contrib/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp

   1 //===- LoopInstSimplify.cpp - Loop Instruction 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 pass performs lightweight instruction simplification on loop bodies.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Transforms/Scalar/LoopInstSimplify.h"
  15 #include "llvm/ADT/PointerIntPair.h"
  16 #include "llvm/ADT/STLExtras.h"
  17 #include "llvm/ADT/SmallPtrSet.h"
  18 #include "llvm/ADT/SmallVector.h"
  19 #include "llvm/ADT/Statistic.h"
  20 #include "llvm/Analysis/AssumptionCache.h"
  21 #include "llvm/Analysis/InstructionSimplify.h"
  22 #include "llvm/Analysis/LoopInfo.h"
  23 #include "llvm/Analysis/LoopPass.h"
  24 #include "llvm/Analysis/TargetLibraryInfo.h"
  25 #include "llvm/IR/BasicBlock.h"
  26 #include "llvm/IR/CFG.h"
  27 #include "llvm/IR/DataLayout.h"
  28 #include "llvm/IR/Dominators.h"
  29 #include "llvm/IR/Instruction.h"
  30 #include "llvm/IR/Instructions.h"
  31 #include "llvm/IR/Module.h"
  32 #include "llvm/IR/PassManager.h"
  33 #include "llvm/IR/User.h"
  34 #include "llvm/Pass.h"
  35 #include "llvm/Support/Casting.h"
  36 #include "llvm/Transforms/Scalar.h"
  37 #include "llvm/Transforms/Utils/Local.h"
  38 #include "llvm/Transforms/Utils/LoopUtils.h"
  39 #include <algorithm>
  40 #include <utility>
  41
  42 using namespace llvm;
  43
  44 #define DEBUG_TYPE "loop-instsimplify"
  45
  46 STATISTIC(NumSimplified, "Number of redundant instructions simplified");
  47
  48 static bool SimplifyLoopInst(Loop *L, DominatorTree *DT, LoopInfo *LI,
  49                              AssumptionCache *AC,
  50                              const TargetLibraryInfo *TLI) {
  51   SmallVector<BasicBlock *, 8> ExitBlocks;
  52   L->getUniqueExitBlocks(ExitBlocks);
  53   array_pod_sort(ExitBlocks.begin(), ExitBlocks.end());
  54
  55   SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
  56
  57   // The bit we are stealing from the pointer represents whether this basic
  58   // block is the header of a subloop, in which case we only process its phis.
  59   using WorklistItem = PointerIntPair<BasicBlock *, 1>;
  60   SmallVector<WorklistItem, 16> VisitStack;
  61   SmallPtrSet<BasicBlock *, 32> Visited;
  62
  63   bool Changed = false;
  64   bool LocalChanged;
  65   do {
  66     LocalChanged = false;
  67
  68     VisitStack.clear();
  69     Visited.clear();
  70
  71     VisitStack.push_back(WorklistItem(L->getHeader(), false));
  72
  73     while (!VisitStack.empty()) {
  74       WorklistItem Item = VisitStack.pop_back_val();
  75       BasicBlock *BB = Item.getPointer();
  76       bool IsSubloopHeader = Item.getInt();
  77       const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
  78
  79       // Simplify instructions in the current basic block.
  80       for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
  81         Instruction *I = &*BI++;
  82
  83         // The first time through the loop ToSimplify is empty and we try to
  84         // simplify all instructions. On later iterations ToSimplify is not
  85         // empty and we only bother simplifying instructions that are in it.
  86         if (!ToSimplify->empty() && !ToSimplify->count(I))
  87           continue;
  88
  89         // Don't bother simplifying unused instructions.
  90         if (!I->use_empty()) {
  91           Value *V = SimplifyInstruction(I, {DL, TLI, DT, AC});
  92           if (V && LI->replacementPreservesLCSSAForm(I, V)) {
  93             // Mark all uses for resimplification next time round the loop.
  94             for (User *U : I->users())
  95               Next->insert(cast<Instruction>(U));
  96
  97             I->replaceAllUsesWith(V);
  98             LocalChanged = true;
  99             ++NumSimplified;
 100           }
 101         }
 102         if (RecursivelyDeleteTriviallyDeadInstructions(I, TLI)) {
 103           // RecursivelyDeleteTriviallyDeadInstruction can remove more than one
 104           // instruction, so simply incrementing the iterator does not work.
 105           // When instructions get deleted re-iterate instead.
 106           BI = BB->begin();
 107           BE = BB->end();
 108           LocalChanged = true;
 109         }
 110
 111         if (IsSubloopHeader && !isa<PHINode>(I))
 112           break;
 113       }
 114
 115       // Add all successors to the worklist, except for loop exit blocks and the
 116       // bodies of subloops. We visit the headers of loops so that we can
 117       // process
 118       // their phis, but we contract the rest of the subloop body and only
 119       // follow
 120       // edges leading back to the original loop.
 121       for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE;
 122            ++SI) {
 123         BasicBlock *SuccBB = *SI;
 124         if (!Visited.insert(SuccBB).second)
 125           continue;
 126
 127         const Loop *SuccLoop = LI->getLoopFor(SuccBB);
 128         if (SuccLoop && SuccLoop->getHeader() == SuccBB &&
 129             L->contains(SuccLoop)) {
 130           VisitStack.push_back(WorklistItem(SuccBB, true));
 131
 132           SmallVector<BasicBlock *, 8> SubLoopExitBlocks;
 133           SuccLoop->getExitBlocks(SubLoopExitBlocks);
 134
 135           for (unsigned i = 0; i < SubLoopExitBlocks.size(); ++i) {
 136             BasicBlock *ExitBB = SubLoopExitBlocks[i];
 137             if (LI->getLoopFor(ExitBB) == L && Visited.insert(ExitBB).second)
 138               VisitStack.push_back(WorklistItem(ExitBB, false));
 139           }
 140
 141           continue;
 142         }
 143
 144         bool IsExitBlock =
 145             std::binary_search(ExitBlocks.begin(), ExitBlocks.end(), SuccBB);
 146         if (IsExitBlock)
 147           continue;
 148
 149         VisitStack.push_back(WorklistItem(SuccBB, false));
 150       }
 151     }
 152
 153     // Place the list of instructions to simplify on the next loop iteration
 154     // into ToSimplify.
 155     std::swap(ToSimplify, Next);
 156     Next->clear();
 157
 158     Changed |= LocalChanged;
 159   } while (LocalChanged);
 160
 161   return Changed;
 162 }
 163
 164 namespace {
 165
 166 class LoopInstSimplifyLegacyPass : public LoopPass {
 167 public:
 168   static char ID; // Pass ID, replacement for typeid
 169
 170   LoopInstSimplifyLegacyPass() : LoopPass(ID) {
 171     initializeLoopInstSimplifyLegacyPassPass(*PassRegistry::getPassRegistry());
 172   }
 173
 174   bool runOnLoop(Loop *L, LPPassManager &LPM) override {
 175     if (skipLoop(L))
 176       return false;
 177     DominatorTreeWrapperPass *DTWP =
 178         getAnalysisIfAvailable<DominatorTreeWrapperPass>();
 179     DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
 180     LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
 181     AssumptionCache *AC =
 182         &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
 183             *L->getHeader()->getParent());
 184     const TargetLibraryInfo *TLI =
 185         &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
 186
 187     return SimplifyLoopInst(L, DT, LI, AC, TLI);
 188   }
 189
 190   void getAnalysisUsage(AnalysisUsage &AU) const override {
 191     AU.addRequired<AssumptionCacheTracker>();
 192     AU.addRequired<TargetLibraryInfoWrapperPass>();
 193     AU.setPreservesCFG();
 194     getLoopAnalysisUsage(AU);
 195   }
 196 };
 197
 198 } // end anonymous namespace
 199
 200 PreservedAnalyses LoopInstSimplifyPass::run(Loop &L, LoopAnalysisManager &AM,
 201                                             LoopStandardAnalysisResults &AR,
 202                                             LPMUpdater &) {
 203   if (!SimplifyLoopInst(&L, &AR.DT, &AR.LI, &AR.AC, &AR.TLI))
 204     return PreservedAnalyses::all();
 205
 206   auto PA = getLoopPassPreservedAnalyses();
 207   PA.preserveSet<CFGAnalyses>();
 208   return PA;
 209 }
 210
 211 char LoopInstSimplifyLegacyPass::ID = 0;
 212
 213 INITIALIZE_PASS_BEGIN(LoopInstSimplifyLegacyPass, "loop-instsimplify",
 214                       "Simplify instructions in loops", false, false)
 215 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 216 INITIALIZE_PASS_DEPENDENCY(LoopPass)
 217 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 218 INITIALIZE_PASS_END(LoopInstSimplifyLegacyPass, "loop-instsimplify",
 219                     "Simplify instructions in loops", false, false)
 220
 221 Pass *llvm::createLoopInstSimplifyPass() {
 222   return new LoopInstSimplifyLegacyPass();
 223 }