llvm-6502/lib/VMCore/Dominators.cpp
2002-05-13 22:03:16 +00:00

410 lines
15 KiB
C++

//===- DominatorSet.cpp - Dominator Set Calculation --------------*- C++ -*--=//
//
// This file provides a simple class to calculate the dominator set of a
// function.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/Dominators.h"
#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
#include "llvm/Support/CFG.h"
#include "Support/DepthFirstIterator.h"
#include "Support/STLExtras.h"
#include "Support/SetOperations.h"
#include <algorithm>
using std::set;
//===----------------------------------------------------------------------===//
// DominatorSet Implementation
//===----------------------------------------------------------------------===//
AnalysisID DominatorSet::ID(AnalysisID::create<DominatorSet>(), true);
AnalysisID DominatorSet::PostDomID(AnalysisID::create<DominatorSet>(), true);
bool DominatorSet::runOnFunction(Function *F) {
Doms.clear(); // Reset from the last time we were run...
if (isPostDominator())
calcPostDominatorSet(F);
else
calcForwardDominatorSet(F);
return false;
}
// dominates - Return true if A dominates B. This performs the special checks
// neccesary if A and B are in the same basic block.
//
bool DominatorSet::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;
}
// calcForwardDominatorSet - This method calculates the forward dominator sets
// for the specified function.
//
void DominatorSet::calcForwardDominatorSet(Function *M) {
Root = M->getEntryNode();
assert(pred_begin(Root) == pred_end(Root) &&
"Root node has predecessors in function!");
bool Changed;
do {
Changed = false;
DomSetType WorkingSet;
df_iterator<Function*> It = df_begin(M), End = df_end(M);
for ( ; It != End; ++It) {
BasicBlock *BB = *It;
pred_iterator PI = pred_begin(BB), PEnd = pred_end(BB);
if (PI != PEnd) { // Is there SOME predecessor?
// Loop until we get to a predecessor that has had it's dom set filled
// in at least once. We are guaranteed to have this because we are
// traversing the graph in DFO and have handled start nodes specially.
//
while (Doms[*PI].size() == 0) ++PI;
WorkingSet = Doms[*PI];
for (++PI; PI != PEnd; ++PI) { // Intersect all of the predecessor sets
DomSetType &PredSet = Doms[*PI];
if (PredSet.size())
set_intersect(WorkingSet, PredSet);
}
}
WorkingSet.insert(BB); // A block always dominates itself
DomSetType &BBSet = Doms[BB];
if (BBSet != WorkingSet) {
BBSet.swap(WorkingSet); // Constant time operation!
Changed = true; // The sets changed.
}
WorkingSet.clear(); // Clear out the set for next iteration
}
} while (Changed);
}
// Postdominator set constructor. This ctor converts the specified function to
// only have a single exit node (return stmt), then calculates the post
// dominance sets for the function.
//
void DominatorSet::calcPostDominatorSet(Function *F) {
// Since we require that the unify all exit nodes pass has been run, we know
// that there can be at most one return instruction in the function left.
// Get it.
//
Root = getAnalysis<UnifyFunctionExitNodes>().getExitNode();
if (Root == 0) { // No exit node for the function? Postdomsets are all empty
for (Function::iterator FI = F->begin(), FE = F->end(); FI != FE; ++FI)
Doms[*FI] = DomSetType();
return;
}
bool Changed;
do {
Changed = false;
set<const BasicBlock*> Visited;
DomSetType WorkingSet;
idf_iterator<BasicBlock*> It = idf_begin(Root), End = idf_end(Root);
for ( ; It != End; ++It) {
BasicBlock *BB = *It;
succ_iterator PI = succ_begin(BB), PEnd = succ_end(BB);
if (PI != PEnd) { // Is there SOME predecessor?
// Loop until we get to a successor that has had it's dom set filled
// in at least once. We are guaranteed to have this because we are
// traversing the graph in DFO and have handled start nodes specially.
//
while (Doms[*PI].size() == 0) ++PI;
WorkingSet = Doms[*PI];
for (++PI; PI != PEnd; ++PI) { // Intersect all of the successor sets
DomSetType &PredSet = Doms[*PI];
if (PredSet.size())
set_intersect(WorkingSet, PredSet);
}
}
WorkingSet.insert(BB); // A block always dominates itself
DomSetType &BBSet = Doms[BB];
if (BBSet != WorkingSet) {
BBSet.swap(WorkingSet); // Constant time operation!
Changed = true; // The sets changed.
}
WorkingSet.clear(); // Clear out the set for next iteration
}
} while (Changed);
}
// getAnalysisUsage - This obviously provides a dominator set, but it also
// uses the UnifyFunctionExitNodes pass if building post-dominators
//
void DominatorSet::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
if (isPostDominator()) {
AU.addProvided(PostDomID);
AU.addRequired(UnifyFunctionExitNodes::ID);
} else {
AU.addProvided(ID);
}
}
//===----------------------------------------------------------------------===//
// ImmediateDominators Implementation
//===----------------------------------------------------------------------===//
AnalysisID ImmediateDominators::ID(AnalysisID::create<ImmediateDominators>(), true);
AnalysisID ImmediateDominators::PostDomID(AnalysisID::create<ImmediateDominators>(), true);
// calcIDoms - Calculate the immediate dominator mapping, given a set of
// dominators for every basic block.
void ImmediateDominators::calcIDoms(const DominatorSet &DS) {
// Loop over all of the nodes that have dominators... figuring out the IDOM
// for each node...
//
for (DominatorSet::const_iterator DI = DS.begin(), DEnd = DS.end();
DI != DEnd; ++DI) {
BasicBlock *BB = DI->first;
const DominatorSet::DomSetType &Dominators = DI->second;
unsigned DomSetSize = Dominators.size();
if (DomSetSize == 1) continue; // Root node... IDom = null
// Loop over all dominators of this node. This corresponds to looping over
// nodes in the dominator chain, looking for a node whose dominator set is
// equal to the current nodes, except that the current node does not exist
// in it. This means that it is one level higher in the dom chain than the
// current node, and it is our idom!
//
DominatorSet::DomSetType::const_iterator I = Dominators.begin();
DominatorSet::DomSetType::const_iterator End = Dominators.end();
for (; I != End; ++I) { // Iterate over dominators...
// All of our dominators should form a chain, where the number of elements
// in the dominator set indicates what level the node is at in the chain.
// We want the node immediately above us, so it will have an identical
// dominator set, except that BB will not dominate it... therefore it's
// dominator set size will be one less than BB's...
//
if (DS.getDominators(*I).size() == DomSetSize - 1) {
IDoms[BB] = *I;
break;
}
}
}
}
//===----------------------------------------------------------------------===//
// DominatorTree Implementation
//===----------------------------------------------------------------------===//
AnalysisID DominatorTree::ID(AnalysisID::create<DominatorTree>(), true);
AnalysisID DominatorTree::PostDomID(AnalysisID::create<DominatorTree>(), true);
// DominatorTree::reset - Free all of the tree node memory.
//
void DominatorTree::reset() {
for (NodeMapType::iterator I = Nodes.begin(), E = Nodes.end(); I != E; ++I)
delete I->second;
Nodes.clear();
}
#if 0
// Given immediate dominators, we can also calculate the dominator tree
DominatorTree::DominatorTree(const ImmediateDominators &IDoms)
: DominatorBase(IDoms.getRoot()) {
const Function *M = Root->getParent();
Nodes[Root] = new Node(Root, 0); // Add a node for the root...
// Iterate over all nodes in depth first order...
for (df_iterator<const Function*> I = df_begin(M), E = df_end(M); I!=E; ++I) {
const BasicBlock *BB = *I, *IDom = IDoms[*I];
if (IDom != 0) { // Ignore the root node and other nasty nodes
// We know that the immediate dominator should already have a node,
// because we are traversing the CFG in depth first order!
//
assert(Nodes[IDom] && "No node for IDOM?");
Node *IDomNode = Nodes[IDom];
// Add a new tree node for this BasicBlock, and link it as a child of
// IDomNode
Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
}
}
}
#endif
void DominatorTree::calculate(const DominatorSet &DS) {
Nodes[Root] = new Node(Root, 0); // Add a node for the root...
if (!isPostDominator()) {
// Iterate over all nodes in depth first order...
for (df_iterator<BasicBlock*> I = df_begin(Root), E = df_end(Root);
I != E; ++I) {
BasicBlock *BB = *I;
const DominatorSet::DomSetType &Dominators = DS.getDominators(BB);
unsigned DomSetSize = Dominators.size();
if (DomSetSize == 1) continue; // Root node... IDom = null
// Loop over all dominators of this node. This corresponds to looping over
// nodes in the dominator chain, looking for a node whose dominator set is
// equal to the current nodes, except that the current node does not exist
// in it. This means that it is one level higher in the dom chain than the
// current node, and it is our idom! We know that we have already added
// a DominatorTree node for our idom, because the idom must be a
// predecessor in the depth first order that we are iterating through the
// function.
//
DominatorSet::DomSetType::const_iterator I = Dominators.begin();
DominatorSet::DomSetType::const_iterator End = Dominators.end();
for (; I != End; ++I) { // Iterate over dominators...
// All of our dominators should form a chain, where the number of
// elements in the dominator set indicates what level the node is at in
// the chain. We want the node immediately above us, so it will have
// an identical dominator set, except that BB will not dominate it...
// therefore it's dominator set size will be one less than BB's...
//
if (DS.getDominators(*I).size() == DomSetSize - 1) {
// We know that the immediate dominator should already have a node,
// because we are traversing the CFG in depth first order!
//
Node *IDomNode = Nodes[*I];
assert(IDomNode && "No node for IDOM?");
// Add a new tree node for this BasicBlock, and link it as a child of
// IDomNode
Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
break;
}
}
}
} else if (Root) {
// Iterate over all nodes in depth first order...
for (idf_iterator<BasicBlock*> I = idf_begin(Root), E = idf_end(Root);
I != E; ++I) {
BasicBlock *BB = *I;
const DominatorSet::DomSetType &Dominators = DS.getDominators(BB);
unsigned DomSetSize = Dominators.size();
if (DomSetSize == 1) continue; // Root node... IDom = null
// Loop over all dominators of this node. This corresponds to looping
// over nodes in the dominator chain, looking for a node whose dominator
// set is equal to the current nodes, except that the current node does
// not exist in it. This means that it is one level higher in the dom
// chain than the current node, and it is our idom! We know that we have
// already added a DominatorTree node for our idom, because the idom must
// be a predecessor in the depth first order that we are iterating through
// the function.
//
DominatorSet::DomSetType::const_iterator I = Dominators.begin();
DominatorSet::DomSetType::const_iterator End = Dominators.end();
for (; I != End; ++I) { // Iterate over dominators...
// All of our dominators should form a chain, where the number
// of elements in the dominator set indicates what level the
// node is at in the chain. We want the node immediately
// above us, so it will have an identical dominator set,
// except that BB will not dominate it... therefore it's
// dominator set size will be one less than BB's...
//
if (DS.getDominators(*I).size() == DomSetSize - 1) {
// We know that the immediate dominator should already have a node,
// because we are traversing the CFG in depth first order!
//
Node *IDomNode = Nodes[*I];
assert(IDomNode && "No node for IDOM?");
// Add a new tree node for this BasicBlock, and link it as a child of
// IDomNode
Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
break;
}
}
}
}
}
//===----------------------------------------------------------------------===//
// DominanceFrontier Implementation
//===----------------------------------------------------------------------===//
AnalysisID DominanceFrontier::ID(AnalysisID::create<DominanceFrontier>(), true);
AnalysisID DominanceFrontier::PostDomID(AnalysisID::create<DominanceFrontier>(), true);
const DominanceFrontier::DomSetType &
DominanceFrontier::calcDomFrontier(const DominatorTree &DT,
const DominatorTree::Node *Node) {
// Loop over CFG successors to calculate DFlocal[Node]
BasicBlock *BB = Node->getNode();
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 = calcDomFrontier(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;
}
const DominanceFrontier::DomSetType &
DominanceFrontier::calcPostDomFrontier(const DominatorTree &DT,
const DominatorTree::Node *Node) {
// Loop over CFG successors to calculate DFlocal[Node]
BasicBlock *BB = Node->getNode();
DomSetType &S = Frontiers[BB]; // The new set to fill in...
if (!Root) return S;
for (pred_iterator SI = pred_begin(BB), SE = pred_end(BB);
SI != SE; ++SI) {
// Does Node immediately dominate this predeccessor?
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 = calcPostDomFrontier(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;
}