forked from OSchip/llvm-project
182 lines
6.7 KiB
C++
182 lines
6.7 KiB
C++
//===-- GlobalStatus.cpp - Compute status info for globals -----------------==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/CallSite.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/Transforms/Utils/GlobalStatus.h"
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using namespace llvm;
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/// Return the stronger of the two ordering. If the two orderings are acquire
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/// and release, then return AcquireRelease.
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///
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static AtomicOrdering strongerOrdering(AtomicOrdering X, AtomicOrdering Y) {
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if (X == Acquire && Y == Release)
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return AcquireRelease;
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if (Y == Acquire && X == Release)
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return AcquireRelease;
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return (AtomicOrdering)std::max(X, Y);
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}
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/// It is safe to destroy a constant iff it is only used by constants itself.
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/// Note that constants cannot be cyclic, so this test is pretty easy to
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/// implement recursively.
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///
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bool llvm::isSafeToDestroyConstant(const Constant *C) {
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if (isa<GlobalValue>(C))
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return false;
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for (const User *U : C->users())
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if (const Constant *CU = dyn_cast<Constant>(U)) {
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if (!isSafeToDestroyConstant(CU))
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return false;
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} else
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return false;
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return true;
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}
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static bool analyzeGlobalAux(const Value *V, GlobalStatus &GS,
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SmallPtrSet<const PHINode *, 16> &PhiUsers) {
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for (const Use &U : V->uses()) {
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const User *UR = U.getUser();
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if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(UR)) {
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GS.HasNonInstructionUser = true;
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// If the result of the constantexpr isn't pointer type, then we won't
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// know to expect it in various places. Just reject early.
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if (!isa<PointerType>(CE->getType()))
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return true;
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if (analyzeGlobalAux(CE, GS, PhiUsers))
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return true;
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} else if (const Instruction *I = dyn_cast<Instruction>(UR)) {
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if (!GS.HasMultipleAccessingFunctions) {
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const Function *F = I->getParent()->getParent();
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if (!GS.AccessingFunction)
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GS.AccessingFunction = F;
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else if (GS.AccessingFunction != F)
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GS.HasMultipleAccessingFunctions = true;
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}
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if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
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GS.IsLoaded = true;
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// Don't hack on volatile loads.
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if (LI->isVolatile())
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return true;
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GS.Ordering = strongerOrdering(GS.Ordering, LI->getOrdering());
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} else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
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// Don't allow a store OF the address, only stores TO the address.
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if (SI->getOperand(0) == V)
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return true;
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// Don't hack on volatile stores.
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if (SI->isVolatile())
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return true;
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GS.Ordering = strongerOrdering(GS.Ordering, SI->getOrdering());
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// If this is a direct store to the global (i.e., the global is a scalar
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// value, not an aggregate), keep more specific information about
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// stores.
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if (GS.StoredType != GlobalStatus::Stored) {
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if (const GlobalVariable *GV =
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dyn_cast<GlobalVariable>(SI->getOperand(1))) {
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Value *StoredVal = SI->getOperand(0);
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if (Constant *C = dyn_cast<Constant>(StoredVal)) {
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if (C->isThreadDependent()) {
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// The stored value changes between threads; don't track it.
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return true;
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}
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}
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if (StoredVal == GV->getInitializer()) {
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if (GS.StoredType < GlobalStatus::InitializerStored)
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GS.StoredType = GlobalStatus::InitializerStored;
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} else if (isa<LoadInst>(StoredVal) &&
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cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
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if (GS.StoredType < GlobalStatus::InitializerStored)
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GS.StoredType = GlobalStatus::InitializerStored;
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} else if (GS.StoredType < GlobalStatus::StoredOnce) {
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GS.StoredType = GlobalStatus::StoredOnce;
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GS.StoredOnceValue = StoredVal;
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} else if (GS.StoredType == GlobalStatus::StoredOnce &&
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GS.StoredOnceValue == StoredVal) {
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// noop.
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} else {
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GS.StoredType = GlobalStatus::Stored;
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}
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} else {
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GS.StoredType = GlobalStatus::Stored;
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}
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}
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} else if (isa<BitCastInst>(I)) {
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if (analyzeGlobalAux(I, GS, PhiUsers))
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return true;
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} else if (isa<GetElementPtrInst>(I)) {
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if (analyzeGlobalAux(I, GS, PhiUsers))
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return true;
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} else if (isa<SelectInst>(I)) {
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if (analyzeGlobalAux(I, GS, PhiUsers))
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return true;
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} else if (const PHINode *PN = dyn_cast<PHINode>(I)) {
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// PHI nodes we can check just like select or GEP instructions, but we
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// have to be careful about infinite recursion.
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if (PhiUsers.insert(PN)) // Not already visited.
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if (analyzeGlobalAux(I, GS, PhiUsers))
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return true;
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} else if (isa<CmpInst>(I)) {
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GS.IsCompared = true;
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} else if (const MemTransferInst *MTI = dyn_cast<MemTransferInst>(I)) {
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if (MTI->isVolatile())
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return true;
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if (MTI->getArgOperand(0) == V)
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GS.StoredType = GlobalStatus::Stored;
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if (MTI->getArgOperand(1) == V)
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GS.IsLoaded = true;
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} else if (const MemSetInst *MSI = dyn_cast<MemSetInst>(I)) {
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assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!");
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if (MSI->isVolatile())
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return true;
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GS.StoredType = GlobalStatus::Stored;
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} else if (ImmutableCallSite C = I) {
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if (!C.isCallee(&U))
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return true;
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GS.IsLoaded = true;
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} else {
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return true; // Any other non-load instruction might take address!
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}
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} else if (const Constant *C = dyn_cast<Constant>(UR)) {
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GS.HasNonInstructionUser = true;
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// We might have a dead and dangling constant hanging off of here.
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if (!isSafeToDestroyConstant(C))
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return true;
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} else {
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GS.HasNonInstructionUser = true;
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// Otherwise must be some other user.
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return true;
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}
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}
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return false;
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}
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bool GlobalStatus::analyzeGlobal(const Value *V, GlobalStatus &GS) {
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SmallPtrSet<const PHINode *, 16> PhiUsers;
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return analyzeGlobalAux(V, GS, PhiUsers);
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}
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GlobalStatus::GlobalStatus()
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: IsCompared(false), IsLoaded(false), StoredType(NotStored),
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StoredOnceValue(nullptr), AccessingFunction(nullptr),
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HasMultipleAccessingFunctions(false), HasNonInstructionUser(false),
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Ordering(NotAtomic) {}
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