lib/Transforms/Scalar/LoopSimplifyCFG.cpp

   1 //===--------- LoopSimplifyCFG.cpp - Loop CFG Simplification Pass ---------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements the Loop SimplifyCFG Pass. This pass is responsible for
  11 // basic loop CFG cleanup, primarily to assist other loop passes. If you
  12 // encounter a noncanonical CFG construct that causes another loop pass to
  13 // perform suboptimally, this is the place to fix it up.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #include "llvm/Transforms/Scalar/LoopSimplifyCFG.h"
  18 #include "llvm/ADT/SmallVector.h"
  19 #include "llvm/ADT/Statistic.h"
  20 #include "llvm/Analysis/AliasAnalysis.h"
  21 #include "llvm/Analysis/BasicAliasAnalysis.h"
  22 #include "llvm/Analysis/AssumptionCache.h"
  23 #include "llvm/Analysis/DependenceAnalysis.h"
  24 #include "llvm/Analysis/GlobalsModRef.h"
  25 #include "llvm/Analysis/LoopInfo.h"
  26 #include "llvm/Analysis/LoopPass.h"
  27 #include "llvm/Analysis/LoopPassManager.h"
  28 #include "llvm/Analysis/ScalarEvolution.h"
  29 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
  30 #include "llvm/Analysis/TargetTransformInfo.h"
  31 #include "llvm/IR/Dominators.h"
  32 #include "llvm/Transforms/Scalar.h"
  33 #include "llvm/Transforms/Utils/Local.h"
  34 #include "llvm/Transforms/Utils/LoopUtils.h"
  35 using namespace llvm;
  36
  37 #define DEBUG_TYPE "loop-simplifycfg"
  38
  39 static bool simplifyLoopCFG(Loop &L, DominatorTree &DT, LoopInfo &LI) {
  40   bool Changed = false;
  41   // Copy blocks into a temporary array to avoid iterator invalidation issues
  42   // as we remove them.
  43   SmallVector<WeakVH, 16> Blocks(L.blocks());
  44
  45   for (auto &Block : Blocks) {
  46     // Attempt to merge blocks in the trivial case. Don't modify blocks which
  47     // belong to other loops.
  48     BasicBlock *Succ = cast_or_null<BasicBlock>(Block);
  49     if (!Succ)
  50       continue;
  51
  52     BasicBlock *Pred = Succ->getSinglePredecessor();
  53     if (!Pred || !Pred->getSingleSuccessor() || LI.getLoopFor(Pred) != &L)
  54       continue;
  55
  56     // Pred is going to disappear, so we need to update the loop info.
  57     if (L.getHeader() == Pred)
  58       L.moveToHeader(Succ);
  59     LI.removeBlock(Pred);
  60     MergeBasicBlockIntoOnlyPred(Succ, &DT);
  61     Changed = true;
  62   }
  63
  64   return Changed;
  65 }
  66
  67 PreservedAnalyses LoopSimplifyCFGPass::run(Loop &L, AnalysisManager<Loop> &AM) {
  68   const auto &FAM =
  69       AM.getResult<FunctionAnalysisManagerLoopProxy>(L).getManager();
  70   Function *F = L.getHeader()->getParent();
  71
  72   auto *LI = FAM.getCachedResult<LoopAnalysis>(*F);
  73   auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(*F);
  74   assert((LI && DT) && "Analyses for LoopSimplifyCFG not available");
  75
  76   if (!simplifyLoopCFG(L, *DT, *LI))
  77     return PreservedAnalyses::all();
  78   return getLoopPassPreservedAnalyses();
  79 }
  80
  81 namespace {
  82 class LoopSimplifyCFGLegacyPass : public LoopPass {
  83 public:
  84   static char ID; // Pass ID, replacement for typeid
  85   LoopSimplifyCFGLegacyPass() : LoopPass(ID) {
  86     initializeLoopSimplifyCFGLegacyPassPass(*PassRegistry::getPassRegistry());
  87   }
  88
  89   bool runOnLoop(Loop *L, LPPassManager &) override {
  90     if (skipLoop(L))
  91       return false;
  92
  93     DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
  94     LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
  95     return simplifyLoopCFG(*L, DT, LI);
  96   }
  97
  98   void getAnalysisUsage(AnalysisUsage &AU) const override {
  99     AU.addPreserved<DependenceAnalysisWrapperPass>();
 100     getLoopAnalysisUsage(AU);
 101   }
 102 };
 103 }
 104
 105 char LoopSimplifyCFGLegacyPass::ID = 0;
 106 INITIALIZE_PASS_BEGIN(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
 107                       "Simplify loop CFG", false, false)
 108 INITIALIZE_PASS_DEPENDENCY(LoopPass)
 109 INITIALIZE_PASS_END(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
 110                     "Simplify loop CFG", false, false)
 111
 112 Pass *llvm::createLoopSimplifyCFGPass() {
 113   return new LoopSimplifyCFGLegacyPass();
 114 }