The sys_dlist_insert_*() functions had a behavior where a NULL
argument for the insertion position to sys_dlist_insert_after/before()
was interpreted as "the end of the list". We never used that
convention (except in one spot internal to dlist.h which was not
itself used anywhere), and of course already have an API for appending
and prepending to a list.
In practice this was a performance disaster. The NULL check is
virtually never provable statically by the compiler, so that test and
branch is present always. And worse, the check and call to another
function was pushing this beyond the complexity limit for gcc to
inline a function (at -Os optimization anyway), forcing us to use
function calls for what should be a ~8 instruction sequence. The
upshot is that dlist insertions were 2-3x slower than they needed to
be.
Deprecate these older APIs and introduce a new sys_dlist_insert() call
which can be much better optimized.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
eda4c027da