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Teach globalsmodref-aa to track scalar pointer global variables which point
to unaliased allocations. Use this information to disambiguate pointers loaded from them. This is a very common case, so it's worthwhile to handle efficiently. This implements Analysis/GlobalsModRef/indirect-global.ll git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@30684 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
parent
b363312940
commit
ab38358fa0
@ -19,6 +19,7 @@
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#include "llvm/Pass.h"
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#include "llvm/Instructions.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/CallGraph.h"
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#include "llvm/Support/InstIterator.h"
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@ -41,7 +42,10 @@ namespace {
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Statistic<>
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NumReadMemFunctions("globalsmodref-aa",
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"Number of functions that only read memory");
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Statistic<>
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NumIndirectGlobalVars("globalsmodref-aa",
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"Number of indirect global objects");
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/// FunctionRecord - One instance of this structure is stored for every
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/// function in the program. Later, the entries for these functions are
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/// removed if the function is found to call an external function (in which
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@ -72,6 +76,14 @@ namespace {
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/// taken.
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std::set<GlobalValue*> NonAddressTakenGlobals;
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/// IndirectGlobals - The memory pointed to by this global is known to be
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/// 'owned' by the global.
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std::set<GlobalValue*> IndirectGlobals;
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/// AllocsForIndirectGlobals - If an instruction allocates memory for an
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/// indirect global, this map indicates which one.
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std::map<Value*, GlobalValue*> AllocsForIndirectGlobals;
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/// FunctionInfo - For each function, keep track of what globals are
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/// modified or read.
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std::map<Function*, FunctionRecord> FunctionInfo;
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@ -131,8 +143,10 @@ namespace {
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void AnalyzeGlobals(Module &M);
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void AnalyzeCallGraph(CallGraph &CG, Module &M);
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void AnalyzeSCC(std::vector<CallGraphNode *> &SCC);
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bool AnalyzeUsesOfGlobal(Value *V, std::vector<Function*> &Readers,
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std::vector<Function*> &Writers);
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bool AnalyzeUsesOfPointer(Value *V, std::vector<Function*> &Readers,
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std::vector<Function*> &Writers,
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GlobalValue *OkayStoreDest = 0);
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bool AnalyzeIndirectGlobalMemory(GlobalValue *GV);
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};
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RegisterPass<GlobalsModRef> X("globalsmodref-aa",
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@ -142,8 +156,30 @@ namespace {
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Pass *llvm::createGlobalsModRefPass() { return new GlobalsModRef(); }
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/// getUnderlyingObject - This traverses the use chain to figure out what object
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/// the specified value points to. If the value points to, or is derived from,
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/// a global object, return it.
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static Value *getUnderlyingObject(Value *V) {
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if (!isa<PointerType>(V->getType())) return V;
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// If we are at some type of object... return it.
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if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) return GV;
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// Traverse through different addressing mechanisms.
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if (Instruction *I = dyn_cast<Instruction>(V)) {
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if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
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return getUnderlyingObject(I->getOperand(0));
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} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
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if (CE->getOpcode() == Instruction::Cast ||
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CE->getOpcode() == Instruction::GetElementPtr)
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return getUnderlyingObject(CE->getOperand(0));
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}
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// Othewise, we don't know what this is, return it as the base pointer.
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return V;
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}
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/// AnalyzeGlobalUses - Scan through the users of all of the internal
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/// AnalyzeGlobals - Scan through the users of all of the internal
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/// GlobalValue's in the program. If none of them have their "Address taken"
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/// (really, their address passed to something nontrivial), record this fact,
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/// and record the functions that they are used directly in.
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@ -151,7 +187,7 @@ void GlobalsModRef::AnalyzeGlobals(Module &M) {
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std::vector<Function*> Readers, Writers;
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for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
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if (I->hasInternalLinkage()) {
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if (!AnalyzeUsesOfGlobal(I, Readers, Writers)) {
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if (!AnalyzeUsesOfPointer(I, Readers, Writers)) {
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// Remember that we are tracking this global.
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NonAddressTakenGlobals.insert(I);
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++NumNonAddrTakenFunctions;
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@ -162,7 +198,7 @@ void GlobalsModRef::AnalyzeGlobals(Module &M) {
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for (Module::global_iterator I = M.global_begin(), E = M.global_end();
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I != E; ++I)
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if (I->hasInternalLinkage()) {
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if (!AnalyzeUsesOfGlobal(I, Readers, Writers)) {
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if (!AnalyzeUsesOfPointer(I, Readers, Writers)) {
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// Remember that we are tracking this global, and the mod/ref fns
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NonAddressTakenGlobals.insert(I);
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for (unsigned i = 0, e = Readers.size(); i != e; ++i)
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@ -172,28 +208,39 @@ void GlobalsModRef::AnalyzeGlobals(Module &M) {
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for (unsigned i = 0, e = Writers.size(); i != e; ++i)
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FunctionInfo[Writers[i]].GlobalInfo[I] |= Mod;
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++NumNonAddrTakenGlobalVars;
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// If this global holds a pointer type, see if it is an indirect global.
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if (isa<PointerType>(I->getType()->getElementType()) &&
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AnalyzeIndirectGlobalMemory(I))
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++NumIndirectGlobalVars;
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}
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Readers.clear(); Writers.clear();
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}
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}
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/// AnalyzeUsesOfGlobal - Look at all of the users of the specified global value
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/// derived pointer. If this is used by anything complex (i.e., the address
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/// escapes), return true. Also, while we are at it, keep track of those
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/// functions that read and write to the value.
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bool GlobalsModRef::AnalyzeUsesOfGlobal(Value *V,
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std::vector<Function*> &Readers,
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std::vector<Function*> &Writers) {
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/// AnalyzeUsesOfPointer - Look at all of the users of the specified pointer.
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/// If this is used by anything complex (i.e., the address escapes), return
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/// true. Also, while we are at it, keep track of those functions that read and
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/// write to the value.
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///
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/// If OkayStoreDest is non-null, stores into this global are allowed.
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bool GlobalsModRef::AnalyzeUsesOfPointer(Value *V,
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std::vector<Function*> &Readers,
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std::vector<Function*> &Writers,
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GlobalValue *OkayStoreDest) {
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if (!isa<PointerType>(V->getType())) return true;
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for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
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if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
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Readers.push_back(LI->getParent()->getParent());
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} else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
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if (V == SI->getOperand(0)) return true; // Storing the pointer
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Writers.push_back(SI->getParent()->getParent());
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if (V == SI->getOperand(1)) {
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Writers.push_back(SI->getParent()->getParent());
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} else if (SI->getOperand(1) != OkayStoreDest) {
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return true; // Storing the pointer
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}
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} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
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if (AnalyzeUsesOfGlobal(GEP, Readers, Writers)) return true;
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if (AnalyzeUsesOfPointer(GEP, Readers, Writers)) return true;
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} else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
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// Make sure that this is just the function being called, not that it is
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// passing into the function.
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@ -207,19 +254,91 @@ bool GlobalsModRef::AnalyzeUsesOfGlobal(Value *V,
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} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) {
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if (CE->getOpcode() == Instruction::GetElementPtr ||
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CE->getOpcode() == Instruction::Cast) {
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if (AnalyzeUsesOfGlobal(CE, Readers, Writers))
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if (AnalyzeUsesOfPointer(CE, Readers, Writers))
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return true;
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} else {
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return true;
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}
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} else if (GlobalValue *GV = dyn_cast<GlobalValue>(*UI)) {
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if (AnalyzeUsesOfGlobal(GV, Readers, Writers)) return true;
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} else if (SetCondInst *SCI = dyn_cast<SetCondInst>(*UI)) {
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if (!isa<ConstantPointerNull>(SCI->getOperand(1)))
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return true; // Allow comparison against null.
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} else if (FreeInst *F = dyn_cast<FreeInst>(*UI)) {
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Writers.push_back(F->getParent()->getParent());
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} else {
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return true;
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}
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return false;
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}
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/// AnalyzeIndirectGlobalMemory - We found an non-address-taken global variable
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/// which holds a pointer type. See if the global always points to non-aliased
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/// heap memory: that is, all initializers of the globals are allocations, and
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/// those allocations have no use other than initialization of the global.
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/// Further, all loads out of GV must directly use the memory, not store the
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/// pointer somewhere. If this is true, we consider the memory pointed to by
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/// GV to be owned by GV and can disambiguate other pointers from it.
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bool GlobalsModRef::AnalyzeIndirectGlobalMemory(GlobalValue *GV) {
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// Keep track of values related to the allocation of the memory, f.e. the
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// value produced by the malloc call and any casts.
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std::vector<Value*> AllocRelatedValues;
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// Walk the user list of the global. If we find anything other than a direct
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// load or store, bail out.
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for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){
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if (LoadInst *LI = dyn_cast<LoadInst>(*I)) {
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// The pointer loaded from the global can only be used in simple ways:
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// we allow addressing of it and loading storing to it. We do *not* allow
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// storing the loaded pointer somewhere else or passing to a function.
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std::vector<Function*> ReadersWriters;
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if (AnalyzeUsesOfPointer(LI, ReadersWriters, ReadersWriters))
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return false; // Loaded pointer escapes.
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// TODO: Could try some IP mod/ref of the loaded pointer.
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} else if (StoreInst *SI = dyn_cast<StoreInst>(*I)) {
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// Storing the global itself.
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if (SI->getOperand(0) == GV) return false;
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// If storing the null pointer, ignore it.
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if (isa<ConstantPointerNull>(SI->getOperand(0)))
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continue;
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// Check the value being stored.
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Value *Ptr = getUnderlyingObject(SI->getOperand(0));
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// FIXME: handle calloc.
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if (isa<MallocInst>(Ptr)) {
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// Okay, easy case.
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} else if (CallInst *CI = dyn_cast<CallInst>(Ptr)) {
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Function *F = CI->getCalledFunction();
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if (!F || !F->isExternal()) return false; // Too hard to analyze.
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if (F->getName() != "calloc") return false; // Not calloc.
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} else {
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return false; // Too hard to analyze.
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}
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// Analyze all uses of the allocation. If any of them are used in a
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// non-simple way (e.g. stored to another global) bail out.
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std::vector<Function*> ReadersWriters;
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if (AnalyzeUsesOfPointer(Ptr, ReadersWriters, ReadersWriters, GV))
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return false; // Loaded pointer escapes.
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// Remember that this allocation is related to the indirect global.
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AllocRelatedValues.push_back(Ptr);
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} else {
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// Something complex, bail out.
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return false;
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}
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}
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// Okay, this is an indirect global. Remember all of the allocations for
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// this global in AllocsForIndirectGlobals.
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while (!AllocRelatedValues.empty()) {
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AllocsForIndirectGlobals[AllocRelatedValues.back()] = GV;
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AllocRelatedValues.pop_back();
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}
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IndirectGlobals.insert(GV);
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return true;
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}
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/// AnalyzeCallGraph - At this point, we know the functions where globals are
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/// immediately stored to and read from. Propagate this information up the call
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/// graph to all callers and compute the mod/ref info for all memory for each
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@ -328,44 +447,62 @@ void GlobalsModRef::AnalyzeSCC(std::vector<CallGraphNode *> &SCC) {
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/// getUnderlyingObject - This traverses the use chain to figure out what object
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/// the specified value points to. If the value points to, or is derived from,
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/// a global object, return it.
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static const GlobalValue *getUnderlyingObject(const Value *V) {
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if (!isa<PointerType>(V->getType())) return 0;
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// If we are at some type of object... return it.
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if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) return GV;
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// Traverse through different addressing mechanisms...
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if (const Instruction *I = dyn_cast<Instruction>(V)) {
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if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
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return getUnderlyingObject(I->getOperand(0));
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} else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
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if (CE->getOpcode() == Instruction::Cast ||
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CE->getOpcode() == Instruction::GetElementPtr)
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return getUnderlyingObject(CE->getOperand(0));
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}
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return 0;
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}
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/// alias - If one of the pointers is to a global that we are tracking, and the
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/// other is some random pointer, we know there cannot be an alias, because the
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/// address of the global isn't taken.
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AliasAnalysis::AliasResult
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GlobalsModRef::alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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GlobalValue *GV1 = const_cast<GlobalValue*>(getUnderlyingObject(V1));
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GlobalValue *GV2 = const_cast<GlobalValue*>(getUnderlyingObject(V2));
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// Get the base object these pointers point to.
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Value *UV1 = getUnderlyingObject(const_cast<Value*>(V1));
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Value *UV2 = getUnderlyingObject(const_cast<Value*>(V2));
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// If either of the underlying values is a global, they may be non-addr-taken
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// globals, which we can answer queries about.
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GlobalValue *GV1 = dyn_cast<GlobalValue>(UV1);
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GlobalValue *GV2 = dyn_cast<GlobalValue>(UV2);
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if (GV1 || GV2) {
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// If the global's address is taken, pretend we don't know it's a pointer to
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// the global.
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if (GV1 && !NonAddressTakenGlobals.count(GV1)) GV1 = 0;
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if (GV2 && !NonAddressTakenGlobals.count(GV2)) GV2 = 0;
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// If the global's address is taken, pretend we don't know it's a pointer to
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// the global.
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if (GV1 && !NonAddressTakenGlobals.count(GV1)) GV1 = 0;
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if (GV2 && !NonAddressTakenGlobals.count(GV2)) GV2 = 0;
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// If the the two pointers are derived from two different non-addr-taken
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// globals, or if one is and the other isn't, we know these can't alias.
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if ((GV1 || GV2) && GV1 != GV2)
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return NoAlias;
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// Otherwise if they are both derived from the same addr-taken global, we
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// can't know the two accesses don't overlap.
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}
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// These pointers may be based on the memory owned by an indirect global. If
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// so, we may be able to handle this. First check to see if the base pointer
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// is a direct load from an indirect global.
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GV1 = GV2 = 0;
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if (LoadInst *LI = dyn_cast<LoadInst>(UV1))
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if (GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0)))
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if (IndirectGlobals.count(GV))
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GV1 = GV;
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if (LoadInst *LI = dyn_cast<LoadInst>(UV2))
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if (GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0)))
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if (IndirectGlobals.count(GV))
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GV2 = GV;
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// These pointers may also be from an allocation for the indirect global. If
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// so, also handle them.
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if (AllocsForIndirectGlobals.count(UV1))
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GV1 = AllocsForIndirectGlobals[UV1];
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if (AllocsForIndirectGlobals.count(UV2))
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GV2 = AllocsForIndirectGlobals[UV2];
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// Now that we know whether the two pointers are related to indirect globals,
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// use this to disambiguate the pointers. If either pointer is based on an
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// indirect global and if they are not both based on the same indirect global,
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// they cannot alias.
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if ((GV1 || GV2) && GV1 != GV2)
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return NoAlias;
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return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
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}
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@ -375,7 +512,7 @@ GlobalsModRef::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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// If we are asking for mod/ref info of a direct call with a pointer to a
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// global we are tracking, return information if we have it.
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if (GlobalValue *GV = const_cast<GlobalValue*>(getUnderlyingObject(P)))
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if (GlobalValue *GV = dyn_cast<GlobalValue>(getUnderlyingObject(P)))
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if (GV->hasInternalLinkage())
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if (Function *F = CS.getCalledFunction())
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if (NonAddressTakenGlobals.count(GV))
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@ -392,8 +529,28 @@ GlobalsModRef::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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// Methods to update the analysis as a result of the client transformation.
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//
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void GlobalsModRef::deleteValue(Value *V) {
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if (GlobalValue *GV = dyn_cast<GlobalValue>(V))
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NonAddressTakenGlobals.erase(GV);
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if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
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if (NonAddressTakenGlobals.erase(GV)) {
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// This global might be an indirect global. If so, remove it and remove
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// any AllocRelatedValues for it.
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if (IndirectGlobals.erase(GV)) {
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// Remove any entries in AllocsForIndirectGlobals for this global.
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for (std::map<Value*, GlobalValue*>::iterator
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I = AllocsForIndirectGlobals.begin(),
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E = AllocsForIndirectGlobals.end(); I != E; ) {
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if (I->second == GV) {
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AllocsForIndirectGlobals.erase(I++);
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} else {
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++I;
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}
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}
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}
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}
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}
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// Otherwise, if this is an allocation related to an indirect global, remove
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// it.
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AllocsForIndirectGlobals.erase(V);
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}
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void GlobalsModRef::copyValue(Value *From, Value *To) {
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