[PATCH] [DOC] LangRef: Clarify when index of temporaries begin at 0

[Mikael Lyngvig]

Great, thank you!


-- Mikael


2013/11/27 Sean Silva <silvas at purdue.edu>

> How does r195812 look to you?
>
> -- Sean Silva
>
>
> On Tue, Nov 26, 2013 at 10:40 PM, Mikael Lyngvig <mikael at lyngvig.org>wrote:
>
>> Would you mind phrasing the sentence?  I'm simply not yet knowledgeable
>> enough about LLVM to be able to take all the many factors and issues into
>> consideration.  I am like a baby learning to walk, not an expert.
>>
>> The purpose of the patch is solely to avoid the possibly frequent
>> experience that people gets confused when LLC complains about the first
>> temporary being named %0.  There's no other purpose with the patch.
>>
>>
>> -- Mikael
>>
>>
>> 2013/11/27 Sean Silva <silvas at purdue.edu>
>>
>>> This is still really not the right way to describe it. There's nothing
>>> special about the entry BB in this regard. Any BB without an explicit label
>>> gets an unnamed integer value assigned to it, and the counter is
>>> incremented.
>>>
>>> -- Sean Silva
>>>
>>>
>>> On Tue, Nov 26, 2013 at 10:24 PM, Mikael Lyngvig <mikael at lyngvig.org>wrote:
>>>
>>>> So what if I add this exact sentence after the place where the LR
>>>> states that temporaries begin at %0:
>>>>
>>>>     If a function entry block does not have an explicit label, it will
>>>> be assigned label “%0”, then the first unnamed temporary in that block will
>>>> be “%1”, etc.
>>>>
>>>> If you accept this, there's a patch for it attached to this message:
>>>>
>>>> diff --git a/docs/LangRef.rst b/docs/LangRef.rst
>>>> index 18d2c9c..5db1a14 100644
>>>> --- a/docs/LangRef.rst
>>>> +++ b/docs/LangRef.rst
>>>> @@ -128,7 +128,9 @@ lexical features of LLVM:
>>>>  #. Unnamed temporaries are created when the result of a computation is
>>>>     not assigned to a named value.
>>>>  #. Unnamed temporaries are numbered sequentially (using a per-function
>>>> -   incrementing counter, starting with 0).
>>>> +   incrementing counter, starting with 0). If a function entry block
>>>> does
>>>> +   not have an explicit label, it will be assigned label "%0", then the
>>>> +   first unnamed temporary in that block will be "%1", etc.
>>>>
>>>>  It also shows a convention that we follow in this document. When
>>>>  demonstrating instructions, we will follow an instruction with a
>>>> comment
>>>>
>>>>
>>>> -- Mikael
>>>>
>>>>
>>>>
>>>> 2013/11/27 Sean Silva <silvas at purdue.edu>
>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Nov 26, 2013 at 10:01 PM, Mikael Lyngvig <mikael at lyngvig.org>wrote:
>>>>>
>>>>>> You're absolutely right (from the LR, I just searched):
>>>>>>
>>>>>>   For example, if a function entry block does not have an explicit
>>>>>> label, it will be assigned label “%0”, then the first unnamed temporary in
>>>>>> that block will be “%1”, etc.
>>>>>>
>>>>>> This is under Functions.  I guess anybody should get that far, but I
>>>>>> personally feel that the clarification I've submitted doesn't harm.
>>>>>>
>>>>>> Your current patch is inaccurate. If you want to duplicate what is
>>>>> mentioned elsewhere about the numbering to make it more likely that someone
>>>>> will see it, that would be OK.
>>>>>
>>>>> -- Sean Silva
>>>>>
>>>>>
>>>>>>
>>>>>> -- Mikael
>>>>>>
>>>>>>
>>>>>> 2013/11/27 Sean Silva <silvas at purdue.edu>
>>>>>>
>>>>>>> It is correct as written. Unnamed BB's are "unnamed temporaries"
>>>>>>> from a counting perspective. If the first BB is unlabeled, then it becomes
>>>>>>> %0. The first instruction then becomes %1, etc.
>>>>>>>
>>>>>>> I swear we mention that somewhere in LangRef (I seem to recall
>>>>>>> reviewing a patch mentioning that), but if not, a patch mentioning that
>>>>>>> would be fine.
>>>>>>>
>>>>>>> -- Sean Silva
>>>>>>>
>>>>>>>
>>>>>>> On Tue, Nov 26, 2013 at 8:50 PM, Mikael Lyngvig <mikael at lyngvig.org>wrote:
>>>>>>>
>>>>>>>> This patch adds the following sentence to the LR after it states
>>>>>>>> that temporaries begin at index 0:
>>>>>>>>
>>>>>>>>    If you do not specify a label for the entry block, the
>>>>>>>> temporaries start at index 1 as index
>>>>>>>>    0 is then used for an implicit label generated by LLVM.
>>>>>>>>
>>>>>>>> This because LLC complains when you use %0 as a temporary and there
>>>>>>>> is no entry point label in the function.  Then you get an error message,
>>>>>>>> which can be quite difficult to figure out why.
>>>>>>>>
>>>>>>>> If this patch is rejected, somebody should probably phrase the
>>>>>>>> above appropriately and submit a new patch.
>>>>>>>>
>>>>>>>>
>>>>>>>> -- Mikael
>>>>>>>>
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> llvm-commits mailing list
>>>>>>>> llvm-commits at cs.uiuc.edu
>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20131127/3a528326/attachment.html>