[GLIBC][PATCH v2] Remove strdup inlines

[Wilco Dijkstra]

Florian Weimer wrote:
> On 12/12/2016 02:02 PM, Wilco Dijkstra wrote:
> > Remove the str(n)dup inlines from string/bits/string2.h.  Although inlining
> > calls with constant strings shows a small (~10%) performance gain, strdup is
> > typically used in error reporting code, so not performance critical.
>
> Where do the performance gains come from?

The strlen is a constant and if small the memcpy can be expanded inline.

> Is it from IFUNC selection for strlen and memcpy, which does not happen 
> in libc.so?

These are direct calls.

> I don't think it's true that strdup is mostly used for error reporting. 
> Why do you think so?

Because strdup is not used in the hot loop of any application. strdup uses in 
GLIBC are related to error reporting and environment processing which is not
performance critical. Like strdupa and explicit use of unaligned accesses, all
this is premature micro optimization. Removing unnecessary string copies
(why is strdup of a constant string a useful idiom that should be optimized?)
or speeding up malloc would be more worthwhile.

Wilco