//===- GlobalsModRef.cpp - Simple Mod/Ref Analysis for Globals ------------===//
-//
+//
// The LLVM Compiler Infrastructure
//
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
-//
+// 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. For this simple (but very common)
-// case, we can provide pretty accurate and useful information.
+// 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.
//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "globalsmodref"
#include "llvm/Analysis/Passes.h"
-#include "llvm/Module.h"
-#include "llvm/Pass.h"
-#include "llvm/Instructions.h"
-#include "llvm/Constants.h"
+#include "llvm/ADT/SCCIterator.h"
+#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CallGraph.h"
-#include "Support/Debug.h"
-#include "Support/Statistic.h"
-#include "Support/SCCIterator.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 <set>
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");
+
namespace {
- Statistic<>
- NumNonAddrTakenGlobalVars("globalsmodref-aa",
- "Number of global vars without address taken");
- Statistic<>
- NumNonAddrTakenFunctions("globalsmodref-aa",
- "Number of functions without address taken");
-
- class GlobalsModRef : public Pass, public AliasAnalysis {
- /// ModRefFns - One instance of this record is kept for each global without
- /// its address taken.
- struct ModRefFns {
- /// RefFns/ModFns - Sets of functions that and write globals.
- std::set<Function*> RefFns, ModFns;
- };
-
- /// NonAddressTakenGlobals - A map of globals that do not have their
- /// addresses taken to their record.
- std::map<GlobalValue*, ModRefFns> NonAddressTakenGlobals;
-
- /// FunctionInfo - For each function, keep track of what globals are
- /// modified or read.
- std::map<std::pair<Function*, GlobalValue*>, unsigned> FunctionInfo;
-
- public:
- bool run(Module &M) {
- InitializeAliasAnalysis(this); // set up super class
- AnalyzeGlobals(M); // find non-addr taken globals
- AnalyzeCallGraph(getAnalysis<CallGraph>(), M); // Propagate on CG
- return false;
- }
+/// FunctionRecord - One instance of this structure is stored for every
+/// function in the program. Later, the entries for these functions are
+/// removed if the function is found to call an external function (in which
+/// case we know nothing about it.
+struct FunctionRecord {
+ /// GlobalInfo - Maintain mod/ref info for all of the globals without
+ /// addresses taken that are read or written (transitively) by this
+ /// function.
+ std::map<const GlobalValue *, unsigned> GlobalInfo;
+
+ /// MayReadAnyGlobal - May read global variables, but it is not known which.
+ bool MayReadAnyGlobal;
+
+ unsigned getInfoForGlobal(const GlobalValue *GV) const {
+ unsigned Effect = MayReadAnyGlobal ? AliasAnalysis::Ref : 0;
+ std::map<const GlobalValue *, unsigned>::const_iterator I =
+ GlobalInfo.find(GV);
+ if (I != GlobalInfo.end())
+ Effect |= I->second;
+ return Effect;
+ }
+
+ /// FunctionEffect - Capture whether or not this function reads or writes to
+ /// ANY memory. If not, we can do a lot of aggressive analysis on it.
+ unsigned FunctionEffect;
+
+ FunctionRecord() : MayReadAnyGlobal(false), FunctionEffect(0) {}
+};
+
+/// GlobalsModRef - The actual analysis pass.
+class GlobalsModRef : public ModulePass, public AliasAnalysis {
+ /// NonAddressTakenGlobals - The globals that do not have their addresses
+ /// taken.
+ std::set<const GlobalValue *> NonAddressTakenGlobals;
+
+ /// IndirectGlobals - The memory pointed to by this global is known to be
+ /// 'owned' by the global.
+ std::set<const GlobalValue *> IndirectGlobals;
+
+ /// AllocsForIndirectGlobals - If an instruction allocates memory for an
+ /// indirect global, this map indicates which one.
+ std::map<const Value *, const GlobalValue *> AllocsForIndirectGlobals;
+
+ /// FunctionInfo - For each function, keep track of what globals are
+ /// modified or read.
+ std::map<const Function *, FunctionRecord> FunctionInfo;
+
+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
+ }
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AliasAnalysis::getAnalysisUsage(AU);
- AU.addRequired<CallGraph>();
- AU.setPreservesAll(); // Does not transform code
+ //------------------------------------------------
+ // Implement the AliasAnalysis API
+ //
+ AliasResult alias(const MemoryLocation &LocA,
+ const MemoryLocation &LocB) override;
+ ModRefResult getModRefInfo(ImmutableCallSite CS,
+ const MemoryLocation &Loc) override;
+ ModRefResult 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.
+ ModRefBehavior getModRefBehavior(const Function *F) override {
+ ModRefBehavior Min = UnknownModRefBehavior;
+
+ if (FunctionRecord *FR = getFunctionInfo(F)) {
+ if (FR->FunctionEffect == 0)
+ Min = DoesNotAccessMemory;
+ else if ((FR->FunctionEffect & Mod) == 0)
+ Min = OnlyReadsMemory;
}
- //------------------------------------------------
- // Implement the AliasAnalysis API
- //
- AliasResult alias(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size);
- ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
- bool hasNoModRefInfoForCalls() const { return false; }
-
- virtual void deleteValue(Value *V);
- virtual void copyValue(Value *From, Value *To);
-
- private:
- void AnalyzeGlobals(Module &M);
- void AnalyzeCallGraph(CallGraph &CG, Module &M);
- bool AnalyzeUsesOfGlobal(Value *V, std::vector<Function*> &Readers,
- std::vector<Function*> &Writers);
- };
-
- RegisterOpt<GlobalsModRef> X("globalsmodref-aa",
- "Simple mod/ref analysis for globals");
- RegisterAnalysisGroup<AliasAnalysis, GlobalsModRef> Y;
+ return ModRefBehavior(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.
+ ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override {
+ ModRefBehavior Min = UnknownModRefBehavior;
+
+ if (const Function *F = CS.getCalledFunction())
+ if (FunctionRecord *FR = getFunctionInfo(F)) {
+ if (FR->FunctionEffect == 0)
+ Min = DoesNotAccessMemory;
+ else if ((FR->FunctionEffect & Mod) == 0)
+ Min = OnlyReadsMemory;
+ }
+
+ return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
+ }
+
+ void deleteValue(Value *V) override;
+ void addEscapingUse(Use &U) override;
+
+ /// 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;
+ }
+
+private:
+ /// getFunctionInfo - Return the function info for the function, or null if
+ /// we don't have anything useful to say about it.
+ FunctionRecord *getFunctionInfo(const Function *F) {
+ std::map<const Function *, FunctionRecord>::iterator I =
+ FunctionInfo.find(F);
+ if (I != FunctionInfo.end())
+ return &I->second;
+ return nullptr;
+ }
+
+ void AnalyzeGlobals(Module &M);
+ void AnalyzeCallGraph(CallGraph &CG, Module &M);
+ bool AnalyzeUsesOfPointer(Value *V, std::vector<Function *> &Readers,
+ std::vector<Function *> &Writers,
+ GlobalValue *OkayStoreDest = nullptr);
+ bool AnalyzeIndirectGlobalMemory(GlobalValue *GV);
+};
}
-Pass *llvm::createGlobalsModRefPass() { return new GlobalsModRef(); }
+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(); }
-/// AnalyzeGlobalUses - Scan through the users of all of the internal
-/// GlobalValue's in the program. If none of them have their "Address taken"
+/// 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) {
- std::vector<Function*> Readers, Writers;
- for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
- if (I->hasInternalLinkage()) {
- if (!AnalyzeUsesOfGlobal(I, Readers, Writers)) {
- // Remember that we are tracking this global, and the mod/ref fns
- ModRefFns &E = NonAddressTakenGlobals[I];
- E.RefFns.insert(Readers.begin(), Readers.end());
- E.ModFns.insert(Writers.begin(), Writers.end());
+ std::vector<Function *> Readers, Writers;
+ for (Function &F : M)
+ if (F.hasLocalLinkage()) {
+ if (!AnalyzeUsesOfPointer(&F, Readers, Writers)) {
+ // Remember that we are tracking this global.
+ NonAddressTakenGlobals.insert(&F);
++NumNonAddrTakenFunctions;
}
- Readers.clear(); Writers.clear();
+ Readers.clear();
+ Writers.clear();
}
- for (Module::giterator I = M.gbegin(), E = M.gend(); I != E; ++I)
- // FIXME: it is kinda dumb to track aliasing properties for constant
- // globals, it will never be particularly useful anyways, 'cause they can
- // never be modified (and the optimizer knows this already)!
- if (I->hasInternalLinkage()) {
- if (!AnalyzeUsesOfGlobal(I, Readers, Writers)) {
+ for (GlobalVariable &GV : M.globals())
+ if (GV.hasLocalLinkage()) {
+ if (!AnalyzeUsesOfPointer(&GV, Readers, Writers)) {
// Remember that we are tracking this global, and the mod/ref fns
- ModRefFns &E = NonAddressTakenGlobals[I];
- E.RefFns.insert(Readers.begin(), Readers.end());
- E.ModFns.insert(Writers.begin(), Writers.end());
+ NonAddressTakenGlobals.insert(&GV);
+
+ for (Function *Reader : Readers)
+ FunctionInfo[Reader].GlobalInfo[&GV] |= Ref;
+
+ if (!GV.isConstant()) // No need to keep track of writers to constants
+ for (Function *Writer : Writers)
+ FunctionInfo[Writer].GlobalInfo[&GV] |= 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();
+ Readers.clear();
+ Writers.clear();
}
}
-/// AnalyzeUsesOfGlobal - Look at all of the users of the specified global value
-/// derived 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.
-bool GlobalsModRef::AnalyzeUsesOfGlobal(Value *V,
- std::vector<Function*> &Readers,
- std::vector<Function*> &Writers) {
- //if (!isa<PointerType>(V->getType())) return true;
-
- for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
- if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
+/// 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,
+ std::vector<Function *> &Readers,
+ std::vector<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)) {
Readers.push_back(LI->getParent()->getParent());
- } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
- if (V == SI->getOperand(0)) return true; // Storing the pointer
- Writers.push_back(SI->getParent()->getParent());
- } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
- if (AnalyzeUsesOfGlobal(GEP, Readers, Writers)) return true;
- } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
- // Make sure that this is just the function being called, not that it is
- // passing into the function.
- for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
- if (CI->getOperand(i) == V) return true;
- } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
- // Make sure that this is just the function being called, not that it is
- // passing into the function.
- for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
- if (CI->getOperand(i) == V) return true;
- } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) {
+ } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+ if (V == SI->getOperand(1)) {
+ Writers.push_back(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.
- for (unsigned i = 3, e = II->getNumOperands(); i != e; ++i)
- if (II->getOperand(i) == V) return true;
- } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) {
- if (CE->getOpcode() == Instruction::GetElementPtr ||
- CE->getOpcode() == Instruction::Cast) {
- if (AnalyzeUsesOfGlobal(CE, Readers, Writers))
- return true;
- } else {
- return true;
- }
- } else if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(*UI)) {
- if (AnalyzeUsesOfGlobal(CPR, Readers, Writers)) return true;
+ if (!CS.isCallee(&U)) {
+ // Detect calls to free.
+ if (isFreeCall(I, TLI))
+ Writers.push_back(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.
+ std::vector<Function *> ReadersWriters;
+ if (AnalyzeUsesOfPointer(LI, ReadersWriters, ReadersWriters))
+ 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.
+ std::vector<Function *> ReadersWriters;
+ if (AnalyzeUsesOfPointer(Ptr, ReadersWriters, ReadersWriters, 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;
+ AllocRelatedValues.pop_back();
+ }
+ IndirectGlobals.insert(GV);
+ 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.
+/// graph to all callers and compute the mod/ref info for all memory for each
+/// function.
void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) {
- if (NonAddressTakenGlobals.empty()) return; // Don't bother, nothing to do.
-
- // Invert the NonAddressTakenGlobals map into the FunctionInfo map.
- for (std::map<GlobalValue*, ModRefFns>::iterator I =
- NonAddressTakenGlobals.begin(), E = NonAddressTakenGlobals.end();
- I != E; ++I) {
- GlobalValue *GV = I->first;
- ModRefFns &MRInfo = I->second;
- for (std::set<Function*>::iterator I = MRInfo.RefFns.begin(),
- E = MRInfo.RefFns.begin(); I != E; ++I)
- FunctionInfo[std::make_pair(*I, GV)] |= Ref;
- MRInfo.RefFns.clear();
- for (std::set<Function*>::iterator I = MRInfo.ModFns.begin(),
- E = MRInfo.ModFns.begin(); I != E; ++I)
- FunctionInfo[std::make_pair(*I, GV)] |= Mod;
- MRInfo.ModFns.clear();
- }
-
// 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), E = scc_end(&CG);
- I != E; ++I) {
- std::map<GlobalValue*, unsigned> ModRefProperties;
+ 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)
+ FunctionInfo.erase(Node->getFunction());
+ continue;
+ }
- // Collect the mod/ref properties due to called functions.
- for (unsigned i = 0, e = SCC.size(); i != e; ++i)
- for (CallGraphNode::iterator CI = SCC[i]->begin(), E = SCC[i]->end();
- CI != E; ++CI) {
- if (Function *Callee = (*CI)->getFunction()) {
- // Otherwise, combine the callee properties into our accumulated set.
- std::map<std::pair<Function*, GlobalValue*>, unsigned>::iterator
- CI = FunctionInfo.lower_bound(std::make_pair(Callee,
- (GlobalValue*)0));
- for (;CI != FunctionInfo.end() && CI->first.first == Callee; ++CI)
- ModRefProperties[CI->first.second] |= CI->second;
+ FunctionRecord &FR = FunctionInfo[SCC[0]->getFunction()];
+
+ bool KnowNothing = false;
+ unsigned FunctionEffect = 0;
+
+ // 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()) {
+ FunctionEffect |= 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.
+ FR.MayReadAnyGlobal = true;
} else {
- // For now assume that external functions could mod/ref anything,
- // since they could call into an escaping function that mod/refs an
- // internal. FIXME: We need better tracking!
- for (std::map<GlobalValue*, ModRefFns>::iterator GI =
- NonAddressTakenGlobals.begin(),
- E = NonAddressTakenGlobals.end(); GI != E; ++GI)
- ModRefProperties[GI->first] = ModRef;
- goto Out;
+ FunctionEffect |= 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;
}
- Out:
- // Set all functions in the CFG to have these properties. FIXME: it would
- // be better to use union find to only store these properties once,
- // PARTICULARLY if it's the universal set.
- for (unsigned i = 0, e = SCC.size(); i != e; ++i)
- if (Function *F = SCC[i]->getFunction()) {
- for (std::map<GlobalValue*, unsigned>::iterator I =
- ModRefProperties.begin(), E = ModRefProperties.end();
- I != E; ++I)
- FunctionInfo[std::make_pair(F, I->first)] = I->second;
- }
- }
-}
+ for (CallGraphNode::iterator CI = SCC[i]->begin(), E = SCC[i]->end();
+ CI != E && !KnowNothing; ++CI)
+ if (Function *Callee = CI->second->getFunction()) {
+ if (FunctionRecord *CalleeFR = getFunctionInfo(Callee)) {
+ // Propagate function effect up.
+ FunctionEffect |= CalleeFR->FunctionEffect;
+
+ // Incorporate callee's effects on globals into our info.
+ for (const auto &G : CalleeFR->GlobalInfo)
+ FR.GlobalInfo[G.first] |= G.second;
+ FR.MayReadAnyGlobal |= CalleeFR->MayReadAnyGlobal;
+ } 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 FunctionInfo map.
+ if (KnowNothing) {
+ for (auto *Node : SCC)
+ FunctionInfo.erase(Node->getFunction());
+ continue;
+ }
+
+ // Scan the function bodies for explicit loads or stores.
+ for (unsigned i = 0, e = SCC.size(); i != e && FunctionEffect != ModRef;
+ ++i)
+ for (inst_iterator II = inst_begin(SCC[i]->getFunction()),
+ E = inst_end(SCC[i]->getFunction());
+ II != E && FunctionEffect != ModRef; ++II)
+ if (LoadInst *LI = dyn_cast<LoadInst>(&*II)) {
+ FunctionEffect |= Ref;
+ if (LI->isVolatile())
+ // Volatile loads may have side-effects, so mark them as writing
+ // memory (for example, a flag inside the processor).
+ FunctionEffect |= Mod;
+ } else if (StoreInst *SI = dyn_cast<StoreInst>(&*II)) {
+ FunctionEffect |= Mod;
+ if (SI->isVolatile())
+ // Treat volatile stores as reading memory somewhere.
+ FunctionEffect |= Ref;
+ } else if (isAllocationFn(&*II, TLI) || isFreeCall(&*II, TLI)) {
+ FunctionEffect |= ModRef;
+ } else if (IntrinsicInst *Intrinsic = dyn_cast<IntrinsicInst>(&*II)) {
+ // The callgraph doesn't include intrinsic calls.
+ Function *Callee = Intrinsic->getCalledFunction();
+ ModRefBehavior Behaviour = AliasAnalysis::getModRefBehavior(Callee);
+ FunctionEffect |= (Behaviour & ModRef);
+ }
+ if ((FunctionEffect & Mod) == 0)
+ ++NumReadMemFunctions;
+ if (FunctionEffect == 0)
+ ++NumNoMemFunctions;
+ FR.FunctionEffect = FunctionEffect;
-/// getUnderlyingObject - This traverses the use chain to figure out what object
-/// the specified value points to. If the value points to, or is derived from,
-/// a global object, return it.
-static const GlobalValue *getUnderlyingObject(const Value *V) {
- //if (!isa<PointerType>(V->getType())) return 0;
-
- // If we are at some type of object... return it.
- if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) return GV;
-
- // Traverse through different addressing mechanisms...
- if (const Instruction *I = dyn_cast<Instruction>(V)) {
- if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
- return getUnderlyingObject(I->getOperand(0));
- } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
- if (CE->getOpcode() == Instruction::Cast ||
- CE->getOpcode() == Instruction::GetElementPtr)
- return getUnderlyingObject(CE->getOperand(0));
- } else if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V)) {
- return CPR->getValue();
+ // 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)
+ FunctionInfo[SCC[i]->getFunction()] = FR;
}
- return 0;
}
/// 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.
-AliasAnalysis::AliasResult
-GlobalsModRef::alias(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size) {
- GlobalValue *GV1 = const_cast<GlobalValue*>(getUnderlyingObject(V1));
- GlobalValue *GV2 = const_cast<GlobalValue*>(getUnderlyingObject(V2));
-
- // 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 = 0;
- if (GV2 && !NonAddressTakenGlobals.count(GV2)) GV2 = 0;
+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, or if one is and the other isn't, we know these can't alias.
+ 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 (AllocsForIndirectGlobals.count(UV1))
+ GV1 = AllocsForIndirectGlobals[UV1];
+ if (AllocsForIndirectGlobals.count(UV2))
+ GV2 = AllocsForIndirectGlobals[UV2];
+
+ // Now that we know whether the two pointers are related to indirect globals,
+ // use this to disambiguate the pointers. If either pointer is based on an
+ // indirect global and if they are not both based on the same indirect global,
+ // they cannot alias.
if ((GV1 || GV2) && GV1 != GV2)
return NoAlias;
- return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
+ return AliasAnalysis::alias(LocA, LocB);
}
AliasAnalysis::ModRefResult
-GlobalsModRef::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
+GlobalsModRef::getModRefInfo(ImmutableCallSite CS, const MemoryLocation &Loc) {
unsigned Known = ModRef;
// If we are asking for mod/ref info of a direct call with a pointer to a
- // global, return information if we have it.
- if (GlobalValue *GV = const_cast<GlobalValue*>(getUnderlyingObject(P)))
- if (GV->hasInternalLinkage())
- if (Function *F = CS.getCalledFunction()) {
- std::map<std::pair<Function*, GlobalValue*>, unsigned>::iterator
- it = FunctionInfo.find(std::make_pair(F, GV));
- if (it != FunctionInfo.end())
- Known = it->second;
- }
+ // 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 FunctionRecord *FR = getFunctionInfo(F))
+ Known = FR->getInfoForGlobal(GV);
if (Known == NoModRef)
return NoModRef; // No need to query other mod/ref analyses
- return ModRefResult(Known & AliasAnalysis::getModRefInfo(CS, P, Size));
+ return ModRefResult(Known & AliasAnalysis::getModRefInfo(CS, Loc));
}
-
//===----------------------------------------------------------------------===//
// Methods to update the analysis as a result of the client transformation.
//
void GlobalsModRef::deleteValue(Value *V) {
if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
- std::map<GlobalValue*, ModRefFns>::iterator I =
- NonAddressTakenGlobals.find(GV);
- if (I != NonAddressTakenGlobals.end())
- NonAddressTakenGlobals.erase(I);
+ if (NonAddressTakenGlobals.erase(GV)) {
+ // This global might be an indirect global. If so, remove it and remove
+ // any AllocRelatedValues for it.
+ if (IndirectGlobals.erase(GV)) {
+ // Remove any entries in AllocsForIndirectGlobals for this global.
+ for (std::map<const Value *, const GlobalValue *>::iterator
+ I = AllocsForIndirectGlobals.begin(),
+ E = AllocsForIndirectGlobals.end();
+ I != E;) {
+ if (I->second == GV) {
+ AllocsForIndirectGlobals.erase(I++);
+ } else {
+ ++I;
+ }
+ }
+ }
+ }
}
+
+ // Otherwise, if this is an allocation related to an indirect global, remove
+ // it.
+ AllocsForIndirectGlobals.erase(V);
+
+ AliasAnalysis::deleteValue(V);
}
-void GlobalsModRef::copyValue(Value *From, Value *To) {
- if (GlobalValue *FromGV = dyn_cast<GlobalValue>(From))
- if (GlobalValue *ToGV = dyn_cast<GlobalValue>(To)) {
- std::map<GlobalValue*, ModRefFns>::iterator I =
- NonAddressTakenGlobals.find(FromGV);
- if (I != NonAddressTakenGlobals.end())
- NonAddressTakenGlobals[ToGV] = I->second;
- }
+void GlobalsModRef::addEscapingUse(Use &U) {
+ // For the purposes of this analysis, it is conservatively correct to treat
+ // a newly escaping value equivalently to a deleted one. We could perhaps
+ // be more precise by processing the new use and attempting to update our
+ // saved analysis results to accommodate it.
+ deleteValue(U);
+
+ AliasAnalysis::addEscapingUse(U);
}