llvm dev - Feb 2011 - [LLVMdev] Segmentation fault on using get parent of a PHINode

I am getting a segmentation fault as soon as I touch the Basic block
*b value defined as :

  std::string getPHIAssigns(const PHINode *PH)
  { const BasicBlock *b = PH->getParent();
    errs() << b->size();


 where as getPHIAssigns is being called from

               for (BasicBlock::iterator ins=b->begin(), e3=b->end();
ins!=e3; ++ins, ++l) // get instructions
                 { if (const PHINode *PH = dyn_cast<PHINode>(&ins)) //
Phi
                       ers() << getPHIAssigns(PH);

 Can you see what is wrong here?

The dump is :

0  opt             0x0000000000bc9cfa
1  opt             0x0000000000bca288
2  libpthread.so.0 0x00000037ef20e540
3  opt             0x0000000000910849 llvm::iplist<llvm::Instruction,
llvm::ilist_traits<llvm::Instruction> >::size() const + 17
4  opt             0x00000000009108a5 llvm::BasicBlock::size() const + 25
5  dfl.so          0x00002aaaaaaf101d
6  dfl.so          0x00002aaaaaaf2965
7  dfl.so          0x00002aaaaaaf308a
8  opt             0x0000000000b467fa
llvm::FPPassManager::runOnFunction(llvm::Function&) + 348
9  opt             0x0000000000b469cf
llvm::FPPassManager::runOnModule(llvm::Module&) + 81
10 opt             0x0000000000b464bd
llvm::MPPassManager::runOnModule(llvm::Module&) + 381
11 opt             0x0000000000b478f7
llvm::PassManagerImpl::run(llvm::Module&) + 111
12 opt             0x0000000000b47959 llvm::PassManager::run(llvm::Module&)
+ 33
13 opt             0x00000000007a14a6 main + 3438
14 libc.so.6       0x00000037ee61e074 __libc_start_main + 244
15 opt             0x00000000007929a9
Stack dump:
0.	Program arguments: opt -load
/u1/suri/llvm-local/build/x86-64/Debug/llvm/Debug/lib/dfl.so -dfl
/u1/suri/suri/testing/cfgs/test99foo.c.bc
1.	Running pass 'Function Pass Manager' on module
'/u1/suri/suri/testing/cfgs/test99foo.c.bc'.
2.	Running pass 'emit cfg in dfl format' on function '@main'

 Surinder
>

Hi Surinder, I don't see anything obviously wrong with your code.  I suggest
that (1) you build LLVM with assertions enabled, (2) you run the verifier on
your bitcode, and (3) run your program under valgrind.

Ciao, Duncan.
>   I am getting a segmentation fault as soon as I touch the Basic block
> *b value defined as :
>
>    std::string getPHIAssigns(const PHINode *PH)
>    { const BasicBlock *b = PH->getParent();
>      errs()<<  b->size();
>
>
>   where as getPHIAssigns is being called from
>
>                 for (BasicBlock::iterator ins=b->begin(),
e3=b->end();
> ins!=e3; ++ins, ++l) // get instructions
>                   { if (const PHINode *PH =
dyn_cast<PHINode>(&ins)) // Phi
>                         ers()<<  getPHIAssigns(PH);
>
>   Can you see what is wrong here?
>
> The dump is :
>
> 0  opt             0x0000000000bc9cfa
> 1  opt             0x0000000000bca288
> 2  libpthread.so.0 0x00000037ef20e540
> 3  opt             0x0000000000910849 llvm::iplist<llvm::Instruction,
> llvm::ilist_traits<llvm::Instruction>  >::size() const + 17
> 4  opt             0x00000000009108a5 llvm::BasicBlock::size() const + 25
> 5  dfl.so          0x00002aaaaaaf101d
> 6  dfl.so          0x00002aaaaaaf2965
> 7  dfl.so          0x00002aaaaaaf308a
> 8  opt             0x0000000000b467fa
> llvm::FPPassManager::runOnFunction(llvm::Function&) + 348
> 9  opt             0x0000000000b469cf
> llvm::FPPassManager::runOnModule(llvm::Module&) + 81
> 10 opt             0x0000000000b464bd
> llvm::MPPassManager::runOnModule(llvm::Module&) + 381
> 11 opt             0x0000000000b478f7
> llvm::PassManagerImpl::run(llvm::Module&) + 111
> 12 opt             0x0000000000b47959
llvm::PassManager::run(llvm::Module&) + 33
> 13 opt             0x00000000007a14a6 main + 3438
> 14 libc.so.6       0x00000037ee61e074 __libc_start_main + 244
> 15 opt             0x00000000007929a9
> Stack dump:
> 0.	Program arguments: opt -load
> /u1/suri/llvm-local/build/x86-64/Debug/llvm/Debug/lib/dfl.so -dfl
> /u1/suri/suri/testing/cfgs/test99foo.c.bc
> 1.	Running pass 'Function Pass Manager' on module
> '/u1/suri/suri/testing/cfgs/test99foo.c.bc'.
> 2.	Running pass 'emit cfg in dfl format' on function
'@main'
>
>   Surinder
>>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

On Feb 5, 2011, at 10:09 AM, Duncan Sands wrote:
> Hi Surinder, I don't see anything obviously wrong with your code.  I
suggest
> that (1) you build LLVM with assertions enabled, (2) you run the verifier
on
> your bitcode, and (3) run your program under valgrind.
I think there might be something unsound in our current dyn_cast implementation;
that is, I'm pretty sure it type-checks for things it's not supposed to
type-check for.

In this example, &ins has type llvm::ilist_iterator<Instruction>*,
because the
iterator type (like most iterator types) does not overload operator&.  This
should
really not compile, and yet it does.

Anyway, the immediate fix is to use the iterator correctly:
>>                for (BasicBlock::iterator ins=b->begin(),
e3=b->end();
>> ins!=e3; ++ins, ++l) // get instructions
>>                  { if (const PHINode *PH =
dyn_cast<PHINode>(&ins)) // Phi
>>                        ers()<<  getPHIAssigns(PH);
This should be dyn_cast<PHINode>(*ins).

John.