Line data Source code
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"
18 : #include "llvm/ADT/DepthFirstIterator.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"
25 : #include "llvm/Support/CommandLine.h"
26 : #include "llvm/Support/Debug.h"
27 : #include "llvm/Support/GenericDomTreeConstruction.h"
28 : #include "llvm/Support/raw_ostream.h"
29 : #include <algorithm>
30 : using namespace llvm;
31 :
32 : bool llvm::VerifyDomInfo = false;
33 : static cl::opt<bool, true>
34 : VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo), cl::Hidden,
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 :
43 303484 : bool BasicBlockEdge::isSingleEdge() const {
44 303484 : const Instruction *TI = Start->getTerminator();
45 : unsigned NumEdgesToEnd = 0;
46 910446 : for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) {
47 606968 : if (TI->getSuccessor(i) == End)
48 303490 : ++NumEdgesToEnd;
49 606968 : 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 :
66 : template class llvm::DomTreeNodeBase<BasicBlock>;
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>(
73 : DomTreeBuilder::BBDomTree &DT);
74 : template void
75 : llvm::DomTreeBuilder::CalculateWithUpdates<DomTreeBuilder::BBDomTree>(
76 : DomTreeBuilder::BBDomTree &DT, BBUpdates U);
77 :
78 : template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree>(
79 : DomTreeBuilder::BBPostDomTree &DT);
80 : // No CalculateWithUpdates<PostDomTree> instantiation, unless a usecase arises.
81 :
82 : template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBDomTree>(
83 : DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To);
84 : template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBPostDomTree>(
85 : DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To);
86 :
87 : template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBDomTree>(
88 : DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To);
89 : template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBPostDomTree>(
90 : DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To);
91 :
92 : template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBDomTree>(
93 : DomTreeBuilder::BBDomTree &DT, DomTreeBuilder::BBUpdates);
94 : template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBPostDomTree>(
95 : DomTreeBuilder::BBPostDomTree &DT, DomTreeBuilder::BBUpdates);
96 :
97 : template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBDomTree>(
98 : const DomTreeBuilder::BBDomTree &DT,
99 : DomTreeBuilder::BBDomTree::VerificationLevel VL);
100 : template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBPostDomTree>(
101 : const DomTreeBuilder::BBPostDomTree &DT,
102 : DomTreeBuilder::BBPostDomTree::VerificationLevel VL);
103 :
104 2249 : bool DominatorTree::invalidate(Function &F, const PreservedAnalyses &PA,
105 : FunctionAnalysisManager::Invalidator &) {
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 3695 : return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
110 1446 : 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!
116 956908 : bool DominatorTree::dominates(const Instruction *Def,
117 : const Instruction *User) const {
118 956908 : const BasicBlock *UseBB = User->getParent();
119 956908 : const BasicBlock *DefBB = Def->getParent();
120 :
121 : // Any unreachable use is dominated, even if Def == User.
122 956908 : if (!isReachableFromEntry(UseBB))
123 : return true;
124 :
125 : // Unreachable definitions don't dominate anything.
126 956902 : if (!isReachableFromEntry(DefBB))
127 : return false;
128 :
129 : // An instruction doesn't dominate a use in itself.
130 956896 : 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 945910 : if (isa<InvokeInst>(Def) || isa<PHINode>(User))
138 479582 : return dominates(Def, UseBB);
139 :
140 466328 : if (DefBB != UseBB)
141 428269 : return dominates(DefBB, UseBB);
142 :
143 : // Loop through the basic block until we find Def or User.
144 : BasicBlock::const_iterator I = DefBB->begin();
145 11199071 : for (; &*I != Def && &*I != User; ++I)
146 : /*empty*/;
147 :
148 38059 : 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.
153 513721 : bool DominatorTree::dominates(const Instruction *Def,
154 : const BasicBlock *UseBB) const {
155 513721 : const BasicBlock *DefBB = Def->getParent();
156 :
157 : // Any unreachable use is dominated, even if DefBB == UseBB.
158 513721 : if (!isReachableFromEntry(UseBB))
159 : return true;
160 :
161 : // Unreachable definitions don't dominate anything.
162 513718 : if (!isReachableFromEntry(DefBB))
163 : return false;
164 :
165 513716 : 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 420571 : return dominates(E, UseBB);
174 : }
175 :
176 65041 : return dominates(DefBB, UseBB);
177 : }
178 :
179 1007357 : bool DominatorTree::dominates(const BasicBlockEdge &BBE,
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 1007357 : const BasicBlock *Start = BBE.getStart();
184 1007357 : const BasicBlock *End = BBE.getEnd();
185 1007357 : 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 90139 : 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 16480 : for (const_pred_iterator PI = pred_begin(End), E = pred_end(End);
215 24833 : PI != E; ++PI) {
216 : const BasicBlock *BB = *PI;
217 24748 : if (BB == Start) {
218 : // If there are multiple edges between Start and End, by definition they
219 : // can't dominate anything.
220 8190 : if (IsDuplicateEdge++)
221 16395 : return false;
222 : continue;
223 : }
224 :
225 16558 : if (!dominates(End, BB))
226 : return false;
227 : }
228 85 : return true;
229 : }
230 :
231 302229 : bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const {
232 302229 : 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 30461 : if (PN && PN->getParent() == BBE.getEnd() &&
236 7146 : 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 296913 : if (PN)
243 : UseBB = PN->getIncomingBlock(U);
244 : else
245 271768 : UseBB = UserInst->getParent();
246 296913 : return dominates(BBE, UseBB);
247 : }
248 :
249 534497 : bool DominatorTree::dominates(const Instruction *Def, const Use &U) const {
250 534497 : Instruction *UserInst = cast<Instruction>(U.getUser());
251 534497 : 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 426283 : UseBB = UserInst->getParent();
261 :
262 : // Any unreachable use is dominated, even if Def == User.
263 534497 : if (!isReachableFromEntry(UseBB))
264 : return true;
265 :
266 : // Unreachable definitions don't dominate anything.
267 533373 : 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 1254 : 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 532119 : if (DefBB != UseBB)
284 438230 : 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 93889 : 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();
294 371 : for (; &*I != Def && &*I != UserInst; ++I)
295 : /*empty*/;
296 :
297 142 : return &*I != UserInst;
298 : }
299 :
300 124 : bool DominatorTree::isReachableFromEntry(const Use &U) const {
301 124 : Instruction *I = dyn_cast<Instruction>(U.getUser());
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 16 : return isReachableFromEntry(PN->getIncomingBlock(U));
310 :
311 : // Everything else uses their operands in their own block.
312 116 : 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 :
324 2907 : DominatorTree DominatorTreeAnalysis::run(Function &F,
325 : FunctionAnalysisManager &) {
326 : DominatorTree DT;
327 2907 : DT.recalculate(F);
328 2907 : return DT;
329 : }
330 :
331 : AnalysisKey DominatorTreeAnalysis::Key;
332 :
333 2 : DominatorTreePrinterPass::DominatorTreePrinterPass(raw_ostream &OS) : OS(OS) {}
334 :
335 3 : PreservedAnalyses DominatorTreePrinterPass::run(Function &F,
336 : FunctionAnalysisManager &AM) {
337 3 : OS << "DominatorTree for function: " << F.getName() << "\n";
338 3 : AM.getResult<DominatorTreeAnalysis>(F).print(OS);
339 :
340 3 : return PreservedAnalyses::all();
341 : }
342 :
343 28 : PreservedAnalyses DominatorTreeVerifierPass::run(Function &F,
344 : FunctionAnalysisManager &AM) {
345 : auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
346 : assert(DT.verify());
347 : (void)DT;
348 28 : 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 :
360 : char DominatorTreeWrapperPass::ID = 0;
361 3394754 : INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree",
362 : "Dominator Tree Construction", true, true)
363 :
364 2123158 : bool DominatorTreeWrapperPass::runOnFunction(Function &F) {
365 2123158 : DT.recalculate(F);
366 2123158 : return false;
367 : }
368 :
369 0 : void DominatorTreeWrapperPass::verifyAnalysis() const {
370 : if (VerifyDomInfo)
371 : assert(DT.verify(DominatorTree::VerificationLevel::Full));
372 : else if (ExpensiveChecksEnabled)
373 : assert(DT.verify(DominatorTree::VerificationLevel::Basic));
374 0 : }
375 :
376 6 : void DominatorTreeWrapperPass::print(raw_ostream &OS, const Module *) const {
377 6 : DT.print(OS);
378 6 : }
379 :
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