[patch v4] malloc: avoid need for tcache == NULL checks

[DJ Delorie]

Florian Weimer <fweimer@redhat.com> writes:
>>> +#if USE_TCACHE
>>
>> Note we are already in a USE_TCACHE block here...
>
> ^^^ DJ, I think you should remove that #if.

Yup, I had already updated my local copy but was waiting for the rest of
the feedback before sending a v5.

> We could complete the call and then initialize tcache for the next call.
> But I think we really should IFUNC malloc in total or just the front end
> routines, compile in tcache for __libc_initial only, and put tcache
> directly into the TCB.  For !__libc_initial, we don't use tcache at all.
> That avoids a bunch of indirections and data loads.

What's the performance impact of adding IFUNC jumps/calls in every fast
path?