1 //===- LowerSwitch.cpp - Eliminate Switch instructions --------------------===//
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 // The LowerSwitch transformation rewrites switch instructions with a sequence
11 // of branches, which allows targets to get away with not implementing the
12 // switch instruction until it is convenient.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Transforms/Scalar.h"
17 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
18 #include "llvm/Constants.h"
19 #include "llvm/Function.h"
20 #include "llvm/Instructions.h"
21 #include "llvm/Pass.h"
22 #include "llvm/ADT/STLExtras.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/Compiler.h"
25 #include "llvm/Support/raw_ostream.h"
30 /// LowerSwitch Pass - Replace all SwitchInst instructions with chained branch
31 /// instructions. Note that this cannot be a BasicBlock pass because it
33 class VISIBILITY_HIDDEN LowerSwitch : public FunctionPass {
35 static char ID; // Pass identification, replacement for typeid
36 LowerSwitch() : FunctionPass(&ID) {}
38 virtual bool runOnFunction(Function &F);
40 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
41 // This is a cluster of orthogonal Transforms
42 AU.addPreserved<UnifyFunctionExitNodes>();
43 AU.addPreservedID(PromoteMemoryToRegisterID);
44 AU.addPreservedID(LowerInvokePassID);
45 AU.addPreservedID(LowerAllocationsID);
53 CaseRange() : Low(0), High(0), BB(0) { }
54 CaseRange(Constant* low, Constant* high, BasicBlock* bb) :
55 Low(low), High(high), BB(bb) { }
58 typedef std::vector<CaseRange> CaseVector;
59 typedef std::vector<CaseRange>::iterator CaseItr;
61 void processSwitchInst(SwitchInst *SI);
63 BasicBlock* switchConvert(CaseItr Begin, CaseItr End, Value* Val,
64 BasicBlock* OrigBlock, BasicBlock* Default);
65 BasicBlock* newLeafBlock(CaseRange& Leaf, Value* Val,
66 BasicBlock* OrigBlock, BasicBlock* Default);
67 unsigned Clusterify(CaseVector& Cases, SwitchInst *SI);
70 /// The comparison function for sorting the switch case values in the vector.
71 /// WARNING: Case ranges should be disjoint!
73 bool operator () (const LowerSwitch::CaseRange& C1,
74 const LowerSwitch::CaseRange& C2) {
76 const ConstantInt* CI1 = cast<const ConstantInt>(C1.Low);
77 const ConstantInt* CI2 = cast<const ConstantInt>(C2.High);
78 return CI1->getValue().slt(CI2->getValue());
83 char LowerSwitch::ID = 0;
84 static RegisterPass<LowerSwitch>
85 X("lowerswitch", "Lower SwitchInst's to branches");
87 // Publically exposed interface to pass...
88 const PassInfo *const llvm::LowerSwitchID = &X;
89 // createLowerSwitchPass - Interface to this file...
90 FunctionPass *llvm::createLowerSwitchPass() {
91 return new LowerSwitch();
94 bool LowerSwitch::runOnFunction(Function &F) {
97 for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
98 BasicBlock *Cur = I++; // Advance over block so we don't traverse new blocks
100 if (SwitchInst *SI = dyn_cast<SwitchInst>(Cur->getTerminator())) {
102 processSwitchInst(SI);
109 // operator<< - Used for debugging purposes.
111 static std::ostream& operator<<(std::ostream &O,
112 const LowerSwitch::CaseVector &C) {
115 for (LowerSwitch::CaseVector::const_iterator B = C.begin(),
116 E = C.end(); B != E; ) {
117 O << *B->Low << " -" << *B->High;
118 if (++B != E) O << ", ";
124 static OStream& operator<<(OStream &O, const LowerSwitch::CaseVector &C) {
125 if (O.stream()) *O.stream() << C;
129 // switchConvert - Convert the switch statement into a binary lookup of
130 // the case values. The function recursively builds this tree.
132 BasicBlock* LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
133 Value* Val, BasicBlock* OrigBlock,
136 unsigned Size = End - Begin;
139 return newLeafBlock(*Begin, Val, OrigBlock, Default);
141 unsigned Mid = Size / 2;
142 std::vector<CaseRange> LHS(Begin, Begin + Mid);
143 DOUT << "LHS: " << LHS << "\n";
144 std::vector<CaseRange> RHS(Begin + Mid, End);
145 DOUT << "RHS: " << RHS << "\n";
147 CaseRange& Pivot = *(Begin + Mid);
148 DEBUG(errs() << "Pivot ==> "
149 << cast<ConstantInt>(Pivot.Low)->getValue() << " -"
150 << cast<ConstantInt>(Pivot.High)->getValue() << "\n";
153 BasicBlock* LBranch = switchConvert(LHS.begin(), LHS.end(), Val,
155 BasicBlock* RBranch = switchConvert(RHS.begin(), RHS.end(), Val,
158 // Create a new node that checks if the value is < pivot. Go to the
159 // left branch if it is and right branch if not.
160 Function* F = OrigBlock->getParent();
161 BasicBlock* NewNode = BasicBlock::Create("NodeBlock");
162 Function::iterator FI = OrigBlock;
163 F->getBasicBlockList().insert(++FI, NewNode);
165 ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_SLT, Val, Pivot.Low, "Pivot");
166 NewNode->getInstList().push_back(Comp);
167 BranchInst::Create(LBranch, RBranch, Comp, NewNode);
171 // newLeafBlock - Create a new leaf block for the binary lookup tree. It
172 // checks if the switch's value == the case's value. If not, then it
173 // jumps to the default branch. At this point in the tree, the value
174 // can't be another valid case value, so the jump to the "default" branch
177 BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val,
178 BasicBlock* OrigBlock,
181 Function* F = OrigBlock->getParent();
182 BasicBlock* NewLeaf = BasicBlock::Create("LeafBlock");
183 Function::iterator FI = OrigBlock;
184 F->getBasicBlockList().insert(++FI, NewLeaf);
187 ICmpInst* Comp = NULL;
188 if (Leaf.Low == Leaf.High) {
189 // Make the seteq instruction...
190 Comp = new ICmpInst(ICmpInst::ICMP_EQ, Val, Leaf.Low,
191 "SwitchLeaf", NewLeaf);
193 // Make range comparison
194 if (cast<ConstantInt>(Leaf.Low)->isMinValue(true /*isSigned*/)) {
195 // Val >= Min && Val <= Hi --> Val <= Hi
196 Comp = new ICmpInst(ICmpInst::ICMP_SLE, Val, Leaf.High,
197 "SwitchLeaf", NewLeaf);
198 } else if (cast<ConstantInt>(Leaf.Low)->isZero()) {
199 // Val >= 0 && Val <= Hi --> Val <=u Hi
200 Comp = new ICmpInst(ICmpInst::ICMP_ULE, Val, Leaf.High,
201 "SwitchLeaf", NewLeaf);
203 // Emit V-Lo <=u Hi-Lo
204 Constant* NegLo = ConstantExpr::getNeg(Leaf.Low);
205 Instruction* Add = BinaryOperator::CreateAdd(Val, NegLo,
206 Val->getName()+".off",
208 Constant *UpperBound = ConstantExpr::getAdd(NegLo, Leaf.High);
209 Comp = new ICmpInst(ICmpInst::ICMP_ULE, Add, UpperBound,
210 "SwitchLeaf", NewLeaf);
214 // Make the conditional branch...
215 BasicBlock* Succ = Leaf.BB;
216 BranchInst::Create(Succ, Default, Comp, NewLeaf);
218 // If there were any PHI nodes in this successor, rewrite one entry
219 // from OrigBlock to come from NewLeaf.
220 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
221 PHINode* PN = cast<PHINode>(I);
222 // Remove all but one incoming entries from the cluster
223 uint64_t Range = cast<ConstantInt>(Leaf.High)->getSExtValue() -
224 cast<ConstantInt>(Leaf.Low)->getSExtValue();
225 for (uint64_t j = 0; j < Range; ++j) {
226 PN->removeIncomingValue(OrigBlock);
229 int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
230 assert(BlockIdx != -1 && "Switch didn't go to this successor??");
231 PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
237 // Clusterify - Transform simple list of Cases into list of CaseRange's
238 unsigned LowerSwitch::Clusterify(CaseVector& Cases, SwitchInst *SI) {
239 unsigned numCmps = 0;
241 // Start with "simple" cases
242 for (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
243 Cases.push_back(CaseRange(SI->getSuccessorValue(i),
244 SI->getSuccessorValue(i),
245 SI->getSuccessor(i)));
246 std::sort(Cases.begin(), Cases.end(), CaseCmp());
248 // Merge case into clusters
250 for (CaseItr I=Cases.begin(), J=next(Cases.begin()); J!=Cases.end(); ) {
251 int64_t nextValue = cast<ConstantInt>(J->Low)->getSExtValue();
252 int64_t currentValue = cast<ConstantInt>(I->High)->getSExtValue();
253 BasicBlock* nextBB = J->BB;
254 BasicBlock* currentBB = I->BB;
256 // If the two neighboring cases go to the same destination, merge them
257 // into a single case.
258 if ((nextValue-currentValue==1) && (currentBB == nextBB)) {
266 for (CaseItr I=Cases.begin(), E=Cases.end(); I!=E; ++I, ++numCmps) {
267 if (I->Low != I->High)
268 // A range counts double, since it requires two compares.
275 // processSwitchInst - Replace the specified switch instruction with a sequence
276 // of chained if-then insts in a balanced binary search.
278 void LowerSwitch::processSwitchInst(SwitchInst *SI) {
279 BasicBlock *CurBlock = SI->getParent();
280 BasicBlock *OrigBlock = CurBlock;
281 Function *F = CurBlock->getParent();
282 Value *Val = SI->getOperand(0); // The value we are switching on...
283 BasicBlock* Default = SI->getDefaultDest();
285 // If there is only the default destination, don't bother with the code below.
286 if (SI->getNumOperands() == 2) {
287 BranchInst::Create(SI->getDefaultDest(), CurBlock);
288 CurBlock->getInstList().erase(SI);
292 // Create a new, empty default block so that the new hierarchy of
293 // if-then statements go to this and the PHI nodes are happy.
294 BasicBlock* NewDefault = BasicBlock::Create("NewDefault");
295 F->getBasicBlockList().insert(Default, NewDefault);
297 BranchInst::Create(Default, NewDefault);
299 // If there is an entry in any PHI nodes for the default edge, make sure
300 // to update them as well.
301 for (BasicBlock::iterator I = Default->begin(); isa<PHINode>(I); ++I) {
302 PHINode *PN = cast<PHINode>(I);
303 int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
304 assert(BlockIdx != -1 && "Switch didn't go to this successor??");
305 PN->setIncomingBlock((unsigned)BlockIdx, NewDefault);
308 // Prepare cases vector.
310 unsigned numCmps = Clusterify(Cases, SI);
312 DOUT << "Clusterify finished. Total clusters: " << Cases.size()
313 << ". Total compares: " << numCmps << "\n";
314 DOUT << "Cases: " << Cases << "\n";
316 BasicBlock* SwitchBlock = switchConvert(Cases.begin(), Cases.end(), Val,
317 OrigBlock, NewDefault);
319 // Branch to our shiny new if-then stuff...
320 BranchInst::Create(SwitchBlock, OrigBlock);
322 // We are now done with the switch instruction, delete it.
323 CurBlock->getInstList().erase(SI);