Re: [PATCH 4/7] Class-fy partial_die_info

[Pedro Alves <palves@redhat.com>]

On 01/30/2018 10:49 AM, Yao Qi wrote:
> Simon Marchi <simark@simark.ca> writes:

>> -  /* Hash table holding all the loaded partial DIEs
>> -     with partial_die->offset.SECT_OFF as hash.  */
>> -  htab_t partial_dies = nullptr;
>> +  /* Hash map holding all the loaded partial DIEs
>> +     with their section offset as the key.  */
>> +  std::unordered_map<sect_offset, partial_die_info *> partial_dies;
>>
> This doesn't compile with my g++ 4.9, as library doesn't provide
> std::hash<T> specialization for enumeration types.  It is available
> since C++ 14.  http://en.cppreference.com/w/cpp/utility/hash
> 
> I can change it to
> 
> std::unordered_map<std::underlying_type<sect_offset>::type,
> 		     partial_die_info *> partial_dies;
> 
> to fix the compiler errors.

Note: in cases like these, we don't need to forgo using the
(strong) enum as key type.  unordered_map's third (defaulted) template
parameter type is the hasher to use.  And we have a convenience
hasher for this:

 [pushed] Add gdb::hash_enum
 https://sourceware.org/ml/gdb-patches/2017-12/msg00210.html

Currently used in dwarf2read.c:

  std::unordered_map<sect_offset,
                     dwarf2_per_cu_data *,
                     gdb::hash_enum<sect_offset>>

Thanks,
Pedro Alves