llvm dev - Jun 2010 - [LLVMdev] Segmentation fault 'cause of accessing function arguments

Hi all, 

I am experimenting to run a pass inherited from CallGraphSCCPass. In
the pass, I iterate all functions in a SCC. In each iteration, I
access all arguments of a function in the following way:

  Function::arg_iterator PI = fun->arg_begin(), PE = fun->arg_end();
  ...

I have no trouble with building. However, I am troubled with 
"segmentation fault" when I run the pass via:

  opt -load ../../build-llvm/Debug/lib/LLVMRCI.dylib -rci < a.out.bc

The error message is attached later. 

So, am I wrong with accessing function arguments?
What are the possible causes?

Thanks, 
Xiaolong

PS: ERROR MESSAGE

Identify an SCC. The number of function: 1
0  opt               0x0000000100426a32 PrintStackTrace(void*) + 38
1  opt               0x0000000100426e8c SignalHandler(int) + 254
2  libSystem.B.dylib 0x00007fff82a9880a _sigtramp + 26
3  LLVMRCI.dylib     0x000000010148e6ae (anonymous namespace)::RCI::ID + 16462
4  opt               0x0000000100010e89 llvm::Function::hasLazyArguments() const
+ 21
5  opt               0x00000001000114e3 llvm::Function::CheckLazyArguments()
const + 21
6  opt               0x000000010013a421 llvm::Function::arg_begin() + 21
7  LLVMRCI.dylib     0x0000000101483e02 (anonymous
namespace)::RCI::runOnSCC(llvm::CallGraphSCC&) + 184
8  opt               0x0000000100205686 (anonymous
namespace)::CGPassManager::RunPassOnSCC(llvm::Pass*, llvm::CallGraphSCC&,
llvm::CallGraph&, bool&, bool&) + 230
9  opt               0x0000000100205abe (anonymous
namespace)::CGPassManager::RunAllPassesOnSCC(llvm::CallGraphSCC&,
llvm::CallGraph&, bool&) + 488
10 opt               0x0000000100205d60 (anonymous
namespace)::CGPassManager::runOnModule(llvm::Module&) + 352
11 opt               0x00000001003bc064
llvm::MPPassManager::runOnModule(llvm::Module&) + 384
12 opt               0x00000001003bd80d
llvm::PassManagerImpl::run(llvm::Module&) + 111
13 opt               0x00000001003bd86f
llvm::PassManager::run(llvm::Module&) + 33
14 opt               0x0000000100066d3b main + 3420
15 opt               0x000000010005c1c4 start + 52
16 opt               0x0000000000000004 start + 4294590068
Stack dump:
0.	Program arguments: opt -load ../../build-llvm/Debug/lib/LLVMRCI.dylib -rci 
1.	Running pass 'CallGraph Pass Manager' on module
'<stdin>'.
Segmentation fault