Other Performance Options

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.
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