llvm dev - Jan 2013 - [LLVMdev] Inconsistent label syntax in LLVM assembly

Hi Duncan
>>   br i1 %38, label %17, label %39
>> ; <label>:39                                      ; preds =
%._crit_edge
>>   ret void
>>
>> However, ";" is a comment-line character. How is this
interpreted, as a
>> meta-comment? (a semantically important comment)?
>
> it's just a comment and has no semantic comment.  You can delete it, it
won't
> make any difference.
OK. However, in this case, how is the branch resolved? I mean that  
there is no obvious %39 label declared in the LLVM translation unit.


Best regards
Nikolaos Kavvadias

Hi Duncan
>>>  br i1 %38, label %17, label %39
>>> ; <label>:39                                      ; preds =
%._crit_edge
>>>  ret void
>>>
>>> However, ";" is a comment-line character. How is this
interpreted, as a
>>> meta-comment? (a semantically important comment)?
>>
>> it's just a comment and has no semantic comment.  You can delete  
>> it, it won't make any difference.
>
> OK. However, in this case, how is the branch resolved? I mean that  
> there is no obvious %39 label declared in the LLVM translation unit.
I can see that there is a certain convention; e.g. %39 is the assumed  
(implicit) label, if the %38 is the last defined temporary at that  
point of the function body.

So, I guess that if the following basic block has no explicit label,  
it acquires one by generating a new temporary. This is my deduction;  
I'm not sure it is correct though.


Best regards
Nikolaos Kavvadias

>
>
> Best regards
> Nikolaos Kavvadias
>
>
>
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>

Hi Nikolaos,

On 20/01/13 13:19, nkavv at physics.auth.gr wrote:
> Hi Duncan
>
>>>   br i1 %38, label %17, label %39
>>> ; <label>:39                                      ; preds =
%._crit_edge
>>>   ret void
>>>
>>> However, ";" is a comment-line character. How is this
interpreted, as a
>>> meta-comment? (a semantically important comment)?
>>
>> it's just a comment and has no semantic comment.  You can delete
it, it won't
>> make any difference.
>
> OK. However, in this case, how is the branch resolved? I mean that there is
no
> obvious %39 label declared in the LLVM translation unit.
labels don't determine where a basic block starts or stops, terminator
instructions do.  It is possible to give a basic block a name, in which
case when writing out a .ll file that name will be output as a
"label",
but the "label" has no functional utility, it's not a label like
in real
assembler.  If a basic block has no name then it is referred to in the .ll
by the number of the basic block, eg %39.

Ciao, Duncan.

Hi Nikolaos,

On 20/01/13 13:46, nkavv at physics.auth.gr wrote:
> Hi Duncan
>
>>>>  br i1 %38, label %17, label %39
>>>> ; <label>:39                                      ; preds
= %._crit_edge
>>>>  ret void
>>>>
>>>> However, ";" is a comment-line character. How is this
interpreted, as a
>>>> meta-comment? (a semantically important comment)?
>>>
>>> it's just a comment and has no semantic comment.  You can
delete it, it won't
>>> make any difference.
>>
>> OK. However, in this case, how is the branch resolved? I mean that
there is no
>> obvious %39 label declared in the LLVM translation unit.
>
> I can see that there is a certain convention; e.g. %39 is the assumed
(implicit)
> label, if the %38 is the last defined temporary at that point of the
function body.
>
> So, I guess that if the following basic block has no explicit label, it
acquires
> one by generating a new temporary. This is my deduction; I'm not sure
it is
> correct though.
that's it.  It's the same for nameless instructions for example.  Note
that
these numbers only exist in the human readable IR.  There has to be some way
when parsing human readable IR to know which basic block is being referred to.
That's what the numbers are for.

Ciao, Duncan.
>
>
> Best regards
> Nikolaos Kavvadias
>
>
>>
>>
>> Best regards
>> Nikolaos Kavvadias
>>
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
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