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llvm-mirror/lib/Analysis/IPA/GlobalsModRef.cpp
Chandler Carruth 017dde1e72 [GMR] Switch the function info we store for every function to be a much 
more dense datastructure. We actually only have 3 bits of information
and an often-null pointer here. This fits very nicely into a
pointer-size value in the DenseMap from Function -> Info. Then we take
one more pointer hop to get to a secondary DenseMap from GlobalValue ->
ModRefInfo when we actually have precise info for particular globals.

This is more code than I would really like to do this packing, but it
ended up reasonably cleanly laid out. It should ensure we don't hit
scaling limitations with more widespread use of GMR.

llvm-svn: 242991
2015-07-23 07:50:52 +00:00

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//===- GlobalsModRef.cpp - Simple Mod/Ref Analysis for Globals ------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This simple pass provides alias and mod/ref information for global values
// that do not have their address taken, and keeps track of whether functions
// read or write memory (are "pure"). For this simple (but very common) case,
// we can provide pretty accurate and useful information.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/Passes.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include <list>
using namespace llvm;
#define DEBUG_TYPE "globalsmodref-aa"
STATISTIC(NumNonAddrTakenGlobalVars,
"Number of global vars without address taken");
STATISTIC(NumNonAddrTakenFunctions,"Number of functions without address taken");
STATISTIC(NumNoMemFunctions, "Number of functions that do not access memory");
STATISTIC(NumReadMemFunctions, "Number of functions that only read memory");
STATISTIC(NumIndirectGlobalVars, "Number of indirect global objects");
// An option to enable unsafe alias results from the GlobalsModRef analysis.
// When enabled, GlobalsModRef will provide no-alias results which in extremely
// rare cases may not be conservatively correct. In particular, in the face of
// transforms which cause assymetry between how effective GetUnderlyingObject
// is for two pointers, it may produce incorrect results.
//
// These unsafe results have been returned by GMR for many years without
// causing significant issues in the wild and so we provide a mechanism to
// re-enable them for users of LLVM that have a particular performance
// sensitivity and no known issues. The option also makes it easy to evaluate
// the performance impact of these results.
static cl::opt<bool> EnableUnsafeGlobalsModRefAliasResults(
"enable-unsafe-globalsmodref-alias-results", cl::init(false), cl::Hidden);
namespace {
/// The mod/ref information collected for a particular function.
///
/// We collect information about mod/ref behavior of a function here, both in
/// general and as pertains to specific globals. We only have this detailed
/// information when we know *something* useful about the behavior. If we
/// saturate to fully general mod/ref, we remove the info for the function.
class FunctionInfo {
typedef SmallDenseMap<const GlobalValue *, ModRefInfo, 16> GlobalInfoMapType;
/// Build a wrapper struct that has 8-byte alignment. All heap allocations
/// should provide this much alignment at least, but this makes it clear we
/// specifically rely on this amount of alignment.
struct LLVM_ALIGNAS(8) AlignedMap {
AlignedMap() {}
AlignedMap(const AlignedMap &Arg) : Map(Arg.Map) {}
GlobalInfoMapType Map;
};
/// Pointer traits for our aligned map.
struct AlignedMapPointerTraits {
static inline void *getAsVoidPointer(AlignedMap *P) { return P; }
static inline AlignedMap *getFromVoidPointer(void *P) {
return (AlignedMap *)P;
}
enum { NumLowBitsAvailable = 3 };
static_assert(AlignOf<AlignedMap>::Alignment >= (1 << NumLowBitsAvailable),
"AlignedMap insufficiently aligned to have enough low bits.");
};
/// The bit that flags that this function may read any global. This is
/// chosen to mix together with ModRefInfo bits.
enum { MayReadAnyGlobal = 4 };
/// Checks to document the invariants of the bit packing here.
static_assert((MayReadAnyGlobal & MRI_ModRef) == 0,
"ModRef and the MayReadAnyGlobal flag bits overlap.");
static_assert(((MayReadAnyGlobal | MRI_ModRef) >>
AlignedMapPointerTraits::NumLowBitsAvailable) == 0,
"Insufficient low bits to store our flag and ModRef info.");
public:
FunctionInfo() : Info() {}
~FunctionInfo() {
delete Info.getPointer();
}
// Spell out the copy ond move constructors and assignment operators to get
// deep copy semantics and correct move semantics in the face of the
// pointer-int pair.
FunctionInfo(const FunctionInfo &Arg)
: Info(nullptr, Arg.Info.getInt()) {
if (const auto *ArgPtr = Arg.Info.getPointer())
Info.setPointer(new AlignedMap(*ArgPtr));
}
FunctionInfo(FunctionInfo &&Arg)
: Info(Arg.Info.getPointer(), Arg.Info.getInt()) {
Arg.Info.setPointerAndInt(nullptr, 0);
}
FunctionInfo &operator=(const FunctionInfo &RHS) {
delete Info.getPointer();
Info.setPointerAndInt(nullptr, RHS.Info.getInt());
if (const auto *RHSPtr = RHS.Info.getPointer())
Info.setPointer(new AlignedMap(*RHSPtr));
return *this;
}
FunctionInfo &operator=(FunctionInfo &&RHS) {
delete Info.getPointer();
Info.setPointerAndInt(RHS.Info.getPointer(), RHS.Info.getInt());
RHS.Info.setPointerAndInt(nullptr, 0);
return *this;
}
/// Returns the \c ModRefInfo info for this function.
ModRefInfo getModRefInfo() const {
return ModRefInfo(Info.getInt() & MRI_ModRef);
}
/// Adds new \c ModRefInfo for this function to its state.
void addModRefInfo(ModRefInfo NewMRI) {
Info.setInt(Info.getInt() | NewMRI);
}
/// Returns whether this function may read any global variable, and we don't
/// know which global.
bool mayReadAnyGlobal() const { return Info.getInt() & MayReadAnyGlobal; }
/// Sets this function as potentially reading from any global.
void setMayReadAnyGlobal() { Info.setInt(Info.getInt() | MayReadAnyGlobal); }
/// Returns the \c ModRefInfo info for this function w.r.t. a particular
/// global, which may be more precise than the general information above.
ModRefInfo getModRefInfoForGlobal(const GlobalValue &GV) const {
ModRefInfo GlobalMRI = mayReadAnyGlobal() ? MRI_Ref : MRI_NoModRef;
if (AlignedMap *P = Info.getPointer()) {
auto I = P->Map.find(&GV);
if (I != P->Map.end())
GlobalMRI = ModRefInfo(GlobalMRI | I->second);
}
return GlobalMRI;
}
/// Add mod/ref info from another function into ours, saturating towards
/// MRI_ModRef.
void addFunctionInfo(const FunctionInfo &FI) {
addModRefInfo(FI.getModRefInfo());
if (FI.mayReadAnyGlobal())
setMayReadAnyGlobal();
if (AlignedMap *P = FI.Info.getPointer())
for (const auto &G : P->Map)
addModRefInfoForGlobal(*G.first, G.second);
}
void addModRefInfoForGlobal(const GlobalValue &GV, ModRefInfo NewMRI) {
AlignedMap *P = Info.getPointer();
if (!P) {
P = new AlignedMap();
Info.setPointer(P);
}
auto &GlobalMRI = P->Map[&GV];
GlobalMRI = ModRefInfo(GlobalMRI | NewMRI);
}
private:
/// All of the information is encoded into a single pointer, with a three bit
/// integer in the low three bits. The high bit provides a flag for when this
/// function may read any global. The low two bits are the ModRefInfo. And
/// the pointer, when non-null, points to a map from GlobalValue to
/// ModRefInfo specific to that GlobalValue.
PointerIntPair<AlignedMap *, 3, unsigned, AlignedMapPointerTraits> Info;
};
/// GlobalsModRef - The actual analysis pass.
class GlobalsModRef : public ModulePass, public AliasAnalysis {
/// The globals that do not have their addresses taken.
SmallPtrSet<const GlobalValue *, 8> NonAddressTakenGlobals;
/// IndirectGlobals - The memory pointed to by this global is known to be
/// 'owned' by the global.
SmallPtrSet<const GlobalValue *, 8> IndirectGlobals;
/// AllocsForIndirectGlobals - If an instruction allocates memory for an
/// indirect global, this map indicates which one.
DenseMap<const Value *, const GlobalValue *> AllocsForIndirectGlobals;
/// For each function, keep track of what globals are modified or read.
DenseMap<const Function *, FunctionInfo> FunctionInfos;
/// Handle to clear this analysis on deletion of values.
struct DeletionCallbackHandle final : CallbackVH {
GlobalsModRef &GMR;
std::list<DeletionCallbackHandle>::iterator I;
DeletionCallbackHandle(GlobalsModRef &GMR, Value *V)
: CallbackVH(V), GMR(GMR) {}
void deleted() override {
Value *V = getValPtr();
if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
if (GMR.NonAddressTakenGlobals.erase(GV)) {
// This global might be an indirect global. If so, remove it and
// remove
// any AllocRelatedValues for it.
if (GMR.IndirectGlobals.erase(GV)) {
// Remove any entries in AllocsForIndirectGlobals for this global.
for (auto I = GMR.AllocsForIndirectGlobals.begin(),
E = GMR.AllocsForIndirectGlobals.end();
I != E; ++I)
if (I->second == GV)
GMR.AllocsForIndirectGlobals.erase(I);
}
}
}
// If this is an allocation related to an indirect global, remove it.
GMR.AllocsForIndirectGlobals.erase(V);
// And clear out the handle.
setValPtr(nullptr);
GMR.Handles.erase(I);
// This object is now destroyed!
}
};
/// List of callbacks for globals being tracked by this analysis. Note that
/// these objects are quite large, but we only anticipate having one per
/// global tracked by this analysis. There are numerous optimizations we
/// could perform to the memory utilization here if this becomes a problem.
std::list<DeletionCallbackHandle> Handles;
public:
static char ID;
GlobalsModRef() : ModulePass(ID) {
initializeGlobalsModRefPass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override {
InitializeAliasAnalysis(this, &M.getDataLayout());
// Find non-addr taken globals.
AnalyzeGlobals(M);
// Propagate on CG.
AnalyzeCallGraph(getAnalysis<CallGraphWrapperPass>().getCallGraph(), M);
return false;
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AliasAnalysis::getAnalysisUsage(AU);
AU.addRequired<CallGraphWrapperPass>();
AU.setPreservesAll(); // Does not transform code
}
/// getAdjustedAnalysisPointer - This method is used when a pass implements
/// an analysis interface through multiple inheritance. If needed, it
/// should override this to adjust the this pointer as needed for the
/// specified pass info.
void *getAdjustedAnalysisPointer(AnalysisID PI) override {
if (PI == &AliasAnalysis::ID)
return (AliasAnalysis *)this;
return this;
}
//------------------------------------------------
// Implement the AliasAnalysis API
//
AliasResult alias(const MemoryLocation &LocA,
const MemoryLocation &LocB) override;
ModRefInfo getModRefInfo(ImmutableCallSite CS,
const MemoryLocation &Loc) override;
ModRefInfo getModRefInfo(ImmutableCallSite CS1,
ImmutableCallSite CS2) override {
return AliasAnalysis::getModRefInfo(CS1, CS2);
}
/// getModRefBehavior - Return the behavior of the specified function if
/// called from the specified call site. The call site may be null in which
/// case the most generic behavior of this function should be returned.
FunctionModRefBehavior getModRefBehavior(const Function *F) override {
FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
if (FunctionInfo *FI = getFunctionInfo(F)) {
if (FI->getModRefInfo() == MRI_NoModRef)
Min = FMRB_DoesNotAccessMemory;
else if ((FI->getModRefInfo() & MRI_Mod) == 0)
Min = FMRB_OnlyReadsMemory;
}
return FunctionModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
}
/// getModRefBehavior - Return the behavior of the specified function if
/// called from the specified call site. The call site may be null in which
/// case the most generic behavior of this function should be returned.
FunctionModRefBehavior getModRefBehavior(ImmutableCallSite CS) override {
FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
if (const Function *F = CS.getCalledFunction())
if (FunctionInfo *FI = getFunctionInfo(F)) {
if (FI->getModRefInfo() == MRI_NoModRef)
Min = FMRB_DoesNotAccessMemory;
else if ((FI->getModRefInfo() & MRI_Mod) == 0)
Min = FMRB_OnlyReadsMemory;
}
return FunctionModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
}
private:
/// Returns the function info for the function, or null if we don't have
/// anything useful to say about it.
FunctionInfo *getFunctionInfo(const Function *F) {
auto I = FunctionInfos.find(F);
if (I != FunctionInfos.end())
return &I->second;
return nullptr;
}
void AnalyzeGlobals(Module &M);
void AnalyzeCallGraph(CallGraph &CG, Module &M);
bool AnalyzeUsesOfPointer(Value *V,
SmallPtrSetImpl<Function *> *Readers = nullptr,
SmallPtrSetImpl<Function *> *Writers = nullptr,
GlobalValue *OkayStoreDest = nullptr);
bool AnalyzeIndirectGlobalMemory(GlobalValue *GV);
};
}
char GlobalsModRef::ID = 0;
INITIALIZE_AG_PASS_BEGIN(GlobalsModRef, AliasAnalysis, "globalsmodref-aa",
"Simple mod/ref analysis for globals", false, true,
false)
INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
INITIALIZE_AG_PASS_END(GlobalsModRef, AliasAnalysis, "globalsmodref-aa",
"Simple mod/ref analysis for globals", false, true,
false)
Pass *llvm::createGlobalsModRefPass() { return new GlobalsModRef(); }
/// AnalyzeGlobals - Scan through the users of all of the internal
/// GlobalValue's in the program. If none of them have their "address taken"
/// (really, their address passed to something nontrivial), record this fact,
/// and record the functions that they are used directly in.
void GlobalsModRef::AnalyzeGlobals(Module &M) {
for (Function &F : M)
if (F.hasLocalLinkage())
if (!AnalyzeUsesOfPointer(&F)) {
// Remember that we are tracking this global.
NonAddressTakenGlobals.insert(&F);
Handles.emplace_front(*this, &F);
Handles.front().I = Handles.begin();
++NumNonAddrTakenFunctions;
}
SmallPtrSet<Function *, 64> Readers, Writers;
for (GlobalVariable &GV : M.globals())
if (GV.hasLocalLinkage()) {
if (!AnalyzeUsesOfPointer(&GV, &Readers,
GV.isConstant() ? nullptr : &Writers)) {
// Remember that we are tracking this global, and the mod/ref fns
NonAddressTakenGlobals.insert(&GV);
Handles.emplace_front(*this, &GV);
Handles.front().I = Handles.begin();
for (Function *Reader : Readers)
FunctionInfos[Reader].addModRefInfoForGlobal(GV, MRI_Ref);
if (!GV.isConstant()) // No need to keep track of writers to constants
for (Function *Writer : Writers)
FunctionInfos[Writer].addModRefInfoForGlobal(GV, MRI_Mod);
++NumNonAddrTakenGlobalVars;
// If this global holds a pointer type, see if it is an indirect global.
if (GV.getType()->getElementType()->isPointerTy() &&
AnalyzeIndirectGlobalMemory(&GV))
++NumIndirectGlobalVars;
}
Readers.clear();
Writers.clear();
}
}
/// AnalyzeUsesOfPointer - Look at all of the users of the specified pointer.
/// If this is used by anything complex (i.e., the address escapes), return
/// true. Also, while we are at it, keep track of those functions that read and
/// write to the value.
///
/// If OkayStoreDest is non-null, stores into this global are allowed.
bool GlobalsModRef::AnalyzeUsesOfPointer(Value *V,
SmallPtrSetImpl<Function *> *Readers,
SmallPtrSetImpl<Function *> *Writers,
GlobalValue *OkayStoreDest) {
if (!V->getType()->isPointerTy())
return true;
for (Use &U : V->uses()) {
User *I = U.getUser();
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
if (Readers)
Readers->insert(LI->getParent()->getParent());
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
if (V == SI->getOperand(1)) {
if (Writers)
Writers->insert(SI->getParent()->getParent());
} else if (SI->getOperand(1) != OkayStoreDest) {
return true; // Storing the pointer
}
} else if (Operator::getOpcode(I) == Instruction::GetElementPtr) {
if (AnalyzeUsesOfPointer(I, Readers, Writers))
return true;
} else if (Operator::getOpcode(I) == Instruction::BitCast) {
if (AnalyzeUsesOfPointer(I, Readers, Writers, OkayStoreDest))
return true;
} else if (auto CS = CallSite(I)) {
// Make sure that this is just the function being called, not that it is
// passing into the function.
if (!CS.isCallee(&U)) {
// Detect calls to free.
if (isFreeCall(I, TLI)) {
if (Writers)
Writers->insert(CS->getParent()->getParent());
} else {
return true; // Argument of an unknown call.
}
}
} else if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
return true; // Allow comparison against null.
} else {
return true;
}
}
return false;
}
/// AnalyzeIndirectGlobalMemory - We found an non-address-taken global variable
/// which holds a pointer type. See if the global always points to non-aliased
/// heap memory: that is, all initializers of the globals are allocations, and
/// those allocations have no use other than initialization of the global.
/// Further, all loads out of GV must directly use the memory, not store the
/// pointer somewhere. If this is true, we consider the memory pointed to by
/// GV to be owned by GV and can disambiguate other pointers from it.
bool GlobalsModRef::AnalyzeIndirectGlobalMemory(GlobalValue *GV) {
// Keep track of values related to the allocation of the memory, f.e. the
// value produced by the malloc call and any casts.
std::vector<Value *> AllocRelatedValues;
// Walk the user list of the global. If we find anything other than a direct
// load or store, bail out.
for (User *U : GV->users()) {
if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
// The pointer loaded from the global can only be used in simple ways:
// we allow addressing of it and loading storing to it. We do *not* allow
// storing the loaded pointer somewhere else or passing to a function.
if (AnalyzeUsesOfPointer(LI))
return false; // Loaded pointer escapes.
// TODO: Could try some IP mod/ref of the loaded pointer.
} else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
// Storing the global itself.
if (SI->getOperand(0) == GV)
return false;
// If storing the null pointer, ignore it.
if (isa<ConstantPointerNull>(SI->getOperand(0)))
continue;
// Check the value being stored.
Value *Ptr = GetUnderlyingObject(SI->getOperand(0),
GV->getParent()->getDataLayout());
if (!isAllocLikeFn(Ptr, TLI))
return false; // Too hard to analyze.
// Analyze all uses of the allocation. If any of them are used in a
// non-simple way (e.g. stored to another global) bail out.
if (AnalyzeUsesOfPointer(Ptr, /*Readers*/ nullptr, /*Writers*/ nullptr,
GV))
return false; // Loaded pointer escapes.
// Remember that this allocation is related to the indirect global.
AllocRelatedValues.push_back(Ptr);
} else {
// Something complex, bail out.
return false;
}
}
// Okay, this is an indirect global. Remember all of the allocations for
// this global in AllocsForIndirectGlobals.
while (!AllocRelatedValues.empty()) {
AllocsForIndirectGlobals[AllocRelatedValues.back()] = GV;
Handles.emplace_front(*this, AllocRelatedValues.back());
Handles.front().I = Handles.begin();
AllocRelatedValues.pop_back();
}
IndirectGlobals.insert(GV);
Handles.emplace_front(*this, GV);
Handles.front().I = Handles.begin();
return true;
}
/// AnalyzeCallGraph - At this point, we know the functions where globals are
/// immediately stored to and read from. Propagate this information up the call
/// graph to all callers and compute the mod/ref info for all memory for each
/// function.
void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) {
// We do a bottom-up SCC traversal of the call graph. In other words, we
// visit all callees before callers (leaf-first).
for (scc_iterator<CallGraph *> I = scc_begin(&CG); !I.isAtEnd(); ++I) {
const std::vector<CallGraphNode *> &SCC = *I;
assert(!SCC.empty() && "SCC with no functions?");
if (!SCC[0]->getFunction()) {
// Calls externally - can't say anything useful. Remove any existing
// function records (may have been created when scanning globals).
for (auto *Node : SCC)
FunctionInfos.erase(Node->getFunction());
continue;
}
FunctionInfo &FI = FunctionInfos[SCC[0]->getFunction()];
bool KnowNothing = false;
// Collect the mod/ref properties due to called functions. We only compute
// one mod-ref set.
for (unsigned i = 0, e = SCC.size(); i != e && !KnowNothing; ++i) {
Function *F = SCC[i]->getFunction();
if (!F) {
KnowNothing = true;
break;
}
if (F->isDeclaration()) {
// Try to get mod/ref behaviour from function attributes.
if (F->doesNotAccessMemory()) {
// Can't do better than that!
} else if (F->onlyReadsMemory()) {
FI.addModRefInfo(MRI_Ref);
if (!F->isIntrinsic())
// This function might call back into the module and read a global -
// consider every global as possibly being read by this function.
FI.setMayReadAnyGlobal();
} else {
FI.addModRefInfo(MRI_ModRef);
// Can't say anything useful unless it's an intrinsic - they don't
// read or write global variables of the kind considered here.
KnowNothing = !F->isIntrinsic();
}
continue;
}
for (CallGraphNode::iterator CI = SCC[i]->begin(), E = SCC[i]->end();
CI != E && !KnowNothing; ++CI)
if (Function *Callee = CI->second->getFunction()) {
if (FunctionInfo *CalleeFI = getFunctionInfo(Callee)) {
// Propagate function effect up.
FI.addFunctionInfo(*CalleeFI);
} else {
// Can't say anything about it. However, if it is inside our SCC,
// then nothing needs to be done.
CallGraphNode *CalleeNode = CG[Callee];
if (std::find(SCC.begin(), SCC.end(), CalleeNode) == SCC.end())
KnowNothing = true;
}
} else {
KnowNothing = true;
}
}
// If we can't say anything useful about this SCC, remove all SCC functions
// from the FunctionInfos map.
if (KnowNothing) {
for (auto *Node : SCC)
FunctionInfos.erase(Node->getFunction());
continue;
}
// Scan the function bodies for explicit loads or stores.
for (auto *Node : SCC) {
if (FI.getModRefInfo() == MRI_ModRef)
break; // The mod/ref lattice saturates here.
for (Instruction &I : inst_range(Node->getFunction())) {
if (FI.getModRefInfo() == MRI_ModRef)
break; // The mod/ref lattice saturates here.
// We handle calls specially because the graph-relevant aspects are
// handled above.
if (auto CS = CallSite(&I)) {
if (isAllocationFn(&I, TLI) || isFreeCall(&I, TLI)) {
// FIXME: It is completely unclear why this is necessary and not
// handled by the above graph code.
FI.addModRefInfo(MRI_ModRef);
} else if (Function *Callee = CS.getCalledFunction()) {
// The callgraph doesn't include intrinsic calls.
if (Callee->isIntrinsic()) {
FunctionModRefBehavior Behaviour =
AliasAnalysis::getModRefBehavior(Callee);
FI.addModRefInfo(ModRefInfo(Behaviour & MRI_ModRef));
}
}
continue;
}
// All non-call instructions we use the primary predicates for whether
// thay read or write memory.
if (I.mayReadFromMemory())
FI.addModRefInfo(MRI_Ref);
if (I.mayWriteToMemory())
FI.addModRefInfo(MRI_Mod);
}
}
if ((FI.getModRefInfo() & MRI_Mod) == 0)
++NumReadMemFunctions;
if (FI.getModRefInfo() == MRI_NoModRef)
++NumNoMemFunctions;
// Finally, now that we know the full effect on this SCC, clone the
// information to each function in the SCC.
for (unsigned i = 1, e = SCC.size(); i != e; ++i)
FunctionInfos[SCC[i]->getFunction()] = FI;
}
}
/// alias - If one of the pointers is to a global that we are tracking, and the
/// other is some random pointer, we know there cannot be an alias, because the
/// address of the global isn't taken.
AliasResult GlobalsModRef::alias(const MemoryLocation &LocA,
const MemoryLocation &LocB) {
// Get the base object these pointers point to.
const Value *UV1 = GetUnderlyingObject(LocA.Ptr, *DL);
const Value *UV2 = GetUnderlyingObject(LocB.Ptr, *DL);
// If either of the underlying values is a global, they may be non-addr-taken
// globals, which we can answer queries about.
const GlobalValue *GV1 = dyn_cast<GlobalValue>(UV1);
const GlobalValue *GV2 = dyn_cast<GlobalValue>(UV2);
if (GV1 || GV2) {
// If the global's address is taken, pretend we don't know it's a pointer to
// the global.
if (GV1 && !NonAddressTakenGlobals.count(GV1))
GV1 = nullptr;
if (GV2 && !NonAddressTakenGlobals.count(GV2))
GV2 = nullptr;
// If the two pointers are derived from two different non-addr-taken
// globals we know these can't alias.
if (GV1 && GV2 && GV1 != GV2)
return NoAlias;
// If one is and the other isn't, it isn't strictly safe but we can fake
// this result if necessary for performance. This does not appear to be
// a common problem in practice.
if (EnableUnsafeGlobalsModRefAliasResults)
if ((GV1 || GV2) && GV1 != GV2)
return NoAlias;
// Otherwise if they are both derived from the same addr-taken global, we
// can't know the two accesses don't overlap.
}
// These pointers may be based on the memory owned by an indirect global. If
// so, we may be able to handle this. First check to see if the base pointer
// is a direct load from an indirect global.
GV1 = GV2 = nullptr;
if (const LoadInst *LI = dyn_cast<LoadInst>(UV1))
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0)))
if (IndirectGlobals.count(GV))
GV1 = GV;
if (const LoadInst *LI = dyn_cast<LoadInst>(UV2))
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(LI->getOperand(0)))
if (IndirectGlobals.count(GV))
GV2 = GV;
// These pointers may also be from an allocation for the indirect global. If
// so, also handle them.
if (!GV1)
GV1 = AllocsForIndirectGlobals.lookup(UV1);
if (!GV2)
GV2 = AllocsForIndirectGlobals.lookup(UV2);
// Now that we know whether the two pointers are related to indirect globals,
// use this to disambiguate the pointers. If the pointers are based on
// different indirect globals they cannot alias.
if (GV1 && GV2 && GV1 != GV2)
return NoAlias;
// If one is based on an indirect global and the other isn't, it isn't
// strictly safe but we can fake this result if necessary for performance.
// This does not appear to be a common problem in practice.
if (EnableUnsafeGlobalsModRefAliasResults)
if ((GV1 || GV2) && GV1 != GV2)
return NoAlias;
return AliasAnalysis::alias(LocA, LocB);
}
ModRefInfo GlobalsModRef::getModRefInfo(ImmutableCallSite CS,
const MemoryLocation &Loc) {
unsigned Known = MRI_ModRef;
// If we are asking for mod/ref info of a direct call with a pointer to a
// global we are tracking, return information if we have it.
const DataLayout &DL = CS.getCaller()->getParent()->getDataLayout();
if (const GlobalValue *GV =
dyn_cast<GlobalValue>(GetUnderlyingObject(Loc.Ptr, DL)))
if (GV->hasLocalLinkage())
if (const Function *F = CS.getCalledFunction())
if (NonAddressTakenGlobals.count(GV))
if (const FunctionInfo *FI = getFunctionInfo(F))
Known = FI->getModRefInfoForGlobal(*GV);
if (Known == MRI_NoModRef)
return MRI_NoModRef; // No need to query other mod/ref analyses
return ModRefInfo(Known & AliasAnalysis::getModRefInfo(CS, Loc));
}
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