src/llvm/lib/Transforms/Utils/GlobalStatus.cpp

   1 //===-- GlobalStatus.cpp - Compute status info for globals -----------------==//
   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 #include "llvm/ADT/SmallPtrSet.h"
  11 #include "llvm/IR/BasicBlock.h"
  12 #include "llvm/IR/CallSite.h"
  13 #include "llvm/IR/GlobalVariable.h"
  14 #include "llvm/IR/IntrinsicInst.h"
  15 #include "llvm/Transforms/Utils/GlobalStatus.h"
  16
  17 using namespace llvm;
  18
  19 /// Return the stronger of the two ordering. If the two orderings are acquire
  20 /// and release, then return AcquireRelease.
  21 ///
  22 static AtomicOrdering strongerOrdering(AtomicOrdering X, AtomicOrdering Y) {
  23   if (X == Acquire && Y == Release)
  24     return AcquireRelease;
  25   if (Y == Acquire && X == Release)
  26     return AcquireRelease;
  27   return (AtomicOrdering)std::max(X, Y);
  28 }
  29
  30 /// It is safe to destroy a constant iff it is only used by constants itself.
  31 /// Note that constants cannot be cyclic, so this test is pretty easy to
  32 /// implement recursively.
  33 ///
  34 bool llvm::isSafeToDestroyConstant(const Constant *C) {
  35   if (isa<GlobalValue>(C))
  36     return false;
  37
  38   if (isa<ConstantInt>(C) || isa<ConstantFP>(C))
  39     return false;
  40
  41   for (const User *U : C->users())
  42     if (const Constant *CU = dyn_cast<Constant>(U)) {
  43       if (!isSafeToDestroyConstant(CU))
  44         return false;
  45     } else
  46       return false;
  47   return true;
  48 }
  49
  50 static bool analyzeGlobalAux(const Value *V, GlobalStatus &GS,
  51                              SmallPtrSetImpl<const PHINode *> &PhiUsers) {
  52   for (const Use &U : V->uses()) {
  53     const User *UR = U.getUser();
  54     if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(UR)) {
  55       GS.HasNonInstructionUser = true;
  56
  57       // If the result of the constantexpr isn't pointer type, then we won't
  58       // know to expect it in various places.  Just reject early.
  59       if (!isa<PointerType>(CE->getType()))
  60         return true;
  61
  62       if (analyzeGlobalAux(CE, GS, PhiUsers))
  63         return true;
  64     } else if (const Instruction *I = dyn_cast<Instruction>(UR)) {
  65       if (!GS.HasMultipleAccessingFunctions) {
  66         const Function *F = I->getParent()->getParent();
  67         if (!GS.AccessingFunction)
  68           GS.AccessingFunction = F;
  69         else if (GS.AccessingFunction != F)
  70           GS.HasMultipleAccessingFunctions = true;
  71       }
  72       if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
  73         GS.IsLoaded = true;
  74         // Don't hack on volatile loads.
  75         if (LI->isVolatile())
  76           return true;
  77         GS.Ordering = strongerOrdering(GS.Ordering, LI->getOrdering());
  78       } else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
  79         // Don't allow a store OF the address, only stores TO the address.
  80         if (SI->getOperand(0) == V)
  81           return true;
  82
  83         // Don't hack on volatile stores.
  84         if (SI->isVolatile())
  85           return true;
  86
  87         GS.Ordering = strongerOrdering(GS.Ordering, SI->getOrdering());
  88
  89         // If this is a direct store to the global (i.e., the global is a scalar
  90         // value, not an aggregate), keep more specific information about
  91         // stores.
  92         if (GS.StoredType != GlobalStatus::Stored) {
  93           if (const GlobalVariable *GV =
  94                   dyn_cast<GlobalVariable>(SI->getOperand(1))) {
  95             Value *StoredVal = SI->getOperand(0);
  96
  97             if (Constant *C = dyn_cast<Constant>(StoredVal)) {
  98               if (C->isThreadDependent()) {
  99                 // The stored value changes between threads; don't track it.
 100                 return true;
 101               }
 102             }
 103
 104             if (StoredVal == GV->getInitializer()) {
 105               if (GS.StoredType < GlobalStatus::InitializerStored)
 106                 GS.StoredType = GlobalStatus::InitializerStored;
 107             } else if (isa<LoadInst>(StoredVal) &&
 108                        cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
 109               if (GS.StoredType < GlobalStatus::InitializerStored)
 110                 GS.StoredType = GlobalStatus::InitializerStored;
 111             } else if (GS.StoredType < GlobalStatus::StoredOnce) {
 112               GS.StoredType = GlobalStatus::StoredOnce;
 113               GS.StoredOnceValue = StoredVal;
 114             } else if (GS.StoredType == GlobalStatus::StoredOnce &&
 115                        GS.StoredOnceValue == StoredVal) {
 116               // noop.
 117             } else {
 118               GS.StoredType = GlobalStatus::Stored;
 119             }
 120           } else {
 121             GS.StoredType = GlobalStatus::Stored;
 122           }
 123         }
 124       } else if (isa<BitCastInst>(I)) {
 125         if (analyzeGlobalAux(I, GS, PhiUsers))
 126           return true;
 127       } else if (isa<GetElementPtrInst>(I)) {
 128         if (analyzeGlobalAux(I, GS, PhiUsers))
 129           return true;
 130       } else if (isa<SelectInst>(I)) {
 131         if (analyzeGlobalAux(I, GS, PhiUsers))
 132           return true;
 133       } else if (const PHINode *PN = dyn_cast<PHINode>(I)) {
 134         // PHI nodes we can check just like select or GEP instructions, but we
 135         // have to be careful about infinite recursion.
 136         if (PhiUsers.insert(PN).second) // Not already visited.
 137           if (analyzeGlobalAux(I, GS, PhiUsers))
 138             return true;
 139       } else if (isa<CmpInst>(I)) {
 140         GS.IsCompared = true;
 141       } else if (const MemTransferInst *MTI = dyn_cast<MemTransferInst>(I)) {
 142         if (MTI->isVolatile())
 143           return true;
 144         if (MTI->getArgOperand(0) == V)
 145           GS.StoredType = GlobalStatus::Stored;
 146         if (MTI->getArgOperand(1) == V)
 147           GS.IsLoaded = true;
 148       } else if (const MemSetInst *MSI = dyn_cast<MemSetInst>(I)) {
 149         assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!");
 150         if (MSI->isVolatile())
 151           return true;
 152         GS.StoredType = GlobalStatus::Stored;
 153       } else if (ImmutableCallSite C = I) {
 154         if (!C.isCallee(&U))
 155           return true;
 156         GS.IsLoaded = true;
 157       } else {
 158         return true; // Any other non-load instruction might take address!
 159       }
 160     } else if (const Constant *C = dyn_cast<Constant>(UR)) {
 161       GS.HasNonInstructionUser = true;
 162       // We might have a dead and dangling constant hanging off of here.
 163       if (!isSafeToDestroyConstant(C))
 164         return true;
 165     } else {
 166       GS.HasNonInstructionUser = true;
 167       // Otherwise must be some other user.
 168       return true;
 169     }
 170   }
 171
 172   return false;
 173 }
 174
 175 bool GlobalStatus::analyzeGlobal(const Value *V, GlobalStatus &GS) {
 176   SmallPtrSet<const PHINode *, 16> PhiUsers;
 177   return analyzeGlobalAux(V, GS, PhiUsers);
 178 }
 179
 180 GlobalStatus::GlobalStatus()
 181     : IsCompared(false), IsLoaded(false), StoredType(NotStored),
 182       StoredOnceValue(nullptr), AccessingFunction(nullptr),
 183       HasMultipleAccessingFunctions(false), HasNonInstructionUser(false),
 184       Ordering(NotAtomic) {}