Advanced optimization
Higher optimization levels can have a tremendous impact on performance, but some trade-offs can occur in terms of code size, compile time, resource requirements, and numeric or algorithmic precision.
After applying Basic optimization and
successfully compiling and executing your application, you can apply
more powerful optimization tools. The XL compiler optimization portfolio
includes many options for directing advanced optimization, and the
transformations that your application undergoes are largely under
your control. The discussion of each optimization level in Table 1 includes
information on the performance benefits and the possible trade-offs
and information on how you can help guide the optimizer to find the
best solutions for your application.
Optimization Level | Additional options implied | Complementary options | Options with possible benefits |
---|---|---|---|
-O3 |
|
|
|
-O4 |
|
|
|
-O5 |
|
|
|
When you compile programs with any of the
following sets of options:
- -O3 -qhot
- -O4
- -O5
In addition to any of the preceding sets of options, when the -qipa option is in effect, if the compiler cannot vectorize, it tries to inline the MASS scalar functions before deciding to call them.