include/llvm/Transforms/Utils/LoopSimplify.h

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