Acceptable Compiler Mode and Processor Architecture Combinations

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 code (instructions) should be generated. Certain -qarch settings will produce code that will run only on RS/6000 systems that support all of the instructions generated by the compiler in response to the chosen -qarch settings.
• -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.

There are three families of RS/6000 machines:

• POWER
• POWER2
• PowerPC

Each of these families have a different instruction set but share a common subset of instructions. The POWER2 instruction set is a superset of the POWER instructions set. The PowerPC instruction set includes additional instructions not available on POWER systems but does not support all of the POWER instruction set. It also includes some but not all of the POWER2 instructions not available in the POWER instruction set. Further, some features found in the POWER2 instruction set may or may not be implemented on particular PowerPC processors. These optional feature groups are:

• support for the graphics instruction group
• support for the sqrt instruction group
• support for 64-bit mode (-q64 compiler option)

If you want to generate code that will run across a variety of processors, use the following guidelines to select the appropriate -qarch and/or -qtune compiler options. Code compiled with:

• -qarch=com will run on any RS/6000.
• -qarch=pwr will run on any POWER or POWER2 machine.
• -qarch=pwr2 (or pwr2s, pwrx, p2sc) will run only on POWER2 machines.
• -qarch=ppc will run only on all PowerPC machines.
• -q64 will run only on PowerPC machines with 64-bit support
• other -qarch options that refer to specific processors will run on any functionally equivalent PowerPC machine. In the examples found in the table below, code compiled with -qarch=pwr3 will also run on a rs64b but not on a rs64a. Similarly, code compiled with -qarch=603 will run on a pwr3 but not on a rs64a.

  Processor	graphics support	sqrt support	64-bit support
  601	no	no	no
  603	yes	no	no
  604	yes	no	no
  rs64a	no	no	yes
  rs64b	yes	yes	yes
  rs64c	yes	yes	yes
  pwr3	yes	yes	yes

If you want to generate code optimized specifically for a particular processor, acceptable combinations of -q32, -q64, -qarch, and -qtune compiler options are shown in the tables below (one eac for 32-bit and 64-bit execution modes). If you specify incompatible combinations of these options, the compiler will assume its own option selections, as described in Specify Compiler Options for Architecture-Specific, 32- or 64-bit Compilation.

The default execution mode is 32-bit unless the OBJECT_MODE environment variable is set to 64.

32-bit Execution Mode

64-bit Execution Mode

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


Built-in Functions for PowerPC Processors
-q32, 64
-qarch
-qtune