[llvm-commits] CVS: llvm/lib/Analysis/PostDominators.cpp
Nate Begeman
natebegeman at mac.com
Fri Mar 10 18:20:58 PST 2006
Changes in directory llvm/lib/Analysis:
PostDominators.cpp updated: 1.54 -> 1.55
---
Log message:
Fix PR681: http://llvm.cs.uiuc.edu/PR681 by using the standard Lengauer and Tarjan algorithm for dominator
set construction, rather than intersecting various std::sets. This reduces
the memory usage for the testcase in PR681: http://llvm.cs.uiuc.edu/PR681 from 496 to 26MB of ram on my
darwin system, and reduces the runtime from 32.8 to 0.8 seconds on a
2.5GHz G5. This also enables future code sharing between Dom and PostDom
now that they share near-identical implementations.
---
Diffs of the changes: (+190 -141)
PostDominators.cpp | 331 ++++++++++++++++++++++++++++++-----------------------
1 files changed, 190 insertions(+), 141 deletions(-)
Index: llvm/lib/Analysis/PostDominators.cpp
diff -u llvm/lib/Analysis/PostDominators.cpp:1.54 llvm/lib/Analysis/PostDominators.cpp:1.55
--- llvm/lib/Analysis/PostDominators.cpp:1.54 Sun Jan 8 02:22:18 2006
+++ llvm/lib/Analysis/PostDominators.cpp Fri Mar 10 20:20:46 2006
@@ -16,9 +16,132 @@
#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
//===----------------------------------------------------------------------===//
@@ -30,119 +153,59 @@
// sets for the function.
//
bool PostDominatorSet::runOnFunction(Function &F) {
- Doms.clear(); // Reset from the last time we were run...
-
// 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) {
- Doms[I]; // Initialize to empty
-
+ 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);
+ //if (Roots.size() > 1)
+ // Doms[0].insert(0);
- bool Changed;
- do {
- Changed = false;
-
- std::set<BasicBlock*> Visited;
- DomSetType WorkingSet;
-
- for (unsigned i = 0, e = Roots.size(); i != e; ++i)
- for (idf_ext_iterator<BasicBlock*> It = idf_ext_begin(Roots[i], Visited),
- E = idf_ext_end(Roots[i], Visited); It != E; ++It) {
- BasicBlock *BB = *It;
- succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
- if (SI != SE) { // Is there SOME successor?
- // 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[*SI].size() == 0) ++SI;
- WorkingSet = Doms[*SI];
-
- for (++SI; SI != SE; ++SI) { // Intersect all of the successor sets
- DomSetType &SuccSet = Doms[*SI];
- if (SuccSet.size())
- set_intersect(WorkingSet, SuccSet);
- }
+ // 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 {
- // If this node has no successors, it must be one of the root nodes.
- // We will already take care of the notion that the node
- // post-dominates itself. The only thing we have to add is that if
- // there are multiple root nodes, we want to insert a special "null"
- // exit node which dominates the roots as well.
- if (Roots.size() > 1)
- WorkingSet.insert(0);
+ DS.insert(IPDom);
+ IPDom = IPD[IPDom];
}
-
- 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);
- return false;
-}
-
-//===----------------------------------------------------------------------===//
-// ImmediatePostDominators Implementation
-//===----------------------------------------------------------------------===//
-
-static RegisterAnalysis<ImmediatePostDominators>
-D("postidom", "Immediate Post-Dominators Construction", true);
-
-
-// calcIDoms - Calculate the immediate dominator mapping, given a set of
-// dominators for every basic block.
-void ImmediatePostDominators::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;
}
+ } 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;
}
//===----------------------------------------------------------------------===//
@@ -152,59 +215,45 @@
static RegisterAnalysis<PostDominatorTree>
F("postdomtree", "Post-Dominator Tree Construction", true);
-void PostDominatorTree::calculate(const PostDominatorSet &DS) {
- if (Roots.empty()) return;
- BasicBlock *Root = Roots.size() == 1 ? Roots[0] : 0;
+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));
+}
- Nodes[Root] = RootNode = new Node(Root, 0); // Add a node for the root...
+void PostDominatorTree::calculate(const ImmediatePostDominators &IPD) {
+ if (Roots.empty()) return;
- // 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) {
- BasicBlock *BB = *I;
- const DominatorSet::DomSetType &Dominators = DS.getDominators(BB);
- unsigned DomSetSize = Dominators.size();
- if (DomSetSize == 1) continue; // Root node... IDom = null
-
- // If we have already computed the immediate dominator for this node,
- // don't revisit. This can happen due to nodes reachable from multiple
- // roots, but which the idf_iterator doesn't know about.
- if (Nodes.find(BB) != Nodes.end()) continue;
-
- // 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.
- //
- for (DominatorSet::DomSetType::const_iterator I = Dominators.begin(),
- E = Dominators.end(); I != E; ++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;
- }
+ // 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
//===----------------------------------------------------------------------===//
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