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/ADT/ScopedHashTable.h"
25 #include "llvm/ADT/Statistic.h"
28 STATISTIC(NumSimplify, "Number of insts simplified or DCE'd");
29 STATISTIC(NumCSE, "Number of insts CSE'd");
32 /// InstValue - Instances of this struct represent available values in the
33 /// scoped hash table.
37 bool isSentinel() const {
38 return Inst == DenseMapInfo<Instruction*>::getEmptyKey() ||
39 Inst == DenseMapInfo<Instruction*>::getTombstoneKey();
42 static bool canHandle(Instruction *Inst) {
43 return isa<CastInst>(Inst) || isa<BinaryOperator>(Inst) ||
44 isa<GetElementPtrInst>(Inst) || isa<CmpInst>(Inst) ||
45 isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
46 isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst) ||
47 isa<ExtractValueInst>(Inst) || isa<InsertValueInst>(Inst);
50 static InstValue get(Instruction *I) {
51 InstValue X; X.Inst = I;
52 assert((X.isSentinel() || canHandle(I)) && "Inst can't be handled!");
60 template<> struct isPodLike<InstValue> {
61 static const bool value = true;
64 template<> struct DenseMapInfo<InstValue> {
65 static inline InstValue getEmptyKey() {
66 return InstValue::get(DenseMapInfo<Instruction*>::getEmptyKey());
68 static inline InstValue getTombstoneKey() {
69 return InstValue::get(DenseMapInfo<Instruction*>::getTombstoneKey());
71 static unsigned getHashValue(InstValue Val);
72 static bool isEqual(InstValue LHS, InstValue RHS);
76 unsigned getHash(const void *V) {
77 return DenseMapInfo<const void*>::getHashValue(V);
80 unsigned DenseMapInfo<InstValue>::getHashValue(InstValue Val) {
81 Instruction *Inst = Val.Inst;
83 // Hash in all of the operands as pointers.
85 for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
86 Res ^= getHash(Inst->getOperand(i)) << i;
88 if (CastInst *CI = dyn_cast<CastInst>(Inst))
89 Res ^= getHash(CI->getType());
90 else if (CmpInst *CI = dyn_cast<CmpInst>(Inst))
91 Res ^= CI->getPredicate();
92 else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Inst)) {
93 for (ExtractValueInst::idx_iterator I = EVI->idx_begin(),
94 E = EVI->idx_end(); I != E; ++I)
96 } else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(Inst)) {
97 for (InsertValueInst::idx_iterator I = IVI->idx_begin(),
98 E = IVI->idx_end(); I != E; ++I)
101 // nothing extra to hash in.
102 assert((isa<BinaryOperator>(Inst) || isa<GetElementPtrInst>(Inst) ||
103 isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
104 isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst)) &&
105 "Invalid/unknown instruction");
108 // Mix in the opcode.
109 return (Res << 1) ^ Inst->getOpcode();
112 bool DenseMapInfo<InstValue>::isEqual(InstValue LHS, InstValue RHS) {
113 Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
115 if (LHS.isSentinel() || RHS.isSentinel())
118 if (LHSI->getOpcode() != RHSI->getOpcode()) return false;
119 return LHSI->isIdenticalTo(RHSI);
125 /// EarlyCSE - This pass does a simple depth-first walk over the dominator
126 /// tree, eliminating trivially redundant instructions and using instsimplify
127 /// to canonicalize things as it goes. It is intended to be fast and catch
128 /// obvious cases so that instcombine and other passes are more effective. It
129 /// is expected that a later pass of GVN will catch the interesting/hard
131 class EarlyCSE : public FunctionPass {
133 const TargetData *TD;
135 ScopedHashTable<InstValue, Instruction*> *AvailableValues;
140 initializeEarlyCSEPass(*PassRegistry::getPassRegistry());
143 bool runOnFunction(Function &F);
147 bool processNode(DomTreeNode *Node);
149 // This transformation requires dominator postdominator info
150 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
151 AU.addRequired<DominatorTree>();
152 AU.setPreservesCFG();
157 char EarlyCSE::ID = 0;
159 // createEarlyCSEPass - The public interface to this file.
160 FunctionPass *llvm::createEarlyCSEPass() {
161 return new EarlyCSE();
164 INITIALIZE_PASS_BEGIN(EarlyCSE, "early-cse", "Early CSE", false, false)
165 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
166 INITIALIZE_PASS_END(EarlyCSE, "early-cse", "Early CSE", false, false)
168 // FIXME: Should bump pointer allocate entries in scoped hash table.
170 bool EarlyCSE::processNode(DomTreeNode *Node) {
171 // Define a scope in the scoped hash table.
172 ScopedHashTableScope<InstValue, Instruction*> Scope(*AvailableValues);
174 BasicBlock *BB = Node->getBlock();
176 bool Changed = false;
178 // See if any instructions in the block can be eliminated. If so, do it. If
179 // not, add them to AvailableValues.
180 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
181 Instruction *Inst = I++;
183 // Dead instructions should just be removed.
184 if (isInstructionTriviallyDead(Inst)) {
185 DEBUG(dbgs() << "EarlyCSE DCE: " << *Inst << '\n');
186 Inst->eraseFromParent();
192 // If the instruction can be simplified (e.g. X+0 = X) then replace it with
193 // its simpler value.
194 if (Value *V = SimplifyInstruction(Inst, TD, DT)) {
195 DEBUG(dbgs() << "EarlyCSE Simplify: " << *Inst << " to: " << *V << '\n');
196 Inst->replaceAllUsesWith(V);
197 Inst->eraseFromParent();
203 // If this instruction is something that we can't value number, ignore it.
204 if (!InstValue::canHandle(Inst))
207 // See if the instruction has an available value. If so, use it.
208 if (Instruction *V = AvailableValues->lookup(InstValue::get(Inst))) {
209 DEBUG(dbgs() << "EarlyCSE CSE: " << *Inst << " to: " << *V << '\n');
210 Inst->replaceAllUsesWith(V);
211 Inst->eraseFromParent();
217 // Otherwise, just remember that this value is available.
218 AvailableValues->insert(InstValue::get(Inst), Inst);
222 for (DomTreeNode::iterator I = Node->begin(), E = Node->end(); I != E; ++I)
223 Changed |= processNode(*I);
228 bool EarlyCSE::runOnFunction(Function &F) {
229 TD = getAnalysisIfAvailable<TargetData>();
230 DT = &getAnalysis<DominatorTree>();
231 ScopedHashTable<InstValue, Instruction*> AVTable;
232 AvailableValues = &AVTable;
233 return processNode(DT->getRootNode());