[LLVMdev] Basic block with two return instructions

[Russell Wallace]

Ah! I didn't know about verifyFunction; it does indeed catch it,
thanks! I'll leave that call in my code for all cases for the moment,
should help identify problems like that.

Is there a recommended way to avoid this problem when compiling a
language that has an explicit and optional return statement?

On Fri, Feb 5, 2010 at 5:25 PM, Garrison Venn <gvenn.cfe.dev at gmail.com> wrote:
> Did your test include running llvm::verifyFunction(...) on the function in question?
> I guess I should test this, but I would have thought this would catch the issue.
>
> Garrison
>
> On Feb 5, 2010, at 12:13, Russell Wallace wrote:
>
>> Fair enough. In that case, is there an elegant way to test whether a
>> basic block already has a terminator instruction?
>>
>> (I can think of several ways to do it in the front-end, but all of
>> them are fairly inelegant. The problem I'm trying to solve is things
>> like 'a return instruction needs to be added to the end of a function,
>> if and only if the programmer didn't already end the function with an
>> explicit return statement', 'if the programmer did write an explicit
>> return statement everything after it must be ignored' etc.)
>>
>> On Fri, Feb 5, 2010 at 4:58 PM, Kenneth Uildriks <kennethuil at gmail.com> wrote:
>>> On Fri, Feb 5, 2010 at 10:56 AM, Russell Wallace
>>> <russell.wallace at gmail.com> wrote:
>>>> When I generate a simple function with a single basic block with two
>>>> return instructions, I had expected that if it did anything at all, it
>>>> would use the first one, but it actually seems to ignore the first one
>>>> and take the value of the second one.
>>>>
>>>> I'm guessing what's going on here is something like "a basic block
>>>> must end in exactly one terminator instruction, having two of them is
>>>> undefined behavior and the code generator is entitled to do anything
>>>> including make demons fly out of your nose"; is this correct?
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>>>
>>> That's pretty much been my experience.  Usually, something crashes
>>> when I try it though.
>>>
>>
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