xref: /freebsd/contrib/llvm-project/llvm/lib/IR/Dominators.cpp (revision 9f23cbd6cae82fd77edfad7173432fa8dccd0a95)
1 //===- Dominators.cpp - 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.  Postdominators are available in libanalysis, but are not
11 // included in libvmcore, because it's not needed.  Forward dominators are
12 // needed to support the Verifier pass.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "llvm/IR/Dominators.h"
17 #include "llvm/ADT/StringRef.h"
18 #include "llvm/Config/llvm-config.h"
19 #include "llvm/IR/CFG.h"
20 #include "llvm/IR/Function.h"
21 #include "llvm/IR/Instruction.h"
22 #include "llvm/IR/Instructions.h"
23 #include "llvm/IR/PassManager.h"
24 #include "llvm/InitializePasses.h"
25 #include "llvm/PassRegistry.h"
26 #include "llvm/Support/Casting.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/raw_ostream.h"
29 
30 #include <cassert>
31 
32 namespace llvm {
33 class Argument;
34 class Constant;
35 class Value;
36 } // namespace llvm
37 using namespace llvm;
38 
39 bool llvm::VerifyDomInfo = false;
40 static cl::opt<bool, true>
41     VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo), cl::Hidden,
42                    cl::desc("Verify dominator info (time consuming)"));
43 
44 #ifdef EXPENSIVE_CHECKS
45 static constexpr bool ExpensiveChecksEnabled = true;
46 #else
47 static constexpr bool ExpensiveChecksEnabled = false;
48 #endif
49 
50 bool BasicBlockEdge::isSingleEdge() const {
51   const Instruction *TI = Start->getTerminator();
52   unsigned NumEdgesToEnd = 0;
53   for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) {
54     if (TI->getSuccessor(i) == End)
55       ++NumEdgesToEnd;
56     if (NumEdgesToEnd >= 2)
57       return false;
58   }
59   assert(NumEdgesToEnd == 1);
60   return true;
61 }
62 
63 //===----------------------------------------------------------------------===//
64 //  DominatorTree Implementation
65 //===----------------------------------------------------------------------===//
66 //
67 // Provide public access to DominatorTree information.  Implementation details
68 // can be found in Dominators.h, GenericDomTree.h, and
69 // GenericDomTreeConstruction.h.
70 //
71 //===----------------------------------------------------------------------===//
72 
73 template class llvm::DomTreeNodeBase<BasicBlock>;
74 template class llvm::DominatorTreeBase<BasicBlock, false>; // DomTreeBase
75 template class llvm::DominatorTreeBase<BasicBlock, true>; // PostDomTreeBase
76 
77 template class llvm::cfg::Update<BasicBlock *>;
78 
79 template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBDomTree>(
80     DomTreeBuilder::BBDomTree &DT);
81 template void
82 llvm::DomTreeBuilder::CalculateWithUpdates<DomTreeBuilder::BBDomTree>(
83     DomTreeBuilder::BBDomTree &DT, BBUpdates U);
84 
85 template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree>(
86     DomTreeBuilder::BBPostDomTree &DT);
87 // No CalculateWithUpdates<PostDomTree> instantiation, unless a usecase arises.
88 
89 template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBDomTree>(
90     DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To);
91 template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBPostDomTree>(
92     DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To);
93 
94 template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBDomTree>(
95     DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To);
96 template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBPostDomTree>(
97     DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To);
98 
99 template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBDomTree>(
100     DomTreeBuilder::BBDomTree &DT, DomTreeBuilder::BBDomTreeGraphDiff &,
101     DomTreeBuilder::BBDomTreeGraphDiff *);
102 template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBPostDomTree>(
103     DomTreeBuilder::BBPostDomTree &DT, DomTreeBuilder::BBPostDomTreeGraphDiff &,
104     DomTreeBuilder::BBPostDomTreeGraphDiff *);
105 
106 template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBDomTree>(
107     const DomTreeBuilder::BBDomTree &DT,
108     DomTreeBuilder::BBDomTree::VerificationLevel VL);
109 template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBPostDomTree>(
110     const DomTreeBuilder::BBPostDomTree &DT,
111     DomTreeBuilder::BBPostDomTree::VerificationLevel VL);
112 
113 bool DominatorTree::invalidate(Function &F, const PreservedAnalyses &PA,
114                                FunctionAnalysisManager::Invalidator &) {
115   // Check whether the analysis, all analyses on functions, or the function's
116   // CFG have been preserved.
117   auto PAC = PA.getChecker<DominatorTreeAnalysis>();
118   return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
119            PAC.preservedSet<CFGAnalyses>());
120 }
121 
122 bool DominatorTree::dominates(const BasicBlock *BB, const Use &U) const {
123   Instruction *UserInst = cast<Instruction>(U.getUser());
124   if (auto *PN = dyn_cast<PHINode>(UserInst))
125     // A phi use using a value from a block is dominated by the end of that
126     // block.  Note that the phi's parent block may not be.
127     return dominates(BB, PN->getIncomingBlock(U));
128   else
129     return properlyDominates(BB, UserInst->getParent());
130 }
131 
132 // dominates - Return true if Def dominates a use in User. This performs
133 // the special checks necessary if Def and User are in the same basic block.
134 // Note that Def doesn't dominate a use in Def itself!
135 bool DominatorTree::dominates(const Value *DefV,
136                               const Instruction *User) const {
137   const Instruction *Def = dyn_cast<Instruction>(DefV);
138   if (!Def) {
139     assert((isa<Argument>(DefV) || isa<Constant>(DefV)) &&
140            "Should be called with an instruction, argument or constant");
141     return true; // Arguments and constants dominate everything.
142   }
143 
144   const BasicBlock *UseBB = User->getParent();
145   const BasicBlock *DefBB = Def->getParent();
146 
147   // Any unreachable use is dominated, even if Def == User.
148   if (!isReachableFromEntry(UseBB))
149     return true;
150 
151   // Unreachable definitions don't dominate anything.
152   if (!isReachableFromEntry(DefBB))
153     return false;
154 
155   // An instruction doesn't dominate a use in itself.
156   if (Def == User)
157     return false;
158 
159   // The value defined by an invoke dominates an instruction only if it
160   // dominates every instruction in UseBB.
161   // A PHI is dominated only if the instruction dominates every possible use in
162   // the UseBB.
163   if (isa<InvokeInst>(Def) || isa<CallBrInst>(Def) || isa<PHINode>(User))
164     return dominates(Def, UseBB);
165 
166   if (DefBB != UseBB)
167     return dominates(DefBB, UseBB);
168 
169   return Def->comesBefore(User);
170 }
171 
172 // true if Def would dominate a use in any instruction in UseBB.
173 // note that dominates(Def, Def->getParent()) is false.
174 bool DominatorTree::dominates(const Instruction *Def,
175                               const BasicBlock *UseBB) const {
176   const BasicBlock *DefBB = Def->getParent();
177 
178   // Any unreachable use is dominated, even if DefBB == UseBB.
179   if (!isReachableFromEntry(UseBB))
180     return true;
181 
182   // Unreachable definitions don't dominate anything.
183   if (!isReachableFromEntry(DefBB))
184     return false;
185 
186   if (DefBB == UseBB)
187     return false;
188 
189   // Invoke results are only usable in the normal destination, not in the
190   // exceptional destination.
191   if (const auto *II = dyn_cast<InvokeInst>(Def)) {
192     BasicBlock *NormalDest = II->getNormalDest();
193     BasicBlockEdge E(DefBB, NormalDest);
194     return dominates(E, UseBB);
195   }
196 
197   // Callbr results are similarly only usable in the default destination.
198   if (const auto *CBI = dyn_cast<CallBrInst>(Def)) {
199     BasicBlock *NormalDest = CBI->getDefaultDest();
200     BasicBlockEdge E(DefBB, NormalDest);
201     return dominates(E, UseBB);
202   }
203 
204   return dominates(DefBB, UseBB);
205 }
206 
207 bool DominatorTree::dominates(const BasicBlockEdge &BBE,
208                               const BasicBlock *UseBB) const {
209   // If the BB the edge ends in doesn't dominate the use BB, then the
210   // edge also doesn't.
211   const BasicBlock *Start = BBE.getStart();
212   const BasicBlock *End = BBE.getEnd();
213   if (!dominates(End, UseBB))
214     return false;
215 
216   // Simple case: if the end BB has a single predecessor, the fact that it
217   // dominates the use block implies that the edge also does.
218   if (End->getSinglePredecessor())
219     return true;
220 
221   // The normal edge from the invoke is critical. Conceptually, what we would
222   // like to do is split it and check if the new block dominates the use.
223   // With X being the new block, the graph would look like:
224   //
225   //        DefBB
226   //          /\      .  .
227   //         /  \     .  .
228   //        /    \    .  .
229   //       /      \   |  |
230   //      A        X  B  C
231   //      |         \ | /
232   //      .          \|/
233   //      .      NormalDest
234   //      .
235   //
236   // Given the definition of dominance, NormalDest is dominated by X iff X
237   // dominates all of NormalDest's predecessors (X, B, C in the example). X
238   // trivially dominates itself, so we only have to find if it dominates the
239   // other predecessors. Since the only way out of X is via NormalDest, X can
240   // only properly dominate a node if NormalDest dominates that node too.
241   int IsDuplicateEdge = 0;
242   for (const BasicBlock *BB : predecessors(End)) {
243     if (BB == Start) {
244       // If there are multiple edges between Start and End, by definition they
245       // can't dominate anything.
246       if (IsDuplicateEdge++)
247         return false;
248       continue;
249     }
250 
251     if (!dominates(End, BB))
252       return false;
253   }
254   return true;
255 }
256 
257 bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const {
258   Instruction *UserInst = cast<Instruction>(U.getUser());
259   // A PHI in the end of the edge is dominated by it.
260   PHINode *PN = dyn_cast<PHINode>(UserInst);
261   if (PN && PN->getParent() == BBE.getEnd() &&
262       PN->getIncomingBlock(U) == BBE.getStart())
263     return true;
264 
265   // Otherwise use the edge-dominates-block query, which
266   // handles the crazy critical edge cases properly.
267   const BasicBlock *UseBB;
268   if (PN)
269     UseBB = PN->getIncomingBlock(U);
270   else
271     UseBB = UserInst->getParent();
272   return dominates(BBE, UseBB);
273 }
274 
275 bool DominatorTree::dominates(const Value *DefV, const Use &U) const {
276   const Instruction *Def = dyn_cast<Instruction>(DefV);
277   if (!Def) {
278     assert((isa<Argument>(DefV) || isa<Constant>(DefV)) &&
279            "Should be called with an instruction, argument or constant");
280     return true; // Arguments and constants dominate everything.
281   }
282 
283   Instruction *UserInst = cast<Instruction>(U.getUser());
284   const BasicBlock *DefBB = Def->getParent();
285 
286   // Determine the block in which the use happens. PHI nodes use
287   // their operands on edges; simulate this by thinking of the use
288   // happening at the end of the predecessor block.
289   const BasicBlock *UseBB;
290   if (PHINode *PN = dyn_cast<PHINode>(UserInst))
291     UseBB = PN->getIncomingBlock(U);
292   else
293     UseBB = UserInst->getParent();
294 
295   // Any unreachable use is dominated, even if Def == User.
296   if (!isReachableFromEntry(UseBB))
297     return true;
298 
299   // Unreachable definitions don't dominate anything.
300   if (!isReachableFromEntry(DefBB))
301     return false;
302 
303   // Invoke instructions define their return values on the edges to their normal
304   // successors, so we have to handle them specially.
305   // Among other things, this means they don't dominate anything in
306   // their own block, except possibly a phi, so we don't need to
307   // walk the block in any case.
308   if (const InvokeInst *II = dyn_cast<InvokeInst>(Def)) {
309     BasicBlock *NormalDest = II->getNormalDest();
310     BasicBlockEdge E(DefBB, NormalDest);
311     return dominates(E, U);
312   }
313 
314   // Callbr results are similarly only usable in the default destination.
315   if (const auto *CBI = dyn_cast<CallBrInst>(Def)) {
316     BasicBlock *NormalDest = CBI->getDefaultDest();
317     BasicBlockEdge E(DefBB, NormalDest);
318     return dominates(E, U);
319   }
320 
321   // If the def and use are in different blocks, do a simple CFG dominator
322   // tree query.
323   if (DefBB != UseBB)
324     return dominates(DefBB, UseBB);
325 
326   // Ok, def and use are in the same block. If the def is an invoke, it
327   // doesn't dominate anything in the block. If it's a PHI, it dominates
328   // everything in the block.
329   if (isa<PHINode>(UserInst))
330     return true;
331 
332   return Def->comesBefore(UserInst);
333 }
334 
335 bool DominatorTree::isReachableFromEntry(const Use &U) const {
336   Instruction *I = dyn_cast<Instruction>(U.getUser());
337 
338   // ConstantExprs aren't really reachable from the entry block, but they
339   // don't need to be treated like unreachable code either.
340   if (!I) return true;
341 
342   // PHI nodes use their operands on their incoming edges.
343   if (PHINode *PN = dyn_cast<PHINode>(I))
344     return isReachableFromEntry(PN->getIncomingBlock(U));
345 
346   // Everything else uses their operands in their own block.
347   return isReachableFromEntry(I->getParent());
348 }
349 
350 // Edge BBE1 dominates edge BBE2 if they match or BBE1 dominates start of BBE2.
351 bool DominatorTree::dominates(const BasicBlockEdge &BBE1,
352                               const BasicBlockEdge &BBE2) const {
353   if (BBE1.getStart() == BBE2.getStart() && BBE1.getEnd() == BBE2.getEnd())
354     return true;
355   return dominates(BBE1, BBE2.getStart());
356 }
357 
358 Instruction *DominatorTree::findNearestCommonDominator(Instruction *I1,
359                                                        Instruction *I2) const {
360   BasicBlock *BB1 = I1->getParent();
361   BasicBlock *BB2 = I2->getParent();
362   if (BB1 == BB2)
363     return I1->comesBefore(I2) ? I1 : I2;
364   if (!isReachableFromEntry(BB2))
365     return I1;
366   if (!isReachableFromEntry(BB1))
367     return I2;
368   BasicBlock *DomBB = findNearestCommonDominator(BB1, BB2);
369   if (BB1 == DomBB)
370     return I1;
371   if (BB2 == DomBB)
372     return I2;
373   return DomBB->getTerminator();
374 }
375 
376 //===----------------------------------------------------------------------===//
377 //  DominatorTreeAnalysis and related pass implementations
378 //===----------------------------------------------------------------------===//
379 //
380 // This implements the DominatorTreeAnalysis which is used with the new pass
381 // manager. It also implements some methods from utility passes.
382 //
383 //===----------------------------------------------------------------------===//
384 
385 DominatorTree DominatorTreeAnalysis::run(Function &F,
386                                          FunctionAnalysisManager &) {
387   DominatorTree DT;
388   DT.recalculate(F);
389   return DT;
390 }
391 
392 AnalysisKey DominatorTreeAnalysis::Key;
393 
394 DominatorTreePrinterPass::DominatorTreePrinterPass(raw_ostream &OS) : OS(OS) {}
395 
396 PreservedAnalyses DominatorTreePrinterPass::run(Function &F,
397                                                 FunctionAnalysisManager &AM) {
398   OS << "DominatorTree for function: " << F.getName() << "\n";
399   AM.getResult<DominatorTreeAnalysis>(F).print(OS);
400 
401   return PreservedAnalyses::all();
402 }
403 
404 PreservedAnalyses DominatorTreeVerifierPass::run(Function &F,
405                                                  FunctionAnalysisManager &AM) {
406   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
407   assert(DT.verify());
408   (void)DT;
409   return PreservedAnalyses::all();
410 }
411 
412 //===----------------------------------------------------------------------===//
413 //  DominatorTreeWrapperPass Implementation
414 //===----------------------------------------------------------------------===//
415 //
416 // The implementation details of the wrapper pass that holds a DominatorTree
417 // suitable for use with the legacy pass manager.
418 //
419 //===----------------------------------------------------------------------===//
420 
421 char DominatorTreeWrapperPass::ID = 0;
422 
423 DominatorTreeWrapperPass::DominatorTreeWrapperPass() : FunctionPass(ID) {
424   initializeDominatorTreeWrapperPassPass(*PassRegistry::getPassRegistry());
425 }
426 
427 INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree",
428                 "Dominator Tree Construction", true, true)
429 
430 bool DominatorTreeWrapperPass::runOnFunction(Function &F) {
431   DT.recalculate(F);
432   return false;
433 }
434 
435 void DominatorTreeWrapperPass::verifyAnalysis() const {
436   if (VerifyDomInfo)
437     assert(DT.verify(DominatorTree::VerificationLevel::Full));
438   else if (ExpensiveChecksEnabled)
439     assert(DT.verify(DominatorTree::VerificationLevel::Basic));
440 }
441 
442 void DominatorTreeWrapperPass::print(raw_ostream &OS, const Module *) const {
443   DT.print(OS);
444 }
445