llvm dev - Oct 2013 - [LLVMdev] LLVM use chains

On 10/24/13 2:13 AM, Rafael Espíndola wrote:
> On 23 October 2013 22:41, Vassil Vassilev <vvasilev at cern.ch>
wrote:
>> Hi,
>>    I have:
>>    ...
>> @.str1 = private unnamed_addr constant [21 x i8] c"Now f is a
>> function\0A\00", align 1
>> ; Function Attrs: ssp uwtable
>> define i32 @_Z1fv() #2 {
>> entry:
>>    %call = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([21
x
>> i8]* @.str1, i32 0, i32 0))
>>    ret i32 0
>> }
>>
>> Then I get after trying to erase the function from the module:
>>
>> 511            GV->eraseFromParent();
>> (gdb) p GV->dump()
>>
>> ; Function Attrs: ssp uwtable
>> define i32 @_Z1fv() #2 {
>> entry:
>>    %call = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([21
x
>> i8]* @.str1, i32 0, i32 0))
>>    ret i32 0
>> }
>>
>> (gdb) n
>> 513        }
>> (gdb) br llvm::AssemblyWriter::printModule(llvm::Module const*)
>> (gdb) p m_CurTransaction->getModule()->dump()
>> llvm::AssemblyWriter::printGlobal (this=0x7fff5fbfe850, GV=0x107274058)
at
>>
/Users/vvassilev/workspace/root/interpreter/llvm/src/lib/IR/AsmWriter.cpp:1444
>> 1444      if (GV->isMaterializable())
>> (gdb) p GV->use_empty()
>> $78 = false
>> (gdb) p GV->use_back()
>> $79 = (class llvm::User *) 0x107279b88
>> (gdb) p GV->use_back()->dump()
>> i8* getelementptr inbounds ([21 x i8]* @.str1, i32 0, i32 0)
>> $80 = void
>> (gdb) p (('llvm::Instruction'*)GV->use_back())
>> $81 = ('llvm::Instruction' *) 0x107279b88
>> (gdb) p
(('llvm::Instruction'*)GV->use_back())->getParent()
>> $82 = (const 'llvm::BasicBlock' *) 0x6c675f7878630046
>>
>> My conclusion was that the use chains weren't updated. Is there any
>> recommended way of deleting a llvm::Function such that the use chain of
the
>> globals that it uses to be updated correspondingly?
> You probably want replaceAllUsesWith.
I am sorry I don't understand. Are you suggesting calling replaceAllUses 
of the .str1? What I really want to do is to 'erase' the function. By 
erasing I'd expect the uses of .str1 to 0 (because in the example I have 
it is used only by f()) and I see they are not.
Vassil
>
>
>> Many thanks,
>> Vassil
>>
>> _______________________________________________
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>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

>> You probably want replaceAllUsesWith.
>
> I am sorry I don't understand. Are you suggesting calling
replaceAllUses of
> the .str1? What I really want to do is to 'erase' the function. By
erasing
> I'd expect the uses of .str1 to 0 (because in the example I have it is
used
> only by f()) and I see they are not.
To remove something, the normal idiom is

Foo->replaceAllUsesWith(UndefValue::get(FooTy));
Foo->eraseFromParent();

Is that what you are trying to do?

Cheers,
Rafael

On 10/24/13 9:43 AM, Rafael Espíndola wrote:
>>> You probably want replaceAllUsesWith.
>> I am sorry I don't understand. Are you suggesting calling
replaceAllUses of
>> the .str1? What I really want to do is to 'erase' the function.
By erasing
>> I'd expect the uses of .str1 to 0 (because in the example I have it
is used
>> only by f()) and I see they are not.
> To remove something, the normal idiom is
>
> Foo->replaceAllUsesWith(UndefValue::get(FooTy));
> Foo->eraseFromParent();
>
> Is that what you are trying to do?
I want llvm to 'forget' already compiled and run function. Both from the
ExecutionEngine/JIT and the llvm::Module. The problem using 
replaceAllUsesWith is that the JIT inserts a invisible use so that it 
can prevent from out-of-sync situations. I already tried using 
ExecutionContext::updateGlobalMapping and it doesn't help.
Vassil
>
> Cheers,
> Rafael