[llvm-commits] [llvm-gcc-4.2] r63087 - /llvm-gcc-4.2/trunk/gcc/tree-nested.c

[Dale Johannesen]

On Jan 27, 2009, at 10:30 AMPST, Dale Johannesen wrote:
> On Jan 27, 2009, at 10:26 AMPST, Duncan Sands wrote:
>
>> Hi Dale,
>>>
>>>> It is here
>>>> because I had to add a bunch of code to fix a long
>>>> standing tree-nested bug in which nested function bodies
>>>> and callers have different opinions as to whether
>>>> the function takes a static chain parameter or not.
>>>> This doesn't matter much for gcc because the parameter
>>>> is passed out of line, but it is rather horrible for
>>>> llvm-gcc because it is added as an explicit parameter
>>>> to the function.  I never got round to pushing this
>>>> upstream, but I really should.  Anyway, the assertion
>>>> is checking that a nested subroutine (the root->outer
>>>> check ensures that this is a nested subroutine) takes
>>>> an extra parameter for passing variables belonging to
>>>> the parent (the "static chain") if and only if either
>>>> it itself accesses a variable belonging to its parent
>>>> (in which case root->chain_field is not null) or one
>>>> of its child nested subroutines does (in which case
>>>> root->chain_decl is not null).
>>>>
>>>>> -      gcc_assert (!root->outer ||
>>>>> -                  DECL_NO_STATIC_CHAIN (root->context) ==
>>>>> -                  !(root->chain_decl || root->chain_field));
>>>>
>>>> If the assertion is failing, it seems to me that something
>>>> bad is going on.
>>>
>>> You may be right, or this may be another case where ObjC isn't doing
>>> what you expect (which you would probably consider abuse).  I
>>> concluded it was the latter, but  you seem to understand what this
>>> code is doing better than I, maybe you could look at the testcase?
>>
>> I will.  Sadly I do understand the horror that is tree-nested, at
>> least I used to.  I had to in order to implement support for nested
>> functions in llvm-gcc :( :)
>
> OK.  I've also got a question in the guy who implemented the  
> "blocks" stuff in ObjC, who fortunately is still here:)  He can  
> probably clarify what ObjC is doing.

He says the intent is that blocks code should never access variables  
in the parent, thus we should never need a static chain.   Ah, I see,  
the default is to assume a static chain (peculiar), so the problem is  
ObjC may need to set that bit explicitly, probably isn't doing  
that...you can put the assertion back if you like.