All,

The attached patch fixes an ICE that occurs in gfc_simplify_tranfer.
The code that causes the problem is

  if (!gfc_is_constant_expr (source)
        || (gfc_init_expr_flag && !gfc_is_constant_expr (mold))
        || !gfc_is_constant_expr (size))
    return NULL;

in particular gfc_is_constant_expr (mold) leads to segfault.  Removing
the 2nd line allows the testcase to compile, but leads to several
regressions.  I went down the rabbit with gdb-8.0.1 to see why this
was dying a horrible death, and came away with a large headache.
After conferring with F95 and F2018, I concluded (and I coudl be
wrong) that mold simply needs to available as a scalar or an
array and it's actual value was not needed.  So, I decided to 
use gfc_reduce_expr (mold) to see if this would fix up some 
rogue pointer, and well it worked.  So, OK to commit?

2018-02-26  Steven G. Kargl  <kargl@gcc.gnu.org>

	PF fortran/51434
	* simplify.c (gfc_simplify_transfer): Reduce mold.

2018-02-26  Steven G. Kargl  <kargl@gcc.gnu.org>

	PF fortran/51434
	* gfortran.dg/pr51434.f90: New test.

-- 
Steve