8.4 POWER/PowerPC options
On systems using the POWER/PowerPC family of processors the option
-mcpu=CPU selects code generation for specific CPU
models. The possible values of
CPU include 'power',
'power2', 'powerpc', 'powerpc64' and 'common', in
addition to other more specific model numbers. Code generated with
-mcpu=common will run on any of the processors.
-maltivec enables use of the Altivec vector
processing instructions, if the appropriate hardware support is
The POWER/PowerPC processors include a combined "multiply and add"
instruction a * x + b, which performs the two operations
simultaneously for speed--this is referred to as a fused multiply
and add, and is used by GCC by default. Due to differences in the way
intermediate values are rounded, the result of a fused instruction may
not be exactly the same as performing the two operations separately. In
cases where strict IEEE arithmetic is required, the use of the combined
instructions can be disabled with the option
On AIX systems, the option
-mminimal-toc decreases the number
of entries GCC puts in the global table of contents (TOC) in
executables, to avoid "TOC overflow" errors at link time.
-mxl-call makes the linking of object files from GCC
compatible with those from IBM's XL compilers.
For applications using POSIX threads, AIX always requires the option
-pthread when compiling, even when the program will only run in