Options are provided to control particular aspects of optimization.
They are often enabled as a group or given default values when a more general
optimization option is enabled.
Selected compiler options for optimizing performance | |
Option | Description |
---|---|
-qcompact | Chooses reduction of final code size over a reduction in execution time when a choice is necessary. Can be used to constrain -O3 and higher optimizations. |
-qsmallstack | Instructs the compiler to limit the use of stack storage in the program. Doing so may increase heap usage. |
-qunroll | Independently controls loop unrolling. Is implicitly activated under -O3 and higher optimizations. |
-qtbtable | Controls the generation of traceback table information. (Applies to 64-bit mode only.) |
-qunwind | Informs the compiler that the stack can be unwound while a routine in this compilation is active. In other words, the compiler is informed that the application may or does rely on program stack unwinding mechanisms. |
-qnounwind | Informs the compiler that the stack will not be unwound while any routine in this compilation is active. The -qnounwind option enables optimization prologue tailoring, which reduces the number of saves and restores of nonvolatile registers. |