defsubst VS defun or defmacro [was RE: Compiled code in Emacs-26 will fail in Emacs-25 if use pcase]

[Tino Calancha <tino.calancha@gmail.com>]

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On Thu, 23 Feb 2017, T.V Raman wrote:

> Please separate your personal opinion from fact. And asserting that
> using defsubst is "misguided "  is not a useful way of carrying on a
> conversation.
>
> Drew Adams writes:
> > > Really? What should we be using, and when was defsubst deprecated?
> > > defun or defmacro
> > It has not been deprecated.
> > I was expressing my opinion: It's rarely, if ever, needed,
> > and misguided uses of it instead of defun are bothersome.

Hi Raman,
I guess Drew meant that defsubst makes debugging harder.  It also 
complicates advising.  I know he does extensively use of advising
in his own libraries.

The manual mention some disadvantages on using defsubst
in `(elisp) inline functions':

"Also, inline functions do not behave well with respect to debugging,
tracing, and advising (*note Advising Functions::).  Since ease of
debugging and the flexibility of redefining functions are important
features of Emacs, you should not make a function inline, even if it’s
small, unless its speed is really crucial, and you’ve timed the code to
verify that using ‘defun’ actually has performance problems."

I find worth to read the whole node.  I used to be confused about when
to use (to not) defsubst.