |
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| 18 | // (blocks which are outside of the loop that have predecessors inside of the |
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| 19 | // loop) only have predecessors from inside of the loop (and are thus dominated |
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| 20 | // by the loop header). This simplifies transformations such as store-sinking |
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| 21 | // that are built into LICM. |
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| 22 | // |
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| 23 | // This pass also guarantees that loops will have exactly one backedge. |
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| 24 | // |
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| 25 | // Indirectbr instructions introduce several complications. If the loop |
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| 26 | // contains or is entered by an indirectbr instruction, it may not be possible |
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| 27 | // to transform the loop and make these guarantees. Client code should check |
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| 28 | // that these conditions are true before relying on them. |
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| 29 | // |
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| 30 | // Note that the simplifycfg pass will clean up blocks which are split out but |
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| 31 | // end up being unnecessary, so usage of this pass should not pessimize |
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| 32 | // generated code. |
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| 33 | // |
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| 34 | // This pass obviously modifies the CFG, but updates loop information and |
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| 35 | // dominator information. |
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| 36 | // |
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| 37 | //===----------------------------------------------------------------------===// |
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| 38 | #ifndef LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H |
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| 39 | #define LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H |
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| 40 | |||
| 41 | #include "llvm/IR/PassManager.h" |
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| 42 | |||
| 43 | namespace llvm { |
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| 44 | |||
| 45 | class AssumptionCache; |
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| 46 | class DominatorTree; |
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| 47 | class Loop; |
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| 48 | class LoopInfo; |
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| 49 | class MemorySSAUpdater; |
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| 50 | class ScalarEvolution; |
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| 51 | |||
| 52 | /// This pass is responsible for loop canonicalization. |
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| 53 | class LoopSimplifyPass : public PassInfoMixin<LoopSimplifyPass> { |
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| 54 | public: |
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| 55 | PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); |
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| 56 | }; |
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| 57 | |||
| 58 | /// Simplify each loop in a loop nest recursively. |
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| 59 | /// |
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| 60 | /// This takes a potentially un-simplified loop L (and its children) and turns |
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| 61 | /// it into a simplified loop nest with preheaders and single backedges. It will |
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| 62 | /// update \c DominatorTree, \c LoopInfo, \c ScalarEvolution and \c MemorySSA |
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| 63 | /// analyses if they're non-null, and LCSSA if \c PreserveLCSSA is true. |
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| 64 | bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, ScalarEvolution *SE, |
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| 65 | AssumptionCache *AC, MemorySSAUpdater *MSSAU, |
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| 66 | bool PreserveLCSSA); |
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| 67 | |||
| 68 | } // end namespace llvm |
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| 69 | |||
| 70 | #endif // LLVM_TRANSFORMS_UTILS_LOOPSIMPLIFY_H |