xref: /freebsd/contrib/llvm-project/llvm/lib/CodeGen/SjLjEHPrepare.cpp (revision 7ef62cebc2f965b0f640263e179276928885e33d)
1 //===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind instructions ---------===//
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 transformation is designed for use by code generators which use SjLj
10 // based exception handling.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/ADT/SetVector.h"
15 #include "llvm/ADT/SmallPtrSet.h"
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/ADT/Statistic.h"
18 #include "llvm/CodeGen/Passes.h"
19 #include "llvm/IR/Constants.h"
20 #include "llvm/IR/DataLayout.h"
21 #include "llvm/IR/DerivedTypes.h"
22 #include "llvm/IR/IRBuilder.h"
23 #include "llvm/IR/Instructions.h"
24 #include "llvm/IR/Intrinsics.h"
25 #include "llvm/IR/Module.h"
26 #include "llvm/InitializePasses.h"
27 #include "llvm/Pass.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include "llvm/Target/TargetMachine.h"
31 #include "llvm/Transforms/Utils/Local.h"
32 using namespace llvm;
33 
34 #define DEBUG_TYPE "sjljehprepare"
35 
36 STATISTIC(NumInvokes, "Number of invokes replaced");
37 STATISTIC(NumSpilled, "Number of registers live across unwind edges");
38 
39 namespace {
40 class SjLjEHPrepare : public FunctionPass {
41   IntegerType *DataTy;
42   Type *doubleUnderDataTy;
43   Type *doubleUnderJBufTy;
44   Type *FunctionContextTy;
45   FunctionCallee RegisterFn;
46   FunctionCallee UnregisterFn;
47   Function *BuiltinSetupDispatchFn;
48   Function *FrameAddrFn;
49   Function *StackAddrFn;
50   Function *StackRestoreFn;
51   Function *LSDAAddrFn;
52   Function *CallSiteFn;
53   Function *FuncCtxFn;
54   AllocaInst *FuncCtx;
55   const TargetMachine *TM;
56 
57 public:
58   static char ID; // Pass identification, replacement for typeid
59   explicit SjLjEHPrepare(const TargetMachine *TM = nullptr)
60       : FunctionPass(ID), TM(TM) {}
61   bool doInitialization(Module &M) override;
62   bool runOnFunction(Function &F) override;
63 
64   void getAnalysisUsage(AnalysisUsage &AU) const override {}
65   StringRef getPassName() const override {
66     return "SJLJ Exception Handling preparation";
67   }
68 
69 private:
70   bool setupEntryBlockAndCallSites(Function &F);
71   void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal);
72   Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst *> LPads);
73   void lowerIncomingArguments(Function &F);
74   void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes);
75   void insertCallSiteStore(Instruction *I, int Number);
76 };
77 } // end anonymous namespace
78 
79 char SjLjEHPrepare::ID = 0;
80 INITIALIZE_PASS(SjLjEHPrepare, DEBUG_TYPE, "Prepare SjLj exceptions",
81                 false, false)
82 
83 // Public Interface To the SjLjEHPrepare pass.
84 FunctionPass *llvm::createSjLjEHPreparePass(const TargetMachine *TM) {
85   return new SjLjEHPrepare(TM);
86 }
87 
88 // doInitialization - Set up decalarations and types needed to process
89 // exceptions.
90 bool SjLjEHPrepare::doInitialization(Module &M) {
91   // Build the function context structure.
92   // builtin_setjmp uses a five word jbuf
93   Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
94   unsigned DataBits =
95       TM ? TM->getSjLjDataSize() : TargetMachine::DefaultSjLjDataSize;
96   DataTy = Type::getIntNTy(M.getContext(), DataBits);
97   doubleUnderDataTy = ArrayType::get(DataTy, 4);
98   doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5);
99   FunctionContextTy = StructType::get(VoidPtrTy,         // __prev
100                                       DataTy,            // call_site
101                                       doubleUnderDataTy, // __data
102                                       VoidPtrTy,         // __personality
103                                       VoidPtrTy,         // __lsda
104                                       doubleUnderJBufTy  // __jbuf
105   );
106 
107   return true;
108 }
109 
110 /// insertCallSiteStore - Insert a store of the call-site value to the
111 /// function context
112 void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) {
113   IRBuilder<> Builder(I);
114 
115   // Get a reference to the call_site field.
116   Type *Int32Ty = Type::getInt32Ty(I->getContext());
117   Value *Zero = ConstantInt::get(Int32Ty, 0);
118   Value *One = ConstantInt::get(Int32Ty, 1);
119   Value *Idxs[2] = { Zero, One };
120   Value *CallSite =
121       Builder.CreateGEP(FunctionContextTy, FuncCtx, Idxs, "call_site");
122 
123   // Insert a store of the call-site number
124   ConstantInt *CallSiteNoC = ConstantInt::get(DataTy, Number);
125   Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/);
126 }
127 
128 /// MarkBlocksLiveIn - Insert BB and all of its predecessors into LiveBBs until
129 /// we reach blocks we've already seen.
130 static void MarkBlocksLiveIn(BasicBlock *BB,
131                              SmallPtrSetImpl<BasicBlock *> &LiveBBs) {
132   if (!LiveBBs.insert(BB).second)
133     return; // already been here.
134 
135   df_iterator_default_set<BasicBlock*> Visited;
136 
137   for (BasicBlock *B : inverse_depth_first_ext(BB, Visited))
138     LiveBBs.insert(B);
139 }
140 
141 /// substituteLPadValues - Substitute the values returned by the landingpad
142 /// instruction with those returned by the personality function.
143 void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
144                                          Value *SelVal) {
145   SmallVector<Value *, 8> UseWorkList(LPI->users());
146   while (!UseWorkList.empty()) {
147     Value *Val = UseWorkList.pop_back_val();
148     auto *EVI = dyn_cast<ExtractValueInst>(Val);
149     if (!EVI)
150       continue;
151     if (EVI->getNumIndices() != 1)
152       continue;
153     if (*EVI->idx_begin() == 0)
154       EVI->replaceAllUsesWith(ExnVal);
155     else if (*EVI->idx_begin() == 1)
156       EVI->replaceAllUsesWith(SelVal);
157     if (EVI->use_empty())
158       EVI->eraseFromParent();
159   }
160 
161   if (LPI->use_empty())
162     return;
163 
164   // There are still some uses of LPI. Construct an aggregate with the exception
165   // values and replace the LPI with that aggregate.
166   Type *LPadType = LPI->getType();
167   Value *LPadVal = PoisonValue::get(LPadType);
168   auto *SelI = cast<Instruction>(SelVal);
169   IRBuilder<> Builder(SelI->getParent(), std::next(SelI->getIterator()));
170   LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
171   LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");
172 
173   LPI->replaceAllUsesWith(LPadVal);
174 }
175 
176 /// setupFunctionContext - Allocate the function context on the stack and fill
177 /// it with all of the data that we know at this point.
178 Value *SjLjEHPrepare::setupFunctionContext(Function &F,
179                                            ArrayRef<LandingPadInst *> LPads) {
180   BasicBlock *EntryBB = &F.front();
181 
182   // Create an alloca for the incoming jump buffer ptr and the new jump buffer
183   // that needs to be restored on all exits from the function. This is an alloca
184   // because the value needs to be added to the global context list.
185   auto &DL = F.getParent()->getDataLayout();
186   const Align Alignment = DL.getPrefTypeAlign(FunctionContextTy);
187   FuncCtx = new AllocaInst(FunctionContextTy, DL.getAllocaAddrSpace(), nullptr,
188                            Alignment, "fn_context", &EntryBB->front());
189 
190   // Fill in the function context structure.
191   for (LandingPadInst *LPI : LPads) {
192     IRBuilder<> Builder(LPI->getParent(),
193                         LPI->getParent()->getFirstInsertionPt());
194 
195     // Reference the __data field.
196     Value *FCData =
197         Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 2, "__data");
198 
199     // The exception values come back in context->__data[0].
200     Value *ExceptionAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
201                                                       0, 0, "exception_gep");
202     Value *ExnVal = Builder.CreateLoad(DataTy, ExceptionAddr, true, "exn_val");
203     ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());
204 
205     Value *SelectorAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
206                                                      0, 1, "exn_selector_gep");
207     Value *SelVal =
208         Builder.CreateLoad(DataTy, SelectorAddr, true, "exn_selector_val");
209 
210     // SelVal must be Int32Ty, so trunc it
211     SelVal = Builder.CreateTrunc(SelVal, Type::getInt32Ty(F.getContext()));
212 
213     substituteLPadValues(LPI, ExnVal, SelVal);
214   }
215 
216   // Personality function
217   IRBuilder<> Builder(EntryBB->getTerminator());
218   Value *PersonalityFn = F.getPersonalityFn();
219   Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(
220       FunctionContextTy, FuncCtx, 0, 3, "pers_fn_gep");
221   Builder.CreateStore(
222       Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()),
223       PersonalityFieldPtr, /*isVolatile=*/true);
224 
225   // LSDA address
226   Value *LSDA = Builder.CreateCall(LSDAAddrFn, {}, "lsda_addr");
227   Value *LSDAFieldPtr =
228       Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 4, "lsda_gep");
229   Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true);
230 
231   return FuncCtx;
232 }
233 
234 /// lowerIncomingArguments - To avoid having to handle incoming arguments
235 /// specially, we lower each arg to a copy instruction in the entry block. This
236 /// ensures that the argument value itself cannot be live out of the entry
237 /// block.
238 void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
239   BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
240   while (isa<AllocaInst>(AfterAllocaInsPt) &&
241          cast<AllocaInst>(AfterAllocaInsPt)->isStaticAlloca())
242     ++AfterAllocaInsPt;
243   assert(AfterAllocaInsPt != F.front().end());
244 
245   for (auto &AI : F.args()) {
246     // Swift error really is a register that we model as memory -- instruction
247     // selection will perform mem-to-reg for us and spill/reload appropriately
248     // around calls that clobber it. There is no need to spill this
249     // value to the stack and doing so would not be allowed.
250     if (AI.isSwiftError())
251       continue;
252 
253     Type *Ty = AI.getType();
254 
255     // Use 'select i8 true, %arg, undef' to simulate a 'no-op' instruction.
256     Value *TrueValue = ConstantInt::getTrue(F.getContext());
257     Value *UndefValue = UndefValue::get(Ty);
258     Instruction *SI = SelectInst::Create(
259         TrueValue, &AI, UndefValue, AI.getName() + ".tmp", &*AfterAllocaInsPt);
260     AI.replaceAllUsesWith(SI);
261 
262     // Reset the operand, because it  was clobbered by the RAUW above.
263     SI->setOperand(1, &AI);
264   }
265 }
266 
267 /// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
268 /// edge and spill them.
269 void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
270                                            ArrayRef<InvokeInst *> Invokes) {
271   // Finally, scan the code looking for instructions with bad live ranges.
272   for (BasicBlock &BB : F) {
273     for (Instruction &Inst : BB) {
274       // Ignore obvious cases we don't have to handle. In particular, most
275       // instructions either have no uses or only have a single use inside the
276       // current block. Ignore them quickly.
277       if (Inst.use_empty())
278         continue;
279       if (Inst.hasOneUse() &&
280           cast<Instruction>(Inst.user_back())->getParent() == &BB &&
281           !isa<PHINode>(Inst.user_back()))
282         continue;
283 
284       // If this is an alloca in the entry block, it's not a real register
285       // value.
286       if (auto *AI = dyn_cast<AllocaInst>(&Inst))
287         if (AI->isStaticAlloca())
288           continue;
289 
290       // Avoid iterator invalidation by copying users to a temporary vector.
291       SmallVector<Instruction *, 16> Users;
292       for (User *U : Inst.users()) {
293         Instruction *UI = cast<Instruction>(U);
294         if (UI->getParent() != &BB || isa<PHINode>(UI))
295           Users.push_back(UI);
296       }
297 
298       // Find all of the blocks that this value is live in.
299       SmallPtrSet<BasicBlock *, 32> LiveBBs;
300       LiveBBs.insert(&BB);
301       while (!Users.empty()) {
302         Instruction *U = Users.pop_back_val();
303 
304         if (!isa<PHINode>(U)) {
305           MarkBlocksLiveIn(U->getParent(), LiveBBs);
306         } else {
307           // Uses for a PHI node occur in their predecessor block.
308           PHINode *PN = cast<PHINode>(U);
309           for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
310             if (PN->getIncomingValue(i) == &Inst)
311               MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
312         }
313       }
314 
315       // Now that we know all of the blocks that this thing is live in, see if
316       // it includes any of the unwind locations.
317       bool NeedsSpill = false;
318       for (InvokeInst *Invoke : Invokes) {
319         BasicBlock *UnwindBlock = Invoke->getUnwindDest();
320         if (UnwindBlock != &BB && LiveBBs.count(UnwindBlock)) {
321           LLVM_DEBUG(dbgs() << "SJLJ Spill: " << Inst << " around "
322                             << UnwindBlock->getName() << "\n");
323           NeedsSpill = true;
324           break;
325         }
326       }
327 
328       // If we decided we need a spill, do it.
329       // FIXME: Spilling this way is overkill, as it forces all uses of
330       // the value to be reloaded from the stack slot, even those that aren't
331       // in the unwind blocks. We should be more selective.
332       if (NeedsSpill) {
333         DemoteRegToStack(Inst, true);
334         ++NumSpilled;
335       }
336     }
337   }
338 
339   // Go through the landing pads and remove any PHIs there.
340   for (InvokeInst *Invoke : Invokes) {
341     BasicBlock *UnwindBlock = Invoke->getUnwindDest();
342     LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
343 
344     // Place PHIs into a set to avoid invalidating the iterator.
345     SmallPtrSet<PHINode *, 8> PHIsToDemote;
346     for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
347       PHIsToDemote.insert(cast<PHINode>(PN));
348     if (PHIsToDemote.empty())
349       continue;
350 
351     // Demote the PHIs to the stack.
352     for (PHINode *PN : PHIsToDemote)
353       DemotePHIToStack(PN);
354 
355     // Move the landingpad instruction back to the top of the landing pad block.
356     LPI->moveBefore(&UnwindBlock->front());
357   }
358 }
359 
360 /// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
361 /// the function context and marking the call sites with the appropriate
362 /// values. These values are used by the DWARF EH emitter.
363 bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
364   SmallVector<ReturnInst *, 16> Returns;
365   SmallVector<InvokeInst *, 16> Invokes;
366   SmallSetVector<LandingPadInst *, 16> LPads;
367 
368   // Look through the terminators of the basic blocks to find invokes.
369   for (BasicBlock &BB : F)
370     if (auto *II = dyn_cast<InvokeInst>(BB.getTerminator())) {
371       if (Function *Callee = II->getCalledFunction())
372         if (Callee->getIntrinsicID() == Intrinsic::donothing) {
373           // Remove the NOP invoke.
374           BranchInst::Create(II->getNormalDest(), II);
375           II->eraseFromParent();
376           continue;
377         }
378 
379       Invokes.push_back(II);
380       LPads.insert(II->getUnwindDest()->getLandingPadInst());
381     } else if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator())) {
382       Returns.push_back(RI);
383     }
384 
385   if (Invokes.empty())
386     return false;
387 
388   NumInvokes += Invokes.size();
389 
390   lowerIncomingArguments(F);
391   lowerAcrossUnwindEdges(F, Invokes);
392 
393   Value *FuncCtx =
394       setupFunctionContext(F, ArrayRef(LPads.begin(), LPads.end()));
395   BasicBlock *EntryBB = &F.front();
396   IRBuilder<> Builder(EntryBB->getTerminator());
397 
398   // Get a reference to the jump buffer.
399   Value *JBufPtr =
400       Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");
401 
402   // Save the frame pointer.
403   Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
404                                                "jbuf_fp_gep");
405 
406   Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
407   Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
408 
409   // Save the stack pointer.
410   Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
411                                                "jbuf_sp_gep");
412 
413   Val = Builder.CreateCall(StackAddrFn, {}, "sp");
414   Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
415 
416   // Call the setup_dispatch intrinsic. It fills in the rest of the jmpbuf.
417   Builder.CreateCall(BuiltinSetupDispatchFn, {});
418 
419   // Store a pointer to the function context so that the back-end will know
420   // where to look for it.
421   Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
422   Builder.CreateCall(FuncCtxFn, FuncCtxArg);
423 
424   // At this point, we are all set up, update the invoke instructions to mark
425   // their call_site values.
426   for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
427     insertCallSiteStore(Invokes[I], I + 1);
428 
429     ConstantInt *CallSiteNum =
430         ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
431 
432     // Record the call site value for the back end so it stays associated with
433     // the invoke.
434     CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
435   }
436 
437   // Mark call instructions that aren't nounwind as no-action (call_site ==
438   // -1). Skip the entry block, as prior to then, no function context has been
439   // created for this function and any unexpected exceptions thrown will go
440   // directly to the caller's context, which is what we want anyway, so no need
441   // to do anything here.
442   for (BasicBlock &BB : F) {
443     if (&BB == &F.front())
444       continue;
445     for (Instruction &I : BB)
446       if (I.mayThrow())
447         insertCallSiteStore(&I, -1);
448   }
449 
450   // Register the function context and make sure it's known to not throw
451   CallInst *Register =
452       CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
453   Register->setDoesNotThrow();
454 
455   // Following any allocas not in the entry block, update the saved SP in the
456   // jmpbuf to the new value.
457   for (BasicBlock &BB : F) {
458     if (&BB == &F.front())
459       continue;
460     for (Instruction &I : BB) {
461       if (auto *CI = dyn_cast<CallInst>(&I)) {
462         if (CI->getCalledFunction() != StackRestoreFn)
463           continue;
464       } else if (!isa<AllocaInst>(&I)) {
465         continue;
466       }
467       Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
468       StackAddr->insertAfter(&I);
469       new StoreInst(StackAddr, StackPtr, true, StackAddr->getNextNode());
470     }
471   }
472 
473   // Finally, for any returns from this function, if this function contains an
474   // invoke, add a call to unregister the function context.
475   for (ReturnInst *Return : Returns) {
476     Instruction *InsertPoint = Return;
477     if (CallInst *CI = Return->getParent()->getTerminatingMustTailCall())
478       InsertPoint = CI;
479     CallInst::Create(UnregisterFn, FuncCtx, "", InsertPoint);
480   }
481 
482   return true;
483 }
484 
485 bool SjLjEHPrepare::runOnFunction(Function &F) {
486   Module &M = *F.getParent();
487   RegisterFn = M.getOrInsertFunction(
488       "_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
489       PointerType::getUnqual(FunctionContextTy));
490   UnregisterFn = M.getOrInsertFunction(
491       "_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
492       PointerType::getUnqual(FunctionContextTy));
493   FrameAddrFn = Intrinsic::getDeclaration(
494       &M, Intrinsic::frameaddress,
495       {Type::getInt8PtrTy(M.getContext(),
496                           M.getDataLayout().getAllocaAddrSpace())});
497   StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
498   StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
499   BuiltinSetupDispatchFn =
500     Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setup_dispatch);
501   LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
502   CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
503   FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);
504 
505   bool Res = setupEntryBlockAndCallSites(F);
506   return Res;
507 }
508