#define DEBUG_TYPE "lower-switch"
namespace {
+ struct IntRange {
+ int64_t Low, High;
+ };
+ // Return true iff R is covered by Ranges.
+ static bool IsInRanges(const IntRange &R,
+ const std::vector<IntRange> &Ranges) {
+ // Note: Ranges must be sorted, non-overlapping and non-adjacent.
+
+ // Find the first range whose High field is >= R.High,
+ // then check if the Low field is <= R.Low. If so, we
+ // have a Range that covers R.
+ auto I = std::lower_bound(
+ Ranges.begin(), Ranges.end(), R,
+ [](const IntRange &A, const IntRange &B) { return A.High < B.High; });
+ return I != Ranges.end() && I->Low <= R.Low;
+ }
+
/// LowerSwitch Pass - Replace all SwitchInst instructions with chained branch
/// instructions.
class LowerSwitch : public FunctionPass {
BasicBlock *switchConvert(CaseItr Begin, CaseItr End,
ConstantInt *LowerBound, ConstantInt *UpperBound,
- Value *Val, BasicBlock *OrigBlock,
- BasicBlock *Default);
+ Value *Val, BasicBlock *Predecessor,
+ BasicBlock *OrigBlock, BasicBlock *Default,
+ const std::vector<IntRange> &UnreachableRanges);
BasicBlock *newLeafBlock(CaseRange &Leaf, Value *Val, BasicBlock *OrigBlock,
BasicBlock *Default);
unsigned Clusterify(CaseVector &Cases, SwitchInst *SI);
return O << "]";
}
+// \brief Update the first occurrence of the "switch statement" BB in the PHI
+// node with the "new" BB. The other occurrences will:
+//
+// 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
+// value. When the switch statement is converted these incoming edges are now
+// coming from multiple BBs.
+// 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
+// number of phi values equal to the number of branches to SuccBB.
+static void fixPhis(BasicBlock *SuccBB, BasicBlock *OrigBB, BasicBlock *NewBB,
+ unsigned NumMergedCases) {
+ for (BasicBlock::iterator I = SuccBB->begin(), IE = SuccBB->getFirstNonPHI();
+ I != IE; ++I) {
+ PHINode *PN = cast<PHINode>(I);
+
+ // Only update the first occurence.
+ unsigned Idx = 0, E = PN->getNumIncomingValues();
+ unsigned LocalNumMergedCases = NumMergedCases;
+ for (; Idx != E; ++Idx) {
+ if (PN->getIncomingBlock(Idx) == OrigBB) {
+ PN->setIncomingBlock(Idx, NewBB);
+ break;
+ }
+ }
+
+ // Remove additional occurences coming from condensed cases and keep the
+ // number of incoming values equal to the number of branches to SuccBB.
+ for (++Idx; LocalNumMergedCases > 0 && Idx < E; ++Idx)
+ if (PN->getIncomingBlock(Idx) == OrigBB) {
+ PN->removeIncomingValue(Idx);
+ LocalNumMergedCases--;
+ }
+ }
+}
+
// switchConvert - Convert the switch statement into a binary lookup of
// the case values. The function recursively builds this tree.
// 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 *OrigBlock,
- BasicBlock *Default) {
+BasicBlock *
+LowerSwitch::switchConvert(CaseItr Begin, CaseItr End, ConstantInt *LowerBound,
+ ConstantInt *UpperBound, Value *Val,
+ BasicBlock *Predecessor, BasicBlock *OrigBlock,
+ BasicBlock *Default,
+ const std::vector<IntRange> &UnreachableRanges) {
unsigned Size = End - Begin;
if (Size == 1) {
// 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) {
+ unsigned NumMergedCases = 0;
+ if (LowerBound && UpperBound)
+ NumMergedCases =
+ UpperBound->getSExtValue() - LowerBound->getSExtValue();
+ fixPhis(Begin->BB, OrigBlock, Predecessor, NumMergedCases);
return Begin->BB;
}
return newLeafBlock(*Begin, Val, OrigBlock, Default);
// 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);
+
+ // Because NewLowerBound is never the smallest representable integer
+ // it is safe here to subtract one.
+ ConstantInt *NewUpperBound = ConstantInt::get(NewLowerBound->getContext(),
+ NewLowerBound->getValue() - 1);
+
+ if (!UnreachableRanges.empty()) {
+ // Check if the gap between LHS's highest and NewLowerBound is unreachable.
+ int64_t GapLow = cast<ConstantInt>(LHS.back().High)->getSExtValue() + 1;
+ int64_t GapHigh = NewLowerBound->getSExtValue() - 1;
+ IntRange Gap = { GapLow, GapHigh };
+ if (GapHigh >= GapLow && IsInRanges(Gap, UnreachableRanges))
+ NewUpperBound = cast<ConstantInt>(LHS.back().High);
}
DEBUG(dbgs() << "LHS Bounds ==> ";
dbgs() << "NONE\n";
});
- BasicBlock *LBranch = switchConvert(LHS.begin(), LHS.end(), LowerBound,
- NewUpperBound, Val, OrigBlock, Default);
- BasicBlock *RBranch = switchConvert(RHS.begin(), RHS.end(), NewLowerBound,
- UpperBound, Val, OrigBlock, Default);
-
// 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 = BasicBlock::Create(Val->getContext(), "NodeBlock");
- Function::iterator FI = OrigBlock;
- F->getBasicBlockList().insert(++FI, NewNode);
ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_SLT,
Val, Pivot.Low, "Pivot");
+
+ BasicBlock *LBranch = switchConvert(LHS.begin(), LHS.end(), LowerBound,
+ NewUpperBound, Val, NewNode, OrigBlock,
+ Default, UnreachableRanges);
+ BasicBlock *RBranch = switchConvert(RHS.begin(), RHS.end(), NewLowerBound,
+ UpperBound, Val, NewNode, OrigBlock,
+ Default, UnreachableRanges);
+
+ Function::iterator FI = OrigBlock;
+ F->getBasicBlockList().insert(++FI, NewNode);
NewNode->getInstList().push_back(Comp);
+
BranchInst::Create(LBranch, RBranch, Comp, NewNode);
return NewNode;
}
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 there is only the default destination, just branch.
if (!SI->getNumCases()) {
- BranchInst::Create(SI->getDefaultDest(), CurBlock);
- CurBlock->getInstList().erase(SI);
+ BranchInst::Create(Default, CurBlock);
+ SI->eraseFromParent();
return;
}
- const bool DefaultIsUnreachable =
- Default->size() == 1 && isa<UnreachableInst>(Default->getTerminator());
+ // 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 *LowerBound = nullptr;
+ ConstantInt *UpperBound = nullptr;
+ std::vector<IntRange> UnreachableRanges;
+
+ if (isa<UnreachableInst>(Default->getFirstNonPHIOrDbg())) {
+ // Make the bounds tightly fitted around the case value range, becase we
+ // know that the value passed to the switch must be exactly one of the case
+ // values.
+ assert(!Cases.empty());
+ LowerBound = cast<ConstantInt>(Cases.front().Low);
+ UpperBound = cast<ConstantInt>(Cases.back().High);
+
+ DenseMap<BasicBlock *, unsigned> Popularity;
+ unsigned MaxPop = 0;
+ BasicBlock *PopSucc = nullptr;
+
+ IntRange R = { INT64_MIN, INT64_MAX };
+ UnreachableRanges.push_back(R);
+ for (const auto &I : Cases) {
+ int64_t Low = cast<ConstantInt>(I.Low)->getSExtValue();
+ int64_t High = cast<ConstantInt>(I.High)->getSExtValue();
+
+ IntRange &LastRange = UnreachableRanges.back();
+ if (LastRange.Low == Low) {
+ // There is nothing left of the previous range.
+ UnreachableRanges.pop_back();
+ } else {
+ // Terminate the previous range.
+ assert(Low > LastRange.Low);
+ LastRange.High = Low - 1;
+ }
+ if (High != INT64_MAX) {
+ IntRange R = { High + 1, INT64_MAX };
+ UnreachableRanges.push_back(R);
+ }
+
+ // Count popularity.
+ int64_t N = High - Low + 1;
+ unsigned &Pop = Popularity[I.BB];
+ if ((Pop += N) > MaxPop) {
+ MaxPop = Pop;
+ PopSucc = I.BB;
+ }
+ }
+#ifndef NDEBUG
+ /* UnreachableRanges should be sorted and the ranges non-adjacent. */
+ for (auto I = UnreachableRanges.begin(), E = UnreachableRanges.end();
+ I != E; ++I) {
+ assert(I->Low <= I->High);
+ auto Next = I + 1;
+ if (Next != E) {
+ assert(Next->Low > I->High);
+ }
+ }
+#endif
+
+ // Use the most popular block as the new default, reducing the number of
+ // cases.
+ assert(MaxPop > 0 && PopSucc);
+ Default = PopSucc;
+ for (CaseItr I = Cases.begin(); I != Cases.end();) {
+ if (I->BB == PopSucc)
+ I = Cases.erase(I);
+ else
+ ++I;
+ }
+
+ // If there are no cases left, just branch.
+ if (Cases.empty()) {
+ BranchInst::Create(Default, CurBlock);
+ SI->eraseFromParent();
+ return;
+ }
+ }
+
// 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 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);
- }
+ BasicBlock *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);
}
- // 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, NewDefault);
+ OrigBlock, OrigBlock, NewDefault, UnreachableRanges);
// Branch to our shiny new if-then stuff...
BranchInst::Create(SwitchBlock, OrigBlock);
// We are now done with the switch instruction, delete it.
+ BasicBlock *OldDefault = SI->getDefaultDest();
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);
- }
+ // If the Default block has no more predecessors just remove it.
+ if (pred_begin(OldDefault) == pred_end(OldDefault))
+ DeleteDeadBlock(OldDefault);
}
projects / oota-llvm.git / blobdiff