[cfe-dev] Patch to allow comment translators implementation

[Abramo Bagnara]

Il 19/01/2010 02:37, Abramo Bagnara ha scritto:
> Il 19/01/2010 02:07, Chris Lattner ha scritto:
>> On Jan 18, 2010, at 5:02 PM, Abramo Bagnara wrote:
>>>>> Looks fine to me. Chris?
>>>>
>>>> Looks good to me, committed in r93795.  I didn't commit the
>>>> lib/Lex/PPDirectives.cpp hunk, because it didn't look necessary.  Please
>>>> correct me if I'm wrong.
>>>
>>> This part of the patch is strictly related to the others: the way for
>>> CommentHandler to push tokens is to call EnterTokenStream and this
>>> method add a TokenLexer (that was ignored by SkipExcludedConditionalBlock)
>>>
>>> Without this part of the patch the pushed tokens related to comments
>>> found inside skipped conditional block are not read until return from
>>> Preprocessor::SkipExcludedConditionalBlock and this is clearly unwanted.
>>
>> I don't see that. According to C, the contents of #if 0 blocks are
>> *completely* skipped and may not even be syntactically valid. Using
>> openmp as an example, it would be perfectly find to have completely
>> malformed openmp comments in #if 0 blocks.
> 
> Perhaps I've explained badly, please follow this example:
> 
> #if 0
> /* openmp comments */
> int a;
> #endif
> 
> The preprocessor see the #if 0 directive and then enter
> SkipExcludedConditionalBlock where the lexing proceed.
> 
> When we lex the comment the CommentHandler is invoked and it push some
> tokens using EnterTokenStream (i.e. setting CurTokenLexer), but none of
> this tokens is read by SkipExcludedConditionalBlock (without the patch
> you've discarded).
> 
> This means that when SkipExcludedConditionalBlock returns and normal
> lexing proceed the Preprocessor will read the tokens previously inserted
> in the bad context i.e. after the #endif.
> 
>> #if 0 skipping is also performance sensitive.

There are a few alternatives wrt to apply the missing part of the
original patch:

1) do not call comment handlers when skipping excluded conditional block

2) have a way inside comment handlers to know that we are inside an
excluded conditional block (so to avoid to call EnterTokenStream)

I think that 2) is better as it is more flexyble.

-- 
Abramo Bagnara

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