1 //===- GlobalsModRef.cpp - Simple Mod/Ref Analysis for Globals ------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This simple pass provides alias and mod/ref information for global values
11 // that do not have their address taken, and keeps track of whether functions
12 // read or write memory (are "pure"). For this simple (but very common) case,
13 // we can provide pretty accurate and useful information.
15 //===----------------------------------------------------------------------===//
17 #define DEBUG_TYPE "globalsmodref-aa"
18 #include "llvm/Analysis/Passes.h"
19 #include "llvm/Module.h"
20 #include "llvm/Pass.h"
21 #include "llvm/Instructions.h"
22 #include "llvm/Constants.h"
23 #include "llvm/Analysis/AliasAnalysis.h"
24 #include "llvm/Analysis/CallGraph.h"
25 #include "llvm/Support/InstIterator.h"
26 #include "Support/CommandLine.h"
27 #include "Support/Debug.h"
28 #include "Support/Statistic.h"
29 #include "Support/SCCIterator.h"
35 NumNonAddrTakenGlobalVars("globalsmodref-aa",
36 "Number of global vars without address taken");
38 NumNonAddrTakenFunctions("globalsmodref-aa",
39 "Number of functions without address taken");
41 NumNoMemFunctions("globalsmodref-aa",
42 "Number of functions that do not access memory");
44 NumReadMemFunctions("globalsmodref-aa",
45 "Number of functions that only read memory");
47 /// FunctionRecord - One instance of this structure is stored for every
48 /// function in the program. Later, the entries for these functions are
49 /// removed if the function is found to call an external function (in which
50 /// case we know nothing about it.
51 struct FunctionRecord {
52 /// GlobalInfo - Maintain mod/ref info for all of the globals without
53 /// addresses taken that are read or written (transitively) by this
55 std::map<GlobalValue*, unsigned> GlobalInfo;
57 unsigned getInfoForGlobal(GlobalValue *GV) const {
58 std::map<GlobalValue*, unsigned>::const_iterator I = GlobalInfo.find(GV);
59 if (I != GlobalInfo.end())
64 /// FunctionEffect - Capture whether or not this function reads or writes to
65 /// ANY memory. If not, we can do a lot of aggressive analysis on it.
66 unsigned FunctionEffect;
69 /// GlobalsModRef - The actual analysis pass.
70 class GlobalsModRef : public Pass, public AliasAnalysis {
71 /// NonAddressTakenGlobals - The globals that do not have their addresses
73 std::set<GlobalValue*> NonAddressTakenGlobals;
75 /// FunctionInfo - For each function, keep track of what globals are
77 std::map<Function*, FunctionRecord> FunctionInfo;
81 InitializeAliasAnalysis(this); // set up super class
82 AnalyzeGlobals(M); // find non-addr taken globals
83 AnalyzeCallGraph(getAnalysis<CallGraph>(), M); // Propagate on CG
87 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
88 AliasAnalysis::getAnalysisUsage(AU);
89 AU.addRequired<CallGraph>();
90 AU.setPreservesAll(); // Does not transform code
93 //------------------------------------------------
94 // Implement the AliasAnalysis API
96 AliasResult alias(const Value *V1, unsigned V1Size,
97 const Value *V2, unsigned V2Size);
98 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
99 bool hasNoModRefInfoForCalls() const { return false; }
101 bool doesNotAccessMemory(Function *F) {
102 if (FunctionRecord *FR = getFunctionInfo(F))
103 if (FR->FunctionEffect == 0)
105 return AliasAnalysis::doesNotAccessMemory(F);
107 bool onlyReadsMemory(Function *F) {
108 if (FunctionRecord *FR = getFunctionInfo(F))
109 if ((FR->FunctionEffect & Mod) == 0)
111 return AliasAnalysis::onlyReadsMemory(F);
115 virtual void deleteValue(Value *V);
116 virtual void copyValue(Value *From, Value *To);
119 /// getFunctionInfo - Return the function info for the function, or null if
120 /// the function calls an external function (in which case we don't have
121 /// anything useful to say about it).
122 FunctionRecord *getFunctionInfo(Function *F) {
123 std::map<Function*, FunctionRecord>::iterator I = FunctionInfo.find(F);
124 if (I != FunctionInfo.end())
129 void AnalyzeGlobals(Module &M);
130 void AnalyzeCallGraph(CallGraph &CG, Module &M);
131 void AnalyzeSCC(std::vector<CallGraphNode *> &SCC);
132 bool AnalyzeUsesOfGlobal(Value *V, std::vector<Function*> &Readers,
133 std::vector<Function*> &Writers);
136 RegisterOpt<GlobalsModRef> X("globalsmodref-aa",
137 "Simple mod/ref analysis for globals");
138 RegisterAnalysisGroup<AliasAnalysis, GlobalsModRef> Y;
141 Pass *llvm::createGlobalsModRefPass() { return new GlobalsModRef(); }
144 /// AnalyzeGlobalUses - Scan through the users of all of the internal
145 /// GlobalValue's in the program. If none of them have their "Address taken"
146 /// (really, their address passed to something nontrivial), record this fact,
147 /// and record the functions that they are used directly in.
148 void GlobalsModRef::AnalyzeGlobals(Module &M) {
149 std::vector<Function*> Readers, Writers;
150 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
151 if (I->hasInternalLinkage()) {
152 if (!AnalyzeUsesOfGlobal(I, Readers, Writers)) {
153 // Remember that we are tracking this global.
154 NonAddressTakenGlobals.insert(I);
155 ++NumNonAddrTakenFunctions;
157 Readers.clear(); Writers.clear();
160 for (Module::giterator I = M.gbegin(), E = M.gend(); I != E; ++I)
161 if (I->hasInternalLinkage()) {
162 if (!AnalyzeUsesOfGlobal(I, Readers, Writers)) {
163 // Remember that we are tracking this global, and the mod/ref fns
164 NonAddressTakenGlobals.insert(I);
165 for (unsigned i = 0, e = Readers.size(); i != e; ++i)
166 FunctionInfo[Readers[i]].GlobalInfo[I] |= Ref;
168 if (!I->isConstant()) // No need to keep track of writers to constants
169 for (unsigned i = 0, e = Writers.size(); i != e; ++i)
170 FunctionInfo[Writers[i]].GlobalInfo[I] |= Mod;
171 ++NumNonAddrTakenGlobalVars;
173 Readers.clear(); Writers.clear();
177 /// AnalyzeUsesOfGlobal - Look at all of the users of the specified global value
178 /// derived pointer. If this is used by anything complex (i.e., the address
179 /// escapes), return true. Also, while we are at it, keep track of those
180 /// functions that read and write to the value.
181 bool GlobalsModRef::AnalyzeUsesOfGlobal(Value *V,
182 std::vector<Function*> &Readers,
183 std::vector<Function*> &Writers) {
184 if (!isa<PointerType>(V->getType())) return true;
186 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
187 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
188 Readers.push_back(LI->getParent()->getParent());
189 } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
190 if (V == SI->getOperand(0)) return true; // Storing the pointer
191 Writers.push_back(SI->getParent()->getParent());
192 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
193 if (AnalyzeUsesOfGlobal(GEP, Readers, Writers)) return true;
194 } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
195 // Make sure that this is just the function being called, not that it is
196 // passing into the function.
197 for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
198 if (CI->getOperand(i) == V) return true;
199 } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
200 // Make sure that this is just the function being called, not that it is
201 // passing into the function.
202 for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
203 if (CI->getOperand(i) == V) return true;
204 } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) {
205 // Make sure that this is just the function being called, not that it is
206 // passing into the function.
207 for (unsigned i = 3, e = II->getNumOperands(); i != e; ++i)
208 if (II->getOperand(i) == V) return true;
209 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) {
210 if (CE->getOpcode() == Instruction::GetElementPtr ||
211 CE->getOpcode() == Instruction::Cast) {
212 if (AnalyzeUsesOfGlobal(CE, Readers, Writers))
217 } else if (GlobalValue *GV = dyn_cast<GlobalValue>(*UI)) {
218 if (AnalyzeUsesOfGlobal(GV, Readers, Writers)) return true;
225 /// AnalyzeCallGraph - At this point, we know the functions where globals are
226 /// immediately stored to and read from. Propagate this information up the call
227 /// graph to all callers and compute the mod/ref info for all memory for each
229 void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) {
230 DEBUG(std::cerr << "GlobalsModRef: Analyze Call Graph\n");
232 // We do a bottom-up SCC traversal of the call graph. In other words, we
233 // visit all callees before callers (leaf-first).
234 for (scc_iterator<CallGraph*> I = scc_begin(&CG), E = scc_end(&CG); I!=E; ++I)
235 // Do not call AnalyzeSCC on the external function node.
236 if ((*I).size() != 1 || (*I)[0]->getFunction())
240 void GlobalsModRef::AnalyzeSCC(std::vector<CallGraphNode *> &SCC) {
241 assert(!SCC.empty() && "SCC with no functions?");
242 FunctionRecord &FR = FunctionInfo[SCC[0]->getFunction()];
244 bool CallsExternal = false;
245 unsigned FunctionEffect = 0;
247 // Collect the mod/ref properties due to called functions. We only compute
249 for (unsigned i = 0, e = SCC.size(); i != e && !CallsExternal; ++i)
250 for (CallGraphNode::iterator CI = SCC[i]->begin(), E = SCC[i]->end();
252 if (Function *Callee = (*CI)->getFunction()) {
253 if (FunctionRecord *CalleeFR = getFunctionInfo(Callee)) {
254 // Propagate function effect up.
255 FunctionEffect |= CalleeFR->FunctionEffect;
257 // Incorporate callee's effects on globals into our info.
258 for (std::map<GlobalValue*, unsigned>::iterator GI =
259 CalleeFR->GlobalInfo.begin(), E = CalleeFR->GlobalInfo.end();
261 FR.GlobalInfo[GI->first] |= GI->second;
264 CallsExternal = true;
268 CallsExternal = true;
272 // If this SCC calls an external function, we can't say anything about it, so
273 // remove all SCC functions from the FunctionInfo map.
275 for (unsigned i = 0, e = SCC.size(); i != e; ++i)
276 FunctionInfo.erase(SCC[i]->getFunction());
280 // Otherwise, unless we already know that this function mod/refs memory, scan
281 // the function bodies to see if there are any explicit loads or stores.
282 if (FunctionEffect != ModRef) {
283 for (unsigned i = 0, e = SCC.size(); i != e && FunctionEffect != ModRef;++i)
284 for (inst_iterator II = inst_begin(SCC[i]->getFunction()),
285 E = inst_end(SCC[i]->getFunction());
286 II != E && FunctionEffect != ModRef; ++II)
287 if (isa<LoadInst>(*II))
288 FunctionEffect |= Ref;
289 else if (isa<StoreInst>(*II))
290 FunctionEffect |= Mod;
293 if ((FunctionEffect & Mod) == 0)
294 ++NumReadMemFunctions;
295 if (FunctionEffect == 0)
297 FR.FunctionEffect = FunctionEffect;
299 // Finally, now that we know the full effect on this SCC, clone the
300 // information to each function in the SCC.
301 for (unsigned i = 1, e = SCC.size(); i != e; ++i)
302 FunctionInfo[SCC[i]->getFunction()] = FR;
307 /// getUnderlyingObject - This traverses the use chain to figure out what object
308 /// the specified value points to. If the value points to, or is derived from,
309 /// a global object, return it.
310 static const GlobalValue *getUnderlyingObject(const Value *V) {
311 if (!isa<PointerType>(V->getType())) return 0;
313 // If we are at some type of object... return it.
314 if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) return GV;
316 // Traverse through different addressing mechanisms...
317 if (const Instruction *I = dyn_cast<Instruction>(V)) {
318 if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
319 return getUnderlyingObject(I->getOperand(0));
320 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
321 if (CE->getOpcode() == Instruction::Cast ||
322 CE->getOpcode() == Instruction::GetElementPtr)
323 return getUnderlyingObject(CE->getOperand(0));
328 /// alias - If one of the pointers is to a global that we are tracking, and the
329 /// other is some random pointer, we know there cannot be an alias, because the
330 /// address of the global isn't taken.
331 AliasAnalysis::AliasResult
332 GlobalsModRef::alias(const Value *V1, unsigned V1Size,
333 const Value *V2, unsigned V2Size) {
334 GlobalValue *GV1 = const_cast<GlobalValue*>(getUnderlyingObject(V1));
335 GlobalValue *GV2 = const_cast<GlobalValue*>(getUnderlyingObject(V2));
337 // If the global's address is taken, pretend we don't know it's a pointer to
339 if (GV1 && !NonAddressTakenGlobals.count(GV1)) GV1 = 0;
340 if (GV2 && !NonAddressTakenGlobals.count(GV2)) GV2 = 0;
342 if ((GV1 || GV2) && GV1 != GV2)
345 return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
348 AliasAnalysis::ModRefResult
349 GlobalsModRef::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
350 unsigned Known = ModRef;
352 // If we are asking for mod/ref info of a direct call with a pointer to a
353 // global we are tracking, return information if we have it.
354 if (GlobalValue *GV = const_cast<GlobalValue*>(getUnderlyingObject(P)))
355 if (GV->hasInternalLinkage())
356 if (Function *F = CS.getCalledFunction())
357 if (NonAddressTakenGlobals.count(GV))
358 if (FunctionRecord *FR = getFunctionInfo(F))
359 Known = FR->getInfoForGlobal(GV);
361 if (Known == NoModRef)
362 return NoModRef; // No need to query other mod/ref analyses
363 return ModRefResult(Known & AliasAnalysis::getModRefInfo(CS, P, Size));
367 //===----------------------------------------------------------------------===//
368 // Methods to update the analysis as a result of the client transformation.
370 void GlobalsModRef::deleteValue(Value *V) {
371 if (GlobalValue *GV = dyn_cast<GlobalValue>(V))
372 NonAddressTakenGlobals.erase(GV);
375 void GlobalsModRef::copyValue(Value *From, Value *To) {