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Re: [PATCH 2/2] PR debug/63240 Add DWARF representation for C++11 defaulted member function.

On Mon, Oct 6, 2014 at 5:55 PM, Jason Merrill <> wrote:
> On 10/06/2014 08:50 PM, Siva Chandra wrote:
>> But, the question is whether it is required to determine the parameter
>> passing ABI. If there is no special marker to indicate that the user
>> declared 'tor is explicitly defaulted, then GDB could (in the absence
>> of other properties which make the 'tor non-trivial) incorrectly
>> conclude that the the 'tor is user defined, and hence not-trivial.
> I've been thinking that we should just mark the 'tor as trivial or not
> directly rather than hint at it.  Does GDB have enough information to
> determine triviality if we just add defaulted info?

Barring some incompleteness, for which patches are very close to
getting committed, I believe GDB has the rest of the information.
After those patches are committed, the algorithm used by GDB to
determine whether a value is returned in a hidden param or not is as

1. If the value is of a dynamic class (as in, has virtual bases or
virtual functions), return in hidden param.
2. Else, go over all methods that are found in the DWARF:
----2a. If a method is marked artificial, ignore it.
----2b. If the method is a copy-constructor or a destructor, conclude
that a pointer to the value is to be returned in the hidden first
-------- This is because, presence of a copy-ctor or dtor which are
nor artificial indicates that they were user declared and not
3. If a decision was not made in 2, do 1 and 2 for base class
subobjects and non-static members.
4. If a decision was not made in 3, then conclude that it should not
be passed in a hidden param.

If an explicitly defaulted copy-ctor or dtor is not marked as such,
step 2 is broken.

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