346 lines
12 KiB
C++
346 lines
12 KiB
C++
//===- Dominators.cpp - Dominator Calculation -----------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements simple dominator construction algorithms for finding
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// forward dominators. Postdominators are available in libanalysis, but are not
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// included in libvmcore, because it's not needed. Forward dominators are
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// needed to support the Verifier pass.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/SetOperations.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/Analysis/DominatorInternals.h"
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#include "llvm/Instructions.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Support/CommandLine.h"
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#include <algorithm>
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using namespace llvm;
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// Always verify dominfo if expensive checking is enabled.
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#ifdef XDEBUG
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bool VerifyDomInfo = true;
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#else
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bool VerifyDomInfo = false;
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#endif
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static cl::opt<bool,true>
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VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo),
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cl::desc("Verify dominator info (time consuming)"));
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//===----------------------------------------------------------------------===//
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// DominatorTree Implementation
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//===----------------------------------------------------------------------===//
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//
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// Provide public access to DominatorTree information. Implementation details
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// can be found in DominatorCalculation.h.
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//
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//===----------------------------------------------------------------------===//
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TEMPLATE_INSTANTIATION(class llvm::DomTreeNodeBase<BasicBlock>);
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TEMPLATE_INSTANTIATION(class llvm::DominatorTreeBase<BasicBlock>);
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char DominatorTree::ID = 0;
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static RegisterPass<DominatorTree>
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E("domtree", "Dominator Tree Construction", true, true);
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bool DominatorTree::runOnFunction(Function &F) {
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DT->recalculate(F);
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return false;
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}
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void DominatorTree::verifyAnalysis() const {
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if (!VerifyDomInfo) return;
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Function &F = *getRoot()->getParent();
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DominatorTree OtherDT;
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OtherDT.getBase().recalculate(F);
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assert(!compare(OtherDT) && "Invalid DominatorTree info!");
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}
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void DominatorTree::print(raw_ostream &OS, const Module *) const {
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DT->print(OS);
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}
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// dominates - Return true if A dominates a use in B. This performs the
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// special checks necessary if A and B are in the same basic block.
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bool DominatorTree::dominates(const Instruction *A, const Instruction *B) const{
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const BasicBlock *BBA = A->getParent(), *BBB = B->getParent();
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// If A is an invoke instruction, its value is only available in this normal
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// successor block.
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if (const InvokeInst *II = dyn_cast<InvokeInst>(A))
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BBA = II->getNormalDest();
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if (BBA != BBB) return dominates(BBA, BBB);
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// It is not possible to determine dominance between two PHI nodes
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// based on their ordering.
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if (isa<PHINode>(A) && isa<PHINode>(B))
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return false;
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// Loop through the basic block until we find A or B.
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BasicBlock::const_iterator I = BBA->begin();
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for (; &*I != A && &*I != B; ++I)
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/*empty*/;
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return &*I == A;
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}
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//===----------------------------------------------------------------------===//
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// DominanceFrontier Implementation
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//===----------------------------------------------------------------------===//
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char DominanceFrontier::ID = 0;
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static RegisterPass<DominanceFrontier>
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G("domfrontier", "Dominance Frontier Construction", true, true);
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void DominanceFrontier::verifyAnalysis() const {
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if (!VerifyDomInfo) return;
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DominatorTree &DT = getAnalysis<DominatorTree>();
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DominanceFrontier OtherDF;
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const std::vector<BasicBlock*> &DTRoots = DT.getRoots();
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OtherDF.calculate(DT, DT.getNode(DTRoots[0]));
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assert(!compare(OtherDF) && "Invalid DominanceFrontier info!");
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}
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// NewBB is split and now it has one successor. Update dominace frontier to
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// reflect this change.
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void DominanceFrontier::splitBlock(BasicBlock *NewBB) {
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assert(NewBB->getTerminator()->getNumSuccessors() == 1
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&& "NewBB should have a single successor!");
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BasicBlock *NewBBSucc = NewBB->getTerminator()->getSuccessor(0);
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SmallVector<BasicBlock*, 8> PredBlocks;
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for (pred_iterator PI = pred_begin(NewBB), PE = pred_end(NewBB);
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PI != PE; ++PI)
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PredBlocks.push_back(*PI);
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if (PredBlocks.empty())
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// If NewBB does not have any predecessors then it is a entry block.
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// In this case, NewBB and its successor NewBBSucc dominates all
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// other blocks.
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return;
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// NewBBSucc inherits original NewBB frontier.
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DominanceFrontier::iterator NewBBI = find(NewBB);
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if (NewBBI != end()) {
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DominanceFrontier::DomSetType NewBBSet = NewBBI->second;
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DominanceFrontier::DomSetType NewBBSuccSet;
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NewBBSuccSet.insert(NewBBSet.begin(), NewBBSet.end());
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addBasicBlock(NewBBSucc, NewBBSuccSet);
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}
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// If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
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// DF(PredBlocks[0]) without the stuff that the new block does not dominate
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// a predecessor of.
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DominatorTree &DT = getAnalysis<DominatorTree>();
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if (DT.dominates(NewBB, NewBBSucc)) {
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DominanceFrontier::iterator DFI = find(PredBlocks[0]);
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if (DFI != end()) {
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DominanceFrontier::DomSetType Set = DFI->second;
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// Filter out stuff in Set that we do not dominate a predecessor of.
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for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
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E = Set.end(); SetI != E;) {
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bool DominatesPred = false;
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for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
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PI != E; ++PI)
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if (DT.dominates(NewBB, *PI))
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DominatesPred = true;
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if (!DominatesPred)
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Set.erase(SetI++);
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else
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++SetI;
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}
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if (NewBBI != end()) {
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for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
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E = Set.end(); SetI != E; ++SetI) {
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BasicBlock *SB = *SetI;
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addToFrontier(NewBBI, SB);
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}
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} else
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addBasicBlock(NewBB, Set);
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}
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} else {
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// DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
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// NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
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// NewBBSucc)). NewBBSucc is the single successor of NewBB.
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DominanceFrontier::DomSetType NewDFSet;
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NewDFSet.insert(NewBBSucc);
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addBasicBlock(NewBB, NewDFSet);
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}
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// Now we must loop over all of the dominance frontiers in the function,
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// replacing occurrences of NewBBSucc with NewBB in some cases. All
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// blocks that dominate a block in PredBlocks and contained NewBBSucc in
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// their dominance frontier must be updated to contain NewBB instead.
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//
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for (Function::iterator FI = NewBB->getParent()->begin(),
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FE = NewBB->getParent()->end(); FI != FE; ++FI) {
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DominanceFrontier::iterator DFI = find(FI);
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if (DFI == end()) continue; // unreachable block.
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// Only consider nodes that have NewBBSucc in their dominator frontier.
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if (!DFI->second.count(NewBBSucc)) continue;
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// Verify whether this block dominates a block in predblocks. If not, do
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// not update it.
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bool BlockDominatesAny = false;
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for (SmallVectorImpl<BasicBlock*>::const_iterator BI = PredBlocks.begin(),
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BE = PredBlocks.end(); BI != BE; ++BI) {
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if (DT.dominates(FI, *BI)) {
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BlockDominatesAny = true;
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break;
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}
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}
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// If NewBBSucc should not stay in our dominator frontier, remove it.
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// We remove it unless there is a predecessor of NewBBSucc that we
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// dominate, but we don't strictly dominate NewBBSucc.
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bool ShouldRemove = true;
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if ((BasicBlock*)FI == NewBBSucc || !DT.dominates(FI, NewBBSucc)) {
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// Okay, we know that PredDom does not strictly dominate NewBBSucc.
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// Check to see if it dominates any predecessors of NewBBSucc.
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for (pred_iterator PI = pred_begin(NewBBSucc),
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E = pred_end(NewBBSucc); PI != E; ++PI)
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if (DT.dominates(FI, *PI)) {
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ShouldRemove = false;
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break;
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}
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}
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if (ShouldRemove)
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removeFromFrontier(DFI, NewBBSucc);
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if (BlockDominatesAny && (&*FI == NewBB || !DT.dominates(FI, NewBB)))
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addToFrontier(DFI, NewBB);
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}
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}
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namespace {
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class DFCalculateWorkObject {
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public:
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DFCalculateWorkObject(BasicBlock *B, BasicBlock *P,
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const DomTreeNode *N,
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const DomTreeNode *PN)
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: currentBB(B), parentBB(P), Node(N), parentNode(PN) {}
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BasicBlock *currentBB;
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BasicBlock *parentBB;
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const DomTreeNode *Node;
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const DomTreeNode *parentNode;
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};
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}
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const DominanceFrontier::DomSetType &
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DominanceFrontier::calculate(const DominatorTree &DT,
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const DomTreeNode *Node) {
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BasicBlock *BB = Node->getBlock();
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DomSetType *Result = NULL;
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std::vector<DFCalculateWorkObject> workList;
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SmallPtrSet<BasicBlock *, 32> visited;
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workList.push_back(DFCalculateWorkObject(BB, NULL, Node, NULL));
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do {
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DFCalculateWorkObject *currentW = &workList.back();
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assert (currentW && "Missing work object.");
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BasicBlock *currentBB = currentW->currentBB;
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BasicBlock *parentBB = currentW->parentBB;
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const DomTreeNode *currentNode = currentW->Node;
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const DomTreeNode *parentNode = currentW->parentNode;
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assert (currentBB && "Invalid work object. Missing current Basic Block");
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assert (currentNode && "Invalid work object. Missing current Node");
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DomSetType &S = Frontiers[currentBB];
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// Visit each block only once.
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if (visited.count(currentBB) == 0) {
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visited.insert(currentBB);
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// Loop over CFG successors to calculate DFlocal[currentNode]
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for (succ_iterator SI = succ_begin(currentBB), SE = succ_end(currentBB);
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SI != SE; ++SI) {
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// Does Node immediately dominate this successor?
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if (DT[*SI]->getIDom() != currentNode)
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S.insert(*SI);
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}
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}
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// At this point, S is DFlocal. Now we union in DFup's of our children...
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// Loop through and visit the nodes that Node immediately dominates (Node's
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// children in the IDomTree)
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bool visitChild = false;
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for (DomTreeNode::const_iterator NI = currentNode->begin(),
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NE = currentNode->end(); NI != NE; ++NI) {
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DomTreeNode *IDominee = *NI;
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BasicBlock *childBB = IDominee->getBlock();
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if (visited.count(childBB) == 0) {
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workList.push_back(DFCalculateWorkObject(childBB, currentBB,
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IDominee, currentNode));
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visitChild = true;
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}
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}
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// If all children are visited or there is any child then pop this block
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// from the workList.
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if (!visitChild) {
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if (!parentBB) {
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Result = &S;
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break;
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}
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DomSetType::const_iterator CDFI = S.begin(), CDFE = S.end();
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DomSetType &parentSet = Frontiers[parentBB];
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for (; CDFI != CDFE; ++CDFI) {
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if (!DT.properlyDominates(parentNode, DT[*CDFI]))
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parentSet.insert(*CDFI);
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}
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workList.pop_back();
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}
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} while (!workList.empty());
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return *Result;
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}
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void DominanceFrontierBase::print(raw_ostream &OS, const Module* ) const {
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for (const_iterator I = begin(), E = end(); I != E; ++I) {
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OS << " DomFrontier for BB ";
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if (I->first)
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WriteAsOperand(OS, I->first, false);
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else
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OS << " <<exit node>>";
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OS << " is:\t";
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const std::set<BasicBlock*> &BBs = I->second;
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for (std::set<BasicBlock*>::const_iterator I = BBs.begin(), E = BBs.end();
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I != E; ++I) {
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OS << ' ';
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if (*I)
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WriteAsOperand(OS, *I, false);
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else
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OS << "<<exit node>>";
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}
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OS << "\n";
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}
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}
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