forked from OSchip/llvm-project
128 lines
4.1 KiB
C++
128 lines
4.1 KiB
C++
//===- MachineDominators.cpp - Machine 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 on machine functions.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/MachineDominators.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/ADT/SmallBitVector.h"
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using namespace llvm;
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namespace llvm {
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TEMPLATE_INSTANTIATION(class DomTreeNodeBase<MachineBasicBlock>);
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TEMPLATE_INSTANTIATION(class DominatorTreeBase<MachineBasicBlock>);
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}
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char MachineDominatorTree::ID = 0;
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INITIALIZE_PASS(MachineDominatorTree, "machinedomtree",
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"MachineDominator Tree Construction", true, true)
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char &llvm::MachineDominatorsID = MachineDominatorTree::ID;
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void MachineDominatorTree::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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bool MachineDominatorTree::runOnMachineFunction(MachineFunction &F) {
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CriticalEdgesToSplit.clear();
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NewBBs.clear();
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DT->recalculate(F);
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return false;
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}
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MachineDominatorTree::MachineDominatorTree()
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: MachineFunctionPass(ID) {
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initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
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DT = new DominatorTreeBase<MachineBasicBlock>(false);
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}
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MachineDominatorTree::~MachineDominatorTree() {
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delete DT;
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}
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void MachineDominatorTree::releaseMemory() {
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DT->releaseMemory();
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}
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void MachineDominatorTree::print(raw_ostream &OS, const Module*) const {
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DT->print(OS);
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}
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void MachineDominatorTree::applySplitCriticalEdges() const {
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// Bail out early if there is nothing to do.
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if (CriticalEdgesToSplit.empty())
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return;
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// For each element in CriticalEdgesToSplit, remember whether or not element
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// is the new immediate domminator of its successor. The mapping is done by
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// index, i.e., the information for the ith element of CriticalEdgesToSplit is
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// the ith element of IsNewIDom.
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SmallBitVector IsNewIDom(CriticalEdgesToSplit.size(), true);
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size_t Idx = 0;
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// Collect all the dominance properties info, before invalidating
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// the underlying DT.
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for (CriticalEdge &Edge : CriticalEdgesToSplit) {
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// Update dominator information.
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MachineBasicBlock *Succ = Edge.ToBB;
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MachineDomTreeNode *SuccDTNode = DT->getNode(Succ);
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for (MachineBasicBlock *PredBB : Succ->predecessors()) {
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if (PredBB == Edge.NewBB)
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continue;
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// If we are in this situation:
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// FromBB1 FromBB2
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// + +
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// + + + +
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// + + + +
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// ... Split1 Split2 ...
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// + +
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// + +
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// +
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// Succ
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// Instead of checking the domiance property with Split2, we check it with
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// FromBB2 since Split2 is still unknown of the underlying DT structure.
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if (NewBBs.count(PredBB)) {
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assert(PredBB->pred_size() == 1 && "A basic block resulting from a "
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"critical edge split has more "
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"than one predecessor!");
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PredBB = *PredBB->pred_begin();
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}
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if (!DT->dominates(SuccDTNode, DT->getNode(PredBB))) {
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IsNewIDom[Idx] = false;
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break;
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}
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}
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++Idx;
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}
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// Now, update DT with the collected dominance properties info.
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Idx = 0;
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for (CriticalEdge &Edge : CriticalEdgesToSplit) {
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// We know FromBB dominates NewBB.
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MachineDomTreeNode *NewDTNode = DT->addNewBlock(Edge.NewBB, Edge.FromBB);
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// If all the other predecessors of "Succ" are dominated by "Succ" itself
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// then the new block is the new immediate dominator of "Succ". Otherwise,
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// the new block doesn't dominate anything.
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if (IsNewIDom[Idx])
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DT->changeImmediateDominator(DT->getNode(Edge.ToBB), NewDTNode);
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++Idx;
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}
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NewBBs.clear();
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CriticalEdgesToSplit.clear();
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}
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