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llvm-project/llvm/lib/Transforms/Scalar/StructurizeCFG.cpp

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//===-- StructurizeCFG.cpp ------------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/RegionInfo.h"
#include "llvm/Analysis/RegionIterator.h"
#include "llvm/Analysis/RegionPass.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
using namespace llvm;
using namespace llvm::PatternMatch;
#define DEBUG_TYPE "structurizecfg"
namespace {
// Definition of the complex types used in this pass.
typedef std::pair<BasicBlock *, Value *> BBValuePair;
typedef SmallVector<RegionNode*, 8> RNVector;
typedef SmallVector<BasicBlock*, 8> BBVector;
typedef SmallVector<BranchInst*, 8> BranchVector;
typedef SmallVector<BBValuePair, 2> BBValueVector;
typedef SmallPtrSet<BasicBlock *, 8> BBSet;
typedef MapVector<PHINode *, BBValueVector> PhiMap;
typedef MapVector<BasicBlock *, BBVector> BB2BBVecMap;
typedef DenseMap<DomTreeNode *, unsigned> DTN2UnsignedMap;
typedef DenseMap<BasicBlock *, PhiMap> BBPhiMap;
typedef DenseMap<BasicBlock *, Value *> BBPredicates;
typedef DenseMap<BasicBlock *, BBPredicates> PredMap;
typedef DenseMap<BasicBlock *, BasicBlock*> BB2BBMap;
// The name for newly created blocks.
static const char *const FlowBlockName = "Flow";
/// @brief Find the nearest common dominator for multiple BasicBlocks
///
/// Helper class for StructurizeCFG
/// TODO: Maybe move into common code
class NearestCommonDominator {
DominatorTree *DT;
DTN2UnsignedMap IndexMap;
BasicBlock *Result;
unsigned ResultIndex;
bool ExplicitMentioned;
public:
/// \brief Start a new query
NearestCommonDominator(DominatorTree *DomTree) {
DT = DomTree;
Result = nullptr;
}
/// \brief Add BB to the resulting dominator
void addBlock(BasicBlock *BB, bool Remember = true) {
DomTreeNode *Node = DT->getNode(BB);
if (!Result) {
unsigned Numbering = 0;
for (;Node;Node = Node->getIDom())
IndexMap[Node] = ++Numbering;
Result = BB;
ResultIndex = 1;
ExplicitMentioned = Remember;
return;
}
for (;Node;Node = Node->getIDom())
if (IndexMap.count(Node))
break;
else
IndexMap[Node] = 0;
assert(Node && "Dominator tree invalid!");
unsigned Numbering = IndexMap[Node];
if (Numbering > ResultIndex) {
Result = Node->getBlock();
ResultIndex = Numbering;
ExplicitMentioned = Remember && (Result == BB);
} else if (Numbering == ResultIndex) {
ExplicitMentioned |= Remember;
}
}
/// \brief Is "Result" one of the BBs added with "Remember" = True?
bool wasResultExplicitMentioned() {
return ExplicitMentioned;
}
/// \brief Get the query result
BasicBlock *getResult() {
return Result;
}
};
/// @brief Transforms the control flow graph on one single entry/exit region
/// at a time.
///
/// After the transform all "If"/"Then"/"Else" style control flow looks like
/// this:
///
/// \verbatim
/// 1
/// ||
/// | |
/// 2 |
/// | /
/// |/
/// 3
/// || Where:
/// | | 1 = "If" block, calculates the condition
/// 4 | 2 = "Then" subregion, runs if the condition is true
/// | / 3 = "Flow" blocks, newly inserted flow blocks, rejoins the flow
/// |/ 4 = "Else" optional subregion, runs if the condition is false
/// 5 5 = "End" block, also rejoins the control flow
/// \endverbatim
///
/// Control flow is expressed as a branch where the true exit goes into the
/// "Then"/"Else" region, while the false exit skips the region
/// The condition for the optional "Else" region is expressed as a PHI node.
/// The incomming values of the PHI node are true for the "If" edge and false
/// for the "Then" edge.
///
/// Additionally to that even complicated loops look like this:
///
/// \verbatim
/// 1
/// ||
/// | |
/// 2 ^ Where:
/// | / 1 = "Entry" block
/// |/ 2 = "Loop" optional subregion, with all exits at "Flow" block
/// 3 3 = "Flow" block, with back edge to entry block
/// |
/// \endverbatim
///
/// The back edge of the "Flow" block is always on the false side of the branch
/// while the true side continues the general flow. So the loop condition
/// consist of a network of PHI nodes where the true incoming values expresses
/// breaks and the false values expresses continue states.
class StructurizeCFG : public RegionPass {
Type *Boolean;
ConstantInt *BoolTrue;
ConstantInt *BoolFalse;
UndefValue *BoolUndef;
Function *Func;
Region *ParentRegion;
DominatorTree *DT;
LoopInfo *LI;
RNVector Order;
BBSet Visited;
BBPhiMap DeletedPhis;
BB2BBVecMap AddedPhis;
PredMap Predicates;
BranchVector Conditions;
BB2BBMap Loops;
PredMap LoopPreds;
BranchVector LoopConds;
RegionNode *PrevNode;
void orderNodes();
void analyzeLoops(RegionNode *N);
Value *invert(Value *Condition);
Value *buildCondition(BranchInst *Term, unsigned Idx, bool Invert);
void gatherPredicates(RegionNode *N);
void collectInfos();
void insertConditions(bool Loops);
void delPhiValues(BasicBlock *From, BasicBlock *To);
void addPhiValues(BasicBlock *From, BasicBlock *To);
void setPhiValues();
void killTerminator(BasicBlock *BB);
void changeExit(RegionNode *Node, BasicBlock *NewExit,
bool IncludeDominator);
BasicBlock *getNextFlow(BasicBlock *Dominator);
BasicBlock *needPrefix(bool NeedEmpty);
BasicBlock *needPostfix(BasicBlock *Flow, bool ExitUseAllowed);
void setPrevNode(BasicBlock *BB);
bool dominatesPredicates(BasicBlock *BB, RegionNode *Node);
bool isPredictableTrue(RegionNode *Node);
void wireFlow(bool ExitUseAllowed, BasicBlock *LoopEnd);
void handleLoops(bool ExitUseAllowed, BasicBlock *LoopEnd);
void createFlow();
void rebuildSSA();
public:
static char ID;
StructurizeCFG() :
RegionPass(ID) {
initializeStructurizeCFGPass(*PassRegistry::getPassRegistry());
}
using Pass::doInitialization;
bool doInitialization(Region *R, RGPassManager &RGM) override;
bool runOnRegion(Region *R, RGPassManager &RGM) override;
const char *getPassName() const override {
return "Structurize control flow";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequiredID(LowerSwitchID);
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<LoopInfoWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
RegionPass::getAnalysisUsage(AU);
}
};
} // end anonymous namespace
char StructurizeCFG::ID = 0;
INITIALIZE_PASS_BEGIN(StructurizeCFG, "structurizecfg", "Structurize the CFG",
false, false)
INITIALIZE_PASS_DEPENDENCY(LowerSwitch)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(RegionInfoPass)
INITIALIZE_PASS_END(StructurizeCFG, "structurizecfg", "Structurize the CFG",
false, false)
/// \brief Initialize the types and constants used in the pass
bool StructurizeCFG::doInitialization(Region *R, RGPassManager &RGM) {
LLVMContext &Context = R->getEntry()->getContext();
Boolean = Type::getInt1Ty(Context);
BoolTrue = ConstantInt::getTrue(Context);
BoolFalse = ConstantInt::getFalse(Context);
BoolUndef = UndefValue::get(Boolean);
return false;
}
/// \brief Build up the general order of nodes
void StructurizeCFG::orderNodes() {
RNVector TempOrder;
ReversePostOrderTraversal<Region*> RPOT(ParentRegion);
TempOrder.append(RPOT.begin(), RPOT.end());
std::map<Loop*, unsigned> LoopBlocks;
// The reverse post-order traversal of the list gives us an ordering close
// to what we want. The only problem with it is that sometimes backedges
// for outer loops will be visited before backedges for inner loops.
for (RegionNode *RN : TempOrder) {
BasicBlock *BB = RN->getEntry();
Loop *Loop = LI->getLoopFor(BB);
if (!LoopBlocks.count(Loop)) {
LoopBlocks[Loop] = 1;
continue;
}
LoopBlocks[Loop]++;
}
unsigned CurrentLoopDepth = 0;
Loop *CurrentLoop = nullptr;
BBSet TempVisited;
for (RNVector::iterator I = TempOrder.begin(), E = TempOrder.end(); I != E; ++I) {
BasicBlock *BB = (*I)->getEntry();
unsigned LoopDepth = LI->getLoopDepth(BB);
if (std::find(Order.begin(), Order.end(), *I) != Order.end())
continue;
if (LoopDepth < CurrentLoopDepth) {
// Make sure we have visited all blocks in this loop before moving back to
// the outer loop.
RNVector::iterator LoopI = I;
while(LoopBlocks[CurrentLoop]) {
LoopI++;
BasicBlock *LoopBB = (*LoopI)->getEntry();
if (LI->getLoopFor(LoopBB) == CurrentLoop) {
LoopBlocks[CurrentLoop]--;
Order.push_back(*LoopI);
}
}
}
CurrentLoop = LI->getLoopFor(BB);
if (CurrentLoop) {
LoopBlocks[CurrentLoop]--;
}
CurrentLoopDepth = LoopDepth;
Order.push_back(*I);
}
// This pass originally used a post-order traversal and then operated on
// the list in reverse. Now that we are using a reverse post-order traversal
// rather than re-working the whole pass to operate on the list in order,
// we just reverse the list and continue to operate on it in reverse.
std::reverse(Order.begin(), Order.end());
}
/// \brief Determine the end of the loops
void StructurizeCFG::analyzeLoops(RegionNode *N) {
if (N->isSubRegion()) {
// Test for exit as back edge
BasicBlock *Exit = N->getNodeAs<Region>()->getExit();
if (Visited.count(Exit))
Loops[Exit] = N->getEntry();
} else {
// Test for sucessors as back edge
BasicBlock *BB = N->getNodeAs<BasicBlock>();
BranchInst *Term = cast<BranchInst>(BB->getTerminator());
for (BasicBlock *Succ : Term->successors())
if (Visited.count(Succ))
Loops[Succ] = BB;
}
}
/// \brief Invert the given condition
Value *StructurizeCFG::invert(Value *Condition) {
// First: Check if it's a constant
if (Condition == BoolTrue)
return BoolFalse;
if (Condition == BoolFalse)
return BoolTrue;
if (Condition == BoolUndef)
return BoolUndef;
// Second: If the condition is already inverted, return the original value
if (match(Condition, m_Not(m_Value(Condition))))
return Condition;
if (Instruction *Inst = dyn_cast<Instruction>(Condition)) {
// Third: Check all the users for an invert
BasicBlock *Parent = Inst->getParent();
for (User *U : Condition->users())
if (Instruction *I = dyn_cast<Instruction>(U))
if (I->getParent() == Parent && match(I, m_Not(m_Specific(Condition))))
return I;
// Last option: Create a new instruction
return BinaryOperator::CreateNot(Condition, "", Parent->getTerminator());
}
if (Argument *Arg = dyn_cast<Argument>(Condition)) {
BasicBlock &EntryBlock = Arg->getParent()->getEntryBlock();
return BinaryOperator::CreateNot(Condition,
Arg->getName() + ".inv",
EntryBlock.getTerminator());
}
llvm_unreachable("Unhandled condition to invert");
}
/// \brief Build the condition for one edge
Value *StructurizeCFG::buildCondition(BranchInst *Term, unsigned Idx,
bool Invert) {
Value *Cond = Invert ? BoolFalse : BoolTrue;
if (Term->isConditional()) {
Cond = Term->getCondition();
if (Idx != (unsigned)Invert)
Cond = invert(Cond);
}
return Cond;
}
/// \brief Analyze the predecessors of each block and build up predicates
void StructurizeCFG::gatherPredicates(RegionNode *N) {
RegionInfo *RI = ParentRegion->getRegionInfo();
BasicBlock *BB = N->getEntry();
BBPredicates &Pred = Predicates[BB];
BBPredicates &LPred = LoopPreds[BB];
for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
PI != PE; ++PI) {
// Ignore it if it's a branch from outside into our region entry
if (!ParentRegion->contains(*PI))
continue;
Region *R = RI->getRegionFor(*PI);
if (R == ParentRegion) {
// It's a top level block in our region
BranchInst *Term = cast<BranchInst>((*PI)->getTerminator());
for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
BasicBlock *Succ = Term->getSuccessor(i);
if (Succ != BB)
continue;
if (Visited.count(*PI)) {
// Normal forward edge
if (Term->isConditional()) {
// Try to treat it like an ELSE block
BasicBlock *Other = Term->getSuccessor(!i);
if (Visited.count(Other) && !Loops.count(Other) &&
!Pred.count(Other) && !Pred.count(*PI)) {
Pred[Other] = BoolFalse;
Pred[*PI] = BoolTrue;
continue;
}
}
Pred[*PI] = buildCondition(Term, i, false);
} else {
// Back edge
LPred[*PI] = buildCondition(Term, i, true);
}
}
} else {
// It's an exit from a sub region
while (R->getParent() != ParentRegion)
R = R->getParent();
// Edge from inside a subregion to its entry, ignore it
if (*R == *N)
continue;
BasicBlock *Entry = R->getEntry();
if (Visited.count(Entry))
Pred[Entry] = BoolTrue;
else
LPred[Entry] = BoolFalse;
}
}
}
/// \brief Collect various loop and predicate infos
void StructurizeCFG::collectInfos() {
// Reset predicate
Predicates.clear();
// and loop infos
Loops.clear();
LoopPreds.clear();
// Reset the visited nodes
Visited.clear();
for (RNVector::reverse_iterator OI = Order.rbegin(), OE = Order.rend();
OI != OE; ++OI) {
DEBUG(dbgs() << "Visiting: " <<
((*OI)->isSubRegion() ? "SubRegion with entry: " : "") <<
(*OI)->getEntry()->getName() << " Loop Depth: " << LI->getLoopDepth((*OI)->getEntry()) << "\n");
// Analyze all the conditions leading to a node
gatherPredicates(*OI);
// Remember that we've seen this node
Visited.insert((*OI)->getEntry());
// Find the last back edges
analyzeLoops(*OI);
}
}
/// \brief Insert the missing branch conditions
void StructurizeCFG::insertConditions(bool Loops) {
BranchVector &Conds = Loops ? LoopConds : Conditions;
Value *Default = Loops ? BoolTrue : BoolFalse;
SSAUpdater PhiInserter;
for (BranchInst *Term : Conds) {
assert(Term->isConditional());
BasicBlock *Parent = Term->getParent();
BasicBlock *SuccTrue = Term->getSuccessor(0);
BasicBlock *SuccFalse = Term->getSuccessor(1);
PhiInserter.Initialize(Boolean, "");
PhiInserter.AddAvailableValue(&Func->getEntryBlock(), Default);
PhiInserter.AddAvailableValue(Loops ? SuccFalse : Parent, Default);
BBPredicates &Preds = Loops ? LoopPreds[SuccFalse] : Predicates[SuccTrue];
NearestCommonDominator Dominator(DT);
Dominator.addBlock(Parent, false);
Value *ParentValue = nullptr;
for (BBPredicates::iterator PI = Preds.begin(), PE = Preds.end();
PI != PE; ++PI) {
if (PI->first == Parent) {
ParentValue = PI->second;
break;
}
PhiInserter.AddAvailableValue(PI->first, PI->second);
Dominator.addBlock(PI->first);
}
if (ParentValue) {
Term->setCondition(ParentValue);
} else {
if (!Dominator.wasResultExplicitMentioned())
PhiInserter.AddAvailableValue(Dominator.getResult(), Default);
Term->setCondition(PhiInserter.GetValueInMiddleOfBlock(Parent));
}
}
}
/// \brief Remove all PHI values coming from "From" into "To" and remember
/// them in DeletedPhis
void StructurizeCFG::delPhiValues(BasicBlock *From, BasicBlock *To) {
PhiMap &Map = DeletedPhis[To];
for (BasicBlock::iterator I = To->begin(), E = To->end();
I != E && isa<PHINode>(*I);) {
PHINode &Phi = cast<PHINode>(*I++);
while (Phi.getBasicBlockIndex(From) != -1) {
Value *Deleted = Phi.removeIncomingValue(From, false);
Map[&Phi].push_back(std::make_pair(From, Deleted));
}
}
}
/// \brief Add a dummy PHI value as soon as we knew the new predecessor
void StructurizeCFG::addPhiValues(BasicBlock *From, BasicBlock *To) {
for (BasicBlock::iterator I = To->begin(), E = To->end();
I != E && isa<PHINode>(*I);) {
PHINode &Phi = cast<PHINode>(*I++);
Value *Undef = UndefValue::get(Phi.getType());
Phi.addIncoming(Undef, From);
}
AddedPhis[To].push_back(From);
}
/// \brief Add the real PHI value as soon as everything is set up
void StructurizeCFG::setPhiValues() {
SSAUpdater Updater;
for (BB2BBVecMap::iterator AI = AddedPhis.begin(), AE = AddedPhis.end();
AI != AE; ++AI) {
BasicBlock *To = AI->first;
BBVector &From = AI->second;
if (!DeletedPhis.count(To))
continue;
PhiMap &Map = DeletedPhis[To];
for (PhiMap::iterator PI = Map.begin(), PE = Map.end();
PI != PE; ++PI) {
PHINode *Phi = PI->first;
Value *Undef = UndefValue::get(Phi->getType());
Updater.Initialize(Phi->getType(), "");
Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
Updater.AddAvailableValue(To, Undef);
NearestCommonDominator Dominator(DT);
Dominator.addBlock(To, false);
for (BBValueVector::iterator VI = PI->second.begin(),
VE = PI->second.end(); VI != VE; ++VI) {
Updater.AddAvailableValue(VI->first, VI->second);
Dominator.addBlock(VI->first);
}
if (!Dominator.wasResultExplicitMentioned())
Updater.AddAvailableValue(Dominator.getResult(), Undef);
for (BBVector::iterator FI = From.begin(), FE = From.end();
FI != FE; ++FI) {
int Idx = Phi->getBasicBlockIndex(*FI);
assert(Idx != -1);
Phi->setIncomingValue(Idx, Updater.GetValueAtEndOfBlock(*FI));
}
}
DeletedPhis.erase(To);
}
assert(DeletedPhis.empty());
}
/// \brief Remove phi values from all successors and then remove the terminator.
void StructurizeCFG::killTerminator(BasicBlock *BB) {
TerminatorInst *Term = BB->getTerminator();
if (!Term)
return;
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
SI != SE; ++SI) {
delPhiValues(BB, *SI);
}
Term->eraseFromParent();
}
/// \brief Let node exit(s) point to NewExit
void StructurizeCFG::changeExit(RegionNode *Node, BasicBlock *NewExit,
bool IncludeDominator) {
if (Node->isSubRegion()) {
Region *SubRegion = Node->getNodeAs<Region>();
BasicBlock *OldExit = SubRegion->getExit();
BasicBlock *Dominator = nullptr;
// Find all the edges from the sub region to the exit
for (pred_iterator I = pred_begin(OldExit), E = pred_end(OldExit);
I != E;) {
BasicBlock *BB = *I++;
if (!SubRegion->contains(BB))
continue;
// Modify the edges to point to the new exit
delPhiValues(BB, OldExit);
BB->getTerminator()->replaceUsesOfWith(OldExit, NewExit);
addPhiValues(BB, NewExit);
// Find the new dominator (if requested)
if (IncludeDominator) {
if (!Dominator)
Dominator = BB;
else
Dominator = DT->findNearestCommonDominator(Dominator, BB);
}
}
// Change the dominator (if requested)
if (Dominator)
DT->changeImmediateDominator(NewExit, Dominator);
// Update the region info
SubRegion->replaceExit(NewExit);
} else {
BasicBlock *BB = Node->getNodeAs<BasicBlock>();
killTerminator(BB);
BranchInst::Create(NewExit, BB);
addPhiValues(BB, NewExit);
if (IncludeDominator)
DT->changeImmediateDominator(NewExit, BB);
}
}
/// \brief Create a new flow node and update dominator tree and region info
BasicBlock *StructurizeCFG::getNextFlow(BasicBlock *Dominator) {
LLVMContext &Context = Func->getContext();
BasicBlock *Insert = Order.empty() ? ParentRegion->getExit() :
Order.back()->getEntry();
BasicBlock *Flow = BasicBlock::Create(Context, FlowBlockName,
Func, Insert);
DT->addNewBlock(Flow, Dominator);
ParentRegion->getRegionInfo()->setRegionFor(Flow, ParentRegion);
return Flow;
}
/// \brief Create a new or reuse the previous node as flow node
BasicBlock *StructurizeCFG::needPrefix(bool NeedEmpty) {
BasicBlock *Entry = PrevNode->getEntry();
if (!PrevNode->isSubRegion()) {
killTerminator(Entry);
if (!NeedEmpty || Entry->getFirstInsertionPt() == Entry->end())
return Entry;
}
// create a new flow node
BasicBlock *Flow = getNextFlow(Entry);
// and wire it up
changeExit(PrevNode, Flow, true);
PrevNode = ParentRegion->getBBNode(Flow);
return Flow;
}
/// \brief Returns the region exit if possible, otherwise just a new flow node
BasicBlock *StructurizeCFG::needPostfix(BasicBlock *Flow,
bool ExitUseAllowed) {
if (Order.empty() && ExitUseAllowed) {
BasicBlock *Exit = ParentRegion->getExit();
DT->changeImmediateDominator(Exit, Flow);
addPhiValues(Flow, Exit);
return Exit;
}
return getNextFlow(Flow);
}
/// \brief Set the previous node
void StructurizeCFG::setPrevNode(BasicBlock *BB) {
PrevNode = ParentRegion->contains(BB) ? ParentRegion->getBBNode(BB)
: nullptr;
}
/// \brief Does BB dominate all the predicates of Node ?
bool StructurizeCFG::dominatesPredicates(BasicBlock *BB, RegionNode *Node) {
BBPredicates &Preds = Predicates[Node->getEntry()];
for (BBPredicates::iterator PI = Preds.begin(), PE = Preds.end();
PI != PE; ++PI) {
if (!DT->dominates(BB, PI->first))
return false;
}
return true;
}
/// \brief Can we predict that this node will always be called?
bool StructurizeCFG::isPredictableTrue(RegionNode *Node) {
BBPredicates &Preds = Predicates[Node->getEntry()];
bool Dominated = false;
// Regionentry is always true
if (!PrevNode)
return true;
for (BBPredicates::iterator I = Preds.begin(), E = Preds.end();
I != E; ++I) {
if (I->second != BoolTrue)
return false;
if (!Dominated && DT->dominates(I->first, PrevNode->getEntry()))
Dominated = true;
}
// TODO: The dominator check is too strict
return Dominated;
}
/// Take one node from the order vector and wire it up
void StructurizeCFG::wireFlow(bool ExitUseAllowed,
BasicBlock *LoopEnd) {
RegionNode *Node = Order.pop_back_val();
Visited.insert(Node->getEntry());
if (isPredictableTrue(Node)) {
// Just a linear flow
if (PrevNode) {
changeExit(PrevNode, Node->getEntry(), true);
}
PrevNode = Node;
} else {
// Insert extra prefix node (or reuse last one)
BasicBlock *Flow = needPrefix(false);
// Insert extra postfix node (or use exit instead)
BasicBlock *Entry = Node->getEntry();
BasicBlock *Next = needPostfix(Flow, ExitUseAllowed);
// let it point to entry and next block
Conditions.push_back(BranchInst::Create(Entry, Next, BoolUndef, Flow));
addPhiValues(Flow, Entry);
DT->changeImmediateDominator(Entry, Flow);
PrevNode = Node;
while (!Order.empty() && !Visited.count(LoopEnd) &&
dominatesPredicates(Entry, Order.back())) {
handleLoops(false, LoopEnd);
}
changeExit(PrevNode, Next, false);
setPrevNode(Next);
}
}
void StructurizeCFG::handleLoops(bool ExitUseAllowed,
BasicBlock *LoopEnd) {
RegionNode *Node = Order.back();
BasicBlock *LoopStart = Node->getEntry();
if (!Loops.count(LoopStart)) {
wireFlow(ExitUseAllowed, LoopEnd);
return;
}
if (!isPredictableTrue(Node))
LoopStart = needPrefix(true);
LoopEnd = Loops[Node->getEntry()];
wireFlow(false, LoopEnd);
while (!Visited.count(LoopEnd)) {
handleLoops(false, LoopEnd);
}
// If the start of the loop is the entry block, we can't branch to it so
// insert a new dummy entry block.
Function *LoopFunc = LoopStart->getParent();
if (LoopStart == &LoopFunc->getEntryBlock()) {
LoopStart->setName("entry.orig");
BasicBlock *NewEntry =
BasicBlock::Create(LoopStart->getContext(),
"entry",
LoopFunc,
LoopStart);
BranchInst::Create(LoopStart, NewEntry);
}
// Create an extra loop end node
LoopEnd = needPrefix(false);
BasicBlock *Next = needPostfix(LoopEnd, ExitUseAllowed);
LoopConds.push_back(BranchInst::Create(Next, LoopStart,
BoolUndef, LoopEnd));
addPhiValues(LoopEnd, LoopStart);
setPrevNode(Next);
}
/// After this function control flow looks like it should be, but
/// branches and PHI nodes only have undefined conditions.
void StructurizeCFG::createFlow() {
BasicBlock *Exit = ParentRegion->getExit();
bool EntryDominatesExit = DT->dominates(ParentRegion->getEntry(), Exit);
DeletedPhis.clear();
AddedPhis.clear();
Conditions.clear();
LoopConds.clear();
PrevNode = nullptr;
Visited.clear();
while (!Order.empty()) {
handleLoops(EntryDominatesExit, nullptr);
}
if (PrevNode)
changeExit(PrevNode, Exit, EntryDominatesExit);
else
assert(EntryDominatesExit);
}
/// Handle a rare case where the disintegrated nodes instructions
/// no longer dominate all their uses. Not sure if this is really nessasary
void StructurizeCFG::rebuildSSA() {
SSAUpdater Updater;
for (auto *BB : ParentRegion->blocks())
for (BasicBlock::iterator II = BB->begin(), IE = BB->end();
II != IE; ++II) {
bool Initialized = false;
for (auto I = II->use_begin(), E = II->use_end(); I != E;) {
Use &U = *I++;
Instruction *User = cast<Instruction>(U.getUser());
if (User->getParent() == BB) {
continue;
} else if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
if (UserPN->getIncomingBlock(U) == BB)
continue;
}
if (DT->dominates(II, User))
continue;
if (!Initialized) {
Value *Undef = UndefValue::get(II->getType());
Updater.Initialize(II->getType(), "");
Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
Updater.AddAvailableValue(BB, II);
Initialized = true;
}
Updater.RewriteUseAfterInsertions(U);
}
}
}
/// \brief Run the transformation for each region found
bool StructurizeCFG::runOnRegion(Region *R, RGPassManager &RGM) {
if (R->isTopLevelRegion())
return false;
Func = R->getEntry()->getParent();
ParentRegion = R;
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
orderNodes();
collectInfos();
createFlow();
insertConditions(false);
insertConditions(true);
setPhiValues();
rebuildSSA();
// Cleanup
Order.clear();
Visited.clear();
DeletedPhis.clear();
AddedPhis.clear();
Predicates.clear();
Conditions.clear();
Loops.clear();
LoopPreds.clear();
LoopConds.clear();
return true;
}
/// \brief Create the pass
Pass *llvm::createStructurizeCFGPass() {
return new StructurizeCFG();
}
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