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llvm-project/llvm/lib/Analysis/PostDominators.cpp

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//===- PostDominators.cpp - Post-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 the post-dominator construction algorithms.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/PostDominators.h"
#include "llvm/Instructions.h"
#include "llvm/Support/CFG.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SetOperations.h"
#include <iostream>
using namespace llvm;
//===----------------------------------------------------------------------===//
// ImmediatePostDominators Implementation
//===----------------------------------------------------------------------===//
static RegisterAnalysis<ImmediatePostDominators>
D("postidom", "Immediate Post-Dominators Construction", true);
unsigned ImmediatePostDominators::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 PostDominators, we want to walk predecessors rather than successors
// as we do in forward Dominators.
for (pred_iterator PI = pred_begin(V), PE = pred_end(V); PI != PE; ++PI) {
InfoRec &SuccVInfo = Info[*PI];
if (SuccVInfo.Semi == 0) {
SuccVInfo.Parent = V;
N = DFSPass(*PI, SuccVInfo, N);
}
}
return N;
}
void ImmediatePostDominators::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 *ImmediatePostDominators::Eval(BasicBlock *V) {
InfoRec &VInfo = Info[V];
// Higher-complexity but faster implementation
if (VInfo.Ancestor == 0)
return V;
Compress(V, VInfo);
return VInfo.Label;
}
void ImmediatePostDominators::Link(BasicBlock *V, BasicBlock *W,
InfoRec &WInfo) {
// Higher-complexity but faster implementation
WInfo.Ancestor = V;
}
bool ImmediatePostDominators::runOnFunction(Function &F) {
IDoms.clear(); // Reset from the last time we were run...
Roots.clear();
// Step #0: Scan the function looking for the root nodes of the post-dominance
// relationships. These blocks, which have no successors, end with return and
// unwind instructions.
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
if (succ_begin(I) == succ_end(I))
Roots.push_back(I);
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]], N);
for (unsigned i = N; i >= 2; --i) {
BasicBlock *W = Vertex[i];
InfoRec &WInfo = Info[W];
// Step #2: Calculate the semidominators of all vertices
for (succ_iterator SI = succ_begin(W), SE = succ_end(W); SI != SE; ++SI)
if (Info.count(*SI)) { // Only if this predecessor is reachable!
unsigned SemiU = Info[Eval(*SI)].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;
}
//===----------------------------------------------------------------------===//
// PostDominatorSet Implementation
//===----------------------------------------------------------------------===//
static RegisterAnalysis<PostDominatorSet>
B("postdomset", "Post-Dominator Set Construction", true);
// Postdominator set construction. This converts the specified function to only
// have a single exit node (return stmt), then calculates the post dominance
// sets for the function.
//
bool PostDominatorSet::runOnFunction(Function &F) {
// Scan the function looking for the root nodes of the post-dominance
// relationships. These blocks end with return and unwind instructions.
// While we are iterating over the function, we also initialize all of the
// domsets to empty.
Roots.clear();
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
if (succ_begin(I) == succ_end(I))
Roots.push_back(I);
// If there are no exit nodes for the function, postdomsets are all empty.
// This can happen if the function just contains an infinite loop, for
// example.
ImmediatePostDominators &IPD = getAnalysis<ImmediatePostDominators>();
Doms.clear(); // Reset from the last time we were run...
if (Roots.empty()) return false;
// If we have more than one root, we insert an artificial "null" exit, which
// has "virtual edges" to each of the real exit nodes.
//if (Roots.size() > 1)
// Doms[0].insert(0);
// 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 *IPDom = IPD[I]) { // Get idom if block is reachable
DomSetType &DS = Doms[I];
assert(DS.empty() && "PostDomset already filled in for this block?");
DS.insert(I); // Blocks always dominate themselves
// Insert all dominators into the set...
while (IPDom) {
// If we have already computed the dominator sets for our immediate post
// dominator, just use it instead of walking all the way up to the root.
DomSetType &IPDS = Doms[IPDom];
if (!IPDS.empty()) {
DS.insert(IPDS.begin(), IPDS.end());
break;
} else {
DS.insert(IPDom);
IPDom = IPD[IPDom];
}
}
} 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;
}
//===----------------------------------------------------------------------===//
// PostDominatorTree Implementation
//===----------------------------------------------------------------------===//
static RegisterAnalysis<PostDominatorTree>
F("postdomtree", "Post-Dominator Tree Construction", true);
DominatorTreeBase::Node *PostDominatorTree::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 postdominator.
BasicBlock *IPDom = getAnalysis<ImmediatePostDominators>()[BB];
Node *IPDomNode = getNodeForBlock(IPDom);
// Add a new tree node for this BasicBlock, and link it as a child of
// IDomNode
return BBNode = IPDomNode->addChild(new Node(BB, IPDomNode));
}
void PostDominatorTree::calculate(const ImmediatePostDominators &IPD) {
if (Roots.empty()) return;
// Add a node for the root. This node might be the actual root, if there is
// one exit block, or it may be the virtual exit (denoted by (BasicBlock *)0)
// which postdominates all real exits if there are multiple exit blocks.
BasicBlock *Root = Roots.size() == 1 ? Roots[0] : 0;
Nodes[Root] = RootNode = new Node(Root, 0);
Function *F = Roots[0]->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 *ImmPostDom = IPD.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 *IPDomNode = getNodeForBlock(ImmPostDom);
// Add a new tree node for this BasicBlock, and link it as a child of
// IDomNode
BBNode = IPDomNode->addChild(new Node(I, IPDomNode));
}
}
}
//===----------------------------------------------------------------------===//
// PostETForest Implementation
//===----------------------------------------------------------------------===//
static RegisterAnalysis<PostETForest>
G("postetforest", "Post-ET-Forest Construction", true);
ETNode *PostETForest::getNodeForBlock(BasicBlock *BB) {
ETNode *&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<ImmediatePostDominators>()[BB];
// If we are unreachable, we may not have an immediate dominator.
if (!IDom)
return BBNode = new ETNode(BB);
else {
ETNode *IDomNode = getNodeForBlock(IDom);
// Add a new tree node for this BasicBlock, and link it as a child of
// IDomNode
BBNode = new ETNode(BB);
BBNode->setFather(IDomNode);
return BBNode;
}
}
void PostETForest::calculate(const ImmediatePostDominators &ID) {
for (unsigned i = 0, e = Roots.size(); i != e; ++i)
Nodes[Roots[i]] = new ETNode(Roots[i]); // Add a node for the root
// Iterate over all nodes in inverse depth first order.
for (unsigned i = 0, e = Roots.size(); i != e; ++i)
for (idf_iterator<BasicBlock*> I = idf_begin(Roots[i]),
E = idf_end(Roots[i]); I != E; ++I) {
BasicBlock *BB = *I;
ETNode *&BBNode = Nodes[BB];
if (!BBNode) {
ETNode *IDomNode = NULL;
if (ID.get(BB))
IDomNode = getNodeForBlock(ID.get(BB));
// Add a new ETNode for this BasicBlock, and set it's parent
// to it's immediate dominator.
BBNode = new ETNode(BB);
if (IDomNode)
BBNode->setFather(IDomNode);
}
}
int dfsnum = 0;
// Iterate over all nodes in depth first order...
for (unsigned i = 0, e = Roots.size(); i != e; ++i)
for (idf_iterator<BasicBlock*> I = idf_begin(Roots[i]),
E = idf_end(Roots[i]); I != E; ++I) {
if (!getNodeForBlock(*I)->hasFather())
getNodeForBlock(*I)->assignDFSNumber(dfsnum);
}
DFSInfoValid = true;
}
//===----------------------------------------------------------------------===//
// PostDominanceFrontier Implementation
//===----------------------------------------------------------------------===//
static RegisterAnalysis<PostDominanceFrontier>
H("postdomfrontier", "Post-Dominance Frontier Construction", true);
const DominanceFrontier::DomSetType &
PostDominanceFrontier::calculate(const PostDominatorTree &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...
if (getRoots().empty()) return S;
if (BB)
for (pred_iterator SI = pred_begin(BB), SE = pred_end(BB);
SI != SE; ++SI)
// Does Node immediately dominate this predecessor?
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 (PostDominatorTree::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->properlyDominates(DT[*CDFI]))
S.insert(*CDFI);
}
}
return S;
}
// Ensure that this .cpp file gets linked when PostDominators.h is used.
DEFINING_FILE_FOR(PostDominanceFrontier)
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