float matrix multiplication problem

[John W. Eaton]

Using the current sources, running Octave with valgrind, and given

  x = single (rand (4, 4) + i*rand (4, 4));

then the expression

  x'*x;

generates the following diagnostics:

  ==12836== Conditional jump or move depends on uninitialised value(s)
  ==12836==    at 0x681224F: bool mx_inline_all_real<float>(unsigned long, 
std::complex<float> const*) (mx-inlines.cc:214)
  ==12836==    by 0x6826504: FloatComplexNDArray::all_elements_are_real() const 
(fCNDArray.cc:536)
  ==12836==    by 0x567F587: 
octave_float_complex_matrix::try_narrowing_conversion() (ov-flt-cx-mat.cc:83)
  ==12836==    by 0x56BF551: octave_value::maybe_mutate() (ov.cc:1148)
  ==12836==    by 0x56CD9B3: octave_value::octave_value(FloatComplexMatrix 
const&, MatrixType const&) (ov.cc:689)
  ==12836==    by 0x57C7A79: oct_binop_herm_mul(octave_base_value const&, 
octave_base_value const&) (op-fcm-fcm.cc:137)
  ==12836==    by 0x56C50E0: do_binary_op(octave_value::compound_binary_op, 
octave_value const&, octave_value const&) (ov.cc:2103)
  ==12836==    by 0x574E833: tree_compound_binary_expression::rvalue1(int) 
(pt-cbinop.cc:212)
  ==12836==    by 0x5755FB4: tree_evaluator::visit_statement(tree_statement&) 
(pt-eval.cc:689)
  ==12836==    by 0x57728F3: tree_statement::accept(tree_walker&) 
(pt-stmt.cc:152)
  ==12836==    by 0x5755DBB: 
tree_evaluator::visit_statement_list(tree_statement_list&) (pt-eval.cc:725)
  ==12836==    by 0x577291F: tree_statement_list::accept(tree_walker&) 
(pt-stmt.cc:216)

As far as I can tell, this is happening at the point where the result
from xgemm is being stuffed into an octave_value object and
maybe_mutate is called to try to narrow the result.

I don't understand why something would be uninitialized here, but the
following change avoids the problem for me:

diff --git a/liboctave/fCMatrix.cc b/liboctave/fCMatrix.cc
--- a/liboctave/fCMatrix.cc
+++ b/liboctave/fCMatrix.cc
@@ -3769,7 +3769,7 @@
         {
          octave_idx_type lda = a.rows ();
 
-          retval = FloatComplexMatrix (a_nr, b_nc);
+          retval = FloatComplexMatrix (a_nr, b_nc, 0.0);
          FloatComplex *c = retval.fortran_vec ();
 
           const char *ctra = get_blas_trans_arg (tra, cja);

I wouldn't think this should be necessary, because I thought CHERK
and the following code to fill in the lower part of the symmetric
matrix would properly initialize everything.

jwe