Specifying compiler options for architecture-specific, 32-bit or 64-bit compilation

You can use the -q32, -q64, -qarch, and -qtune compiler options to optimize the output of the compiler to suit:

• The broadest possible selection of target processors
• A range of processors within a given processor architecture family
• A single specific processor

Generally speaking, the options do the following:

• -q32 selects 32-bit execution mode.
• -q64 selects 64-bit execution mode.
• -qarch selects the general family processor architecture for which instruction code should be generated. Certain -qarch settings produce code that will run only on systems that support all of the instructions generated by the compiler in response to a chosen -qarch setting.
• -qtune selects the specific processor for which compiler output is optimized. Some -qtune settings can also be specified as -qarch options, in which case they do not also need to be specified as a -qtune option. The -qtune option influences only the performance of the code when running on a particular system but does not determine where the code will run.

The compiler evaluates compiler options in the following order, with the last allowable one found determining the compiler mode:

1. Internal default (32-bit mode)
2. OBJECT_MODE environment variable setting
3. Configuration file settings
4. Command line compiler options (-q32, -q64, -qarch, -qtune)
5. Source file statements (#pragma options tune=suboption)

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:

• Compiler mode is set according to the last-found instance of the -q32 or -q64 compiler options. If neither of these compiler options is set, the compiler mode is set by the value of the OBJECT_MODE environment variable. If the OBJECT_MODE environment variable is also not set, the compiler assumes 32-bit compilation mode.
• Architecture target is set according to the last-found instance of the -qarch compiler option, provided that the specified -qarch setting is compatible with the compiler mode setting. If the -qarch option is not set, the compiler sets -qarch to the appropriate default based on the effective compiler mode setting. See -qarch for details.
• Tuning of the architecture target is set according to the last-found instance of the -qtune compiler option, provided that the -qtune setting is compatible with the architecture target and compiler mode settings. If the -qtune option is not set, the compiler assumes a default -qtune setting according to the -qarch setting in use. If -qarch is not specified, the compiler sets -qtune to the appropriate default based on the effective -qarch as selected by default based on the effective compiler mode setting.

Allowable combinations of these options are found in -qtune.

The following list describes possible option conflicts and compiler resolution of these conflicts:

• -q32 or -q64 setting is incompatible with user-selected -qarch option.

  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.

• -qarch option is incompatible with user-selected -qtune option.

  Resolution: Compiler issues a warning message, and sets -qtune to the -qarch setting's default -qtune value.

• Selected -qarch or -qtune options are not known to the compiler.

  Resolution: Compiler issues a warning message, sets -qarch and -qtune to their default settings. The compiler mode (32-bit or 64-bit) is determined by the OBJECT_MODE environment variable or -q32/-q64 compiler settings.