llvm dev - Dec 2012 - [LLVMdev] LLVM segmentation fault / need use Instruction instead of Instruction*

Hello John,

I was following your procedures and I isolated the problem. The problem are
represented by the basic blocks with only one element.


for (Function::iterator II = F.begin(), EE = F.end(); II != EE; ++II, ++ii)
{
BasicBlock* BB=II;


if (BB->getTerminator())
    {
        Instruction* current = BB->getTerminator();

        Instruction* previous;

        errs()<<"AAA\n";
        if(*current->getPrevNode()*)
        {
            errs()<<"BBB\n";
            previous = current->getPrevNode();
            ok=1;
        }

        if (ok){
           errs()<<"CCC\n";
              ........


It does print AAA, but then I have the segfault. So when I am evaluating
the *current->getPrevNode() *condition, I got the segfault.
Do you know how can I solve this?

Thank you
Alex
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I may be mistaken as I just took a quick look, but in ilist_node the
function "getPrevNode()" actually calls a method on the previous node:

NodeTy *getPrevNode() {
  NodeTy *Prev = this->getPrev();

  // Check for sentinel.
  if (!Prev->getNext())
    return 0;

  return Prev;
}

http://llvm.org/docs/doxygen/html/ilist__node_8h_source.html#l00058

Try checking if current->getPrev() is null before calling
current->getPrevNode().

Stephen


On 20 December 2012 10:42, Alexandru Ionut Diaconescu <
alexandruionutdiaconescu at gmail.com> wrote:
> Hello John,
>
> I was following your procedures and I isolated the problem. The problem
> are represented by the basic blocks with only one element.
>
>
> for (Function::iterator II = F.begin(), EE = F.end(); II != EE; ++II,
> ++ii)
> {
> BasicBlock* BB=II;
>
>
> if (BB->getTerminator())
>     {
>         Instruction* current = BB->getTerminator();
>
>         Instruction* previous;
>
>         errs()<<"AAA\n";
>         if(*current->getPrevNode()*)
>         {
>             errs()<<"BBB\n";
>             previous = current->getPrevNode();
>             ok=1;
>         }
>
>         if (ok){
>            errs()<<"CCC\n";
>               ........
>
>
> It does print AAA, but then I have the segfault. So when I am evaluating
> the *current->getPrevNode() *condition, I got the segfault.
> Do you know how can I solve this?
>
> Thank you
> Alex
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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Alexandru Ionut Diaconescu <alexandruionutdiaconescu at gmail.com> writes:
> I was following your procedures and I isolated the problem. The problem are
> represented by the basic blocks with only one element.
>
>
> for (Function::iterator II = F.begin(), EE = F.end(); II != EE; ++II, ++ii)
> {
> BasicBlock* BB=II;
>
>
> if (BB->getTerminator())
>     {
>         Instruction* current = BB->getTerminator();
>
>         Instruction* previous;
>
>         errs()<<"AAA\n";
>         if(*current->getPrevNode()*)
>         {
>             errs()<<"BBB\n";
>             previous = current->getPrevNode();
>             ok=1;
>         }
>
>         if (ok){
>            errs()<<"CCC\n";
>               ........
>
>
> It does print AAA, but then I have the segfault. So when I am evaluating
> the *current->getPrevNode() *condition, I got the segfault.
> Do you know how can I solve this?
The documentation for BasickBlock::getTerminator says:

  /// getTerminator() - If this is a well formed basic block, then this returns
  /// a pointer to the terminator instruction.  If it is not, then you get a
  /// null pointer back.

Maybe BB is not well formed (it doesn't have proper terminator) and
BB->getTerminator returns NULL ?

Hello,

Thank you for your answer. If I want to use

then I have

error: ‘NodeTy* llvm::ilist_half_node<NodeTy>::getPrev() [with NodeTy
llvm::Instruction]’ is protected
error: ‘llvm::ilist_half_node<llvm::Instruction>’ is not an accessible
base
of ‘llvm::Instruction’

Do you know any other method to access the previous instruction of a
terminator instruction? PS: back() is not an option.

On Thu, Dec 20, 2012 at 12:06 PM, Stephen McGruer <stephen.mcgruer at
gmail.com
> wrote:
> current->getPrev()



-- 
Best regards,
Alexandru Ionut Diaconescu
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