1//===- EscapeEnumerator.cpp -----------------------------------------------===//
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// Defines a helper class that enumerates all possible exits from a function,
10// including exception handling.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Transforms/Utils/EscapeEnumerator.h"
15#include "llvm/ADT/Triple.h"
16#include "llvm/Analysis/EHPersonalities.h"
17#include "llvm/IR/Module.h"
18#include "llvm/Transforms/Utils/Local.h"
19
20using namespace llvm;
21
22static FunctionCallee getDefaultPersonalityFn(Module *M) {
23  LLVMContext &C = M->getContext();
24  Triple T(M->getTargetTriple());
25  EHPersonality Pers = getDefaultEHPersonality(T);
26  return M->getOrInsertFunction(getEHPersonalityName(Pers),
27                                FunctionType::get(Type::getInt32Ty(C), true));
28}
29
30IRBuilder<> *EscapeEnumerator::Next() {
31  if (Done)
32    return nullptr;
33
34  // Find all 'return', 'resume', and 'unwind' instructions.
35  while (StateBB != StateE) {
36    BasicBlock *CurBB = &*StateBB++;
37
38    // Branches and invokes do not escape, only unwind, resume, and return
39    // do.
40    Instruction *TI = CurBB->getTerminator();
41    if (!isa<ReturnInst>(TI) && !isa<ResumeInst>(TI))
42      continue;
43
44    if (CallInst *CI = CurBB->getTerminatingMustTailCall())
45      TI = CI;
46    Builder.SetInsertPoint(TI);
47    return &Builder;
48  }
49
50  Done = true;
51
52  if (!HandleExceptions)
53    return nullptr;
54
55  if (F.doesNotThrow())
56    return nullptr;
57
58  // Find all 'call' instructions that may throw.
59  // We cannot tranform calls with musttail tag.
60  SmallVector<Instruction *, 16> Calls;
61  for (BasicBlock &BB : F)
62    for (Instruction &II : BB)
63      if (CallInst *CI = dyn_cast<CallInst>(&II))
64        if (!CI->doesNotThrow() && !CI->isMustTailCall())
65          Calls.push_back(CI);
66
67  if (Calls.empty())
68    return nullptr;
69
70  // Create a cleanup block.
71  LLVMContext &C = F.getContext();
72  BasicBlock *CleanupBB = BasicBlock::Create(C, CleanupBBName, &F);
73  Type *ExnTy = StructType::get(Type::getInt8PtrTy(C), Type::getInt32Ty(C));
74  if (!F.hasPersonalityFn()) {
75    FunctionCallee PersFn = getDefaultPersonalityFn(F.getParent());
76    F.setPersonalityFn(cast<Constant>(PersFn.getCallee()));
77  }
78
79  if (isScopedEHPersonality(classifyEHPersonality(F.getPersonalityFn()))) {
80    report_fatal_error("Scoped EH not supported");
81  }
82
83  LandingPadInst *LPad =
84      LandingPadInst::Create(ExnTy, 1, "cleanup.lpad", CleanupBB);
85  LPad->setCleanup(true);
86  ResumeInst *RI = ResumeInst::Create(LPad, CleanupBB);
87
88  // Transform the 'call' instructions into 'invoke's branching to the
89  // cleanup block. Go in reverse order to make prettier BB names.
90  SmallVector<Value *, 16> Args;
91  for (unsigned I = Calls.size(); I != 0;) {
92    CallInst *CI = cast<CallInst>(Calls[--I]);
93    changeToInvokeAndSplitBasicBlock(CI, CleanupBB, DTU);
94  }
95
96  Builder.SetInsertPoint(RI);
97  return &Builder;
98}
99