1 //===- EarlyCSE.cpp - Simple and fast CSE pass ----------------------------===//
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 pass performs a simple dominator tree walk that eliminates trivially
11 // redundant instructions.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "early-cse"
16 #include "llvm/Transforms/Scalar.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/Pass.h"
19 #include "llvm/Analysis/Dominators.h"
20 #include "llvm/Analysis/InstructionSimplify.h"
21 #include "llvm/Target/TargetData.h"
22 #include "llvm/Transforms/Utils/Local.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/RecyclingAllocator.h"
25 #include "llvm/ADT/ScopedHashTable.h"
26 #include "llvm/ADT/Statistic.h"
29 STATISTIC(NumSimplify, "Number of insts simplified or DCE'd");
30 STATISTIC(NumCSE, "Number of insts CSE'd");
33 /// InstValue - Instances of this struct represent available values in the
34 /// scoped hash table.
38 bool isSentinel() const {
39 return Inst == DenseMapInfo<Instruction*>::getEmptyKey() ||
40 Inst == DenseMapInfo<Instruction*>::getTombstoneKey();
43 static bool canHandle(Instruction *Inst) {
44 return isa<CastInst>(Inst) || isa<BinaryOperator>(Inst) ||
45 isa<GetElementPtrInst>(Inst) || isa<CmpInst>(Inst) ||
46 isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
47 isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst) ||
48 isa<ExtractValueInst>(Inst) || isa<InsertValueInst>(Inst);
51 static InstValue get(Instruction *I) {
52 InstValue X; X.Inst = I;
53 assert((X.isSentinel() || canHandle(I)) && "Inst can't be handled!");
61 template<> struct isPodLike<InstValue> {
62 static const bool value = true;
65 template<> struct DenseMapInfo<InstValue> {
66 static inline InstValue getEmptyKey() {
67 return InstValue::get(DenseMapInfo<Instruction*>::getEmptyKey());
69 static inline InstValue getTombstoneKey() {
70 return InstValue::get(DenseMapInfo<Instruction*>::getTombstoneKey());
72 static unsigned getHashValue(InstValue Val);
73 static bool isEqual(InstValue LHS, InstValue RHS);
77 unsigned getHash(const void *V) {
78 return DenseMapInfo<const void*>::getHashValue(V);
81 unsigned DenseMapInfo<InstValue>::getHashValue(InstValue Val) {
82 Instruction *Inst = Val.Inst;
84 // Hash in all of the operands as pointers.
86 for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
87 Res ^= getHash(Inst->getOperand(i)) << i;
89 if (CastInst *CI = dyn_cast<CastInst>(Inst))
90 Res ^= getHash(CI->getType());
91 else if (CmpInst *CI = dyn_cast<CmpInst>(Inst))
92 Res ^= CI->getPredicate();
93 else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Inst)) {
94 for (ExtractValueInst::idx_iterator I = EVI->idx_begin(),
95 E = EVI->idx_end(); I != E; ++I)
97 } else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(Inst)) {
98 for (InsertValueInst::idx_iterator I = IVI->idx_begin(),
99 E = IVI->idx_end(); I != E; ++I)
102 // nothing extra to hash in.
103 assert((isa<BinaryOperator>(Inst) || isa<GetElementPtrInst>(Inst) ||
104 isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
105 isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst)) &&
106 "Invalid/unknown instruction");
109 // Mix in the opcode.
110 return (Res << 1) ^ Inst->getOpcode();
113 bool DenseMapInfo<InstValue>::isEqual(InstValue LHS, InstValue RHS) {
114 Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
116 if (LHS.isSentinel() || RHS.isSentinel())
119 if (LHSI->getOpcode() != RHSI->getOpcode()) return false;
120 return LHSI->isIdenticalTo(RHSI);
126 /// EarlyCSE - This pass does a simple depth-first walk over the dominator
127 /// tree, eliminating trivially redundant instructions and using instsimplify
128 /// to canonicalize things as it goes. It is intended to be fast and catch
129 /// obvious cases so that instcombine and other passes are more effective. It
130 /// is expected that a later pass of GVN will catch the interesting/hard
132 class EarlyCSE : public FunctionPass {
134 const TargetData *TD;
136 typedef RecyclingAllocator<BumpPtrAllocator,
137 ScopedHashTableVal<InstValue, Instruction*> > AllocatorTy;
138 typedef ScopedHashTable<InstValue, Instruction*, DenseMapInfo<InstValue>,
139 AllocatorTy> ScopedHTType;
140 ScopedHTType *AvailableValues;
145 initializeEarlyCSEPass(*PassRegistry::getPassRegistry());
148 bool runOnFunction(Function &F);
152 bool processNode(DomTreeNode *Node);
154 // This transformation requires dominator postdominator info
155 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
156 AU.addRequired<DominatorTree>();
157 AU.setPreservesCFG();
162 char EarlyCSE::ID = 0;
164 // createEarlyCSEPass - The public interface to this file.
165 FunctionPass *llvm::createEarlyCSEPass() {
166 return new EarlyCSE();
169 INITIALIZE_PASS_BEGIN(EarlyCSE, "early-cse", "Early CSE", false, false)
170 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
171 INITIALIZE_PASS_END(EarlyCSE, "early-cse", "Early CSE", false, false)
173 bool EarlyCSE::processNode(DomTreeNode *Node) {
174 // Define a scope in the scoped hash table.
175 ScopedHashTableScope<InstValue, Instruction*, DenseMapInfo<InstValue>,
176 AllocatorTy> Scope(*AvailableValues);
178 BasicBlock *BB = Node->getBlock();
180 bool Changed = false;
182 // See if any instructions in the block can be eliminated. If so, do it. If
183 // not, add them to AvailableValues.
184 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
185 Instruction *Inst = I++;
187 // Dead instructions should just be removed.
188 if (isInstructionTriviallyDead(Inst)) {
189 DEBUG(dbgs() << "EarlyCSE DCE: " << *Inst << '\n');
190 Inst->eraseFromParent();
196 // If the instruction can be simplified (e.g. X+0 = X) then replace it with
197 // its simpler value.
198 if (Value *V = SimplifyInstruction(Inst, TD, DT)) {
199 DEBUG(dbgs() << "EarlyCSE Simplify: " << *Inst << " to: " << *V << '\n');
200 Inst->replaceAllUsesWith(V);
201 Inst->eraseFromParent();
207 // If this instruction is something that we can't value number, ignore it.
208 if (!InstValue::canHandle(Inst))
211 // See if the instruction has an available value. If so, use it.
212 if (Instruction *V = AvailableValues->lookup(InstValue::get(Inst))) {
213 DEBUG(dbgs() << "EarlyCSE CSE: " << *Inst << " to: " << *V << '\n');
214 Inst->replaceAllUsesWith(V);
215 Inst->eraseFromParent();
221 // Otherwise, just remember that this value is available.
222 AvailableValues->insert(InstValue::get(Inst), Inst);
226 for (DomTreeNode::iterator I = Node->begin(), E = Node->end(); I != E; ++I)
227 Changed |= processNode(*I);
232 bool EarlyCSE::runOnFunction(Function &F) {
233 TD = getAnalysisIfAvailable<TargetData>();
234 DT = &getAnalysis<DominatorTree>();
235 ScopedHTType AVTable;
236 AvailableValues = &AVTable;
237 return processNode(DT->getRootNode());