[Bug target/97653] Incorrect long double calculation with -mabi=ibmlongdouble

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97653

--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #11)
> That tells me that using --with-long-double-format={ibm,ieee} chooses
> *which* of the 128-bit long double formats you want, and so
> --with-long-double-128 is implied. Maybe I'm reading it wrong.

At least from seeing what my cross-compiler does it is not implied.
If I compile with those 
-mno-gnu-attribute -mabi=ibmlongdouble
options, scp assembly to gcc112, compile there (system compiler defaults to
-mlong-double-128), it fails, if I compile locally with
-mno-gnu-attribute -mabi=ibmlongdouble -mlong-double-128
and scp and do the same, it works.
And I can't reproduce on gcc112 with 11.0.0 20210126 gcc natively built there
which defaults to -mlong-double-128:
~/gcc/obj31/gcc/xgcc -B ~/gcc/obj31/gcc/ -B
~/gcc/obj31/powerpc64le-unknown-linux-gnu/libgcc/ -o pr97653{,.c}
-static-libgcc -mno-gnu-attribute -mabi=ibmlongdouble
./pr97653
256 * 0.100000 = 25
256 * 0.200000 = 51
256 * 0.500000 = 128
256 * 0.900000 = 230