[LLVMdev] eraseFromParent and stack dump

[Will Dietz]

Indeed, it'd be helpful to know the contents of the function
locate_instruction().

Also, a quick suggestion: ensure the FaultInjectionPass doesn't have
any datastructures that are invalidated by your IR modifications,
in particular look for collections of llvm::Instruction* (or
llvm::Value*) that might be used in later code to reference
instructions you've erased.  These datastructures are commonly used
for worklists and for mapping from LLVM constructs to analysis
information.

Otherwise a bit more detail on your code and workflow (you say you get
a crash when you run the IR--but the stack dump is from an LLVM
pass--is this part of some interpreter?) would likely help us sort out
your issue :).

Hope this helps,

~Will

On Thu, Jun 26, 2014 at 10:29 AM, John Criswell <criswell at illinois.edu> wrote:
> On 6/26/14, 4:38 AM, Vasileios Koutsoumpos wrote:
>>
>> Hello,
>>
>> I am creating a new instruction and I want to replace the use of a
>> specified instruction.
>> This is the code I have written
>>
>> Instruction *new_instr = BinaryOperator::Create(Instruction::Sub, op1,
>> op2, "");
>
>
> As a matter of style, I'd use the version of BinaryOperator::Create() that
> takes an Instruction * as an insert point and use it to insert the new
> instruction *before* the old instruction.  It shouldn't matter whether it
> goes before or after, and it avoids having to do a separate operation to
> insert the BinaryOperator into the basic block.
>
>
>> b->getInstList().insertAfter(old_instr, new_instr);  //b is the BasicBlock
>> old_instr->replaceAllUsesWith(new_instr);
>> old_instr->eraseFromParent();
>>
>> When I print the basic block, I see that my instruction was inserted  and
>> replaces the old instruction, however I get a stack dump, when I run the
>> instrumented IR file.
>>
>> 0  opt             0x00000000014680df
>> llvm::sys::PrintStackTrace(_IO_FILE*) + 38
>> 1  opt             0x000000000146835c
>> 2  opt             0x0000000001467dd8
>> 3  libpthread.so.0 0x00007f8934eecbb0
>> 4  llfi-passes.so  0x00007f89340a39b2 llvm::Value::getValueID() const + 12
>> 5  llfi-passes.so  0x00007f89340a3aa4 llvm::Instruction::getOpcode() const
>> + 24
>> 6  llfi-passes.so  0x00007f89340a331c
>> llfi::FaultInjectionPass::locate_instruction(llvm::Module&, llvm::Function*,
>> llvm::LoopInfo&, int) + 282
>> 7  llfi-passes.so  0x00007f89340a2e50
>> llfi::FaultInjectionPass::finalize(llvm::Module&, int) + 506
>> 8  llfi-passes.so  0x00007f89340a3509
>> llfi::FaultInjectionPass::runOnModule(llvm::Module&) + 113
>> 9  opt             0x0000000001362a1e
>> llvm::MPPassManager::runOnModule(llvm::Module&) + 502
>> 10 opt             0x0000000001362fee
>> llvm::PassManagerImpl::run(llvm::Module&) + 244
>> 11 opt             0x00000000013631f9
>> llvm::PassManager::run(llvm::Module&) + 39
>> 12 opt             0x00000000008719e8 main + 5698
>> 13 libc.so.6       0x00007f8934318de5 __libc_start_main + 245
>> 14 opt             0x0000000000863779
>> Stack dump:
>>
>> I replace the uses of the old instruction, before deleting it. I am not
>> sure why this is happening.
>> any suggestions?
>
> I'm assuming that FaultInjectionPass is your code, correct?
>
> If so, if you look at your stack dump, you'll see that it crashes calling
> Instruction::getOpcode() in the method locate_instruction() in your passes
> finalize() method.
>
> I recommend finding the line in locate_instruction that is causing the
> problem.  If it's one of the 4 lines you list at the top of this email,
> check that the old instruction pointer is non-NULL and points to an actual
> instruction.
>
> You may also want to check and see if the old instruction is a phi-node.
> That might cause issues.
>
> Finally, if you're building a FaultInjector pass, we built a very simple one
> for SAFECode that tries to create memory safety errors. You may or may not
> find it helpful for what you're doing.
>
> Regards,
>
> John Criswell
>
>
>>
>> Vasileios
>>
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>
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