[llvm-dev] Error Calling eraseFromParent()

[Zhang via llvm-dev]

Hmmmm.
One more guess is that since you used IRBuilder to insert new Instructions, you are still actually modifying the BB and thus invalidated the iterator. I just picked up some old work regarding this and in my example I just wrote something like this:
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Inst)) {
     BinaryOperator *newBO = llvm::BinaryOperator::Create(newOp, BO->getOperand(0),BO->getOperand(1));
     llvm::ReplaceInstWithInst(BO, newBO);
}



Sorry for the bad formatting, I typed this on mobile. Hope this helps : )


Zhang
 
------------------ Original ------------------
From:  "Ahmad Nouralizadeh"<ahmadnouralizadeh at gmail.com>;
Date:  Thu, Aug 9, 2018 02:00 AM
To:  "mayuyu.io"<admin at mayuyu.io>; 
Cc:  "llvm-dev"<llvm-dev at lists.llvm.org>; 
Subject:  Re: [llvm-dev] Error Calling eraseFromParent()

 
LLVM is built in Release mode. The version is 6.0.0. I think that a similar code worked on verison 3.9.0. It is probably a null pointer dereference occurring in eraseFromParent(). I checked and reconfirmed that the instruction had no uses. Perhaps I should rebuild LLVM. Thanks.


On Wed, Aug 8, 2018 at 9:03 PM, mayuyu.io <admin at mayuyu.io> wrote:
Hmmmm that’s strange. Do you get an assert when you build LLVM with this code in Debug Mode or is it simply null pointer dereference? On a side note, usually when doing transforms similar to yours I use IRBuilder’s CreateXXX followed by a ReplaceInstWithInst which works perfectly fine for me.

Zhang

在 2018年8月9日，00:29，Ahmad Nouralizadeh <ahmadnouralizadeh at gmail.com> 写道：


Hi. Thanks. I changed the code but the problem exists. This is my new code which is again very simple:...
bool runOnFunction(Function &F) override {


vector<Instruction *> dels;
dels.clear();


for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
	Instruction *I = &*(It++);


	if (auto* op = dyn_cast<BinaryOperator>(I)) {
		IRBuilder<NoFolder> builder(op);


		Value* lhs = op->getOperand(0);
		Value* rhs = op->getOperand(1);
		Value* mul = builder.CreateMul(lhs, rhs);


		for (auto& U : op->uses()) {
		  User* user = U.getUser();
		  user->setOperand(U.getOperandNo(), mul);
		}
		//I->eraseFromParent();
		dels.push_back(I);
	}
}	


for (auto &I : dels) {
	I->eraseFromParent();
}

...


On Wed, Aug 8, 2018 at 6:16 PM, mayuyu.io <admin at mayuyu.io> wrote:
Hi:As stated in the documentation you shouldn’t modify it while iterating as this invalidates the iterator. Try save the pointers to a vector outside your loop and perform erasing in a new loop following your current one.

Zhang

在 2018年8月8日，07:54，Ahmad Nouralizadeh via llvm-dev <llvm-dev at lists.llvm.org> 写道：


Thanks Bjorn! But The problem is still there.

On Wed, Aug 8, 2018 at 2:04 AM, Björn Pettersson A <bjorn.a.pettersson at ericsson.com> wrote:
It looks quite dangerous to erase the instruction I inside the loop when iterating over all instructions in the function.
 I guess it depends on how the range based iterator is implemented if that works or not.
 
 I think that you, for example, can change the range based iteration
 
    for (auto &I : instructions(F))
 
 into something like this
 
    for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
       Instruction *I = &*(It++);
       ...
     }
 
 That will make sure that you step the iterator before modifying the data structure you iterate over.
 
 Regards,
 Björn
 ________________________________________
 From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Ahmad Nouralizadeh via llvm-dev <llvm-dev at lists.llvm.org>
 Sent: Tuesday, August 7, 2018 22:26
 To: paul.robinson at sony.com
 Cc: llvm-dev at lists.llvm.org
 Subject: Re: [llvm-dev] Error Calling eraseFromParent()
 
 The code is really simple. But I can not the reason for the segmentation fault. I only know that the eraseFromParent() function leads to it. The whole code is:
 ...
 bool runOnFunction(Function &F) override {
 
 for (auto &I : instructions(F)) {
 
 if (auto* op = dyn_cast<BinaryOperator>(&I)) {
 IRBuilder<> builder(op);
 
 Value* lhs = op->getOperand(0);
 Value* rhs = op->getOperand(1);
 Value* mul = builder.CreateMul(lhs, rhs);
 
 for (auto& U : op->uses()) {
   User* user = U.getUser();
   user->setOperand(U.getOperandNo(), mul);
 }
 
 I.eraseFromParent();
     }
 
 }
 ...
 And I think that the code worked well with LLVM-3.6.0 that I tested one year ago. Now, I use LLVM-6.0.0.
 Regards.
 




 


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