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    Builder.SetInsertPoint(TI);
45    return &Builder;
46  }
47
48  Done = true;
49
50  if (!HandleExceptions)
51    return nullptr;
52
53  if (F.doesNotThrow())
54    return nullptr;
55
56  // Find all 'call' instructions that may throw.
57  SmallVector<Instruction *, 16> Calls;
58  for (BasicBlock &BB : F)
59    for (Instruction &II : BB)
60      if (CallInst *CI = dyn_cast<CallInst>(&II))
61        if (!CI->doesNotThrow())
62          Calls.push_back(CI);
63
64  if (Calls.empty())
65    return nullptr;
66
67  // Create a cleanup block.
68  LLVMContext &C = F.getContext();
69  BasicBlock *CleanupBB = BasicBlock::Create(C, CleanupBBName, &F);
70  Type *ExnTy = StructType::get(Type::getInt8PtrTy(C), Type::getInt32Ty(C));
71  if (!F.hasPersonalityFn()) {
72    FunctionCallee PersFn = getDefaultPersonalityFn(F.getParent());
73    F.setPersonalityFn(cast<Constant>(PersFn.getCallee()));
74  }
75
76  if (isScopedEHPersonality(classifyEHPersonality(F.getPersonalityFn()))) {
77    report_fatal_error("Scoped EH not supported");
78  }
79
80  LandingPadInst *LPad =
81      LandingPadInst::Create(ExnTy, 1, "cleanup.lpad", CleanupBB);
82  LPad->setCleanup(true);
83  ResumeInst *RI = ResumeInst::Create(LPad, CleanupBB);
84
85  // Transform the 'call' instructions into 'invoke's branching to the
86  // cleanup block. Go in reverse order to make prettier BB names.
87  SmallVector<Value *, 16> Args;
88  for (unsigned I = Calls.size(); I != 0;) {
89    CallInst *CI = cast<CallInst>(Calls[--I]);
90    changeToInvokeAndSplitBasicBlock(CI, CleanupBB);
91  }
92
93  Builder.SetInsertPoint(RI);
94  return &Builder;
95}
96