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llvm-mirror/lib/CodeGen/MachineDominators.cpp
Chandler Carruth ae65e281f3 Update the file headers across all of the LLVM projects in the monorepo
to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636
2019-01-19 08:50:56 +00:00

153 lines
5.0 KiB
C++

//===- 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();
}