[LLVMdev] A basicblock iterator bug in llvm

[hc2428 at columbia.edu]

Quoting Gabor Greif <ggreif at gmail.com>:

Hi Gabor,
     I can not open the link, can you send again?

> AAAH!
>
> I see you are still at 2.5. Then this patch (the fix)
> is relevant for you:
>
> <http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/
> ilist.h?r1=66061&r2=68785&diff_format=h>
>
> Cheers,
>
>     Gabor
>
>
>
> On 27 Sep., 05:45, hc2... at columbia.edu wrote:
>> Dear developers:
>>      When I am doing basicblock pass, I meet a bug: there is an  
>> iterator "I" in a basicblock, and it is not pointing to the first  
>> instruction in this basicblock. However, "I--;" will fail by an  
>> assertion.
>>
>> The basic block ("I" is pointing to the second instruction) in test.ll:
>> bb:             ; preds = %bb1
>>         %1 = call i32 (i8*, ...)* @printf(i8* noalias getelementptr ([42 x  
>> i8]* @.str1, i32 0, i32 0)) nounwind            ; <i32> [#uses=0]
>>         %2 = call i32 (i8*, ...)* @printf(i8* noalias getelementptr ([40 x  
>> i8]* @.str2, i32 0, i32 0)) nounwind            ; <i32> [#uses=0]
>>         %3 = call i32 (i8*, ...)* @printf(i8* noalias getelementptr ([40 x  
>> i8]* @.str3, i32 0, i32 0)) nounwind            ; <i32> [#uses=0]
>>         %4 = call i32 (i8*, ...)* @printf(i8* noalias getelementptr ([42 x  
>> i8]* @.str, i32 0, i32 0)) nounwind             ; <i32> [#uses=0]
>>         br label %bb1
>>
>> The code slice in verify-fixrace.cpp in attachment:
>>
>> cerr << "IsFirst Current Inst: " << *I;
>> cerr << "IsFirst First Inst: " << *BB->begin();
>> I--;
>>
>> Output is:
>> Inst:   %2 = call i32 (i8*, ...)* @printf(i8* noalias getelementptr  
>> ([40 x i8]* @.str2, i32 0, i32 0)) nounwind             ; <i32> [#uses=0]
>> Backward Visit BB: bb
>> IsFirst Current Inst:   %2 = call i32 (i8*, ...)* @printf(i8* noalias  
>> getelementptr ([40 x i8]* @.str2, i32 0, i32 0)) nounwind            
>>      ; <i32>  
>> [#uses=0]
>> IsFirst First Inst:     %1 = call i32 (i8*, ...)* @printf(i8* noalias  
>> getelementptr ([42 x i8]* @.str1, i32 0, i32 0)) nounwind            
>>      ; <i32>  
>> [#uses=0]
>> opt: /home/heming/defens/llvm-2.5/include/llvm/ADT/ilist.h:173:  
>> llvm::ilist_iterator<NodeTy>&  
>> llvm::ilist_iterator<NodeTy>::operator--() [with NodeTy =  
>> llvm::Instruction]: Assertion `Traits::getNext(NodePtr) && "--'d off  
>> the beginning of an ilist!"' failed.
>> 0   opt                    0x08642be4
>> 1   opt                    0x08642f26
>> 2                          0xb7f7f420 __kernel_sigreturn + 0
>> 3   libc.so.6              0xb7d0ca01 abort + 257
>> 4   libc.so.6              0xb7d0410e __assert_fail + 238
>> 5   opt                    0x08357997  
>> llvm::ilist_iterator<llvm::Instruction>::operator--() + 87
>> 6   opt                    0x08367104  
>> llvm::ilist_iterator<llvm::Instruction>::operator--(int) + 28
>> 7   verify-fixrace-stub.so 0xb7f781be  
>> defens::verify_fixrace_stub::DFSBackward(llvm::Instruction*,  
>> std::string&, int, bool) + 826
>> 8   verify-fixrace-stub.so 0xb7f78311  
>> defens::verify_fixrace_stub::runOnBasicBlock(llvm::BasicBlock&) + 261
>> 9   opt                    0x085cdaf4
>> 10  opt                    0x085cee1c  
>> llvm::FPPassManager::runOnFunction(llvm::Function&) + 250
>> 11  opt                    0x085cefb8  
>> llvm::FPPassManager::runOnModule(llvm::Module&) + 98
>> 12  opt                    0x085cd8a3  
>> llvm::MPPassManager::runOnModule(llvm::Module&) + 197
>> 13  opt                    0x085cf256  
>> llvm::PassManagerImpl::run(llvm::Module&) + 116
>> 14  opt                    0x085cf2af  
>> llvm::PassManager::run(llvm::Module&) + 27
>> 15  opt                    0x082f91d0 main + 4452
>> 16  libc.so.6              0xb7cf6450 __libc_start_main + 224
>> 17  opt                    0x082e9c11 __gxx_personality_v0 + 849
>>
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>
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