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//===- MachineDominators.cpp - Machine Dominator Calculation --------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements simple dominator construction algorithms for finding
// forward dominators on machine functions.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Support/CommandLine.h"
using namespace llvm;
// Always verify dominfo if expensive checking is enabled.
#ifdef EXPENSIVE_CHECKS
static bool VerifyMachineDomInfo = true;
#else
static bool VerifyMachineDomInfo = false;
#endif
static cl::opt<bool, true> VerifyMachineDomInfoX(
"verify-machine-dom-info", cl::location(VerifyMachineDomInfo), cl::Hidden,
cl::desc("Verify machine dominator info (time consuming)"));
namespace llvm {
template class DomTreeNodeBase<MachineBasicBlock>;
template class DominatorTreeBase<MachineBasicBlock, false>; // DomTreeBase
}
char MachineDominatorTree::ID = 0;
INITIALIZE_PASS(MachineDominatorTree, "machinedomtree",
"MachineDominator Tree Construction", true, true)
char &llvm::MachineDominatorsID = MachineDominatorTree::ID;
void MachineDominatorTree::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
MachineFunctionPass::getAnalysisUsage(AU);
}
bool MachineDominatorTree::runOnMachineFunction(MachineFunction &F) {
CriticalEdgesToSplit.clear();
NewBBs.clear();
DT.reset(new DomTreeBase<MachineBasicBlock>());
DT->recalculate(F);
return false;
}
MachineDominatorTree::MachineDominatorTree()
: MachineFunctionPass(ID) {
initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
}
void MachineDominatorTree::releaseMemory() {
CriticalEdgesToSplit.clear();
DT.reset(nullptr);
}
void MachineDominatorTree::verifyAnalysis() const {
if (DT && VerifyMachineDomInfo) {
MachineFunction &F = *getRoot()->getParent();
DomTreeBase<MachineBasicBlock> OtherDT;
OtherDT.recalculate(F);
if (getRootNode()->getBlock() != OtherDT.getRootNode()->getBlock() ||
DT->compare(OtherDT)) {
errs() << "MachineDominatorTree for function " << F.getName()
<< " is not up to date!\nComputed:\n";
DT->print(errs());
errs() << "\nActual:\n";
OtherDT.print(errs());
abort();
}
}
}
void MachineDominatorTree::print(raw_ostream &OS, const Module*) const {
if (DT)
DT->print(OS);
}
void MachineDominatorTree::applySplitCriticalEdges() const {
// Bail out early if there is nothing to do.
if (CriticalEdgesToSplit.empty())
return;
// For each element in CriticalEdgesToSplit, remember whether or not element
// is the new immediate domminator of its successor. The mapping is done by
// index, i.e., the information for the ith element of CriticalEdgesToSplit is
// the ith element of IsNewIDom.
SmallBitVector IsNewIDom(CriticalEdgesToSplit.size(), true);
size_t Idx = 0;
// Collect all the dominance properties info, before invalidating
// the underlying DT.
for (CriticalEdge &Edge : CriticalEdgesToSplit) {
// Update dominator information.
MachineBasicBlock *Succ = Edge.ToBB;
MachineDomTreeNode *SuccDTNode = DT->getNode(Succ);
for (MachineBasicBlock *PredBB : Succ->predecessors()) {
if (PredBB == Edge.NewBB)
continue;
// If we are in this situation:
// FromBB1 FromBB2
// + +
// + + + +
// + + + +
// ... Split1 Split2 ...
// + +
// + +
// +
// Succ
// Instead of checking the domiance property with Split2, we check it with
// FromBB2 since Split2 is still unknown of the underlying DT structure.
if (NewBBs.count(PredBB)) {
assert(PredBB->pred_size() == 1 && "A basic block resulting from a "
"critical edge split has more "
"than one predecessor!");
PredBB = *PredBB->pred_begin();
}
if (!DT->dominates(SuccDTNode, DT->getNode(PredBB))) {
IsNewIDom[Idx] = false;
break;
}
}
++Idx;
}
// Now, update DT with the collected dominance properties info.
Idx = 0;
for (CriticalEdge &Edge : CriticalEdgesToSplit) {
// We know FromBB dominates NewBB.
MachineDomTreeNode *NewDTNode = DT->addNewBlock(Edge.NewBB, Edge.FromBB);
// If all the other predecessors of "Succ" are dominated by "Succ" itself
// then the new block is the new immediate dominator of "Succ". Otherwise,
// the new block doesn't dominate anything.
if (IsNewIDom[Idx])
DT->changeImmediateDominator(DT->getNode(Edge.ToBB), NewDTNode);
++Idx;
}
NewBBs.clear();
CriticalEdgesToSplit.clear();
}
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