Slow handling of C++ symbol names

[Andrew Cagney]

> 
> Well, I remember fixing some startup time issues since then :P  For
> instance, the cache shared between minimal and partial symbols should
> cut demangling time about in half.

Ah, this: symbol_set_names?  I was looking at the demangler.

> Which leads to the question.  Why does GDB demangle symbols?  My 
>> simplistic understanding of the code is that GDB only needs the "iw" 
>> (a.k.a., demangled string up to  but excluding the lparen and ignoring 
>> white space) part of the symbol in the search table (the rest isn't so 
>> critical and can be constructed on-demand).
> 
> 
> A substantial amount of  demangling is needed to produce the part of
> the symbol before the lparen; consider templates.  Also, we need the
> full names in the minimal symbol for break 'foo(int)' with quotes to
> work.  And there are assumptions of unique symbol names in our
> hashing/searching, IIRC.

But without looking at the data we've no idea how substantial any 
particular part really is.  For instance, when analysing the bcache 
found that when debugging a C program every entry is 28 bytes in size!

'foo(int)' can be broken down into "foo" "(int)" the latter only being 
demanged and stored on-demand.

> I'm sure there are tricks we can do to cut down on how early or often
> we demangle, but it still seems to be necessary.