C++ JumpDest::getScopeDepth方法代码示例

/// isObviouslyBranchWithoutCleanups - Return true if a branch to the
/// specified destination obviously has no cleanups to run.  'false' is always
/// a conservatively correct answer for this method.
bool CodeGenFunction::isObviouslyBranchWithoutCleanups(JumpDest Dest) const {
  assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
         && "stale jump destination");
  
  // Calculate the innermost active normal cleanup.
  EHScopeStack::stable_iterator TopCleanup =
    EHStack.getInnermostActiveNormalCleanup();
  
  // If we're not in an active normal cleanup scope, or if the
  // destination scope is within the innermost active normal cleanup
  // scope, we don't need to worry about fixups.
  if (TopCleanup == EHStack.stable_end() ||
      TopCleanup.encloses(Dest.getScopeDepth())) // works for invalid
    return true;

  // Otherwise, we might need some cleanups.
  return false;
}

/// Terminate the current block by emitting a branch which might leave
/// the current cleanup-protected scope.  The target scope may not yet
/// be known, in which case this will require a fixup.
///
/// As a side-effect, this method clears the insertion point.
void CodeGenFunction::EmitBranchThroughCleanup(JumpDest Dest) {
  assert(Dest.getScopeDepth().encloses(EHStack.stable_begin())
         && "stale jump destination");

  if (!HaveInsertPoint())
    return;

  // Create the branch.
  llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock());

  // Calculate the innermost active normal cleanup.
  EHScopeStack::stable_iterator
    TopCleanup = EHStack.getInnermostActiveNormalCleanup();

  // If we're not in an active normal cleanup scope, or if the
  // destination scope is within the innermost active normal cleanup
  // scope, we don't need to worry about fixups.
  if (TopCleanup == EHStack.stable_end() ||
      TopCleanup.encloses(Dest.getScopeDepth())) { // works for invalid
    Builder.ClearInsertionPoint();
    return;
  }

  // If we can't resolve the destination cleanup scope, just add this
  // to the current cleanup scope as a branch fixup.
  if (!Dest.getScopeDepth().isValid()) {
    BranchFixup &Fixup = EHStack.addBranchFixup();
    Fixup.Destination = Dest.getBlock();
    Fixup.DestinationIndex = Dest.getDestIndex();
    Fixup.InitialBranch = BI;
    Fixup.OptimisticBranchBlock = nullptr;

    Builder.ClearInsertionPoint();
    return;
  }

  // Otherwise, thread through all the normal cleanups in scope.

  // Store the index at the start.
  llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex());
  new llvm::StoreInst(Index, getNormalCleanupDestSlot(), BI);

  // Adjust BI to point to the first cleanup block.
  {
    EHCleanupScope &Scope =
      cast<EHCleanupScope>(*EHStack.find(TopCleanup));
    BI->setSuccessor(0, CreateNormalEntry(*this, Scope));
  }

  // Add this destination to all the scopes involved.
  EHScopeStack::stable_iterator I = TopCleanup;
  EHScopeStack::stable_iterator E = Dest.getScopeDepth();
  if (E.strictlyEncloses(I)) {
    while (true) {
      EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(I));
      assert(Scope.isNormalCleanup());
      I = Scope.getEnclosingNormalCleanup();

      // If this is the last cleanup we're propagating through, tell it
      // that there's a resolved jump moving through it.
      if (!E.strictlyEncloses(I)) {
        Scope.addBranchAfter(Index, Dest.getBlock());
        break;
      }

      // Otherwise, tell the scope that there's a jump propoagating
      // through it.  If this isn't new information, all the rest of
      // the work has been done before.
      if (!Scope.addBranchThrough(Dest.getBlock()))
        break;
    }
  }
  
  Builder.ClearInsertionPoint();
}