r177164 - Force column info only for direct inlined functions. This should strike

[Adrian Prantl]

On Mar 19, 2013, at 8:57 AM, David Blaikie <dblaikie at gmail.com> wrote:

> On Fri, Mar 15, 2013 at 11:31 AM, Adrian Prantl <aprantl at apple.com> wrote:
>> 
>> On Mar 15, 2013, at 11:26 AM, David Blaikie <dblaikie at gmail.com> wrote:
>> 
>>> On Fri, Mar 15, 2013 at 10:46 AM, Adrian Prantl <aprantl at apple.com> wrote:
>>>> 
>>>> On Mar 15, 2013, at 10:25 AM, David Blaikie <dblaikie at gmail.com> wrote:
>>>> 
>>>>> On Fri, Mar 15, 2013 at 10:09 AM, Adrian Prantl <aprantl at apple.com> wrote:
>>>>>> Author: adrian
>>>>>> Date: Fri Mar 15 12:09:05 2013
>>>>>> New Revision: 177164
>>>>>> 
>>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=177164&view=rev
>>>>>> Log:
>>>>>> Force column info only for direct inlined functions. This should strike
>>>>>> the balance between expected behavior and compatibility with the gdb
>>>>>> testsuite.
>>>>>> 
>>>>>> (GDB gets confused if we break an expression into multiple debug
>>>>>> stmts so we enable this behavior only for inlined functions. For the
>>>>>> full experience people can still use -gcolumn-info.)
>>>>> 
>>>>> I'm not sure I understand how this will address the issue... Perhaps
>>>>> I'm misunderstanding something about this change. I have a few
>>>>> questions/uncertainties:
>>>> 
>>>>> 1) You can't really determine in the frontend if a function will
>>>>> actually be inlined - trying to predicate debug info on that seems
>>>>> like we'll get surprising/varying debug behavior based on whether the
>>>>> backend chooses to inline the function
>>>> 
>>>> That is correct. My thinking was that the backend would only inline at >O0 and if you need more precise debug info you could always use -gcolumn-info. But for those cases where function is inlined at O0 (which happens for inline-attributed functions and is done by the frontend) users will get the expected behavior.
>>>> This is not very elegant, but I’m trying to find a middle ground between not breaking gdb’s testsuite and fixing the debug experience for inlined functions.
>>> 
>>> Sure - I'm not suggesting that we should not fix the original bug you
>>> set out to fix, just that the solution that Eric & I were
>>> discussing/suggesting wasn't what you've implemented here. I thought
>>> what we were discussing was changing the backend to not emit separate
>>> line table entries when the line is the same but the column is
>>> different. This would be consistent with the debug experience users
>>> expect (given GDB's lack of column information) in all cases, no
>>> matter what things were inlined or not inlined, if I'm not mistaken.
>> 
>> As I mentioned earlier, the problem is that for inlined functions we need to do exactly that otherwise a breakpoint at the inlined function (appearing twice on one line) would be hit only once.
> 
> Still feels  wrong in some way - mostly because of the inlining
> possibilities (both not inlining when your frontend heuristic would
> indicate that it does, and inlining when it doesn't), even at -O0 (we
> still do inlining, even on non-always_inline functions, at -O0 - for
> simple functions like get/set, etc)

No need to convince me that it’s ugly...

> FWIW, GCC does exhibit the same behavior you described when it inlines
> a function (if I use the func(foo(), bar()) example & make foo/bar
> always_inline, then stepping through goes foo/func call/bar and
> stepping through without the always_inline goes foo/bar)

That is interesting! Does it create only a single if_stmt in the line table in both cases?

> I would like this to be done right so it behaves appropriately
> regardless of whether the backend chooses to inline the foo/bar calls.

Absolutely, I just want to make sure to find a solution that works well with gdb _and_ behaves as expected with inlined functions in the func(foo(), foo()) case.

cheers,
Adrian