aboutsummaryrefslogtreecommitdiff
path: root/contrib/llvm-project/llvm/lib/Transforms/Utils/LowerSwitch.cpp
diff options
context:
space:
mode:
Diffstat (limited to 'contrib/llvm-project/llvm/lib/Transforms/Utils/LowerSwitch.cpp')
-rw-r--r--contrib/llvm-project/llvm/lib/Transforms/Utils/LowerSwitch.cpp611
1 files changed, 611 insertions, 0 deletions
diff --git a/contrib/llvm-project/llvm/lib/Transforms/Utils/LowerSwitch.cpp b/contrib/llvm-project/llvm/lib/Transforms/Utils/LowerSwitch.cpp
new file mode 100644
index 000000000000..227de425ff85
--- /dev/null
+++ b/contrib/llvm-project/llvm/lib/Transforms/Utils/LowerSwitch.cpp
@@ -0,0 +1,611 @@
+//===- LowerSwitch.cpp - Eliminate Switch instructions --------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// 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/Utils/LowerSwitch.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallPtrSet.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/CFG.h"
+#include "llvm/IR/ConstantRange.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/InstrTypes.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/IR/Value.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/KnownBits.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <iterator>
+#include <limits>
+#include <vector>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "lower-switch"
+
+namespace {
+
+struct IntRange {
+ APInt Low, High;
+};
+
+} // end anonymous namespace
+
+namespace {
+// Return true iff R is covered by Ranges.
+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 = llvm::lower_bound(
+ Ranges, R, [](IntRange A, IntRange B) { return A.High.slt(B.High); });
+ return I != Ranges.end() && I->Low.sle(R.Low);
+}
+
+struct CaseRange {
+ ConstantInt *Low;
+ ConstantInt *High;
+ BasicBlock *BB;
+
+ CaseRange(ConstantInt *low, ConstantInt *high, BasicBlock *bb)
+ : Low(low), High(high), BB(bb) {}
+};
+
+using CaseVector = std::vector<CaseRange>;
+using CaseItr = std::vector<CaseRange>::iterator;
+
+/// The comparison function for sorting the switch case values in the vector.
+/// WARNING: Case ranges should be disjoint!
+struct CaseCmp {
+ bool operator()(const CaseRange &C1, const CaseRange &C2) {
+ const ConstantInt *CI1 = cast<const ConstantInt>(C1.Low);
+ const ConstantInt *CI2 = cast<const ConstantInt>(C2.High);
+ return CI1->getValue().slt(CI2->getValue());
+ }
+};
+
+/// Used for debugging purposes.
+LLVM_ATTRIBUTE_USED
+raw_ostream &operator<<(raw_ostream &O, const CaseVector &C) {
+ O << "[";
+
+ for (CaseVector::const_iterator B = C.begin(), E = C.end(); B != E;) {
+ O << "[" << B->Low->getValue() << ", " << B->High->getValue() << "]";
+ if (++B != E)
+ O << ", ";
+ }
+
+ return O << "]";
+}
+
+/// 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.
+void FixPhis(BasicBlock *SuccBB, BasicBlock *OrigBB, BasicBlock *NewBB,
+ const APInt &NumMergedCases) {
+ for (auto &I : SuccBB->phis()) {
+ PHINode *PN = cast<PHINode>(&I);
+
+ // Only update the first occurrence if NewBB exists.
+ unsigned Idx = 0, E = PN->getNumIncomingValues();
+ APInt LocalNumMergedCases = NumMergedCases;
+ for (; Idx != E && NewBB; ++Idx) {
+ if (PN->getIncomingBlock(Idx) == OrigBB) {
+ PN->setIncomingBlock(Idx, NewBB);
+ break;
+ }
+ }
+
+ // Skip the updated incoming block so that it will not be removed.
+ if (NewBB)
+ ++Idx;
+
+ // Remove additional occurrences coming from condensed cases and keep the
+ // number of incoming values equal to the number of branches to SuccBB.
+ SmallVector<unsigned, 8> Indices;
+ for (; LocalNumMergedCases.ugt(0) && Idx < E; ++Idx)
+ if (PN->getIncomingBlock(Idx) == OrigBB) {
+ Indices.push_back(Idx);
+ LocalNumMergedCases -= 1;
+ }
+ // Remove incoming values in the reverse order to prevent invalidating
+ // *successive* index.
+ for (unsigned III : llvm::reverse(Indices))
+ PN->removeIncomingValue(III);
+ }
+}
+
+/// 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
+/// 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.
+BasicBlock *NewLeafBlock(CaseRange &Leaf, Value *Val, ConstantInt *LowerBound,
+ ConstantInt *UpperBound, BasicBlock *OrigBlock,
+ BasicBlock *Default) {
+ Function *F = OrigBlock->getParent();
+ BasicBlock *NewLeaf = BasicBlock::Create(Val->getContext(), "LeafBlock");
+ F->insert(++OrigBlock->getIterator(), 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 (Leaf.Low == LowerBound) {
+ // Val >= Min && Val <= Hi --> Val <= Hi
+ Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High,
+ "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()) {
+ // 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.BB;
+ BranchInst::Create(Succ, Default, Comp, NewLeaf);
+
+ // Update the PHI incoming value/block for the default.
+ for (auto &I : Default->phis()) {
+ PHINode *PN = cast<PHINode>(&I);
+ auto *V = PN->getIncomingValueForBlock(OrigBlock);
+ PN->addIncoming(V, 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
+ APInt Range = Leaf.High->getValue() - Leaf.Low->getValue();
+ for (APInt j(Range.getBitWidth(), 0, true); j.slt(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;
+}
+
+/// 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 *SwitchConvert(CaseItr Begin, CaseItr End, ConstantInt *LowerBound,
+ ConstantInt *UpperBound, Value *Val,
+ BasicBlock *Predecessor, BasicBlock *OrigBlock,
+ BasicBlock *Default,
+ const std::vector<IntRange> &UnreachableRanges) {
+ assert(LowerBound && UpperBound && "Bounds must be initialized");
+ unsigned Size = End - Begin;
+
+ 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) {
+ APInt NumMergedCases = UpperBound->getValue() - LowerBound->getValue();
+ FixPhis(Begin->BB, OrigBlock, Predecessor, NumMergedCases);
+ return Begin->BB;
+ }
+ return NewLeafBlock(*Begin, Val, LowerBound, UpperBound, OrigBlock,
+ Default);
+ }
+
+ unsigned Mid = Size / 2;
+ std::vector<CaseRange> LHS(Begin, Begin + Mid);
+ LLVM_DEBUG(dbgs() << "LHS: " << LHS << "\n");
+ std::vector<CaseRange> RHS(Begin + Mid, End);
+ LLVM_DEBUG(dbgs() << "RHS: " << RHS << "\n");
+
+ CaseRange &Pivot = *(Begin + Mid);
+ LLVM_DEBUG(dbgs() << "Pivot ==> [" << Pivot.Low->getValue() << ", "
+ << 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 = Pivot.Low;
+
+ // 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.
+ APInt GapLow = LHS.back().High->getValue() + 1;
+ APInt GapHigh = NewLowerBound->getValue() - 1;
+ IntRange Gap = {GapLow, GapHigh};
+ if (GapHigh.sge(GapLow) && IsInRanges(Gap, UnreachableRanges))
+ NewUpperBound = LHS.back().High;
+ }
+
+ LLVM_DEBUG(dbgs() << "LHS Bounds ==> [" << LowerBound->getValue() << ", "
+ << NewUpperBound->getValue() << "]\n"
+ << "RHS Bounds ==> [" << NewLowerBound->getValue() << ", "
+ << UpperBound->getValue() << "]\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 = BasicBlock::Create(Val->getContext(), "NodeBlock");
+
+ 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);
+
+ F->insert(++OrigBlock->getIterator(), NewNode);
+ Comp->insertInto(NewNode, NewNode->end());
+
+ BranchInst::Create(LBranch, RBranch, Comp, NewNode);
+ return NewNode;
+}
+
+/// 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 Clusterify(CaseVector &Cases, SwitchInst *SI) {
+ unsigned NumSimpleCases = 0;
+
+ // Start with "simple" cases
+ for (auto Case : SI->cases()) {
+ if (Case.getCaseSuccessor() == SI->getDefaultDest())
+ continue;
+ Cases.push_back(CaseRange(Case.getCaseValue(), Case.getCaseValue(),
+ Case.getCaseSuccessor()));
+ ++NumSimpleCases;
+ }
+
+ llvm::sort(Cases, CaseCmp());
+
+ // Merge case into clusters
+ if (Cases.size() >= 2) {
+ CaseItr I = Cases.begin();
+ for (CaseItr J = std::next(I), E = Cases.end(); J != E; ++J) {
+ const APInt &nextValue = J->Low->getValue();
+ const APInt &currentValue = I->High->getValue();
+ BasicBlock *nextBB = J->BB;
+ BasicBlock *currentBB = I->BB;
+
+ // If the two neighboring cases go to the same destination, merge them
+ // into a single case.
+ assert(nextValue.sgt(currentValue) &&
+ "Cases should be strictly ascending");
+ if ((nextValue == currentValue + 1) && (currentBB == nextBB)) {
+ I->High = J->High;
+ // FIXME: Combine branch weights.
+ } else if (++I != J) {
+ *I = *J;
+ }
+ }
+ Cases.erase(std::next(I), Cases.end());
+ }
+
+ return NumSimpleCases;
+}
+
+/// Replace the specified switch instruction with a sequence of chained if-then
+/// insts in a balanced binary search.
+void ProcessSwitchInst(SwitchInst *SI,
+ SmallPtrSetImpl<BasicBlock *> &DeleteList,
+ AssumptionCache *AC, LazyValueInfo *LVI) {
+ BasicBlock *OrigBlock = SI->getParent();
+ Function *F = OrigBlock->getParent();
+ Value *Val = SI->getCondition(); // The value we are switching on...
+ BasicBlock *Default = SI->getDefaultDest();
+
+ // Don't handle unreachable blocks. If there are successors with phis, this
+ // would leave them behind with missing predecessors.
+ if ((OrigBlock != &F->getEntryBlock() && pred_empty(OrigBlock)) ||
+ OrigBlock->getSinglePredecessor() == OrigBlock) {
+ DeleteList.insert(OrigBlock);
+ return;
+ }
+
+ // Prepare cases vector.
+ CaseVector Cases;
+ const unsigned NumSimpleCases = Clusterify(Cases, SI);
+ IntegerType *IT = cast<IntegerType>(SI->getCondition()->getType());
+ const unsigned BitWidth = IT->getBitWidth();
+ // Explictly use higher precision to prevent unsigned overflow where
+ // `UnsignedMax - 0 + 1 == 0`
+ APInt UnsignedZero(BitWidth + 1, 0);
+ APInt UnsignedMax = APInt::getMaxValue(BitWidth);
+ 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 (Cases.empty()) {
+ BranchInst::Create(Default, OrigBlock);
+ // Remove all the references from Default's PHIs to OrigBlock, but one.
+ FixPhis(Default, OrigBlock, OrigBlock, UnsignedMax);
+ SI->eraseFromParent();
+ return;
+ }
+
+ ConstantInt *LowerBound = nullptr;
+ ConstantInt *UpperBound = nullptr;
+ bool DefaultIsUnreachableFromSwitch = false;
+
+ if (isa<UnreachableInst>(Default->getFirstNonPHIOrDbg())) {
+ // 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
+ // values.
+ LowerBound = Cases.front().Low;
+ 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);
+ // TODO Shouldn't this create a signed range?
+ ConstantRange KnownBitsRange =
+ ConstantRange::fromKnownBits(Known, /*IsSigned=*/false);
+ const ConstantRange LVIRange = LVI->getConstantRange(Val, 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.
+ const APInt &Low = Cases.front().Low->getValue();
+ const 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 *, APInt> Popularity;
+ APInt MaxPop(UnsignedZero);
+ BasicBlock *PopSucc = nullptr;
+
+ APInt SignedMax = APInt::getSignedMaxValue(BitWidth);
+ APInt SignedMin = APInt::getSignedMinValue(BitWidth);
+ IntRange R = {SignedMin, SignedMax};
+ UnreachableRanges.push_back(R);
+ for (const auto &I : Cases) {
+ const APInt &Low = I.Low->getValue();
+ const APInt &High = I.High->getValue();
+
+ IntRange &LastRange = UnreachableRanges.back();
+ if (LastRange.Low.eq(Low)) {
+ // There is nothing left of the previous range.
+ UnreachableRanges.pop_back();
+ } else {
+ // Terminate the previous range.
+ assert(Low.sgt(LastRange.Low));
+ LastRange.High = Low - 1;
+ }
+ if (High.ne(SignedMax)) {
+ IntRange R = {High + 1, SignedMax};
+ UnreachableRanges.push_back(R);
+ }
+
+ // Count popularity.
+ assert(High.sge(Low) && "Popularity shouldn't be negative.");
+ APInt N = High.sext(BitWidth + 1) - Low.sext(BitWidth + 1) + 1;
+ // Explict insert to make sure the bitwidth of APInts match
+ APInt &Pop = Popularity.insert({I.BB, APInt(UnsignedZero)}).first->second;
+ if ((Pop += N).ugt(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.sle(I->High));
+ auto Next = I + 1;
+ if (Next != E) {
+ assert(Next->Low.sgt(I->High));
+ }
+ }
+#endif
+
+ // As the default block in the switch is unreachable, update the PHI nodes
+ // (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);
+
+ // Use the most popular block as the new default, reducing the number of
+ // cases.
+ Default = PopSucc;
+ llvm::erase_if(Cases,
+ [PopSucc](const CaseRange &R) { return R.BB == PopSucc; });
+
+ // If there are no cases left, just branch.
+ if (Cases.empty()) {
+ BranchInst::Create(Default, OrigBlock);
+ SI->eraseFromParent();
+ // As all the cases have been replaced with a single branch, only keep
+ // one entry in the PHI nodes.
+ if (!MaxPop.isZero())
+ for (APInt I(UnsignedZero); I.ult(MaxPop - 1); ++I)
+ PopSucc->removePredecessor(OrigBlock);
+ return;
+ }
+
+ // If the condition was a PHI node with the switch block as a predecessor
+ // removing predecessors may have caused the condition to be erased.
+ // Getting the condition value again here protects against that.
+ Val = SI->getCondition();
+ }
+
+ BasicBlock *SwitchBlock =
+ SwitchConvert(Cases.begin(), Cases.end(), LowerBound, UpperBound, Val,
+ OrigBlock, OrigBlock, Default, UnreachableRanges);
+
+ // We have added incoming values for newly-created predecessors in
+ // NewLeafBlock(). The only meaningful work we offload to FixPhis() is to
+ // remove the incoming values from OrigBlock. There might be a special case
+ // that SwitchBlock is the same as Default, under which the PHIs in Default
+ // are fixed inside SwitchConvert().
+ if (SwitchBlock != Default)
+ FixPhis(Default, OrigBlock, nullptr, UnsignedMax);
+
+ // 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();
+ SI->eraseFromParent();
+
+ // If the Default block has no more predecessors just add it to DeleteList.
+ if (pred_empty(OldDefault))
+ DeleteList.insert(OldDefault);
+}
+
+bool LowerSwitch(Function &F, LazyValueInfo *LVI, AssumptionCache *AC) {
+ bool Changed = false;
+ SmallPtrSet<BasicBlock *, 8> DeleteList;
+
+ // We use make_early_inc_range here so that we don't traverse new blocks.
+ for (BasicBlock &Cur : llvm::make_early_inc_range(F)) {
+ // If the block is a dead Default block that will be deleted later, don't
+ // waste time processing it.
+ if (DeleteList.count(&Cur))
+ continue;
+
+ if (SwitchInst *SI = dyn_cast<SwitchInst>(Cur.getTerminator())) {
+ Changed = true;
+ ProcessSwitchInst(SI, DeleteList, AC, LVI);
+ }
+ }
+
+ for (BasicBlock *BB : DeleteList) {
+ LVI->eraseBlock(BB);
+ DeleteDeadBlock(BB);
+ }
+
+ return Changed;
+}
+
+/// Replace all SwitchInst instructions with chained branch instructions.
+class LowerSwitchLegacyPass : public FunctionPass {
+public:
+ // Pass identification, replacement for typeid
+ static char ID;
+
+ LowerSwitchLegacyPass() : FunctionPass(ID) {
+ initializeLowerSwitchLegacyPassPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnFunction(Function &F) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<LazyValueInfoWrapperPass>();
+ }
+};
+
+} // end anonymous namespace
+
+char LowerSwitchLegacyPass::ID = 0;
+
+// Publicly exposed interface to pass...
+char &llvm::LowerSwitchID = LowerSwitchLegacyPass::ID;
+
+INITIALIZE_PASS_BEGIN(LowerSwitchLegacyPass, "lowerswitch",
+ "Lower SwitchInst's to branches", false, false)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(LazyValueInfoWrapperPass)
+INITIALIZE_PASS_END(LowerSwitchLegacyPass, "lowerswitch",
+ "Lower SwitchInst's to branches", false, false)
+
+// createLowerSwitchPass - Interface to this file...
+FunctionPass *llvm::createLowerSwitchPass() {
+ return new LowerSwitchLegacyPass();
+}
+
+bool LowerSwitchLegacyPass::runOnFunction(Function &F) {
+ LazyValueInfo *LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
+ auto *ACT = getAnalysisIfAvailable<AssumptionCacheTracker>();
+ AssumptionCache *AC = ACT ? &ACT->getAssumptionCache(F) : nullptr;
+ return LowerSwitch(F, LVI, AC);
+}
+
+PreservedAnalyses LowerSwitchPass::run(Function &F,
+ FunctionAnalysisManager &AM) {
+ LazyValueInfo *LVI = &AM.getResult<LazyValueAnalysis>(F);
+ AssumptionCache *AC = AM.getCachedResult<AssumptionAnalysis>(F);
+ return LowerSwitch(F, LVI, AC) ? PreservedAnalyses::none()
+ : PreservedAnalyses::all();
+}
generated by cgit v1.2.3 (git 2.25.1) at 2025-10-21 04:02:14 +0000