[PATCH] D36993: [llvm-dwarfdump] Print type names in DW_AT_type DIEs

Fri Sep 1 14:04:24 PDT 2017

> On Sep 1, 2017, at 1:56 PM, David Blaikie <dblaikie at gmail.com> wrote:
> 
> 
> 
> On Fri, Sep 1, 2017 at 1:50 PM Adrian Prantl <aprantl at apple.com <mailto:aprantl at apple.com>> wrote:
>> On Sep 1, 2017, at 1:46 PM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
>> 
>> 
>> 
>> On Fri, Sep 1, 2017 at 1:41 PM Adrian Prantl <aprantl at apple.com <mailto:aprantl at apple.com>> wrote:
>>> On Sep 1, 2017, at 1:36 PM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
>>> 
>>> Could we get reasonable test cases for them up-front, to see where things are?
>> 
>> You mean for the cases that do work as expected? That seems reasonable.
>> 
>> All the cases, actually - so we can see what they are, whether they need improvement, track what those improvements are, etc.
> 
> That seems excessive to me, since you'd have to create them manually (unless yaml-obj makes that trivial?). What about all C(++) types that can be produced by clang?
> 
> Doesn't seem too hideously expensive to produce by hand, are they? maybe 10-15 lines of assembly (even including the abbreviation) per thing? (It can be really simple DWARF - like a bunch of DW_TAG_variables that have only a DW_AT_type (no name, no other attributes), etc)

Perhaps, but you'll also need to dig through the specification to understand how each is supposed to be used (for example, a variable with a DW_AT_type(DW_TAG_thrown_type <>) doesn't actually make sense). I don't know, maybe I'm overestimating how much work this would be.

>  
> 
> -- adrian
>>  
>> 
>> -- adrian
>> 
>>> 
>>> (I still find it a bit weird to get const/volatile falling out through this process, but yeah, if there's a whole bunch of other cases that fall through this way for now, guess it makes  sense)
>>> 
>>> On Fri, Sep 1, 2017 at 1:24 PM Adrian Prantl via Phabricator <reviews at reviews.llvm.org <mailto:reviews at reviews.llvm.org>> wrote:
>>> aprantl added a comment.
>>> 
>>> In https://reviews.llvm.org/D36993#859034 <https://reviews.llvm.org/D36993#859034>, @dblaikie wrote:
>>> 
>>> > In https://reviews.llvm.org/D36993#858768 <https://reviews.llvm.org/D36993#858768>, @JDevlieghere wrote:
>>> >
>>> > > In https://reviews.llvm.org/D36993#858121 <https://reviews.llvm.org/D36993#858121>, @dblaikie wrote:
>>> > >
>>> > > > In https://reviews.llvm.org/D36993#858093 <https://reviews.llvm.org/D36993#858093>, @JDevlieghere wrote:
>>> > > >
>>> > > > > David, apologies for missing your e-mail. I really hate that it doesn't automatically show up in Phabricator! 🙁
>>> > > > >
>>> > > > > If the tag doesn't have a name attribute, everything will go through this function except: `DW_TAG_pointer_type`, `DW_TAG_ptr_to_member_type`, `DW_TAG_reference_type`, `DW_TAG_rvalue_reference_type`. The first part explains why `class` and `struct` don't show up. I prefer this approach because it's guaranteed to be robust. Every `DW_TAG_*_type` encountered without a name will have something meaningful printed.
>>> > > > >
>>> > > > > IIRC, the original switch had between 20 and 25 cases.
>>> > > >
>>> > > >
>>> > > > I'm curious what those 20-25 cases were - do you have a copy/roughly describe their contents? Because while 'const' does print nicely, (& volatile would be similar) I'm not sure what the other 10 or so cases might be and whether that's a reasonable way to print them.
>>> > >
>>> > >
>>> > > Here's the list of cases I had originally:
>>> > >
>>> > >   case DW_TAG_array_type:
>>> > >   case DW_TAG_base_type:
>>> > >   case DW_TAG_class_type:
>>> > >   case DW_TAG_const_type:
>>> > >   case DW_TAG_enumeration_type:
>>> > >   case DW_TAG_file_type:
>>> > >   case DW_TAG_interface_type:
>>> > >   case DW_TAG_packed_type:
>>> > >   case DW_TAG_pointer_type:
>>> > >   case DW_TAG_ptr_to_member_type:
>>> > >   case DW_TAG_reference_type:
>>> > >   case DW_TAG_restrict_type:
>>> > >   case DW_TAG_set_type:
>>> > >   case DW_TAG_shared_type:
>>> > >   case DW_TAG_string_type
>>> > >   case DW_TAG_structure_type:
>>> > >   case DW_TAG_subrange_type:
>>> > >   case DW_TAG_subroutine_type:
>>> > >   case DW_TAG_thrown_type:
>>> > >   case DW_TAG_union_type:
>>> > >   case DW_TAG_unspecified_type:
>>> > >   case DW_TAG_volatile_type:
>>> > >
>>> >
>>> >
>>> > Ah, thanks!
>>> >
>>> > I feel like maybe this should be examined more closely (an example of how each of these would be printed would be ideal, though that might be a bit much) - for example I don't think it makes sense to print out subroutine types like "int subroutine" (rather than "int(float, double)", say) which I /think/ is how they might look based on the current code)
>>> 
>>> 
>>> Generally agreed, but I think it might make sense to improve this in separate follow-on patches on a case-by-case basis. Getting the pretty-printing entirely right would mean that we would have to implement different pretty-printers for each DW_LANG_foo, since e.g., a C function type would have to be rendered very differently from the same DWARF type-representation in an. e.g., Swift or Fortran context. And even if we choose to always render types as C types it is unclear what to do with types such as DW_TAG_set_type.
>>> 
>>> 
>>> Repository:
>>>   rL LLVM
>>> 
>>> https://reviews.llvm.org/D36993 <https://reviews.llvm.org/D36993>
>>> 
>>> 
>>> 

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