llvm/lib/Transforms/Utils/EscapeEnumerator.cpp

   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/IR/EHPersonalities.h"
  16 #include "llvm/IR/Module.h"
  17 #include "llvm/TargetParser/Triple.h"
  18 #include "llvm/Transforms/Utils/Local.h"
  19
  20 using namespace llvm;
  21
  22 static 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
  30 IRBuilder<> *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(PointerType::getUnqual(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 }