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From: Jeff King <peff@peff.net>
To: Edmundo Carmona Antoranz <eantoranz@gmail.com>
Cc: "Derrick Stolee" <stolee@gmail.com>,
	"René Scharfe" <l.s.r@web.de>,
	whydoubt@gmail.com, "Git List" <git@vger.kernel.org>
Subject: Re: [PATCH] blame.c: replace instance of !oidcmp for oideq
Date: Wed, 9 Sep 2020 15:13:45 -0400	[thread overview]
Message-ID: <20200909191345.GA2511547@coredump.intra.peff.net> (raw)
In-Reply-To: <CAOc6etZS3mGxsPPh25XFi2-qR0TNzq0Gx1NrydgQwmHbsjxejA@mail.gmail.com>

On Wed, Sep 09, 2020 at 08:00:57AM -0600, Edmundo Carmona Antoranz wrote:

> On Wed, Sep 9, 2020 at 3:11 AM Jeff King <peff@peff.net> wrote:
> >
> > Yeah, it looks obviously correct. I am puzzled why "make coccicheck"
> > doesn't find this, though. +cc René, as my favorite target for
> > coccinelle nerd-snipes. :)
> >
> 
> I added this to contrib/coccinelle/object_id.cocci in v2.27.0
> 
> @@
> identifier f != oideq;
> expression E1, E2;
> @@
> - !oidcmp(E1, E2)
> + oideq(E1, E2)
> 
> And it found it:

Interesting. The existing rule is:

  struct object_id *OIDPTR1;
  struct object_id *OIDPTR2;
  @@
  - oidcmp(OIDPTR1, OIDPTR2) == 0
  + oideq(OIDPTR1, OIDPTR2)

The "== 0" part looks like it might be significant, but it's not.
Coccinelle knows that "!foo" is the same as "foo == 0" (and you can
confirm by tweaking it).

The addition of "identifer f != oideq" here isn't necessary (we don't
even define an "f" in the semantic patch part). And anyway, we use
hasheq() inside oideq(), so no need to override the rule there.

So the relevant part is probably that our existing rule specifies the
exact type, whereas your rule allows any expression.

And indeed, if I do this, it works:

diff --git a/contrib/coccinelle/object_id.cocci b/contrib/coccinelle/object_id.cocci
index ddf4f22bd7..62a6cee0eb 100644
--- a/contrib/coccinelle/object_id.cocci
+++ b/contrib/coccinelle/object_id.cocci
@@ -55,8 +55,8 @@ struct object_id OID;
 + oidcmp(&OID, OIDPTR)
 
 @@
-struct object_id *OIDPTR1;
-struct object_id *OIDPTR2;
+expression OIDPTR1;
+expression OIDPTR2;
 @@
 - oidcmp(OIDPTR1, OIDPTR2) == 0
 + oideq(OIDPTR1, OIDPTR2)

Which really _seems_ like a bug in coccinelle, unless I am missing
something. Because both of those parameters look like object_id pointers
(and the compiler would be complaining if it were not the case).  But I
also wonder if giving the specific types in the coccinelle rule is
buying us anything. If you passed two void pointers or ints or whatever
to !oidcmp(), we'd still want to rewrite it as oideq().

-Peff

  parent reply	other threads:[~2020-09-09 19:13 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-07 17:16 [PATCH] blame.c: replace instance of !oidcmp for oideq Edmundo Carmona Antoranz
2020-09-07 17:21 ` Edmundo Carmona Antoranz
2020-09-08 13:55   ` Edmundo Carmona Antoranz
2020-09-08 19:07 ` Derrick Stolee
2020-09-09  9:11   ` Jeff King
2020-09-09 14:00     ` Edmundo Carmona Antoranz
2020-09-09 17:48       ` Jeff Smith
2020-09-09 19:13       ` Jeff King [this message]
2020-09-09 19:17         ` Jeff King
2020-09-09 19:54           ` René Scharfe
2020-09-09 19:58             ` Jeff King
2020-09-09 20:03             ` Junio C Hamano
2020-09-09 20:06           ` Junio C Hamano
2020-09-09 20:43         ` René Scharfe

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