1 //===- MemoryDependenceAnalysis.cpp - Mem Deps Implementation --*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the Owen Anderson and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements an analysis that determines, for a given memory
11 // operation, what preceding memory operations it depends on. It builds on
12 // alias analysis information, and tries to provide a lazy, caching interface to
13 // a common kind of alias information query.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
18 #include "llvm/Constants.h"
19 #include "llvm/Instructions.h"
20 #include "llvm/Function.h"
21 #include "llvm/Analysis/AliasAnalysis.h"
22 #include "llvm/Support/CFG.h"
23 #include "llvm/Target/TargetData.h"
27 char MemoryDependenceAnalysis::ID = 0;
29 Instruction* const MemoryDependenceAnalysis::NonLocal = (Instruction*)-3;
30 Instruction* const MemoryDependenceAnalysis::None = (Instruction*)-4;
32 // Register this pass...
33 static RegisterPass<MemoryDependenceAnalysis> X("memdep",
34 "Memory Dependence Analysis");
36 /// getAnalysisUsage - Does not modify anything. It uses Alias Analysis.
38 void MemoryDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
40 AU.addRequiredTransitive<AliasAnalysis>();
41 AU.addRequiredTransitive<TargetData>();
44 /// getCallSiteDependency - Private helper for finding the local dependencies
46 Instruction* MemoryDependenceAnalysis::getCallSiteDependency(CallSite C,
50 AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
51 TargetData& TD = getAnalysis<TargetData>();
52 BasicBlock::iterator blockBegin = C.getInstruction()->getParent()->begin();
53 BasicBlock::iterator QI = C.getInstruction();
55 // If the starting point was specifiy, use it
58 blockBegin = start->getParent()->end();
59 // If the starting point wasn't specified, but the block was, use it
60 } else if (!start && block) {
62 blockBegin = block->end();
65 // Walk backwards through the block, looking for dependencies
66 while (QI != blockBegin) {
69 // If this inst is a memory op, get the pointer it accessed
71 uint64_t pointerSize = 0;
72 if (StoreInst* S = dyn_cast<StoreInst>(QI)) {
73 pointer = S->getPointerOperand();
74 pointerSize = TD.getTypeSize(S->getOperand(0)->getType());
75 } else if (LoadInst* L = dyn_cast<LoadInst>(QI)) {
76 pointer = L->getPointerOperand();
77 pointerSize = TD.getTypeSize(L->getType());
78 } else if (AllocationInst* AI = dyn_cast<AllocationInst>(QI)) {
80 if (ConstantInt* C = dyn_cast<ConstantInt>(AI->getArraySize()))
81 pointerSize = C->getZExtValue() * \
82 TD.getTypeSize(AI->getAllocatedType());
85 } else if (VAArgInst* V = dyn_cast<VAArgInst>(QI)) {
86 pointer = V->getOperand(0);
87 pointerSize = TD.getTypeSize(V->getType());
88 } else if (FreeInst* F = dyn_cast<FreeInst>(QI)) {
89 pointer = F->getPointerOperand();
91 // FreeInsts erase the entire structure
93 } else if (CallSite::get(QI).getInstruction() != 0) {
94 if (AA.getModRefInfo(C, CallSite::get(QI)) != AliasAnalysis::NoModRef) {
95 if (!start && !block) {
96 depGraphLocal.insert(std::make_pair(C.getInstruction(),
97 std::make_pair(QI, true)));
98 reverseDep[QI].insert(C.getInstruction());
107 if (AA.getModRefInfo(C, pointer, pointerSize) != AliasAnalysis::NoModRef) {
108 if (!start && !block) {
109 depGraphLocal.insert(std::make_pair(C.getInstruction(),
110 std::make_pair(QI, true)));
111 reverseDep[QI].insert(C.getInstruction());
117 // No dependence found
118 depGraphLocal.insert(std::make_pair(C.getInstruction(),
119 std::make_pair(NonLocal, true)));
120 reverseDep[NonLocal].insert(C.getInstruction());
124 /// nonLocalHelper - Private helper used to calculate non-local dependencies
125 /// by doing DFS on the predecessors of a block to find its dependencies
126 void MemoryDependenceAnalysis::nonLocalHelper(Instruction* query,
128 DenseMap<BasicBlock*, Value*>& resp) {
129 // Set of blocks that we've already visited in our DFS
130 SmallPtrSet<BasicBlock*, 4> visited;
131 // Current stack of the DFS
132 SmallVector<BasicBlock*, 4> stack;
133 stack.push_back(block);
136 while (!stack.empty()) {
137 BasicBlock* BB = stack.back();
139 // If we've already visited this block, no need to revist
140 if (visited.count(BB)) {
145 // If we find a new block with a local dependency for query,
146 // then we insert the new dependency and backtrack.
150 Instruction* localDep = getDependency(query, 0, BB);
151 if (localDep != NonLocal) {
152 resp.insert(std::make_pair(BB, localDep));
157 // If we re-encounter the starting block, we still need to search it
158 // because there might be a dependency in the starting block AFTER
159 // the position of the query. This is necessary to get loops right.
160 } else if (BB == block && stack.size() > 1) {
163 Instruction* localDep = getDependency(query, 0, BB);
164 if (localDep != query)
165 resp.insert(std::make_pair(BB, localDep));
172 // If we didn't find anything, recurse on the precessors of this block
173 bool predOnStack = false;
174 bool inserted = false;
175 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
177 if (!visited.count(*PI)) {
178 stack.push_back(*PI);
183 // If we inserted a new predecessor, then we'll come back to this block
186 // If we didn't insert because we have no predecessors, then this
187 // query has no dependency at all.
188 else if (!inserted && !predOnStack) {
189 resp.insert(std::make_pair(BB, None));
190 // If we didn't insert because our predecessors are already on the stack,
191 // then we might still have a dependency, but it will be discovered during
193 } else if (!inserted && predOnStack){
194 resp.insert(std::make_pair(BB, NonLocal));
201 /// getNonLocalDependency - Fills the passed-in map with the non-local
202 /// dependencies of the queries. The map will contain NonLocal for
203 /// blocks between the query and its dependencies.
204 void MemoryDependenceAnalysis::getNonLocalDependency(Instruction* query,
205 DenseMap<BasicBlock*, Value*>& resp) {
206 if (depGraphNonLocal.count(query)) {
207 resp = depGraphNonLocal[query];
211 // First check that we don't actually have a local dependency.
212 Instruction* localDep = getDependency(query);
213 if (localDep != NonLocal) {
214 resp.insert(std::make_pair(query->getParent(),localDep));
218 // If not, go ahead and search for non-local ones.
219 nonLocalHelper(query, query->getParent(), resp);
221 // Update the non-local dependency cache
222 for (DenseMap<BasicBlock*, Value*>::iterator I = resp.begin(), E = resp.end();
224 depGraphNonLocal[query].insert(*I);
225 reverseDepNonLocal[I->second].insert(query);
229 /// getDependency - Return the instruction on which a memory operation
230 /// depends. The local paramter indicates if the query should only
231 /// evaluate dependencies within the same basic block.
232 Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
235 // Start looking for dependencies with the queried inst
236 BasicBlock::iterator QI = query;
238 // Check for a cached result
239 std::pair<Instruction*, bool> cachedResult = depGraphLocal[query];
240 // If we have a _confirmed_ cached entry, return it
241 if (cachedResult.second)
242 return cachedResult.first;
243 else if (cachedResult.first && cachedResult.first != NonLocal)
244 // If we have an unconfirmed cached entry, we can start our search from there
245 QI = cachedResult.first;
249 else if (!start && block)
252 AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
253 TargetData& TD = getAnalysis<TargetData>();
255 // Get the pointer value for which dependence will be determined
257 uint64_t dependeeSize = 0;
258 bool queryIsVolatile = false;
259 if (StoreInst* S = dyn_cast<StoreInst>(query)) {
260 dependee = S->getPointerOperand();
261 dependeeSize = TD.getTypeSize(S->getOperand(0)->getType());
262 queryIsVolatile = S->isVolatile();
263 } else if (LoadInst* L = dyn_cast<LoadInst>(query)) {
264 dependee = L->getPointerOperand();
265 dependeeSize = TD.getTypeSize(L->getType());
266 queryIsVolatile = L->isVolatile();
267 } else if (VAArgInst* V = dyn_cast<VAArgInst>(query)) {
268 dependee = V->getOperand(0);
269 dependeeSize = TD.getTypeSize(V->getType());
270 } else if (FreeInst* F = dyn_cast<FreeInst>(query)) {
271 dependee = F->getPointerOperand();
273 // FreeInsts erase the entire structure, not just a field
275 } else if (CallSite::get(query).getInstruction() != 0)
276 return getCallSiteDependency(CallSite::get(query), start, block);
277 else if (isa<AllocationInst>(query))
282 BasicBlock::iterator blockBegin = block ? block->begin()
283 : query->getParent()->begin();
285 // Walk backwards through the basic block, looking for dependencies
286 while (QI != blockBegin) {
289 // If this inst is a memory op, get the pointer it accessed
291 uint64_t pointerSize = 0;
292 if (StoreInst* S = dyn_cast<StoreInst>(QI)) {
293 // All volatile loads/stores depend on each other
294 if (queryIsVolatile && S->isVolatile()) {
295 if (!start && !block) {
296 depGraphLocal.insert(std::make_pair(query, std::make_pair(S, true)));
297 reverseDep[S].insert(query);
303 pointer = S->getPointerOperand();
304 pointerSize = TD.getTypeSize(S->getOperand(0)->getType());
305 } else if (LoadInst* L = dyn_cast<LoadInst>(QI)) {
306 // All volatile loads/stores depend on each other
307 if (queryIsVolatile && L->isVolatile()) {
308 if (!start && !block) {
309 depGraphLocal.insert(std::make_pair(query, std::make_pair(L, true)));
310 reverseDep[L].insert(query);
316 pointer = L->getPointerOperand();
317 pointerSize = TD.getTypeSize(L->getType());
318 } else if (AllocationInst* AI = dyn_cast<AllocationInst>(QI)) {
320 if (ConstantInt* C = dyn_cast<ConstantInt>(AI->getArraySize()))
321 pointerSize = C->getZExtValue() * \
322 TD.getTypeSize(AI->getAllocatedType());
325 } else if (VAArgInst* V = dyn_cast<VAArgInst>(QI)) {
326 pointer = V->getOperand(0);
327 pointerSize = TD.getTypeSize(V->getType());
328 } else if (FreeInst* F = dyn_cast<FreeInst>(QI)) {
329 pointer = F->getPointerOperand();
331 // FreeInsts erase the entire structure
333 } else if (CallSite::get(QI).getInstruction() != 0) {
334 // Call insts need special handling. Check if they can modify our pointer
335 AliasAnalysis::ModRefResult MR = AA.getModRefInfo(CallSite::get(QI),
336 dependee, dependeeSize);
338 if (MR != AliasAnalysis::NoModRef) {
339 // Loads don't depend on read-only calls
340 if (isa<LoadInst>(query) && MR == AliasAnalysis::Ref)
343 if (!start && !block) {
344 depGraphLocal.insert(std::make_pair(query,
345 std::make_pair(QI, true)));
346 reverseDep[QI].insert(query);
355 // If we found a pointer, check if it could be the same as our pointer
357 AliasAnalysis::AliasResult R = AA.alias(pointer, pointerSize,
358 dependee, dependeeSize);
360 if (R != AliasAnalysis::NoAlias) {
361 // May-alias loads don't depend on each other
362 if (isa<LoadInst>(query) && isa<LoadInst>(QI) &&
363 R == AliasAnalysis::MayAlias)
366 if (!start && !block) {
367 depGraphLocal.insert(std::make_pair(query,
368 std::make_pair(QI, true)));
369 reverseDep[QI].insert(query);
377 // If we found nothing, return the non-local flag
378 if (!start && !block) {
379 depGraphLocal.insert(std::make_pair(query,
380 std::make_pair(NonLocal, true)));
381 reverseDep[NonLocal].insert(query);
387 /// removeInstruction - Remove an instruction from the dependence analysis,
388 /// updating the dependence of instructions that previously depended on it.
389 /// This method attempts to keep the cache coherent using the reverse map.
390 void MemoryDependenceAnalysis::removeInstruction(Instruction* rem) {
391 // Figure out the new dep for things that currently depend on rem
392 Instruction* newDep = NonLocal;
394 depMapType::iterator depGraphEntry = depGraphLocal.find(rem);
396 if (depGraphEntry != depGraphLocal.end()) {
397 if (depGraphEntry->second.first != NonLocal &&
398 depGraphEntry->second.second) {
399 // If we have dep info for rem, set them to it
400 BasicBlock::iterator RI = depGraphEntry->second.first;
403 } else if (depGraphEntry->second.first == NonLocal &&
404 depGraphEntry->second.second ) {
405 // If we have a confirmed non-local flag, use it
408 // Otherwise, use the immediate successor of rem
409 // NOTE: This is because, when getDependence is called, it will first
410 // check the immediate predecessor of what is in the cache.
411 BasicBlock::iterator RI = rem;
416 SmallPtrSet<Instruction*, 4>& set = reverseDep[rem];
417 for (SmallPtrSet<Instruction*, 4>::iterator I = set.begin(), E = set.end();
419 // Insert the new dependencies
420 // Mark it as unconfirmed as long as it is not the non-local flag
421 depGraphLocal[*I] = std::make_pair(newDep, !newDep);
424 reverseDep.erase(rem);
427 if (depGraphNonLocal.count(rem)) {
428 SmallPtrSet<Instruction*, 4>& set = reverseDepNonLocal[rem];
429 for (SmallPtrSet<Instruction*, 4>::iterator I = set.begin(), E = set.end();
431 depGraphNonLocal.erase(*I);
433 reverseDepNonLocal.erase(rem);
436 getAnalysis<AliasAnalysis>().deleteValue(rem);