[llvm-dev] Error Calling eraseFromParent()

[Ahmad Nouralizadeh via llvm-dev]

Well, the problem was with the LLVM build. I re-extracted the sources and
recompiled the whole tool and then SegFaul disappeared! :D
Many Thanks all you guys especially Zhang!

On Wed, Aug 8, 2018 at 10:36 PM, mats petersson <mats at planetcatfish.com>
wrote:

>
>
> On 8 August 2018 at 18:30, Ahmad Nouralizadeh via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> 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.
>>
> Ahmad,
>
> I would highly recommend, at least if you are running into problems, that
> debug using asserts enabled. This will (most of the time) give you a better
> "explanation" as to what you've done wrong. Not every time, but for many of
> the "we expect someone to get this wrong at some pont" type of problems.
>
> Trying to figure out why something failed in a release build without
> asserts is often painfully hard, because when you crash, the "reason" for
> the crash is in code that has been inlined, the actual understanding of
> what went wrong is several layers of calls above the crash-point.
>
> --
> Mats
>
>>
>> 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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>>
>
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