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+//===- Dominators.cpp - Dominator Calculation -----------------------------===//
+//
+// 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/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/IR/Instructions.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+using namespace llvm;
+
+// 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;
+}
+
+//===----------------------------------------------------------------------===//
+// DominatorTree Implementation
+//===----------------------------------------------------------------------===//
+//
+// Provide public access to DominatorTree information. Implementation details
+// can be found in DominatorInternals.h.
+//
+//===----------------------------------------------------------------------===//
+
+TEMPLATE_INSTANTIATION(class llvm::DomTreeNodeBase<BasicBlock>);
+TEMPLATE_INSTANTIATION(class llvm::DominatorTreeBase<BasicBlock>);
+
+char DominatorTree::ID = 0;
+INITIALIZE_PASS(DominatorTree, "domtree",
+ "Dominator Tree Construction", true, true)
+
+bool DominatorTree::runOnFunction(Function &F) {
+ DT->recalculate(F);
+ return false;
+}
+
+void DominatorTree::verifyAnalysis() const {
+ if (!VerifyDomInfo) return;
+
+ Function &F = *getRoot()->getParent();
+
+ 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);
+}
+
+// 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();
+
+ // Any unreachable use is dominated, even if DefBB == UseBB.
+ if (!isReachableFromEntry(UseBB))
+ return true;
+
+ // Unreachable definitions don't dominate anything.
+ if (!isReachableFromEntry(DefBB))
+ return false;
+
+ if (DefBB == UseBB)
+ return false;
+
+ const InvokeInst *II = dyn_cast<InvokeInst>(Def);
+ if (!II)
+ return dominates(DefBB, UseBB);
+
+ // 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);
+}
+
+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);
+ }
+
+ // If the def and use are in different blocks, do a simple CFG dominator
+ // tree query.
+ if (DefBB != UseBB)
+ return dominates(DefBB, UseBB);
+
+ // 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;
+
+ // 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 &*I != UserInst;
+}
+
+bool DominatorTree::isReachableFromEntry(const Use &U) const {
+ Instruction *I = dyn_cast<Instruction>(U.getUser());
+
+ // 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));
+
+ // Everything else uses their operands in their own block.
+ return isReachableFromEntry(I->getParent());
+}
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