As you compile with higher levels of the -xalias_level option, the compiler makes increasingly extensive assumptions about the pointers in your code. You have greater programming freedom when the compiler makes fewer assumptions. However, the optimizations that result from these narrow assumptions may not result in significant runtime performance improvement. If you code in accordance with the compiler assumptions of the more advanced levels of the -xalias_level option, there is a greater chance that the resulting optimizations will enhance runtime performance.
The -xalias_level option specifies which alias level applies to each translation unit. For cases where more detail is beneficial, you can use new pragmas to override whatever alias levels are in effect so that you can explicitly specify the aliasing relationships between individual types or pointer variables in the translation unit. These pragmas are most useful when the pointer usage in a translation unit is covered by one of the available alias levels, but a few specific pointer variables are used in an irregular way that is not allowed by one of the available levels.