Re: [Sbcl-devel] SBCL compiler bug? Overzealous optimization?

[Patrick S. <pa...@nk...>]

So, there's no accounting for the fact that this division might have side-effects?

… Patrick


On May 15, 2012, at 9:52 PM, Stas Boukarev wrote:

> Patrick Stein <pa...@nk...> writes:
> 
>> In looking over the errors generated by a cl-test-grid run, I looked
>> into the trivial-backtrace test that was failing. [1] I think that
>> I've uncovered a subtle bug in the SBCL compiler.
>> 
>>    [1] http://cl-test-grid.appspot.com/blob?key=100025
>> 
>> I'm using almost-the-latest SBCL (1.0.55.0-abb03f9-dirty) compiled for
>> 64-bit with threading on MacOSX Lion (10.7.3).
>> 
>> This is the simplest I can seem to get the same problem to arise is
>> this:
>> 
>>    (defun absorbs ()
>>      (let ((ret 'no-error))
>>        (handler-case
>>            (let ((y 0))
>>              (/ y))
>>          (division-by-zero (c) (setf ret c)))
>>        ret))
>> 
>> When that compiles, it gives no warnings.  When invoked, it returns
>> NO-ERROR.
> Yes, this is intended, the compiler elides division operations when
> the result is not used, and when safety is not high enough, even if it's
> divided by zero. Add (declare (optimize safety )) to get the error.
> 
> -- 
> With best regards, Stas.