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Re: emacs-module.c, eassert, and nonnull args

From: Philipp Stephani
Subject: Re: emacs-module.c, eassert, and nonnull args
Date: Mon, 12 Jun 2017 14:34:50 +0000

Philipp Stephani <address@hidden> schrieb am So., 11. Juni 2017 um 22:34 Uhr:
Paul Eggert <address@hidden> schrieb am So., 11. Juni 2017 um 19:45 Uhr:
Philipp Stephani wrote:
> Here's a new patch. It makes this change, and also changes the allocation
> slightly so that objects have unique addresses (useful for checking).

Thanks for working on this. Some comments.

Have you looked into the runtime overhead of this approach, assuming
-module-assertions is not specified? Currently lisp_to_value and value_to_lisp
typically  are optimized away (i.e., zero machine instructions), and that
wouldn't be true under the proposed patch even when -module-assertions is not
used. Granted, module calls need not be super-fast, but it might be nice to
avoid the overhead in the typical case if that is easy.

I've run a simple benchmark (5000000 iterations of mod-test-sum). Result for the base case (module assertions not compiled) is 4.602 seconds, with the new code it's 4.605 seconds. That's probably good enough.

What happens if -module-assertions is enabled for Emacs, Emacs dumps itself, and
-module-assertions is not enabled when the dumped Emacs is run?

Good question. I've now just made -module-assertions during dumping an error.
Or vice versa.

That's the normal case, which should work just fine.

Are the FOR_EACH_TAIL_SAFE macro calls needed? This macro is needed only for
lists that might be circular (e.g., the lists are available to Lisp code, which
can call setcdr on their components). If the calls are not needed I suggest just
an ordinary for loop.


A small point: the FOR_EACH... loops should be indented like ordinary for-loops.

Done. (Would be great if CC-Mode knew about this.) 

I've now pushed this commit and also a commit that uses __attribute__((nonnull)) to master.

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