[LLVMdev] LLVM problem, please do not ignore

[John Criswell]

On 11/3/2011 4:55 AM, Arshak Nazaryan wrote:
> Dear sir or madam,
>
> I am a 4-th year student at Yerevan State University, Armenia; and I 
> am studying LLVM in order to write my Bachelor thesis.

Hi Arshak.


> I am trying to write an llvm pass that just removes all "Add" commands 
> and gives some statstics.
> Nevertheless, I get this segmentation fault:

The problem is most likely that you're not modifying uses of the add 
instructions.  The LLVM IR has explicit def-use chains, so if you want 
to remove an instruction, you need to modify any other instruction *that 
uses that instruction* so that it does not use that instruction any more.

In this case, an instruction that is using the add instruction will 
still reference the add instruction even after you've deleted it.  The 
error you're seeing is most likely due to a dangling pointer.

To fix it, create a constant integer (ConstantInt object) and use the 
replaceAllUsesWith() method of the Instruction class to replace uses of 
the add with the integer.  Then you can erase the add from the program.

By the way, it looks like you don't have a build with assertions 
enabled.  I recommend compiling with

gmake ENABLE_OPTIMIZED=0 DISABLE_ASSERTIONS=1

if you're going to be developing an LLVM pass.

-- John T.

>
> ................some rows about functions, that are not changed by my 
> pass. The errors occurs after it has modified a "@_Z3addii" function.
> store i32 %b.0, i32* %4  and the type is ddddbbm 28
>   %5 = load i32* %a_addr, align 4  and the type is ddddbbm 27
>   %6 = load i32* %b_addr, align 4  and the type is ddddbbm 27
>   %7 = add nsw i32 %5, %6  and the type is ddddbbm 8
>   store i32 %7, i32* %0, align 4  and the type is ddddbbm 28
>   %7 = add nsw i32 %5, %6   is erased, ba!
>   %7 = load i32* %0, align 4  and the type is ddddbbm 27
>   store i32 %7, i32* %retval, align 4  and the type is ddddbbm 28
>   br label %return  and the type is ddddbbm 2
>   ret i32 %retval1  and the type is ddddbbm 1
> 0  opt             0x00000000008ed93f
> 1  opt             0x00000000008edcea
> 2  libpthread.so.0 0x00007f9ba1183c60
> 3  opt             0x00000000004b3615 llvm::PATypeHolder::get() const + 21
> 4  opt             0x00000000008a4f11
> 5  opt             0x00000000008a9404
> 6  opt             0x0000000000882557 
> llvm::FPPassManager::runOnFunction(llvm::Function&) + 551
> 7  opt             0x00000000008825db 
> llvm::FPPassManager::runOnModule(llvm::Module&) + 75
> 8  opt             0x0000000000882197 
> llvm::MPPassManager::runOnModule(llvm::Module&) + 503
> 9  opt             0x0000000000882299 
> llvm::PassManagerImpl::run(llvm::Module&) + 137
> 10 opt             0x00000000004ac451 main + 4881
> 11 libc.so.6       0x00007f9ba0459eff __libc_start_main + 255
> 12 opt             0x000000000049f5f9
> Stack dump:
> 0.Program arguments: opt hello.bc -load 
> ../llvm/llvm-2.9/plugin/BasicBlockStats.so -basic-block-stats -stats 
> -o newhello.bc
> 1.Running pass 'Function Pass Manager' on module 'hello.bc'.
> 2.Running pass 'Module Verifier' on function '@_Z3addii'
> Segmentation fault
>
> Please find the source of my pass attached.
> Hope to get a reply soon.
>
> Regards,
> Arshak Nazaryan
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20111103/4cd4f283/attachment.html>