//
// The LLVM Compiler Infrastructure
//
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
-// The LowerSwitch transformation rewrites switch statements with a sequence of
-// branches, which allows targets to get away with not implementing the switch
-// statement until it is convenient.
+// The LowerSwitch transformation rewrites switch instructions with a sequence
+// of branches, which allows targets to get away with not implementing the
+// switch instruction until it is convenient.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
-#include "llvm/Constants.h"
-#include "llvm/Function.h"
-#include "llvm/Instructions.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/CFG.h"
#include "llvm/Pass.h"
+#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
-#include "llvm/Support/Visibility.h"
-#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
#include <algorithm>
-#include <iostream>
using namespace llvm;
-namespace {
- Statistic<> NumLowered("lowerswitch", "Number of SwitchInst's replaced");
+#define DEBUG_TYPE "lower-switch"
+namespace {
/// LowerSwitch Pass - Replace all SwitchInst instructions with chained branch
- /// instructions. Note that this cannot be a BasicBlock pass because it
- /// modifies the CFG!
- class VISIBILITY_HIDDEN LowerSwitch : public FunctionPass {
+ /// instructions.
+ class LowerSwitch : public FunctionPass {
public:
- virtual bool runOnFunction(Function &F);
-
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- // This is a cluster of orthogonal Transforms
+ static char ID; // Pass identification, replacement for typeid
+ LowerSwitch() : FunctionPass(ID) {
+ initializeLowerSwitchPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnFunction(Function &F) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ // This is a cluster of orthogonal Transforms
AU.addPreserved<UnifyFunctionExitNodes>();
- AU.addPreservedID(PromoteMemoryToRegisterID);
- AU.addPreservedID(LowerSelectID);
+ AU.addPreserved("mem2reg");
AU.addPreservedID(LowerInvokePassID);
- AU.addPreservedID(LowerAllocationsID);
}
-
- typedef std::pair<Constant*, BasicBlock*> Case;
- typedef std::vector<Case>::iterator CaseItr;
+
+ struct CaseRange {
+ Constant* Low;
+ Constant* High;
+ BasicBlock* BB;
+
+ CaseRange(Constant *low = nullptr, Constant *high = nullptr,
+ BasicBlock *bb = nullptr) :
+ Low(low), High(high), BB(bb) { }
+ };
+
+ typedef std::vector<CaseRange> CaseVector;
+ typedef std::vector<CaseRange>::iterator CaseItr;
private:
void processSwitchInst(SwitchInst *SI);
- BasicBlock* switchConvert(CaseItr Begin, CaseItr End, Value* Val,
- BasicBlock* OrigBlock, BasicBlock* Default);
- BasicBlock* newLeafBlock(Case& Leaf, Value* Val,
- BasicBlock* OrigBlock, BasicBlock* Default);
+ BasicBlock *switchConvert(CaseItr Begin, CaseItr End,
+ ConstantInt *LowerBound, ConstantInt *UpperBound,
+ Value *Val, BasicBlock *Predecessor,
+ BasicBlock *OrigBlock, BasicBlock *Default);
+ BasicBlock *newLeafBlock(CaseRange &Leaf, Value *Val, BasicBlock *OrigBlock,
+ BasicBlock *Default);
+ unsigned Clusterify(CaseVector &Cases, SwitchInst *SI);
};
/// The comparison function for sorting the switch case values in the vector.
+ /// WARNING: Case ranges should be disjoint!
struct CaseCmp {
- bool operator () (const LowerSwitch::Case& C1,
- const LowerSwitch::Case& C2) {
- if (const ConstantUInt* U1 = dyn_cast<const ConstantUInt>(C1.first))
- return U1->getValue() < cast<const ConstantUInt>(C2.first)->getValue();
+ bool operator () (const LowerSwitch::CaseRange& C1,
+ const LowerSwitch::CaseRange& C2) {
- const ConstantSInt* S1 = dyn_cast<const ConstantSInt>(C1.first);
- return S1->getValue() < cast<const ConstantSInt>(C2.first)->getValue();
+ const ConstantInt* CI1 = cast<const ConstantInt>(C1.Low);
+ const ConstantInt* CI2 = cast<const ConstantInt>(C2.High);
+ return CI1->getValue().slt(CI2->getValue());
}
};
-
- RegisterOpt<LowerSwitch>
- X("lowerswitch", "Lower SwitchInst's to branches");
}
-// Publically exposed interface to pass...
-const PassInfo *llvm::LowerSwitchID = X.getPassInfo();
+char LowerSwitch::ID = 0;
+INITIALIZE_PASS(LowerSwitch, "lowerswitch",
+ "Lower SwitchInst's to branches", false, false)
+
+// Publicly exposed interface to pass...
+char &llvm::LowerSwitchID = LowerSwitch::ID;
// createLowerSwitchPass - Interface to this file...
FunctionPass *llvm::createLowerSwitchPass() {
return new LowerSwitch();
// operator<< - Used for debugging purposes.
//
-std::ostream& operator<<(std::ostream &O,
- const std::vector<LowerSwitch::Case> &C) {
+static raw_ostream& operator<<(raw_ostream &O,
+ const LowerSwitch::CaseVector &C)
+ LLVM_ATTRIBUTE_USED;
+static raw_ostream& operator<<(raw_ostream &O,
+ const LowerSwitch::CaseVector &C) {
O << "[";
- for (std::vector<LowerSwitch::Case>::const_iterator B = C.begin(),
+ for (LowerSwitch::CaseVector::const_iterator B = C.begin(),
E = C.end(); B != E; ) {
- O << *B->first;
+ O << *B->Low << " -" << *B->High;
if (++B != E) O << ", ";
}
return O << "]";
}
+static void fixPhis(BasicBlock *Succ,
+ BasicBlock *OrigBlock,
+ BasicBlock *NewNode) {
+ for (BasicBlock::iterator I = Succ->begin(),
+ E = Succ->getFirstNonPHI();
+ I != E; ++I) {
+ PHINode *PN = cast<PHINode>(I);
+
+ for (unsigned I = 0, E = PN->getNumIncomingValues(); I != E; ++I) {
+ if (PN->getIncomingBlock(I) == OrigBlock)
+ PN->setIncomingBlock(I, NewNode);
+ }
+ }
+}
+
// switchConvert - Convert the switch statement into a binary lookup of
// the case values. The function recursively builds this tree.
-//
-BasicBlock* LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
- Value* Val, BasicBlock* OrigBlock,
- BasicBlock* Default)
-{
+// LowerBound and UpperBound are used to keep track of the bounds for Val
+// that have already been checked by a block emitted by one of the previous
+// calls to switchConvert in the call stack.
+BasicBlock *LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
+ ConstantInt *LowerBound,
+ ConstantInt *UpperBound, Value *Val,
+ BasicBlock *Predecessor,
+ BasicBlock *OrigBlock,
+ BasicBlock *Default) {
unsigned Size = End - Begin;
- if (Size == 1)
+ if (Size == 1) {
+ // Check if the Case Range is perfectly squeezed in between
+ // already checked Upper and Lower bounds. If it is then we can avoid
+ // emitting the code that checks if the value actually falls in the range
+ // because the bounds already tell us so.
+ if (Begin->Low == LowerBound && Begin->High == UpperBound) {
+ fixPhis(Begin->BB, OrigBlock, Predecessor);
+ return Begin->BB;
+ }
return newLeafBlock(*Begin, Val, OrigBlock, Default);
+ }
unsigned Mid = Size / 2;
- std::vector<Case> LHS(Begin, Begin + Mid);
- DEBUG(std::cerr << "LHS: " << LHS << "\n");
- std::vector<Case> RHS(Begin + Mid, End);
- DEBUG(std::cerr << "RHS: " << RHS << "\n");
-
- Case& Pivot = *(Begin + Mid);
- DEBUG(std::cerr << "Pivot ==> "
- << (int64_t)cast<ConstantInt>(Pivot.first)->getRawValue()
- << "\n");
+ std::vector<CaseRange> LHS(Begin, Begin + Mid);
+ DEBUG(dbgs() << "LHS: " << LHS << "\n");
+ std::vector<CaseRange> RHS(Begin + Mid, End);
+ DEBUG(dbgs() << "RHS: " << RHS << "\n");
+
+ CaseRange &Pivot = *(Begin + Mid);
+ DEBUG(dbgs() << "Pivot ==> "
+ << cast<ConstantInt>(Pivot.Low)->getValue()
+ << " -" << cast<ConstantInt>(Pivot.High)->getValue() << "\n");
+
+ // NewLowerBound here should never be the integer minimal value.
+ // This is because it is computed from a case range that is never
+ // the smallest, so there is always a case range that has at least
+ // a smaller value.
+ ConstantInt *NewLowerBound = cast<ConstantInt>(Pivot.Low);
+ ConstantInt *NewUpperBound;
+
+ // If we don't have a Default block then it means that we can never
+ // have a value outside of a case range, so set the UpperBound to the highest
+ // value in the LHS part of the case ranges.
+ if (Default != nullptr) {
+ // Because NewLowerBound is never the smallest representable integer
+ // it is safe here to subtract one.
+ NewUpperBound = ConstantInt::get(NewLowerBound->getContext(),
+ NewLowerBound->getValue() - 1);
+ } else {
+ CaseItr LastLHS = LHS.begin() + LHS.size() - 1;
+ NewUpperBound = cast<ConstantInt>(LastLHS->High);
+ }
- BasicBlock* LBranch = switchConvert(LHS.begin(), LHS.end(), Val,
- OrigBlock, Default);
- BasicBlock* RBranch = switchConvert(RHS.begin(), RHS.end(), Val,
- OrigBlock, Default);
+ DEBUG(dbgs() << "LHS Bounds ==> ";
+ if (LowerBound) {
+ dbgs() << cast<ConstantInt>(LowerBound)->getSExtValue();
+ } else {
+ dbgs() << "NONE";
+ }
+ dbgs() << " - " << NewUpperBound->getSExtValue() << "\n";
+ dbgs() << "RHS Bounds ==> ";
+ dbgs() << NewLowerBound->getSExtValue() << " - ";
+ if (UpperBound) {
+ dbgs() << cast<ConstantInt>(UpperBound)->getSExtValue() << "\n";
+ } else {
+ dbgs() << "NONE\n";
+ });
// Create a new node that checks if the value is < pivot. Go to the
// left branch if it is and right branch if not.
Function* F = OrigBlock->getParent();
- BasicBlock* NewNode = new BasicBlock("NodeBlock");
- F->getBasicBlockList().insert(OrigBlock->getNext(), NewNode);
+ BasicBlock* NewNode = BasicBlock::Create(Val->getContext(), "NodeBlock");
+
+ ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_SLT,
+ Val, Pivot.Low, "Pivot");
- SetCondInst* Comp = new SetCondInst(Instruction::SetLT, Val, Pivot.first,
- "Pivot");
+ BasicBlock *LBranch = switchConvert(LHS.begin(), LHS.end(), LowerBound,
+ NewUpperBound, Val, NewNode, OrigBlock,
+ Default);
+ BasicBlock *RBranch = switchConvert(RHS.begin(), RHS.end(), NewLowerBound,
+ UpperBound, Val, NewNode, OrigBlock,
+ Default);
+
+ Function::iterator FI = OrigBlock;
+ F->getBasicBlockList().insert(++FI, NewNode);
NewNode->getInstList().push_back(Comp);
- new BranchInst(LBranch, RBranch, Comp, NewNode);
+
+ BranchInst::Create(LBranch, RBranch, Comp, NewNode);
return NewNode;
}
// can't be another valid case value, so the jump to the "default" branch
// is warranted.
//
-BasicBlock* LowerSwitch::newLeafBlock(Case& Leaf, Value* Val,
+BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val,
BasicBlock* OrigBlock,
BasicBlock* Default)
{
Function* F = OrigBlock->getParent();
- BasicBlock* NewLeaf = new BasicBlock("LeafBlock");
- F->getBasicBlockList().insert(OrigBlock->getNext(), NewLeaf);
-
- // Make the seteq instruction...
- SetCondInst* Comp = new SetCondInst(Instruction::SetEQ, Val,
- Leaf.first, "SwitchLeaf");
- NewLeaf->getInstList().push_back(Comp);
+ BasicBlock* NewLeaf = BasicBlock::Create(Val->getContext(), "LeafBlock");
+ Function::iterator FI = OrigBlock;
+ F->getBasicBlockList().insert(++FI, NewLeaf);
+
+ // Emit comparison
+ ICmpInst* Comp = nullptr;
+ if (Leaf.Low == Leaf.High) {
+ // Make the seteq instruction...
+ Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_EQ, Val,
+ Leaf.Low, "SwitchLeaf");
+ } else {
+ // Make range comparison
+ if (cast<ConstantInt>(Leaf.Low)->isMinValue(true /*isSigned*/)) {
+ // Val >= Min && Val <= Hi --> Val <= Hi
+ Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High,
+ "SwitchLeaf");
+ } else if (cast<ConstantInt>(Leaf.Low)->isZero()) {
+ // Val >= 0 && Val <= Hi --> Val <=u Hi
+ Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Val, Leaf.High,
+ "SwitchLeaf");
+ } else {
+ // Emit V-Lo <=u Hi-Lo
+ Constant* NegLo = ConstantExpr::getNeg(Leaf.Low);
+ Instruction* Add = BinaryOperator::CreateAdd(Val, NegLo,
+ Val->getName()+".off",
+ NewLeaf);
+ Constant *UpperBound = ConstantExpr::getAdd(NegLo, Leaf.High);
+ Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Add, UpperBound,
+ "SwitchLeaf");
+ }
+ }
// Make the conditional branch...
- BasicBlock* Succ = Leaf.second;
- new BranchInst(Succ, Default, Comp, NewLeaf);
+ BasicBlock* Succ = Leaf.BB;
+ BranchInst::Create(Succ, Default, Comp, NewLeaf);
// If there were any PHI nodes in this successor, rewrite one entry
// from OrigBlock to come from NewLeaf.
for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
PHINode* PN = cast<PHINode>(I);
+ // Remove all but one incoming entries from the cluster
+ uint64_t Range = cast<ConstantInt>(Leaf.High)->getSExtValue() -
+ cast<ConstantInt>(Leaf.Low)->getSExtValue();
+ for (uint64_t j = 0; j < Range; ++j) {
+ PN->removeIncomingValue(OrigBlock);
+ }
+
int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
assert(BlockIdx != -1 && "Switch didn't go to this successor??");
PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
return NewLeaf;
}
+// Clusterify - Transform simple list of Cases into list of CaseRange's
+unsigned LowerSwitch::Clusterify(CaseVector& Cases, SwitchInst *SI) {
+ unsigned numCmps = 0;
+
+ // Start with "simple" cases
+ for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
+ Cases.push_back(CaseRange(i.getCaseValue(), i.getCaseValue(),
+ i.getCaseSuccessor()));
+
+ std::sort(Cases.begin(), Cases.end(), CaseCmp());
+
+ // Merge case into clusters
+ if (Cases.size()>=2)
+ for (CaseItr I = Cases.begin(), J = std::next(Cases.begin());
+ J != Cases.end();) {
+ int64_t nextValue = cast<ConstantInt>(J->Low)->getSExtValue();
+ int64_t currentValue = cast<ConstantInt>(I->High)->getSExtValue();
+ BasicBlock* nextBB = J->BB;
+ BasicBlock* currentBB = I->BB;
+
+ // If the two neighboring cases go to the same destination, merge them
+ // into a single case.
+ if ((nextValue-currentValue==1) && (currentBB == nextBB)) {
+ I->High = J->High;
+ J = Cases.erase(J);
+ } else {
+ I = J++;
+ }
+ }
+
+ for (CaseItr I=Cases.begin(), E=Cases.end(); I!=E; ++I, ++numCmps) {
+ if (I->Low != I->High)
+ // A range counts double, since it requires two compares.
+ ++numCmps;
+ }
+
+ return numCmps;
+}
+
// processSwitchInst - Replace the specified switch instruction with a sequence
// of chained if-then insts in a balanced binary search.
//
BasicBlock *CurBlock = SI->getParent();
BasicBlock *OrigBlock = CurBlock;
Function *F = CurBlock->getParent();
- Value *Val = SI->getOperand(0); // The value we are switching on...
+ Value *Val = SI->getCondition(); // The value we are switching on...
BasicBlock* Default = SI->getDefaultDest();
// If there is only the default destination, don't bother with the code below.
- if (SI->getNumOperands() == 2) {
- new BranchInst(SI->getDefaultDest(), CurBlock);
+ if (!SI->getNumCases()) {
+ BranchInst::Create(SI->getDefaultDest(), CurBlock);
CurBlock->getInstList().erase(SI);
return;
}
+ const bool DefaultIsUnreachable =
+ Default->size() == 1 && isa<UnreachableInst>(Default->getTerminator());
// Create a new, empty default block so that the new hierarchy of
// if-then statements go to this and the PHI nodes are happy.
- BasicBlock* NewDefault = new BasicBlock("NewDefault");
- F->getBasicBlockList().insert(Default, NewDefault);
-
- new BranchInst(Default, NewDefault);
-
+ // if the default block is set as an unreachable we avoid creating one
+ // because will never be a valid target.
+ BasicBlock *NewDefault = nullptr;
+ if (!DefaultIsUnreachable) {
+ NewDefault = BasicBlock::Create(SI->getContext(), "NewDefault");
+ F->getBasicBlockList().insert(Default, NewDefault);
+
+ BranchInst::Create(Default, NewDefault);
+ }
// If there is an entry in any PHI nodes for the default edge, make sure
// to update them as well.
for (BasicBlock::iterator I = Default->begin(); isa<PHINode>(I); ++I) {
PN->setIncomingBlock((unsigned)BlockIdx, NewDefault);
}
- std::vector<Case> Cases;
-
- // Expand comparisons for all of the non-default cases...
- for (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
- Cases.push_back(Case(SI->getSuccessorValue(i), SI->getSuccessor(i)));
-
- std::sort(Cases.begin(), Cases.end(), CaseCmp());
- DEBUG(std::cerr << "Cases: " << Cases << "\n");
- BasicBlock* SwitchBlock = switchConvert(Cases.begin(), Cases.end(), Val,
- OrigBlock, NewDefault);
+ // Prepare cases vector.
+ CaseVector Cases;
+ unsigned numCmps = Clusterify(Cases, SI);
+
+ DEBUG(dbgs() << "Clusterify finished. Total clusters: " << Cases.size()
+ << ". Total compares: " << numCmps << "\n");
+ DEBUG(dbgs() << "Cases: " << Cases << "\n");
+ (void)numCmps;
+
+ ConstantInt *UpperBound = nullptr;
+ ConstantInt *LowerBound = nullptr;
+
+ // Optimize the condition where Default is an unreachable block. In this case
+ // we can make the bounds tightly fitted around the case value ranges,
+ // because we know that the value passed to the switch should always be
+ // exactly one of the case values.
+ if (DefaultIsUnreachable) {
+ CaseItr LastCase = Cases.begin() + Cases.size() - 1;
+ UpperBound = cast<ConstantInt>(LastCase->High);
+ LowerBound = cast<ConstantInt>(Cases.begin()->Low);
+ }
+ BasicBlock *SwitchBlock =
+ switchConvert(Cases.begin(), Cases.end(), LowerBound, UpperBound, Val,
+ OrigBlock, OrigBlock, NewDefault);
// Branch to our shiny new if-then stuff...
- new BranchInst(SwitchBlock, OrigBlock);
+ BranchInst::Create(SwitchBlock, OrigBlock);
// We are now done with the switch instruction, delete it.
CurBlock->getInstList().erase(SI);
+
+ pred_iterator PI = pred_begin(Default), E = pred_end(Default);
+ // If the Default block has no more predecessors just remove it
+ if (PI == E) {
+ DeleteDeadBlock(Default);
+ }
}
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