LLVM  9.0.0svn
MachineDominators.cpp
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1 //===- MachineDominators.cpp - Machine Dominator Calculation --------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements simple dominator construction algorithms for finding
10 // forward dominators on machine functions.
11 //
12 //===----------------------------------------------------------------------===//
13 
16 #include "llvm/CodeGen/Passes.h"
18 
19 using namespace llvm;
20 
21 // Always verify dominfo if expensive checking is enabled.
22 #ifdef EXPENSIVE_CHECKS
23 static bool VerifyMachineDomInfo = true;
24 #else
25 static bool VerifyMachineDomInfo = false;
26 #endif
28  "verify-machine-dom-info", cl::location(VerifyMachineDomInfo), cl::Hidden,
29  cl::desc("Verify machine dominator info (time consuming)"));
30 
31 namespace llvm {
33 template class DominatorTreeBase<MachineBasicBlock, false>; // DomTreeBase
34 }
35 
37 
38 INITIALIZE_PASS(MachineDominatorTree, "machinedomtree",
39  "MachineDominator Tree Construction", true, true)
40 
42 
43 void MachineDominatorTree::getAnalysisUsage(AnalysisUsage &AU) const {
44  AU.setPreservesAll();
46 }
47 
49  CriticalEdgesToSplit.clear();
50  NewBBs.clear();
51  DT.reset(new DomTreeBase<MachineBasicBlock>());
52  DT->recalculate(F);
53  return false;
54 }
55 
57  : MachineFunctionPass(ID) {
59 }
60 
62  CriticalEdgesToSplit.clear();
63  DT.reset(nullptr);
64 }
65 
67  if (DT && VerifyMachineDomInfo) {
69 
71  OtherDT.recalculate(F);
72  if (getRootNode()->getBlock() != OtherDT.getRootNode()->getBlock() ||
73  DT->compare(OtherDT)) {
74  errs() << "MachineDominatorTree for function " << F.getName()
75  << " is not up to date!\nComputed:\n";
76  DT->print(errs());
77  errs() << "\nActual:\n";
78  OtherDT.print(errs());
79  abort();
80  }
81  }
82 }
83 
85  if (DT)
86  DT->print(OS);
87 }
88 
89 void MachineDominatorTree::applySplitCriticalEdges() const {
90  // Bail out early if there is nothing to do.
91  if (CriticalEdgesToSplit.empty())
92  return;
93 
94  // For each element in CriticalEdgesToSplit, remember whether or not element
95  // is the new immediate domminator of its successor. The mapping is done by
96  // index, i.e., the information for the ith element of CriticalEdgesToSplit is
97  // the ith element of IsNewIDom.
98  SmallBitVector IsNewIDom(CriticalEdgesToSplit.size(), true);
99  size_t Idx = 0;
100 
101  // Collect all the dominance properties info, before invalidating
102  // the underlying DT.
103  for (CriticalEdge &Edge : CriticalEdgesToSplit) {
104  // Update dominator information.
105  MachineBasicBlock *Succ = Edge.ToBB;
106  MachineDomTreeNode *SuccDTNode = DT->getNode(Succ);
107 
108  for (MachineBasicBlock *PredBB : Succ->predecessors()) {
109  if (PredBB == Edge.NewBB)
110  continue;
111  // If we are in this situation:
112  // FromBB1 FromBB2
113  // + +
114  // + + + +
115  // + + + +
116  // ... Split1 Split2 ...
117  // + +
118  // + +
119  // +
120  // Succ
121  // Instead of checking the domiance property with Split2, we check it with
122  // FromBB2 since Split2 is still unknown of the underlying DT structure.
123  if (NewBBs.count(PredBB)) {
124  assert(PredBB->pred_size() == 1 && "A basic block resulting from a "
125  "critical edge split has more "
126  "than one predecessor!");
127  PredBB = *PredBB->pred_begin();
128  }
129  if (!DT->dominates(SuccDTNode, DT->getNode(PredBB))) {
130  IsNewIDom[Idx] = false;
131  break;
132  }
133  }
134  ++Idx;
135  }
136 
137  // Now, update DT with the collected dominance properties info.
138  Idx = 0;
139  for (CriticalEdge &Edge : CriticalEdgesToSplit) {
140  // We know FromBB dominates NewBB.
141  MachineDomTreeNode *NewDTNode = DT->addNewBlock(Edge.NewBB, Edge.FromBB);
142 
143  // If all the other predecessors of "Succ" are dominated by "Succ" itself
144  // then the new block is the new immediate dominator of "Succ". Otherwise,
145  // the new block doesn't dominate anything.
146  if (IsNewIDom[Idx])
147  DT->changeImmediateDominator(DT->getNode(Edge.ToBB), NewDTNode);
148  ++Idx;
149  }
150  NewBBs.clear();
151  CriticalEdgesToSplit.clear();
152 }
MachineBasicBlock * getRoot() const
raw_ostream & errs()
This returns a reference to a raw_ostream for standard error.
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
This is a &#39;bitvector&#39; (really, a variable-sized bit array), optimized for the case when the array is ...
This class represents lattice values for constants.
Definition: AllocatorList.h:23
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:65
char & MachineDominatorsID
MachineDominators - This pass is a machine dominators analysis pass.
void recalculate(ParentType &Func)
recalculate - compute a dominator tree for the given function
F(f)
void verifyAnalysis() const override
verifyAnalysis() - This member can be implemented by a analysis pass to check state of analysis infor...
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
static cl::opt< bool, true > VerifyMachineDomInfoX("verify-machine-dom-info", cl::location(VerifyMachineDomInfo), cl::Hidden, cl::desc("Verify machine dominator info (time consuming)"))
Base class for the actual dominator tree node.
StringRef getName() const
getName - Return the name of the corresponding LLVM function.
Core dominator tree base class.
Definition: LoopInfo.h:60
void initializeMachineDominatorTreePass(PassRegistry &)
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
void releaseMemory() override
releaseMemory() - This member can be implemented by a pass if it wants to be able to release its memo...
Represent the analysis usage information of a pass.
iterator_range< pred_iterator > predecessors()
DomTreeNodeBase< NodeT > * getRootNode()
getRootNode - This returns the entry node for the CFG of the function.
size_t size() const
Definition: SmallVector.h:52
void print(raw_ostream &O) const
print - Convert to human readable form
#define INITIALIZE_PASS(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:33
MachineDomTreeNode * getRootNode() const
bool runOnMachineFunction(MachineFunction &F) override
runOnMachineFunction - This method must be overloaded to perform the desired machine code transformat...
const MachineFunction * getParent() const
Return the MachineFunction containing this basic block.
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:55
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
static bool VerifyMachineDomInfo
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:45
void print(raw_ostream &OS, const Module *) const override
print - Print out the internal state of the pass.
DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to compute a normal dominat...
LocationClass< Ty > location(Ty &L)
Definition: CommandLine.h:439