On Wed, May 30, 2018 at 12:58:49PM +0000, Segher Boessenkool wrote:
> This patch changes the (C++) mangling of the 128-bit float types:
>
> __ieee128 becomes u9__ieee128
> __ibm128 becomes u8__ieee128
^^^^^^ what is the advantage/reason for the above, rather than mangling it
as g?
> __float128 is not a type anymore
> IEEE long double becomes u9__ieee128
> IBM long double stays g
I mean, the above change will mean a significant burden e.g. on libstdc++,
when we have to export all symbols that refer to the
long double/__ieee128/__ibm128 types 4 times, once as aliases to symbols
with double instead (with the exception when there is no such double
symbol) using mangling e, then make sure libstdc++ files are all compiled
with long double equal to IBM to get the g mangling, then add aliases to
those for u8__ieee128 and finally build with __ieee128 or long double equal
to IEEE754 quad to get the u9__ieee128 mangling.
And besides libstdc++ on everything else that wants to achieve ABI
compatibility with both formats.
The above doesn't make long double distinct type from __ieee128 when it
is the same binary type anyway, so why should long double be distinct from
__ibm128 when long double is the same binary type as __ibm128?
If you need to keep g for compatibility (you do), then why not just have
e (long double is double)
g (long double when matching __ibm128, or explicit __ibm128)
u9__ieee128 (long double when matching __ieee128, or explicit __ieee128)
Jakub
