https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114742
--- Comment #4 from Michael Meissner <meissner at gcc dot gnu.org> --- The minimum architecture for IEEE 128-bit support is power7, because it needs the VSX registers to pass and return IEEE 128-bit values. Now, in theory, IEEE 128-bit support could have required only Altivec support (i.e. power6 adding -maltivec), but it was decided that the minimum processor to support IEEE 128-bit would be power7. Note, that the minimum CPU support for little endian is power8. So, using -mcpu=power6 or -mcpu=power7 on a LE system is not supported. On power8 systems, IEEE 128-bit is emulated in software. On power9 systems, IEEE 128-bit has hardware support. The macro __LONG_DOUBLE_IEEE128__ is defined if long double uses the IEEE 128-bit format, and __LONG_DOUBLE_IBM128__ is defined if long double uses the IBM 128-bit format that uses a pair of doubles.
