--- /dev/null
+//===- 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;
+ }
+}
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