eq? problem at -O2 since Guile 3.0.5

DoneSubmitted by Marius Bakke.
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3 participants
  • Ludovic Courtès
  • Marius Bakke
  • Andy Wingo
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M
M
Marius Bakke wrote on 11 May 2021 22:49
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(address . bug-guile@gnu.org)
87pmxxhu7k.fsf@gnu.org
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Hi!

I haven't been able to make a reproducer for this, but for illustrative
purposes, here is a code snippet that fails with -O2 on Guile 3.0.5 and
later (excerpt from GNU Shepherd):

(define (run-command socket-file action service args)
"Perform ACTION with ARGS on SERVICE, and display the result. Connect to
the daemon via SOCKET-FILE."
(with-system-error-handling
(let ((sock (open-connection socket-file))
(action* (if (and (eq? action 'detailed-status)
(memq service '(root shepherd)))
'status
action)))
;; Send the command.
(write-command (shepherd-command action* service #:arguments args)
sock)

https://git.savannah.gnu.org/cgit/shepherd.git/tree/modules/shepherd/scripts/herd.scm#n124

At -O2, (eq? action 'detailed-status) evaluates to true no matter what
symbol ACTION holds.

Interestingly, adding (pk action*) between LET and WRITE-COMMAND gives
the expected result and mitigates the problem(!).

There are other issues that can be observed by running the Shepherd test
suite (i.e. make -j4 check). With -O1 all pass.
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M
M
Marius Bakke wrote on 23 May 2021 17:23
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Re: bug#47172: Shepherd 0.8.1 tests fail on core-updates
(address . 48368@debbugs.gnu.org)
875yz9qxrv.fsf@gnu.org
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Ludovic Courtès <ludo@gnu.org> skriver:

Toggle quote (36 lines)
> Ludovic Courtès <ludo@gnu.org> skribis:
>
>> This turns out to be due to a… miscompilation bug.
>>
>> In (shepherd scripts herd), ‘run-command’ has this code:
>>
>> (let ((sock (open-connection socket-file))
>> (action* (if (and (eq? action 'detailed-status)
>> (memq service '(root shepherd)))
>> 'status
>> action)))
>> …)
>>
>> Problem is that everything works as if (eq? action 'detailed-status)
>> was omitted, such that ‘herd stop root’ is interpreted as ‘herd status
>> root’.
>
> A workaround that works with 3.0.7 is swapping the two ‘and’
> sub-expressions:
>
> diff --git a/modules/shepherd/scripts/herd.scm b/modules/shepherd/scripts/herd.scm
> index 106de1e..39d2e34 100644
> --- a/modules/shepherd/scripts/herd.scm
> +++ b/modules/shepherd/scripts/herd.scm
> @@ -126,8 +126,8 @@ of pairs."
> the daemon via SOCKET-FILE."
> (with-system-error-handling
> (let ((sock (open-connection socket-file))
> - (action* (if (and (eq? action 'detailed-status)
> - (memq service '(root shepherd)))
> + (action* (if (and (memq service '(root shepherd))
> + (eq? action 'detailed-status))
> 'status
> action)))
> ;; Send the command.

Cc'ing the relevant Guile bug:

https://bugs.gnu.org/48368

See also commit 79be6a985799adc6d663890250f4fb7c12f015b4 on
'core-updates' that builds with -O1 as a less satisfactory workaround.
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L
L
Ludovic Courtès wrote on 23 May 2021 23:43
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(name . Marius Bakke)(address . marius@gnu.org)
87lf853z4i.fsf@gnu.org
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Hello,

Marius Bakke <marius@gnu.org> skribis:

Toggle quote (2 lines)
> Ludovic Courtès <ludo@gnu.org> skriver:

[...]

Toggle quote (23 lines)
>> A workaround that works with 3.0.7 is swapping the two ‘and’
>> sub-expressions:
>>
>> diff --git a/modules/shepherd/scripts/herd.scm b/modules/shepherd/scripts/herd.scm
>> index 106de1e..39d2e34 100644
>> --- a/modules/shepherd/scripts/herd.scm
>> +++ b/modules/shepherd/scripts/herd.scm
>> @@ -126,8 +126,8 @@ of pairs."
>> the daemon via SOCKET-FILE."
>> (with-system-error-handling
>> (let ((sock (open-connection socket-file))
>> - (action* (if (and (eq? action 'detailed-status)
>> - (memq service '(root shepherd)))
>> + (action* (if (and (memq service '(root shepherd))
>> + (eq? action 'detailed-status))
>> 'status
>> action)))
>> ;; Send the command.
>
> Cc'ing the relevant Guile bug:
>
> https://bugs.gnu.org/48368

Oh nice! (It would have saved me a bit of time to catch up on email
beforehand. :-))

Toggle quote (3 lines)
> See also commit 79be6a985799adc6d663890250f4fb7c12f015b4 on
> 'core-updates' that builds with -O1 as a less satisfactory workaround.

I found that ‘-O2 -Ono-resolve-primitives’ also does the trick.

If we manually replace ‘memq’ by two ‘eq?’ tests (which is what the
compiler does), the same problem is exhibited:
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Toggle diff (14 lines)
diff --git a/modules/shepherd/scripts/herd.scm b/modules/shepherd/scripts/herd.scm
index 106de1e..513508f 100644
--- a/modules/shepherd/scripts/herd.scm
+++ b/modules/shepherd/scripts/herd.scm
@@ -127,7 +127,8 @@ the daemon via SOCKET-FILE."
   (with-system-error-handling
    (let ((sock    (open-connection socket-file))
          (action* (if (and (eq? action 'detailed-status)
-                           (memq service '(root shepherd)))
+                           (or (eq? service 'root)
+                               (eq? service 'shepherd)))
                       'status
                       action)))
      ;; Send the command.
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‘-Ono-resolve-primitives’ also helps in this case.

‘-Ono-optimize-branch-chains’ has no effect.

So, not much progress, but at least we have a workaround.

Thanks,
Ludo’.
A
A
Andy Wingo wrote on 24 May 2021 10:14
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reduced test case
(address . 48368@debbugs.gnu.org)
87lf841rb5.fsf@igalia.com
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Test case:

(define (f a b)
(let ((c (if (and (eq? a 'foo)
(eq? b 'bar))
'ERROR
a)))
(pk c)))

If you run as (f 'not-foo 'bar), you get 'ERROR. Yeeps!
A
A
Andy Wingo wrote on 24 May 2021 14:19
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thanks
(address . 48368-done@debbugs.gnu.org)
87cztg1fzp.fsf@igalia.com
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Fixed in 17aab66e75136cf23c7f0d4942b61d6947f98f9b. Thanks for the
report :)
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