Specifying Compiler Options for Architecture-Specific, 32- or 64-bit Compilation

You can use IBM C and C++ Compilers 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:

1. Internal default (32-bit mode)
2. OBJECT_MODE environment variable setting, as follows:

   OBJECT_MODE Setting	User-selected compilation-mode behavior, unless overridden by configuration file or command-line options
   not set	32-bit compiler mode.
   32	32-bit compiler mode.
   64	64-bit compiler mode.
   32_64	Fatal error and stop with following message, 1501-054 OBJECT_MODE=32_64 is not a valid setting for the compiler unless an explicit configuration file or command-line compiler-mode setting exists.
   any other	Fatal error and stop with following message, 1501-055 OBJECT_MODE setting is not recognized and is not a valid setting for the compiler unless an explicit configuration file or command-line compiler-mode setting exists.

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 acording to the last-found instance of the -q32 or -q64 compiler options. If neither of these compiler options is chosen, the compiler mode is set by the value of the OBJECT_MODE environment variable.
• 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 assumes a -qarch setting of com.
• 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.

Allowable combinations of these options are found in the Acceptable Compiler Mode and Processor Architecture Combinations table.

Possible option conflicts and compiler resolution of these conflicts are described below:

• -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 option to com, and sets -qtune option to the -qarch setting's default -qtune value.

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

  Resolution: -q32 or -q64 setting overrides -qtune option; compiler issues a warning message, and sets -qtune option to the -qarch setting's default -qtune 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 to com, and sets -qtune to the -qarch setting's default -qtune setting. The compiler mode (32- or 64-bit) is determined by the OBJECT_MODE environment variable or -q32/-q64 compiler settings.

Specifying Compiler Options

Invoking the Compiler
Setting Up the Compilation Environment
Specifying Compiler Options in Your Source Program
Specifying Compiler Options in a Configuration File

Acceptable Compiler Mode and Processor Architecture Combinations
Resolving Conflicting Compiler Options
List of Compiler Options and Their Defaults