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Differential D58096 Diff 187932 llvm/trunk/lib/Transforms/Utils/LowerSwitch.cpp

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llvm/trunk/lib/Transforms/Utils/LowerSwitch.cpp

Show All 10 Lines
// switch instruction until it is convenient. // switch instruction until it is convenient.
// //
//===----------------------------------------------------------------------===// //===----------------------------------------------------------------------===//
#include "llvm/ADT/DenseMap.h" #include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h" #include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h" #include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/BasicBlock.h" #include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h" #include "llvm/IR/CFG.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h" #include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h" #include "llvm/IR/Function.h"
#include "llvm/IR/InstrTypes.h" #include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instructions.h" #include "llvm/IR/Instructions.h"
#include "llvm/IR/Value.h" #include "llvm/IR/Value.h"
#include "llvm/Pass.h" #include "llvm/Pass.h"
#include "llvm/Support/Casting.h" #include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h" #include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h" #include "llvm/Support/Debug.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/raw_ostream.h" #include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils.h" #include "llvm/Transforms/Utils.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include <algorithm> #include <algorithm>
#include <cassert> #include <cassert>
#include <cstdint> #include <cstdint>
#include <iterator> #include <iterator>
#include <limits> #include <limits>
Show All 34 Lines public:
static char ID; static char ID;
LowerSwitch() : FunctionPass(ID) { LowerSwitch() : FunctionPass(ID) {
initializeLowerSwitchPass(*PassRegistry::getPassRegistry()); initializeLowerSwitchPass(*PassRegistry::getPassRegistry());
} }
bool runOnFunction(Function &F) override; bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LazyValueInfoWrapperPass>();
}
struct CaseRange { struct CaseRange {
ConstantInt* Low; ConstantInt* Low;
ConstantInt* High; ConstantInt* High;
BasicBlock* BB; BasicBlock* BB;
CaseRange(ConstantInt *low, ConstantInt *high, BasicBlock *bb) CaseRange(ConstantInt *low, ConstantInt *high, BasicBlock *bb)
: Low(low), High(high), BB(bb) {} : Low(low), High(high), BB(bb) {}
}; };
using CaseVector = std::vector<CaseRange>; using CaseVector = std::vector<CaseRange>;
using CaseItr = std::vector<CaseRange>::iterator; using CaseItr = std::vector<CaseRange>::iterator;
private: private:
void processSwitchInst(SwitchInst *SI, SmallPtrSetImpl<BasicBlock*> &DeleteList); void processSwitchInst(SwitchInst *SI,
SmallPtrSetImpl<BasicBlock *> &DeleteList,
AssumptionCache *AC, LazyValueInfo *LVI);
BasicBlock *switchConvert(CaseItr Begin, CaseItr End, BasicBlock *switchConvert(CaseItr Begin, CaseItr End,
ConstantInt *LowerBound, ConstantInt *UpperBound, ConstantInt *LowerBound, ConstantInt *UpperBound,
Value *Val, BasicBlock *Predecessor, Value *Val, BasicBlock *Predecessor,
BasicBlock *OrigBlock, BasicBlock *Default, BasicBlock *OrigBlock, BasicBlock *Default,
const std::vector<IntRange> &UnreachableRanges); const std::vector<IntRange> &UnreachableRanges);
BasicBlock *newLeafBlock(CaseRange &Leaf, Value *Val, BasicBlock *OrigBlock, BasicBlock *newLeafBlock(CaseRange &Leaf, Value *Val,
BasicBlock *Default); ConstantInt *LowerBound, ConstantInt *UpperBound,
BasicBlock *OrigBlock, BasicBlock *Default);
unsigned Clusterify(CaseVector &Cases, SwitchInst *SI); unsigned Clusterify(CaseVector &Cases, SwitchInst *SI);
}; };
/// The comparison function for sorting the switch case values in the vector. /// The comparison function for sorting the switch case values in the vector.
/// WARNING: Case ranges should be disjoint! /// WARNING: Case ranges should be disjoint!
struct CaseCmp { struct CaseCmp {
bool operator()(const LowerSwitch::CaseRange& C1, bool operator()(const LowerSwitch::CaseRange& C1,
const LowerSwitch::CaseRange& C2) { const LowerSwitch::CaseRange& C2) {
const ConstantInt* CI1 = cast<const ConstantInt>(C1.Low); const ConstantInt* CI1 = cast<const ConstantInt>(C1.Low);
const ConstantInt* CI2 = cast<const ConstantInt>(C2.High); const ConstantInt* CI2 = cast<const ConstantInt>(C2.High);
return CI1->getValue().slt(CI2->getValue()); return CI1->getValue().slt(CI2->getValue());
} }
}; };
} // end anonymous namespace } // end anonymous namespace
char LowerSwitch::ID = 0; char LowerSwitch::ID = 0;
// Publicly exposed interface to pass... // Publicly exposed interface to pass...
char &llvm::LowerSwitchID = LowerSwitch::ID; char &llvm::LowerSwitchID = LowerSwitch::ID;
INITIALIZE_PASS(LowerSwitch, "lowerswitch", INITIALIZE_PASS_BEGIN(LowerSwitch, "lowerswitch",
"Lower SwitchInst's to branches", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(LazyValueInfoWrapperPass)
INITIALIZE_PASS_END(LowerSwitch, "lowerswitch",
"Lower SwitchInst's to branches", false, false) "Lower SwitchInst's to branches", false, false)
// createLowerSwitchPass - Interface to this file... // createLowerSwitchPass - Interface to this file...
FunctionPass *llvm::createLowerSwitchPass() { FunctionPass *llvm::createLowerSwitchPass() {
return new LowerSwitch(); return new LowerSwitch();
} }
bool LowerSwitch::runOnFunction(Function &F) { bool LowerSwitch::runOnFunction(Function &F) {
LazyValueInfo *LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
auto *ACT = getAnalysisIfAvailable<AssumptionCacheTracker>();
AssumptionCache *AC = ACT ? &ACT->getAssumptionCache(F) : nullptr;
// Prevent LazyValueInfo from using the DominatorTree as LowerSwitch does not
// preserve it and it becomes stale (when available) pretty much immediately.
// Currently the DominatorTree is only used by LowerSwitch indirectly via LVI
// and computeKnownBits to refine isValidAssumeForContext's results. Given
// that the latter can handle some of the simple cases w/o a DominatorTree,
// it's easier to refrain from using the tree than to keep it up to date.
LVI->disableDT();
bool Changed = false; bool Changed = false;
SmallPtrSet<BasicBlock*, 8> DeleteList; SmallPtrSet<BasicBlock*, 8> DeleteList;
for (Function::iterator I = F.begin(), E = F.end(); I != E; ) { for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
BasicBlock *Cur = &*I++; // Advance over block so we don't traverse new blocks BasicBlock *Cur = &*I++; // Advance over block so we don't traverse new blocks
// If the block is a dead Default block that will be deleted later, don't // If the block is a dead Default block that will be deleted later, don't
// waste time processing it. // waste time processing it.
if (DeleteList.count(Cur)) if (DeleteList.count(Cur))
continue; continue;
if (SwitchInst *SI = dyn_cast<SwitchInst>(Cur->getTerminator())) { if (SwitchInst *SI = dyn_cast<SwitchInst>(Cur->getTerminator())) {
Changed = true; Changed = true;
processSwitchInst(SI, DeleteList); processSwitchInst(SI, DeleteList, AC, LVI);
} }
} }
for (BasicBlock* BB: DeleteList) { for (BasicBlock* BB: DeleteList) {
LVI->eraseBlock(BB);
DeleteDeadBlock(BB); DeleteDeadBlock(BB);
} }
return Changed; return Changed;
} }
/// Used for debugging purposes. /// Used for debugging purposes.
LLVM_ATTRIBUTE_USED LLVM_ATTRIBUTE_USED
static raw_ostream &operator<<(raw_ostream &O, static raw_ostream &operator<<(raw_ostream &O,
const LowerSwitch::CaseVector &C) { const LowerSwitch::CaseVector &C) {
O << "["; O << "[";
for (LowerSwitch::CaseVector::const_iterator B = C.begin(), for (LowerSwitch::CaseVector::const_iterator B = C.begin(), E = C.end();
E = C.end(); B != E; ) { B != E;) {
O << *B->Low << " -" << *B->High; O << "[" << B->Low->getValue() << ", " << B->High->getValue() << "]";
if (++B != E) O << ", "; if (++B != E)
O << ", ";
} }
return O << "]"; return O << "]";
} }
/// Update the first occurrence of the "switch statement" BB in the PHI /// Update the first occurrence of the "switch statement" BB in the PHI
/// node with the "new" BB. The other occurrences will: /// node with the "new" BB. The other occurrences will:
/// ///
/// 1) Be updated by subsequent calls to this function. Switch statements may /// 1) Be updated by subsequent calls to this function. Switch statements may
/// have more than one outcoming edge into the same BB if they all have the same /// have more than one outcoming edge into the same BB if they all have the same
/// value. When the switch statement is converted these incoming edges are now /// value. When the switch statement is converted these incoming edges are now
/// coming from multiple BBs. /// coming from multiple BBs.
/// 2) Removed if subsequent incoming values now share the same case, i.e., /// 2) Removed if subsequent incoming values now share the same case, i.e.,
/// multiple outcome edges are condensed into one. This is necessary to keep the /// multiple outcome edges are condensed into one. This is necessary to keep the
/// number of phi values equal to the number of branches to SuccBB. /// number of phi values equal to the number of branches to SuccBB.
static void fixPhis(BasicBlock *SuccBB, BasicBlock *OrigBB, BasicBlock *NewBB, static void
unsigned NumMergedCases) { fixPhis(BasicBlock *SuccBB, BasicBlock *OrigBB, BasicBlock *NewBB,
const unsigned NumMergedCases = std::numeric_limits<unsigned>::max()) {
for (BasicBlock::iterator I = SuccBB->begin(), for (BasicBlock::iterator I = SuccBB->begin(),
IE = SuccBB->getFirstNonPHI()->getIterator(); IE = SuccBB->getFirstNonPHI()->getIterator();
I != IE; ++I) { I != IE; ++I) {
PHINode *PN = cast<PHINode>(I); PHINode *PN = cast<PHINode>(I);
// Only update the first occurrence. // Only update the first occurrence.
unsigned Idx = 0, E = PN->getNumIncomingValues(); unsigned Idx = 0, E = PN->getNumIncomingValues();
unsigned LocalNumMergedCases = NumMergedCases; unsigned LocalNumMergedCases = NumMergedCases;
Show All 25 Lines
/// a block emitted by one of the previous calls to switchConvert in the call /// a block emitted by one of the previous calls to switchConvert in the call
/// stack. /// stack.
BasicBlock * BasicBlock *
LowerSwitch::switchConvert(CaseItr Begin, CaseItr End, ConstantInt *LowerBound, LowerSwitch::switchConvert(CaseItr Begin, CaseItr End, ConstantInt *LowerBound,
ConstantInt *UpperBound, Value *Val, ConstantInt *UpperBound, Value *Val,
BasicBlock *Predecessor, BasicBlock *OrigBlock, BasicBlock *Predecessor, BasicBlock *OrigBlock,
BasicBlock *Default, BasicBlock *Default,
const std::vector<IntRange> &UnreachableRanges) { const std::vector<IntRange> &UnreachableRanges) {
assert(LowerBound && UpperBound && "Bounds must be initialized");
unsigned Size = End - Begin; unsigned Size = End - Begin;
if (Size == 1) { if (Size == 1) {
// Check if the Case Range is perfectly squeezed in between // Check if the Case Range is perfectly squeezed in between
// already checked Upper and Lower bounds. If it is then we can avoid // 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 // emitting the code that checks if the value actually falls in the range
// because the bounds already tell us so. // because the bounds already tell us so.
if (Begin->Low == LowerBound && Begin->High == UpperBound) { if (Begin->Low == LowerBound && Begin->High == UpperBound) {
unsigned NumMergedCases = 0; unsigned NumMergedCases = 0;
if (LowerBound && UpperBound) NumMergedCases = UpperBound->getSExtValue() - LowerBound->getSExtValue();
NumMergedCases =
UpperBound->getSExtValue() - LowerBound->getSExtValue();
fixPhis(Begin->BB, OrigBlock, Predecessor, NumMergedCases); fixPhis(Begin->BB, OrigBlock, Predecessor, NumMergedCases);
return Begin->BB; return Begin->BB;
} }
return newLeafBlock(*Begin, Val, OrigBlock, Default); return newLeafBlock(*Begin, Val, LowerBound, UpperBound, OrigBlock,
Default);
} }
unsigned Mid = Size / 2; unsigned Mid = Size / 2;
std::vector<CaseRange> LHS(Begin, Begin + Mid); std::vector<CaseRange> LHS(Begin, Begin + Mid);
LLVM_DEBUG(dbgs() << "LHS: " << LHS << "\n"); LLVM_DEBUG(dbgs() << "LHS: " << LHS << "\n");
std::vector<CaseRange> RHS(Begin + Mid, End); std::vector<CaseRange> RHS(Begin + Mid, End);
LLVM_DEBUG(dbgs() << "RHS: " << RHS << "\n"); LLVM_DEBUG(dbgs() << "RHS: " << RHS << "\n");
CaseRange &Pivot = *(Begin + Mid); CaseRange &Pivot = *(Begin + Mid);
LLVM_DEBUG(dbgs() << "Pivot ==> " << Pivot.Low->getValue() << " -" LLVM_DEBUG(dbgs() << "Pivot ==> [" << Pivot.Low->getValue() << ", "
<< Pivot.High->getValue() << "\n"); << Pivot.High->getValue() << "]\n");
// NewLowerBound here should never be the integer minimal value. // NewLowerBound here should never be the integer minimal value.
// This is because it is computed from a case range that is never // 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 // the smallest, so there is always a case range that has at least
// a smaller value. // a smaller value.
ConstantInt *NewLowerBound = Pivot.Low; ConstantInt *NewLowerBound = Pivot.Low;
// Because NewLowerBound is never the smallest representable integer // Because NewLowerBound is never the smallest representable integer
// it is safe here to subtract one. // it is safe here to subtract one.
ConstantInt *NewUpperBound = ConstantInt::get(NewLowerBound->getContext(), ConstantInt *NewUpperBound = ConstantInt::get(NewLowerBound->getContext(),
NewLowerBound->getValue() - 1); NewLowerBound->getValue() - 1);
if (!UnreachableRanges.empty()) { if (!UnreachableRanges.empty()) {
// Check if the gap between LHS's highest and NewLowerBound is unreachable. // Check if the gap between LHS's highest and NewLowerBound is unreachable.
int64_t GapLow = LHS.back().High->getSExtValue() + 1; int64_t GapLow = LHS.back().High->getSExtValue() + 1;
int64_t GapHigh = NewLowerBound->getSExtValue() - 1; int64_t GapHigh = NewLowerBound->getSExtValue() - 1;
IntRange Gap = { GapLow, GapHigh }; IntRange Gap = { GapLow, GapHigh };
if (GapHigh >= GapLow && IsInRanges(Gap, UnreachableRanges)) if (GapHigh >= GapLow && IsInRanges(Gap, UnreachableRanges))
NewUpperBound = LHS.back().High; NewUpperBound = LHS.back().High;
} }
LLVM_DEBUG(dbgs() << "LHS Bounds ==> "; if (LowerBound) { LLVM_DEBUG(dbgs() << "LHS Bounds ==> [" << LowerBound->getSExtValue() << ", "
dbgs() << LowerBound->getSExtValue(); << NewUpperBound->getSExtValue() << "]\n"
} else { dbgs() << "NONE"; } dbgs() << " - " << "RHS Bounds ==> [" << NewLowerBound->getSExtValue()
<< NewUpperBound->getSExtValue() << "\n"; << ", " << UpperBound->getSExtValue() << "]\n");
dbgs() << "RHS Bounds ==> ";
dbgs() << NewLowerBound->getSExtValue() << " - "; if (UpperBound) {
dbgs() << UpperBound->getSExtValue() << "\n";
} else { dbgs() << "NONE\n"; });
// Create a new node that checks if the value is < pivot. Go to the // Create a new node that checks if the value is < pivot. Go to the
// left branch if it is and right branch if not. // left branch if it is and right branch if not.
Function* F = OrigBlock->getParent(); Function* F = OrigBlock->getParent();
BasicBlock* NewNode = BasicBlock::Create(Val->getContext(), "NodeBlock"); BasicBlock* NewNode = BasicBlock::Create(Val->getContext(), "NodeBlock");
ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_SLT, ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_SLT,
Val, Pivot.Low, "Pivot"); Val, Pivot.Low, "Pivot");
Show All 11 LinesLowerSwitch::switchConvert(CaseItr Begin, CaseItr End, ConstantInt *LowerBound,
BranchInst::Create(LBranch, RBranch, Comp, NewNode); BranchInst::Create(LBranch, RBranch, Comp, NewNode);
return NewNode; return NewNode;
} }
/// Create a new leaf block for the binary lookup tree. It checks if the /// Create a new leaf block for the binary lookup tree. It checks if the
/// switch's value == the case's value. If not, then it jumps to the default /// switch's value == the case's value. If not, then it jumps to the default
/// branch. At this point in the tree, the value can't be another valid case /// branch. At this point in the tree, the value can't be another valid case
/// value, so the jump to the "default" branch is warranted. /// value, so the jump to the "default" branch is warranted.
BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val, BasicBlock *LowerSwitch::newLeafBlock(CaseRange &Leaf, Value *Val,
ConstantInt *LowerBound,
ConstantInt *UpperBound,
BasicBlock* OrigBlock, BasicBlock *OrigBlock,
BasicBlock* Default) { BasicBlock *Default) {
Function* F = OrigBlock->getParent(); Function* F = OrigBlock->getParent();
BasicBlock* NewLeaf = BasicBlock::Create(Val->getContext(), "LeafBlock"); BasicBlock* NewLeaf = BasicBlock::Create(Val->getContext(), "LeafBlock");
F->getBasicBlockList().insert(++OrigBlock->getIterator(), NewLeaf); F->getBasicBlockList().insert(++OrigBlock->getIterator(), NewLeaf);
// Emit comparison // Emit comparison
ICmpInst* Comp = nullptr; ICmpInst* Comp = nullptr;
if (Leaf.Low == Leaf.High) { if (Leaf.Low == Leaf.High) {
// Make the seteq instruction... // Make the seteq instruction...
Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_EQ, Val, Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_EQ, Val,
Leaf.Low, "SwitchLeaf"); Leaf.Low, "SwitchLeaf");
} else { } else {
// Make range comparison // Make range comparison
if (Leaf.Low->isMinValue(true /*isSigned*/)) { if (Leaf.Low == LowerBound) {
// Val >= Min && Val <= Hi --> Val <= Hi // Val >= Min && Val <= Hi --> Val <= Hi
Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High, Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High,
"SwitchLeaf"); "SwitchLeaf");
} else if (Leaf.High == UpperBound) {
// Val <= Max && Val >= Lo --> Val >= Lo
Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SGE, Val, Leaf.Low,
"SwitchLeaf");
} else if (Leaf.Low->isZero()) { } else if (Leaf.Low->isZero()) {
// Val >= 0 && Val <= Hi --> Val <=u Hi // Val >= 0 && Val <= Hi --> Val <=u Hi
Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Val, Leaf.High, Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Val, Leaf.High,
"SwitchLeaf"); "SwitchLeaf");
} else { } else {
// Emit V-Lo <=u Hi-Lo // Emit V-Lo <=u Hi-Lo
Constant* NegLo = ConstantExpr::getNeg(Leaf.Low); Constant* NegLo = ConstantExpr::getNeg(Leaf.Low);
Instruction* Add = BinaryOperator::CreateAdd(Val, NegLo, Instruction* Add = BinaryOperator::CreateAdd(Val, NegLo,
Show All 23 Lines for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
int BlockIdx = PN->getBasicBlockIndex(OrigBlock); int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
assert(BlockIdx != -1 && "Switch didn't go to this successor??"); assert(BlockIdx != -1 && "Switch didn't go to this successor??");
PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf); PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
} }
return NewLeaf; return NewLeaf;
} }
/// Transform simple list of Cases into list of CaseRange's. /// Transform simple list of \p SI's cases into list of CaseRange's \p Cases.
/// \post \p Cases wouldn't contain references to \p SI's default BB.
/// \returns Number of \p SI's cases that do not reference \p SI's default BB.
unsigned LowerSwitch::Clusterify(CaseVector& Cases, SwitchInst *SI) { unsigned LowerSwitch::Clusterify(CaseVector& Cases, SwitchInst *SI) {
unsigned numCmps = 0; unsigned NumSimpleCases = 0;
// Start with "simple" cases // Start with "simple" cases
for (auto Case : SI->cases()) for (auto Case : SI->cases()) {
if (Case.getCaseSuccessor() == SI->getDefaultDest())
continue;
Cases.push_back(CaseRange(Case.getCaseValue(), Case.getCaseValue(), Cases.push_back(CaseRange(Case.getCaseValue(), Case.getCaseValue(),
Case.getCaseSuccessor())); Case.getCaseSuccessor()));
++NumSimpleCases;
}
llvm::sort(Cases, CaseCmp()); llvm::sort(Cases, CaseCmp());
// Merge case into clusters // Merge case into clusters
if (Cases.size() >= 2) { if (Cases.size() >= 2) {
CaseItr I = Cases.begin(); CaseItr I = Cases.begin();
for (CaseItr J = std::next(I), E = Cases.end(); J != E; ++J) { for (CaseItr J = std::next(I), E = Cases.end(); J != E; ++J) {
int64_t nextValue = J->Low->getSExtValue(); int64_t nextValue = J->Low->getSExtValue();
Show All 9 Lines for (CaseItr J = std::next(I), E = Cases.end(); J != E; ++J) {
// FIXME: Combine branch weights. // FIXME: Combine branch weights.
} else if (++I != J) { } else if (++I != J) {
*I = *J; *I = *J;
} }
} }
Cases.erase(std::next(I), Cases.end()); Cases.erase(std::next(I), Cases.end());
} }
for (CaseItr I=Cases.begin(), E=Cases.end(); I!=E; ++I, ++numCmps) { return NumSimpleCases;
if (I->Low != I->High)
// A range counts double, since it requires two compares.
++numCmps;
} }
return numCmps; static ConstantRange getConstantRangeFromKnownBits(const KnownBits &Known) {
APInt Lower = Known.One;
APInt Upper = ~Known.Zero + 1;
if (Upper == Lower)
return ConstantRange(Known.getBitWidth(), /*isFullSet=*/true);
return ConstantRange(Lower, Upper);
} }
/// Replace the specified switch instruction with a sequence of chained if-then /// Replace the specified switch instruction with a sequence of chained if-then
/// insts in a balanced binary search. /// insts in a balanced binary search.
void LowerSwitch::processSwitchInst(SwitchInst *SI, void LowerSwitch::processSwitchInst(SwitchInst *SI,
SmallPtrSetImpl<BasicBlock*> &DeleteList) { SmallPtrSetImpl<BasicBlock *> &DeleteList,
BasicBlock *CurBlock = SI->getParent(); AssumptionCache *AC, LazyValueInfo *LVI) {
BasicBlock *OrigBlock = CurBlock; BasicBlock *OrigBlock = SI->getParent();
Function *F = CurBlock->getParent(); Function *F = OrigBlock->getParent();
Value *Val = SI->getCondition(); // The value we are switching on... Value *Val = SI->getCondition(); // The value we are switching on...
BasicBlock* Default = SI->getDefaultDest(); BasicBlock* Default = SI->getDefaultDest();
// Don't handle unreachable blocks. If there are successors with phis, this // Don't handle unreachable blocks. If there are successors with phis, this
// would leave them behind with missing predecessors. // would leave them behind with missing predecessors.
if ((CurBlock != &F->getEntryBlock() && pred_empty(CurBlock)) || if ((OrigBlock != &F->getEntryBlock() && pred_empty(OrigBlock)) ||
CurBlock->getSinglePredecessor() == CurBlock) { OrigBlock->getSinglePredecessor() == OrigBlock) {
DeleteList.insert(CurBlock); DeleteList.insert(OrigBlock);
return; return;
} }
// Prepare cases vector.
CaseVector Cases;
const unsigned NumSimpleCases = Clusterify(Cases, SI);
LLVM_DEBUG(dbgs() << "Clusterify finished. Total clusters: " << Cases.size()
<< ". Total non-default cases: " << NumSimpleCases
<< "\nCase clusters: " << Cases << "\n");
// If there is only the default destination, just branch. // If there is only the default destination, just branch.
if (!SI->getNumCases()) { if (Cases.empty()) {
BranchInst::Create(Default, CurBlock); BranchInst::Create(Default, OrigBlock);
// Remove all the references from Default's PHIs to OrigBlock, but one.
fixPhis(Default, OrigBlock, OrigBlock);
SI->eraseFromParent(); SI->eraseFromParent();
return; return;
} }
// Prepare cases vector.
CaseVector Cases;
unsigned numCmps = Clusterify(Cases, SI);
LLVM_DEBUG(dbgs() << "Clusterify finished. Total clusters: " << Cases.size()
<< ". Total compares: " << numCmps << "\n");
LLVM_DEBUG(dbgs() << "Cases: " << Cases << "\n");
(void)numCmps;
ConstantInt *LowerBound = nullptr; ConstantInt *LowerBound = nullptr;
ConstantInt *UpperBound = nullptr; ConstantInt *UpperBound = nullptr;
std::vector<IntRange> UnreachableRanges; bool DefaultIsUnreachableFromSwitch = false;
if (isa<UnreachableInst>(Default->getFirstNonPHIOrDbg())) { if (isa<UnreachableInst>(Default->getFirstNonPHIOrDbg())) {
// Make the bounds tightly fitted around the case value range, because we // Make the bounds tightly fitted around the case value range, because we
// know that the value passed to the switch must be exactly one of the case // know that the value passed to the switch must be exactly one of the case
// values. // values.
assert(!Cases.empty());
LowerBound = Cases.front().Low; LowerBound = Cases.front().Low;
UpperBound = Cases.back().High; UpperBound = Cases.back().High;
DefaultIsUnreachableFromSwitch = true;
} else {
// Constraining the range of the value being switched over helps eliminating
// unreachable BBs and minimizing the number of `add` instructions
// newLeafBlock ends up emitting. Running CorrelatedValuePropagation after
// LowerSwitch isn't as good, and also much more expensive in terms of
// compile time for the following reasons:
// 1. it processes many kinds of instructions, not just switches;
// 2. even if limited to icmp instructions only, it will have to process
// roughly C icmp's per switch, where C is the number of cases in the
// switch, while LowerSwitch only needs to call LVI once per switch.
const DataLayout &DL = F->getParent()->getDataLayout();
KnownBits Known = computeKnownBits(Val, DL, /*Depth=*/0, AC, SI);
ConstantRange KnownBitsRange = getConstantRangeFromKnownBits(Known);
const ConstantRange LVIRange = LVI->getConstantRange(Val, OrigBlock, SI);
ConstantRange ValRange = KnownBitsRange.intersectWith(LVIRange);
// We delegate removal of unreachable non-default cases to other passes. In
// the unlikely event that some of them survived, we just conservatively
// maintain the invariant that all the cases lie between the bounds. This
// may, however, still render the default case effectively unreachable.
APInt Low = Cases.front().Low->getValue();
APInt High = Cases.back().High->getValue();
APInt Min = APIntOps::smin(ValRange.getSignedMin(), Low);
APInt Max = APIntOps::smax(ValRange.getSignedMax(), High);
LowerBound = ConstantInt::get(SI->getContext(), Min);
UpperBound = ConstantInt::get(SI->getContext(), Max);
DefaultIsUnreachableFromSwitch = (Min + (NumSimpleCases - 1) == Max);
}
std::vector<IntRange> UnreachableRanges;
if (DefaultIsUnreachableFromSwitch) {
DenseMap<BasicBlock *, unsigned> Popularity; DenseMap<BasicBlock *, unsigned> Popularity;
unsigned MaxPop = 0; unsigned MaxPop = 0;
BasicBlock *PopSucc = nullptr; BasicBlock *PopSucc = nullptr;
IntRange R = {std::numeric_limits<int64_t>::min(), IntRange R = {std::numeric_limits<int64_t>::min(),
std::numeric_limits<int64_t>::max()}; std::numeric_limits<int64_t>::max()};
UnreachableRanges.push_back(R); UnreachableRanges.push_back(R);
for (const auto &I : Cases) { for (const auto &I : Cases) {
Show All 30 Lines for (auto I = UnreachableRanges.begin(), E = UnreachableRanges.end();
auto Next = I + 1; auto Next = I + 1;
if (Next != E) { if (Next != E) {
assert(Next->Low > I->High); assert(Next->Low > I->High);
} }
} }
#endif #endif
// As the default block in the switch is unreachable, update the PHI nodes // As the default block in the switch is unreachable, update the PHI nodes
// (remove the entry to the default block) to reflect this. // (remove all of the references to the default block) to reflect this.
const unsigned NumDefaultEdges = SI->getNumCases() + 1 - NumSimpleCases;
for (unsigned I = 0; I < NumDefaultEdges; ++I)
Default->removePredecessor(OrigBlock); Default->removePredecessor(OrigBlock);
// Use the most popular block as the new default, reducing the number of // Use the most popular block as the new default, reducing the number of
// cases. // cases.
assert(MaxPop > 0 && PopSucc); assert(MaxPop > 0 && PopSucc);
Default = PopSucc; Default = PopSucc;
Cases.erase( Cases.erase(
llvm::remove_if( llvm::remove_if(
Cases, [PopSucc](const CaseRange &R) { return R.BB == PopSucc; }), Cases, [PopSucc](const CaseRange &R) { return R.BB == PopSucc; }),
Cases.end()); Cases.end());
// If there are no cases left, just branch. // If there are no cases left, just branch.
if (Cases.empty()) { if (Cases.empty()) {
BranchInst::Create(Default, CurBlock); BranchInst::Create(Default, OrigBlock);
SI->eraseFromParent(); SI->eraseFromParent();
// As all the cases have been replaced with a single branch, only keep // As all the cases have been replaced with a single branch, only keep
// one entry in the PHI nodes. // one entry in the PHI nodes.
for (unsigned I = 0 ; I < (MaxPop - 1) ; ++I) for (unsigned I = 0 ; I < (MaxPop - 1) ; ++I)
PopSucc->removePredecessor(OrigBlock); PopSucc->removePredecessor(OrigBlock);
return; return;
} }
} }
unsigned NrOfDefaults = (SI->getDefaultDest() == Default) ? 1 : 0;
for (const auto &Case : SI->cases())
if (Case.getCaseSuccessor() == Default)
NrOfDefaults++;
// Create a new, empty default block so that the new hierarchy of // Create a new, empty default block so that the new hierarchy of
// if-then statements go to this and the PHI nodes are happy. // if-then statements go to this and the PHI nodes are happy.
BasicBlock *NewDefault = BasicBlock::Create(SI->getContext(), "NewDefault"); BasicBlock *NewDefault = BasicBlock::Create(SI->getContext(), "NewDefault");
F->getBasicBlockList().insert(Default->getIterator(), NewDefault); F->getBasicBlockList().insert(Default->getIterator(), NewDefault);
BranchInst::Create(Default, NewDefault); BranchInst::Create(Default, NewDefault);
BasicBlock *SwitchBlock = BasicBlock *SwitchBlock =
switchConvert(Cases.begin(), Cases.end(), LowerBound, UpperBound, Val, switchConvert(Cases.begin(), Cases.end(), LowerBound, UpperBound, Val,
OrigBlock, OrigBlock, NewDefault, UnreachableRanges); OrigBlock, OrigBlock, NewDefault, UnreachableRanges);
// If there are entries in any PHI nodes for the default edge, make sure // If there are entries in any PHI nodes for the default edge, make sure
// to update them as well. // to update them as well.
fixPhis(Default, OrigBlock, NewDefault, NrOfDefaults); fixPhis(Default, OrigBlock, NewDefault);
// Branch to our shiny new if-then stuff... // Branch to our shiny new if-then stuff...
BranchInst::Create(SwitchBlock, OrigBlock); BranchInst::Create(SwitchBlock, OrigBlock);
// We are now done with the switch instruction, delete it. // We are now done with the switch instruction, delete it.
BasicBlock *OldDefault = SI->getDefaultDest(); BasicBlock *OldDefault = SI->getDefaultDest();
CurBlock->getInstList().erase(SI); OrigBlock->getInstList().erase(SI);
// If the Default block has no more predecessors just add it to DeleteList. // If the Default block has no more predecessors just add it to DeleteList.
if (pred_begin(OldDefault) == pred_end(OldDefault)) if (pred_begin(OldDefault) == pred_end(OldDefault))
DeleteList.insert(OldDefault); DeleteList.insert(OldDefault);
} }