Re: [PATCH 3/3] lib/regexec: Resolve unused variable

[Paul Eggert <eggert@cs.ucla.edu>]

[-- Attachment #1: Type: text/plain, Size: 1378 bytes --]

On 8/23/21 3:38 AM, Darren Kenny wrote:

> What I did here was to not overwrite the value if DEBUG is set,
> since it appeared to never be checked anyway within the for-loop.

Yes, but although your patch pacified Coverity I still don't understand 
exactly why. I'd like to get to the bottom of it before continuing.

> I can only assume (pun not intended) that this
> is ending up as a no-op for our build, which means that Coverity sees it
> as never being read after the for-loop.
I'm working blind here, since Coverity's documentation is secret, which 
means you'll need to help out by reading its documentation and/or 
running Coverity yourself. Can you do that and let us know the following?

* What values does Coverity define the macros __GNUC__ and 
__GNUC_MINOR__ to? Or does it leave these symbols undefined?

* Similarly for _MSC_VER (defined by Microsoft C compilers).

* Does Coverity support the __builtin_unreachable and/or __builtin_trap 
functions, like GCC does? (See their use in verify.h.)

* Does Coverity support __assume, like Microsoft C does? (Also see 
verify.h.)

* Does Coverity support __has_builtin, like GCC and Clang do? (Again, 
see verify.h.)

* Are you compiling with -DGCC_LINT and/or -Dlint?

* Does the attached patch work for you? If not, why not, and what sort 
of improvements could be made?

Thanks.

[-- Attachment #2: coverity2.diff --]
[-- Type: text/x-patch, Size: 576 bytes --]

diff --git a/lib/verify.h b/lib/verify.h
index a8ca59b09..3cd71b280 100644
--- a/lib/verify.h
+++ b/lib/verify.h
@@ -305,6 +305,8 @@ template <int w>
      --enable-gcc-warnings, which compiles with -Dlint.  It's nicer
      when 'assume' silences warnings even with older GCCs.  */
 # define assume(R) ((R) ? (void) 0 : __builtin_trap ())
+#elif defined __COVERITY__
+# define assume(R) ((R) ? (void) 0 : __coverity_panic__ ())
 #else
   /* Some tools grok NOTREACHED, e.g., Oracle Studio 12.6.  */
 # define assume(R) ((R) ? (void) 0 : /*NOTREACHED*/ (void) 0)