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From: "bugdal at aerifal dot cx" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/91970] arm: 64bit int to double conversion does not
 respect rounding mode
Date: Sat, 18 Apr 2020 16:47:42 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D91970

--- Comment #12 from Rich Felker <bugdal at aerifal dot cx> ---
There's some awful hand-written asm in libgcc/config/arm/ieee754-df.S repla=
cing
the standard libgcc2.c versions; that's the problem. But in order to use the
latter it would need to be compiled with -mfloat-abi=3Dsoftfp since the
__aeabi_l2d function (and all the __aeabi_* apparently) use the standard
soft-float EABI even on EABIHF targets.

I'm not sure why you want a library function to be called for this on hardf=
loat
targets anyway. Inlining the hi*0x1p32+lo is almost surely smaller than the
function call, counting spills and conversion of the result back from GP
registers to an FP register. It seems like GCC should be able to inline this
idiom at a high level for *all* targets that lack a floatdidf operation but
have floatsidf.

Of course a high level fix is going to be hell to backport, and this really
needs a backportable fix or workaround (maintained in mcm not upstream gcc)
from musl perspective. Maybe the easiest way to do that is just to hack the
right preprocessor conditions for a hardfloat implementation into
ieee754-df.S...=