bugGNU Octave - Bugs: bug #54465, Short Circuit Operators not...

 
 

bug #54465: Short Circuit Operators not working with negation operator

Submitter:  Andrew Lofts <andrewlofts>
Submitted:  Wed 08 Aug 2018 06:19:04 PM UTC
   
 
Category:  Interpreter Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Matlab Compatibility
Status:  Fixed Assigned to:  None
Originator Name:  AndrewLofts Open/Closed:  * Closed
Release:  * 4.4.1-rc2 Operating System:  * GNU/Linux
Fixed Release:  None Planned Release:  None
* Mandatory Fields

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Tue 28 Aug 2018 11:42:52 PM UTC, comment #10: 

I commented out two functions to suppress the compilation warnings in this cset (https://hg.savannah.gnu.org/hgweb/octave/rev/d0062829754a).

Rik <rik5>
Group administrator
Tue 28 Aug 2018 08:36:20 PM UTC, comment #9: 

Yeah, I eliminated the only call to that function.  We can just comment it out for now.

John W. Eaton <jwe>
Group administrator
Tue 28 Aug 2018 07:55:59 PM UTC, comment #8: 

The change seems to work.  I used


cd test
test parser.tst


and all 52 tests pass.

I get this warning during compilation though:


 CXX      libinterp/parse-tree/libinterp_parse_tree_libparse_tree_la-oct-parse.lo
libinterp/parse-tree/pt-cbinop.cc:130:3: warning: ‘octave_value::compound_binary_op octave::simplify_and_or_op(octave::tree_expression*&, octave::tree_expression*&, octave_value::binary_op)’ defined but not used [-Wunused-function]
   simplify_and_or_op (tree_expression_ptr_t& a, tree_expression_ptr_t& b,
   ^




Rik <rik5>
Group administrator
Tue 28 Aug 2018 06:03:37 PM UTC, comment #7: 

How about the following change?

http://hg.savannah.gnu.org/hgweb/octave/rev/8ac4bfa55053

With more work, maybe the optimization for the compound negation and elementwise logical operators could be preserved when the expression is not eligible for short circuiting.

John W. Eaton <jwe>
Group administrator
Tue 28 Aug 2018 03:32:16 PM UTC, comment #6: 

@jwe: This patch seems to have introduced a regression in performance which is documented at bug #45890.

Is there a way to be more clever about this so that certain compound expressions like


A * B'


can be recognized as a single operation (pass multiply with appropriate flag to BLAS) rather than two operations (multiply done by BLAS, transpose done by Octave)?

Rik <rik5>
Group administrator
Thu 09 Aug 2018 04:47:43 PM UTC, comment #5: 

I see that jwe just pushed the patch for this to the stable branch.  Marking as fixed and closing report.

Rik <rik5>
Group administrator
Wed 08 Aug 2018 08:46:36 PM UTC, comment #4: 

The patch seems to work.  Here are two tests


%!test
%! x = 0;
%! if (! 0 || (x = 1))
%! endif
%! assert (x == 0);

%!test
%! x = 0;
%! if (! 0 | (x = 1))
%! endif
%! assert (x == 0);


Also attached as a file.  They should probably go in test/parser.tst and have a bug number associated.


(file #44743)

Rik <rik5>
Group administrator
Wed 08 Aug 2018 08:23:03 PM UTC, comment #3: 

I think the attached patch should fix the problem.  But before committing, it needs a test and we should probably see whether it makes sense to try to preserve the compound binary operator optimization or simply remove it.


(file #44742)

John W. Eaton <jwe>
Group administrator
Wed 08 Aug 2018 07:20:56 PM UTC, comment #2: 

This problem appears to be some kind of incorrect handling of precedence.  The evaluator is evaluating the "b == 2" expression first.

In any case, I recommend using || and && if you want short-circuit evaluation.

John W. Eaton <jwe>
Group administrator
Wed 08 Aug 2018 07:01:54 PM UTC, comment #1: 

Confirmed.  Incidentally, version 4.2.1 is very old and no longer supported.  You will have a better experience if you can update to the latest stable version.  But, I confirmed this on the current development code as well.

Here is an even more concise example:


clear b;

if ((! 0) || b == 2)
  disp ('Octave short-circuit');
end

if ((! 0) | b == 2)
  disp ('Matlab short-circuit');
end


I used Octave's own negation operator just to make sure there wasn't something funny going on.  I also removed the call to exist() and just use a constant.  Octave's own short-circuiting operator works in this case, so this is an error in the parser because within if statements the '|' operator should map to '||' for logical statements.

Adding jwe to the CC list since he has spent the most time with this code. 



(file #44741)

Rik <rik5>
Group administrator
Wed 08 Aug 2018 06:19:04 PM UTC, original submission:  

Hello, I am working on porting MATLAB to Octave, normally | and & will short circuit in if() statements just like MATLAB. However if a function with a negative is used like ~exist(),~strcmp() or ~isempty(), the statements do not seam to short circuit like MATLABs do. ~= and the functions without ~, however do work. Example: (Octave/Matlab)


%From an empty workspace
%Octave
if ~exist('a','var') | b == 2
     disp('TRUE');
end
error: 'b' undefined near line 1 column 27

%Matlab
if ~exist('a','var') | b == 2
     disp('TRUE');
end
TRUE


Setting do_braindead_shortcircuit_evaluation doesn't seam to change anything.
Thank you for your help,
Andrew

Andrew Lofts <andrewlofts>

 

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Attached Files
file #44743:  tst_sc2.m added by rik5 (138B - text/x-matlab)
file #44742:  diffs.txt added by jwe (447B - text/plain)
file #44741:  tst_sc.m added by rik5 (127B - text/x-matlab)

 

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    Follow 13 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2018-08-09 rik5 StatusPatch Reviewed Fixed
        Open/ClosedOpen Closed
        Releasedev 4.4.1-rc2
    2018-08-08 rik5 Attached File- Added tst_sc2.m, #44743
        CategoryNone Interpreter
        StatusConfirmed Patch Reviewed
    2018-08-08 jwe Attached File- Added diffs.txt, #44742
    2018-08-08 rik5 Carbon-Copy- Added jwe
    2018-08-08 rik5 Attached File- Added tst_sc.m, #44741
        StatusNone Confirmed
        Release4.2.1 dev
        SummaryShort Circuit Operators not working for ~functions Short Circuit Operators not working with negation operator
    2018-08-08 andrewlofts Carbon-Copy- Added andrewlofts

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