Re: dead code or otherwise, was Alternative C compilers on x86_64 Linux?

From	George Neuner <gneuner2@comcast.net>
Newsgroups	comp.compilers
Subject	Re: dead code or otherwise, was Alternative C compilers on x86_64 Linux?
Date	2016-09-08 11:58 -0400
Organization	A noiseless patient Spider
Message-ID	<16-09-015@comp.compilers> (permalink)
References	<16-09-001@comp.compilers> <16-09-005@comp.compilers> <16-09-009@comp.compilers> <16-09-012@comp.compilers>

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On Tue, 6 Sep 2016 21:35:30 +0100, BartC <bc@freeuk.com> wrote:

>On 06/09/2016 03:15, Kaz Kylheku wrote:
>
>> A duplicate condition in an if-else chain is unreachable code, which is
>> probably a bug.
>>
>>    if (foo) {
>>      ...
>>    } else if (foo) {
>>      /* unreachable */
>>    } else if (bar) {
>>      ...
>>    }
>
>It's not necessarily unreachable. For example:
>
>  if (foo()) { ...}
>  elsif if (foo()) { ... }
>
>foo() could return false the first time and true the second time.

In such cases foo doesn't need to be function - it only needs to be a
[moral equivalent of a C] volatile to exhibit strange behavior.

Writing an IF chain with multiple identical tests probably should be a
style warning in and of itself.


>In general detecting duplication conditions for if-else can involve
>comparing expressions of arbitrary complexity, and it can be harder to
>determine if they will always yield the same value.

Yes.  It's infeasible in most circumstances.

George

Thread

Alternative C compilers on x86_64 Linux? arnold@skeeve.com (Aharon Robbins) - 2016-09-02 03:01 +0000
  Re: Alternative C compilers on x86_64 Linux? jacobnavia <jacob@jacob.remcomp.fr> - 2016-09-05 00:20 +0200
    Re: Alternative C compilers on x86_64 Linux? alexfrunews@gmail.com - 2016-09-05 17:26 -0700
      Re: diagnosing C errors, was Alternative C compilers on x86_64 Linux? BartC <bc@freeuk.com> - 2016-09-09 12:31 +0100
        Re: diagnosing C errors, was Alternative C compilers on x86_64 Linux? Kaz Kylheku <221-501-9011@kylheku.com> - 2016-09-09 16:06 +0000
        Re: diagnosing C errors, was Alternative C compilers on x86_64 Linux? Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2016-09-10 00:38 +0200
  Re: Alternative C compilers on x86_64 Linux? Nemo <nemo@invalid.invalid> - 2016-09-04 18:32 -0400
  Re: Alternative C compilers on x86_64 Linux? Kaz Kylheku <221-501-9011@kylheku.com> - 2016-09-04 23:48 +0000
  Re: Alternative C compilers on x86_64 Linux? BartC <bc@freeuk.com> - 2016-09-05 13:19 +0100
    Re: Alternative C compilers on x86_64 Linux? Kaz Kylheku <221-501-9011@kylheku.com> - 2016-09-06 02:15 +0000
      Re: Alternative C compilers on x86_64 Linux? BartC <bc@freeuk.com> - 2016-09-06 21:35 +0100
        Re: dead code or otherwise, was Alternative C compilers on x86_64 Linux? George Neuner <gneuner2@comcast.net> - 2016-09-08 11:58 -0400
          Re: dead code or otherwise, was Alternative C compilers on x86_64 Linux? Kaz Kylheku <221-501-9011@kylheku.com> - 2016-09-08 22:54 +0000
            Re: dead code or otherwise, was Alternative C compilers on x86_64 Linux? George Neuner <gneuner2@comcast.net> - 2016-09-09 00:51 -0400
              Re: dead code or otherwise, was Alternative C compilers on x86_64 Linux? Kaz Kylheku <221-501-9011@kylheku.com> - 2016-09-09 06:05 +0000
                Re: dead code or otherwise, was Alternative C compilers on x86_64 Linux? George Neuner <gneuner2@comcast.net> - 2016-09-09 14:02 -0400
                Re: dead code or otherwise, was Alternative C compilers on x86_64 Linux? Kaz Kylheku <221-501-9011@kylheku.com> - 2016-09-09 19:57 +0000
      Re: duplicate cases, was Alternative C compilers on x86_64 Linux? Andy Walker <anw@cuboid.co.uk> - 2016-09-07 17:01 +0100
  Re: Alternative C compilers on x86_64 Linux? Florian Weimer <fw@deneb.enyo.de> - 2016-09-05 20:06 +0200
  Re: Alternative C compilers on x86_64 Linux? alexfrunews@gmail.com - 2016-09-05 17:22 -0700
    Re: Alternative C compilers on x86_64 Linux? Kaz Kylheku <221-501-9011@kylheku.com> - 2016-09-06 02:18 +0000
  Re: Alternative C compilers on x86_64 Linux? rockbrentwood@gmail.com - 2016-09-07 17:00 -0700
  Re: Alternative C compilers on x86_64 Linux? arnold@skeeve.com (Aharon Robbins) - 2016-09-12 18:42 +0000
    Re: Alternative C compilers on x86_64 Linux? BartC <bc@freeuk.com> - 2016-09-12 22:37 +0100
      Re: Alternative C compilers on x86_64 Linux? arnold@skeeve.com (Aharon Robbins) - 2016-09-13 17:35 +0000
        Re: Alternative C compilers on x86_64 Linux? arnold@skeeve.com (Aharon Robbins) - 2016-09-14 18:14 +0000
  Re: Alternative C compilers on x86_64 Linux? rugxulo@gmail.com - 2016-09-26 15:29 -0700
    Re: Alternative C compilers on x86_64 Linux? arnold@skeeve.com (Aharon Robbins) - 2016-09-27 05:40 +0000
      Re: Alternative C compilers on x86_64 Linux? rugxulo@gmail.com - 2016-09-27 16:36 -0700
        Re: Alternative C compilers on x86_64 Linux? BartC <bc@freeuk.com> - 2016-09-28 18:16 +0100
          Re: Alternative C compilers on x86_64 Linux? BartC <bc@freeuk.com> - 2016-09-29 14:03 +0100
            Re: Alternative C compilers on x86_64 Linux? George Neuner <gneuner2@comcast.net> - 2016-09-29 22:57 -0400
            Re: Alternative C compilers on x86_64 Linux? Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2016-09-30 05:03 +0200
              Re: Alternative C compilers on x86_64 Linux? BartC <bc@freeuk.com> - 2016-09-30 12:00 +0100
                Re: Alternative C compilers on x86_64 Linux? Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2016-09-30 20:15 +0200
                Re: Alternative C compilers on x86_64 Linux? BartC <bc@freeuk.com> - 2016-10-01 22:17 +0100
            Re: Alternative C compilers on x86_64 Linux? BartC <bc@freeuk.com> - 2016-09-30 12:28 +0100
              Re: Alternative C compilers on x86_64 Linux? BartC <bc@freeuk.com> - 2016-10-17 22:49 +0100
        Re: Alternative C compilers on x86_64 Linux? George Neuner <gneuner2@comcast.net> - 2016-09-28 21:24 -0400
      Re: Alternative C compilers on x86_64 Linux? George Neuner <gneuner2@comcast.net> - 2016-09-28 01:01 -0400
        Re: Alternative C compilers on x86_64 Linux? arnold@skeeve.com (Aharon Robbins) - 2016-09-29 02:55 +0000
      Re: Alternative C compilers on x86_64 Linux? arnold@skeeve.com - 2016-09-29 05:30 -0600
        Re: Alternative C compilers on x86_64 Linux? arnold@skeeve.com (Aharon Robbins) - 2016-09-30 10:13 +0000

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