[Octave-bug-tracker] [bug #64704] VM error with chained indexing expression

[Arun Giridhar]

URL:
  <https://savannah.gnu.org/bugs/?64704>

                 Summary: VM error with chained indexing expression
                   Group: GNU Octave
               Submitter: arungiridhar
               Submitted: Thu 21 Sep 2023 08:47:54 AM EDT
                Category: JIT Acceleration
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Unexpected Error or Warning
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: dev
         Discussion Lock: Any
        Operating System: GNU/Linux
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


-------------------------------------------------------
Date: Thu 21 Sep 2023 08:47:54 AM EDT By: Arun Giridhar <arungiridhar>
The VM has some difficulty with evaluating chained indexing expressions as in
the last line of this example. This minimum reproducer was distilled from
production code where this kind of indexing was happening.


  lst = rand (285, 16);
  areas = rand (285, 1);
  ii = true (285, 1);
  ii([18 33 34 38 45 57 74 91 130 154 176 213 246 279]) = 0;
  areas(ii) = lst(ii,:) = [];


The VM gives a size mismatch error, and only one of the arrays has been
reduced. The other is still untouched, and the error message indicates that it
interpreted "= []" as an array assignment instead of a deletion.


octave:1> echo on
octave:2> testvm
+ ## test VM
+ 
+ lst = rand (285, 16);
+ areas = rand (285, 1);
+ ii = true (285, 1);
+ ii([18 33 34 38 45 57 74 91 130 154 176 213 246 279]) = 0;
+ areas(ii) = lst(ii,:) = [];
error: =: nonconformant arguments (op1 is 271x1, op2 is 0x0)
error: called from
    testvm at line 5 column 4
octave:3> 
octave:3> whos
Variables visible from the current scope:

variables in scope: top scope

  Attr   Name        Size                     Bytes  Class
  ====   ====        ====                     =====  ===== 
         areas     285x1                       2280  double
         ii        285x1                        285  logical
         lst        14x16                      1792  double

Total is 794 elements using 4357 bytes


Without the VM, the code evaluates as intended:


octave:4> clear all
octave:5> __enable_vm_eval__ (0)
octave:6> 
octave:6> testvm
+ ## test VM
+ 
+ lst = rand (285, 16);
+ areas = rand (285, 1);
+ ii = true (285, 1);
+ ii([18 33 34 38 45 57 74 91 130 154 176 213 246 279]) = 0;
+ areas(ii) = lst(ii,:) = [];
+ 
+ 
octave:7> whos
Variables visible from the current scope:

variables in scope: top scope

  Attr   Name        Size                     Bytes  Class
  ====   ====        ====                     =====  ===== 
         areas      14x1                        112  double
         ii        285x1                        285  logical
         lst        14x16                      1792  double

Total is 523 elements using 2189 bytes









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