[llvm-dev] Error Calling eraseFromParent()

[Ahmad Nouralizadeh via llvm-dev]

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.
>>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
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