Re: [RFA 2/2] Simplify the psymbol hash function

[Pedro Alves <palves at redhat dot com>]

On 11/04/2017 04:13 PM, Tom Tromey wrote:
> This patch simplifies the psymbol_hash function, by changing it not to
> examine the contents of the symbol's name.  This change just mirrors
> what psymbol_compare already does -- it is checking for name equality,
> which is presumably ok because symbol names are generally interned.

Can you expand a bit more on the "presumably ok" part?  I think
it'd be nice to mention/explain this assumption in a comment
in the code.

> This change speeds up psymbol reading.  "gdb -nx -batch gdb"
> previously took ~1.8 seconds on my machine, and with this patch it now
> takes ~1.7 seconds.

That sounds great however I do wonder whether the bug is the other 
way around though.  What do the statistics say, e.g., debugging
gdb and firefox?  Do we end up deduping more or fewer
symbols in the bcache?

I read the original thread that added these custom functions,
and the original patch used strcmp in both hash and compare,
and then somehow the end result was what we have today.

See:
 https://sourceware.org/ml/gdb-patches/2010-08/msg00218.html
and:
 https://sourceware.org/ml/gdb-patches/2010-08/msg00242.html

So I'd love it that your patch is correct.  I'd just appreciate
a bit more detail since I'm not awfully familiar with this area.

Thanks,
Pedro Alves