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

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//===- LoopSimplify.cpp - Loop Canonicalization Pass ----------------------===//
//
// 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 pass performs several transformations to transform natural loops into a
// simpler form, which makes subsequent analyses and transformations simpler and
// more effective.
//
// Loop pre-header insertion guarantees that there is a single, non-critical
// entry edge from outside of the loop to the loop header. This simplifies a
// number of analyses and transformations, such as LICM.
//
// Loop exit-block insertion guarantees that all exit blocks from the loop
// (blocks which are outside of the loop that have predecessors inside of the
// loop) only have predecessors from inside of the loop (and are thus dominated
// by the loop header). This simplifies transformations such as store-sinking
// that are built into LICM.
//
// This pass also guarantees that loops will have exactly one backedge.
//
// Note that the simplifycfg pass will clean up blocks which are split out but
// end up being unnecessary, so usage of this pass should not pessimize
// generated code.
//
// This pass obviously modifies the CFG, but updates loop information and
// dominator information.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/Function.h"
#include "llvm/iTerminators.h"
#include "llvm/iPHINode.h"
#include "llvm/Constant.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Support/CFG.h"
#include "Support/SetOperations.h"
#include "Support/Statistic.h"
#include "Support/DepthFirstIterator.h"
using namespace llvm;
namespace {
Statistic<>
NumInserted("loopsimplify", "Number of pre-header or exit blocks inserted");
struct LoopSimplify : public FunctionPass {
virtual bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
// We need loop information to identify the loops...
AU.addRequired<LoopInfo>();
AU.addRequired<DominatorSet>();
AU.addPreserved<LoopInfo>();
AU.addPreserved<DominatorSet>();
AU.addPreserved<ImmediateDominators>();
AU.addPreserved<DominatorTree>();
AU.addPreserved<DominanceFrontier>();
AU.addPreservedID(BreakCriticalEdgesID); // No crit edges added....
}
private:
bool ProcessLoop(Loop *L);
BasicBlock *SplitBlockPredecessors(BasicBlock *BB, const char *Suffix,
const std::vector<BasicBlock*> &Preds);
void RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
void InsertPreheaderForLoop(Loop *L);
void InsertUniqueBackedgeBlock(Loop *L);
void UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
std::vector<BasicBlock*> &PredBlocks);
};
RegisterOpt<LoopSimplify>
X("loopsimplify", "Canonicalize natural loops", true);
}
// Publically exposed interface to pass...
const PassInfo *llvm::LoopSimplifyID = X.getPassInfo();
Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
/// runOnFunction - Run down all loops in the CFG (recursively, but we could do
/// it in any convenient order) inserting preheaders...
///
bool LoopSimplify::runOnFunction(Function &F) {
bool Changed = false;
LoopInfo &LI = getAnalysis<LoopInfo>();
for (LoopInfo::iterator I = LI.begin(), E = LI.end(); I != E; ++I)
Changed |= ProcessLoop(*I);
return Changed;
}
/// ProcessLoop - Walk the loop structure in depth first order, ensuring that
/// all loops have preheaders.
///
bool LoopSimplify::ProcessLoop(Loop *L) {
bool Changed = false;
// Does the loop already have a preheader? If so, don't modify the loop...
if (L->getLoopPreheader() == 0) {
InsertPreheaderForLoop(L);
NumInserted++;
Changed = true;
}
// Next, check to make sure that all exit nodes of the loop only have
// predecessors that are inside of the loop. This check guarantees that the
// loop preheader/header will dominate the exit blocks. If the exit block has
// predecessors from outside of the loop, split the edge now.
for (unsigned i = 0, e = L->getExitBlocks().size(); i != e; ++i) {
BasicBlock *ExitBlock = L->getExitBlocks()[i];
for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
PI != PE; ++PI)
if (!L->contains(*PI)) {
RewriteLoopExitBlock(L, ExitBlock);
NumInserted++;
Changed = true;
break;
}
}
// The preheader may have more than two predecessors at this point (from the
// preheader and from the backedges). To simplify the loop more, insert an
// extra back-edge block in the loop so that there is exactly one backedge.
if (L->getNumBackEdges() != 1) {
InsertUniqueBackedgeBlock(L);
NumInserted++;
Changed = true;
}
for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
Changed |= ProcessLoop(*I);
return Changed;
}
/// SplitBlockPredecessors - Split the specified block into two blocks. We want
/// to move the predecessors specified in the Preds list to point to the new
/// block, leaving the remaining predecessors pointing to BB. This method
/// updates the SSA PHINode's, but no other analyses.
///
BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB,
const char *Suffix,
const std::vector<BasicBlock*> &Preds) {
// Create new basic block, insert right before the original block...
BasicBlock *NewBB = new BasicBlock(BB->getName()+Suffix, BB->getParent(), BB);
// The preheader first gets an unconditional branch to the loop header...
BranchInst *BI = new BranchInst(BB, NewBB);
// For every PHI node in the block, insert a PHI node into NewBB where the
// incoming values from the out of loop edges are moved to NewBB. We have two
// possible cases here. If the loop is dead, we just insert dummy entries
// into the PHI nodes for the new edge. If the loop is not dead, we move the
// incoming edges in BB into new PHI nodes in NewBB.
//
if (!Preds.empty()) { // Is the loop not obviously dead?
// Check to see if the values being merged into the new block need PHI
// nodes. If so, insert them.
for (BasicBlock::iterator I = BB->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I) {
// Check to see if all of the values coming in are the same. If so, we
// don't need to create a new PHI node.
Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
for (unsigned i = 1, e = Preds.size(); i != e; ++i)
if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
InVal = 0;
break;
}
// If the values coming into the block are not the same, we need a PHI.
if (InVal == 0) {
// Create the new PHI node, insert it into NewBB at the end of the block
PHINode *NewPHI = new PHINode(PN->getType(), PN->getName()+".ph", BI);
// Move all of the edges from blocks outside the loop to the new PHI
for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
Value *V = PN->removeIncomingValue(Preds[i]);
NewPHI->addIncoming(V, Preds[i]);
}
InVal = NewPHI;
} else {
// Remove all of the edges coming into the PHI nodes from outside of the
// block.
for (unsigned i = 0, e = Preds.size(); i != e; ++i)
PN->removeIncomingValue(Preds[i], false);
}
// Add an incoming value to the PHI node in the loop for the preheader
// edge.
PN->addIncoming(InVal, NewBB);
}
// Now that the PHI nodes are updated, actually move the edges from
// Preds to point to NewBB instead of BB.
//
for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
TerminatorInst *TI = Preds[i]->getTerminator();
for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s)
if (TI->getSuccessor(s) == BB)
TI->setSuccessor(s, NewBB);
}
} else { // Otherwise the loop is dead...
for (BasicBlock::iterator I = BB->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I)
// Insert dummy values as the incoming value...
PN->addIncoming(Constant::getNullValue(PN->getType()), NewBB);
}
return NewBB;
}
// ChangeExitBlock - This recursive function is used to change any exit blocks
// that use OldExit to use NewExit instead. This is recursive because children
// may need to be processed as well.
//
static void ChangeExitBlock(Loop *L, BasicBlock *OldExit, BasicBlock *NewExit) {
if (L->hasExitBlock(OldExit)) {
L->changeExitBlock(OldExit, NewExit);
for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
ChangeExitBlock(*I, OldExit, NewExit);
}
}
/// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
/// preheader, this method is called to insert one. This method has two phases:
/// preheader insertion and analysis updating.
///
void LoopSimplify::InsertPreheaderForLoop(Loop *L) {
BasicBlock *Header = L->getHeader();
// Compute the set of predecessors of the loop that are not in the loop.
std::vector<BasicBlock*> OutsideBlocks;
for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
PI != PE; ++PI)
if (!L->contains(*PI)) // Coming in from outside the loop?
OutsideBlocks.push_back(*PI); // Keep track of it...
// Split out the loop pre-header
BasicBlock *NewBB =
SplitBlockPredecessors(Header, ".preheader", OutsideBlocks);
//===--------------------------------------------------------------------===//
// Update analysis results now that we have performed the transformation
//
// We know that we have loop information to update... update it now.
if (Loop *Parent = L->getParentLoop())
Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
// If the header for the loop used to be an exit node for another loop, then
// we need to update this to know that the loop-preheader is now the exit
// node. Note that the only loop that could have our header as an exit node
// is a sibling loop, ie, one with the same parent loop, or one if it's
// children.
//
LoopInfo::iterator ParentLoops, ParentLoopsE;
if (Loop *Parent = L->getParentLoop()) {
ParentLoops = Parent->begin();
ParentLoopsE = Parent->end();
} else { // Must check top-level loops...
ParentLoops = getAnalysis<LoopInfo>().begin();
ParentLoopsE = getAnalysis<LoopInfo>().end();
}
// Loop over all sibling loops, performing the substitution (recursively to
// include child loops)...
for (; ParentLoops != ParentLoopsE; ++ParentLoops)
ChangeExitBlock(*ParentLoops, Header, NewBB);
DominatorSet &DS = getAnalysis<DominatorSet>(); // Update dominator info
{
// The blocks that dominate NewBB are the blocks that dominate Header,
// minus Header, plus NewBB.
DominatorSet::DomSetType DomSet = DS.getDominators(Header);
DomSet.insert(NewBB); // We dominate ourself
DomSet.erase(Header); // Header does not dominate us...
DS.addBasicBlock(NewBB, DomSet);
// The newly created basic block dominates all nodes dominated by Header.
for (Function::iterator I = Header->getParent()->begin(),
E = Header->getParent()->end(); I != E; ++I)
if (DS.dominates(Header, I))
DS.addDominator(I, NewBB);
}
// Update immediate dominator information if we have it...
if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) {
// Whatever i-dominated the header node now immediately dominates NewBB
ID->addNewBlock(NewBB, ID->get(Header));
// The preheader now is the immediate dominator for the header node...
ID->setImmediateDominator(Header, NewBB);
}
// Update DominatorTree information if it is active.
if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
// The immediate dominator of the preheader is the immediate dominator of
// the old header.
//
DominatorTree::Node *HeaderNode = DT->getNode(Header);
DominatorTree::Node *PHNode = DT->createNewNode(NewBB,
HeaderNode->getIDom());
// Change the header node so that PNHode is the new immediate dominator
DT->changeImmediateDominator(HeaderNode, PHNode);
}
// Update dominance frontier information...
if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
// The DF(NewBB) is just (DF(Header)-Header), because NewBB dominates
// everything that Header does, and it strictly dominates Header in
// addition.
assert(DF->find(Header) != DF->end() && "Header node doesn't have DF set?");
DominanceFrontier::DomSetType NewDFSet = DF->find(Header)->second;
NewDFSet.erase(Header);
DF->addBasicBlock(NewBB, NewDFSet);
// Now we must loop over all of the dominance frontiers in the function,
// replacing occurrences of Header with NewBB in some cases. If a block
// dominates a (now) predecessor of NewBB, but did not strictly dominate
// Header, it will have Header in it's DF set, but should now have NewBB in
// its set.
for (unsigned i = 0, e = OutsideBlocks.size(); i != e; ++i) {
// Get all of the dominators of the predecessor...
const DominatorSet::DomSetType &PredDoms =
DS.getDominators(OutsideBlocks[i]);
for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(),
PDE = PredDoms.end(); PDI != PDE; ++PDI) {
BasicBlock *PredDom = *PDI;
// If the loop header is in DF(PredDom), then PredDom didn't dominate
// the header but did dominate a predecessor outside of the loop. Now
// we change this entry to include the preheader in the DF instead of
// the header.
DominanceFrontier::iterator DFI = DF->find(PredDom);
assert(DFI != DF->end() && "No dominance frontier for node?");
if (DFI->second.count(Header)) {
DF->removeFromFrontier(DFI, Header);
DF->addToFrontier(DFI, NewBB);
}
}
}
}
}
void LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
DominatorSet &DS = getAnalysis<DominatorSet>();
assert(std::find(L->getExitBlocks().begin(), L->getExitBlocks().end(), Exit)
!= L->getExitBlocks().end() && "Not a current exit block!");
std::vector<BasicBlock*> LoopBlocks;
for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
if (L->contains(*I))
LoopBlocks.push_back(*I);
assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
BasicBlock *NewBB = SplitBlockPredecessors(Exit, ".loopexit", LoopBlocks);
// Update Loop Information - we know that the new block will be in the parent
// loop of L.
if (Loop *Parent = L->getParentLoop())
Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
// Replace any instances of Exit with NewBB in this and any nested loops...
for (df_iterator<Loop*> I = df_begin(L), E = df_end(L); I != E; ++I)
if (I->hasExitBlock(Exit))
I->changeExitBlock(Exit, NewBB); // Update exit block information
// Update dominator information (set, immdom, domtree, and domfrontier)
UpdateDomInfoForRevectoredPreds(NewBB, LoopBlocks);
}
/// InsertUniqueBackedgeBlock - This method is called when the specified loop
/// has more than one backedge in it. If this occurs, revector all of these
/// backedges to target a new basic block and have that block branch to the loop
/// header. This ensures that loops have exactly one backedge.
///
void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L) {
assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
// Get information about the loop
BasicBlock *Preheader = L->getLoopPreheader();
BasicBlock *Header = L->getHeader();
Function *F = Header->getParent();
// Figure out which basic blocks contain back-edges to the loop header.
std::vector<BasicBlock*> BackedgeBlocks;
for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
if (*I != Preheader) BackedgeBlocks.push_back(*I);
// Create and insert the new backedge block...
BasicBlock *BEBlock = new BasicBlock(Header->getName()+".backedge", F);
BranchInst *BETerminator = new BranchInst(Header, BEBlock);
// Move the new backedge block to right after the last backedge block.
Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
// Now that the block has been inserted into the function, create PHI nodes in
// the backedge block which correspond to any PHI nodes in the header block.
for (BasicBlock::iterator I = Header->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I) {
PHINode *NewPN = new PHINode(PN->getType(), PN->getName()+".be",
BETerminator);
NewPN->op_reserve(2*BackedgeBlocks.size());
// Loop over the PHI node, moving all entries except the one for the
// preheader over to the new PHI node.
unsigned PreheaderIdx = ~0U;
bool HasUniqueIncomingValue = true;
Value *UniqueValue = 0;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *IBB = PN->getIncomingBlock(i);
Value *IV = PN->getIncomingValue(i);
if (IBB == Preheader) {
PreheaderIdx = i;
} else {
NewPN->addIncoming(IV, IBB);
if (HasUniqueIncomingValue) {
if (UniqueValue == 0)
UniqueValue = IV;
else if (UniqueValue != IV)
HasUniqueIncomingValue = false;
}
}
}
// Delete all of the incoming values from the old PN except the preheader's
assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
if (PreheaderIdx != 0) {
PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
}
PN->op_erase(PN->op_begin()+2, PN->op_end());
// Finally, add the newly constructed PHI node as the entry for the BEBlock.
PN->addIncoming(NewPN, BEBlock);
// As an optimization, if all incoming values in the new PhiNode (which is a
// subset of the incoming values of the old PHI node) have the same value,
// eliminate the PHI Node.
if (HasUniqueIncomingValue) {
NewPN->replaceAllUsesWith(UniqueValue);
BEBlock->getInstList().erase(NewPN);
}
}
// Now that all of the PHI nodes have been inserted and adjusted, modify the
// backedge blocks to just to the BEBlock instead of the header.
for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
if (TI->getSuccessor(Op) == Header)
TI->setSuccessor(Op, BEBlock);
}
//===--- Update all analyses which we must preserve now -----------------===//
// Update Loop Information - we know that this block is now in the current
// loop and all parent loops.
L->addBasicBlockToLoop(BEBlock, getAnalysis<LoopInfo>());
// Replace any instances of Exit with NewBB in this and any nested loops...
for (df_iterator<Loop*> I = df_begin(L), E = df_end(L); I != E; ++I)
if (I->hasExitBlock(Header))
I->changeExitBlock(Header, BEBlock); // Update exit block information
// Update dominator information (set, immdom, domtree, and domfrontier)
UpdateDomInfoForRevectoredPreds(BEBlock, BackedgeBlocks);
}
/// UpdateDomInfoForRevectoredPreds - This method is used to update the four
/// different kinds of dominator information (dominator sets, immediate
/// dominators, dominator trees, and dominance frontiers) after a new block has
/// been added to the CFG.
///
/// This only supports the case when an existing block (known as "NewBBSucc"),
/// had some of its predecessors factored into a new basic block. This
/// transformation inserts a new basic block ("NewBB"), with a single
/// unconditional branch to NewBBSucc, and moves some predecessors of
/// "NewBBSucc" to now branch to NewBB. These predecessors are listed in
/// PredBlocks, even though they are the same as
/// pred_begin(NewBB)/pred_end(NewBB).
///
void LoopSimplify::UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
std::vector<BasicBlock*> &PredBlocks) {
assert(!PredBlocks.empty() && "No predblocks??");
assert(succ_begin(NewBB) != succ_end(NewBB) &&
++succ_begin(NewBB) == succ_end(NewBB) &&
"NewBB should have a single successor!");
BasicBlock *NewBBSucc = *succ_begin(NewBB);
DominatorSet &DS = getAnalysis<DominatorSet>();
// The newly inserted basic block will dominate existing basic blocks iff the
// PredBlocks dominate all of the non-pred blocks. If all predblocks dominate
// the non-pred blocks, then they all must be the same block!
bool NewBBDominatesNewBBSucc = true;
{
BasicBlock *OnePred = PredBlocks[0];
for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i)
if (PredBlocks[i] != OnePred) {
NewBBDominatesNewBBSucc = false;
break;
}
if (NewBBDominatesNewBBSucc)
for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
PI != E; ++PI)
if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) {
NewBBDominatesNewBBSucc = false;
break;
}
}
// Update dominator information... The blocks that dominate NewBB are the
// intersection of the dominators of predecessors, plus the block itself.
// The newly created basic block does not dominate anything except itself.
//
DominatorSet::DomSetType NewBBDomSet = DS.getDominators(PredBlocks[0]);
for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i)
set_intersect(NewBBDomSet, DS.getDominators(PredBlocks[i]));
NewBBDomSet.insert(NewBB); // All blocks dominate themselves...
DS.addBasicBlock(NewBB, NewBBDomSet);
// If NewBB dominates some blocks, then it will dominate all blocks that
// NewBBSucc does.
if (NewBBDominatesNewBBSucc) {
BasicBlock *PredBlock = PredBlocks[0];
Function *F = NewBB->getParent();
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
if (DS.dominates(NewBBSucc, I))
DS.addDominator(I, NewBB);
}
// Update immediate dominator information if we have it...
BasicBlock *NewBBIDom = 0;
if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) {
// To find the immediate dominator of the new exit node, we trace up the
// immediate dominators of a predecessor until we find a basic block that
// dominates the exit block.
//
BasicBlock *Dom = PredBlocks[0]; // Some random predecessor...
while (!NewBBDomSet.count(Dom)) { // Loop until we find a dominator...
assert(Dom != 0 && "No shared dominator found???");
Dom = ID->get(Dom);
}
// Set the immediate dominator now...
ID->addNewBlock(NewBB, Dom);
NewBBIDom = Dom; // Reuse this if calculating DominatorTree info...
// If NewBB strictly dominates other blocks, we need to update their idom's
// now. The only block that need adjustment is the NewBBSucc block, whose
// idom should currently be set to PredBlocks[0].
if (NewBBDominatesNewBBSucc) {
assert(ID->get(NewBBSucc) == PredBlocks[0] &&
"Immediate dominator update code broken!");
ID->setImmediateDominator(NewBBSucc, NewBB);
}
}
// Update DominatorTree information if it is active.
if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
// If we don't have ImmediateDominator info around, calculate the idom as
// above.
DominatorTree::Node *NewBBIDomNode;
if (NewBBIDom) {
NewBBIDomNode = DT->getNode(NewBBIDom);
} else {
NewBBIDomNode = DT->getNode(PredBlocks[0]); // Random pred
while (!NewBBDomSet.count(NewBBIDomNode->getBlock())) {
NewBBIDomNode = NewBBIDomNode->getIDom();
assert(NewBBIDomNode && "No shared dominator found??");
}
}
// Create the new dominator tree node... and set the idom of NewBB.
DominatorTree::Node *NewBBNode = DT->createNewNode(NewBB, NewBBIDomNode);
// If NewBB strictly dominates other blocks, then it is now the immediate
// dominator of NewBBSucc. Update the dominator tree as appropriate.
if (NewBBDominatesNewBBSucc) {
DominatorTree::Node *NewBBSuccNode = DT->getNode(NewBBSucc);
assert(NewBBSuccNode->getIDom()->getBlock() == PredBlocks[0] &&
"Immediate tree update code broken!");
DT->changeImmediateDominator(NewBBSuccNode, NewBBNode);
}
}
// Update dominance frontier information...
if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
// If NewBB dominates NewBBSucc, then the global dominance frontiers are not
// changed. DF(NewBB) is now going to be the DF(PredBlocks[0]) without the
// stuff that the new block does not dominate a predecessor of.
if (NewBBDominatesNewBBSucc) {
DominanceFrontier::iterator DFI = DF->find(PredBlocks[0]);
if (DFI != DF->end()) {
DominanceFrontier::DomSetType Set = DFI->second;
// Filter out stuff in Set that we do not dominate a predecessor of.
for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
E = Set.end(); SetI != E;) {
bool DominatesPred = false;
for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
PI != E; ++PI)
if (DS.dominates(NewBB, *PI))
DominatesPred = true;
if (!DominatesPred)
Set.erase(SetI++);
else
++SetI;
}
DF->addBasicBlock(NewBB, Set);
}
} else {
// DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
// NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
// NewBBSucc)). NewBBSucc is the single successor of NewBB.
DominanceFrontier::DomSetType NewDFSet;
NewDFSet.insert(NewBBSucc);
DF->addBasicBlock(NewBB, NewDFSet);
// Now we must loop over all of the dominance frontiers in the function,
// replacing occurrences of NewBBSucc with NewBB in some cases. All
// blocks that dominate a block in PredBlocks and contained NewBBSucc in
// their dominance frontier must be updated to contain NewBB instead.
//
for (unsigned i = 0, e = PredBlocks.size(); i != e; ++i) {
BasicBlock *Pred = PredBlocks[i];
// Get all of the dominators of the predecessor...
const DominatorSet::DomSetType &PredDoms = DS.getDominators(Pred);
for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(),
PDE = PredDoms.end(); PDI != PDE; ++PDI) {
BasicBlock *PredDom = *PDI;
// If the NewBBSucc node is in DF(PredDom), then PredDom didn't
// dominate NewBBSucc but did dominate a predecessor of it. Now we
// change this entry to include NewBB in the DF instead of NewBBSucc.
DominanceFrontier::iterator DFI = DF->find(PredDom);
assert(DFI != DF->end() && "No dominance frontier for node?");
if (DFI->second.count(NewBBSucc)) {
DF->removeFromFrontier(DFI, NewBBSucc);
DF->addToFrontier(DFI, NewBB);
}
}
}
}
}
}
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