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llvm-project/llvm/lib/VMCore/Dominators.cpp

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//===- Dominators.cpp - Dominator Calculation -----------------------------===//
//
// 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 file implements simple dominator construction algorithms for finding
// forward dominators. Postdominators are available in libanalysis, but are not
// included in libvmcore, because it's not needed. Forward dominators are
// needed to support the Verifier pass.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/CFG.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SetOperations.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Instructions.h"
#include "llvm/Support/Streams.h"
#include "DominatorCalculation.h"
#include <algorithm>
using namespace llvm;
namespace llvm {
static std::ostream &operator<<(std::ostream &o,
const std::set<BasicBlock*> &BBs) {
for (std::set<BasicBlock*>::const_iterator I = BBs.begin(), E = BBs.end();
I != E; ++I)
if (*I)
WriteAsOperand(o, *I, false);
else
o << " <<exit node>>";
return o;
}
}
//===----------------------------------------------------------------------===//
// DominatorTree Implementation
//===----------------------------------------------------------------------===//
//
// Provide public access to DominatorTree information. Implementation details
// can be found in DominatorCalculation.h.
//
//===----------------------------------------------------------------------===//
char DominatorTree::ID = 0;
static RegisterPass<DominatorTree>
E("domtree", "Dominator Tree Construction", true);
// NewBB is split and now it has one successor. Update dominator tree to
// reflect this change.
void DominatorTree::splitBlock(BasicBlock *NewBB) {
assert(NewBB->getTerminator()->getNumSuccessors() == 1
&& "NewBB should have a single successor!");
BasicBlock *NewBBSucc = NewBB->getTerminator()->getSuccessor(0);
std::vector<BasicBlock*> PredBlocks;
for (pred_iterator PI = pred_begin(NewBB), PE = pred_end(NewBB);
PI != PE; ++PI)
PredBlocks.push_back(*PI);
assert(!PredBlocks.empty() && "No predblocks??");
// 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];
unsigned i = 1, e = PredBlocks.size();
for (i = 1; !isReachableFromEntry(OnePred); ++i) {
assert(i != e && "Didn't find reachable pred?");
OnePred = PredBlocks[i];
}
for (; i != e; ++i)
if (PredBlocks[i] != OnePred && isReachableFromEntry(OnePred)) {
NewBBDominatesNewBBSucc = false;
break;
}
if (NewBBDominatesNewBBSucc)
for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
PI != E; ++PI)
if (*PI != NewBB && !dominates(NewBBSucc, *PI)) {
NewBBDominatesNewBBSucc = false;
break;
}
}
// The other scenario where the new block can dominate its successors are when
// all predecessors of NewBBSucc that are not NewBB are dominated by NewBBSucc
// already.
if (!NewBBDominatesNewBBSucc) {
NewBBDominatesNewBBSucc = true;
for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
PI != E; ++PI)
if (*PI != NewBB && !dominates(NewBBSucc, *PI)) {
NewBBDominatesNewBBSucc = false;
break;
}
}
// Find NewBB's immediate dominator and create new dominator tree node for
// NewBB.
BasicBlock *NewBBIDom = 0;
unsigned i = 0;
for (i = 0; i < PredBlocks.size(); ++i)
if (isReachableFromEntry(PredBlocks[i])) {
NewBBIDom = PredBlocks[i];
break;
}
assert(i != PredBlocks.size() && "No reachable preds?");
for (i = i + 1; i < PredBlocks.size(); ++i) {
if (isReachableFromEntry(PredBlocks[i]))
NewBBIDom = findNearestCommonDominator(NewBBIDom, PredBlocks[i]);
}
assert(NewBBIDom && "No immediate dominator found??");
// Create the new dominator tree node... and set the idom of NewBB.
DomTreeNode *NewBBNode = addNewBlock(NewBB, NewBBIDom);
// If NewBB strictly dominates other blocks, then it is now the immediate
// dominator of NewBBSucc. Update the dominator tree as appropriate.
if (NewBBDominatesNewBBSucc) {
DomTreeNode *NewBBSuccNode = getNode(NewBBSucc);
changeImmediateDominator(NewBBSuccNode, NewBBNode);
}
}
void DominatorTreeBase::updateDFSNumbers() {
unsigned DFSNum = 0;
SmallVector<std::pair<DomTreeNode*, DomTreeNode::iterator>, 32> WorkStack;
for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
DomTreeNode *ThisRoot = getNode(Roots[i]);
WorkStack.push_back(std::make_pair(ThisRoot, ThisRoot->begin()));
ThisRoot->DFSNumIn = DFSNum++;
while (!WorkStack.empty()) {
DomTreeNode *Node = WorkStack.back().first;
DomTreeNode::iterator ChildIt = WorkStack.back().second;
// If we visited all of the children of this node, "recurse" back up the
// stack setting the DFOutNum.
if (ChildIt == Node->end()) {
Node->DFSNumOut = DFSNum++;
WorkStack.pop_back();
} else {
// Otherwise, recursively visit this child.
DomTreeNode *Child = *ChildIt;
++WorkStack.back().second;
WorkStack.push_back(std::make_pair(Child, Child->begin()));
Child->DFSNumIn = DFSNum++;
}
}
}
SlowQueries = 0;
DFSInfoValid = true;
}
/// isReachableFromEntry - Return true if A is dominated by the entry
/// block of the function containing it.
const bool DominatorTreeBase::isReachableFromEntry(BasicBlock* A) {
assert (!isPostDominator()
&& "This is not implemented for post dominators");
return dominates(&A->getParent()->getEntryBlock(), A);
}
// dominates - Return true if A dominates B. THis performs the
// special checks necessary if A and B are in the same basic block.
bool DominatorTreeBase::dominates(Instruction *A, Instruction *B) {
BasicBlock *BBA = A->getParent(), *BBB = B->getParent();
if (BBA != BBB) return dominates(BBA, BBB);
// It is not possible to determine dominance between two PHI nodes
// based on their ordering.
if (isa<PHINode>(A) && isa<PHINode>(B))
return false;
// Loop through the basic block until we find A or B.
BasicBlock::iterator I = BBA->begin();
for (; &*I != A && &*I != B; ++I) /*empty*/;
if(!IsPostDominators) {
// A dominates B if it is found first in the basic block.
return &*I == A;
} else {
// A post-dominates B if B is found first in the basic block.
return &*I == B;
}
}
// DominatorTreeBase::reset - Free all of the tree node memory.
//
void DominatorTreeBase::reset() {
for (DomTreeNodeMapType::iterator I = DomTreeNodes.begin(),
E = DomTreeNodes.end(); I != E; ++I)
delete I->second;
DomTreeNodes.clear();
IDoms.clear();
Roots.clear();
Vertex.clear();
RootNode = 0;
}
DomTreeNode *DominatorTreeBase::getNodeForBlock(BasicBlock *BB) {
if (DomTreeNode *BBNode = DomTreeNodes[BB])
return BBNode;
// Haven't calculated this node yet? Get or calculate the node for the
// immediate dominator.
BasicBlock *IDom = getIDom(BB);
DomTreeNode *IDomNode = getNodeForBlock(IDom);
// Add a new tree node for this BasicBlock, and link it as a child of
// IDomNode
DomTreeNode *C = new DomTreeNode(BB, IDomNode);
return DomTreeNodes[BB] = IDomNode->addChild(C);
}
/// findNearestCommonDominator - Find nearest common dominator basic block
/// for basic block A and B. If there is no such block then return NULL.
BasicBlock *DominatorTreeBase::findNearestCommonDominator(BasicBlock *A,
BasicBlock *B) {
assert (!isPostDominator()
&& "This is not implemented for post dominators");
assert (A->getParent() == B->getParent()
&& "Two blocks are not in same function");
// If either A or B is a entry block then it is nearest common dominator.
BasicBlock &Entry = A->getParent()->getEntryBlock();
if (A == &Entry || B == &Entry)
return &Entry;
// If B dominates A then B is nearest common dominator.
if (dominates(B, A))
return B;
// If A dominates B then A is nearest common dominator.
if (dominates(A, B))
return A;
DomTreeNode *NodeA = getNode(A);
DomTreeNode *NodeB = getNode(B);
// Collect NodeA dominators set.
SmallPtrSet<DomTreeNode*, 16> NodeADoms;
NodeADoms.insert(NodeA);
DomTreeNode *IDomA = NodeA->getIDom();
while (IDomA) {
NodeADoms.insert(IDomA);
IDomA = IDomA->getIDom();
}
// Walk NodeB immediate dominators chain and find common dominator node.
DomTreeNode *IDomB = NodeB->getIDom();
while(IDomB) {
if (NodeADoms.count(IDomB) != 0)
return IDomB->getBlock();
IDomB = IDomB->getIDom();
}
return NULL;
}
void DomTreeNode::setIDom(DomTreeNode *NewIDom) {
assert(IDom && "No immediate dominator?");
if (IDom != NewIDom) {
std::vector<DomTreeNode*>::iterator I =
std::find(IDom->Children.begin(), IDom->Children.end(), this);
assert(I != IDom->Children.end() &&
"Not in immediate dominator children set!");
// I am no longer your child...
IDom->Children.erase(I);
// Switch to new dominator
IDom = NewIDom;
IDom->Children.push_back(this);
}
}
static std::ostream &operator<<(std::ostream &o, const DomTreeNode *Node) {
if (Node->getBlock())
WriteAsOperand(o, Node->getBlock(), false);
else
o << " <<exit node>>";
o << " {" << Node->getDFSNumIn() << "," << Node->getDFSNumOut() << "}";
return o << "\n";
}
static void PrintDomTree(const DomTreeNode *N, std::ostream &o,
unsigned Lev) {
o << std::string(2*Lev, ' ') << "[" << Lev << "] " << N;
for (DomTreeNode::const_iterator I = N->begin(), E = N->end();
I != E; ++I)
PrintDomTree(*I, o, Lev+1);
}
/// eraseNode - Removes a node from the domiantor tree. Block must not
/// domiante any other blocks. Removes node from its immediate dominator's
/// children list. Deletes dominator node associated with basic block BB.
void DominatorTreeBase::eraseNode(BasicBlock *BB) {
DomTreeNode *Node = getNode(BB);
assert (Node && "Removing node that isn't in dominator tree.");
assert (Node->getChildren().empty() && "Node is not a leaf node.");
// Remove node from immediate dominator's children list.
DomTreeNode *IDom = Node->getIDom();
if (IDom) {
std::vector<DomTreeNode*>::iterator I =
std::find(IDom->Children.begin(), IDom->Children.end(), Node);
assert(I != IDom->Children.end() &&
"Not in immediate dominator children set!");
// I am no longer your child...
IDom->Children.erase(I);
}
DomTreeNodes.erase(BB);
delete Node;
}
void DominatorTreeBase::print(std::ostream &o, const Module* ) const {
o << "=============================--------------------------------\n";
o << "Inorder Dominator Tree: ";
if (DFSInfoValid)
o << "DFSNumbers invalid: " << SlowQueries << " slow queries.";
o << "\n";
PrintDomTree(getRootNode(), o, 1);
}
void DominatorTreeBase::dump() {
print(llvm::cerr);
}
bool DominatorTree::runOnFunction(Function &F) {
reset(); // Reset from the last time we were run...
Roots.push_back(&F.getEntryBlock());
DTcalculate(*this, F);
return false;
}
//===----------------------------------------------------------------------===//
// DominanceFrontier Implementation
//===----------------------------------------------------------------------===//
char DominanceFrontier::ID = 0;
static RegisterPass<DominanceFrontier>
G("domfrontier", "Dominance Frontier Construction", true);
// NewBB is split and now it has one successor. Update dominace frontier to
// reflect this change.
void DominanceFrontier::splitBlock(BasicBlock *NewBB) {
assert(NewBB->getTerminator()->getNumSuccessors() == 1
&& "NewBB should have a single successor!");
BasicBlock *NewBBSucc = NewBB->getTerminator()->getSuccessor(0);
std::vector<BasicBlock*> PredBlocks;
for (pred_iterator PI = pred_begin(NewBB), PE = pred_end(NewBB);
PI != PE; ++PI)
PredBlocks.push_back(*PI);
if (PredBlocks.empty())
// If NewBB does not have any predecessors then it is a entry block.
// In this case, NewBB and its successor NewBBSucc dominates all
// other blocks.
return;
// NewBBSucc inherits original NewBB frontier.
DominanceFrontier::iterator NewBBI = find(NewBB);
if (NewBBI != end()) {
DominanceFrontier::DomSetType NewBBSet = NewBBI->second;
DominanceFrontier::DomSetType NewBBSuccSet;
NewBBSuccSet.insert(NewBBSet.begin(), NewBBSet.end());
addBasicBlock(NewBBSucc, NewBBSuccSet);
}
// If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
// DF(PredBlocks[0]) without the stuff that the new block does not dominate
// a predecessor of.
DominatorTree &DT = getAnalysis<DominatorTree>();
if (DT.dominates(NewBB, NewBBSucc)) {
DominanceFrontier::iterator DFI = find(PredBlocks[0]);
if (DFI != 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 (DT.dominates(NewBB, *PI))
DominatesPred = true;
if (!DominatesPred)
Set.erase(SetI++);
else
++SetI;
}
if (NewBBI != end()) {
DominanceFrontier::DomSetType NewBBSet = NewBBI->second;
NewBBSet.insert(Set.begin(), Set.end());
} else
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);
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 (Function::iterator FI = NewBB->getParent()->begin(),
FE = NewBB->getParent()->end(); FI != FE; ++FI) {
DominanceFrontier::iterator DFI = find(FI);
if (DFI == end()) continue; // unreachable block.
// Only consider nodes that have NewBBSucc in their dominator frontier.
if (!DFI->second.count(NewBBSucc)) continue;
// Verify whether this block dominates a block in predblocks. If not, do
// not update it.
bool BlockDominatesAny = false;
for (std::vector<BasicBlock*>::const_iterator BI = PredBlocks.begin(),
BE = PredBlocks.end(); BI != BE; ++BI) {
if (DT.dominates(FI, *BI)) {
BlockDominatesAny = true;
break;
}
}
if (!BlockDominatesAny)
continue;
// If NewBBSucc should not stay in our dominator frontier, remove it.
// We remove it unless there is a predecessor of NewBBSucc that we
// dominate, but we don't strictly dominate NewBBSucc.
bool ShouldRemove = true;
if ((BasicBlock*)FI == NewBBSucc || !DT.dominates(FI, NewBBSucc)) {
// Okay, we know that PredDom does not strictly dominate NewBBSucc.
// Check to see if it dominates any predecessors of NewBBSucc.
for (pred_iterator PI = pred_begin(NewBBSucc),
E = pred_end(NewBBSucc); PI != E; ++PI)
if (DT.dominates(FI, *PI)) {
ShouldRemove = false;
break;
}
}
if (ShouldRemove)
removeFromFrontier(DFI, NewBBSucc);
addToFrontier(DFI, NewBB);
}
}
namespace {
class DFCalculateWorkObject {
public:
DFCalculateWorkObject(BasicBlock *B, BasicBlock *P,
const DomTreeNode *N,
const DomTreeNode *PN)
: currentBB(B), parentBB(P), Node(N), parentNode(PN) {}
BasicBlock *currentBB;
BasicBlock *parentBB;
const DomTreeNode *Node;
const DomTreeNode *parentNode;
};
}
const DominanceFrontier::DomSetType &
DominanceFrontier::calculate(const DominatorTree &DT,
const DomTreeNode *Node) {
BasicBlock *BB = Node->getBlock();
DomSetType *Result = NULL;
std::vector<DFCalculateWorkObject> workList;
SmallPtrSet<BasicBlock *, 32> visited;
workList.push_back(DFCalculateWorkObject(BB, NULL, Node, NULL));
do {
DFCalculateWorkObject *currentW = &workList.back();
assert (currentW && "Missing work object.");
BasicBlock *currentBB = currentW->currentBB;
BasicBlock *parentBB = currentW->parentBB;
const DomTreeNode *currentNode = currentW->Node;
const DomTreeNode *parentNode = currentW->parentNode;
assert (currentBB && "Invalid work object. Missing current Basic Block");
assert (currentNode && "Invalid work object. Missing current Node");
DomSetType &S = Frontiers[currentBB];
// Visit each block only once.
if (visited.count(currentBB) == 0) {
visited.insert(currentBB);
// Loop over CFG successors to calculate DFlocal[currentNode]
for (succ_iterator SI = succ_begin(currentBB), SE = succ_end(currentBB);
SI != SE; ++SI) {
// Does Node immediately dominate this successor?
if (DT[*SI]->getIDom() != currentNode)
S.insert(*SI);
}
}
// At this point, S is DFlocal. Now we union in DFup's of our children...
// Loop through and visit the nodes that Node immediately dominates (Node's
// children in the IDomTree)
bool visitChild = false;
for (DomTreeNode::const_iterator NI = currentNode->begin(),
NE = currentNode->end(); NI != NE; ++NI) {
DomTreeNode *IDominee = *NI;
BasicBlock *childBB = IDominee->getBlock();
if (visited.count(childBB) == 0) {
workList.push_back(DFCalculateWorkObject(childBB, currentBB,
IDominee, currentNode));
visitChild = true;
}
}
// If all children are visited or there is any child then pop this block
// from the workList.
if (!visitChild) {
if (!parentBB) {
Result = &S;
break;
}
DomSetType::const_iterator CDFI = S.begin(), CDFE = S.end();
DomSetType &parentSet = Frontiers[parentBB];
for (; CDFI != CDFE; ++CDFI) {
if (!DT.properlyDominates(parentNode, DT[*CDFI]))
parentSet.insert(*CDFI);
}
workList.pop_back();
}
} while (!workList.empty());
return *Result;
}
void DominanceFrontierBase::print(std::ostream &o, const Module* ) const {
for (const_iterator I = begin(), E = end(); I != E; ++I) {
o << " DomFrontier for BB";
if (I->first)
WriteAsOperand(o, I->first, false);
else
o << " <<exit node>>";
o << " is:\t" << I->second << "\n";
}
}
void DominanceFrontierBase::dump() {
print (llvm::cerr);
}
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