[llvm-commits] CVS: llvm/lib/VMCore/Dominators.cpp
Chris Lattner
lattner at cs.uiuc.edu
Sat Dec 6 18:39:00 PST 2003
Changes in directory llvm/lib/VMCore:
Dominators.cpp updated: 1.52 -> 1.53
---
Log message:
Completely rewrite domset, idom, and domtree implementation. Now it is based
on the algorithm for directly computing immediate dominators presented in this
paper:
A Fast Algorithm for Finding Dominators in a Flowgraph
T. Lengauer & R. Tarjan, ACM TOPLAS July 1979, pgs 121-141.
This _substantially_ speeds up construction of all dominator related information.
Post-dominators to follow.
---
Diffs of the changes: (+266 -159)
Index: llvm/lib/VMCore/Dominators.cpp
diff -u llvm/lib/VMCore/Dominators.cpp:1.52 llvm/lib/VMCore/Dominators.cpp:1.53
--- llvm/lib/VMCore/Dominators.cpp:1.52 Fri Nov 21 14:23:48 2003
+++ llvm/lib/VMCore/Dominators.cpp Sat Dec 6 18:38:08 2003
@@ -22,11 +22,218 @@
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 {
+ for (const_iterator I = begin(), E = end(); I != E; ++I) {
+ o << " Immediate Dominator For Basic Block:";
+ if (I->first)
+ WriteAsOperand(o, I->first, false);
+ else
+ o << " <<exit node>>";
+ o << " is:";
+ if (I->second)
+ WriteAsOperand(o, I->second, false);
+ else
+ o << " <<exit node>>";
+ o << "\n";
+ }
+ o << "\n";
+}
+
+
+
+//===----------------------------------------------------------------------===//
// DominatorSet Implementation
//===----------------------------------------------------------------------===//
static RegisterAnalysis<DominatorSet>
-A("domset", "Dominator Set Construction", true);
+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.
@@ -44,53 +251,45 @@
}
-void DominatorSet::calculateDominatorsFromBlock(BasicBlock *RootBB) {
- bool Changed;
- Doms[RootBB].insert(RootBB); // Root always dominates itself...
- do {
- Changed = false;
-
- DomSetType WorkingSet;
- df_iterator<BasicBlock*> It = df_begin(RootBB), End = df_end(RootBB);
- 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 its 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,
- // except when there are unreachable blocks.
- //
- while (PI != PEnd && Doms[*PI].empty()) ++PI;
- if (PI != PEnd) { // Not unreachable code case?
- WorkingSet = Doms[*PI];
-
- // Intersect all of the predecessor sets
- for (++PI; PI != PEnd; ++PI) {
- DomSetType &PredSet = Doms[*PI];
- if (PredSet.size())
- set_intersect(WorkingSet, PredSet);
- }
+void DominatorSet::recalculate() {
+ ImmediateDominators &ID = getAnalysis<ImmediateDominators>();
+ Doms.clear();
+ if (Roots.empty()) return;
+
+ // Root nodes only dominate themselves.
+ for (unsigned i = 0, e = Roots.size(); i != e; ++i)
+ Doms[Roots[i]].insert(Roots[i]);
+
+ Function *F = Roots.back()->getParent();
+
+ // 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 {
- assert(Roots.size() == 1 && BB == Roots[0] &&
- "We got into unreachable code somehow!");
- }
-
- WorkingSet.insert(BB); // A block always dominates itself
- DomSetType &BBSet = Doms[BB];
- if (BBSet != WorkingSet) {
- //assert(WorkingSet.size() > BBSet.size() && "Must only grow sets!");
- BBSet.swap(WorkingSet); // Constant time operation!
- Changed = true; // The sets changed.
}
- WorkingSet.clear(); // Clear out the set for next iteration
+ } 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];
}
- } while (Changed);
}
-
-
// runOnFunction - This method calculates the forward dominator sets for the
// specified function.
//
@@ -104,21 +303,6 @@
return false;
}
-void DominatorSet::recalculate() {
- assert(Roots.size() == 1 && "DominatorSet should have single root block!");
- Doms.clear(); // Reset from the last time we were run...
-
- // Calculate dominator sets for the reachable basic blocks...
- calculateDominatorsFromBlock(Roots[0]);
-
-
- // Loop through the function, ensuring that every basic block has at least an
- // empty set of nodes. This is important for the case when there is
- // unreachable blocks.
- Function *F = Roots[0]->getParent();
- for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) Doms[I];
-}
-
namespace llvm {
static std::ostream &operator<<(std::ostream &o,
const std::set<BasicBlock*> &BBs) {
@@ -144,67 +328,6 @@
}
//===----------------------------------------------------------------------===//
-// ImmediateDominators Implementation
-//===----------------------------------------------------------------------===//
-
-static RegisterAnalysis<ImmediateDominators>
-C("idom", "Immediate Dominators Construction", true);
-
-// calcIDoms - Calculate the immediate dominator mapping, given a set of
-// dominators for every basic block.
-void ImmediateDominatorsBase::calcIDoms(const DominatorSetBase &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;
- }
- }
- }
-}
-
-void ImmediateDominatorsBase::print(std::ostream &o) const {
- for (const_iterator I = begin(), E = end(); I != E; ++I) {
- o << " Immediate Dominator For Basic Block:";
- if (I->first)
- WriteAsOperand(o, I->first, false);
- else
- o << " <<exit node>>";
- o << " is:";
- if (I->second)
- WriteAsOperand(o, I->second, false);
- else
- o << " <<exit node>>";
- o << "\n";
- }
- o << "\n";
-}
-
-
-//===----------------------------------------------------------------------===//
// DominatorTree Implementation
//===----------------------------------------------------------------------===//
@@ -236,55 +359,39 @@
}
}
+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 DominatorSet &DS) {
+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...
- // Iterate over all nodes in depth first order...
- for (df_iterator<BasicBlock*> I = df_begin(Root), E = df_end(Root);
+ // Loop over all of the reachable blocks in the function...
+ for (ImmediateDominators::const_iterator I = ID.begin(), E = ID.end();
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;
- }
+ Node *&BBNode = Nodes[I->first];
+ if (!BBNode) { // Haven't calculated this node yet?
+ // Get or calculate the node for the immediate dominator
+ Node *IDomNode = getNodeForBlock(I->second);
+
+ // Add a new tree node for this BasicBlock, and link it as a child of
+ // IDomNode
+ BBNode = IDomNode->addChild(new Node(I->first, IDomNode));
}
}
}
-
static std::ostream &operator<<(std::ostream &o,
const DominatorTreeBase::Node *Node) {
More information about the llvm-commits
mailing list