[LLVMdev] Branching to Entry block

[Chris Lattner]

On Thu, 17 Feb 2005, Tanu Sharma wrote:

> Thanks a lot for replying...but I am not doing any deleting or removing node ...I am trying to insert a "new" entry node in an existing list.
> In another reply I understood (also mentioned on the site) that no other block can branch to the entry block.
>
> How do I achieve this ? Is it feasible?Let me know if there is any example.

Can you provide a stack trace for the failed assertion?

-Chris

> Chris Lattner <sabre at nondot.org> wrote:
> On Thu, 17 Feb 2005, Tanu Sharma wrote:
>> I created a new block and inserted it into the present basic block list
>> , but I get this error:
>>
>> opt: BasicBlock.cpp:83: virtual llvm::BasicBlock::~BasicBlock(): Assertion `getParent() == 0 && "BasicBlock still linked into the program!"' failed.
>>
>> The program completes its task and i get this in the end. I am unable to
>> resolve this.
>
> The problem there is that you're trying to delete some basic block that is
> still embedded into a function. There are several ways to accomplish
> this:
>
> BasicBlock *BB = ...
>
> // Approach number 1, the easy way:
> BB->eraseFromParent();
>
> // Approach number 2, the more explicit way:
> BB->getParent()->getInstList().erase(BB); // Remove from list & delete
>
> // Approach number 3, remove from the list, then delete it explicitly:
> BB->getParent()->getInstList().remove(BB); // Just remove from list
> delete BB; // Delete block
>
>
> I strongly suggest using approach #1, but I listed all of them so you can
> see the relation between remove and erase.
>
> -Chris
>
>
>> John Criswell wrote:
>> Tanu Sharma wrote:
>>> Hello,
>>>
>>> In an attempt to randomise the basic blocks in a function, is it
>>> possible that I can randomise the entry block as well? And maybe insert
>>> some instructions in the pass to call entry block while running the
>>> program ?
>>>
>>> Is it feasible?
>>>
>>> What does entry block consist of ?
>>
>> The entry block, by definition, is the first basic block (BB) to be
>> executed by a function. As I understand it, it has the additional
>> restriction that it cannot be dominated by other basic blocks (i.e. no
>> other BBs in the function can branch to it).
>>
>> If your entry BB performs useful computations and you want to move it,
>> you could create a new entry BB that does nothing but branch to the old
>> entry BB. The old entry BB (now just a regular BB) can then be moved.
>>
>> I'm assuming thus far that you're randomizing the basic block order at
>> the LLVM level (i.e. take LLVM function, randomize order of BBs, and
>> then codegen each BB in order). Another approach, as I see it, would be
>> to change the code generator so that it codegens the BBs in a random
>> order, instead of codegen'ing them in order.
>>
>> The first approach, I think, is a lot easier.
>>
>> Regards,
>>
>> -- John T.
>>
>>>
>>> Thanks
>>>
>>> Tanu
>>>
>>>
>>>
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>
> -Chris
>
>

-Chris

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