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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 <algorithm>
using namespace llvm;
//===----------------------------------------------------------------------===//
// ImmediateDominators Implementation
//===----------------------------------------------------------------------===//
//
// Immediate Dominators construction - This pass constructs immediate dominator
// information for a flow-graph based on the algorithm described in this
// document:
//
// A Fast Algorithm for Finding Dominators in a Flowgraph
// T. Lengauer & R. Tarjan, ACM TOPLAS July 1979, pgs 121-141.
//
// This implements both the O(n*ack(n)) and the O(n*log(n)) versions of EVAL and
// LINK, but it turns out that the theoretically slower O(n*log(n))
// implementation is actually faster than the "efficient" algorithm (even for
// large CFGs) because the constant overheads are substantially smaller. The
// lower-complexity version can be enabled with the following #define:
//
#define BALANCE_IDOM_TREE 0
//
//===----------------------------------------------------------------------===//
static RegisterAnalysis<ImmediateDominators>
C("idom", "Immediate Dominators Construction", true);
unsigned ImmediateDominators::DFSPass(BasicBlock *V, InfoRec &VInfo,
unsigned N) {
VInfo.Semi = ++N;
VInfo.Label = V;
Vertex.push_back(V); // Vertex[n] = V;
//Info[V].Ancestor = 0; // Ancestor[n] = 0
//Child[V] = 0; // Child[v] = 0
VInfo.Size = 1; // Size[v] = 1
for (succ_iterator SI = succ_begin(V), E = succ_end(V); SI != E; ++SI) {
InfoRec &SuccVInfo = Info[*SI];
if (SuccVInfo.Semi == 0) {
SuccVInfo.Parent = V;
N = DFSPass(*SI, SuccVInfo, N);
}
}
return N;
}
void ImmediateDominators::Compress(BasicBlock *V, InfoRec &VInfo) {
BasicBlock *VAncestor = VInfo.Ancestor;
InfoRec &VAInfo = Info[VAncestor];
if (VAInfo.Ancestor == 0)
return;
Compress(VAncestor, VAInfo);
BasicBlock *VAncestorLabel = VAInfo.Label;
BasicBlock *VLabel = VInfo.Label;
if (Info[VAncestorLabel].Semi < Info[VLabel].Semi)
VInfo.Label = VAncestorLabel;
VInfo.Ancestor = VAInfo.Ancestor;
}
BasicBlock *ImmediateDominators::Eval(BasicBlock *V) {
InfoRec &VInfo = Info[V];
#if !BALANCE_IDOM_TREE
// Higher-complexity but faster implementation
if (VInfo.Ancestor == 0)
return V;
Compress(V, VInfo);
return VInfo.Label;
#else
// Lower-complexity but slower implementation
if (VInfo.Ancestor == 0)
return VInfo.Label;
Compress(V, VInfo);
BasicBlock *VLabel = VInfo.Label;
BasicBlock *VAncestorLabel = Info[VInfo.Ancestor].Label;
if (Info[VAncestorLabel].Semi >= Info[VLabel].Semi)
return VLabel;
else
return VAncestorLabel;
#endif
}
void ImmediateDominators::Link(BasicBlock *V, BasicBlock *W, InfoRec &WInfo){
#if !BALANCE_IDOM_TREE
// Higher-complexity but faster implementation
WInfo.Ancestor = V;
#else
// Lower-complexity but slower implementation
BasicBlock *WLabel = WInfo.Label;
unsigned WLabelSemi = Info[WLabel].Semi;
BasicBlock *S = W;
InfoRec *SInfo = &Info[S];
BasicBlock *SChild = SInfo->Child;
InfoRec *SChildInfo = &Info[SChild];
while (WLabelSemi < Info[SChildInfo->Label].Semi) {
BasicBlock *SChildChild = SChildInfo->Child;
if (SInfo->Size+Info[SChildChild].Size >= 2*SChildInfo->Size) {
SChildInfo->Ancestor = S;
SInfo->Child = SChild = SChildChild;
SChildInfo = &Info[SChild];
} else {
SChildInfo->Size = SInfo->Size;
S = SInfo->Ancestor = SChild;
SInfo = SChildInfo;
SChild = SChildChild;
SChildInfo = &Info[SChild];
}
}
InfoRec &VInfo = Info[V];
SInfo->Label = WLabel;
assert(V != W && "The optimization here will not work in this case!");
unsigned WSize = WInfo.Size;
unsigned VSize = (VInfo.Size += WSize);
if (VSize < 2*WSize)
std::swap(S, VInfo.Child);
while (S) {
SInfo = &Info[S];
SInfo->Ancestor = V;
S = SInfo->Child;
}
#endif
}
bool ImmediateDominators::runOnFunction(Function &F) {
IDoms.clear(); // Reset from the last time we were run...
BasicBlock *Root = &F.getEntryBlock();
Roots.clear();
Roots.push_back(Root);
Vertex.push_back(0);
// Step #1: Number blocks in depth-first order and initialize variables used
// in later stages of the algorithm.
unsigned N = 0;
for (unsigned i = 0, e = Roots.size(); i != e; ++i)
N = DFSPass(Roots[i], Info[Roots[i]], 0);
for (unsigned i = N; i >= 2; --i) {
BasicBlock *W = Vertex[i];
InfoRec &WInfo = Info[W];
// Step #2: Calculate the semidominators of all vertices
for (pred_iterator PI = pred_begin(W), E = pred_end(W); PI != E; ++PI)
if (Info.count(*PI)) { // Only if this predecessor is reachable!
unsigned SemiU = Info[Eval(*PI)].Semi;
if (SemiU < WInfo.Semi)
WInfo.Semi = SemiU;
}
Info[Vertex[WInfo.Semi]].Bucket.push_back(W);
BasicBlock *WParent = WInfo.Parent;
Link(WParent, W, WInfo);
// Step #3: Implicitly define the immediate dominator of vertices
std::vector<BasicBlock*> &WParentBucket = Info[WParent].Bucket;
while (!WParentBucket.empty()) {
BasicBlock *V = WParentBucket.back();
WParentBucket.pop_back();
BasicBlock *U = Eval(V);
IDoms[V] = Info[U].Semi < Info[V].Semi ? U : WParent;
}
}
// Step #4: Explicitly define the immediate dominator of each vertex
for (unsigned i = 2; i <= N; ++i) {
BasicBlock *W = Vertex[i];
BasicBlock *&WIDom = IDoms[W];
if (WIDom != Vertex[Info[W].Semi])
WIDom = IDoms[WIDom];
}
// Free temporary memory used to construct idom's
Info.clear();
std::vector<BasicBlock*>().swap(Vertex);
return false;
}
void ImmediateDominatorsBase::print(std::ostream &o, const Module* ) const {
Function *F = getRoots()[0]->getParent();
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
o << " Immediate Dominator For Basic Block:";
WriteAsOperand(o, I, false);
o << " is:";
if (BasicBlock *ID = get(I))
WriteAsOperand(o, ID, false);
else
o << " <<exit node>>";
o << "\n";
}
o << "\n";
}
//===----------------------------------------------------------------------===//
// DominatorSet Implementation
//===----------------------------------------------------------------------===//
static RegisterAnalysis<DominatorSet>
B("domset", "Dominator Set Construction", true);
// dominates - Return true if A dominates B. This performs the special checks
// necessary if A and B are in the same basic block.
//
bool DominatorSetBase::dominates(Instruction *A, Instruction *B) const {
BasicBlock *BBA = A->getParent(), *BBB = B->getParent();
if (BBA != BBB) return dominates(BBA, BBB);
// Loop through the basic block until we find A or B.
BasicBlock::iterator I = BBA->begin();
for (; &*I != A && &*I != B; ++I) /*empty*/;
// A dominates B if it is found first in the basic block...
return &*I == A;
}
// runOnFunction - This method calculates the forward dominator sets for the
// specified function.
//
bool DominatorSet::runOnFunction(Function &F) {
BasicBlock *Root = &F.getEntryBlock();
Roots.clear();
Roots.push_back(Root);
assert(pred_begin(Root) == pred_end(Root) &&
"Root node has predecessors in function!");
ImmediateDominators &ID = getAnalysis<ImmediateDominators>();
Doms.clear();
if (Roots.empty()) return false;
// Root nodes only dominate themselves.
for (unsigned i = 0, e = Roots.size(); i != e; ++i)
Doms[Roots[i]].insert(Roots[i]);
// Loop over all of the blocks in the function, calculating dominator sets for
// each function.
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
if (BasicBlock *IDom = ID[I]) { // Get idom if block is reachable
DomSetType &DS = Doms[I];
assert(DS.empty() && "Domset already filled in for this block?");
DS.insert(I); // Blocks always dominate themselves
// Insert all dominators into the set...
while (IDom) {
// If we have already computed the dominator sets for our immediate
// dominator, just use it instead of walking all the way up to the root.
DomSetType &IDS = Doms[IDom];
if (!IDS.empty()) {
DS.insert(IDS.begin(), IDS.end());
break;
} else {
DS.insert(IDom);
IDom = ID[IDom];
}
}
} else {
// Ensure that every basic block has at least an empty set of nodes. This
// is important for the case when there is unreachable blocks.
Doms[I];
}
return false;
}
void DominatorSet::stub() {}
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;
}
}
void DominatorSetBase::print(std::ostream &o, const Module* ) const {
for (const_iterator I = begin(), E = end(); I != E; ++I) {
o << " DomSet For BB: ";
if (I->first)
WriteAsOperand(o, I->first, false);
else
o << " <<exit node>>";
o << " is:\t" << I->second << "\n";
}
}
//===----------------------------------------------------------------------===//
// DominatorTree Implementation
//===----------------------------------------------------------------------===//
static RegisterAnalysis<DominatorTree>
E("domtree", "Dominator Tree Construction", true);
// DominatorTreeBase::reset - Free all of the tree node memory.
//
void DominatorTreeBase::reset() {
for (NodeMapType::iterator I = Nodes.begin(), E = Nodes.end(); I != E; ++I)
delete I->second;
Nodes.clear();
RootNode = 0;
}
void DominatorTreeBase::Node::setIDom(Node *NewIDom) {
assert(IDom && "No immediate dominator?");
if (IDom != NewIDom) {
std::vector<Node*>::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);
}
}
DominatorTreeBase::Node *DominatorTree::getNodeForBlock(BasicBlock *BB) {
Node *&BBNode = Nodes[BB];
if (BBNode) return BBNode;
// Haven't calculated this node yet? Get or calculate the node for the
// immediate dominator.
BasicBlock *IDom = getAnalysis<ImmediateDominators>()[BB];
Node *IDomNode = getNodeForBlock(IDom);
// Add a new tree node for this BasicBlock, and link it as a child of
// IDomNode
return BBNode = IDomNode->addChild(new Node(BB, IDomNode));
}
void DominatorTree::calculate(const ImmediateDominators &ID) {
assert(Roots.size() == 1 && "DominatorTree should have 1 root block!");
BasicBlock *Root = Roots[0];
Nodes[Root] = RootNode = new Node(Root, 0); // Add a node for the root...
Function *F = Root->getParent();
// Loop over all of the reachable blocks in the function...
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
if (BasicBlock *ImmDom = ID.get(I)) { // Reachable block.
Node *&BBNode = Nodes[I];
if (!BBNode) { // Haven't calculated this node yet?
// Get or calculate the node for the immediate dominator
Node *IDomNode = getNodeForBlock(ImmDom);
// Add a new tree node for this BasicBlock, and link it as a child of
// IDomNode
BBNode = IDomNode->addChild(new Node(I, IDomNode));
}
}
}
static std::ostream &operator<<(std::ostream &o,
const DominatorTreeBase::Node *Node) {
if (Node->getBlock())
WriteAsOperand(o, Node->getBlock(), false);
else
o << " <<exit node>>";
return o << "\n";
}
static void PrintDomTree(const DominatorTreeBase::Node *N, std::ostream &o,
unsigned Lev) {
o << std::string(2*Lev, ' ') << "[" << Lev << "] " << N;
for (DominatorTreeBase::Node::const_iterator I = N->begin(), E = N->end();
I != E; ++I)
PrintDomTree(*I, o, Lev+1);
}
void DominatorTreeBase::print(std::ostream &o, const Module* ) const {
o << "=============================--------------------------------\n"
<< "Inorder Dominator Tree:\n";
PrintDomTree(getRootNode(), o, 1);
}
//===----------------------------------------------------------------------===//
// DominanceFrontier Implementation
//===----------------------------------------------------------------------===//
static RegisterAnalysis<DominanceFrontier>
G("domfrontier", "Dominance Frontier Construction", true);
const DominanceFrontier::DomSetType &
DominanceFrontier::calculate(const DominatorTree &DT,
const DominatorTree::Node *Node) {
// Loop over CFG successors to calculate DFlocal[Node]
BasicBlock *BB = Node->getBlock();
DomSetType &S = Frontiers[BB]; // The new set to fill in...
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
SI != SE; ++SI) {
// Does Node immediately dominate this successor?
if (DT[*SI]->getIDom() != Node)
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)
//
for (DominatorTree::Node::const_iterator NI = Node->begin(), NE = Node->end();
NI != NE; ++NI) {
DominatorTree::Node *IDominee = *NI;
const DomSetType &ChildDF = calculate(DT, IDominee);
DomSetType::const_iterator CDFI = ChildDF.begin(), CDFE = ChildDF.end();
for (; CDFI != CDFE; ++CDFI) {
if (!Node->dominates(DT[*CDFI]))
S.insert(*CDFI);
}
}
return S;
}
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";
}
}
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