1 //===- SLPVectorizer.cpp - A bottom up SLP Vectorizer ---------------------===//
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 //===----------------------------------------------------------------------===//
9 // This pass implements the Bottom Up SLP vectorizer. It detects consecutive
10 // stores that can be put together into vector-stores. Next, it attempts to
11 // construct vectorizable tree using the use-def chains. If a profitable tree
12 // was found, the SLP vectorizer performs vectorization on the tree.
14 // The pass is inspired by the work described in the paper:
15 // "Loop-Aware SLP in GCC" by Ira Rosen, Dorit Nuzman, Ayal Zaks.
17 //===----------------------------------------------------------------------===//
18 #define SV_NAME "slp-vectorizer"
19 #define DEBUG_TYPE SV_NAME
22 #include "llvm/Transforms/Vectorize.h"
23 #include "llvm/Analysis/AliasAnalysis.h"
24 #include "llvm/Analysis/ScalarEvolution.h"
25 #include "llvm/Analysis/TargetTransformInfo.h"
26 #include "llvm/Analysis/Verifier.h"
27 #include "llvm/Analysis/LoopInfo.h"
28 #include "llvm/IR/DataLayout.h"
29 #include "llvm/IR/Instructions.h"
30 #include "llvm/IR/IntrinsicInst.h"
31 #include "llvm/IR/Module.h"
32 #include "llvm/IR/Type.h"
33 #include "llvm/IR/Value.h"
34 #include "llvm/Pass.h"
35 #include "llvm/Support/CommandLine.h"
36 #include "llvm/Support/Debug.h"
37 #include "llvm/Support/raw_ostream.h"
43 SLPCostThreshold("slp-threshold", cl::init(0), cl::Hidden,
44 cl::desc("Only vectorize trees if the gain is above this "
45 "number. (gain = -cost of vectorization)"));
48 /// The SLPVectorizer Pass.
49 struct SLPVectorizer : public FunctionPass {
50 typedef std::map<Value*, BoUpSLP::StoreList> StoreListMap;
52 /// Pass identification, replacement for typeid
55 explicit SLPVectorizer() : FunctionPass(ID) {
56 initializeSLPVectorizerPass(*PassRegistry::getPassRegistry());
61 TargetTransformInfo *TTI;
65 virtual bool runOnFunction(Function &F) {
66 SE = &getAnalysis<ScalarEvolution>();
67 DL = getAnalysisIfAvailable<DataLayout>();
68 TTI = &getAnalysis<TargetTransformInfo>();
69 AA = &getAnalysis<AliasAnalysis>();
70 LI = &getAnalysis<LoopInfo>();
75 // Must have DataLayout. We can't require it because some tests run w/o
80 for (Function::iterator it = F.begin(), e = F.end(); it != e; ++it) {
82 bool BBChanged = false;
84 // Use the bollom up slp vectorizer to construct chains that start with
85 // he store instructions.
86 BoUpSLP R(BB, SE, DL, TTI, AA);
88 // Vectorize trees that end at reductions.
89 BBChanged |= vectorizeReductions(BB, R);
91 // Vectorize trees that end at stores.
92 if (collectStores(BB, R)) {
93 DEBUG(dbgs()<<"SLP: Found stores to vectorize.\n");
94 BBChanged |= vectorizeStoreChains(R);
97 // Try to hoist some of the scalarization code to the preheader.
98 if (BBChanged) hoistGatherSequence(LI, BB, R);
100 Changed |= BBChanged;
104 DEBUG(dbgs()<<"SLP: vectorized \""<<F.getName()<<"\"\n");
105 DEBUG(verifyFunction(F));
110 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
111 FunctionPass::getAnalysisUsage(AU);
112 AU.addRequired<ScalarEvolution>();
113 AU.addRequired<AliasAnalysis>();
114 AU.addRequired<TargetTransformInfo>();
115 AU.addRequired<LoopInfo>();
120 /// \brief Collect memory references and sort them according to their base
121 /// object. We sort the stores to their base objects to reduce the cost of the
122 /// quadratic search on the stores. TODO: We can further reduce this cost
123 /// if we flush the chain creation every time we run into a memory barrier.
124 bool collectStores(BasicBlock *BB, BoUpSLP &R);
126 /// \brief Try to vectorize a chain that starts at two arithmetic instrs.
127 bool tryToVectorizePair(Value *A, Value *B, BoUpSLP &R);
129 /// \brief Try to vectorize a chain that may start at the operands of \V;
130 bool tryToVectorize(BinaryOperator *V, BoUpSLP &R);
132 /// \brief Vectorize the stores that were collected in StoreRefs.
133 bool vectorizeStoreChains(BoUpSLP &R);
135 /// \brief Try to hoist gather sequences outside of the loop in cases where
136 /// all of the sources are loop invariant.
137 void hoistGatherSequence(LoopInfo *LI, BasicBlock *BB, BoUpSLP &R);
139 /// \brief Scan the basic block and look for reductions that may start a
140 /// vectorization chain.
141 bool vectorizeReductions(BasicBlock *BB, BoUpSLP &R);
144 StoreListMap StoreRefs;
147 bool SLPVectorizer::collectStores(BasicBlock *BB, BoUpSLP &R) {
149 for (BasicBlock::iterator it = BB->begin(), e = BB->end(); it != e; ++it) {
150 StoreInst *SI = dyn_cast<StoreInst>(it);
154 // Check that the pointer points to scalars.
155 if (SI->getValueOperand()->getType()->isAggregateType())
158 // Find the base of the GEP.
159 Value *Ptr = SI->getPointerOperand();
160 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr))
161 Ptr = GEP->getPointerOperand();
163 // Save the store locations.
164 StoreRefs[Ptr].push_back(SI);
169 bool SLPVectorizer::tryToVectorizePair(Value *A, Value *B, BoUpSLP &R) {
170 if (!A || !B) return false;
171 BoUpSLP::ValueList VL;
174 int Cost = R.getTreeCost(VL);
175 int ExtrCost = R.getScalarizationCost(VL);
176 DEBUG(dbgs()<<"SLP: Cost of pair:" << Cost <<
177 " Cost of extract:" << ExtrCost << ".\n");
178 if ((Cost+ExtrCost) >= -SLPCostThreshold) return false;
179 DEBUG(dbgs()<<"SLP: Vectorizing pair.\n");
180 R.vectorizeArith(VL);
184 bool SLPVectorizer::tryToVectorize(BinaryOperator *V, BoUpSLP &R) {
185 if (!V) return false;
186 // Try to vectorize V.
187 if (tryToVectorizePair(V->getOperand(0), V->getOperand(1), R))
190 BinaryOperator *A = dyn_cast<BinaryOperator>(V->getOperand(0));
191 BinaryOperator *B = dyn_cast<BinaryOperator>(V->getOperand(1));
193 if (B && B->hasOneUse()) {
194 BinaryOperator *B0 = dyn_cast<BinaryOperator>(B->getOperand(0));
195 BinaryOperator *B1 = dyn_cast<BinaryOperator>(B->getOperand(1));
196 if (tryToVectorizePair(A, B0, R)) {
200 if (tryToVectorizePair(A, B1, R)) {
207 if (A && A->hasOneUse()) {
208 BinaryOperator *A0 = dyn_cast<BinaryOperator>(A->getOperand(0));
209 BinaryOperator *A1 = dyn_cast<BinaryOperator>(A->getOperand(1));
210 if (tryToVectorizePair(A0, B, R)) {
214 if (tryToVectorizePair(A1, B, R)) {
222 bool SLPVectorizer::vectorizeReductions(BasicBlock *BB, BoUpSLP &R) {
223 bool Changed = false;
224 for (BasicBlock::iterator it = BB->begin(), e = BB->end(); it != e; ++it) {
225 if (isa<DbgInfoIntrinsic>(it)) continue;
227 // Try to vectorize reductions that use PHINodes.
228 if (PHINode *P = dyn_cast<PHINode>(it)) {
229 // Check that the PHI is a reduction PHI.
230 if (P->getNumIncomingValues() != 2) return Changed;
231 Value *Rdx = (P->getIncomingBlock(0) == BB ? P->getIncomingValue(0) :
232 (P->getIncomingBlock(1) == BB ? P->getIncomingValue(1) :
234 // Check if this is a Binary Operator.
235 BinaryOperator *BI = dyn_cast_or_null<BinaryOperator>(Rdx);
239 Value *Inst = BI->getOperand(0);
240 if (Inst == P) Inst = BI->getOperand(1);
241 Changed |= tryToVectorize(dyn_cast<BinaryOperator>(Inst), R);
245 // Try to vectorize trees that start at compare instructions.
246 if (CmpInst *CI = dyn_cast<CmpInst>(it)) {
247 if (tryToVectorizePair(CI->getOperand(0), CI->getOperand(1), R)) {
251 for (int i = 0; i < 2; ++i)
252 if (BinaryOperator *BI = dyn_cast<BinaryOperator>(CI->getOperand(i)))
253 Changed |= tryToVectorize(BI, R);
261 bool SLPVectorizer::vectorizeStoreChains(BoUpSLP &R) {
262 bool Changed = false;
263 // Attempt to sort and vectorize each of the store-groups.
264 for (StoreListMap::iterator it = StoreRefs.begin(), e = StoreRefs.end();
266 if (it->second.size() < 2)
269 DEBUG(dbgs()<<"SLP: Analyzing a store chain of length " <<
270 it->second.size() << ".\n");
272 Changed |= R.vectorizeStores(it->second, -SLPCostThreshold);
277 void SLPVectorizer::hoistGatherSequence(LoopInfo *LI, BasicBlock *BB,
279 // Check if this block is inside a loop.
280 Loop *L = LI->getLoopFor(BB);
284 // Check if it has a preheader.
285 BasicBlock *PreHeader = L->getLoopPreheader();
289 // Mark the insertion point for the block.
290 Instruction *Location = PreHeader->getTerminator();
292 BoUpSLP::ValueList &Gathers = R.getGatherSeqInstructions();
293 for (BoUpSLP::ValueList::iterator it = Gathers.begin(), e = Gathers.end();
295 InsertElementInst *Insert = dyn_cast<InsertElementInst>(*it);
297 // The InsertElement sequence can be simplified into a constant.
301 // If the vector or the element that we insert into it are
302 // instructions that are defined in this basic block then we can't
303 // hoist this instruction.
304 Instruction *CurrVec = dyn_cast<Instruction>(Insert->getOperand(0));
305 Instruction *NewElem = dyn_cast<Instruction>(Insert->getOperand(1));
306 if (CurrVec && L->contains(CurrVec)) continue;
307 if (NewElem && L->contains(NewElem)) continue;
309 // We can hoist this instruction. Move it to the pre-header.
310 Insert->moveBefore(Location);
314 } // end anonymous namespace
316 char SLPVectorizer::ID = 0;
317 static const char lv_name[] = "SLP Vectorizer";
318 INITIALIZE_PASS_BEGIN(SLPVectorizer, SV_NAME, lv_name, false, false)
319 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
320 INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
321 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
322 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
323 INITIALIZE_PASS_END(SLPVectorizer, SV_NAME, lv_name, false, false)
326 Pass *createSLPVectorizerPass() {
327 return new SLPVectorizer();