As is discussed in section D.11 of the Numerical Computation Guide, even standard-conforming implementations of IEEE arithmetic might produce different results. Often these results are equally good, but equally often it is tedious or difficult to prove that. For many purposes, it's better to sacrifice some performance to reduce the amount of error analysis necessary to validate results. It's not obvious when minor or major differences in output are equally good, and whether they are due to user program errors, compiler optimization errors, or hardware errors.
There are several principal root causes of varying results of IEEE floating-point arithmetic. The following lists these causes and describes some approaches to reducing gratuitous variation across the releases and supported platforms of Oracle Solaris Studio. Note that each approach increases reproducibility while potentially reducing performance. Sometimes the performance loss can be noticeable.