[Octave-bug-tracker] [bug #36656] deleting rows from sparse matrices leads to failed assertion sometimes

[Jordi Gutiérrez Hermoso]

Update of bug #36656 (project octave):

                 Release:                   3.6.2 => 3.6.1                  

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Follow-up Comment #5:

The failed assertion turns out to be just one case of UB. The second example I
posted distilled from the first exhibits UB in other ways.

At any rate, I attempted your suggested fix:


diff --git a/liboctave/Sparse.h b/liboctave/Sparse.h
--- a/liboctave/Sparse.h
+++ b/liboctave/Sparse.h
@@ -81,15 +81,9 @@
           c[i] = 0;
       }
 
-    SparseRep (octave_idx_type nr, octave_idx_type nc) : d (0), r (0), c (new
octave_idx_type [nc+1]), nzmx (0),
-      nrows (nr), ncols (nc), count (1)
-      {
-        for (octave_idx_type i = 0; i < nc + 1; i++)
-          c[i] = 0;
-      }
-
-    SparseRep (octave_idx_type nr, octave_idx_type nc, octave_idx_type nz) :
d (new T [nz]),
-      r (new octave_idx_type [nz]), c (new octave_idx_type [nc+1]), nzmx
(nz), nrows (nr),
+    SparseRep (octave_idx_type nr, octave_idx_type nc, octave_idx_type nz=0)
+      : d (new T [nz]), r (new octave_idx_type [nz]),
+      c (new octave_idx_type [nc+1]), nzmx (nz), nrows (nr),
       ncols (nc), count (1)
       {
         for (octave_idx_type i = 0; i < nc + 1; i++)



but even with this change, the UB and valgrind's unhappiness persists.

I am very suspicious of cset fdccd69d26bd. There have been some pretty deep
modifications to the sparse code since your initial implementation, David.

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