You can use IBM XL C/C++ compiler options to optimize compiler output for use on specific processor architectures. You can also instruct the compiler to compile in either 32- or 64-bit mode.
The compiler evaluates compiler options in the following order, with the last allowable one found determining the compiler mode:
The compilation mode actually used by the compiler depends on a combination of the settings of the -q32, -q64, -qarch and -qtune compiler options, subject to the following conditions:
Possible option conflicts and compiler resolution of these conflicts are described below:
Resolution: -q32 or -q64 setting overrides -qarch option; compiler issues a warning message, sets -qarch to its default setting, and sets the -qtune option accordingly to its default value.
Resolution: -q32 or -q64 setting overrides -qtune option; compiler issues a warning message, and sets -qtune to the -qarch setting's default -qtune value.
Resolution: Compiler issues a warning message, and sets -qtune to the -qarch setting's default -qtune value.
Resolution: Compiler issues a warning message, sets -qarch and -qtune to their default settings. The compiler mode (32- or 64-bit) is determined by the -q32/-q64 compiler settings.
Invoke the Compiler
Specify Compiler Options on the Command Line
Compiler Command Line Options
Resolving Conflicting Compiler Options