Allocatable array valued function. gfortran vs ifort

Question

Why is there different behavior between ifort and gfortran here? Compiled with ifort it returns false and with gfortran true. I ran into this problem before in my own code a

Answer 1

When compiling with ifort before version 17.0.1, the default behaviour is for the compiler not to use the Fortran rules for automatic allocation on intrinsic assignment.

You will need to use an option like -assume realloc-lhs.