LLVM  8.0.0svn
Dominators.cpp
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1 //===- Dominators.cpp - Dominator Calculation -----------------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements simple dominator construction algorithms for finding
11 // forward dominators. Postdominators are available in libanalysis, but are not
12 // included in libvmcore, because it's not needed. Forward dominators are
13 // needed to support the Verifier pass.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "llvm/IR/Dominators.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/Config/llvm-config.h"
21 #include "llvm/IR/CFG.h"
22 #include "llvm/IR/Constants.h"
23 #include "llvm/IR/Instructions.h"
24 #include "llvm/IR/PassManager.h"
26 #include "llvm/Support/Debug.h"
29 #include <algorithm>
30 using namespace llvm;
31 
32 bool llvm::VerifyDomInfo = false;
35  cl::desc("Verify dominator info (time consuming)"));
36 
37 #ifdef EXPENSIVE_CHECKS
38 static constexpr bool ExpensiveChecksEnabled = true;
39 #else
40 static constexpr bool ExpensiveChecksEnabled = false;
41 #endif
42 
44  const Instruction *TI = Start->getTerminator();
45  unsigned NumEdgesToEnd = 0;
46  for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) {
47  if (TI->getSuccessor(i) == End)
48  ++NumEdgesToEnd;
49  if (NumEdgesToEnd >= 2)
50  return false;
51  }
52  assert(NumEdgesToEnd == 1);
53  return true;
54 }
55 
56 //===----------------------------------------------------------------------===//
57 // DominatorTree Implementation
58 //===----------------------------------------------------------------------===//
59 //
60 // Provide public access to DominatorTree information. Implementation details
61 // can be found in Dominators.h, GenericDomTree.h, and
62 // GenericDomTreeConstruction.h.
63 //
64 //===----------------------------------------------------------------------===//
65 
67 template class llvm::DominatorTreeBase<BasicBlock, false>; // DomTreeBase
68 template class llvm::DominatorTreeBase<BasicBlock, true>; // PostDomTreeBase
69 
70 template class llvm::cfg::Update<BasicBlock *>;
71 
72 template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBDomTree>(
74 template void
75 llvm::DomTreeBuilder::CalculateWithUpdates<DomTreeBuilder::BBDomTree>(
77 
78 template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree>(
80 // No CalculateWithUpdates<PostDomTree> instantiation, unless a usecase arises.
81 
82 template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBDomTree>(
84 template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBPostDomTree>(
86 
87 template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBDomTree>(
89 template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBPostDomTree>(
91 
92 template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBDomTree>(
94 template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBPostDomTree>(
96 
97 template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBDomTree>(
98  const DomTreeBuilder::BBDomTree &DT,
100 template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBPostDomTree>(
103 
106  // Check whether the analysis, all analyses on functions, or the function's
107  // CFG have been preserved.
108  auto PAC = PA.getChecker<DominatorTreeAnalysis>();
109  return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
110  PAC.preservedSet<CFGAnalyses>());
111 }
112 
113 // dominates - Return true if Def dominates a use in User. This performs
114 // the special checks necessary if Def and User are in the same basic block.
115 // Note that Def doesn't dominate a use in Def itself!
117  const Instruction *User) const {
118  const BasicBlock *UseBB = User->getParent();
119  const BasicBlock *DefBB = Def->getParent();
120 
121  // Any unreachable use is dominated, even if Def == User.
122  if (!isReachableFromEntry(UseBB))
123  return true;
124 
125  // Unreachable definitions don't dominate anything.
126  if (!isReachableFromEntry(DefBB))
127  return false;
128 
129  // An instruction doesn't dominate a use in itself.
130  if (Def == User)
131  return false;
132 
133  // The value defined by an invoke dominates an instruction only if it
134  // dominates every instruction in UseBB.
135  // A PHI is dominated only if the instruction dominates every possible use in
136  // the UseBB.
137  if (isa<InvokeInst>(Def) || isa<PHINode>(User))
138  return dominates(Def, UseBB);
139 
140  if (DefBB != UseBB)
141  return dominates(DefBB, UseBB);
142 
143  // Loop through the basic block until we find Def or User.
145  for (; &*I != Def && &*I != User; ++I)
146  /*empty*/;
147 
148  return &*I == Def;
149 }
150 
151 // true if Def would dominate a use in any instruction in UseBB.
152 // note that dominates(Def, Def->getParent()) is false.
154  const BasicBlock *UseBB) const {
155  const BasicBlock *DefBB = Def->getParent();
156 
157  // Any unreachable use is dominated, even if DefBB == UseBB.
158  if (!isReachableFromEntry(UseBB))
159  return true;
160 
161  // Unreachable definitions don't dominate anything.
162  if (!isReachableFromEntry(DefBB))
163  return false;
164 
165  if (DefBB == UseBB)
166  return false;
167 
168  // Invoke results are only usable in the normal destination, not in the
169  // exceptional destination.
170  if (const auto *II = dyn_cast<InvokeInst>(Def)) {
171  BasicBlock *NormalDest = II->getNormalDest();
172  BasicBlockEdge E(DefBB, NormalDest);
173  return dominates(E, UseBB);
174  }
175 
176  return dominates(DefBB, UseBB);
177 }
178 
180  const BasicBlock *UseBB) const {
181  // If the BB the edge ends in doesn't dominate the use BB, then the
182  // edge also doesn't.
183  const BasicBlock *Start = BBE.getStart();
184  const BasicBlock *End = BBE.getEnd();
185  if (!dominates(End, UseBB))
186  return false;
187 
188  // Simple case: if the end BB has a single predecessor, the fact that it
189  // dominates the use block implies that the edge also does.
190  if (End->getSinglePredecessor())
191  return true;
192 
193  // The normal edge from the invoke is critical. Conceptually, what we would
194  // like to do is split it and check if the new block dominates the use.
195  // With X being the new block, the graph would look like:
196  //
197  // DefBB
198  // /\ . .
199  // / \ . .
200  // / \ . .
201  // / \ | |
202  // A X B C
203  // | \ | /
204  // . \|/
205  // . NormalDest
206  // .
207  //
208  // Given the definition of dominance, NormalDest is dominated by X iff X
209  // dominates all of NormalDest's predecessors (X, B, C in the example). X
210  // trivially dominates itself, so we only have to find if it dominates the
211  // other predecessors. Since the only way out of X is via NormalDest, X can
212  // only properly dominate a node if NormalDest dominates that node too.
213  int IsDuplicateEdge = 0;
214  for (const_pred_iterator PI = pred_begin(End), E = pred_end(End);
215  PI != E; ++PI) {
216  const BasicBlock *BB = *PI;
217  if (BB == Start) {
218  // If there are multiple edges between Start and End, by definition they
219  // can't dominate anything.
220  if (IsDuplicateEdge++)
221  return false;
222  continue;
223  }
224 
225  if (!dominates(End, BB))
226  return false;
227  }
228  return true;
229 }
230 
231 bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const {
232  Instruction *UserInst = cast<Instruction>(U.getUser());
233  // A PHI in the end of the edge is dominated by it.
234  PHINode *PN = dyn_cast<PHINode>(UserInst);
235  if (PN && PN->getParent() == BBE.getEnd() &&
236  PN->getIncomingBlock(U) == BBE.getStart())
237  return true;
238 
239  // Otherwise use the edge-dominates-block query, which
240  // handles the crazy critical edge cases properly.
241  const BasicBlock *UseBB;
242  if (PN)
243  UseBB = PN->getIncomingBlock(U);
244  else
245  UseBB = UserInst->getParent();
246  return dominates(BBE, UseBB);
247 }
248 
249 bool DominatorTree::dominates(const Instruction *Def, const Use &U) const {
250  Instruction *UserInst = cast<Instruction>(U.getUser());
251  const BasicBlock *DefBB = Def->getParent();
252 
253  // Determine the block in which the use happens. PHI nodes use
254  // their operands on edges; simulate this by thinking of the use
255  // happening at the end of the predecessor block.
256  const BasicBlock *UseBB;
257  if (PHINode *PN = dyn_cast<PHINode>(UserInst))
258  UseBB = PN->getIncomingBlock(U);
259  else
260  UseBB = UserInst->getParent();
261 
262  // Any unreachable use is dominated, even if Def == User.
263  if (!isReachableFromEntry(UseBB))
264  return true;
265 
266  // Unreachable definitions don't dominate anything.
267  if (!isReachableFromEntry(DefBB))
268  return false;
269 
270  // Invoke instructions define their return values on the edges to their normal
271  // successors, so we have to handle them specially.
272  // Among other things, this means they don't dominate anything in
273  // their own block, except possibly a phi, so we don't need to
274  // walk the block in any case.
275  if (const InvokeInst *II = dyn_cast<InvokeInst>(Def)) {
276  BasicBlock *NormalDest = II->getNormalDest();
277  BasicBlockEdge E(DefBB, NormalDest);
278  return dominates(E, U);
279  }
280 
281  // If the def and use are in different blocks, do a simple CFG dominator
282  // tree query.
283  if (DefBB != UseBB)
284  return dominates(DefBB, UseBB);
285 
286  // Ok, def and use are in the same block. If the def is an invoke, it
287  // doesn't dominate anything in the block. If it's a PHI, it dominates
288  // everything in the block.
289  if (isa<PHINode>(UserInst))
290  return true;
291 
292  // Otherwise, just loop through the basic block until we find Def or User.
293  BasicBlock::const_iterator I = DefBB->begin();
294  for (; &*I != Def && &*I != UserInst; ++I)
295  /*empty*/;
296 
297  return &*I != UserInst;
298 }
299 
302 
303  // ConstantExprs aren't really reachable from the entry block, but they
304  // don't need to be treated like unreachable code either.
305  if (!I) return true;
306 
307  // PHI nodes use their operands on their incoming edges.
308  if (PHINode *PN = dyn_cast<PHINode>(I))
309  return isReachableFromEntry(PN->getIncomingBlock(U));
310 
311  // Everything else uses their operands in their own block.
312  return isReachableFromEntry(I->getParent());
313 }
314 
315 //===----------------------------------------------------------------------===//
316 // DominatorTreeAnalysis and related pass implementations
317 //===----------------------------------------------------------------------===//
318 //
319 // This implements the DominatorTreeAnalysis which is used with the new pass
320 // manager. It also implements some methods from utility passes.
321 //
322 //===----------------------------------------------------------------------===//
323 
326  DominatorTree DT;
327  DT.recalculate(F);
328  return DT;
329 }
330 
331 AnalysisKey DominatorTreeAnalysis::Key;
332 
334 
337  OS << "DominatorTree for function: " << F.getName() << "\n";
339 
340  return PreservedAnalyses::all();
341 }
342 
345  auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
346  assert(DT.verify());
347  (void)DT;
348  return PreservedAnalyses::all();
349 }
350 
351 //===----------------------------------------------------------------------===//
352 // DominatorTreeWrapperPass Implementation
353 //===----------------------------------------------------------------------===//
354 //
355 // The implementation details of the wrapper pass that holds a DominatorTree
356 // suitable for use with the legacy pass manager.
357 //
358 //===----------------------------------------------------------------------===//
359 
362  "Dominator Tree Construction", true, true)
363 
365  DT.recalculate(F);
366  return false;
367 }
368 
370  if (VerifyDomInfo)
372  else if (ExpensiveChecksEnabled)
374 }
375 
377  DT.print(OS);
378 }
379 
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:770
This class represents lattice values for constants.
Definition: AllocatorList.h:24
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:64
BasicBlock * getSuccessor(unsigned Idx) const
Return the specified successor. This instruction must be a terminator.
void recalculate(ParentType &Func)
recalculate - compute a dominator tree for the given function
static constexpr bool ExpensiveChecksEnabled
Definition: Dominators.cpp:40
Analysis pass which computes a DominatorTree.
Definition: Dominators.h:231
F(f)
const BasicBlock * getEnd() const
Definition: Dominators.h:95
const Instruction * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:138
bool isReachableFromEntry(const Use &U) const
Provide an overload for a Use.
Definition: Dominators.cpp:300
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:269
bool isSingleEdge() const
Check if this is the only edge between Start and End.
Definition: Dominators.cpp:43
PreservedAnalysisChecker getChecker() const
Build a checker for this PreservedAnalyses and the specified analysis type.
Definition: PassManager.h:305
void verifyAnalysis() const override
verifyAnalysis() - This member can be implemented by a analysis pass to check state of analysis infor...
Definition: Dominators.cpp:369
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
User * getUser() const LLVM_READONLY
Returns the User that contains this Use.
Definition: Use.cpp:41
DominatorTreePrinterPass(raw_ostream &OS)
Definition: Dominators.cpp:333
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:145
unsigned getNumSuccessors() const
Return the number of successors that this instruction has.
static bool runOnFunction(Function &F, bool PostInlining)
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:154
const BasicBlock * getSinglePredecessor() const
Return the predecessor of this block if it has a single predecessor block.
Definition: BasicBlock.cpp:236
LLVM Basic Block Representation.
Definition: BasicBlock.h:58
DominatorTree run(Function &F, FunctionAnalysisManager &)
Run the analysis pass over a function and produce a dominator tree.
Definition: Dominators.cpp:324
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
This file contains the declarations for the subclasses of Constant, which represent the different fla...
Interval::pred_iterator pred_begin(Interval *I)
pred_begin/pred_end - define methods so that Intervals may be used just like BasicBlocks can with the...
Definition: Interval.h:113
Interval::pred_iterator pred_end(Interval *I)
Definition: Interval.h:116
static void print(raw_ostream &Out, object::Archive::Kind Kind, T Val)
bool VerifyDomInfo
Enables verification of dominator trees.
Definition: Dominators.cpp:32
ArrayRef< llvm::cfg::Update< BasicBlock * > > BBUpdates
Definition: Dominators.h:46
INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree", "Dominator Tree Construction", true, true) bool DominatorTreeWrapperPass
Definition: Dominators.cpp:361
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:160
Iterator for intrusive lists based on ilist_node.
BlockVerifier::State From
Generic dominator tree construction - This file provides routines to construct immediate dominator in...
bool dominates(const Instruction *Def, const Use &U) const
Return true if Def dominates a use in User.
Definition: Dominators.cpp:249
static cl::opt< bool, true > VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo), cl::Hidden, cl::desc("Verify dominator info (time consuming)"))
void print(raw_ostream &OS, const Module *M=nullptr) const override
print - Print out the internal state of the pass.
Definition: Dominators.cpp:376
bool invalidate(Function &F, const PreservedAnalyses &PA, FunctionAnalysisManager::Invalidator &)
Handle invalidation explicitly.
Definition: Dominators.cpp:104
Represents analyses that only rely on functions&#39; control flow.
Definition: PassManager.h:115
This file provides various utilities for inspecting and working with the control flow graph in LLVM I...
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:215
#define I(x, y, z)
Definition: MD5.cpp:58
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:323
API to communicate dependencies between analyses during invalidation.
Definition: PassManager.h:642
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
This templated class represents "all analyses that operate over <a particular IR unit>" (e...
Definition: PassManager.h:92
const BasicBlock * getStart() const
Definition: Dominators.h:91
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Definition: Dominators.cpp:335
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:46
Invoke instruction.
A container for analyses that lazily runs them and caches their results.
Legacy analysis pass which computes a DominatorTree.
Definition: Dominators.h:260
This header defines various interfaces for pass management in LLVM.
A special type used by analysis passes to provide an address that identifies that particular analysis...
Definition: PassManager.h:71
LocationClass< Ty > location(Ty &L)
Definition: CommandLine.h:435
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Definition: Dominators.cpp:343
const BasicBlock * getParent() const
Definition: Instruction.h:67