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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/IR/CFG.h"
21 #include "llvm/IR/Instructions.h"
22 #include "llvm/IR/PassManager.h"
24 #include "llvm/Support/Debug.h"
27 #include <algorithm>
28 using namespace llvm;
29 
30 // Always verify dominfo if expensive checking is enabled.
31 #ifdef EXPENSIVE_CHECKS
32 bool llvm::VerifyDomInfo = true;
33 #else
34 bool llvm::VerifyDomInfo = false;
35 #endif
36 static cl::opt<bool,true>
37 VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo),
38  cl::desc("Verify dominator info (time consuming)"));
39 
41  const TerminatorInst *TI = Start->getTerminator();
42  unsigned NumEdgesToEnd = 0;
43  for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) {
44  if (TI->getSuccessor(i) == End)
45  ++NumEdgesToEnd;
46  if (NumEdgesToEnd >= 2)
47  return false;
48  }
49  assert(NumEdgesToEnd == 1);
50  return true;
51 }
52 
53 //===----------------------------------------------------------------------===//
54 // DominatorTree Implementation
55 //===----------------------------------------------------------------------===//
56 //
57 // Provide public access to DominatorTree information. Implementation details
58 // can be found in Dominators.h, GenericDomTree.h, and
59 // GenericDomTreeConstruction.h.
60 //
61 //===----------------------------------------------------------------------===//
62 
64 template class llvm::DominatorTreeBase<BasicBlock, false>; // DomTreeBase
65 template class llvm::DominatorTreeBase<BasicBlock, true>; // PostDomTreeBase
66 
67 template void
68 llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBDomTree, Function>(
70 template void
71 llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree, Function>(
73 
74 template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBDomTree>(
76 template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBPostDomTree>(
78 
79 template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBDomTree>(
81 template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBPostDomTree>(
83 
84 template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBDomTree>(
85  const DomTreeBuilder::BBDomTree &DT);
86 template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBPostDomTree>(
88 
91  // Check whether the analysis, all analyses on functions, or the function's
92  // CFG have been preserved.
93  auto PAC = PA.getChecker<DominatorTreeAnalysis>();
94  return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
95  PAC.preservedSet<CFGAnalyses>());
96 }
97 
98 // dominates - Return true if Def dominates a use in User. This performs
99 // the special checks necessary if Def and User are in the same basic block.
100 // Note that Def doesn't dominate a use in Def itself!
102  const Instruction *User) const {
103  const BasicBlock *UseBB = User->getParent();
104  const BasicBlock *DefBB = Def->getParent();
105 
106  // Any unreachable use is dominated, even if Def == User.
107  if (!isReachableFromEntry(UseBB))
108  return true;
109 
110  // Unreachable definitions don't dominate anything.
111  if (!isReachableFromEntry(DefBB))
112  return false;
113 
114  // An instruction doesn't dominate a use in itself.
115  if (Def == User)
116  return false;
117 
118  // The value defined by an invoke dominates an instruction only if it
119  // dominates every instruction in UseBB.
120  // A PHI is dominated only if the instruction dominates every possible use in
121  // the UseBB.
122  if (isa<InvokeInst>(Def) || isa<PHINode>(User))
123  return dominates(Def, UseBB);
124 
125  if (DefBB != UseBB)
126  return dominates(DefBB, UseBB);
127 
128  // Loop through the basic block until we find Def or User.
130  for (; &*I != Def && &*I != User; ++I)
131  /*empty*/;
132 
133  return &*I == Def;
134 }
135 
136 // true if Def would dominate a use in any instruction in UseBB.
137 // note that dominates(Def, Def->getParent()) is false.
139  const BasicBlock *UseBB) const {
140  const BasicBlock *DefBB = Def->getParent();
141 
142  // Any unreachable use is dominated, even if DefBB == UseBB.
143  if (!isReachableFromEntry(UseBB))
144  return true;
145 
146  // Unreachable definitions don't dominate anything.
147  if (!isReachableFromEntry(DefBB))
148  return false;
149 
150  if (DefBB == UseBB)
151  return false;
152 
153  // Invoke results are only usable in the normal destination, not in the
154  // exceptional destination.
155  if (const auto *II = dyn_cast<InvokeInst>(Def)) {
156  BasicBlock *NormalDest = II->getNormalDest();
157  BasicBlockEdge E(DefBB, NormalDest);
158  return dominates(E, UseBB);
159  }
160 
161  return dominates(DefBB, UseBB);
162 }
163 
165  const BasicBlock *UseBB) const {
166  // If the BB the edge ends in doesn't dominate the use BB, then the
167  // edge also doesn't.
168  const BasicBlock *Start = BBE.getStart();
169  const BasicBlock *End = BBE.getEnd();
170  if (!dominates(End, UseBB))
171  return false;
172 
173  // Simple case: if the end BB has a single predecessor, the fact that it
174  // dominates the use block implies that the edge also does.
175  if (End->getSinglePredecessor())
176  return true;
177 
178  // The normal edge from the invoke is critical. Conceptually, what we would
179  // like to do is split it and check if the new block dominates the use.
180  // With X being the new block, the graph would look like:
181  //
182  // DefBB
183  // /\ . .
184  // / \ . .
185  // / \ . .
186  // / \ | |
187  // A X B C
188  // | \ | /
189  // . \|/
190  // . NormalDest
191  // .
192  //
193  // Given the definition of dominance, NormalDest is dominated by X iff X
194  // dominates all of NormalDest's predecessors (X, B, C in the example). X
195  // trivially dominates itself, so we only have to find if it dominates the
196  // other predecessors. Since the only way out of X is via NormalDest, X can
197  // only properly dominate a node if NormalDest dominates that node too.
198  int IsDuplicateEdge = 0;
199  for (const_pred_iterator PI = pred_begin(End), E = pred_end(End);
200  PI != E; ++PI) {
201  const BasicBlock *BB = *PI;
202  if (BB == Start) {
203  // If there are multiple edges between Start and End, by definition they
204  // can't dominate anything.
205  if (IsDuplicateEdge++)
206  return false;
207  continue;
208  }
209 
210  if (!dominates(End, BB))
211  return false;
212  }
213  return true;
214 }
215 
216 bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const {
217  Instruction *UserInst = cast<Instruction>(U.getUser());
218  // A PHI in the end of the edge is dominated by it.
219  PHINode *PN = dyn_cast<PHINode>(UserInst);
220  if (PN && PN->getParent() == BBE.getEnd() &&
221  PN->getIncomingBlock(U) == BBE.getStart())
222  return true;
223 
224  // Otherwise use the edge-dominates-block query, which
225  // handles the crazy critical edge cases properly.
226  const BasicBlock *UseBB;
227  if (PN)
228  UseBB = PN->getIncomingBlock(U);
229  else
230  UseBB = UserInst->getParent();
231  return dominates(BBE, UseBB);
232 }
233 
234 bool DominatorTree::dominates(const Instruction *Def, const Use &U) const {
235  Instruction *UserInst = cast<Instruction>(U.getUser());
236  const BasicBlock *DefBB = Def->getParent();
237 
238  // Determine the block in which the use happens. PHI nodes use
239  // their operands on edges; simulate this by thinking of the use
240  // happening at the end of the predecessor block.
241  const BasicBlock *UseBB;
242  if (PHINode *PN = dyn_cast<PHINode>(UserInst))
243  UseBB = PN->getIncomingBlock(U);
244  else
245  UseBB = UserInst->getParent();
246 
247  // Any unreachable use is dominated, even if Def == User.
248  if (!isReachableFromEntry(UseBB))
249  return true;
250 
251  // Unreachable definitions don't dominate anything.
252  if (!isReachableFromEntry(DefBB))
253  return false;
254 
255  // Invoke instructions define their return values on the edges to their normal
256  // successors, so we have to handle them specially.
257  // Among other things, this means they don't dominate anything in
258  // their own block, except possibly a phi, so we don't need to
259  // walk the block in any case.
260  if (const InvokeInst *II = dyn_cast<InvokeInst>(Def)) {
261  BasicBlock *NormalDest = II->getNormalDest();
262  BasicBlockEdge E(DefBB, NormalDest);
263  return dominates(E, U);
264  }
265 
266  // If the def and use are in different blocks, do a simple CFG dominator
267  // tree query.
268  if (DefBB != UseBB)
269  return dominates(DefBB, UseBB);
270 
271  // Ok, def and use are in the same block. If the def is an invoke, it
272  // doesn't dominate anything in the block. If it's a PHI, it dominates
273  // everything in the block.
274  if (isa<PHINode>(UserInst))
275  return true;
276 
277  // Otherwise, just loop through the basic block until we find Def or User.
278  BasicBlock::const_iterator I = DefBB->begin();
279  for (; &*I != Def && &*I != UserInst; ++I)
280  /*empty*/;
281 
282  return &*I != UserInst;
283 }
284 
287 
288  // ConstantExprs aren't really reachable from the entry block, but they
289  // don't need to be treated like unreachable code either.
290  if (!I) return true;
291 
292  // PHI nodes use their operands on their incoming edges.
293  if (PHINode *PN = dyn_cast<PHINode>(I))
294  return isReachableFromEntry(PN->getIncomingBlock(U));
295 
296  // Everything else uses their operands in their own block.
297  return isReachableFromEntry(I->getParent());
298 }
299 
301  // Perform the expensive checks only when VerifyDomInfo is set.
302  if (VerifyDomInfo && !verify()) {
303  errs() << "\n~~~~~~~~~~~\n\t\tDomTree verification failed!\n~~~~~~~~~~~\n";
304  print(errs());
305  abort();
306  }
307 
308  Function &F = *getRoot()->getParent();
309 
310  DominatorTree OtherDT;
311  OtherDT.recalculate(F);
312  if (compare(OtherDT)) {
313  errs() << "DominatorTree is not up to date!\nComputed:\n";
314  print(errs());
315  errs() << "\nActual:\n";
316  OtherDT.print(errs());
317  abort();
318  }
319 }
320 
321 //===----------------------------------------------------------------------===//
322 // DominatorTreeAnalysis and related pass implementations
323 //===----------------------------------------------------------------------===//
324 //
325 // This implements the DominatorTreeAnalysis which is used with the new pass
326 // manager. It also implements some methods from utility passes.
327 //
328 //===----------------------------------------------------------------------===//
329 
332  DominatorTree DT;
333  DT.recalculate(F);
334  return DT;
335 }
336 
337 AnalysisKey DominatorTreeAnalysis::Key;
338 
340 
343  OS << "DominatorTree for function: " << F.getName() << "\n";
344  AM.getResult<DominatorTreeAnalysis>(F).print(OS);
345 
346  return PreservedAnalyses::all();
347 }
348 
351  AM.getResult<DominatorTreeAnalysis>(F).verifyDomTree();
352 
353  return PreservedAnalyses::all();
354 }
355 
356 //===----------------------------------------------------------------------===//
357 // DominatorTreeWrapperPass Implementation
358 //===----------------------------------------------------------------------===//
359 //
360 // The implementation details of the wrapper pass that holds a DominatorTree
361 // suitable for use with the legacy pass manager.
362 //
363 //===----------------------------------------------------------------------===//
364 
367  "Dominator Tree Construction", true, true)
368 
369 bool DominatorTreeWrapperPass::runOnFunction(Function &F) {
370  DT.recalculate(F);
371  return false;
372 }
373 
375  if (VerifyDomInfo)
376  DT.verifyDomTree();
377 }
378 
380  DT.print(OS);
381 }
382 
raw_ostream & errs()
This returns a reference to a raw_ostream for standard error.
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:687
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:63
BasicBlock * getSuccessor(unsigned idx) const
Return the specified successor.
Analysis pass which computes a DominatorTree.
Definition: Dominators.h:232
const BasicBlock * getEnd() const
Definition: Dominators.h:84
bool isReachableFromEntry(const Use &U) const
Provide an overload for a Use.
Definition: Dominators.cpp:285
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:252
bool isSingleEdge() const
Check if this is the only edge between Start and End.
Definition: Dominators.cpp:40
PreservedAnalysisChecker getChecker() const
Build a checker for this PreservedAnalyses and the specified analysis type.
Definition: PassManager.h:304
void verifyAnalysis() const override
verifyAnalysis() - This member can be implemented by a analysis pass to check state of analysis infor...
Definition: Dominators.cpp:374
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
#define F(x, y, z)
Definition: MD5.cpp:55
DominatorTreePrinterPass(raw_ostream &OS)
Definition: Dominators.cpp:339
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:134
void verifyDomTree() const
Verify the correctness of the domtree by re-computing it.
Definition: Dominators.cpp:300
Subclasses of this class are all able to terminate a basic block.
Definition: InstrTypes.h:54
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:153
const BasicBlock * getSinglePredecessor() const
Return the predecessor of this block if it has a single predecessor block.
Definition: BasicBlock.cpp:217
bool dominates(const BasicBlockEdge &BBE, const BasicBlock *BB) const
Definition: Dominators.cpp:164
LLVM Basic Block Representation.
Definition: BasicBlock.h:59
DominatorTree run(Function &F, FunctionAnalysisManager &)
Run the analysis pass over a function and produce a dominator tree.
Definition: Dominators.cpp:330
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:116
Interval::pred_iterator pred_end(Interval *I)
Definition: Interval.h:119
bool VerifyDomInfo
Enables verification of dominator trees.
Definition: Dominators.cpp:34
INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree", "Dominator Tree Construction", true, true) bool DominatorTreeWrapperPass
Definition: Dominators.cpp:366
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:159
bool verify(const TargetRegisterInfo &TRI) const
Check that information hold by this instance make sense for the given TRI.
void print(raw_ostream &O) const
print - Convert to human readable form
static cl::opt< bool, true > VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo), cl::desc("Verify dominator info (time consuming)"))
Iterator for intrusive lists based on ilist_node.
#define E
Definition: LargeTest.cpp:27
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:234
void print(raw_ostream &OS, const Module *M=nullptr) const override
print - Print out the internal state of the pass.
Definition: Dominators.cpp:379
bool invalidate(Function &F, const PreservedAnalyses &PA, FunctionAnalysisManager::Invalidator &)
Handle invalidation explicitly.
Definition: Dominators.cpp:89
Represents analyses that only rely on functions&#39; control flow.
Definition: PassManager.h:114
void recalculate(FT &F)
recalculate - compute a dominator tree for the given function
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:218
#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:559
int compare(DigitsT LDigits, int16_t LScale, DigitsT RDigits, int16_t RScale)
Compare two scaled numbers.
Definition: ScaledNumber.h:252
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
This templated class represents "all analyses that operate over <a particular IR unit>" (e...
Definition: PassManager.h:91
unsigned getNumSuccessors() const
Return the number of successors that this terminator has.
const BasicBlock * getStart() const
Definition: Dominators.h:80
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Definition: Dominators.cpp:341
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:44
Invoke instruction.
A container for analyses that lazily runs them and caches their results.
Legacy analysis pass which computes a DominatorTree.
Definition: Dominators.h:261
const TerminatorInst * 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:120
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:70
LocationClass< Ty > location(Ty &L)
Definition: CommandLine.h:420
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Definition: Dominators.cpp:349
const BasicBlock * getParent() const
Definition: Instruction.h:66