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 instructions simplified or DCE'd");
30 STATISTIC(NumCSE, "Number of instructions CSE'd");
31 STATISTIC(NumCSELoad, "Number of load instructions CSE'd");
32 STATISTIC(NumCSECall, "Number of call instructions CSE'd");
34 static unsigned getHash(const void *V) {
35 return DenseMapInfo<const void*>::getHashValue(V);
38 //===----------------------------------------------------------------------===//
40 //===----------------------------------------------------------------------===//
43 /// SimpleValue - Instances of this struct represent available values in the
44 /// scoped hash table.
48 SimpleValue(Instruction *I) : Inst(I) {
49 assert((isSentinel() || canHandle(I)) && "Inst can't be handled!");
52 bool isSentinel() const {
53 return Inst == DenseMapInfo<Instruction*>::getEmptyKey() ||
54 Inst == DenseMapInfo<Instruction*>::getTombstoneKey();
57 static bool canHandle(Instruction *Inst) {
58 return isa<CastInst>(Inst) || isa<BinaryOperator>(Inst) ||
59 isa<GetElementPtrInst>(Inst) || isa<CmpInst>(Inst) ||
60 isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
61 isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst) ||
62 isa<ExtractValueInst>(Inst) || isa<InsertValueInst>(Inst);
68 // SimpleValue is POD.
69 template<> struct isPodLike<SimpleValue> {
70 static const bool value = true;
73 template<> struct DenseMapInfo<SimpleValue> {
74 static inline SimpleValue getEmptyKey() {
75 return DenseMapInfo<Instruction*>::getEmptyKey();
77 static inline SimpleValue getTombstoneKey() {
78 return DenseMapInfo<Instruction*>::getTombstoneKey();
80 static unsigned getHashValue(SimpleValue Val);
81 static bool isEqual(SimpleValue LHS, SimpleValue RHS);
85 unsigned DenseMapInfo<SimpleValue>::getHashValue(SimpleValue Val) {
86 Instruction *Inst = Val.Inst;
88 // Hash in all of the operands as pointers.
90 for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
91 Res ^= getHash(Inst->getOperand(i)) << i;
93 if (CastInst *CI = dyn_cast<CastInst>(Inst))
94 Res ^= getHash(CI->getType());
95 else if (CmpInst *CI = dyn_cast<CmpInst>(Inst))
96 Res ^= CI->getPredicate();
97 else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Inst)) {
98 for (ExtractValueInst::idx_iterator I = EVI->idx_begin(),
99 E = EVI->idx_end(); I != E; ++I)
101 } else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(Inst)) {
102 for (InsertValueInst::idx_iterator I = IVI->idx_begin(),
103 E = IVI->idx_end(); I != E; ++I)
106 // nothing extra to hash in.
107 assert((isa<BinaryOperator>(Inst) || isa<GetElementPtrInst>(Inst) ||
108 isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) ||
109 isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst)) &&
110 "Invalid/unknown instruction");
113 // Mix in the opcode.
114 return (Res << 1) ^ Inst->getOpcode();
117 bool DenseMapInfo<SimpleValue>::isEqual(SimpleValue LHS, SimpleValue RHS) {
118 Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
120 if (LHS.isSentinel() || RHS.isSentinel())
123 if (LHSI->getOpcode() != RHSI->getOpcode()) return false;
124 return LHSI->isIdenticalTo(RHSI);
127 //===----------------------------------------------------------------------===//
129 //===----------------------------------------------------------------------===//
132 /// CallValue - Instances of this struct represent available call values in
133 /// the scoped hash table.
137 CallValue(Instruction *I) : Inst(I) {
138 assert((isSentinel() || canHandle(I)) && "Inst can't be handled!");
141 bool isSentinel() const {
142 return Inst == DenseMapInfo<Instruction*>::getEmptyKey() ||
143 Inst == DenseMapInfo<Instruction*>::getTombstoneKey();
146 static bool canHandle(Instruction *Inst) {
147 if (CallInst *CI = dyn_cast<CallInst>(Inst))
148 return CI->onlyReadsMemory();
156 template<> struct isPodLike<CallValue> {
157 static const bool value = true;
160 template<> struct DenseMapInfo<CallValue> {
161 static inline CallValue getEmptyKey() {
162 return DenseMapInfo<Instruction*>::getEmptyKey();
164 static inline CallValue getTombstoneKey() {
165 return DenseMapInfo<Instruction*>::getTombstoneKey();
167 static unsigned getHashValue(CallValue Val);
168 static bool isEqual(CallValue LHS, CallValue RHS);
171 unsigned DenseMapInfo<CallValue>::getHashValue(CallValue Val) {
172 Instruction *Inst = Val.Inst;
173 // Hash in all of the operands as pointers.
175 for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
176 Res ^= getHash(Inst->getOperand(i)) << i;
177 // Mix in the opcode.
178 return (Res << 1) ^ Inst->getOpcode();
181 bool DenseMapInfo<CallValue>::isEqual(CallValue LHS, CallValue RHS) {
182 Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
183 if (LHS.isSentinel() || RHS.isSentinel())
185 return LHSI->isIdenticalTo(RHSI);
189 //===----------------------------------------------------------------------===//
191 //===----------------------------------------------------------------------===//
195 /// EarlyCSE - This pass does a simple depth-first walk over the dominator
196 /// tree, eliminating trivially redundant instructions and using instsimplify
197 /// to canonicalize things as it goes. It is intended to be fast and catch
198 /// obvious cases so that instcombine and other passes are more effective. It
199 /// is expected that a later pass of GVN will catch the interesting/hard
201 class EarlyCSE : public FunctionPass {
203 const TargetData *TD;
205 typedef RecyclingAllocator<BumpPtrAllocator,
206 ScopedHashTableVal<SimpleValue, Value*> > AllocatorTy;
207 typedef ScopedHashTable<SimpleValue, Value*, DenseMapInfo<SimpleValue>,
208 AllocatorTy> ScopedHTType;
210 /// AvailableValues - This scoped hash table contains the current values of
211 /// all of our simple scalar expressions. As we walk down the domtree, we
212 /// look to see if instructions are in this: if so, we replace them with what
213 /// we find, otherwise we insert them so that dominated values can succeed in
215 ScopedHTType *AvailableValues;
217 /// AvailableLoads - This scoped hash table contains the current values
218 /// of loads. This allows us to get efficient access to dominating loads when
219 /// we have a fully redundant load. In addition to the most recent load, we
220 /// keep track of a generation count of the read, which is compared against
221 /// the current generation count. The current generation count is
222 /// incremented after every possibly writing memory operation, which ensures
223 /// that we only CSE loads with other loads that have no intervening store.
224 typedef ScopedHashTable<Value*, std::pair<Value*, unsigned> > LoadHTType;
225 LoadHTType *AvailableLoads;
227 /// AvailableCalls - This scoped hash table contains the current values
228 /// of read-only call values. It uses the same generation count as loads.
229 typedef ScopedHashTable<CallValue, std::pair<Value*, unsigned> > CallHTType;
230 CallHTType *AvailableCalls;
232 /// CurrentGeneration - This is the current generation of the memory value.
233 unsigned CurrentGeneration;
236 explicit EarlyCSE() : FunctionPass(ID) {
237 initializeEarlyCSEPass(*PassRegistry::getPassRegistry());
240 bool runOnFunction(Function &F);
244 bool processNode(DomTreeNode *Node);
246 // This transformation requires dominator postdominator info
247 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
248 AU.addRequired<DominatorTree>();
249 AU.setPreservesCFG();
254 char EarlyCSE::ID = 0;
256 // createEarlyCSEPass - The public interface to this file.
257 FunctionPass *llvm::createEarlyCSEPass() {
258 return new EarlyCSE();
261 INITIALIZE_PASS_BEGIN(EarlyCSE, "early-cse", "Early CSE", false, false)
262 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
263 INITIALIZE_PASS_END(EarlyCSE, "early-cse", "Early CSE", false, false)
265 bool EarlyCSE::processNode(DomTreeNode *Node) {
266 // Define a scope in the scoped hash table. When we are done processing this
267 // domtree node and recurse back up to our parent domtree node, this will pop
268 // off all the values we install.
269 ScopedHTType::ScopeTy Scope(*AvailableValues);
271 // Define a scope for the load values so that anything we add will get
272 // popped when we recurse back up to our parent domtree node.
273 LoadHTType::ScopeTy LoadScope(*AvailableLoads);
275 // Define a scope for the call values so that anything we add will get
276 // popped when we recurse back up to our parent domtree node.
277 CallHTType::ScopeTy CallScope(*AvailableCalls);
279 BasicBlock *BB = Node->getBlock();
281 // If this block has a single predecessor, then the predecessor is the parent
282 // of the domtree node and all of the live out memory values are still current
283 // in this block. If this block has multiple predecessors, then they could
284 // have invalidated the live-out memory values of our parent value. For now,
285 // just be conservative and invalidate memory if this block has multiple
287 if (BB->getSinglePredecessor() == 0)
290 bool Changed = false;
292 // See if any instructions in the block can be eliminated. If so, do it. If
293 // not, add them to AvailableValues.
294 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
295 Instruction *Inst = I++;
297 // Dead instructions should just be removed.
298 if (isInstructionTriviallyDead(Inst)) {
299 DEBUG(dbgs() << "EarlyCSE DCE: " << *Inst << '\n');
300 Inst->eraseFromParent();
306 // If the instruction can be simplified (e.g. X+0 = X) then replace it with
307 // its simpler value.
308 if (Value *V = SimplifyInstruction(Inst, TD, DT)) {
309 DEBUG(dbgs() << "EarlyCSE Simplify: " << *Inst << " to: " << *V << '\n');
310 Inst->replaceAllUsesWith(V);
311 Inst->eraseFromParent();
317 // If this is a simple instruction that we can value number, process it.
318 if (SimpleValue::canHandle(Inst)) {
319 // See if the instruction has an available value. If so, use it.
320 if (Value *V = AvailableValues->lookup(Inst)) {
321 DEBUG(dbgs() << "EarlyCSE CSE: " << *Inst << " to: " << *V << '\n');
322 Inst->replaceAllUsesWith(V);
323 Inst->eraseFromParent();
329 // Otherwise, just remember that this value is available.
330 AvailableValues->insert(Inst, Inst);
334 // If this is a non-volatile load, process it.
335 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
336 // Ignore volatile loads.
337 if (LI->isVolatile()) continue;
339 // If we have an available version of this load, and if it is the right
340 // generation, replace this instruction.
341 std::pair<Value*, unsigned> InVal =
342 AvailableLoads->lookup(Inst->getOperand(0));
343 if (InVal.first != 0 && InVal.second == CurrentGeneration) {
344 DEBUG(dbgs() << "EarlyCSE CSE LOAD: " << *Inst << " to: "
345 << *InVal.first << '\n');
346 if (!Inst->use_empty()) Inst->replaceAllUsesWith(InVal.first);
347 Inst->eraseFromParent();
353 // Otherwise, remember that we have this instruction.
354 AvailableLoads->insert(Inst->getOperand(0),
355 std::pair<Value*, unsigned>(Inst, CurrentGeneration));
359 // If this is a read-only call, process it.
360 if (CallValue::canHandle(Inst)) {
361 // If we have an available version of this call, and if it is the right
362 // generation, replace this instruction.
363 std::pair<Value*, unsigned> InVal = AvailableCalls->lookup(Inst);
364 if (InVal.first != 0 && InVal.second == CurrentGeneration) {
365 DEBUG(dbgs() << "EarlyCSE CSE CALL: " << *Inst << " to: "
366 << *InVal.first << '\n');
367 if (!Inst->use_empty()) Inst->replaceAllUsesWith(InVal.first);
368 Inst->eraseFromParent();
374 // Otherwise, remember that we have this instruction.
375 AvailableCalls->insert(Inst,
376 std::pair<Value*, unsigned>(Inst, CurrentGeneration));
380 // Okay, this isn't something we can CSE at all. Check to see if it is
381 // something that could modify memory. If so, our available memory values
382 // cannot be used so bump the generation count.
383 if (Inst->mayWriteToMemory())
387 unsigned LiveOutGeneration = CurrentGeneration;
388 for (DomTreeNode::iterator I = Node->begin(), E = Node->end(); I != E; ++I) {
389 Changed |= processNode(*I);
390 // Pop any generation changes off the stack from the recursive walk.
391 CurrentGeneration = LiveOutGeneration;
397 bool EarlyCSE::runOnFunction(Function &F) {
398 TD = getAnalysisIfAvailable<TargetData>();
399 DT = &getAnalysis<DominatorTree>();
401 // Tables that the pass uses when walking the domtree.
402 ScopedHTType AVTable;
403 AvailableValues = &AVTable;
404 LoadHTType LoadTable;
405 AvailableLoads = &LoadTable;
406 CallHTType CallTable;
407 AvailableCalls = &CallTable;
409 CurrentGeneration = 0;
410 return processNode(DT->getRootNode());