1 //===- LoopDependenceAnalysis.cpp - LDA Implementation ----------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This is the (beginning) of an implementation of a loop dependence analysis
11 // framework, which is used to detect dependences in memory accesses in loops.
13 // Please note that this is work in progress and the interface is subject to
16 // TODO: adapt as implementation progresses.
18 //===----------------------------------------------------------------------===//
20 #define DEBUG_TYPE "lda"
21 #include "llvm/Analysis/AliasAnalysis.h"
22 #include "llvm/Analysis/LoopDependenceAnalysis.h"
23 #include "llvm/Analysis/LoopPass.h"
24 #include "llvm/Analysis/ScalarEvolution.h"
25 #include "llvm/Instructions.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/ErrorHandling.h"
28 #include "llvm/Target/TargetData.h"
31 LoopPass *llvm::createLoopDependenceAnalysisPass() {
32 return new LoopDependenceAnalysis();
35 static RegisterPass<LoopDependenceAnalysis>
36 R("lda", "Loop Dependence Analysis", false, true);
37 char LoopDependenceAnalysis::ID = 0;
39 //===----------------------------------------------------------------------===//
41 //===----------------------------------------------------------------------===//
43 static inline bool IsMemRefInstr(const Value *V) {
44 const Instruction *I = dyn_cast<const Instruction>(V);
45 return I && (I->mayReadFromMemory() || I->mayWriteToMemory());
48 static void GetMemRefInstrs(
49 const Loop *L, SmallVectorImpl<Instruction*> &memrefs) {
50 for (Loop::block_iterator b = L->block_begin(), be = L->block_end();
52 for (BasicBlock::iterator i = (*b)->begin(), ie = (*b)->end();
58 static bool IsLoadOrStoreInst(Value *I) {
59 return isa<LoadInst>(I) || isa<StoreInst>(I);
62 static Value *GetPointerOperand(Value *I) {
63 if (LoadInst *i = dyn_cast<LoadInst>(I))
64 return i->getPointerOperand();
65 if (StoreInst *i = dyn_cast<StoreInst>(I))
66 return i->getPointerOperand();
67 llvm_unreachable("Value is no load or store instruction!");
72 //===----------------------------------------------------------------------===//
74 //===----------------------------------------------------------------------===//
76 bool LoopDependenceAnalysis::isDependencePair(const Value *x,
77 const Value *y) const {
78 return IsMemRefInstr(x) &&
80 (cast<const Instruction>(x)->mayWriteToMemory() ||
81 cast<const Instruction>(y)->mayWriteToMemory());
84 bool LoopDependenceAnalysis::depends(Value *src, Value *dst) {
85 assert(isDependencePair(src, dst) && "Values form no dependence pair!");
86 DOUT << "== LDA test ==\n" << *src << *dst;
88 // We only analyse loads and stores; for possible memory accesses by e.g.
89 // free, call, or invoke instructions we conservatively assume dependence.
90 if (!IsLoadOrStoreInst(src) || !IsLoadOrStoreInst(dst))
93 Value *srcPtr = GetPointerOperand(src);
94 Value *dstPtr = GetPointerOperand(dst);
95 const Value *srcObj = srcPtr->getUnderlyingObject();
96 const Value *dstObj = dstPtr->getUnderlyingObject();
97 AliasAnalysis::AliasResult alias = AA->alias(
98 srcObj, AA->getTargetData().getTypeStoreSize(srcObj->getType()),
99 dstObj, AA->getTargetData().getTypeStoreSize(dstObj->getType()));
101 // If we don't know whether or not the two objects alias, assume dependence.
102 if (alias == AliasAnalysis::MayAlias)
105 // If the objects noalias, they are distinct, accesses are independent.
106 if (alias == AliasAnalysis::NoAlias)
109 // TODO: the underlying objects MustAlias, test for dependence
111 // We couldn't establish a more precise result, so we have to conservatively
112 // assume full dependence.
116 //===----------------------------------------------------------------------===//
117 // LoopDependenceAnalysis Implementation
118 //===----------------------------------------------------------------------===//
120 bool LoopDependenceAnalysis::runOnLoop(Loop *L, LPPassManager &) {
122 AA = &getAnalysis<AliasAnalysis>();
123 SE = &getAnalysis<ScalarEvolution>();
127 void LoopDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
128 AU.setPreservesAll();
129 AU.addRequiredTransitive<AliasAnalysis>();
130 AU.addRequiredTransitive<ScalarEvolution>();
133 static void PrintLoopInfo(
134 raw_ostream &OS, LoopDependenceAnalysis *LDA, const Loop *L) {
135 if (!L->empty()) return; // ignore non-innermost loops
137 SmallVector<Instruction*, 8> memrefs;
138 GetMemRefInstrs(L, memrefs);
140 OS << "Loop at depth " << L->getLoopDepth() << ", header block: ";
141 WriteAsOperand(OS, L->getHeader(), false);
144 OS << " Load/store instructions: " << memrefs.size() << "\n";
145 for (SmallVector<Instruction*, 8>::const_iterator x = memrefs.begin(),
146 end = memrefs.end(); x != end; ++x)
147 OS << "\t" << (x - memrefs.begin()) << ": " << **x;
149 OS << " Pairwise dependence results:\n";
150 for (SmallVector<Instruction*, 8>::const_iterator x = memrefs.begin(),
151 end = memrefs.end(); x != end; ++x)
152 for (SmallVector<Instruction*, 8>::const_iterator y = x + 1;
154 if (LDA->isDependencePair(*x, *y))
155 OS << "\t" << (x - memrefs.begin()) << "," << (y - memrefs.begin())
156 << ": " << (LDA->depends(*x, *y) ? "dependent" : "independent")
160 void LoopDependenceAnalysis::print(raw_ostream &OS, const Module*) const {
161 // TODO: doc why const_cast is safe
162 PrintLoopInfo(OS, const_cast<LoopDependenceAnalysis*>(this), this->L);
165 void LoopDependenceAnalysis::print(std::ostream &OS, const Module *M) const {
166 raw_os_ostream os(OS);