1 //===- MachineDominators.cpp - Machine Dominator Calculation --------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements simple dominator construction algorithms for finding
11 // forward dominators on machine functions.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/CodeGen/MachineDominators.h"
16 #include "llvm/ADT/SmallBitVector.h"
17 #include "llvm/CodeGen/Passes.h"
18 #include "llvm/Support/CommandLine.h"
22 // Always verify dominfo if expensive checking is enabled.
23 #ifdef EXPENSIVE_CHECKS
24 static bool VerifyMachineDomInfo = true;
26 static bool VerifyMachineDomInfo = false;
28 static cl::opt<bool, true> VerifyMachineDomInfoX(
29 "verify-machine-dom-info", cl::location(VerifyMachineDomInfo), cl::Hidden,
30 cl::desc("Verify machine dominator info (time consuming)"));
33 template class DomTreeNodeBase<MachineBasicBlock>;
34 template class DominatorTreeBase<MachineBasicBlock, false>; // DomTreeBase
37 char MachineDominatorTree::ID = 0;
39 INITIALIZE_PASS(MachineDominatorTree, "machinedomtree",
40 "MachineDominator Tree Construction", true, true)
42 char &llvm::MachineDominatorsID = MachineDominatorTree::ID;
44 void MachineDominatorTree::getAnalysisUsage(AnalysisUsage &AU) const {
46 MachineFunctionPass::getAnalysisUsage(AU);
49 bool MachineDominatorTree::runOnMachineFunction(MachineFunction &F) {
50 CriticalEdgesToSplit.clear();
52 DT.reset(new DomTreeBase<MachineBasicBlock>());
57 MachineDominatorTree::MachineDominatorTree()
58 : MachineFunctionPass(ID) {
59 initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
62 void MachineDominatorTree::releaseMemory() {
63 CriticalEdgesToSplit.clear();
67 void MachineDominatorTree::verifyAnalysis() const {
68 if (DT && VerifyMachineDomInfo)
72 void MachineDominatorTree::print(raw_ostream &OS, const Module*) const {
77 void MachineDominatorTree::applySplitCriticalEdges() const {
78 // Bail out early if there is nothing to do.
79 if (CriticalEdgesToSplit.empty())
82 // For each element in CriticalEdgesToSplit, remember whether or not element
83 // is the new immediate domminator of its successor. The mapping is done by
84 // index, i.e., the information for the ith element of CriticalEdgesToSplit is
85 // the ith element of IsNewIDom.
86 SmallBitVector IsNewIDom(CriticalEdgesToSplit.size(), true);
89 // Collect all the dominance properties info, before invalidating
91 for (CriticalEdge &Edge : CriticalEdgesToSplit) {
92 // Update dominator information.
93 MachineBasicBlock *Succ = Edge.ToBB;
94 MachineDomTreeNode *SuccDTNode = DT->getNode(Succ);
96 for (MachineBasicBlock *PredBB : Succ->predecessors()) {
97 if (PredBB == Edge.NewBB)
99 // If we are in this situation:
104 // ... Split1 Split2 ...
109 // Instead of checking the domiance property with Split2, we check it with
110 // FromBB2 since Split2 is still unknown of the underlying DT structure.
111 if (NewBBs.count(PredBB)) {
112 assert(PredBB->pred_size() == 1 && "A basic block resulting from a "
113 "critical edge split has more "
114 "than one predecessor!");
115 PredBB = *PredBB->pred_begin();
117 if (!DT->dominates(SuccDTNode, DT->getNode(PredBB))) {
118 IsNewIDom[Idx] = false;
125 // Now, update DT with the collected dominance properties info.
127 for (CriticalEdge &Edge : CriticalEdgesToSplit) {
128 // We know FromBB dominates NewBB.
129 MachineDomTreeNode *NewDTNode = DT->addNewBlock(Edge.NewBB, Edge.FromBB);
131 // If all the other predecessors of "Succ" are dominated by "Succ" itself
132 // then the new block is the new immediate dominator of "Succ". Otherwise,
133 // the new block doesn't dominate anything.
135 DT->changeImmediateDominator(DT->getNode(Edge.ToBB), NewDTNode);
139 CriticalEdgesToSplit.clear();
142 void MachineDominatorTree::verifyDomTree() const {
145 MachineFunction &F = *getRoot()->getParent();
147 DomTreeBase<MachineBasicBlock> OtherDT;
148 OtherDT.recalculate(F);
149 if (getRootNode()->getBlock() != OtherDT.getRootNode()->getBlock() ||
150 DT->compare(OtherDT)) {
151 errs() << "MachineDominatorTree for function " << F.getName()
152 << " is not up to date!\nComputed:\n";
154 errs() << "\nActual:\n";
155 OtherDT.print(errs());