diff options
Diffstat (limited to 'lib/Analysis')
| -rw-r--r-- | lib/Analysis/IPA/GlobalsModRef.cpp | 327 |
1 files changed, 327 insertions, 0 deletions
diff --git a/lib/Analysis/IPA/GlobalsModRef.cpp b/lib/Analysis/IPA/GlobalsModRef.cpp new file mode 100644 index 0000000..c3f6ba9 --- /dev/null +++ b/lib/Analysis/IPA/GlobalsModRef.cpp @@ -0,0 +1,327 @@ +//===- 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 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. +// +//===----------------------------------------------------------------------===// + +#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/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/CallGraph.h" +#include "Support/Debug.h" +#include "Support/Statistic.h" +#include "Support/SCCIterator.h" +#include <set> +using namespace llvm; + +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; + } + + 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 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; +} + +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" +/// (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()); + ++NumNonAddrTakenFunctions; + } + 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)) { + // 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()); + ++NumNonAddrTakenGlobalVars; + } + 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)) { + 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)) { + // 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; + } else { + return true; + } + return false; +} + +/// 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. +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; + const std::vector<CallGraphNode *> &SCC = *I; + + // 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; + } 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; + } + } + 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; + } + } +} + + + +/// 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(); + } + 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; + + if ((GV1 || GV2) && GV1 != GV2) + return NoAlias; + + return AliasAnalysis::alias(V1, V1Size, V2, V2Size); +} + +AliasAnalysis::ModRefResult +GlobalsModRef::getModRefInfo(CallSite CS, Value *P, unsigned Size) { + 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; + } + + if (Known == NoModRef) + return NoModRef; // No need to query other mod/ref analyses + return ModRefResult(Known & AliasAnalysis::getModRefInfo(CS, P, Size)); +} + + +//===----------------------------------------------------------------------===// +// 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); + } +} + +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; + } +} |