1//===- DwarfEHPrepare - Prepare exception handling for code generation ----===//
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 pass mulches exception handling code into a form adapted to code
10// generation. Required if using dwarf exception handling.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/CodeGen/DwarfEHPrepare.h"
15#include "llvm/ADT/BitVector.h"
16#include "llvm/ADT/SmallVector.h"
17#include "llvm/ADT/Statistic.h"
18#include "llvm/Analysis/CFG.h"
19#include "llvm/Analysis/DomTreeUpdater.h"
20#include "llvm/Analysis/TargetTransformInfo.h"
21#include "llvm/CodeGen/RuntimeLibcalls.h"
22#include "llvm/CodeGen/TargetLowering.h"
23#include "llvm/CodeGen/TargetPassConfig.h"
24#include "llvm/CodeGen/TargetSubtargetInfo.h"
25#include "llvm/IR/BasicBlock.h"
26#include "llvm/IR/Constants.h"
27#include "llvm/IR/DebugInfoMetadata.h"
28#include "llvm/IR/DerivedTypes.h"
29#include "llvm/IR/Dominators.h"
30#include "llvm/IR/EHPersonalities.h"
31#include "llvm/IR/Function.h"
32#include "llvm/IR/Instructions.h"
33#include "llvm/IR/Module.h"
34#include "llvm/IR/Type.h"
35#include "llvm/InitializePasses.h"
36#include "llvm/Pass.h"
37#include "llvm/Support/Casting.h"
38#include "llvm/Target/TargetMachine.h"
39#include "llvm/TargetParser/Triple.h"
40#include "llvm/Transforms/Utils/Local.h"
41#include <cstddef>
42
43using namespace llvm;
44
45#define DEBUG_TYPE "dwarf-eh-prepare"
46
47STATISTIC(NumResumesLowered, "Number of resume calls lowered");
48STATISTIC(NumCleanupLandingPadsUnreachable,
49 "Number of cleanup landing pads found unreachable");
50STATISTIC(NumCleanupLandingPadsRemaining,
51 "Number of cleanup landing pads remaining");
52STATISTIC(NumNoUnwind, "Number of functions with nounwind");
53STATISTIC(NumUnwind, "Number of functions with unwind");
54
55namespace {
56
57class DwarfEHPrepare {
58 CodeGenOptLevel OptLevel;
59
60 Function &F;
61 const TargetLowering &TLI;
62 DomTreeUpdater *DTU;
63 const TargetTransformInfo *TTI;
64 const Triple &TargetTriple;
65
66 /// Return the exception object from the value passed into
67 /// the 'resume' instruction (typically an aggregate). Clean up any dead
68 /// instructions, including the 'resume' instruction.
69 Value *GetExceptionObject(ResumeInst *RI);
70
71 /// Replace resumes that are not reachable from a cleanup landing pad with
72 /// unreachable and then simplify those blocks.
73 size_t
74 pruneUnreachableResumes(SmallVectorImpl<ResumeInst *> &Resumes,
75 SmallVectorImpl<LandingPadInst *> &CleanupLPads);
76
77 /// Convert the ResumeInsts that are still present
78 /// into calls to the appropriate _Unwind_Resume function.
79 bool InsertUnwindResumeCalls();
80
81public:
82 DwarfEHPrepare(CodeGenOptLevel OptLevel_, Function &F_,
83 const TargetLowering &TLI_, DomTreeUpdater *DTU_,
84 const TargetTransformInfo *TTI_, const Triple &TargetTriple_)
85 : OptLevel(OptLevel_), F(F_), TLI(TLI_), DTU(DTU_), TTI(TTI_),
86 TargetTriple(TargetTriple_) {}
87
88 bool run();
89};
90
91} // namespace
92
93Value *DwarfEHPrepare::GetExceptionObject(ResumeInst *RI) {
94 Value *V = RI->getOperand(i_nocapture: 0);
95 Value *ExnObj = nullptr;
96 InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(Val: V);
97 LoadInst *SelLoad = nullptr;
98 InsertValueInst *ExcIVI = nullptr;
99 bool EraseIVIs = false;
100
101 if (SelIVI) {
102 if (SelIVI->getNumIndices() == 1 && *SelIVI->idx_begin() == 1) {
103 ExcIVI = dyn_cast<InsertValueInst>(Val: SelIVI->getOperand(i_nocapture: 0));
104 if (ExcIVI && isa<UndefValue>(Val: ExcIVI->getOperand(i_nocapture: 0)) &&
105 ExcIVI->getNumIndices() == 1 && *ExcIVI->idx_begin() == 0) {
106 ExnObj = ExcIVI->getOperand(i_nocapture: 1);
107 SelLoad = dyn_cast<LoadInst>(Val: SelIVI->getOperand(i_nocapture: 1));
108 EraseIVIs = true;
109 }
110 }
111 }
112
113 if (!ExnObj)
114 ExnObj = ExtractValueInst::Create(Agg: RI->getOperand(i_nocapture: 0), Idxs: 0, NameStr: "exn.obj",
115 InsertBefore: RI->getIterator());
116
117 RI->eraseFromParent();
118
119 if (EraseIVIs) {
120 if (SelIVI->use_empty())
121 SelIVI->eraseFromParent();
122 if (ExcIVI->use_empty())
123 ExcIVI->eraseFromParent();
124 if (SelLoad && SelLoad->use_empty())
125 SelLoad->eraseFromParent();
126 }
127
128 return ExnObj;
129}
130
131size_t DwarfEHPrepare::pruneUnreachableResumes(
132 SmallVectorImpl<ResumeInst *> &Resumes,
133 SmallVectorImpl<LandingPadInst *> &CleanupLPads) {
134 assert(DTU && "Should have DomTreeUpdater here.");
135
136 BitVector ResumeReachable(Resumes.size());
137 size_t ResumeIndex = 0;
138 for (auto *RI : Resumes) {
139 for (auto *LP : CleanupLPads) {
140 if (isPotentiallyReachable(From: LP, To: RI, ExclusionSet: nullptr, DT: &DTU->getDomTree())) {
141 ResumeReachable.set(ResumeIndex);
142 break;
143 }
144 }
145 ++ResumeIndex;
146 }
147
148 // If everything is reachable, there is no change.
149 if (ResumeReachable.all())
150 return Resumes.size();
151
152 LLVMContext &Ctx = F.getContext();
153
154 // Otherwise, insert unreachable instructions and call simplifycfg.
155 size_t ResumesLeft = 0;
156 for (size_t I = 0, E = Resumes.size(); I < E; ++I) {
157 ResumeInst *RI = Resumes[I];
158 if (ResumeReachable[I]) {
159 Resumes[ResumesLeft++] = RI;
160 } else {
161 BasicBlock *BB = RI->getParent();
162 new UnreachableInst(Ctx, RI->getIterator());
163 RI->eraseFromParent();
164 simplifyCFG(BB, TTI: *TTI, DTU);
165 }
166 }
167 Resumes.resize(N: ResumesLeft);
168 return ResumesLeft;
169}
170
171bool DwarfEHPrepare::InsertUnwindResumeCalls() {
172 SmallVector<ResumeInst *, 16> Resumes;
173 SmallVector<LandingPadInst *, 16> CleanupLPads;
174 if (F.doesNotThrow())
175 NumNoUnwind++;
176 else
177 NumUnwind++;
178 for (BasicBlock &BB : F) {
179 if (auto *RI = dyn_cast<ResumeInst>(Val: BB.getTerminator()))
180 Resumes.push_back(Elt: RI);
181 if (auto *LP = BB.getLandingPadInst())
182 if (LP->isCleanup())
183 CleanupLPads.push_back(Elt: LP);
184 }
185
186 NumCleanupLandingPadsRemaining += CleanupLPads.size();
187
188 if (Resumes.empty())
189 return false;
190
191 // Check the personality, don't do anything if it's scope-based.
192 EHPersonality Pers = classifyEHPersonality(Pers: F.getPersonalityFn());
193 if (isScopedEHPersonality(Pers))
194 return false;
195
196 LLVMContext &Ctx = F.getContext();
197
198 size_t ResumesLeft = Resumes.size();
199 if (OptLevel != CodeGenOptLevel::None) {
200 ResumesLeft = pruneUnreachableResumes(Resumes, CleanupLPads);
201#if LLVM_ENABLE_STATS
202 unsigned NumRemainingLPs = 0;
203 for (BasicBlock &BB : F) {
204 if (auto *LP = BB.getLandingPadInst())
205 if (LP->isCleanup())
206 NumRemainingLPs++;
207 }
208 NumCleanupLandingPadsUnreachable += CleanupLPads.size() - NumRemainingLPs;
209 NumCleanupLandingPadsRemaining -= CleanupLPads.size() - NumRemainingLPs;
210#endif
211 }
212
213 if (ResumesLeft == 0)
214 return true; // We pruned them all.
215
216 // RewindFunction - _Unwind_Resume or the target equivalent.
217 FunctionCallee RewindFunction;
218 CallingConv::ID RewindFunctionCallingConv;
219 FunctionType *FTy;
220 const char *RewindName;
221 bool DoesRewindFunctionNeedExceptionObject;
222
223 if ((Pers == EHPersonality::GNU_CXX || Pers == EHPersonality::GNU_CXX_SjLj) &&
224 TargetTriple.isTargetEHABICompatible()) {
225 RewindName = TLI.getLibcallName(Call: RTLIB::CXA_END_CLEANUP);
226 FTy = FunctionType::get(Result: Type::getVoidTy(C&: Ctx), isVarArg: false);
227 RewindFunctionCallingConv =
228 TLI.getLibcallCallingConv(Call: RTLIB::CXA_END_CLEANUP);
229 DoesRewindFunctionNeedExceptionObject = false;
230 } else {
231 RewindName = TLI.getLibcallName(Call: RTLIB::UNWIND_RESUME);
232 FTy = FunctionType::get(Result: Type::getVoidTy(C&: Ctx), Params: PointerType::getUnqual(C&: Ctx),
233 isVarArg: false);
234 RewindFunctionCallingConv = TLI.getLibcallCallingConv(Call: RTLIB::UNWIND_RESUME);
235 DoesRewindFunctionNeedExceptionObject = true;
236 }
237 RewindFunction = F.getParent()->getOrInsertFunction(Name: RewindName, T: FTy);
238
239 // Create the basic block where the _Unwind_Resume call will live.
240 if (ResumesLeft == 1) {
241 // Instead of creating a new BB and PHI node, just append the call to
242 // _Unwind_Resume to the end of the single resume block.
243 ResumeInst *RI = Resumes.front();
244 BasicBlock *UnwindBB = RI->getParent();
245 Value *ExnObj = GetExceptionObject(RI);
246 llvm::SmallVector<Value *, 1> RewindFunctionArgs;
247 if (DoesRewindFunctionNeedExceptionObject)
248 RewindFunctionArgs.push_back(Elt: ExnObj);
249
250 // Call the rewind function.
251 CallInst *CI =
252 CallInst::Create(Func: RewindFunction, Args: RewindFunctionArgs, NameStr: "", InsertAtEnd: UnwindBB);
253 // The verifier requires that all calls of debug-info-bearing functions
254 // from debug-info-bearing functions have a debug location (for inlining
255 // purposes). Assign a dummy location to satisfy the constraint.
256 Function *RewindFn = dyn_cast<Function>(Val: RewindFunction.getCallee());
257 if (RewindFn && RewindFn->getSubprogram())
258 if (DISubprogram *SP = F.getSubprogram())
259 CI->setDebugLoc(DILocation::get(Context&: SP->getContext(), Line: 0, Column: 0, Scope: SP));
260 CI->setCallingConv(RewindFunctionCallingConv);
261
262 // We never expect _Unwind_Resume to return.
263 CI->setDoesNotReturn();
264 new UnreachableInst(Ctx, UnwindBB);
265 return true;
266 }
267
268 std::vector<DominatorTree::UpdateType> Updates;
269 Updates.reserve(n: Resumes.size());
270
271 llvm::SmallVector<Value *, 1> RewindFunctionArgs;
272
273 BasicBlock *UnwindBB = BasicBlock::Create(Context&: Ctx, Name: "unwind_resume", Parent: &F);
274 PHINode *PN = PHINode::Create(Ty: PointerType::getUnqual(C&: Ctx), NumReservedValues: ResumesLeft,
275 NameStr: "exn.obj", InsertAtEnd: UnwindBB);
276
277 // Extract the exception object from the ResumeInst and add it to the PHI node
278 // that feeds the _Unwind_Resume call.
279 for (ResumeInst *RI : Resumes) {
280 BasicBlock *Parent = RI->getParent();
281 BranchInst::Create(IfTrue: UnwindBB, InsertAtEnd: Parent);
282 Updates.push_back(x: {DominatorTree::Insert, Parent, UnwindBB});
283
284 Value *ExnObj = GetExceptionObject(RI);
285 PN->addIncoming(V: ExnObj, BB: Parent);
286
287 ++NumResumesLowered;
288 }
289
290 if (DoesRewindFunctionNeedExceptionObject)
291 RewindFunctionArgs.push_back(Elt: PN);
292
293 // Call the function.
294 CallInst *CI =
295 CallInst::Create(Func: RewindFunction, Args: RewindFunctionArgs, NameStr: "", InsertAtEnd: UnwindBB);
296 CI->setCallingConv(RewindFunctionCallingConv);
297
298 // We never expect _Unwind_Resume to return.
299 CI->setDoesNotReturn();
300 new UnreachableInst(Ctx, UnwindBB);
301
302 if (DTU)
303 DTU->applyUpdates(Updates);
304
305 return true;
306}
307
308bool DwarfEHPrepare::run() {
309 bool Changed = InsertUnwindResumeCalls();
310
311 return Changed;
312}
313
314static bool prepareDwarfEH(CodeGenOptLevel OptLevel, Function &F,
315 const TargetLowering &TLI, DominatorTree *DT,
316 const TargetTransformInfo *TTI,
317 const Triple &TargetTriple) {
318 DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
319
320 return DwarfEHPrepare(OptLevel, F, TLI, DT ? &DTU : nullptr, TTI,
321 TargetTriple)
322 .run();
323}
324
325namespace {
326
327class DwarfEHPrepareLegacyPass : public FunctionPass {
328
329 CodeGenOptLevel OptLevel;
330
331public:
332 static char ID; // Pass identification, replacement for typeid.
333
334 DwarfEHPrepareLegacyPass(CodeGenOptLevel OptLevel = CodeGenOptLevel::Default)
335 : FunctionPass(ID), OptLevel(OptLevel) {}
336
337 bool runOnFunction(Function &F) override {
338 const TargetMachine &TM =
339 getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
340 const TargetLowering &TLI = *TM.getSubtargetImpl(F)->getTargetLowering();
341 DominatorTree *DT = nullptr;
342 const TargetTransformInfo *TTI = nullptr;
343 if (auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>())
344 DT = &DTWP->getDomTree();
345 if (OptLevel != CodeGenOptLevel::None) {
346 if (!DT)
347 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
348 TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
349 }
350 return prepareDwarfEH(OptLevel, F, TLI, DT, TTI, TargetTriple: TM.getTargetTriple());
351 }
352
353 void getAnalysisUsage(AnalysisUsage &AU) const override {
354 AU.addRequired<TargetPassConfig>();
355 AU.addRequired<TargetTransformInfoWrapperPass>();
356 if (OptLevel != CodeGenOptLevel::None) {
357 AU.addRequired<DominatorTreeWrapperPass>();
358 AU.addRequired<TargetTransformInfoWrapperPass>();
359 }
360 AU.addPreserved<DominatorTreeWrapperPass>();
361 }
362
363 StringRef getPassName() const override {
364 return "Exception handling preparation";
365 }
366};
367
368} // end anonymous namespace
369
370PreservedAnalyses DwarfEHPreparePass::run(Function &F,
371 FunctionAnalysisManager &FAM) {
372 const auto &TLI = *TM->getSubtargetImpl(F)->getTargetLowering();
373 auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(IR&: F);
374 const TargetTransformInfo *TTI = nullptr;
375 auto OptLevel = TM->getOptLevel();
376 if (OptLevel != CodeGenOptLevel::None) {
377 if (!DT)
378 DT = &FAM.getResult<DominatorTreeAnalysis>(IR&: F);
379 TTI = &FAM.getResult<TargetIRAnalysis>(IR&: F);
380 }
381 bool Changed =
382 prepareDwarfEH(OptLevel, F, TLI, DT, TTI, TargetTriple: TM->getTargetTriple());
383
384 if (!Changed)
385 return PreservedAnalyses::all();
386 PreservedAnalyses PA;
387 PA.preserve<DominatorTreeAnalysis>();
388 return PA;
389}
390
391char DwarfEHPrepareLegacyPass::ID = 0;
392
393INITIALIZE_PASS_BEGIN(DwarfEHPrepareLegacyPass, DEBUG_TYPE,
394 "Prepare DWARF exceptions", false, false)
395INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
396INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
397INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
398INITIALIZE_PASS_END(DwarfEHPrepareLegacyPass, DEBUG_TYPE,
399 "Prepare DWARF exceptions", false, false)
400
401FunctionPass *llvm::createDwarfEHPass(CodeGenOptLevel OptLevel) {
402 return new DwarfEHPrepareLegacyPass(OptLevel);
403}
404

source code of llvm/lib/CodeGen/DwarfEHPrepare.cpp