-//===- DominatorSet.cpp - Dominator Set Calculation --------------*- C++ -*--=//
+//===- Dominators.cpp - Dominator Calculation -----------------------------===//
//
-// This file provides a simple class to calculate the dominator set of a
-// function.
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements simple dominator construction algorithms for finding
+// forward dominators. Postdominators are available in libanalysis, but are not
+// included in libvmcore, because it's not needed. Forward dominators are
+// needed to support the Verifier pass.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/Dominators.h"
-#include "llvm/Transforms/Scalar/UnifyFunctionExitNodes.h"
#include "llvm/Support/CFG.h"
-#include "Support/DepthFirstIterator.h"
-#include "Support/STLExtras.h"
-#include "Support/SetOperations.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Analysis/DominatorInternals.h"
+#include "llvm/Assembly/Writer.h"
+#include "llvm/Instructions.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/CommandLine.h"
#include <algorithm>
-using std::set;
-
-//===----------------------------------------------------------------------===//
-// DominatorSet Implementation
-//===----------------------------------------------------------------------===//
+using namespace llvm;
-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;
+// Always verify dominfo if expensive checking is enabled.
+#ifdef XDEBUG
+static bool VerifyDomInfo = true;
+#else
+static bool VerifyDomInfo = false;
+#endif
+static cl::opt<bool,true>
+VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo),
+ cl::desc("Verify dominator info (time consuming)"));
+
+bool BasicBlockEdge::isSingleEdge() const {
+ const TerminatorInst *TI = Start->getTerminator();
+ unsigned NumEdgesToEnd = 0;
+ for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) {
+ if (TI->getSuccessor(i) == End)
+ ++NumEdgesToEnd;
+ if (NumEdgesToEnd >= 2)
+ return false;
+ }
+ assert(NumEdgesToEnd == 1);
+ return true;
}
-
-// calcForwardDominatorSet - This method calculates the forward dominator sets
-// for the specified function.
+//===----------------------------------------------------------------------===//
+// DominatorTree Implementation
+//===----------------------------------------------------------------------===//
//
-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.
+// Provide public access to DominatorTree information. Implementation details
+// can be found in DominatorInternals.h.
//
-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;
- }
+TEMPLATE_INSTANTIATION(class llvm::DomTreeNodeBase<BasicBlock>);
+TEMPLATE_INSTANTIATION(class llvm::DominatorTreeBase<BasicBlock>);
- 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);
-}
+char DominatorTree::ID = 0;
+INITIALIZE_PASS(DominatorTree, "domtree",
+ "Dominator Tree Construction", true, true)
-// 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);
- }
+bool DominatorTree::runOnFunction(Function &F) {
+ DT->recalculate(F);
+ return false;
}
+void DominatorTree::verifyAnalysis() const {
+ if (!VerifyDomInfo) return;
-//===----------------------------------------------------------------------===//
-// ImmediateDominators Implementation
-//===----------------------------------------------------------------------===//
-
-AnalysisID ImmediateDominators::ID(AnalysisID::create<ImmediateDominators>(), true);
-AnalysisID ImmediateDominators::PostDomID(AnalysisID::create<ImmediateDominators>(), true);
+ Function &F = *getRoot()->getParent();
-// 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 OtherDT;
+ OtherDT.getBase().recalculate(F);
+ if (compare(OtherDT)) {
+ errs() << "DominatorTree is not up to date!\nComputed:\n";
+ print(errs());
+ errs() << "\nActual:\n";
+ OtherDT.print(errs());
+ abort();
}
}
+void DominatorTree::print(raw_ostream &OS, const Module *) const {
+ DT->print(OS);
+}
-//===----------------------------------------------------------------------===//
-// 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();
+// dominates - Return true if Def dominates a use in User. This performs
+// the special checks necessary if Def and User are in the same basic block.
+// Note that Def doesn't dominate a use in Def itself!
+bool DominatorTree::dominates(const Instruction *Def,
+ const Instruction *User) const {
+ const BasicBlock *UseBB = User->getParent();
+ const BasicBlock *DefBB = Def->getParent();
+
+ // Any unreachable use is dominated, even if Def == User.
+ if (!isReachableFromEntry(UseBB))
+ return true;
+
+ // Unreachable definitions don't dominate anything.
+ if (!isReachableFromEntry(DefBB))
+ return false;
+
+ // An instruction doesn't dominate a use in itself.
+ if (Def == User)
+ return false;
+
+ // The value defined by an invoke dominates an instruction only if
+ // it dominates every instruction in UseBB.
+ // A PHI is dominated only if the instruction dominates every possible use
+ // in the UseBB.
+ if (isa<InvokeInst>(Def) || isa<PHINode>(User))
+ return dominates(Def, UseBB);
+
+ if (DefBB != UseBB)
+ return dominates(DefBB, UseBB);
+
+ // Loop through the basic block until we find Def or User.
+ BasicBlock::const_iterator I = DefBB->begin();
+ for (; &*I != Def && &*I != User; ++I)
+ /*empty*/;
+
+ return &*I == Def;
}
+// true if Def would dominate a use in any instruction in UseBB.
+// note that dominates(Def, Def->getParent()) is false.
+bool DominatorTree::dominates(const Instruction *Def,
+ const BasicBlock *UseBB) const {
+ const BasicBlock *DefBB = Def->getParent();
-#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();
+ // Any unreachable use is dominated, even if DefBB == UseBB.
+ if (!isReachableFromEntry(UseBB))
+ return true;
- Nodes[Root] = new Node(Root, 0); // Add a node for the root...
+ // Unreachable definitions don't dominate anything.
+ if (!isReachableFromEntry(DefBB))
+ return false;
- // 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 (DefBB == UseBB)
+ return false;
- 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];
+ const InvokeInst *II = dyn_cast<InvokeInst>(Def);
+ if (!II)
+ return dominates(DefBB, UseBB);
- // Add a new tree node for this BasicBlock, and link it as a child of
- // IDomNode
- Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
- }
- }
+ // Invoke results are only usable in the normal destination, not in the
+ // exceptional destination.
+ BasicBlock *NormalDest = II->getNormalDest();
+ BasicBlockEdge E(DefBB, NormalDest);
+ return dominates(E, UseBB);
}
-#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;
- }
- }
- }
+bool DominatorTree::dominates(const BasicBlockEdge &BBE,
+ const BasicBlock *UseBB) const {
+ // Assert that we have a single edge. We could handle them by simply
+ // returning false, but since isSingleEdge is linear on the number of
+ // edges, the callers can normally handle them more efficiently.
+ assert(BBE.isSingleEdge());
+
+ // If the BB the edge ends in doesn't dominate the use BB, then the
+ // edge also doesn't.
+ const BasicBlock *Start = BBE.getStart();
+ const BasicBlock *End = BBE.getEnd();
+ if (!dominates(End, UseBB))
+ return false;
+
+ // Simple case: if the end BB has a single predecessor, the fact that it
+ // dominates the use block implies that the edge also does.
+ if (End->getSinglePredecessor())
+ return true;
+
+ // The normal edge from the invoke is critical. Conceptually, what we would
+ // like to do is split it and check if the new block dominates the use.
+ // With X being the new block, the graph would look like:
+ //
+ // DefBB
+ // /\ . .
+ // / \ . .
+ // / \ . .
+ // / \ | |
+ // A X B C
+ // | \ | /
+ // . \|/
+ // . NormalDest
+ // .
+ //
+ // Given the definition of dominance, NormalDest is dominated by X iff X
+ // dominates all of NormalDest's predecessors (X, B, C in the example). X
+ // trivially dominates itself, so we only have to find if it dominates the
+ // other predecessors. Since the only way out of X is via NormalDest, X can
+ // only properly dominate a node if NormalDest dominates that node too.
+ for (const_pred_iterator PI = pred_begin(End), E = pred_end(End);
+ PI != E; ++PI) {
+ const BasicBlock *BB = *PI;
+ if (BB == Start)
+ continue;
+
+ if (!dominates(End, BB))
+ return false;
}
+ return true;
}
+bool DominatorTree::dominates(const BasicBlockEdge &BBE,
+ const Use &U) const {
+ // Assert that we have a single edge. We could handle them by simply
+ // returning false, but since isSingleEdge is linear on the number of
+ // edges, the callers can normally handle them more efficiently.
+ assert(BBE.isSingleEdge());
+
+ Instruction *UserInst = cast<Instruction>(U.getUser());
+ // A PHI in the end of the edge is dominated by it.
+ PHINode *PN = dyn_cast<PHINode>(UserInst);
+ if (PN && PN->getParent() == BBE.getEnd() &&
+ PN->getIncomingBlock(U) == BBE.getStart())
+ return true;
+
+ // Otherwise use the edge-dominates-block query, which
+ // handles the crazy critical edge cases properly.
+ const BasicBlock *UseBB;
+ if (PN)
+ UseBB = PN->getIncomingBlock(U);
+ else
+ UseBB = UserInst->getParent();
+ return dominates(BBE, UseBB);
+}
+bool DominatorTree::dominates(const Instruction *Def,
+ const Use &U) const {
+ Instruction *UserInst = cast<Instruction>(U.getUser());
+ const BasicBlock *DefBB = Def->getParent();
+
+ // Determine the block in which the use happens. PHI nodes use
+ // their operands on edges; simulate this by thinking of the use
+ // happening at the end of the predecessor block.
+ const BasicBlock *UseBB;
+ if (PHINode *PN = dyn_cast<PHINode>(UserInst))
+ UseBB = PN->getIncomingBlock(U);
+ else
+ UseBB = UserInst->getParent();
+
+ // Any unreachable use is dominated, even if Def == User.
+ if (!isReachableFromEntry(UseBB))
+ return true;
+
+ // Unreachable definitions don't dominate anything.
+ if (!isReachableFromEntry(DefBB))
+ return false;
+
+ // Invoke instructions define their return values on the edges
+ // to their normal successors, so we have to handle them specially.
+ // Among other things, this means they don't dominate anything in
+ // their own block, except possibly a phi, so we don't need to
+ // walk the block in any case.
+ if (const InvokeInst *II = dyn_cast<InvokeInst>(Def)) {
+ BasicBlock *NormalDest = II->getNormalDest();
+ BasicBlockEdge E(DefBB, NormalDest);
+ return dominates(E, U);
+ }
-//===----------------------------------------------------------------------===//
-// DominanceFrontier Implementation
-//===----------------------------------------------------------------------===//
+ // If the def and use are in different blocks, do a simple CFG dominator
+ // tree query.
+ if (DefBB != UseBB)
+ return dominates(DefBB, UseBB);
-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);
- }
+ // Ok, def and use are in the same block. If the def is an invoke, it
+ // doesn't dominate anything in the block. If it's a PHI, it dominates
+ // everything in the block.
+ if (isa<PHINode>(UserInst))
+ return true;
- // 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);
- }
- }
+ // Otherwise, just loop through the basic block until we find Def or User.
+ BasicBlock::const_iterator I = DefBB->begin();
+ for (; &*I != Def && &*I != UserInst; ++I)
+ /*empty*/;
- return S;
+ return &*I != UserInst;
}
-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);
- }
+bool DominatorTree::isReachableFromEntry(const Use &U) const {
+ Instruction *I = dyn_cast<Instruction>(U.getUser());
- // 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);
- }
- }
+ // ConstantExprs aren't really reachable from the entry block, but they
+ // don't need to be treated like unreachable code either.
+ if (!I) return true;
+
+ // PHI nodes use their operands on their incoming edges.
+ if (PHINode *PN = dyn_cast<PHINode>(I))
+ return isReachableFromEntry(PN->getIncomingBlock(U));
- return S;
+ // Everything else uses their operands in their own block.
+ return isReachableFromEntry(I->getParent());
}
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