llvm-6502/lib/Transforms/Utils/LoopSimplify.cpp
Chris Lattner 85ebd541fa Fix a regression from this patch:
http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20040308/013095.html

Basically, this patch only updated the immediate dominatees of the header node
to tell them that the preheader also dominated them.  In practice, ALL
dominatees of the header node are also dominated by the preheader.

This fixes: LoopSimplify/2004-03-15-IncorrectDomUpdate.
and PR293


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12434 91177308-0d34-0410-b5e6-96231b3b80d8
2004-03-16 06:00:15 +00:00

691 lines
28 KiB
C++

//===- 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/Constant.h"
#include "llvm/iTerminators.h"
#include "llvm/iPHINode.h"
#include "llvm/Function.h"
#include "llvm/Type.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.addRequired<DominatorTree>();
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;
// Check to see that no blocks (other than the header) in the loop have
// predecessors that are not in the loop. This is not valid for natural
// loops, but can occur if the blocks are unreachable. Since they are
// unreachable we can just shamelessly destroy their terminators to make them
// not branch into the loop!
assert(L->getBlocks()[0] == L->getHeader() &&
"Header isn't first block in loop?");
for (unsigned i = 1, e = L->getBlocks().size(); i != e; ++i) {
BasicBlock *LoopBB = L->getBlocks()[i];
Retry:
for (pred_iterator PI = pred_begin(LoopBB), E = pred_end(LoopBB);
PI != E; ++PI)
if (!L->contains(*PI)) {
// This predecessor is not in the loop. Kill its terminator!
BasicBlock *DeadBlock = *PI;
for (succ_iterator SI = succ_begin(DeadBlock), E = succ_end(DeadBlock);
SI != E; ++SI)
(*SI)->removePredecessor(DeadBlock); // Remove PHI node entries
// Delete the dead terminator.
DeadBlock->getInstList().pop_back();
Value *RetVal = 0;
if (LoopBB->getParent()->getReturnType() != Type::VoidTy)
RetVal = Constant::getNullValue(LoopBB->getParent()->getReturnType());
new ReturnInst(RetVal, DeadBlock);
goto Retry; // We just invalidated the pred_iterator. Retry.
}
}
// 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
DominatorTree &DT = getAnalysis<DominatorTree>();
// Update the dominator tree information.
// The immediate dominator of the preheader is the immediate dominator of
// the old header.
DominatorTree::Node *PHDomTreeNode =
DT.createNewNode(NewBB, DT.getNode(Header)->getIDom());
// Change the header node so that PNHode is the new immediate dominator
DT.changeImmediateDominator(DT.getNode(Header), PHDomTreeNode);
{
// The blocks that dominate NewBB are the blocks that dominate Header,
// minus Header, plus NewBB.
DominatorSet::DomSetType DomSet = DS.getDominators(Header);
DomSet.erase(Header); // Header does not dominate us...
DS.addBasicBlock(NewBB, DomSet);
// The newly created basic block dominates all nodes dominated by Header.
for (df_iterator<DominatorTree::Node*> DFI = df_begin(PHDomTreeNode),
E = df_end(PHDomTreeNode); DFI != E; ++DFI)
DS.addDominator((*DFI)->getBlock(), 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 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);
}
}
}
}
}
}