[LLVMdev] Manipulating basic blocks with the C bindings

[Kenneth Uildriks]

On Thu, May 27, 2010 at 8:46 PM, Evan Shaw <chickencha at gmail.com> wrote:
> On Thu, May 27, 2010 at 6:38 PM, Kenneth Uildriks <kennethuil at gmail.com> wrote:
>> On Thu, May 27, 2010 at 5:47 PM, Evan Shaw <chickencha at gmail.com> wrote:
>>> I'm writing a frontend with the LLVM C bindings for a language that
>>> has a goto statement, similar to C's. I'm having some trouble figuring
>>> out what to do for the case where the label is declared after the
>>> goto, like this:
>>>
>>> goto label;
>>> ...
>>> label:
>>> ...
>>>
>>> When I generate the code for the goto, I'd like to create a basic
>>> block that's not inserted anywhere in particular and then put it in
>>> the right place when I hit the label (or error out appropriately if I
>>> never find it). It looks like the C++ API allows one to do what I'm
>>> describing, but I don't see a way to do it with the C bindings.\
>>
>> When you hit the "goto", create an empty basic block with
>> LLVMAppendBasicBlockInContext and put in an unconditional branch to
>> it.  Later, when you hit the label, put another unconditional branch
>> to that same block, then call LLVMPositionBuilderAtEnd(labelBlock) and
>> continue on your way.
> That would work. It just seems like there ought to be a better way. Thanks.
>
> - Evan
>

If you keep in mind that blocks (other than the entry) aren't really
ordered by anything other than branches, I can't see anything
unintuitive about it.