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