If performance is your primary concern and you want your program to be relatively safe but do not mind if results are slightly different (generally more precise) from what they would be otherwise, optimize the program with the -O option, and specify -qfloat=rsqrt:hssngl:fltint. The following section describes the functions of these suboptions:
To detect single-precision floating-point overflows and underflows, rounding operations are still inserted when double-precision results are stored into single-precision memory locations. However, if optimization removes such a store operation, hssngl also removes the corresponding rounding operation, possibly preventing the exception. (Depending on the characteristics of your program, you may or may not care whether the exception happens.)
The hssngl suboption is safe for all types of programs because it always only increases the precision of floating-point calculations. Program results may differ because of the increased precision and because of avoidance of some exceptions.