[llvm-commits] CVS: llvm/lib/Analysis/PostDominators.cpp
Chris Lattner
lattner at cs.uiuc.edu
Wed Sep 10 15:38:10 PDT 2003
Changes in directory llvm/lib/Analysis:
PostDominators.cpp updated: 1.39 -> 1.40
---
Log message:
Rework post dominator information so that we do not have to
unify all exit nodes of a function to compute post-dominance information.
This does not work with functions that have both unwind and return nodes,
because we cannot unify these blocks. The new implementation is better
anyway. :)
---
Diffs of the changes:
Index: llvm/lib/Analysis/PostDominators.cpp
diff -u llvm/lib/Analysis/PostDominators.cpp:1.39 llvm/lib/Analysis/PostDominators.cpp:1.40
--- llvm/lib/Analysis/PostDominators.cpp:1.39 Wed Sep 10 11:08:03 2003
+++ llvm/lib/Analysis/PostDominators.cpp Wed Sep 10 15:37:08 2003
@@ -5,7 +5,7 @@
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/PostDominators.h"
-#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
+#include "llvm/iTerminators.h"
#include "llvm/Support/CFG.h"
#include "Support/DepthFirstIterator.h"
#include "Support/SetOperations.h"
@@ -23,75 +23,77 @@
//
bool PostDominatorSet::runOnFunction(Function &F) {
Doms.clear(); // Reset from the last time we were run...
- // 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 false;
+
+ // 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
+
+ if (isa<ReturnInst>(I->getTerminator()) ||
+ isa<UnwindInst>(I->getTerminator()))
+ 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.
+ 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);
+
bool Changed;
do {
Changed = false;
std::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);
- }
- } else if (BB != Root) {
- // If this isn't the root basic block and it has no successors, it must
- // be an non-returning block. Fib a bit by saying that the root node
- // postdominates this unreachable node. This isn't exactly true,
- // because there is no path from this node to the root node, but it is
- // sorta true because any paths to the exit node would have to go
- // through this node.
- //
- // This allows for postdominator properties to be built for code that
- // doesn't return in a reasonable manner.
- //
- WorkingSet = Doms[Root];
- }
+
+ for (unsigned i = 0, e = Roots.size(); i != e; ++i)
+ for (idf_iterator<BasicBlock*> It = idf_begin(Roots[i]),
+ E = idf_end(Roots[i]); 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);
+ }
+ } 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);
+ }
- 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.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
}
- WorkingSet.clear(); // Clear out the set for next iteration
- }
} while (Changed);
return false;
}
-// getAnalysisUsage - This obviously provides a post-dominator set, but it also
-// requires the UnifyFunctionExitNodes pass.
-//
-void PostDominatorSet::getAnalysisUsage(AnalysisUsage &AU) const {
- AU.setPreservesAll();
- AU.addRequired<UnifyFunctionExitNodes>();
-}
-
//===----------------------------------------------------------------------===//
// ImmediatePostDominators Implementation
//===----------------------------------------------------------------------===//
@@ -107,17 +109,25 @@
F("postdomtree", "Post-Dominator Tree Construction", true);
void PostDominatorTree::calculate(const PostDominatorSet &DS) {
- Nodes[Root] = new Node(Root, 0); // Add a node for the root...
+ if (Roots.empty()) return;
+ BasicBlock *Root = Roots.size() == 1 ? Roots[0] : 0;
- 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) {
+ Nodes[Root] = RootNode = new Node(Root, 0); // Add a node for the root...
+
+ // 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
@@ -130,28 +140,27 @@
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?");
+ // 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 new tree node for this BasicBlock, and link it as a child of
+ // IDomNode
+ Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
+ break;
+ }
}
}
- }
}
//===----------------------------------------------------------------------===//
@@ -167,14 +176,14 @@
// 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;
+ if (getRoots().empty()) 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);
- }
+ if (BB)
+ 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
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