id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
1819	x86 native codegen implements float2int# incorrectly	simonmar		"`float2Int#` is supposed to truncate towards zero, but the x86 native codegen implements it as rounding (or rather, whatever rounding mode the x87 FPU is set to, which is normally rounding).  The right thing appears to be to save/restore the x87 control word around the conversion operation, and temporarily set it to truncation.  This is what gcc does.  Code generated by gcc for truncation:

{{{
        fnstcw  -2(%ebp)
        movw    -2(%ebp), %ax
        movb    $12, %ah
        movw    %ax, -4(%ebp)
        flds    8(%ebp)
        fldcw   -4(%ebp)
        fistpl  -8(%ebp)
        fldcw   -2(%ebp)
        movl    -8(%ebp), %eax
}}}

Test case:

{{{
import GHC.Exts
main = print (f2i (-2.9))

{-# NOINLINE f2i #-}
f2i :: Float -> Int
f2i (F# x) = I# (float2Int# x)
}}}

Also `arith005` triggers this, when -O is on and the libraries were compiled with `-fasm`.

Related: #1254
"	bug	closed	normal	6.8.3	Compiler (NCG)	6.8.1	duplicate			Unknown/Multiple	x86		Unknown	arith005 (see description)